This document provides information about cell biology and different types of cells. It begins by outlining the cell theory. It then discusses unicellular and multicellular organisms. It describes the key differences between akaryotes (viruses), prokaryotes (bacteria), and eukaryotic cells (plant and animal cells). The document discusses the structures and functions of organelles in eukaryotic cells. It provides examples of specialized cells like sperm, muscle, and red blood cells. In the end, it provides exercises for students related to topics covered.

1. CELL BIOLOGY• CELL THEORY
• CONCEPT OF THE CELL
• UNICELLULAR AND MULTICELLULAR ORGANISMS
• AKARYOTES (VIRUSES )
• PROKARYOTES (BACTERIA )
• DIFFERENCE BETWEEN AKARYOTES AND PROKARYOTES
• EUKARYOTIC CELLS (PLANT AND ANIMAL CELLS )
• SPECIALISED CELLS
• LEVEL OF ORGANISATION
• FORMS OF CELLS
• MOVEMENT OF SUBSTANCES IN AND OUT OF CELLS

2. CELL THEORY
The cell theory was proposed by two German scientists,
Theodore Schwann and Matthias Schleiden . They proposed the
following in 1839;
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in
organisms.
3. Cells arise from pre-existing cells.

3. CONCEPT OF THE CELL
Cells are the basic units from which living things are built and each cell is capable
of carrying out life processes.
There are two main groups of organism based on the number of cells
1. Unicellular organisms ; these are organisms that consist of one cell only. The
organism is the cell . They are also called single-celled organisms . E.g include
amoeba, paramecium, euglena ,trypanosome
Amoeba proteus Euglena spp. Paramecium sp.

5. MULTICELLULAR ORGANISMS
• These are organisms that are made up of multiple cells

6. AKARYOTESThese are particles that lack nucleus, cytoplasm and cell membrane . An
example is a virus. They require the body of a living organism to reproduce.
They cannot live on their own . For this reason, they are regarded as particles
and not organisms. Viruses are so small that they can only be seen with an
electron microscope. There are several shapes of viruses . These include rod-
shaped , spherical, spiral, hexagonal etc.
A typical virus is made up of a protein coat and an inner core of nucleic acids.
Viruses have either DNA or RNA.
Viruses cause diseases in both plants and animals. Examples of viruses and the
diseases they cause

7. EXAMPLES OF VIRAL DISEASES
• smallpox
• the common cold and different types of flu
• measles, mumps, rubella, chicken pox, and shingles
• hepatitis
• herpes and cold sores
• polio
• rabies
• Ebola and Hanta fever
• HIV, the virus that causes AIDS
• Severe acute respiratory syndrome (SARS)
• dengue fever, Zika, and Epstein-Barr

8. EXAMPLES OF VIRUSES

9. FEATURES OF VIRUSES
1. they are smaller than bacteria
2. can only be seen under an electron microscope
3. there are several shapes
4. has either DNA or RNA
5. can only reproduce within living cells
6. they cause diseases
7. they lack nucleus, cytoplasm & cell membrane
8. have a protein coat

10. Viruses as living organisms
1. they can reproduce
2. they can feed
3. they have genetic material
Viruses as non-living organisms (particles)
1. they can’t reproduce on their own
2. They don’t grow

11. LIFE CYCLE OF VIRUSES
Life Cycle of viruses
1. the virus first attaches to the host cell
2. the protein coat breaks and the chromosome enters the host cell
3. the viral DNA then replicate
4. the new viral chromosomes are surrounded by protein coats
5. the cell wall of the host cell breaks to release the virus particles
6. they invade other cells
Mechanism of Transmission of Viruses
1. through droplet infection
2. through insect bites
3. through physical contact with infected humans, objects or animals

12. PROKARYOTES
• These are unicellular organisms that lack membrane-bound nucleus. They
are mostly bacteria and blue green algae. The bacteria cell is made up of a
cell wall with a cell membrane within that surrounds the cytoplasm. Their
nuclear material is found within the cytoplasm but is not bound by a
membrane.

