Cell : The Basic Unit Of Life
Section I
A. Name the following.
1. The protective covering of plant cells.
= Cell Wall;
2. Granular structures that either exist freely in the cytoplasm or are attracted to the endoplasmic reticulum.
= Ribosome;
3. The cell organelle also called the "powerhouse of a cell".
= Mitochondria;
4. Membrane-bound sacs in the cytoplasm of animal cell that contain digestive enzymes.
= Lysosomes;
5. Colourless plastids.
= Leucoplasts;
B. Choose the correct option.
1. Which of the following is single-celled organism?
a. Bacteria. [ ]
b. Amoeba. [ ]
c. Yeast. [ ]
d. All of these. [✓]
2. Membrane-bound bodies found in the cytoplasm of a cell and performing definite functions:
a. Cell membrane. [ ]
b. Cell wall. [ ]
c. Cell organelles. [✓]
d. Plasma membrane. [ ]
3. The nucleus consists of all the following except this.
a. Nucleoplasm. [ ]
b. Chromosome. [ ]
c. Centrosome. [✓]
d. Nucleolus. [ ]
4. The shape of plant cell is
a. oval. [ ]
b. spherical. [ ]
c. geometrical. [✓]
d. irregular. [ ]
5. The structure present in animal cell but not in plant cell is this.
a. Golgi body. [ ]
b. Vacuole. [ ]
c. Ribosome. [ ]
d. Centrosome. [✓]
C. Write T for true and F for false.
1. Plant cells have different shapes. [F]
2. The cell membrane is freely permeable. [F]
3. The longest cell is that of an ostrich egg. [F]
4. The colours imported by chromoplasts promote pollination. [T]
5. Centrosomes help in cell division. [T]
D. Match the items in Column A with that which is most appropriate in Column B.
=
Column A | Column B |
|---|
1. Protoplasm | a. Brain Cell. [5] |
2. Mitochondria | b. Suicidal bag. [4] |
3. Leucoplast | c. Powerhouse of cell. [2] |
4. Lysosome | d. Life giving substance. [1] |
5. Nucleus | e. Imparts colour[3] |
| f. Make food. [ ] |
| g. Store food. [ ] |
E. State the exact location of the following.
1. Cytoplasm.
= Nucleus;
2. Cell wall.
= Plant cells;
3. Endoplasmic reticulum.
= Nuclear membrane to the cell membrane;
4. Chlorophyll.
= Chloroplasts;
5. Ribosome.
= Ether in the cytoplasm or to the endoplasmic reticulum;
F. Write functions of each of the following.
1. Cell membrane.
= It is selectively permeable i.e., it allows some substances to pass through but not others.
2. Chromatin.
= Chromatin fibres thicken to form structures called chromosomes during cell division.
3. Ribosome.
= Ribosomes take part in the synthesis of proteins.
4. Golgi bodies.
= Golgi bodies are involved in the packaging of substances such as enzymes and hormones. They also help in the formation of lysosomes.
5. Chlorophyll.
= They trap sunlight and convert it into chemical energy in the form of food through the process of photosynthesis.
Section II
G. Give reasons for the following.
1. Red blood cells are bi-concave and disc-like in shape.
= Red blood cells are bi-concave and disc-like in the shape for providing a greater surface are for absorbing oxygen.
2. The nucleus is called the brain of the cell.
= The nucleus controls all activities of the cell and hence it is called the "brain of the cell".
3. Mitochondria are known as the "powerhouse of a cell".
= Mitochondria are responsible for oxidising food to release energy during a process called respiration.
4. A cell will die if the nucleus is removed from it.
= A cell will die if the nucleus is removed from it as it controls all activities of a cell.
5. Leaves are green in colour.
= The leaves are green in colour as chloroplast is present there.
H. Differentiate between the following.
1. Unicellular organisms and multicellular organisms.
=
Unicellular Organisms | Multicellular Organisms |
|---|
1. The body is made of a single cell. | 1. The body is made up of many cells. |
2. Organisms are mostly microscopic. | 2. Organisms are mostly macroscopic. |
3. The single cells perform all life functions. Cell differentiation (in which different types of cells carry out different and specific functions) is absent. | 3. Different life functions are brought about by various groups of cells, which form tissues, organs, and organ systems. |
4. They have simple body organization. | 4. They have a complex body organization. |
Lifespan is short. | 5. They have a longer lifespan. |
2. Cell wall and cell membrane.
=
Cell Wall | Cell Membrane |
|---|
1. It is found only in the plant cells. | 1. It is found both in plant and animal cells. |
2. The cell wall is non-living. | 2. The cell membrane is living. |
3. It is freely permeable. It allows all the substances to enter the cell through diffusion. | 3. It is selectively permeable. It allows some substances to pass through but not others. |
