HBSC1203 BIOLOGY I

INTRODUCTION
Life comprises living and non-living things. There are millions of living things on
Earth, consisting of plants and animal species. The species range from simple to
complex organisms. Before we go any further, let us take a look at Figure 1.1.
What common characteristics do these living organisms have?
Figure 1.1: Living organisms
Topic
1
Characteristics
of Living
Things
LEARNING OUTCOMES
By the end of this topic, you should be able to:
1. List the seven basic living processes;
2. Explain the life processes in humans and animals;
3. Explain the life processes in plants;
4. Describe the basic needs of humans and animals; and
5. Describe the basic needs of plants.

TOPIC 1 CHARACTERISTICS OF LIVING THINGS
2
This is what we are going to learn in this topic. We will discuss their common
characteristics and also differences. Due to their characteristics as living
organisms, they need basic things in order to survive. What are they? LetÊs read
more.
BASIC LIVING PROCESSES
1.1
Living things comprise animals and plants. Although all living things look
different from each other, they all have seven things in common. These seven
things are called life processes. You must be wondering, what are the seven basic
life processes? These seven basic life processes are shown in Figure 1.2.
Figure 1.2: Seven basic life processes
Things are only alive if they engage in all the seven processes as shown in Figure
1.1. When they have the capacity to carry out these seven life processes, they are
characterised as living organisms. Some non-living things may have one or two
of these characteristics but living things will have all the seven characteristics.
SELF-CHECK 1.1
List the basic seven life processes in living organisms.

TOPIC 1 CHARACTERISTICS OF LIVING THINGS 3
LIFE PROCESSES IN HUMANS AND
ANIMALS
1.2
As mentioned previously, living organisms have the capacity to carry out the
seven life processes as shown in Figure 1.1. Firstly, letÊs take a look at the life
processes that happen specifically in humans and animals.
1.2.1 Nutrition
Animals and human beings are in the animal group. They feed or eat from the
day they are born until they die. Right after birth, they are fed by their mothers
with the simplest form of food. Many of them feed on their mothersÊ milk.
However, as they develop and grow up, they eat different kinds of foods. Some
animals feed on plants only, some eat meat of other animals and others eat both
meat and plants.
Animals that eat only plants, algae and photosynthesising bacteria like fungi,
belong to the class called herbivores. On the other hand, animals that feed on the
meat of other animals are called carnivores. Animals that consume both animals
and plants as their primary food source are in the group called omnivores.
1.2.2 Movement
The second characteristic of animals is that they can move. They move from one
place to another for many reasons, namely in search of living places, food, safety,
breeding, and escaping from predators. Some of them move just like human
beings do, because of occupation; finding a place that is safer or suitable for
living; or other reasons. Animals move in one of various ways. The various types
of movement are walking, running, leaping, hopping, slithering, burrowing,
swimming and flying.
1.2.3 Respiration
The third characteristic of living things is that they breathe. Human beings and
animals breathe oxygen into their lungs and then breathe out carbon dioxide
through a process called breathing. Therefore, breathing refers to the process that
brings about an exchange of gases between an organism and its environment.
The oxygen from the lungs is then transported to each cell via the circulatory
system and then is used to oxidise glucose through the process of respiration in
every cell.

4 TOPIC 1 CHARACTERISTICS OF LIVING THINGS
1.2.4 Excretion
The fourth characteristic of living things is that they must eliminate the waste
products of metabolism and other non-useful materials from their bodies. The
way of removing this waste is called excretion. If this waste is to remain in the
body, it may be poisonous and harm them. Humans and animals produce liquid
waste called urine. Both of them also excrete waste when they exhale. Thus, all
living things have to remove waste from their bodies.
1.2.5 Growth
Human beings and animals are small in size when they are newborn. They need
energy from food and water to develop and grow. With food, they become
bigger and taller because this energy is used in growth. Living things develop
and become larger and more complicated as they grow. Look at how small a
baby elephant is when it was born (Figure 1.3). Then look at its size some years
later! If you have a younger sibling, can you remember how small he or she was
at birth? How tall or big he or she is now? What do you know about this
phenomenon?

Figure 1.3: A baby elephant and its mother
Source: http://www.saburchill.com

1.2.6 Sensitivity
The other characteristic of living things is that they are sensitive. They can react
or respond to the conditions around them through light, touch, pain, heat, cold,
sound and others. Animals and humans can respond to stimuli as they possess
sense organs that are made up of nerve cells. Certain microbes curl into tiny balls
when something touches them. Human beings blink when light shines into their
eyes. Some people become disturbed if the environment around them is too
noisy.
1.2.7 Reproduction
Living things are capable of multiplying or reproducing themselves. If one
organism fails to reproduce, the population will decrease and finally become
extinct. Several factors can affect the existing number of living things. They may
become fewer, then disappear because their members die due to old age, get
infected by diseases or involved in accidents, are hunted by others (man or
animals), get killed in territorial disputes, wars, power struggles and so on. It is a
fundamental law of biology that living things can only be reproduced by other
living things to survive. Almost every living organism exists due to the
reproductive activities of other organisms.
There are two types of reproduction for living things. They are:
(a) Asexual
Asexual reproduction involves no exchange of genetic material between
organisms. It is a simple replication to produce a new organism. An
organism reproduced in this way has little or no genetic variation from the
parent organism. Single celled-animals like Protozoa and Hydra (Figure 1.4
and 1.5) are examples of animals that reproduce asexually.

6 TOPIC 1 CHARACTERISTICS OF LIVING THINGS

Figure 1.4: Protozoa
Source: http://www.microimaging.ca

Figure 1.5: Hydra
Source: http://www.saburchill.com

(b) Sexual
Sexual reproduction involves two organisms, male and female. Human
beings make babies, kangaroos produce joeys, and chickens and ducks lay
eggs. The process involves the combining of genetic materials from the two
parent organisms during mating. The offspring or babies from the sexual
reproduction generally will have some of the characteristics of both parents.
Sexual reproduction from the parent organisms gives rise to reproductive
cells called gametes. Sexual reproduction ensures that a high degree of
variation occurs within populations.


SELF-CHECK 1.2
Explain living processes in humans and animals.
1. Name five examples of animals (apart from Protozoa and
Hydra) that reproduce asexually.
2. Do research on how a baby in its motherÊs womb excretes its
waste. Share the information with your classmates.
3. Look at Figures 1.6 to 1.8. Which animal is a herbivore, carnivore
and omnivore?
Figure 1.6: Horse
Figure 1.7: Lion
Figure 1.8: Crow
ACTIVITY 1.1

TOPIC 1 CHARACTERISTICS OF LIVING THINGS
8
1. Figures 1.9 to 1.16 show different kinds of animal movement. Can you
name other examples of animals that move according to this type of
movement?
Figure 1.9:
People walking
Source:
http://www.li
fetrek-slovenia.
com
Activity 1.1
Figure 1.10: A
running fox
Source:
http://artfiles.art
.com
Figure 1.11: A
leaping lemur
Source:
http://www.magm
a.nationalgeographi
c.com
Figure 1.12: A
hopping
kangaroo
Source:
http://www.bio.
davidson.edu
Figure 1.13: A
flying eagle
Source:
http://www.h
ickerphoto.
com
Figure 1.14: A
burrowing owl
Source:
http://members.
cox.net
Figure 1.15: A
slithering snake
Source:
http://coolinsights.
blogspot.com
Figure 1.16: A
swimming tiger
Source:
http://www.mc
cullagh.org
ACTIVITY 1.2

LIFE PROCESSES IN PLANTS
1.3
Plants also carry out the seven life processes but they differ in some aspects when
compared to animals and humans. Now, let us learn about the life processes in
plants.
1.3.1 Nutrition
Plants make their own food through the process of photosynthesis. They are able
to do so because they have chlorophyll that capture sunlight and the energy
needed to start photosynthesis. The end product of photosynthesis is glucose
which is then stored as starch.
1.3.2 Movement
Unlike animals, only certain parts of the plants move. Plants move slowly,
usually by growing in one direction, such as towards a source of light. Plant
movement occurs both above ground, in the form of leaves and shoots, and
below ground, where roots spread out and move deeper into the earth in order to
provide stronger support and get a greater supply of nutrients.
1.3.3 Respiration
Just as humans and animals breathe, plants use respiration as a means of
releasing energy, using up nutrients and oxygen and producing water and
carbon dioxide. Respiration is essentially the opposite of photosynthesis, the
process by which plants create food and matter.
1.3.4 Excretion
Plants have no special organs for the removal of wastes. The waste products of
respiration and photosynthesis are used as raw materials for each other. Oxygen,
produced as a by-product of photosynthesis, is used up during respiration and
carbon dioxide (produced during respiration) is used up during photosynthesis.

1 0 TOPIC 1 CHARACTERISTICS OF LIVING THINGS
Excretion is carried out in the plants in the following ways:
(a) The gaseous wastes, oxygen, carbon dioxide and water vapour are
removed through stomata of leaves and lenticels of stems.
(b) Some waste products collect in the leaves and bark of trees. When the
leaves and bark are shed, the wastes are eliminated.
(c) Some waste products are rendered harmless and then stored in the stem as
solid bodies. Raphides, tannins, resins, gum, rubber and essential oils are
some such wastes.
1.3.5 Growth
Growth in plants occurs chiefly at meristems where rapid mitosis provides new
cells. In stems, mitosis in the apical meristem (Figure 1.17) of the shoot apex (also
called the terminal bud) produces cells that enable the stem to grow longer and
periodically produces cells that will give rise to leaves. The point on the stem
where leaves develop is called a node. The region between a pair of adjacent
nodes is called the internode.

Figure 1.17: Apical meristem
Source: http://www.doctortee.com
The internodes in the terminal bud are very short so that the developing leaves
grow above the apical meristem that produced them and thus protect it. New
meristems, the lateral buds, develop at the nodes, each just above the point
where a leaf is attached. When the lateral buds develop, they produce new stem
tissues, thus branches are formed.

Growth also occurs at the root tip as can be seen in Figure 1.18. The root tip
consists of a:
(a) Meristem a region of rapid mitosis, which produces the new cells for root
growth; and
(b) Root cap a sheath of cells that protects the meristem from abrasion and
damage as the root tip grows through the soil.

Figure 1.18: Growth at root tip of plants
Source: http://www.doctortee.com
1.3.6 Sensitivity
Like animals, plants sense changes in their surroundings and respond to them.
Plants are able to detect and respond to light, gravity, changes in temperature,
chemicals, and even touch. Unlike animals, plants do not have nerves or muscles,
so they cannot move very fast. A plant usually responds to change by gradually
altering its growth rate or its direction of growth. The slow movements that
plants make towards or away from a stimulus, such as light, are known as
tropisms. Tropisms are controlled with the help of special chemicals called plant
growth regulators. Roots push down through soil because of the effect of gravity.
They may also be drawn towards water, or away from bright light as illustrated
in Figure 1.19.


