Exploring the Invisible Living World: Cells, Microorganisms, and Their Roles

THE INVISIBLE LIVING
WORLD: BEYOND OUR
NAKED EYE
CHAPTER - 2

TOPICS TO BE COVERED IN THIS CHAPTER -
 Introduction
 What is a cell?
 Basic structure of a cell
 Comparison between a plant cell and an animal cell
 Variation in shape of cells
 Levels of organization in the body of a living
organism
 What are microorganisms?
 How are we connected to microbes?
 Key players in cleaning the environment
 Microorganisms and food
 Microalgae – Tiny helpers in water
 Why is cell considered to be a basic unit of life?

INTRODUCTION
Q. Have you ever wondered what you might
see if the invisible world around you became
visible?
Q. How do you think your observation of this
hidden world might change the way you think
about size, complexity or even what counts as
‘living’?
Q. Have you thought how these tiny living
beings interact with each other?

• In 1665, Robert Hooke published his book ‘Micrographia’.
• In this book, he showed detailed drawings of tiny things
that people had never seen before.
• His self made microscope made things look 200-300
times bigger.
• One day he looked at a thin slice of cork and saw it was
made up of many small empty spaces. These
compartments reminded him of a honeycomb. He drew
what he saw and called each small space a cell. This was
the first time the word cell was used in science.
• Antonie van Leeuwenhoek, a Dutch scientist, made
better lenses that allowed him to build more useful
microscope.
• He was the first person to clearly see and describe tiny
living things like bacteria and blood cells. Because of
this he is known as the ‘Father of Microbiology’.
Discovery of cells

WHAT IS A CELL?
 Cells are the basic structural and functional
units of life.
 All living organisms are made up of one or
more cells.
 Cells can be observed under a microscope.

ACTIVITIES TO STUDY CELLS
Onion peel cell (plant cells) Cheek cell (animal cell)
 Rectangular shaped
cells.
 Parts seen under the
microscope –
 Cell wall
 Cell membrane
 Cytoplasm
 Nucleus
 Polygon shaped cells.
 Parts seen under the
microscope –
 Cell membrane
 Cytoplasm
 Nucleus

CONCLUSION
 A cell typically consists of three parts – cell
membrane, cytoplasm and nucleus.
 In plant cell, an extra outer layer called cell
wall is present.

DIFFERENCE BETWEEN PLANT
CELL AND ANIMAL CELL
Feature Plant cell Animal cell
Shape Rectangular/fixed Irregular / round
Cell wall Present Absent
Chloroplast Present Absent
Vacuole Large central vacuole Small or absent

Cell wall:
• It is the outermost layer in the plant cell.
• It is porous, rigid and permeable in nature.
• It provides protection to the plant cell.
• It also provides rigidity and strength to the plants.
Cell membrane:
• It is the outermost layer in the animal cell and present below the cell wall in the
plant cell.
• It is porous, elastic and semi permeable in nature.
• It provides protection to the inner content of the cell and separate one cell from
the other.
Cytoplasm:
• It is the jelly-like substance present between the cell membrane and nucleus.
• It contains carbohydrates, proteins, fats and mineral salts.
• Most of the processes takes place within the cytoplasm.
Nucleus:
• It is the round structure present in the middle of the cell.
• It regulates all the activities of the cell.
• It also regulates growth.
Plastids:
• These are the tiny rod-shaped structures found only in plant cells.
• Chloroplasts are green coloured plastids containing chlorophyll which help in
photosynthesis.
Vacuole:
• It is the empty looking spaces which helps in storing important substances, get rid
of waste and maintain the shape of the cell.
• It also gives strength and support to the plant.
• In animal cells, vacuoles are generally absent. If present, they are usually small.
Parts
of
a
cell

VARIATION IN SHAPE OF CELLS
Type of Cell Shape Function
Muscle Cell Long, spindle-shaped Helps in contraction and movement
Nerve Cell Long, branched
Carries messages between body
parts
Red Blood Cell
Round, disc-shaped
(biconcave)
Carries oxygen throughout the body
White Blood Cell Irregular, amoeba-like Destroys germs and fights infections
Fat Cell
Round, large with storage
space
Stores fat and energy
Bone Cell Star-shaped
Provides structure and support to
the body
Skin Cell Flat, thin, tightly packed Covers and protects body surface
Guard Cell (Plant) Kidney-shaped Opens and closes stomata in leaves
Xylem Cell (Plant) Long, tube-like
Conducts water and minerals in
plants
Phloem Cell (Plant) Elongated, tube-like Conducts food in plants

LEVEL OF ORGANISATION IN THE
BODY OF A LIVING ORGANISM
Level Description
Cell
Basic unit of life (e.g., stomach
cell).
Tissue
Group of similar cells working
together (e.g., muscle tissue).
Organ
Group of tissues forming a
specific body part (e.g.,
stomach).
Organ System
Group of organs performing a
major body function (e.g.,
digestive system).
Organism
A complete living being (e.g.,
human, plant).
Flow:
Cell Tissue Organ Organ System Organism
→ → → →

TYPES OF ORGANISMS
Unicellular organisms
 The organisms made up of
only one cell are called
unicellular organisms.
 Examples include amoeba,
paramecium, bacteria.
Multicellular organisms
 The organisms made up of
more than one cell are called
multicellular organisms.
 Examples include plants,
animals including human
beings.
Note: 1. The life of all the multicellular organisms start from a
single cell i.e. egg.
2. The largest cell is the ostrich egg (yolk of egg).