13. Features of Prokaryotes
they are unicellular organisms but they mostly live in colonies
• they can only be seen with a microscope
• they occur in all environments and can tolerate the harshest of environmental
conditions.
• Many bacteria cause diseases like diphtheria, tuberculosis, meningitis, pneumonia,
cholera, Gonorrhoea, Syphilis, Tetanus, Typhoid, Anthrax
• They have nuclear material with no membrane
• They have cell wall
• They possess membrane that surrounds the cytoplasm
• They reproduce mainly by binary fission. One bacterium divides into two bacteria.
Each bacteria produced is identical to the parent bacteria.
• Some bacteria reproduce sexually by either conjugation or genetic recombination
• They possess whip-like flagella used for movement
• Bacteria excrete carbon dioxide and water mainly by exocytosis
• Some bacteria can produce their own food (autotrophic bacteria) while others mostly
feed on dead organic matter.

14. FORMS OF BACTERIAThere are four main forms(shapes) of bacteria;
1. Cocci (Spherical shaped )
Cocci bacteria, singular; coccus, are spherical-shaped bacteria. When cocci
bacteria divide or reproduce, they create different patterns and these are
named depending on how their bacteria are arranged.
Types of coccus bacteria include
a. Coccus – single-celled spherical
b. Diplococcus bacteria – occur in pairs
c. Streptococcus bacteria – occur in chains
d. Staphylococcus bacteria – occur in a grape-like cluster
e. Sarcina – occur in a cube-like structure (8 bacteria or more)
f. Tetrad bacteria- group of four

15. 2. Bacilli (Cylindrical /rod/ sausage-shaped )
Bacilli bacteria , singular; bacillus are cylindrical/rod-shaped bacteria. The
most common rod-shaped bacteria is Bacillus anthracis, the bacteria that
causes anthrax in livestock. Another example of a bacillus is the bacteria
that causes typhoid fever, Bacillus typhosus.

16. 3. Vibrio (Comma-shaped)
These are groups of bacteria that possess a curved-rod/ comma shape,
several species of which can cause foodborne infection. The most common
vibrio bacteria is Vibrio cholerae, the bacteria that causes cholera.

17. 4. Spirilli (Spiral shaped/twisted)
These are large, elongate, spiral shaped bacteria.

18. HOMEWORK
1. Tabulate 10 differences between akaryotes and prokaryotes .
2. Make a labelled diagram of a typical bacteria
3. Make a labelled diagram of a typical virus .

19. CLASS EXERCISE 1
1. a. Explain the meaning of biology. (2 marks)
b. State six reasons why Biology should be studied in schools (6 marks)
2. List three ways in which Biology has been beneficial in
a. The Home
b. Hospitals
c. Sanitation
d. Agriculture. (12 marks)

20. CLASS EXERCISE 2 (10 MINS)
1. Outline the cell theory. ( 6 marks)
2. Explain the statement “ A cell is the basic unit of life”. (4 marks)
CLASS EXERCISE 3 (10 MINS)
1. State three living and two non-living features of viruses . (5 marks)
2. List the main forms of bacteria. ( 4 marks)
3. Classify the following diseases as either viral or bacteria disease;
Pneumonia, cholera, Ebola, influenza, poliomyelitis, hepatitis, measles,
gonorrhea, dengue, meningitis, HIV/AIDS. (11 marks)

21. VIRAL DISEASES BACTERIAL DISEASES
Ebola Pneumonia
Influenza Cholera
Poliomyelitis Gonorrhea
Hepatitis Meningitis
Measles
Dengue
HIV/AIDS

22. EUKARYOTIC CELLS
By the end of the Topic, Students should be able to;
i. State the functions of the organelles of cells
ii. Relate the structure of cell organelles to their functions
iii. Differentiate between a cell wall and cell membrane
iv. Make a drawing of a generalized animal cell
v. Make a drawing of a generalized plant cell
vi. State the differences between animal and plant cells
vii. State the similarities between the plant cell and animal cell
viii. identify specialized eukaryotic cells and outline their functions

23. EUKARYOTIC CELLS
Eukaryotes are organisms whose cells have a nucleus enclosed within
membranes. They are said to have a true nucleus.
Eukaryotes include fungi, protoctists, plants and animals and have eukaryotic
cells.
 A typical eukaryotic cell has an outer cell membrane, a prominent true
nucleus, a cytoplasm within which there are organelles.