Figure 1.19: PlantsÊ sensitivity
Did you notice that sunflowers face east in the morning but west by the evening?
This is called phototropism, which means the movement of part of a body
towards light (Figure 1.20).

Figure 1.20: Sunflowers respond towards light

1.3.7 Reproduction
Plants also reproduce in two ways; asexual and sexually. The process of
reproduction is the same as in animals. Plants growing from tubers or bulbs,
such as sweet potatoes and onions, are examples of plants that reproduce
asexually. This can be seen in Figure 1.21.

Figure 1.21: Asexual reproduction in plants
Sexual reproduction is the formation of offspring by the fusion of gametes. In
higher plants, the offspring are packaged in protective seeds, which are long-lived
and can be dispersed farther away from the parents. In flowering plants
(angiosperms), the seeds themselves are contained inside the fruit, which may
protect the developing seeds and aid in their dispersal.


SELF-CHECK 1.3
Tick [] the following statements that are true.
Green leaves have chlorophyll that can capture sunlight,
the energy needed to start photosynthesis.
Shoots of plants move away from sunlight while the roots
move downward.
3. Plants carry out photosynthesis but not respiration.
4. Plants take in carbon dioxide as well as oxygen.
5. Tannin, resin and gum are the waste products of plants.
6. Growth only happens at the shoot tip and root tip.
7. Plants respond to sunlight for growth.
Bulb, tuber and rhizome are examples of asexual
reproduction in plants.
9. Flowers enable plants to reproduce sexually.
10. Plants can also reproduce sexually through spores.

BASIC NEEDS OF HUMANS AND ANIMALS
1.4
1.
2.
8.
You have learned the basic life processes of humans, animals and plants. Now,
letÊs go through the basic needs of humans and animals first. Then, we will go
through the basic needs of plants. But bear in mind that the basic needs of
animals and humans are quite similar to plants and differ only in certain things.
1.4.1 Water
The most important nutrient for survival is water. Water is the medium in which
all chemical reactions take place within an animal's body. If an animal loses one-tenth
of its water for any reason, the results are fatal. Water also functions in
excretion of wastes, regulating body temperature and transporting food.

Animals get water from streams, lakes, ponds or even puddles. Others drink
water that collects on leaves after a rainfall. But do you know that some animals
do not drink water? Instead, they get water from the food that they eat.
1.4.2 Food
Animals and humans get their food by eating other animals or plants or both.
Different classes of food have different functions on the animals. For example,
protein is needed for building and repairing cells, carbohydrate and fats provide
energy. Energy is needed for bodily functions such as respiration, movement and
growth. Food, or lack of it, often affects animals in dramatic ways. Food scarcity
can trigger great migrations such as the year round movements of caribou and
the winter migrations of many birds.
Adaptation enables all animals to get food. Toothed herbivores, for example,
have large, flat, round teeth that help them grind plant leaves and grasses. Some
carnivorous animals, such as bears, dogs and the big cats have sharp canines and
incisors for chewing through meat with ease. The digestive systems of animals
have proteins known as enzymes that break down food and convert it into
energy. Some animals eat insects as their food.
1.4.3 Air
All animals must breathe in oxygen in order to survive. Land-dwelling species
receive oxygen from the air, which they inhale directly to their lungs. Marine and
freshwater species filter oxygen from water by using their gills. Oxygen is much
needed in respiration that provides energy for animals and humans. It is also
important in destroying harmful bacteria in an animal's body without sacrificing
the body's necessary bacteria.
1.4.4 Temperature
External temperature is a major factor in the survival of animals. The vertebrate
groups, amphibians, reptiles and fish are said to be cold-blooded they take on
the temperature of their environment. Most have thin skin. On the other hand,
birds and mammals, which are termed warm-blooded, can regulate their own
body temperature.
Let us take a look at an example of the Monarch butterflies (Figure 1.22). They are
unable to survive the cold winters. In order to escape the cold weather, they will
migrate to the south.


Figure 1.22: Monarch butterfly
Source: http://animals.nationalgeographic.com

However, some mammals, such as bears, gophers (Figure 1.23) and bats,
hibernate during winter and live off their body fat. They can drop their body
temperature to about 50 degrees Fahrenheit.

Figure 1.23: Gopher
Source: http://animal-wildlife.blogspot.com/2011/10/gopher.htm
1.4.5 Shelter
Every animal needs a place to live · a place where it can find food, water,
oxygen and the proper temperature. Shelter provides cover from adverse
weather, protection from predators and a place to rest and have their young. It is
also a place to prevent death due to exposure that directly affects the
reproductive success. Good sites greatly increase the chance of survival for
young animals. Animals live in various types of shelter as illustrated in
Figure 1.24.

Figure 1.24: Examples of shelters
Source: http://marzukitm.edublogs.org
Animals also depend on their physical features to help them obtain food, keep
safe, build homes, withstand weather and attract mates. These physical features
are called physical adaptations. Physical adaptations do not develop during an
animalÊs life but over many generations. The shape of a birdÊs beak, the number
of fingers, colour of the fur, the thickness or thinness of the fur, the shape of the
nose or ears are all examples of physical adaptations which help different
animals to survive.
You could read more about animal adaptations at:
(a) http://www.oaklandzoo.org/atoz/azhgehog.html; and
(b) http://www.pbs.org/kratts/world/index.html.
SELF-CHECK 1.4
1. Explain the basic needs of humans and animals.
2. Is mating a basic need for an animal?
ACTIVITY 1.3
List a few animals that eat insects.

1.5 BASIC NEEDS OF PLANTS
Plants are living things that have needs in order to stay alive. Do you know what
are the basic needs of plants? LetÊs read further in order to know the basic needs
of plants.
1.5.1 Sunlight
Why do you think sunlight is important to plants? Sunlight is very important for
plants as it supplies the energy required for photosynthesis to take place.
Photosynthesis depends upon the absorption of light by pigments in the leaves of
plants. The most important of these is chlorophyll-a.
Figure 1.25 shows the spectra of sunlight before and after its journey of being
absorbed by a green leaf.

Figure 1.25: Spectrum of light being absorbed by plants
Source: http://www.tomatosphere.org
As can be seen in Figure 1.25, when sunlight falls on a green leaf, some of the
sunlight is absorbed by chlorophyll.

1.5.2 Carbon Dioxide
Without sufficient quantities of dissolved carbon dioxide, photosynthesis cannot
take place. Some plants do not need much carbon dioxide (CO2) and some plants
like Cryptocorynes seemed to worsen with higher levels of CO2. Typical levels of
CO2 in a non-CO2 injected aquarium are in the range of 13 ppm. Most plants
will flourish at the levels of 1020 ppm but this requires some types of CO2
injection. With lower levels of CO2, the plants will not be able to utilise high
levels of light and nutrients. Figure 1.26 shows how CO2 concentration affects the
rate of photosynthesis.

Figure 1.26: The effect of CO2 concentration upon rate of photosynthesis
Source: http://science.halleyhosting.com/
1.5.3 Nutrients
The minerals available in soil is absorbed by roots and transported to other parts
of the plants along with water in the xylem vessel. Essential plant elements
include, carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur,
calcium, iron, magnesium sodium, chlorine, copper, manganese, cobalt, zinc,
molybdenum and boron to name the most common. Other minerals are also
required, but they vary greatly from plant to plant. For example, some algae need
large amounts of iodine and silicon, while some locoweed species need selenium.

When any of these elements are lacking in the soil and the deficiencies are not
compensated for by adding fertiliser compounds of compost, the plant will
demonstrate symptoms characteristic of mineral deficiencies. Most commercial
fertilisers contain some ratio of nitrogen, phosphorus and potassium. Thus, they
are able to compensate for a wide variety of insufficiency.
1.5.4 Water
All living things need water to stay alive, but plants use much more water than
animals do. Plants are 90 percent water, compared to animals with as little as
75 percent water by weight. Plants use water directly when they capture light
energy from the sun and transform it into useful food molecules.
Water is also needed to support the stem of plants. Plants need water to maintain
turgor pressure. Turgor pressure helps to keep the plant erect and is
accomplished when the plasma membrane pushes against the cell wall. Without
water, the plantÊs cells will shrink and the stem will wilt. Water is also used to
cool down a plant through evaporation. Plants absorb water and minerals from
soil through roots and transport them to cells through xylem.
1.5.5 Oxygen
Plants need oxygen for their respiration process. During the day, plants produce
far more oxygen from photosynthesis than the production of carbon dioxide
from respiration. During the night, plants actually use the leftover oxygen
produced from the daylight photosynthesis or take in oxygen from the air
surrounding the plants to meet their energy needs.
The exchange of oxygen and carbon dioxide in the leaves occurs through pores
called stomata as can be seen in Figure 1.27(a), while in roots and stems through
lenticels as can be seen in Figure 1.27(b).


(a) (b)
Figure 1.27: Stoma (a) and lenticel (b)
Source: http://users.rcn.com
SELF-CHECK 1.5
Describe the basic needs of plants. Is soil a basic need for a plant?
ACTIVITY 1.4
In groups, surf the Internet or other resources to find out experiments
that you can do to show that plants need oxygen, sunlight and water to
live. Try the experiments and share your findings with the other
groups.

Living things can be categorised into humans, plants and animals.
Living things undergo seven basic living processes such as nutrition,
movement, respiration, excretion, growth, sensitivity and reproduction.
Plants make their own food through photosynthesis while animals and
humans have to rely on the plants or other animals for food.
Animals and humans move their whole bodies from one place to another
while only certain parts of the plants move.
Both plants and animals undergo cellular respiration in the same way.
Both plants and animals experience changes in size and mass when they
grow.
Both plants and animals reproduce asexually and sexually.
Both plants and animals can respond to external stimuli.
Both plants and animals excrete their wastes but the waste products of
animals and plants are different.
The basic needs of animals are food, water, air, temperature and shelter.
The basic needs of plants are sunlight, water, nutrients, carbon dioxide and
oxygen.

