Cell : The Unit of Life QUESTIONS.
Q. 1. Who proposed cell theory and what „ modifications Rudolf Virchow made in it?
Ans. M.J. Schleiden and Theodore Schwann (1838-39) proposed the cell theory which states that
(i) All living things are made up of cells and cell products.
(ii) Cells are the units of structure and function of all living organisms.
(iii) All metabolic reactions in living things take place within the cell.
Later on, the cell theory was modified by Rudolf Virchow (1855) who stated that "all cells arise from the pre-existing cells"
Q. 2. Name the scientists who proposed "cell theory". Discuss main points of this theory. [Annual Exam. 2001]
Ans. Cell Theory : In the year 1838 two German scientists - Mathias Jacob Schleiden and Theodore Schwann gave the famous cell theory which states as follows :
1. All living things are composed of cells and cell products.
2. Cells are the structural and functional units of all living things.
3. All metabolic reactions in living things (unicellular or multicellular) take place within the cell.
The cell theory was later modified by Rudolf Virchow (1885) who stated that all the cells arise from pre-existing cell to the division of work that we have in our society. You know our society is made up of many individuals which perform different functions. Doctors cure patients, washermen wash clothes, cobblers make shoes, engineers make houses, bridges, factories, etc. Each of these are specialized for specific purposes.
Q. 3. What are the advantage of multicellularity over unicellularity ?
Ans. Advantage of Multicellularity : 1. As a result of multicellularity, division of labour (distribution of work)occurs in the body of an organism. 2. As a result of division of labour, tissue formation takes place. 3. Tissues perform only specialised functions for which they
are meant and no other function. 4. Tissues from organs and organs form organ systems. 5. The various organ systems work in coordinating way for the benefit of the multicellular organisms.
Q. 4. "Cell is an open dynamic system". Justify this statement.
Ans. The cell permits input and output of matter and energy in it. So it is considered to be an open system. The cell uses energy for metabolism. It excretes waste products. Many substances are excreted by the cells. It oxidises food to get energy. A cell always remains in a steady state and homeostasis.
Q. 5. Is there any relationship between the size of the cell and the organism in which it is present ? [V. Imp.]
Ans. There is practically no relationship between the size of the cell and the organism. For example; the cells of elephant or whale may not be large. However, their number is more in them so as to increase the bulk of the animals.
Q. 6. What is the significance of the plasma membrane ? „ [V. Imp.]
Ans. The cell membrane or plasma membrane. It is in extremely thin membrane. It is also called as plasmalemma. It is present as an outer covering of animal cells. In plant cells, it is present below the cell wall surrounding the protoplasm of the cell.
Significance of Plasma membrane : (i) It forms the outer boundary of the cell. Thus it helps in giving cell a definite shape.
(ii) It protects the inner contents of the cell.
(iii) It allows the passage of excreta substances through it. Hence it acts as a selectively permeable membrane.
(iv) It forms a molecular boundary between cell and its environment.
Q. 7. List the functions of golgi bodies.
Ans. The functions of golgi bodies are :
1. Storage, condensation and packaging of the material.
2. Several enzymes are localized in golgi bodies.
3. During spermatogenesis, golgi apparatus forms the curosome.
4. Mucilage and gums are secreted in plant cells due to the action of golgi apparatus.
. 8. What is polysome ?
Ans. Polysome : It is also called polyribosome according to Rich (J.963). Some ribosomes are linked together to form polysomes. Magnesium ion concentration is responsible for the linking of ribosomes on mRNA chain.
Q. 9. Explain cell theory as understood today.
Ans. Cell Theory
(i) All living organisms are composed of cells and the products of cells.
(ii) All the cells arise from pre-existing cells.