25. CELL ORGANELLES
An organelle refers to a structure bounded by a membrane
found within the cytoplasm of an eukaryotic cell and
performs a specific function.
CELL WALL- A cell wall is a rigid structure made up of
cellulose which surrounds the cell membrane of some cells .
The cell wall forms a framework which protects, supports
and gives shape to the cell. They are fully permeable to all substances
and are non-living. They are found in bacteria, archaea, fungi,
plants, and some algae.

27. CELL MEMBRANE
The cell membrane (also known as the plasma membrane or cytoplasmic
membrane or cell surface membrane is a biological membrane that separates
the interior of all cells from the outside environment. The cell membrane is
flexible and partially permeable/ semi-permeable. The cell membrane controls
the movement of materials in and out of the cell. It is composed of
phospholipids, globular proteins and 2 layers of lipids(fats)

28. DIFFERENCES BETWEEN CELL MEMBRANE AND CELL
WALL
CELL MEMBRANE CELL WALL
1. Its flexible Its rigid
2. semi-permeable Fully permeable
3. Made up of phospholipids and proteins Made up of cellulose
4. Its thin Its thick
5. Present in both plant and animal cell Present in plant cells only
6. Cell membrane is metabolically active and
living
Cell wall is non-living and metabolically
inactive
7. Cell membrane encloses the cytoplasm Cell wall encloses the cell membrane and

30. CYTOPLASM
The cytoplasm consists of a watery ground substances within which several
organelles and cell inclusions are found. The ground substance is 90% water
with some salts, sugars, fats, proteins and enzymes in it. The cytoplasm moves ,
thus moving the cell organelles. This type of movement is called cytoplasmic
streaming.

31. NUCLEUS
The nucleus is the main control centre of the cell. It comprises an outer nuclear
membrane/ nuclear envelope within which there are pores for the movement
of materials in and out of the nucleus.
Within the nucleus is a spherical body called nucleolus. This is the site of
ribosome production.
Nuclear envelope/membrane
Nuclear pore
Nucleoplasm
Chromatin
Nucleolus

32. MITOCHONDRIA
Mitochondria are minute spherical or sausage-shaped organelles. Each
mitochondrion is bounded by two membranes and separated by a fluid-filled
space.
The inner of the two membranes is folded into cristae (singular: crista). There
are enzymes on the cristae that are involved in the release energy during
respiration.
The number and location of mitochondria in the cell depends on the energy
requirements of the cell. Therefore cells that require a lot of energy contain
many mitochondria .
The sperm cell for example has a high concentration of mitochondria close to
its tail because energy is required in movement of the sperm cell towards the
egg cell.

33. MITOCHONDRIA

34. ENDOPLASMIC RETICULUM
This is a network of channels that run through the cytoplasm and are
bound by membrane. The endoplasmic reticulum is continuous with the
nuclear membrane.
There are two types of endoplasmic reticulum; smooth endoplasmic
reticulum and rough endoplasmic reticulum.
The rough endoplasmic reticulum appears rough due to the presence of
ribosomes while smooth endoplasmic reticulum lacks ribosomes.

35. ROUGH ENDOPLASMIC RETICULUM

36. SMOOTH ENDOPLASMIC RETICULUM

37. ENDOPLASMIC RETICULUM

38. ENDOPLASMIC RETICULUM
The rough endoplasmic reticulum is the pathway for the transport of protein
from the ribosomes.
The smooth endoplasmic reticulum is the pathway for the transport of other
materials in the cell.
The endoplasmic reticulum also provides surfaces for chemical reactions
within the cell.

39. RIBOSOMES
Ribosomes are minute organelles found in large numbers in the cytoplasm of all
prokaryotic and eukaryotic cells . Some occur freely in the cytoplasm while
others are bound to the endoplasmic reticulum. They comprise mainly RNA
(ribosomal RNA) and protein and are the sites of protein synthesis (protein
formation). A ribosome comprises two subunits; the large subunit and small
subunit.