Basic needs
Excretion
Growth
Living processes
Movement
Nutrition
Reproduction
Respiration
Sensitivity


Ainslie, K. (1994). Why do my plants need so much water?. Retrieved March 20,
2012, from http://www.pa.msu.edu/sciencet/ask_st/092194.html
Allen, J. (2012). Seven life processes of a plant. Retrieved March 20, 2012, from
http://www.ehow.com/list_6731235_seven-life-processes-plant.html
Campbell, N. A., Reece, J. B., Mitchell, L. G., Taylor, M. R. (2003). Biology
(4th ed.). San Francisco, CA: Benjamin Cummings.
Green, N. P., Stout, G. W, Taylor, D. J. (1993). Biological science (2nd ed.).
Oxford, UK: Oxford University Press.
Johnson, G. B. (2000). The living world (2nd ed.). Boston, MA: McGraw Hill Higher
Education.
Kindersley, D. (2007). Plant sensitivity. Retrieved March 20, 2012, from
http://www.teachervision.fen.com/dk/science/encyclopedia/plant-sensitivity.
html
RCN.(2011). Roots. Retrieved March 20, 2012, from
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Roots.html
Schultz, S. T. (2012). Reproduction in plants. Retrieved March 20, 2012, from
http://www.biologyreference.com/Re-Se/Reproduction-in-Plants.html

Topic
2
Cell Structure
and
Organisation
LEARNING OUTCOMES
1. Describe the levels of organisation of life;
2. Differentiate prokaryotic and eukaryotic cells;
3. Describe animal cell structures and their functions;
4. Describe plant cell structures and their functions; and
5. Explain the movement of substances across the membranes.
INTRODUCTION
A living thing is called an organism. Life on earth is represented by a great
variety of organisms. There are single-cell organisms called prokaryotes and
multicellular organisms called eukaryotes. The general structure of an animal cell
and a plant cell is quite similar with some differences between them.
In this topic, we will be looking at the levels of organisation of life, prokaryotes
and eukaryotes, the structure of the animal and plant cells, its parts and the
organelles in them. Lastly we will look at the different methods of movement of
substances across the cell membranes.

TOPIC 2 CELL STRUCTURE AND ORGANISATION 25
INTRODUCTION TO LIFE AND LEVELS OF
ORGANISATION
2.1
Life on earth started as a unicellular organism. Later, some evolved into
multicellular organisms. In unicellular (single-celled) organisms, the single cell
performs all life functions. It functions independently. However, multicellular
(many celled) organisms have various levels of organisation within them.
Individual cells may perform specific functions and also work together for the
good of the entire organism. The cells become dependent on one another.
Multicellular organisms have the following five levels of organisation ranging
from the simplest to the most complex. This can be seen in Figure 2.1.
Figure 2.1: Levels of organisation
Now, let us take a look at Table 2.1 to learn more about each level. There are also
examples for each level of organisation.

TOPIC 2 CELL STRUCTURE AND ORGANISATION
26
Table 2.1: Levels of Organisation
Level Description Example
Cells The basic unit of structure and function
in living things.
May serve a specific function within the
organism.
Blood cells, nerve cells, bone
cells.
Tissues Made up of cells that are similar in
structure and function which work
together to perform a specific activity.
Connective, epithelial, muscle
and nerve.
Organs Made up of tissues that work together
to perform a specific activity
Heart, brain, skin.
Systems Groups of two or more tissues that
work together to perform a specific
function for the organism.
Circulatory system, nervous
system, skeletal system.
Organism Entire living things that can carry out all
basic life processes. Meaning, they can
take in materials, release energy from
food, release wastes, grow, respond to
the environment and reproduce.
Usually made up of organ systems, but
an organism may be made up of only
one cell such as bacteria or protist.
Bacteria, amoeba, mushroom.
SELF-CHECK 2.1
1. Describe the five levels of organisation in an organism.
2. Does this sequence represent the levels of organisation from the
simplest to the most complex?

ACTIVITY 2.1
The levels of organisation also happen in multicellular plants. Can you
name some examples of cells, tissues, organs and systems in plants?
Post your answer in the forum.
PROKARYOTIC AND EUKARYOTIC CELLS
2.2
We have learned that a cell is the basic unit of life. It is the basic unit of an
organism and consists of a jelly-like material surrounded by a cell membrane. In
the cell itself, there are structures or organelles that have different functions for
the cell.
According to the organisation of their structures, living cells come in two basic
types, prokaryotic (also spelt as procaryotic) and eukaryotic (also spelt as
eucaryotic) cells. These two cells can be seen in Figure 2.2.
(a) (b)
Figure 2.2: Prokaryote (a) and eukaryote (b)
Source: http://www.daviddarling.info
2.2.1 Prokaryotic Cells
The Greek word ÂkaryoseÊ means ÂkernelÊ, as in a kernel of grain. In biology, this
root word is used to refer to the nucleus of a cell. ÂProÊ means ÂbeforeÊ, and ÂeuÊ
means ÂtrueÊ, or ÂgoodÊ. Thus,ÊProkaryoticÊ means Âbefore a nucleusÊ. Bacteria and
other single or unicellular organisms are in the prokaryotic class.

28
Prokaryotic cells are smaller and simpler compared to eukaryotic. The cell is
structurally simple because of its small size. In many single organisms, the
smaller a cell is, the greater is its surface-to-volume ratio (the surface area of a cell
compared to its volume). This can be seen in a prokaryotic spherical cell
of 2 micrometers (m) in diameter. It has a surface-to-volume ratio of
approximately 3:1, while a spherical cell having a diameter of 20 m has a
surface-to-volume ratio of around 0.3:1. A large surface-to-volume ratio, as seen
in smaller prokaryotic cells, means that nutrients can be easily and rapidly
transferred and sent to any interior part of the cells.
2.2.2 Eukaryotic Cells
Eukaryotic, on the other hand, means Âpossessing a true nucleusÂ. Human beings,
animals, plants, fungi, protozoans and algae cells are all eukaryotic cells. This is a
big clue on the differences between these two cell types. Prokaryotic cells have no
nuclei, while eukaryotic cells have true nuclei.
Eukaryotic cell is much bigger in size compared to the prokaryotic cell. Due to
the large size, it has a limited surface area when compared to its volume. It
means that nutrients cannot rapidly diffuse to all interior parts of the cell easily.
Thus, the eukaryotic organism cells require a variety of specialised internal
structures or organelles to carry out metabolism, provide energy and transport
chemicals throughout the cell. However, both Prokaryote and Eukaryote cells
must carry out the same functions for life processes.
2.2.3 Prokaryotic versus Eukaryotic Cells
Both Prokaryote and Eukaryote cells have some similarities and differences.
Learning these terms will help us understand a cell better by recognising them in
terms of these elements:
(a) Structural (cytoskeleton, flagella and cilia);
(b) Endomembrane (plasma membrane, nucleus, Golgi apparatus, lysosome);
(c) Energy-producing organelles (mitochondria, chloroplasts); and
(d) Genetic materials (chromosomes, nucleolus, ribosomes).

Unfortunately, not all elements mentioned are present in all type of cells. It
means that if one particular element is present in the prokaryotic organism, that
element may not be found in the eukaryotic cells and vice-versa. Let us examine
these features of elements of the type of cells in Table 2.2.
Table 2.2: Prokaryotic versus Eukaryotic Cells
Prokaryotic Eukaryotic
Features Bacteria Plant Animal
Size (diameter) 0.55 m 40 m 15 m
Cell wall Yes
(contains peptidoglycan)
Yes
(contains
cellulose)
No
Genetic material A single circular molecule and
DNA is naked.
DNA linear, associated with
histones (proteins), in a
nucleus, surrounded by a
nuclear envelope.
Ribosomes 70S ribosomes (smaller) 80S ribosomes (larger)
ER, Golgi
apparatus No Yes
Mitochondria No
(respiration occurs on an
unfolding of the cell
membrane called the
mesosome.)
Yes
Chloroplasts No Yes No
Source: http://www.dr-sanderson.org
SELF-CHECK 2.2
Explain the differences between prokaryotic and eukaryotic cells.

30
ANIMAL CELLS
2.3
Eukaryotic cells are found in two classes of living things. They are animals and
plants. As indicated in the earlier subtopic, an eukaryotic cell is much bigger in
size, more complex and requires a variety of specialised internal structures or
organelles to carry out metabolism, provide energy and transport chemicals
throughout the cell. In this subtopic, we are going to look at animal cells.
2.3.1 General Structure of Animal Cells
Animal cells are eukaryotes or have true nuclei. They are bigger compared to
prokaryotic cells. This larger size means that there is a lot more space inside the
cell like your studio apartment. Eukaryotic cell is like a gigantic warehouse. In
order to make this huge space relatively as efficient as the small space, a lot of
compartmentalisation and internal specialisation is required. Therefore, the cell
has many organelles to do specific functions.
However, the majority of the eukaryotic cells, like in the animal cells, will have
structures namely:
(a) Plasma membrane;
(b) A nucleus;
(c) Chromosomes;
(d) Numerous membrane-bound cytoplasm organelles: mitochondria, rough
endoplasmic reticulum (rer), smooth endoplasmic reticulum (ser);
(e) Lysosomes;
(f) Ribosomes;
(g) Golgi body or apparatus; and
(h) A Cytoskeleton.

Now, let us have a look at Figure 2.3 which shows a cell of an animal.
Figure 2.3: A cell of an animal
Source: Johnson (2000)
You have just learned the features of animal cells. Now you need to conduct an
experiment (Activity 2.2) in the Biology laboratory about animal cells taken from
your body. In doing this, you need to take a sample from your inner cheek and
examine it very carefully using the right procedures under a light microscope.
However, before you start the experiment, note that a human cheek cell should
look like the one in Figure 2.4.
Figure 2.4: Human cheek cell
Source: http://www.aber.ac.uk

32
ACTIVITY 2.2
Do the following experiment to observe the appearance of your cheek
cells under a light microscope.
Title of Experiment: Examining the structure of human cheek cells under
a microscope.
Materials Needed: A light microscope, several glass slides and cover
slips, forceps, a dropping pipette, 5% iodine methelyne blue solution,
cotton, a scalpel for scrapping the upper layer of your cheek and some
prepared slides of stained human cheek cells.
Procedure:
1. Using a scalpel, scrape your inner cheek and wipe it on a piece of
glass slide. Spread it wide to get a large area. Apply a small drop of
iodine methelyne blue solution using a dropping pipette.
2. Using forceps, cover the cheek sample with the cover slip
CAUTION: Iodine solution is an irritant poison. Avoid skin/eye
contact; do not ingest it. Should this happen, flush the spill and
splash it with water for 15 minutes; rinse your mouth with water
and call your tutor.
3. Put the slide under the microscope and examine it starting with the
low power first and then with the high power.
4. Sketch a few cells as they appear under the high power. How many
dimensions do the cells appear to have when viewed under high
power? Sketch a cell as it would appear if you could see it in three
dimensions.
5. Identify the features of your cheek cells compared to the animal cells
that you have learned.
6. Replace your cheek sample slide with the prepared stained human
cheek cells.
7. Examine the cheek cells under the low and then the high power of
the microscope. Compare the similarities and differences of the
cheek cells you prepared with the one purchased. Draw several of
the cells seen from both slides.
8. Make an analysis of your experiment.
9. Compare your results with those of your classmates.
10. Extra journey: Browse the Internet for more information, diagrams,
pictures and other similar experiments.