Q. 10. Distinguish between a plant cell and an animal cell.
Ans. Difference between a plant cell and an animal cell :
Animal cell | Plant cell | |
| 1. | No cell wall | Cell wall made up of |
| cellulose. | ||
| 2. | Centrioles with centr- | Centrioles with centro- |
| osome present. | some absent. | |
| 3. | Plastids absent. | Plastids present. |
| 4." | Golgi bodies are loca | Golgi bodies are in form |
| lized and consist of | of many dictyosomes. | |
| connected complexes. | ||
| 5. | Vacuoles either ab | Vacuoles large in size |
| sent or few. | and more in number. | |
Q. 11. Draw a well labelled diagram to show a three-dimensional view of it. Mention its role also.
Ans. Rough ER : It is known as the granular endoplasmic reticulum because ribosome particles are pre.sent on the outer surface of ER. It is found in those cells which are actively engaged in protein synthesis. Rough
ER is much developed. Ribosomes are the sites for protein synthesis. It also takes part in transporting materials.
RER SER Golgi body Primary Lysosome —> Out of cell
Q. 12. What are the cell inclusions in a prokaryotic cell ?
Ans. Cell inclusions : In prokaryotic cells there are stage granules or inclusion bodies. They he freely in cytoplasm. Example phosphate granule, glycogen granules, sulphur granules, gas vacuole, poly-B-hydroxybutyrate. There may be metachromtatic granules.
Q. 13. Describe functions of flagella and cilia.
Ans. Functions of flagella and cilia.
1. Flagella and cilia help the organisms in movement and locomotion.
2. They help to swim the organism in water.
3. So cilia and flagella are associated with motility of cells.
Q. 14. Give the difference between cell walls of Gram-positive and Gram-negative bacteria.
Ans. Differences between Gram positive and Gram-negative bacteria:
Gram positive bacteria | Gram negative bacteria |
| 1. Their cell wall is only single-layered and 100-200 A thick. | Their cell wall consist of two layers and is 70-120 A in thickness. |
Gram positive bacteria | Gram negative bacteria |
| 2. They are stained by gram stain. 3. They do not have pili. 4. In gram positive bacteria there are mesosomes. | They are not stained by gram stain. They have pili. In gram negative bacteria there are no mesosomes, if present they are poorly developed. |
. Q. 15. List the fundamental similarities in all cells. [V. Imp.]
Ans. Fundamental Similarities in all Cells. These are two types of cells—plant cells and animals cells.
Plant Vs. Animal Cell : The living organisms are made up of small building units called the ceMs. The various life processes of the body result from the combined activity of these cells. Each cell consists of three parts :
(a) Plasma membrane; (b) Cytoplasm and (c) Nucleus.
There are present large number of cell organelles which perform different functions. Basically the structure of all cells found in the living organisms is the same but modification in size, appearances and behaviour differ because of the functions they have to perform
Q. 16. List the various shapes of cells that you know.
Ans. The cells differ from each other in shape and size. They may be oral or spherical, flat or elongated, spindle shaped or lobose, many sided or cylindrical or changeable. In Fig. 8.15 given are shown some different types of cells
Ans. Differentiated Cells : These are the post mitotic cells which have undergone specialization. They may show division of labour. These cells perform a specific function. The muscle cells perform movement in animals. In plants, the mesophyll cells are involved in the synthesis of food by photosynthesis. Red blood corpuscles in man transport oxygen and C02in body.
Q. 18. Write note on dedifferentiated cells.
Ans. Dedifferentiated Cells : These are differentiated cells which are capable of reverting back to the undifferentiated meristematic stage. These are essential for secondary growth. In animals, they are needed in wound healing.
Q. 19. Write a brief note on bacterial cell wall.
Ans. Cell Wall of Bacteria : It is formed of murein or peptidoglycon. It consists of polysaccharide cross linked with short amino acid chains. In Gram-ve bacteria, covering is formed of lipopolysaccharide and present around cell
wall. It may provide specific adhesion properties to these cells. It determines the shape of the cell.
wall. It may provide specific adhesion properties to these cells. It determines the shape of the cell.
