N.S.N.

MEMORIAL SENIOR SECONDARY SCHOOL

Thirumurugan Salai, Thirumurugan Nagar, Chitlapakkam, Chennai –
600064

TERM: II
CLASS: VIII SUBJECT: BIOLOGY
CHAPTER: 8- THE CELL
ONE MARK QUESTIONS
1.________ coined the term ‘cell’?
2. Organisms made up of more than one cell are called __________
organisms.
3. The single – celled organisms are called __________ organisms.
4. The false feet of Amoeba are called __________.
5.The red blood cell of humans is spherical shaped. True/ False.
6.The muscle cell of human is __________ shape.
7. Plant cell has an outer covering over the cell membrane called __________.
8.Cell wall is present in bacterial cell. True/ False.
9.The longest cell in human body is __________.
10. The bacterial cell measures ______ to ______ micrometre.
11. The white material in hen’s egg is called __________.
12. The yellow part in hen’s egg is called __________.
13. The basic structural unit in a living organism is __________.
14. Group of similar cells performing specific function is called __________.
15. The cell membrane is also called __________.
16.__________ membrane is porous and allows movement of substances
inward and outward of the cell.
17. The jelly-like substance between the nucleus and the cell membrane is
__________.
18. Various cell organelles are present in __________.
19. Nucleus is separated from the cytoplasm by__________.
20.__________ help in inheritance of characters from the parents to the
offspring.
21.__________ is called the living substance of a cell.
22. The small spherical body inside the nucleus is called __________.
23.__________ are coloured bodies present in plant cells only.
24.Green coloured plastids are called __________.
25.Large vacuoles are seen in __________ cells.
ASSERTION AND REASON
Each question consists of two statements, namely, Assertion (A) and Reason
(R).For selecting the correct answer, use the following options:
(a) Both Assertion (A) and Reason (R) are the true and Reason (R) is a correct
explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are the true but Reason (R) is not a
correct explanation of Assertion (A).
(c) Assertion (A) is true and Reason (R) is false.
(d) Assertion (A) is false and Reason (R) is true.
1. Assertion: The nucleus is present in both plant and animals cell.
Reason: Nucleus are spherical and contain thread like structure called
chromosomes.
2. Assertion: Organisms are made up of cells.
Reason: Cells are structural unit of living organisms.
3. Assertion: Cell wall is not found in animal cell.
Reason: Animal cells are covered by cell membrane.
4. Assertion: Leaves have green colour.
Reason: Green colour plastids / pigments( Chlorophyll) are present in
leaves.
5. Assertion :Lysosomes digest old, worn out organelles of the cell .
Reason: Lysosomes contain destructive enzymes.
6. Assertion : Chromosomes transfer characteristics from parents to their
offsprings.
Reason: Chromosomes contain genes which carry genetic information.
7. Assertion: The plant cell has a fixed shape and rigidity.
Reason: The cell membrane gives fixed shape and rigidity to the cell.
8. Assertion : Proteins are used to repair and build new cells and carry out
many other functions.
Reason: Golgi bodies manufacture proteins.
9. Assertion: Protoplast is the living substance of a cell.
Reason: The nucleus and the cytoplasm together make up the protoplasm.
10. Assertion: Cheek cells are irregular in shape shape.
Reason: Cheek cell is an animal cell.
CASE BASED QUESTIONS
Case study 1
Discovery of the Cell Robert Hooke in 1665 observed slices of cork under a
simple magnifying device. Cork is a part of the bark of a tree. He took thin
slices of cork and observed them under a microscope. He noticed partitioned
boxes or compartments in the cork slice. These boxes appeared like a
honeycomb. He also noticed that one box was separated from the other by a
wall or partition. Hooke coined the term ‘cell 'for each box. What Hooke
observed as boxes or cells in the cork were actually dead cells. Cells of living
organisms could be observed only after the discovery of improved
microscopes. Very little was known about the cell for the next 150years after
Robert Hooke’s observations. Today, we know a lot about cell structure and
its functions because of improved microscopes having high magnification. The
Cell Both, bricks in a building and cells in the living organisms, are basic
structural units. The buildings, though built of similar bricks, have different
designs, shapes and sizes. Similarly, in the living world, organisms differ from
one another but all are made up of cells. Cells in the living organisms are
complex. The egg of a hen represents a single cell and is big enough to be seen
by the unaided eye. How do scientists observe and study the living cells? They
use microscopes which magnify objects. Stains (dyes) are used to colour parts
of the cell to study the detailed structure. There are millions of living
organisms. They are of different shapes and sizes. Their organs also vary in
shape, size and number of cells. Let us study about some of them. Number of
Cells: Can you guess the number of cells in at all tree or in a huge animal like
the elephant? The number runs in to billions and trillions. Human body has
trillions of cells which vary in shapes and sizes. Different groups of cells
perform a variety of functions. Organisms made of more than one cell are
called multicellular (multi: many; cellular: cell) organisms. The number of
cells being less in smaller organisms does not, in any way, affect the
functioning of the organisms. You will be surprised to know that an organism
with billions of cells begins life as a single cell which is the fertilised egg. The
fertilised egg cell multiplies and the number of cells increase as development
proceeds. The single-celled organisms are called unicellular (uni: one;
cellular: cell)organisms. A single-celled organism performs all the necessary
functions that multicellular organisms perform. A single-celled organism, like
amoeba, captures and digests food, respires, excretes, Grows and reproduces.
Similar functions in multicellular organisms are carried out by groups of
specialised cells forming different tissues. Tissues, in turn, form organs. You
may say that the shape appears irregular. In fact, amoeba has no definite
shape, unlike other organisms. It keeps on changing its shape. Observe the
projections of varying lengths protruding out of its body. These are called
pseudopodia (pseudo: false; podia: feet). These projections appear and
disappear as amoeba moves or feeds. A white blood cell (WBC) in human blood
is another example of a single cell which can change its shape. But while WBC
is a cell, amoeba is a full-fledged organism capable of independent existence.
What shape would you expect in organisms with millions of cells? As blood,
muscle and nerve of human beings. The different shapes are related to their
specific functions. Generally, cells are round, spherical or elongated. Some
cells are long and pointed at both ends. They exhibit a spindle shape. Cells
sometimes are quite long. Some are branched like the nerve cell or a neuron.
The nerve cell receives and transfers messages, thereby helping to control and
coordinate the working of different parts of the body. Components of the cell
are enclosed in a membrane. This membrane provides shape to the cells of
plants and animals. Cell wall is an additional covering over the cell membrane