2.3.2 Function of Animal Cell Structures
As you have learned previously, an animal cell contains many structures. These
structures perform different functions. Let us take a look at the function of each
of the structures listed in Table 2.3.
Table 2.3: Function of Animal Cell Structures
Animal Cell
Structure Function
Cell
Membrane
Among the various membranes of the animal cell, the plasmalemma is
the cell surface membrane (Figure 2.5). It consists of two layers of lipids
(phospholipid bilayers) sandwiched between two types of protein layers
molecule. It is semi-permeable and controls the exchange of substances
between the cell and its environment.
Figure 2.5: Plasmalemma
Source: Green, Stout, Taylor (1993)
Nucleus The nucleusis the largest cell organelle or structure that is enclosed by an
envelope of two membranes (Figure 2.6).
Figure 2.6: Nucleus
As can be seen in Figure 2.6, this envelope is perforated by nuclear pores.
It contains chromatin which is the extended form taken by chromosomes
during interphase. The nucleus contains a nucleolus. In the
chromosomes, DNA molecule of inheritance of that particular organism
can be found. DNA is organised into genes that control all activities of
the cell. During the replication process, nuclear division occurs.
Ribosomes containing proteins are manufactured by nucleolus.

34
Endoplasmic
Reticulum
(ER)
The extensive system of internal membranes is the endoplasmic
reticulum (ER) (Figure 2.7). Endoplasmic means Âwithin the cytoplasmÊ,
while reticulum is a Latin word meaning Âlittle netÊ.
Figure 2.7: Endoplasmic reticulum
As can be seen in Figure 2.7, ER is a kind of weaving sacs that creates a
series of channels and interconnections to form tubes called cisternae.
On the surface of ER is a place where carbohydrates and lipids
are manufactured by cells. If ribosomes are found on the surface of
endoplasmic reticulum it is called rough ER. However, if ribosomes are
absent, it is called smooth ER. Smooth ER is the site of lipid and steroid
synthesis.
Ribosomes As mentioned earlier, ribosomes are found on the surface of rough ER
and freely suspended in cytoplasm ER (Figure 2.8). They are very small
organelles consisting of a large and small subunit, made of protein
(polypeptide) and RNA. However, they are slightly smaller ribosomes
found in mitochondria (and chloroplasts in plants). Their functions are
the sites of protein synthesis.
Figure 2.8: Ribosome
Mitochondria Mitochondria (singular: mitochondrion) are organelles that convert
energy from chemical form to another. They are the ÂpowerhousesÊ of the
cell (Figure 2.9). They carry out cellular respiration, where chemical
energy of foods (like sugars) are converted into molecules called
adenosine triphosphates (ATP). ATP is the main energy source for
cellular work.

Figure 2.9: Mitochondria
Sources: www.modares.ac.ir
As can be seen in Figure 2.9, a mitochondrion is surrounded by an
envelope consisting of two membranes. The inner membrane is in folded
form; cristae (singular: crista) which increases the membraneÊs surface
area, thus enhancing the mitochondrionÊs ability to produce ATP. It
contains a matrix with ribosomes, that is a circular DNA molecule and
phosphate granules. The matrix is the site of Krebs cycle enzymes and
fatty acid oxidation.
Golgi
apparatus
Golgi apparatus was named after the Italian biologist, Camillo Golgi.
This apparatus is a stack of flattened, membrane-bound sacs
(Figure 2.10). Stacks may form discrete dictyosomes in plant cells or an
extensive network as in many animal cells. The Golgi apparatus
performs several functions in close partnership with the ER. Golgi
apparatus receives and modifies substances made by the ER.
Figure 2.10: Golgi apparatus
Sources: www.modares.ac.ir

36
Lysosome A lysosome is a simple spherical sac bound by a single membrane
(Figure 2.11).
Figure 2.11: Lysosomes
Sources: www.biologie.uni-hamburg.de
It contains digestive enzyme (hydrolytic enzyme). The word ÂlysosomeÊ
in Greek means Âbreakdown bodyÊ. Its main function is related to
breaking down the enzymes or molecules in the cell. The lysosomal
compartments store digestive enzyme safely isolated from the rest of the
cytoplasm. In addition, lysosome also helps to destroy harmful bacteria.
White blood cells ingest bacteria into vacuoles, the lysosomal enzymes
emptied into them and then destroy the bacteria cell walls. Thus,
lysosome serves as recycling centres for damaged organelles.
Microbodies The other important organelle in animal cells is microbodies.
(Figure 2.12).
Figure 2.12: Microbodies
Sources: www.bio.mtu.edu
They possess a single membrane, frequently spherical and typically
measure from 20 to 60 nanometres in diameter. These contain fine
granules or crystals. Microbodies contain catalase, an enzyme that
functions to break down hydrogen peroxide. All are associated with
oxidation reactions.

SELF-CHECK 2.3
Explain the function of these animal cell structures:
(a) Cell Membrane:________________________________________
(b) Nucleus: ______________________________________________
(c) Mitochondria: _________________________________________
PLANT CELLS
2.4
Now, let us take a look at plant cells. Plant cells are similar to animal cells.They
are eukaryotic and have similar components as animal cells. However, they have
three major differences that animal cells do not have. The three differences are:
(a) Plant cell wall is somewhat different from animal cell wall. The cell walls
reinforce the structures containing cellulose and lignin to make them rigid.
(b) Plants are autotrophic. They are energetically self supporting by making
their own foods using light energy from the sun. The light energy and
chloroplasts (containing chlorophyll and enzymes) are factors in carrying
out photosynthesis to manufacture foods.
(c) Plant cells have very large vacuoles. This vacuole is a single membrane
organelle used for storing organic acids, salts, etc. in the process of making
foods during photosynthesis.
2.4.1 General Structure of Plant Cells
A plant cell is larger in size compared to an animal cell. The cell wall typically
consists of more or less rigid cell wall and a protoplast (from the word
ÂprotoplasmÊ). A protoplast consists of cytoplasm and a nucleus. In the
cytoplasm, there are certain distinct organelles and systems of membranes. In a
plant cell, there are plasma membrane, nucleus, plastids, mitochondria,
microbodies, vacuoles, ribosomes, endoplasmic reticulum (ER) and microtubules.
This can be seen in Figure 2.13.

38
Figure 2.13: Eukaryotic cell (Plant)
Source: Johnson (2000)
2.4.2 Structure of Onion Cell
After learning the features of animal and plant cells, you should be able to
discuss their similarities and differences in the structures. Do another experiment
(Activity 2.3) in the Biology laboratory on plant cells. Bring two bulbs of onions
from home. Take an example of a plant cell from the onion skin. You need to
examine these very carefully using the right procedures in the lab. See the
structures and draw diagrams of the onion cell as you see it using the microscope
and then compare it with the prepared stained slide.
Before you begin the experiment, here is the structure of an onion cell and its
nucleus as shown in Figure 2.14.
(a) (b)
Figure 2.14: Onion cell (a) and its nucleus (b)
Source: http://biology.clc.uc.edu

ACTIVITY 2.3
Do the following experiment to observe the appearance of onion cells
under a light microscope.
Title of Experiment: Examining the structure of onion cells under a
microscope.
Materials Needed: A light microscope, several glass slides and cover
slips, forceps, a dropping pipette, Wright Stain, 5% iodine solution, a
razor blade, tissue paper and some prepared slides of the onion cell.
Procedure:
1. Scrape the inner side of the onion skin using a razor blade. This
membrane is called the epidermis. Using forceps, pull away the
epidermis from the inner surface.
CAUTION: Be careful not to wrinkle the membrane.
2. Put it on a glass slide carefully and apply a droplet of water. Cover
with the cover slip and place it on the microscope stage. Examine
the unstained specimen using the low power and draw diagrams of
the cell structure.
3. Remove the specimen from the microscope stage. Apply a little
amount of Wright Stain, then re-examine using the low power. Add
a drop of iodine to the specimen from the edge of the cover slip.
Draw the fluid underneath using a scrap of tissue paper.
4. View the stained onion specimen, first using the low power, then
the high power.
5. Look and draw the nucleus, cell wall, vacuole, cytoplasm and other
structures as seen.
6. Remove the wet specimen. Now, replace it with the prepared slide
of the onion cell specimen. View, first using the low power, then
the high power.
7. Draw a table, write the similarities and differences you see for both
wet and prepared slides, in terms of their structures.
8. Make an analysis of your experiment.
9. Compare your results with those of your classmates.
10. Extra journey: Browse the Internet for more information, diagrams,
pictures and other works of this experiment.

40
2.4.3 Function of Plant Cell Structures
As mentioned earlier, cells of higher plants contain all organelle or structures
found and have similar functions as in the animal cells. However, there are
exceptions. Certain organelles not found in animals are found in plants of higher
order. They are the cell wall, organelle called chloroplast and large vacuoles.
Let us take a look at Table 2.3 which shows the function of each plant cell
structure.
Table 2.3: Function of Plant Cell Structures
Plant Cell
Structure Function
Cell wall Animal cells have plasma membrane. Plant cells have cell walls thick,
rigid membranes surrounding the plant cells (Figure 2.15).
Figure 2.15: Plant cells (cell walls and nuclei are visible)
Source: http://www.physicalgeography.net
These plant cell walls are composed totally or partially of a carbohydrate
called cellulose that is different from the proteins of prokaryotic cell walls.
The function of this cell wall is to support and together with the central
vacuole, create stiffness and turgidity in plant structures (in the leaves).

Large
vacuole
Plant cells contain a specialised vacuole called the central vacuole or large
vacuole (Figure 2.16).
Figure 2.16: Large vacuole
Source: http://www.physicalgeography.net
This is a large, fluid-filled sac structure bounded by a single membrane.
The vacuole is filled mostly with water but also some impurities
including mineral or protein. Thus, the water concentration is always less
than 100%. When the cell is filled with enough water, osmosis causes the
central vacuole to swell. This also causes the cell plasma membrane to
press against the inside of the cell wall and the leafÊs tissues to be stiff or
turgid.
Plastids Plastids are organelles found only in plant cells and in higher plants,
develop from small bodies called proplastids. Proplastids are found in
meristematic regions. Plastids are family organelles containing:
(a) Chloroplasts composed of a double layer of modified membrane-bound
(protein, chlorophyll, lipid) like mitochondria (Figure 2.17).
The membrane contains chlorophyll and carotenoid pigments. They
have a special function, that is, to carry out photosynthesis. Just like
mitochondria, their inner membrane is very complicated. In fact, it
is formed into many thylakoid structures that perform similar
function as performed by the thylakoids in prokaryotic cells.