40. CHLOROPLASTS
They are large egg-shaped organelles with double membranes found in the
cytoplasm of plant cells. They are also present in other organisms like green
algae(spirogyra) and euglena. Chloroplasts contain the green pigment
chlorophyll. Chlorophyll helps in the trapping of sunlight for photosynthesis.
Organisms that possess chloroplast and can manufacture their food through
photosynthesis are called Autotrophs and their mode of feeding is termed as
autotrophic nutrition. A chloroplast has the following parts ;

41. i. Stroma: it is the medium in which the grana(singular; granum) and is the
site of the dark stage of photosynthesis
ii. Grana: It is the site of light stage of photosynthesis and contains
chlorophyll

43. GOLGI BODY (GOLGI APPARATUS)
It refers to a stack of flattened , membrane bound sacs with numerous vesicles
at the edges. They are present in eukaryotic cells only.
The main functions of the Golgi bodies are
1. To produce cell membranes
2. To package carbohydrates, proteins and other substances by forming
vesicles around them.

44. DICTYOSOMES
These are the Golgi bodies of plant cells. They play an important role in the
formation of a new cell wall after cell division in plant cells.
LYSOSOMES
Lysosomes are organelles that contain digestive enzymes. They digest
excess or worn out organelles, food particles, and engulfed viruses or
bacteria.

45. VACUOLE
Vacuoles are organelles that appear as sacs filled with fluid. They are present in
all cells but differ in size.
Animal cells possess small vacuoles while plant cells possess larger vacuoles.
Vacuoles are the "storage system" of the cell. They store nutrients, waste,
enzymes, and water.
There are three types of vacuoles ;
1. central vacuole - helps maintain plants' shape and structure by storing
water .
2. contractile vacuole - pumps water out of protozoan cells to maintain a
suitable concentration (osmoregulation).
3. food vacuole - storage for molecules that is a food source for the cell.

46. Other organelles in cells include
centrioles and peroxisomes.

47. PLANT CELL
Plant cells have an outer cell wall enclosing the cell membrane with the
organelles within the cytoplasm.

49. DIFFERENCES BETWEEN PLANT AND ANIMAL CELL
PLANT CELL ANIMAL CELL
1. Possess cell wall Lack cell wall
2. have fixed shape Lack a fixed shape
3. Possess chloroplast Lack chloroplast
4. Lack centrioles Possess centrioles
5. Store food as starch Store food as glycogen
6. Possess large vacuoles Possess small vacuoles
7. Vacuoles are permanent Vacuoles are temporary

50. SIMILARITIES BETWEEN PLANT AND ANIMAL CELLS
They both possess
1. Nucleus
2. Cytoplasm
3. Cell membrane
4. Mitochondrion
5. Ribosomes
6. Endoplasmic reticulum
7. Lysosomes
8.

51. SPECIALISED EUKARYOTIC CELLS
• A specialized cell refers to a cell that is modified/ adapted to perform a
specific function. Examples of specialized cells include ;
1. Sperm cell- The sperm cell is specialized in the following ways
a. The tail helps the sperm to move to the egg.
b. Lots of energy is sorted in the middle section of the sperm cell.
c. The head contains enzymes that enables the cell to penetrate into the egg cell

52. MUSCLE CELLS
Muscle cells have protein fibres with lots of mitochondria to provide the
energy needed for contraction to produce movement .

53. Red blood cells
Red blood cells - Red blood cells carry oxygen around the body.
They are specialized by having ;
1. Lack a nucleus to allow them to contain more haemoglobin.
2. Have a biconcave shape to increase their surface area to increase the amount
of oxygen absorbed quickly

54. WHITE BLOOD CELLS
White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the
immune system that are involved in protecting the body against both infectious disease
and foreign invaders. White blood cells originate in the bone marrow but circulate
throughout the bloodstream. There are five major types of white blood cells:
1. neutrophils
2. lymphocytes
3. eosinophils
4. monocytes
5. basophils

55. NERVE CELL/NEURON
They are long and thin so messages can be carried all over the body. They are
specialized to carry electrical signals. They have connections at each end that
allows easy transmission of impulses. There are three types of neurons; motor
neurons, sensory neurons and interneurons.

56. Palisade cells
They are arranged cylindrically to allow sunlight to reach them easily. They also
contain numerous chloroplasts which makes them efficient at producing food
by photosynthesis.