in plant cells. It gives shape and rigidity to these cells. Bacterial cell also has
a cell wall. Size of Cells: The size of cells in living organisms maybe as small
as a millionth of a metre (micrometre or micron) or may be as large as a few
centimetres. However, most of the cells are microscopic in size and are not
visible to the unaided eye. They need to be enlarged or magnified by a
microscope. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest
cell measuring170 mm ×130 mm, is the egg of an ostrich. The size of the cells
has no relation with the size of the body of the animal or plant. It is not
necessary that the cells in the elephant be much bigger than those in a rat.
The size of the cell is related to its function. For example, nerve cells, both in
the elephant and rat, are long and branched. They perform the same function
that of transferring messages.
1) Which among the following scientists coined the term “cell” for the very
first time?
(a) Anton von Leuwenhoek
(b) Robert Brown
(c) Robert Hook
(d) Aristotle
2) …………. are used to colour the parts of cell to study the detailed
structure.
(a) Stains
(b) Microscopes
(c) Slides
(d) Sections
3) Which among the following cells have a characteristic branched shape?
(a) WBC
(b) Neuron
(c) RBC
(d) Amoeba
4) Define unicellular organisms and name one example.
5) Name some of the different shapes of cells that are observed.
Case study 2
You have learnt that each living organism has many organs. You have studied
in Class VII about the digestive organs which together constitute the digestive
system. Each organ in the system performs different functions such as
digestion, assimilation and absorption. Similarly, different organs of a plant
perform specific/specialised functions. For example, roots help in the
absorption of water and minerals. Leaves, as you have learnt in Class VII, are
responsible for synthesis of food. Each organ is further made up of smaller
parts called tissues. A tissue is a group of similar cells performing a specific
function. Paheli realised that an organ is made up of tissues which in turn,
are made up of cells. The cell in a living organism is the basic structural unit.
Cell Membrane: The basic components of a cell are cell membrane, cytoplasm
and nucleus. The cytoplasm and nucleus are enclosed within the cell
membrane, also called the plasma membrane. The membrane separates cells
from one another and also the cell from the surrounding medium. The plasma
membrane is porous and allows the movement of substances or materials
both inward and outward. The boundary of the onion cell is the cell membrane
covered by another thick covering called the cell wall. The central dense round
body in the centre is called the nucleus. The jelly-like substance between the
nucleus and the cell membrane is called cytoplasm. You have learnt earlier
that the cell membrane gives shape to the cell. In addition to the cell
membrane, there is an outer thick layer in cells of plants called cell wall. This
additional layer surrounding the cell membrane is required by plants for
protection. Plant cells need protection against variations in temperature, high
wind speed, atmospheric moisture etc. They are exposed to these variations
because they cannot move. Cells can be observed in the leaf peel of
Tradescantia, Elodea or Rhoeo. You can prepare a slide as in the case of onion.
1) The jelly like substance between the nucleus and the cell membrane is
called the……….
(a) Plasma membrane
(b) Vacuole
(c) Mitochondria
(d) Cytoplasm
2) Which of the following organelle is NOT a basic component of a cell?
(a) Cell membrane
(b) Cytoplasm
(c) Cell wall
(d) Nucleus
3) A ……………….. is a group of cells performing a specific function.
(a) Tissue
(b) Organ
(c) Organ system
(d) Organism
4) Why do only plants cells have cell wall?
5) Explain some of the characteristics of plasma membrane.
Case study 3
Cytoplasm: It is the jelly-like substance present between the cell membrane
and the nucleus. Various other components, or organelles, of cells are present
in the cytoplasm. These are mitochondria, Golgi bodies, ribosomes, etc. You
will learn about them in later classes. Nucleus: It is an important component
of the living cell. It is generally spherical and located in the centre of the cell.
It can be stained and seen easily with the help of a microscope. Nucleus is
separated from the cytoplasm by a membrane called the nuclear membrane.
This membrane is also porous and allows the movement of materials between
the cytoplasm and the inside of the nucleus. With a microscope of higher
magnification, we can see a smaller spherical body in the nucleus. It is called
the nucleolus. In addition, nucleus contains thread-like structures called
chromosomes. These carry genes and help in inheritance or transfer of
characters from the parents to the offspring. The chromosomes can be seen
only when the cell divides. Gene is a unit of inheritance in living organisms.
It controls the transfer of a hereditary characteristic from parents to offspring.
This means that your parents pass some of their characteristics on to you. If
your father has brown eyes, you may also have brown eyes. If your mother
has curly hair, you might also end up having curly hair. However, the different
combination of genes from parents results in different characteristics.
Nucleus, in addition to its role in inheritance, acts as control centre of the
activities of the cell. The entire content of a living cell is known as protoplasm.
It includes the cytoplasm and the nucleus. Protoplasm is called the living
substance of the cell. The nucleus of the bacterial cell is not well-organised
like the cells of multicellular organisms. There is no nuclear membrane. The
cells having nuclear material without nuclear membrane are termed
prokaryotic cells. The organisms with these kinds of cells are called
prokaryotes (pro: primitive; karyon: nucleus). Examples are bacteria and blue
green algae. The cells, like onion cells and cheek cells having well-organised
nucleus with a nuclear membrane are designated as eukaryotic cells. All
organisms other than bacteria and blue green algae are called eukaryotes.
(eu: true; karyon: nucleus).While observing the onion cells under the
microscope, did you notice any blank-looking structures in the cytoplasm? It
is called vacuole. It could be single and big as in an onion cell. Cheek cells
have smaller vacuoles. Large vacuoles are common in plant cells. Vacuoles in
animal cells are much smaller. You might have noticed several small coloured
bodies in the cytoplasm of the cells of Tradescantia leaf. They are scattered in
the cytoplasm of the leaf cells. These are called plastids. They are of different
colours. Some of them contain green Pigment called chlorophyll. Green
coloured plastids are called chloroplasts. They provide green colour to the
leaves. You may recall that chlorophyll in the chloroplasts of leaves, is
essential for photosynthesis.
1) The porous membrane present between the nucleus and the cytoplasm is
called?
(a) Cell wall
(b) Nuclear membrane
(c) Cell membrane
(d) Golgi body
2)…………………. is known as the entire content of living cell that include
the cytoplasm and nucleus.
(a) Protoplasm
(b) Nucleoplasm
(c) Sarcoplasm
(d) Plastid
3) Bacteria and blue-green algae are the examples of which of the following
category?
(a) Eukaryotes
(b) Archaea
(c) Fungi
(d) Prokaryotes
4) Define the term “gene”.
5) What are chloroplasts and what are its functions.