42
Figure 2.17: Plant cells with visible chloroplasts (granules)
Source: http://news.softpedia.com/
(b) Chromoplasts are non-photosynthetic coloured plastids. These
contain mainly red, orange or yellow pigments (carotenoid). These
colours are associated with fruits, such as tomato, pepper, and
carrot roots.
(c) Leucoplasts are colourless plastids. They lack pigmentation and are
usually modified for food storage mostly in plant organs like roots,
seeds and young leaves.
Chlorophyll Chlorophyll is a green substance pigment in plant cells (Figure 2.18).
Figure 2.18: Chlorophyll, the green substance
Source: http://www.nature-education.org
Chlorophyll and enzymes help plants to carry out photosynthesis to
manufacture food. During photosynthesis, chlorophyll takes in energy by
absorbing light energy from sunlight and breaks down water molecules
into hydrogen and oxygen. The hydrogen then combines with carbon
dioxide to make sugars or glucose. The oxygen is released back into the
atmosphere for us.

SELF-CHECK 2.4
1. Do all plant cells contain organelles?
2. Which organelles are found in a plant cell but not in an animal cell?
Why?
3. Explain the functions of the different plant cell structures.
MOVEMENT OF SUBSTANCES ACROSS THE
MEMBRANE
2.5
The plasma membrane is a semi-permeable lipid bilayer found in all cells that
controls water and certain substances in and out of the cell. Figure 2.19 shows the
structure of a cell membrane. Scientists describe the organisation of the
phospholipids and proteins usingthe fluid mosaic model. That model shows that
the phospholipids are in the shape of head and a tail. The heads like water
(hydrophilic) and the tails do not like water (hydrophobic). The tails bump up
against each other and the heads are out facing the watery area surrounding the
cell. The two layers of cells are called the bilayer.
Figure 2.19: Structure of a cell membrane
Source: http://www.biology4kids.com
Do you know why substances moves in and out of the cell? This is to ensure that:
(a) The nutrients can be easily transported into the cells;
(b) The gases can be exchanged;
(c) The metabolic waste from the cell can be got rid of; and

44
(d) The ph value and ionic concentration of the cell can be maintained
(Figure 2.20).
Figure 2.20: Substances in and out of cells
Source: http://spmbiology403.blogspot.com
Substances can be moved in and out through the membrane by different
methods; diffusion, facilitated diffusion, osmosis and active transport. Let us take
a look at each method in detail.
2.5.1 Diffusion
One method of movement through the membrane is diffusion. Diffusion is the
movement of molecules from a region of higher concentration to one of lower
concentration. This movement occurs because the molecules are constantly
colliding with one another. The net movement of the molecules is to move away
from the region of high concentration to the region of low concentration.
Diffusion is a random movement of molecules down the pathway called the
concentration gradient. Molecules are said to move down the concentration
gradient because they move from a region of higher concentration to a region of
lower concentration. A drop of dye placed in a beaker of water illustrates
diffusion as the dye molecules spread out and colour the water. When diffusion
between two concentrations is equal, there is no more movement and the system
is said to have reached diffusion equilibrium.

2.5.2 Facilitated Diffusion
A second mechanism for movement across the plasma membrane is facilitated
diffusion. Facilitated diffusion is a type of passive transport that allows
substances to cross membranes with the assistance of special transport proteins.
Some molecules and ions such as glucose, sodium ions and chloride ions are
unable to pass through the lipid bilayer of cell membranes.
Certain proteins in the membrane assist facilitated diffusion by permitting only
certain molecules to pass across the membrane. The proteins encourage
movement in the direction that diffusion would normally take place, from a
region with a higher concentration of molecules to a region of lower
concentration.
Through the use of ion channel proteins and carrier proteins that are embedded
in the cell membrane these substance can be transported into the cell. Ion channel
proteins allow specific ions to pass through the protein channel. The ion channels
are regulated by the cell and are either open or closed to control the passage of
substances into the cell. Carrier proteins are bound to specific molecules, change
shape and then deposit the molecules across the membrane. Once the transaction
is completed the proteins return to their original position. Figure 2.21 illustrates
facilitated diffusion.
Figure 2.21: Facilitated diffusion
Source: http://biology.about.com
2.5.3 Osmosis
Another method of movement across the membrane is osmosis. Osmosis is the
movement of water from a region of higher concentration of water to one of
lower concentration. ItÊs the movement of water from a low concentration of
solute to a higher concentration of solute. Osmosis often occurs across a

46
membrane that is semipermeable. A selectively permeable membrane is one that
allows unrestricted passage of water, but not solute molecules or ions.
Thus,the direction of the movement of water depends on the types of solution as
can be seen in Table 2.4.
Table 2.4: Types of Solution
Types of
Solution Description
Isotonic ÂIsoÊ means Âthe sameÊ. If the concentration of solute (salt) is equal on
both sides, the water will move back and forth. It will not have any
result on the overall amount of water on either side (Figure 2.22).
Figure 2.22: Isotonic solution
Hypotonic The word ÂhypoÊ means ÂlessÊ. In this case, there are less solute (salt)
molecules outside the cell; since salt sucks, water will move into the cell
(Figure 2.23). The cell will gain water and grow larger.
Figure 2.23: Hypotonic solution

In plant cells, the central vacuoles will fill and the plant becomes stiff
and rigid, the cell wall keeps the plant from bursting.
In animal cells, the cell may be in danger of bursting, organelles
called contractile vacuoles will pump water out of the cell to prevent
this.
Hypertonic The word ÂhyperÊ means ÂmoreÊ. In this case, there are more solute (salt)
molecules outside the cell, which causes the water to be sucked out
towards that direction (Figure 2.24).
Figure 2.24: Hypertonic solution
In plant cells, the central vacuole loses water and the cells shrink,
causing wilting.
In animal cells, the cells also shrink.
In both cases, the cells may die.
This is why it is dangerous to drink sea water. There is a myth that
drinking sea water will cause you to go insane and people stranded at
sea will speed up dehydration (and death) by drinking sea water.
This is also why „salting fields‰ was a common tactic used during wars,
it would kill the crops in the field, thus causing food shortages.
Source:http://www.biologycorner.com

48
2.5.4 Active Transport
A fourth method for movement across the membrane is active transport. When
active transport takes place, a protein moves a certain material across the
membrane from a region of lower concentration to a region of higher
concentration. Because this movement is against the concentration gradient, the
cell must expend energy that is usually derived from a substance called
adenosine triphosphate or ATP. An example of active transport occurs in human
nerve cells. Here, sodium ions are constantly transported out of the cell into the
external fluid bathing it, a region of high concentration of sodium. This transport
of sodium sets up the nerve cell for the impulse that will occur within it later.
2.5.5 Endocytosis and Exocytosis
We have discussed the substances movement into and out of the cell membrane
through passive or active transport. However, large food particles, whether they
be grains of sugar or other organisms, cannot simply diffuse across the
membrane; they are just too big.
As a cell approaches a food particle, either the food particle pushes into the cell
membrane forming an indentation, or pseudopodia which is extended from the
cell around the particle. When the two extensions of the cell membrane meet on
the other side of the particle, they close and form a vacuole around the food
inside the cell. This process is called endocytosis.
Meanwhile, exocytosis is a very similar process. In fact, it is just endocytosis in a
reverse order. A vacuole within the cell moves toward and fuses with the cell
membrane. In this manner, the contents of the vacuole are expelled into the
external environment. This may occur, for example, after a cell has taken in a
large particle through endocytosis, digested it using the enzymes in the
lysosome, and then needs to expel the waste products.

Endocytosis and exocytosis are general terms to describe the process by which
anything is taken into or expelled from the cell through the action of vacuoles. If
the particles are in the form of solid, then the process is called phagocytosis. If
the particles are in the form of liquid the process is called pinocytosis. Figure 2.25
illustrates endocytosis and exocytosis.
Figure 2.25: Endocytosis and exocytosis
Source: http://www.kscience.co.uk
SELF-CHECK 2.5
From the list given, circle the passive transport methods.
(a) Osmosis
(b) Diffusion
(c) Facilitated diffusion

50
ACTIVITY 2.4
1. Figure 2.26 shows two containers of equal volume. They are
separated by a membrane that allows free passage of water,
but totally restricts passage of solute molecules. Solution A has
3 molecules of the protein albumin (molecular weight 66,000) and
Solution B contains 15 molecules of glucose (molecular weight
180). Into which compartment will water flow, or will there be no
movement of water? Discuss with your classmates.
Figure 2.26:Two containers of equal volume
2. Watch the videos and animations in the links given and draw
diagrams to describe the movement of substances across the
membrane through the various methods:
(a) http://www.northland.cc.mn.us/biology/biology1111/ani
mations/passive3.swf; and
(b) http://highered.mcgraw-hill.
com/sites/dl/free/0072464631/291136/facDiffusion.s
wf.
3. Active transport is quite difficult to visualise. Surf the Internet to
find videos or animation that illustrate this method of
transportation. Watch and understand the active transport
mechanism. Explain the process to your classmates with the help
of diagrams.

There are five levels of organisation in living things. These levels in sequence
are the cells, tissues, organs, organ systems and organisms.
Organisms are composed of functional structures called cells. Cells are
categorised into two: (i) single or unicellular and (ii) multicellular.
Single or unicellular organisms are prokaryotes while multicellulars are
eukaryotes.
Multicellular organisms are plants and animals.
Eukaryotic cells, in plants and animals, have similar organelles and functions.
However, there are differences between plant and animal cells.
Substances move across the cell membrane through passive or active
transport.
Passive transport of substances across membrane include diffusion,
facilitated diffusion and osmosis.
Diffusion is the movement of molecules from a region of higher concentration
to one of lower concentration
Facilitated diffusion is a type of passive transport that allows substances to
cross membranes with the assistance of special transport proteins.
Osmosis is the movement of water from a region of higher concentration of
water to one of lower concentration
Active transport takes place when a protein moves a certain material across
the membrane from a region of lower concentration to a region of higher
concentration.
Energy is needed in active transport, usually derived from a substance called
adenosine triphosphate or ATP.