3. Chromosome and centrosome.
=
Chromosome | Centrosome |
|---|
1. These are present in animal and plant cells. | 1. These are present inside the nucleus of only animal cells. |
2. They are membrane-bound. | 2. They are not membrane-bound. |
3. There are 23 pairs of chromosomes inside the nucleus of a human cell (46 in total). | 3. centrosomes are represented by an area of clear cytoplasm containing two cylindrical bodies positioned at right angles to each other. |
4. Lysosome and vacuole.
=
Lysosome | Vacuoles |
|---|
1. These are present mostly in animal cells. | 1. These are mostly present in plant cells. |
2. They contain many digestive enzymes. | 2. They store various substances in a solution. |
3. They digest old, worn-out cells as well as organelles. They even destroy foreign bodies such as bacteria. | 3. They store dissolved substances like sugar, minerals, and even waste products. |
5. Mitochondria and chloroplast.
=
Mitochondria | Chloroplasts |
|---|
1 They are situated in the nucleus of the cell. | 1. They are situated in the green parts of plants. |
2. They are responsible for oxidizing food to release energy during a process called cellular respiration. | 2. They trap solar energy and convert it into chemical energy in the form of food through the process of photosynthesis. |
I. Short answer questions.
1. Who proposed the cell theory?
= In 1838, German biologists, Matthias Schleiden and Theodor Schwann, put forward the cell theory of life, which states the following.
All animals and plants are made up of cells.
Cells are the basic units of structure and function in all organisms.
In 1868, Rudolph Virchow, a German scientist, proposed an addition to the cell theory. He stated that new cells are produced from pre-existing cells by cell division.
2. How was the term "cell" derived? Who proposed the term?
= The term "cell" comes from the Latin word 'Cellula' meaning small rooms.
Robert Hooke proposed the term.
3. Define protoplasm.
= Protoplasm is the living content of the cell enclosed by the thin membrane called cell membrane.
4. What is the function of cell membrane?
= Cell membrane is selectively permeable i.e., it allows some substances to pass through but not others.
5. Where are genes located and what is their function?
= The chromatin contains hereditary units called genes that are passed on from the parent to the offspring. During cell division, chromatin fibres thicken to form structures called chromosomes.
J. Long answer questions.
1. What does the cell theory state?
= In 1838, German biologists, Matthias Schleiden and Theodor Schwann, put forward the cell theory of life, which states the following:
i) All animals and plants are made up of cells.
ii) Cells are the basic units of structure and function in all organisms.
In, 1868, Rudolph Virchow, a German scientist, proposed an addition to the cell theory. He stated that new cells are produced from pre-existing cells by cell division.
2. Are multicellular organisms advanced as compared to the unicellular organisms? Give three reasons in support of your answer.
= Yes, multicellular organisms are advanced as compared to the unicellular organisms.
Three reasons are -
i) They have a longer lifespan.
ii) Different life functions are brought about by various groups of cells, which form tissues, organs and organ systems.
iii) Organisms are mostly macroscopic.
3. Explain the structure of the nucleus with the help of a labelled diagram.
= The nucleus is usually spherical in shape. It controls all activities of the cell, and hence it is called the "brain off the cell". It is surrounded by a double-layered membrane, the nuclear membrane. This membrane contains many nuclear pores. The nuclear membrane surrounds a jelly-like fluid, the nucleoplasm. The nucleoplasm contains one or more spherical bodies called nucleoli (singular: nucleolus). It also contains a network of thread-like structures called chromatin.
The chromatin contains hereditary units called genes that are passed on from the parent to the offspring. During cell division, chromatin fibres thicken to form structures called chromosomes.
Labelled diagram of a nucleus
4. What are plastids? Write an account on the different types of plastids found in plants.
= Plastids are found in plant cells. They are bound by a double membrane and can be oval, spherical, or discoid in shape. Based on their colour, they are classified into the following three types.
Chloroplasts : - They are green plastids as they contain a green pigment called chlorophyll. They trap solar energy in the form of food through the process of photosynthesis. Chloroplasts are present in the green parts of plants and in algae.
Chromoplasts :- These are coloured plastids. They are contain red, orange, and yellow pigments. These colours attract insects and other animals for pollination. They are mostly found in the petals of flowers and fruits.
Leucoplasts :- These are colourless plastids that store food in the form of starch, proteins and fats. they are found in non-photosynthetic parts like roots and seeds of the plant.
5. Draw a labelled diagram of a typical animal cell.
=
6. Differentiate between a plant cell and an animal cell.
=
Plant Cells | Animal Cells |
|---|
1. Plant cells have a fixed geometrical shape. | 1. Shapes of animal cells vary. |
2. Cell wall is present. | 2. Cell wall is absent. |
3. Plastids are present in the cytoplasm. | 3. Plastids are absent. |
4. Lysosomes are absent. | 4. Lysosomes are present in the cytoplasm. |
5. Large permanent vacuoles are present. They fill about ninety per cent of the space inside the cell. | 5. Vacuoles, if present, are small. |
6. Centrosomes are absent. | 6. Centrosomes are present. |
7. Nucleus is marginal in position. | 7. Nucleus is central in position. |