Q. 20. What are the characteristics of prokaryotic cells ? [NCERT T.B.Q. 8]
Ans. Characteristics of Prokaryotic cells :
1. These are represented by PPLO, Mycoplasma, BGA and bacteria.
2. These are smaller mostly and multiply more rapidly.
3. Very greatly in size and shape etc.
4. All prokaryotes have cell wall enclosing cell membrane, cytoplasm and DNA circle (plasmid/naked chromosome) that is not bounded by nuclear membrane.
Q. 21. What is cell coat ? Give two examples.
Ans. Cell Coat : The plasma membrane in animals and some protista is not surrounded by the cell wall made up of cellulose but there is a thin layer of oligosaccharides called cell coat. Its main function is the protection of a plasma membrane in them.
Q. 22. Differentiate between Cilia and flagella.
Ans. Differences between Cilia and flagella.
| Points | Cilia | Flagella | |
| 1. | Size | Short, 2-10 (im | Long, 150 fim |
| long. | in length. | ||
| 2. | Number | More in number | Few in number. |
| 3. | Movement | Pendular move | Undulating |
| ment | movement | ||
| 4. | Co-ordination | Cilia move in co | Flagella do not |
| ordination with | move in co-ordi | ||
| each other. | nation. | ||
Q. 23. What structural and functional characteristics of cilia, flagella and centrioles have in common ?
Ans. The common structural feature of cilia, flagella and centriole is that all of them have basal bodies as starting point which has (9 + 2) arrangement of triplets of microtubules. Functionally, they show contraction and expansion causing movement or migration.
Q. 24. Write two functions of the cell wall.
Ans. Cell wall performs the following two functions in plants only :
(i) Cell wall provides a definite shape and also protects the inner contents of the cell.
(ii) It allows the transport of various substances from one cell to the other.
Q. 25. Write the composition of peptido-glycan. What makes it a strong and flexible framework ? [Annual Exam 2005]
Endoplasmic reticulum provides mechanical support to cytoplasmic matrix. Write four more functions of ER other than this.
Peptidoglycan (murein or mucopeptide) is made of repeating framework of long glycan strands (N-acetyl muramic acid and N-acetyl glucosamine). These strands are cross linked by short peptide chains to give strong but flexible support framework. Lysozyme hydrolyses peptidoglycan.
Or
1. Synthesis of the lipids.
2. Detoxification of the drugs.
3. Associated to muscle contraction by release as well as the uptake of Ca2+ ions.
4. The synthesis of secretory/lysosomal or the membrane proteins on the ER 'membrane and its transport through the endoplasmic reticulum lumen.
Ans. Chromatophores : These are internal membrane systems found in the prokaryotic cells. They are extensive and complex in photo-synthetic forms. Examples are cyanobacteria and purple-bacteria. These membranes form aggregates of spherical, flattened or tubular vesicles in nitrifying bacteria. They help to increase membrane surface for greater metabolic activities.
Ans. Inclusion Bodies and their Examples : Reserve material in bacteria is stored in the cytoplasm which is called inclusion body or storage granule. They are not enclosed by any membrane system. These lie freely in the cytoplasm. Examples are phosphate granules, cyanophycean granules and glycogen granules. Inclusion bodies may be surrounded by a single layer non-unit membrane. This unit membrane may be 2—4 nm thick. Example of this type of inclusion bodies are : other examples are gas vacuoles found in purple, green photosynthetic bacteria and cyanobacteria poly-$-hydroxybutyrate granules, sulphur granules gas, vacuoles and carboxysomes.
Ans. Glycocalyx : It protects the cells. It helps in adhesion. The outer covering is immunogenic in bacterial cells.