52
Active transport
Cell membrane
Diffusion
Endoplasmic reticulum
Eukaryo
Facilitated diffusion
Golgi body
Mitochondria
Multicellular
Nucleus
Osmosis
Proka
Ribosomes
Unicellular
Biology-Online. (2005). Movement of substances across membrane. Retrieved
March 20, 2012, from http://www.biology-online.org/9/3_movement_
molecules.htm.
Campbell, N. A., Reece, J. B., Mitchell, L. G., Taylor, M. R. (2003). Biology
(4th ed.). San Francisco, CA: Benjamin Cummings.
CikguJes. (2008).What is active transport? Retrieved March 20, 2012, from
http://spmbiology403.blogspot.com/2008/08/active-transport.html.
CliffsNotes. (2012). Movement through plasma membrane. Retrieved March 20,
2012, from http://www.cliffsnotes.com/study_guide/Movement-through-the-
Plasma-Membrane.topicArticleId-8741,articleId-8588.html.
Fankhauser, D. B. (2011). Cells: the functional units of organisms. Retrieved
March 20, 2012, from
http://biology.clc.uc.edu/fankhauser/ labs/cell_biology/cells_lab/cells.htm
Green, N. P., Stout, G. W., Taylor, D. J. (1993). Biological science (2nd ed.).
Oxford, UK: Oxford University Press.
Johnson, G. B. (2000). The living world (2nd ed.). Boston, MA: McGraw Hill Higher
Education.

Neumeyer, R. (2003). Protozoa.Retrieved March 20, 2012, from
http://www.microimaging.ca/protozoa.htm.
Westbroek, G. (2000). Levels of organization. Retrieved March 20, 2012, from
http://utahscience.oremjr.alpine.k12.ut.us/sciber00/7th/cells/sciber/level
org.htm.

Topic
3

Nutrition
and Classes
of Food

LEARNING OUTCOMES
1. Describe the different types of nutrition;
2. List the characteristics of the different classes of food;
3. Explain the concept of a balanced diet;
4. Define food chains, food webs and energy pyramids;
5. List the various nutrients needed by plants;
6. Explain the process of photosynthesis;
7. Describe food technology, including genetically modified food; and
8. Explain how to practise a healthy lifestyle.
INTRODUCTION
All living things need food to survive. Food provides us with energy for all living
processes such as growth and development and also to maintain optimal health.
In this topic, you will learn about the different types of nutrition, the classes of
food, the concept of a balanced diet, food technology and how to practise a
healthy life style. You will also explore nutrition in plants, the process of
photosynthesis and the concepts of food chains, food webs and energy pyramids.

TOPIC 3 NUTRITION AND CLASSES OF FOOD 55
TYPES OF NUTRITION
What exactly is nutrition? Nutrition is the process by which organisms obtain
energy from food for growth, maintenance and repair of damaged tissues.
Nutrients are the useful substances that are present in food.
We shall first look at the different types of nutrition. There are two main types of
nutrition as can be seen in Table 3.1.
Table 3.1: Types of Nutrition
Autotrophic Nutrition Heterotrophic Nutrition
It is a process in which organisms make
their own food from simple inorganic
raw materials such as carbon dioxide,
and water by using light or chemical
energy.
In photosynthesis, organisms make
complex organic compounds from
carbon dioxide and water using light
energy in the presence of chlorophyll.
Example: all green plants.
In chemosynthesis, organisms make
complex organic materials from carbon
dioxide and water using chemical
energy. Example: certain types of
bacteria.
It is a process in which organisms feed
on complex, ready-made organic foods
to obtain the nutrients they require.
The three main types of heterotrophic
nutrition are holozoic nutrition,
saprophytic nutrition and parasitic
nutrition.
In holozoic nutrition, organisms feed on
solid organic material derived from the
bodies of other organisms. Examples:
humans and cows.
In saprophytic nutrition, organisms
feed on the dead and decaying matter
on which they live and grow. Examples:
fungi and certain bacteria.
In parasitic nutrition, organisms feed on
other living organisms known as hosts.
Examples: tapeworms and ticks.
3.1

5 6 TOPIC 3 NUTRITION AND CLASSES OF FOOD
Now, let us take a look at Figure 3.1 which summarises the various types of
nutrition.
Figure 3.1: Types of nutrition
3.1.1 Holozoic Nutrition
Let us take a closer look at holozoic nutrition. Can you recall what holozoic
nutrition is? Yes. Holozoic organisms feed on solid organic matter which can be
either plants or animals. Holozoic organisms may be classified according to their
diet; whether their diet is made up of plants, animals or both. Study Figure 3.2
which shows how holozoic animals are classified according to what they eat.


Figure 3.2: Classification of animals according to what they eat

SELF-CHECK 3.1
1. In your own words, explain the term „nutrition‰ and „nutrients‰.
2. Explain each of the following types of nutrition. Give one example
for each type:
(a) Autotrophic nutrition;
(b) Heterotropic nutrition; and
(c) Holozoic nutrition.
3. Classify the following animals into herbivores, carnivores or
omnivores: eagles, lions, goats, bears, elephants and chickens.
4. Discuss how the animals named in Question 3 have adaptations to
suit their diet.
CLASSES OF FOOD
3.2
The nutrients in food can be divided into seven classes based on their functions
as shown in Figure 3.3.

Figure 3.3: Classes of food
Let us look at each of them in detail.

3.2.1 Carbohydrates
Carbohydrates are the main source of energy and should be the major part of our
daily intake. Carbohydrates consist of three elements:
(a) Carbon;
(b) Hydrogen; and
(c) Oxygen.
There are three main types of carbohydrates based on the number of simple
sugars in the molecules. This is shown in Table 3.2.

Table 3.2: Types of Carbohydrates
Type Number of Simple Sugar Example
Monosaccharide
(simple sugars)
One unit Glucose, fructose, galactose.
Disaccharide
(complex sugars)
Two units Lactose, maltose, sucrose.
Polysaccharide Many units Starch, glycogen, cellulose.

Now, let us learn the terms used in Table 3.1. Sugars are sweet crystalline
compounds, which can dissolve in water and are found in syrup, honey, sugar
cane and fruits. Starch is found in rice, bread and potatoes and is the main energy
storage compound in plants. Glycogen is the main storage compound in animals
and is stored in the liver and muscle cells. Cellulose is the substance that plant
cell walls are made up of. Vegetables and fruits are two examples of food
containing cellulose. All carbohydrates are broken down into simple sugars
(monosaccharide) by enzymes in the digestive tract. However humans cannot
digest cellulose like herbivores because humans do not have the enzyme
cellulose. This means that we cannot get energy from cellulose but it still
performs a useful function: it forms dietary fibre (roughage). We will learn about
the importance of fibre later in this topic.

Before we end the discussion about carbohydrates, let us look at Figure 3.4 which
summarises the main characteristics of carbohydrates.

Figure 3.4: Characteristics of carbohydrates
3.2.2 Proteins
Proteins are complex organic substances which are made up of carbon,
hydrogen, oxygen and nitrogen. Most proteins also contain sulphur and
phosphorus. Foods that are rich in protein include fish, meat, milk, nuts, cheese,
and eggs as shown in Figure 3.5.

Figure 3.5: Sources of protein
Source: http://www.buzzle.com

The basic unit of protein is amino acid. There are 20 naturally occurring amino
acids. These can be divided into two groups:
(a) Essential Amino Acids
Essential amino acids are amino acids that cannot be made by the body. We
must get them from our diet. There are altogether nine essential amino
acids. They are vital for good health and the absence of just one can have
severe consequences.
(b) Non-essential Amino Acids
Non-essential amino acids are amino acids that can be made by the body.
These amino acids are formed from other amino acids. There are eleven
non-essential amino acids.
Animal proteins such as meat contain all the essential amino acids and are
considered as a „complete protein‰. Animal proteins are known as first class
proteins. Plant proteins such as beans are „incomplete proteins‰ in that they do
not contain every essential amino acid. Plant proteins are known as second class
proteins. The common sources of all essential amino acids are food from animal
sources such as eggs and milk while a variety of plant products must be taken
together to provide all the other necessary proteins.
Proteins form the main structure of our body. Therefore, we need protein for
growth of new cells and repairing worn out or damaged body tissues. We also
need proteins to produce enzymes, hormones and some components of
antibodies. In addition, proteins can provide energy when needed. Figure 3.6
summarises the characteristics of proteins.

Figure 3.6: Characteristics of proteins

3.2.3 Fats
Fats are a subgroup of the compound known as lipids. Fats are organic
compounds that contain carbon, hydrogen and oxygen, but unlike
carbohydrates, they contain much less oxygen. Fats are insoluble in water.
Fats are also known as triglycerides. A triglyceride is formed from a molecule of
glycerol and three molecules of fatty acids. Figure 3.7 shows the structure of fat.

Figure 3.7: Structure of fat
Fatty acids are either saturated or unsaturated. Fats containing saturated fatty
acids are called saturated fats while those containing unsaturated fatty acids are
called unsaturated fats. Saturated fats are solids at room temperature. Examples
of saturated fats are animal fats such as butter. An unsaturated fat is usually
liquid at room temperature and is called oil. Examples of unsaturated fats are
vegetable oils such as corn oil. Cholesterol which is the major component of the
plasma membrane is mostly found in saturated fats.
Fats serve as an efficient source of energy. They also act as a solvent for fat-soluble
vitamins and other vital substances such as hormones. Fats keep our
body warm by building a heat insulator under the skin. This may reduce the rate
of heat loss from the skin during the cold season. The oily secretion from certain
glands in the skin can reduce the rate of evaporation of water. Fats are also
important in forming the cell membrane. Figure 3.8 summarises the
characteristics of fats.


Figure 3.8: Characteristics of fats
3.2.4 Vitamins
Vitamins are organic compounds needed by the body in small quantities to
maintain good health. There are two groups of vitamins:
(a) Fat Soluble Vitamins
Fat soluble vitamins such as vitamins A, D, E and K can be stored in body
fat.
(b) Water Soluble Vitamins
Water soluble vitamins cannot be stored in the body and have to be
continuously supplied in the daily diet. Vitamins B and C are water soluble
vitamins.

Figure 3.9 shows the various sources of vitamins.

Figure 3.9: Various sources of vitamins
Source: http://thebest-healthy-foods.com
A varied diet of fresh fruits and vegetables is important to obtain most of
the vitamins that we need. The characteristics of vitamins are summarised in
Figure 3.10.

Figure3.10:Characteristicsofvitamins
3.2.5 Minerals
Minerals are inorganic chemical elements that are usually found in the body.
They are present in the form of ions and are needed in small quantities. They are
required to regulate body processes, build bones, form blood cells, maintain
health and avoid diseases.