ANSWER THE FOLLOWING

1. Explain in detail about discovery of cell.
2.Define cell.
3. A hen’s egg can be seen easily. Is it a cell or group of cells?
4. Differentiate unicellular and multicellular organisms.
5. Draw and name any 2 unicellular organisms.
6. What advantage does amoeba derive by changing its shape?
7. Mention any 3 different shapes of cells and give example for each.
8.Draw the human nerve cell. What function do nerve cells perform?
9.The size of the cells of an organism has no relation with the size of its
body. Justify.
10.Many tissues together form an organ that carries out a particular
function. Justify
11. List out the parts of a cell.
12.Why do plant cells have an additional layer surrounding the cell
membrane? What is this layer called?
13. Why is cell membrane important in a cell?
14.What is cytoplasm?
15. List out the cell organelles present in a plant cell.
16. Which cell organelle is called the “power house” of the cell and why?
17. Differentiate rough and smooth endoplasmic reticulum.
18. Write in detail about the structure and functions of nucleus.
19.Which part of a cell contains chromosomes? State the function of
chromosomes.
20.Differentiate prokaryotic and eukaryotic cell.
21.Why plant cells need chloroplast?
22. What are plastids?
23. Draw and explain the plant cell.
24. Draw and explain the animal cell.
25. Tabulate the differences and similarities between plant cell and animal
cell.