57. Leaf epidermal cell
These cells fit together perfectly and produce a waxy substance called cuticle
that helps to reduce water loss from the leaf.
Guard Cell
Guard cells are cells surrounding each stoma. They help to regulate the rate of
transpiration by opening and closing the stomata. They are located beneath the
leaf to decrease the rate of
Water loss

58. LEVEL OF ORGANISATION IN LIVING THINGS
• Multicellular organisms are made up of many cells. These cells do not function alone but
they are grouped in similar types to form tissue , which are further grouped to form organs.
Groups of organs form the organ system and the organ systems collectively form the
organism.
There are five levels of organisation in multicellular organisms. These are;
ORGANISM
ORGAN
SYSTEM
ORGANTISSUECELL

59. • Cell Cardial muscle tissue Heart (organ) Circulatory system
Human body (organism)
Plant cell Plant tissues Plant leaf(organ) Shoot system of the plant Plant(organism)

60. 1. Cells are the basic building blocks of all organisms. Although cells are made of
smaller parts, none of those parts could survive on their own. Cells are the
simplest level of organization.
2. Tissue- Many cells working together form tissue. A tissue is a group of cells
which are similar in shape and size and perform similar functions. The cells in a
tissue are specialized to cooperate with each other to accomplish one common
goal. Examples of tissues in plants and animals include; muscle tissue, blood,
bone, connective tissue, epithelial tissue, xylem, phloem, palisade tissue etc

61. 3. Organ- When there are layers of tissue working together, they form an organ.
All animals and plants contain organs. These organs include kidneys, lungs, liver,
heart, brain, leaf, stem, flower, branch etc
4. Organ system - When organs work together, they form organ systems. Organ
systems keep the body regulated and in a stable state. These systems often work
together and rarely work in isolation. The human body has 11 organ systems
which include respiratory system, immune system, circulatory system,
reproductive system , nervous system, endocrine system, integumentary
system, excretory system, digestive system, muscular system, skeletal system

62. Organ system Organs Tissue Cells present
Muscular system Muscles Muscle tissue Muscle cells
Nervous system Brain, nerves and
spinal cord
Nerve tissue Nerve cells/neuron
Circulatory system Heart, veins, arteries,
capillaries
Blood , epithelial
tissue, cardiac tissue
Red blood cells,
white blood cells,
epithelial cells
Shoot system Leaf, branch,stem Xylem, Phloem,
Strengthening tissue,
Photosynthetic tissue
Parenchyma cells,
mesophyll cells,
palisade cells,
chlorenchyma,
sclerenchyma,
collenchyma
Root system Roots Xylem, phloem,
Strengthening tissue
Collenchyma,
sclerenchyma, root
tip cells
Reproductive system Testes, ovaries,
uterus,
Muscular tissue,
vascular tissue,
epithelial tissue
Sperm cells, egg cells,
muscle cells

63. MOVEMENT OF SUBSTANCES INTO AND OUT OF
CELLS
In order for cells to function and survive, they need to take in substances from the outside
and eliminate waste. There is therefore the need for transport of substances in and out of
cells. Examples of substances that are transported in and out of cells include;
a. Food nutrients
b. Ions
c. Salts
d. Waste products
e. Oxygen
f. Carbon dioxide
g. Amino acid
h. Water
i. Hormones
j. Enzymes
k. other useful substances

64. WHY SUBSTANCES MOVE IN AND OUT OF CELLS
1. Food nutrients are needed by cell for energy production and growth
2. Amino acids and minerals are needed by the cell to construct cell
components
3. Ions must be moved in and out of cells to allow for nerve impulses to be
sent
4. Waste substances must be eliminated from the cells
5. Oxygen must be taken into the cell and carbon dioxide must be taken away
from the cell
6. Hormones and enzymes must be transported from the manufacturing cell
to different parts of the body
7. The products of photosynthesis have to be taken away from manufacturing
cells

65. WAYS OF TRANSPORT IN AND OUT OF CELLS
Substances that move in and out cells are mainly in solution. These substances are mainly
moving through the cell membrane and cell walls in plants. Cell membranes and cell walls
allow water, carbon dioxide, oxygen and nutrients to pass through them.
The main ways in which substances are transported within cells are;
1. DIFFUSION
2. OSMOSIS
3. ACTIVE TRANSPORT
4. EXOCYTOSIS
5. ENDOCYTOSIS

66. DIFFUSION
It is the movement of molecules(solid, gases, ions) move from an area of high
concentration to an area of low concentration until the molecules are evenly
distributed. There are several factors that will affect the rate of diffusion and these
include ;
1. Concentration gradient /Difference in concentration
2. Temperature
3. Diffusion distance
4. Size of molecules
5. Stirring

67. CONCENTRATION GRADIENT
Concentration gradient refers to the difference in concentration between two
regions. The steeper(greater) the concentration gradient, the higher the rate of
diffusion.