Minerals are divided into two groups:

(a) Major Elements
Some major elements needed in large quantities are potassium, sodium,
calcium, magnesium, iron, iodine and phosphorus.

(b) Trace Elements
Some trace elements needed in small quantities are fluorine and chlorine.

Figure 3.11 summarises the characteristics of minerals.

Figure 3.11: Characteristics of minerals
3.2.6 Fibre
Dietary fibre (roughage) is made up of the indigestible cellulose walls of plant
material. Fibre provides bulk to the contents of the large intestine and stimulates
peristalsis. This leads to defecation and prevents constipation. The presence of
adequate dietary fibre in the diet helps to prevent heart and intestinal disorders.
Fibre also absorbs toxic substances in the large intestine and reduces blood
cholesterol level. Figure 3.12 summarises the characteristics of fibre.

Figure 3.12: Characteristics of fibre

TOPIC 3 NUTRITION AND CLASSES OF FOOD
66
3.2.7 Water
Water makes up 70% of our body weight. The main sources of water are fruits,
vegetables and drinking water. It is a very important compound in our body and
mainly acts as a solvent in the transport of wastes and food substances; a
medium for enzymatic reactions; to regulate body temperature; and to maintain
blood concentration. It is also needed in all metabolic processes. Figure 3.13
summarises the characteristics of water.
Figure 3.13: Characteristics of water
SELF-CHECK 3.2
1. Name the different classes of food.
2. Discuss the functions of each of the different classes of foods.
ACTIVITY 3.1
The diseases shown below are due to the lack of a certain vitamin or
mineral. Research these diseases and suggest the vitamin or mineral that
is lacking:
Rickets Night-blindness Anaemia Pellagra Goitre Scurvy Beri beri

BALANCED DIET
The food we consume every day makes up our diet. This includes what we drink
as well as what we eat. Our diet must include all the seven classes of food
described in the previous subtopic. A diet which contains all of these substances
in the right quantities is called a balanced diet. The composition of a balanced
diet varies from one individual to another according to age, sex, job, size, age,
climate and state of health. A balanced diet is important mainly to maintain our
body health and growth, to repair or replace old and damaged cells and provide
enough energy.
A balanced diet will be able to meet the daily energy requirements of the body.
Energy in food is measured in joules (J) or calories (Cal). One calorie equals to 4.2
joules. The amount of heat energy released when one gram of food is completely
burnt in the air is known as its calorific value. Each type of food has a different
calorific value. Therefore, we should choose the correct types of food to ensure
our bodies get sufficient energy. We can use the food pyramid as a guide for a
balanced diet as shown in Figure 3.14.
Let us take a look at the food pyramid based on the Malaysian Dietary
Guidelines (MDG) 2010 as shown in Figure 3.14.

Figure 3.14: The food pyramid
3.3

The food pyramid is one way for people to understand how to eat healthily.
When choosing a healthy diet, simply follow the food pyramid guidelines. Select
the suggested number of servings from the five basic food groups as shown in
the previous Figure 3.14. The food pyramid shows you what and how much food
you should eat to remain healthy. These are the recommendations according to
the food pyramid:
(a) Eat adequately: Rice, noodles, breads, cereals, cereal products and tubers
(48 servings/day);
(b) Eat plenty: Vegetables (3 servings/day);
(c) Eat plenty: Fruits (2 servings/day);
(d) Eat in moderation: Milk and milk products (13 servings/day); and
(e) Eat in moderation: Fish, poultry, meat and legumes (2 servings of
poultry/meat/day, 1 serving of fish/day, 1 serving of legumes/day).
The sixth group (fats, oil, sugar and salt) consists mostly of items that are
pleasing to the palate, but high in fat and calories. These should be eaten in
moderation or the intake should be limited.

ACTIVITY 3.2
Your friend is a champion in bodybuilding sports. Explain to him the
reasons bodybuilders need more proteins such as eggs and meat in
their diet.
FOOD CHAINS, FOOD WEBS AND ENERGY
PYRAMIDS
3.4
The main energy source on earth is the Sun. Solar energy is used by plants to
make food. Green plants which are autotrophs store solar energy in
carbohydrates during photosynthesis. Green plants are also known as producers
as they are capable of producing their own food. Heterotrophs are known as
consumers as they feed on producers. Herbivores are known as primary
consumers as they feed on the producer organisms. Carnivores are secondary
consumers as they eat the primary consumers. What do you think tertiary
consumers are?

3.4.1 Food Chain
Producers and consumers play different roles in a community. The linear feeding
relationship which indicates the transfer of energy from producers to consumers
is known as a food chain. Study Figure 3.15 which shows a food chain.

Figure 3.15: A food chain
Source: http://www.kidsgeo.com
As can be seen in Figure 3.15, notice how all organisms are linked in the food
chain. Each stage of a food chain is called a trophic level. The arrows in the food
chain represent the flow of energy through the ecosystem. Can you identify the
herbivore and carnivores in this food chain? Additionally, try to determine the
primary, secondary and tertiary consumers as well.

3.4.2 Food Web
In reality, an organism usually feeds on several different types of food. Instead of
one simple food chain, there are many food chains which share the same
organism. Many food chains interconnect to form a food web. A food web helps
to maintain a balanced environment by controlling the number of organisms at
each level of the food chain. Study Figure 3.16. How many food chains can you
detect from this food web?

Figure 3.16: A food web
Source: http://ed101.bu.edu
3.4.3 Energy Pyramids
Do you know why there are more herbivores than carnivores in any ecosystem?
Energy flows in one direction along a food chain. Energy is transferred along the
food chain from the photosynthetic producers through several levels of
consumers. The more levels in the food chain, the lesser the energy at the end of
the chain. For example, when a herbivore eats, only a fraction of the energy (that
it gets from the plant food) becomes new body mass; the rest of the energy is lost
as waste or used up by the herbivore to carry out its life processes (e.g.,
movement, digestion, reproduction). Therefore, when the herbivore is eaten by a
carnivore, it passes only a small amount of total energy (that it has received) to
the carnivore. Of the energy transferred from the herbivore to the carnivore,
some energy will be „wasted‰ or „used up‰ by the carnivore.

An energy pyramid is a graphical representation of the energy at each level in a
food chain. They are called pyramids because of the shape of these graphs. An
energy pyramid shows maximum energy at the base and steadily diminishing
amounts at higher levels. This is shown in Figure 3.17.

Figure 3.17: An energy pyramid
Source: http://www.vtaide.com
The energy pyramid shown in Figure 3.17 shows many trees and shrubs
providing food and energy to giraffes. Note that as we go up, there are fewer
giraffes than trees and shrubs and even fewer lions than giraffes. In other words,
a large mass of living things at the base is required to support a few at the top.
Many herbivores are needed to support a few carnivores. This is why there are
more herbivores than carnivores.

SELF-CHECK 3.3
Define food chains, food webs and energy pyramids. Give examples for
each.
ACTIVITY 3.3
Using producers and consumers from a community near where you
live, draw several interconnecting food chains that form a simple food
web.

NUTRIENTS IN PLANTS
3.5
Plants also need nutrients for healthy growth and development. Plants need
carbon, hydrogen, oxygen, phosphorus, sulphur, magnesium, potassium and
iron elements in large quantities. For this reason these elements are called major
elements or macronutrients. In addition to the major elements, certain other
elements are required as well. These are required in small amounts and known as
trace elements or micronutrients. Examples of micronutrients are iron, copper,
manganese, molybdenum and boron. Carbon, hydrogen and oxygen are
macronutrients that can be easily absorbed from carbon dioxide in the
atmosphere and water from the soil. Therefore, deficiency in these nutrients
rarely occurs. The remaining mineral elements are obtained in the form of
inorganic ions from the soil. Table 3.3 shows some essential nutrients in plants.

Table 3.3: Essential Nutrients in Plants
Nutrients Needed by Plants
Major nutrients from water and CO2 C Carbon
H Hydrogen
O Oxygen
Primary Macronutrients N Nitrogen
P Phosphorus
K Potassium
Secondary Macronutrients Ca Calcium
Mg Magnesium
S Sulphur
Micronutrients Fe Iron
Cu Copper
Mn Manganese
Mo Molybdenum
B Boron

Macronutrients and micronutrients are involved in the synthesis of chemical
substances essential for the healthy growth of plants. They are also required for
the various metabolic processes which take place in plants. The absence of one or
more of these nutrients can lead to mineral deficiencies in plants. Table 3.4 shows
the effects of nutrient deficiencies in plants.

Table 3.4: Effects of Nutrient Deficiencies in Plants
Type of
Nutrients Elements Symptoms
Macronutrients Oxygen Growth retardation
Nitrogen Chlorosis; leaves turn yellow
Potassium Occur in mature tissues, growth retardation,
leaves turn to yellowish brown
Calcium Occur in young tissues, drying of the tips of root
and leaf, twisted leaf morphology, retardation of
root growth and decrease in plant growth rate
Magnesium Chlorosis in veins mainly in young leaves,
necrotic at the tip of the leaves, severe deficiency,
necrosis occurs in the entire leaves
Phosphorus Old leaves turn to dark green, appearance of dark
purple pigment (anthocyanin), delayed maturity
Micronutrients Iron Occur in young tissues
Manganese Appear in young leaves in the form of white spots
and interveinal chlorosis
Zinc Spots of necrosis
Copper Necrosis of the leaf margin and reduction in the
concentration of plastocynin pigment
Molybdenum Chlorosis and retardation of plant growth
Figure 3.18 shows phosphorus and calcium deficiency in bean plants.

Figure 3.18: Phosphorus and calcium deficiency in bean plants


SELF-CHECK 3.4
1. List all the elements that are needed in large amounts by
plants.
2. Name three elements that will result in the yellowing of leaves
(chlorosis) in plants if a deficiency of these elements occurs.
PHOTOSYNTHESIS
3.6
Photosynthesis is derived from two words: ÂphotoÊ which means light, and
ÂsynthesisÊ which means making. Therefore, photosynthesis means the making of
food with the help of light. Photosynthesis can be defined as a process carried out
by green plants to make glucose from carbon dioxide and water in the presence
of sunlight and chlorophyll. Oxygen is a by-product of photosynthesis. Here is
the equation for photosynthesis.