WHAT ARE MICROORGANISMS?
 These are tiny living organisms made of one
or few cells.
 They can not be seen with naked eyes.
 They can found everywhere: air, water, soil,
inside living beings.
 Examples:
 Unicellular: Bacteria, Amoeba
 Multicellular: Algae, fungi

ACTIVITY – 2.4
(Observing pond water/stagnant water under the microscope)
Name of the
organsism
Diagram Remarks
Amoeba
(Protozoa)
Single cell, moving,
irregular shape
Paramecium
(protozoa)
Single cell, moving
from one place to
another with the help
of special structures
called cilia.
Chlamydomonas
(Algae)
Single cell, green,
moving takes place
with the help of
special structures
called flagella.

ACTIVITY – 2.5
(Observing soil suspension under the microscope)
Name of the
organsism
Diagram Remarks
Rhizopus(Bread
mould)
Fungi
Branched filament without
chlorophyll having sac like
structures.
Mould (Fungi) Branched filament without
chlorophyll having brush like
structures.
Algae Single cell, green, moving
takes place with the help of
special structures called
flagella.
Bacteria Spherical, comma, spiral or
rod shaped, one long hair-like
structure and many small hair-
like structure around the cell

VIRUS
• Viruses are
microscopic and
acellular.
• These multiply only
when they enter a
living cell.
• They may infect
plants, animals or
bacterial cells and
may cause disease.

HOW ARE WE CONNECTED TO MICROBES
Microorganisms in our daily life:
 Microorganisms are present everywhere: air,
water, soil, plants, animals, and even inside
our bodies.
 They can grow on old or left over food, like
tomatoes, lemons, or oranges forming white
cotton-like layers due to fungal infection.
Why do pickles and murabbas not spoil easily?
 They contain high salt or sugar, which
prevents the microbial growth by creating an
unsuitable environment.

ROLE OF MICROORGANISMS IN
THE ENVIRONMENT
1. Key players in cleaning the environment:
 Microorganisms like bacteria and fungi (called
decomposers) break down peels of fruits and
vegetables into a dark coloured material called
manure which is rich in nutrients.
 This process improves soil fertility.
 Microorganisms also decompose bodies of dead
animals and thus help in recycle of waste and
return of important nutrients in nature.

MICROBES AS A SOURCE OF BIOGAS
 Many microorganisms like bacteria and fungi
can live in an oxygen free environment.
 Some of these bacteria have the ability to
decompose plant and animal waste present
in the environment or household wastewater.
 During the process, they release a mixture of
gases containing carbon dioxide and a high
proportion of another gas called methane.
This gas is used as a fuel source for cooking,
heating, generating electricity and also to
even run vehicles.

MICROORGANISMS IN OUR KITCHEN: MAKING FOOD
Role of yeast(fungi):
 It grows in warm and moist conditions.
 It ferments sugar to produce carbon dioxide
and alcohol.
 It makes dough rise and become soft and
fluffy.
 Used in making bread, cakes, idli, dosa,
bhatura.

ACTIVITY 2.8: OBSERVE DOUGH
RISING (EFFECT OF YEAST)
 Take two bowls(A & B) with flour and sugar.
 Bowl A: Add yeast and warm water, knead
dough.
 Bowl B: No yeast.
 Keep both in warm places for 4-5 hours.
 Observation: Bowl A dough rises, become
fluffy due to carbon dioxide gas released by
yeast.

ACTIVITY 2.9: CURD FORMATION
(EFFECT OF WARMTH)
 Take two bowls(A & B) with milk.
 Bowl A: Lukewarm milk + curd
 Bowl B: Cold milk + curd
 Observe after few hours.
 Observation: Curd forms in warm milk faster than due to bacteria
like Lactobacillus.
Testing for curd formation using milk in different conditions
Condition Change in
appearance
Change in
colour
Possible reason
Bowl A Milk thickness
(curd)
Slight change Bacteria acted
faster
Bowl B Little or no
change
No change Cold prevented
bacterial
activity

CONTRIBUTION OF DR. ANANDA
MOHAN CHAKRABARTY
 In 1971, he developed a special bacterium
that could break down oil spills, helping to
clean the environment.
 His discovery showed how microorganisms
can be used to solve environmental problems
like pollution.
 His discovery received a patent in 1980.
 Patent is a copyright given to a person so
that no one else can copy, use or sell his/her
invention without permission.

NITROGEN FIXING BACTERIA
(RHIZOBIUM)
 Live in root nodules of
legumes (beans, peas,
lentils).
 Convert atmospheric
nitrogen gas into a
usable form for plants.
 Reduce the need for
fertilizers for farmers.
 Improves the soil
fertility naturally.

MICROALGAE (TINY HELPERS IN WATER)
 They live in water, soil, air
and even trees.
 Examples: Spirulina,
Chlorella, Diatoms.
 Benefits:
 Produce oxygen (more than half
of the earth’s oxygen supply)
 Clean water
 Provide food for aquatic animals
 Serve as superfoods (Spirulina)
rich in vitamin B12 and protein.
 Used in medicine, supplements,
biofuel.

HOW TO CULTIVATE SPIRULINA
 Set up a glass tank,
add pond water.
 Collect and add
living Spirulina.
 Stir regularly.
 Ready for harvest in
3-6 weeks.
 Used for nutrition
and livelihood
improvement.

WHY IS CELL CONSIDERED THE
BASIC UNIT OF LIFE?
 All living organisms are made of cells.
 Unicellular organisms: One cell performs all life
processes. Examples: Bacteria, protozoa, fungi
like yeast.
 Multicellular organisms: Many cells work
together, with specialized functions. Examples:
Algae, fungi like mould.
 Like plants and animals, microorganisms’ cells
are surrounded by cell membrane.
 Fungi cells: Have cell walls but no chloroplasts.
 Bacterial cell: Have no true nucleus (nucleoid
region only)

Exploring the Invisible Living World: Cells, Microorganisms, and Their Roles