68. TEMPERATURE
Increasing the temperature increases the diffusion rate by adding energy to
each particle. Similarly, lowering the temperature will lower the diffusion rate
by lowering the energy of each particle.

69. SIZE OF MOLECULES
The smaller the size of the molecules , the higher the rate of diffusion.
DIFFUSION DISTANCE
Particles moving through smaller distances result in faster diffusion rates and
larger distances result in slower diffusion rates. For example, a gas diffuses
through a thin wall much faster than it would diffuse through a thick wall.

70. DIFFUSION IN A LIQUID

71. DIFFUSION IN AIR

72. EXAMPLES OF DIFFUSION IN LIVING THINGS
1. The uptake of nutrients from the soil by the roots in plants
2. The distribution of nutrients to all the parts of the plant
3. Diffusion of Carbon dioxide into the leaf of the plants during photosynthesis
4. Release of oxygen out of the stomata of the leaf in plants
5. Oxygen diffuses into the cell in animals
6. Glucose diffuses into animal cells by diffusion

73. 7. Carbon dioxide diffuses out of cells in animals
8. Oxygen diffuses into the bloodstream by diffusion in animals
9. Carbon dioxide diffuses out of the bloodstream into the lungs by diffusion in
animals
10. Selective reabsorption of nutrients in the kidney of animals
11. The movement of materials in and out of unicellular organisms is by diffusion

74. OSMOSIS
Osmosis refers to the movement of water molecules from a region of higher
water concentration(dilute solution) to a region of lower water concentration
(more concentrated solution) through a semi-permeable membrane. Osmosis
therefore takes place only in living things because it can only occur through a
living cell membrane , that is semi-permeable.
NB: A dilute solution is a solution with a high water concentration.
A concentrated solution is a solution with very low water concentration

75. EXAMPLES OF OSMOSIS IN LIVING
THINGS
1. The uptake of water from the soil by the roots
2. The movement of water through the stem to the leaves
3. The evaporation of water from leaves through the stomata
4. The movement of water into the cytoplasm in unicellular organisms
such as paramecium and Amoeba.
5. Re-absorption of water in the kidney of mammals

76. SIMILARITIES BETWEEN OSMOSIS AND DIFFUSION
1. Both osmosis and diffusion equalize the concentration of two solutions.
2. Both diffusion and osmosis are passive transport processes, which means
they do not require any input of extra energy to occur.
3. In both diffusion and osmosis, particles move from an area of higher
concentration to a lower concentrated region.

77. DIFFERENCES BETWEEN OSMOSIS AND DIFFUSION
DIFFUSION OSMOSIS
1. Does not require a semi-permeable
membrane
Requires a semi-permeable
membrane
2. Involves movement of solids, gases
and ions
Involves movement of liquids (water)
3. Occurs in living and non-living
organisms
Occurs in only living organisms
4. Free movement of solute particles Movement of solute particles are
restricted
5. Diffusion is fast
6. Increase in temperature increases
the rate of diffusion
Osmosis is slow
Increases in temperature does not
have an effect on osmosis

78. Higher concentrated region – high solute, less water
Lower concentrated region – low solute , high water (dilute solution)

79. SOLUTIONS
There are three types of solutions that cells can be
associated with;
a. Isotonic solution
b. Hypotonic solution
c. Hypertonic solution

80. ISOTONIC SOLUTION
When a cell is found in a solution that has the same
concentration as the cell, the solution is said to be
an isotonic solution.
An isotonic solution therefore is a solution
whose concentration is the same as the cell.
There is no net movement of water between
the cell and the solution. The fluid that surrounds most body cells is isotonic.