Leucoplast | Chromoplast |
| 1. Colourless plastids, devoid of any pigment. 2. They have the capacity to develop pigment when needed. Leuco-plasts are of three types—any toplast, proteoplast and elaioplast. | 1. May contain pigments other than chlorophyll. 2. They synthesize and store other pigments such as carotenoid. |
Q. 30. Define osmosis. Give its significance in the life of a plant and cite example to explain the role of osmosis.
Ans. In plants, the cell is enclosed by a cellulose cell wall. The cytoplasm and other structures are surrounded by a semi-permeable membrane. Osmosis is defined as diffusion of water (solvent) through a semi-permeable membrane form low concentration to high concentration. The water movement into the cell is controlled by semipermeable membrane. Osmotic pressure in the cell is developed due to the concentration of cell sap present in the vacuole in the cell. '
If the cell is placed in water due to osmotic pressure, the water enters the cell and increases a pressure on the cell wall which is called turgor pressure. The cell wall exerts an equal and reverse pressure on the cell sap named as wall pressure. The whole change in the cell is due to osmosis.
Ans. Fluidity of a Membrane : The fluidity of the membrane can be demonstrated by the following simple experiment:Take two different cells. Label one of them with red fluorescent dye and the other with green dye. Fuse the two cells. View the fused cell immediately under the microscope. You will see one half of the cell as green and other half as red. Again after sometime at 37°C you will observe the colour to be mixed uniformly. This was possible only if the lipid layer was fluid and the labelled proteins could move about in it. The above fact can further be proved by keeping the fused cells immediately at 0°C. At 0°C, they fail to show any mixing of the colours. This is because of the fact that lipids solidify at low temperatures and lose their, fluidity.
Ans. Differences between contriole and. basal body :
| Feature | Centriole | Basal |
| Body | ||
| 1. Name | It is also known | It is also known |
| as cell centre. | as cell centre. | |
| 2. Number | There are only | There are only |
| two centrioles in | two centrioles in | |
| a cell. | a cell. | |
| 3. Position | It is fotind near | It is found near |
| nuclear mem | to nuclear mem | |
| brane. | brane. | |
| 4. Size | Smaller in size. | Smaller in size. |
| 5. Function | Aster formation | Aster formation |
| during cell | during cell | |
| division. | division. |
Q. 32. How do microfilaments and microtubules differ ?
Ans. Difference between Micro filaments and Microtubules :
| Points | Microfilaments | Microtubules | |
| 1. Structure | Actin is the main | a and (3 tubulin | |
| component | of | proteins are the | |
| microfilament | main components | ||
| and so they | are | of the microtu | |
| contractile. | bules and so they are non-contractile. | ||
| 2. Diameter | 5-6 nm. | 25 nm | |
| 3. Sub-units | Absent. | 13 protofilments form a microtubule. | |
Q. 33. Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus (ii) Centrosome.
[NCERT T.B.Q. 13] Ans. (i) Structure of Nucleus : Nucleus is one of the most important components of the cell.
It is, therefore, called the control centre of the cell as it controls the various metabolic activities of the cell. Nucleus is situated in the cytoplasm of the cell. Usually it is round but many.different shaped nuclei can be seen in some cells. It is surrounded by two porous membranes called nuclear membranes which remain continuous"with the E.R. Within the nuclear membrane is present a liquid substance called nucleoplasm The nucleoplasm contains chromatin material of two types : heterochromatin and euchromatin.(ii) Structure of Centrosome : This organelle contain 2 centrioles, the cylindrical structures. They are enclosed by amorphous pericentriolar materials. Centrioles lie perpendicular to each other in centrosome. Each possesses cartwheel organisation and made of a peripheral fibrils of tubulin. Each peripheral fibril is a triplet.Central part of centriole is hub that is united to tubules of peripheral triplet by radial spokes
Q. 34. Why are lysosomes called "suicidal bags" ?
Q. 34. Why are lysosomes called "suicidal bags" ?
Ans. Lysosomes are suicidal bags of the cell: These are sac-like structures bounded by a single membrane. These sacs contain several digestive enzymes. These enzymes when released from the lysosomes bring about breakdown of the various cytoplasmic structures. Lysosomes help in digestion of food particles, other foreign bodies, old worn out organelles of the cells often resulting in the death of the cell. So they are often referred assuicidal bags or digestive bags of the cell.