Sunlight
Carbon dioxide + Water Glucose + Oxygen
Chlorophyll
3.6.1 Requirements of Photosynthesis
Photosynthesis requires carbon dioxide, chlorophyll, sunlight and water. Carbon
dioxide is absorbed from the air through stomata into the chloroplast.
Chlorophyll is the pigment in chloroplasts which captures sunlight. Sunlight
provides the energy needed for photosynthesis. Water is absorbed through the
roots.
3.6.2 Importance of Photosynthesis
Photosynthesis is important because it:

(a) Provides the Basic Food Source
Plants use light energy to make their own food. Most organisms depend
directly or indirectly on plants for food. Plants are producers and are very
important in providing the basic food source for other life forms on earth.

(b) Maintains the Oxygen Balance
Animals and plants continuously use up oxygen. Combustion (burning of
fuels) and daily human activities (e.g. cooking) also uses up oxygen
through respiration. Through photosynthesis, plants release oxygen into
the environment and replace the oxygen that has been consumed.
3.6.3 Experiment to Show that Photosynthesis has
Taken Place
How can you determine if photosynthesis has taken place in plants? When the
process of photosynthesis takes place, glucose is formed as a product. The
glucose produced during photosynthesis is stored in the plant in the form of
starch. Iodine reacts with starch to produce a deep dark blue (almost black)
colour. The presence of starch in leaves shows that photosynthesis has taken
place.
Carry out the following experiment to determine whether photosynthesis has
taken place in a plant.

Title:
Experiment to determine if photosynthesis has taken place.
Procedure:
1. Pluck a leaf from a plant, which has been exposed to sunlight for a few
hours.
2. Immerse the leaf in a beaker of boiling water to kill it.
3. Place the softened leaf inside a boiling tube containing ethanol.
4. Place the boiling tube inside a beaker of hot water to remove
chlorophyll.
5. Return the leaf to a beaker of hot water to soften leaf and allow
penetration of iodine.
6. Place the leaf on a white tile.
7. Drop iodine solution onto the leaf surface.
8. Record your observation.
Observation:
1. The leaf turns the iodine to dark blue.
2. This shows the presence of starch in the green leaf.
3. This proves that photosynthesis has taken place in the green leaf.


SELF-CHECK 3.5
1. Define photosynthesis.
2. Explain the significance of photosynthesis.
ACTIVITY 3.4
Draw a flow chart to show the relationship between the following:
water carbohydrates oxygen chlorophyll carbon
FOOD TECHNOLOGY
3.7
dioxide chloroplast light
The increase of the world population means there is a need for greater food
supply. The quality and quantity of food production should also be improved to
meet the demands of this increasing population. Food technology is a branch
of food science that deals with the production processes to make foods.
Development of food technology occurs in two ways:
(a) Technological Development to Improve Quality and Quantity of Food
Production
Various methods are employed to improve the quality and quantity of food
production such as direct seeding for rice, hydroponics and aeroponics,
breeding of plants and animals, tissue culture, genetic engineering, soil
management, and biological control.
(b) Technological Development in Food Processing
Technology development in food processing includes the activities
involved in the preparation and preservation of food. This is to ensure that
the food remains safe for consumption whether eaten immediately or later.
The main purpose of food processing is to preserve food by overcoming the
factors that can cause food spoilage. Examples of food processing and
preservation methods are freezing, pickling, fermentation, dehydration,
canning, pasteurisation, radiation and sterilisation.

What is genetic engineering? Genetic engineering is a technique that can increase
the quality and quantity of food production. It is a technique that enables the
characteristics of an organism to be altered by changing the genetic composition
of the organism. For example, genes from plants can be inserted into the DNA of
animal cells and vice versa. The genetically modified organism (GMO) is called a
transgenic organism. Developments in genetic engineering have enabled
transgenic crop plants such as wheat, paddy, tomatoes, legumes, soya beans and
potatoes to be cultivated commercially. These crop plants contain genes from
other organisms to enhance their growth or nutritional properties. Figure 3.19
shows an example of how genetically modified plants are created.

Figure 3.19: Creation of a genetically modified pest resistant plant
Source: http://www.gmac.gov.sg

ACTIVITY 3.5
Currently there is a controversy over the use of genetically modified
(GM) foods. Research this issue and discuss the pros and cons of GM
foods.

DEVELOPING GOOD EATING HABITS
It is important to practise good eating habits. Figure 3.20 shows some guidelines
on how to develop good eating habits.

Figure 3.20: Guidelines on how to develop good eating habits
Do you realise that there are many types of diseases related to imbalanced diets?
Table 3.5 shows the different types of nutrient deficiency diseases in humans.
Table 3.5: Nutrient Deficiency Diseases in Humans
Name of
Diseases
Nutrient
Deficiency Symptoms
Kwashiorkor Protein Dry and scaly skin.
Hair loss.
Wasting muscles.
Loss of appetite and diarrhoea.
Easily tired
Distended abdomen.
Oedema Protein Loose muscles and skin.
Some parts of body become swollen.
Marasmus Energy-producing
food
Very thin.
Very weak.
Starvation.
Anaemia Iron Shortness of breath and headache.
Some parts of body lack oxygen.
Chest pain.
Lips are pale and cracked.
3.8

TOPIC 3 NUTRITION AND CLASSES OF FOOD
79
Goitre Iodine Thyroid gland becomes swollen.
Swelling will press the surface of trachea and
oesophagus.
Breathing difficulties.
Cretinism Iodine Mental retardation and stunted growth.
Rough skin.
Tongue becomes swollen.
Scurvy Vitamin C Walls of blood vessels break easily.
Bruises appear under skin surface.
Bleeding and swollen gums.
Joints become swollen and painful.
Beri beri Vitamin B Diarrhoea.
Swelling at ankles and legs.
Numbness of legs and hands.
Stiffness of muscle.
Mental deterioration.
Heartbeats become faster.
Pellagra Vitamin B Pain in the mouth and tongue.
Dry and reddish skin.
Diarrhoea.
Slow thinking and memory loss.
Rickets Vitamin D Incomplete development of teeth and bones.
Soft and pliable bones.
Head becomes big.
Figure 3.21 shows a photo of a child suffering from kwashiorkor.
Figure 3.21: A child suffering from Kwashiorkor
Source: http://www.asnom.org

SELF-CHECK 3.6
1. Define the term balanced diet.
2. Explain the special food requirements of:
(a) A child;
(b) A pregnant woman; and
(c) A man who does hard physical work.
3. Give examples of nutrient deficiency diseases in plants and
humans.
Nutrition is the process by which organisms obtain energy from food for growth,
maintenance and repair of damaged tissues.
There are two main types of nutrition: autotrophic nutrition and heterotrophic
nutrition.
Autotrophic nutrition is the process by which organisms make their own
food from simple inorganic raw materials such as carbon dioxide and water
by using light or chemical energy.
Heterotrophic nutrition is the process by which organisms feed on complex,
ready-made organic foods to obtain the nutrients they require.
Heterotrophic nutrition consists of holozoic nutrition, saprophytic nutrition
and parasitic nutrition.
Holozoic organisms may be classified according to their diets. Herbivores eat
only plants, carnivores eat only animals and omnivores eat both animals and
plants.
Food can be divided into seven classes carbohydrates, proteins, fats,
vitamins, minerals, fibre and water.

Carbohydrates provide energy; proteins provide materials for growth and
repair and fats are a source and storage of energy.
Vitamins and minerals are needed in small quantities for optimal health.
Fibre is required for the proper functioning of the digestive system.
A balanced diet contains all the classes of food in the right quantity and ratio
according to our bodily needs.
A food chain shows the feeding relationships among organisms.
The interconnections of many food chains form a food web.
An energy pyramid is a graphical representation of the energy at each level in
a food chain.
Plants need both macronutrients and micronutrients for healthy growth and
development.
Photosynthesis is a process carried out by green plants to make glucose from
carbon dioxide and water in the presence of sunlight and chlorophyll.
Photosynthesis requires carbon dioxide, chlorophyll, sunlight and water.
Photosynthesis provides the basic source of food and also maintains the
oxygen balance in the atmosphere.
Food technology is a branch of food science that deals with the production
processes to make foods.
Development of food technology occurs in two ways: development in food
production and development in food processing.
Genetically modified foods are foods that are derived from genetically
modified organisms. Genetically modified organisms have had specific
changes introduced into their DNA by genetic engineering techniques.
An imbalanced diet can lead to health problems, mainly deficiency diseases.

Autotrophic nutrition
Carbohydrates
Carnivore
Chemosynthesis
Deficiency diseases
Energy pyramid
Fats
Fibre
Food chain
Food technology
Food web
Genetically modified foods
Herbivore
Heterotrophic nutrition
Holozoic nutrition
Macronutrients
Micronutrients
Minerals
Nutrition
Omnivore
Parasitic nutrition
Photosynthesis
Primary consumer
Producer
Proteins
Saprophytic nutrition
Secondary consumer
Trophic level
Vitamins
Water
MDG. (2010). Executive summary. Retrieved March 20, 2012 from
http://www.nutriweb.org.my/downloads/Executive%20summary.pdf
nutriWEB. (2011). Latest news. Retrieved March 20, 2012 from
http://www.nutriweb.org.my/
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V.,
Jackson, R. B. (2010).Campbell biology (9th ed.). San Francisco: Pearson -
Benjamin Cummings Pub.
Slim With Yoga. (2011). Nutritious food. Retrieved March 20, 2012 from
http://slimwithyoga.com/nutritious/index.html
Taylor, D. J., Green, N. P. O., Stout, G. W. (2004). Biological science 1:
Organisms, energy and environment (3rd ed.). R. Soper Editor, New York:
Cambridge University Press.

Topic
4
Digestive
System
LEARNING OUTCOMES
1. Explain the process of physical digestion and chemical digestion;
2. Describe the structure of the human digestive system;
3. Explain the process of digestion in humans;
4. Describe digestion in ruminants;
5. Describe digestion in rodents; and
6. Explain how excretion occurs in plants.
INTRODUCTION
In Topic 3, we looked at the various classes of food that are needed by our body.
Have you ever wondered about what happens to these foods after we have eaten
them? The foods that we eat are in quite a different state from the one that can be
used by the cells in our body. Before the foods can be used, they need to be
converted into smaller units, so that they can be easily absorbed by our body
cells. This process is called digestion.
Basically, digestion is the process of breaking down food from complex
substances into simpler soluble molecules to be absorbed by the body. Starch,
protein and fat are large insoluble food molecules. At the end of digestion, starch
is broken down into glucose, protein is broken down into amino acids and fats
are broken down into fatty acids and glycerol. Glucose, amino acids, fatty acids
and glycerol are in the simplest form and are easily absorbed into the body cells.
But, how does digestion take place?

HBSC1203 BIOLOGY I

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HBSC1203 BIOLOGY I