81. If an animal cell is placed in a isotonic solution, water will move in and out of the
cell at the same rate and the cell will remain intact.
Water moves
in and out of
the cell
membrane at
equal rates.

82. HYPOTONIC SOLUTION
A hypotonic solution refers to a solution whose concentration is lower than the
cell around it. Such a solution has a higher water concentration than the cell and
there is movement of water into the cell.
This results in an increase in pressure inside the cell called turgor pressure in
plants and osmotic pressure in animals.
When a plant cell is placed in a hypotonic solution, water moves into the cell
continuously and fills the vacuole. The vacuole pushes against the cell membrane
and the cell wall until the cell becomes turgid. The plant cell would not burst
because of the thickness of the cell wall

83. Turgor pressure is the force within the plant cell that pushes the cell
membrane against the cell wall when the plant cell is placed in a hypotonic
solution.
Turgidity is the state of a cell being turgid or swollen.

84. Importance of turgidity in Plant cells
1. Gives the plant cell shape and makes the plant stand upright
2. Turgidity in guard cells ensures the opening of the stomata
3. It helps in the movement of nutrient solutions from cell to
cell

86. When an animal cell is placed in a hypotonic solution, water enters the animal cell
continuously till the cell bursts. This happens because the cell membrane is thin
and cannot withstand the osmotic pressure. The bursting of
the cell is called cytolysis.
The bursting of the
Red blood cell is called hemolysis.
Water
moves
into the
cell

87. HYPERTONIC SOLUTION
A hypertonic solution refers to a solution whose concentration is greater (has more
solute) than the cell which is found in it. Such a solution has a low water concentration
and will take up water from the cell.
When a plant cell is placed in a hypertonic solution, the cell loses water continuously
from the vacuole till the cell contents pull away from the cell wall.
The shrinking away of the cell contents from the cell wall as a result of excessive loss of
water by the plant cell when placed in a hypertonic solution is known as plasmolysis.
The plant cell will lose its definite shape and if it occurs for long , will result in wilting.

90. When an animal cell(red blood cell for
example) is placed in a hypertonic
solution, the cell loses water to the
solution continuously till it shrinks and
Shrivels completely. The cell is said to
have undergone crenation.

92. Identify the solution in which the red blood cell is
placed in each of the following

93. FACILITATED DIFFUSION
Facilitated Diffusion is the movement of larger molecules like glucose through
the cell membrane . These larger molecules must be “helped” in order to be
carried through the cell membrane.
Proteins form protein channels in the cell membrane for large molecules to
pass through.

94. ACTIVE TRANSPORT
This refers to the movement of solute
molecules from a region of lower
concentration to a region of higher
concentration against concentration
gradient using energy (ATP).
Active transport uses transport/carrier
proteins (protein pumps) that are embedded
in the plasma membrane.

95. EXAMPLES OF ACTIVE TRANSPORT
1. Absorption of sugars and amino acids into the blood stream
from the small intestine in humans
2. Absorption of some mineral salts from the soil by roots in
plants

96. ENDOCYTOSIS
Is the process by which large molecules such as proteins are transported into cells by
forming vesicles..
There are two main types of endocytosis depending on the material being taken into
the cell
1. Phagocytosis – refers to the intake of large solid molecules. Can be called Cell
eating”. White blood cells(macrophages) engulf bacteria by this mechanism
2. Pinocytosis – refers to the intake of small droplets of liquid. Can be called ”Cell
Drinking”

98. EXOCYTOSIS
Exocytosis is a form of bulk transport in which a cell transports
molecules out of the cell by secreting vesicles around them
and requires the use of energy.
The secretion of hormones and enzymes and their release is by
exocytosis.

99. EXERCISE
1. List three features of organisms belonging to kingdom protoctista
2. List 4 major phyla under kingdom protoctista

100. HOMEWORK
MAKE A DRAWING OF AN AMOEBA AND
LABEL THE PARTS FULLY

101. HOMEWORK
MAKE A DRAWING OF A PARAMECIUM AND
LABEL THE PARTS FULLY

102. MAKE A DRAWING OF AN EUGLENA AND
LABEL THE PARTS FULLY

104. Active Transport against the concentration
gradient