Q. 35. What is the difference between cell wall and ribosomes of a prokaryotic and a eukaryotic cell ?[Annual Exam. 2003]
Ans. Difference between Cell wall and Ribosomes of a prokaryotic and a Eukaryotic cell:
Q. 36. Compare euchromatin with heterochromatin.
Ans. Comparison between Euchromatin and Heterochromatin :
Q. 37. Where should the following structures be found in cell ?
(a) microtubules, (b) thylakoids, (c) F0-Fj complex, (d) ribosomes, (q) nucleolus.
Ans. (a) In centrioles.
(b) In the stroma of chloroplasts (plastids)
(c) Inner membrane and cristae of mitochondria.
(d) On rough endoplasmic reticulum.
(e) Inside the nucleus.
Q 38 what are the four differences between cilia and flagella:
Q. 39. Compare autophagy with autolysis.
Ans. Comparison between Autophagy and autolysis :
Q. 40. Point out some differences between a prokaryotic and a eukaryotic ribosome.
Ans. Differences between Prokaryotic and Eukaryotic ribosomes :
Q. 41. Point out differences between Leucoplast and Chromoplast.
Ans. Differences between Leucoplast and Chromoplast :
Q. 42. Differentiate between chromatin and chromosome.
Ans. Differences between Chromatin and Chromosome :
Q. 43. What are Gram-negative and Gram positive bacteria ?[Annual Exam 2000 C]
Ans. Gram-Positive Bacteria : Their cell walls is only single layered and 100-200 A thick. They are stained by Gram stain. They do not have pilli. There are mesosomes. These bacteria retain their blue colour even after they, are washed with alcohol after iodine treatment e.g., Mycobacterium and Clostridium tetani.Gram-Negative bacteria : These cell walls are two-layered and 70-120 A in thickness. They are not stained by Gram stain. They have pilli. In* Gram-negative bacteria, there are no mesosomes but if present they are poorly developed with dyecrystal violet, all they stain blue. When such stained cells are treated with Iodine and washed with alcohol, the bacteria who lose their blue colour are said to be gram-negative. Example : E. coli andPseudomonas.
Q. 44. Which cell organelle is known as "Power-house of cell'"! Give its two methods of origin. [Annual Exam. 2000 C]
Ans. Mitochondria : These were first discovered by Kolliker (1880). [Mito
Two methods of origin of Mitochondria:
(i) Self-duplicating organelles due to DNA present in them. New mitochondria are formed by division and growth of pre-existing mitochondria.
(ii) According to symbiotic or prokaryotic hypothsesis of mitochondrial origin, these semi-autonomous organelles were independent organisms and they entrapped in big eukaryotic cells where they lived as symbionts.And then they were changed into a constituent of cells.
Q. 45. Explain the functions of the following cell organelles :
(i) Lysosome, (ii) Centrosome, and (iii) Chloroplast. [Annual Exam. 1999]
Ans. (i) Functions of Lysosomes :
(a) They help in heterotrophic nutrition by intracellular digestion and under special conditions by extracellular digestion also.
(b) They work as scavengers..
(c) Destroy by lysis of the obstructing structures.
(d) Lysosomes are associated with programmed cellular breakdown associated with ageing and so they are called as "suicidal bags of cells".
| Q. 46. How bacterial flagellum differs from eukaryotic flagellum ? Ans. Differences between bacterial flagellum and Eukaryotic Flagellum:Bacteria Flagellum | Eukaryotic Flagellum | |
| 1. Single stranded made up of only one spirally* | 1. | It has 9 + 2 structure (having 2 tubulin mole |
| coiled molecule of flagellin. | cules in the centre and 9 tubulins sur | |
| rounding in the periphery). | ||
| 2. Not bound by a membrane. | 2. | Bound by cell-membrane. |
| 3. Bacterial flagellum has antigenic properties. | 3. | Lacks antigenic properties. |
| 4. It is 100% proteinaceous. | 4. | It has 70% protein, 20% lipid and 10% poly |
| saccharides | ||
