CELL : THE UNIT OF LIFE - Q&A

PROGRESS CHECK - 1

1. Name the following:
(i) The kind of microscope that consists of a single biconvex lens.
Simple microscope

(ii) The kind of mirror used for throwing light on the object in Hooke's microscope.
Concave mirror

2. What is the maximum magnification that can usually be achieved by
(i) a compound microscope, (ii) an electron microscope
(i) Compound microscope: About 2,000 times.
(ii) Electron microscope: Over 200,000 times.

1. Name the following:

(i) Any two one-celled organisms.
Bacteria, Yeast (or Amoeba).

(ii) The longest cells in animals.
Nerve cells.

(iii) Amoeboid cells in humans.
White blood cells (WBCs).

(iv) Outermost layer in plant cells.
Cell wall.

(v) A cell component which is visible only in cell division stages.
Chromosomes.

2. List three categories of substances which are ensured greater diffusion due to large surface/volume ratio of the cells.
1. Nutrients.
2. Metabolic wastes.
3. Respiratory gases (Oxygen and Carbon dioxide).

1. Name the part of a cell in which
(i) many chemical reactions occur with the help of enzymes.
Cytoplasm

(ii) a network of chromatin fibres occurs.
Nucleus (specifically in the nucleoplasm)

(iii) cellulose forms the main component.
Cell wall

2. Differentiate between
(i) an organ and an organelle
An organ is a part of the body (like the heart or brain) composed of tissues performing a specific function for the organism. An organelle is a specific part within a cell (like mitochondria or nucleus) that performs a specific function for the cell.

(ii) a plant cell and an animal cell pertaining to the presence of plastids
Plant cells contain plastids (such as chloroplasts, chromoplasts, and leucoplasts), whereas animal cells do not contain plastids.

3. Name the cell organelles concerned with
(i) Secretion of enzymes
Golgi apparatus
(ii) Trapping of solar energy
Chloroplasts
(iii) Synthesis of proteins
Ribosomes
(iv) Intracellular digestion
Lysosomes
(v) Production of ATP
Mitochondria

4. Name the cell part which is
(i) composed of cellulose
Cell wall
(ii) formed of an irregular network of tubular double membranes
Endoplasmic reticulum
(iii) a clear space with water or other substances in solution
Vacuole

5. Mention if the following statements are true or false. If false, suggest the change in the information underlined.
(i) Prokaryotic cells have larger ribosomes.
False. Prokaryotic cells have smaller ribosomes.

(ii) Eukaryotic cells have mitochondria.
True.

(iii) Amoeba is an example of Prokaryotes.
False. Amoeba is an example of Eukaryotes.

(iv) Bacteria have no nuclear membrane but possess chloroplasts.
False. Bacteria have no nuclear membrane but possess ribosomes (Bacteria do not have chloroplasts).

1. Column I lists a few activities of living organisms and column II the activity of cells related to them. Match the items in the two columns.

Correct Matching:
(i) Repair — (c) Cell division
(ii) Cooling of body — (d) Gland cells give out sweat for evaporation
(iii) Movement — (a) Contractility of cells
(iv) Protection from diseases — (b) Cells devour germs

2. Which cell organelle is the key to the life of the cell?
The Nucleus. (It regulates all cell functions; if removed, the cell dies).

3. How do you say that a cell also has a life span and death like an organism? Give one example.
Cells are not immortal; they grow, function, age, and die, often being replaced by new ones. For example, red blood cells in humans live for about 120 days and then die.

4. All organisms excrete. Does an individual cell also do it? Give one example.
Yes, individual cells also excrete metabolic wastes. For example, carbon dioxide produced during respiration diffuses out of the cell through the cell membrane.

5. Every organism needs food. Does a cell also need it? Explain very briefly.
Yes, a cell needs food (nutrients) to generate energy for its activities and to synthesize materials for growth and repair.

REVIEW QUESTIONS

A. MULTIPLE CHOICE TYPE

1. Which one of the following cell organelles is correctly matched with its function?
(a) Ribosomes — Synthesis of proteins
(b) Mitochondria — Secretion of enzymes
(c) Plasma membrane — Freely permeable
(d) Centrosome — Carries genes
Answer: (a) Ribosomes — Synthesis of proteins
(Explanation: Mitochondria are for respiration, Plasma membrane is semi-permeable, Centrosomes are for cell division).

2. All life starts as
(a) an egg
(b) a single cell
(c) a gene
(d) a chromosome
Answer: (b) a single cell

3. Which one of the following is found both in the cells of a mango plant and a monkey?
(a) chloroplasts
(b) centrioles
(c) cell wall
(d) cell membrane
Answer: (d) cell membrane

4. A plant cell can be identified from an animal cell by the:
(a) absence of centrosome.
(b) presence of cell membrane.
(c) presence of vacuoles
(d) none of the above
Answer: (a) absence of centrosome.
(Explanation: While both have vacuoles, plant cells typically lack centrosomes which are present in animal cells).

5. Plant cell has a cell wall made of:
(a) Protein
(b) Fructose
(c) Cellulose
(d) Fatty acids
Answer: (c) Cellulose

6. The cell organelle that helps in respiration of the cell is:
(a) Mitochondria
(b) Lysosome
(c) Ribosome
(d) Centrosome
Answer: (a) Mitochondria

B. VERY SHORT ANSWER TYPE

1. Name the part of the cell concerned with the following?
(a) Liberation of energy
Mitochondria
(b) Synthesis of proteins
Ribosomes
(c) Transmission of hereditary characters from parents to offspring
Nucleus (specifically Chromosomes/Genes)
(d) Initiation of cell division
Centrosome (in animal cells)
(e) Hydrolytic in function
Lysosomes
(f) Entry of only certain substances into and out of the cell.
Cell membrane (Plasma membrane)

2. State whether the following statements are true (T) or false (F):
(a) All animal cells contain a cell wall.
False (F)
(b) The cell wall is made of protein.
False (F)
(c) Centrosome occurs in animal cells.
True (T)
(d) Plant cells contain large vacuoles.
True (T)
(e) Protoplasm is the part of the cell which surrounds the nucleus.
False (F) - (The part surrounding the nucleus is Cytoplasm; Protoplasm includes both Cytoplasm and Nucleus).
(f) Genes are located in chromosomes.
True (T)
(g) Anthocyanins are the pigments of flowers, which are dissolved in cell-sap.
True (T)

C. SHORT ANSWER TYPE

1. It is said that the protoplasm cannot be analysed chemically. Why?
Protoplasm is living matter. It cannot be analyzed chemically accurately because as soon as it is removed from the organism or the cell to be analyzed, it dies and ceases to be protoplasm, becoming merely a mixture of chemical compounds.

2. What is the difference between an organ and an organelle?
An organ is a large part of an organism (like eye, heart, leaf) made of tissues functioning together. An organelle is a microscopic structure inside a cell (like mitochondrion, ribosome) performing a specific cellular function.

3. Do you think the cells of an elephant would be larger than the cells of a rat? Explain briefly.
No, the cells of an elephant are not necessarily larger than those of a rat. The size of an organism depends mainly on the number of cells, not the size of individual cells. Cells generally remain small to maintain efficiency in diffusion and communication.

4. Differentiate between the following pairs of terms:
(a) Protoplasm and cytoplasm
Protoplasm is the total living substance of the cell (Nucleus + Cytoplasm). Cytoplasm is the part of the protoplasm excluding the nucleus (Protoplasm - Nucleus).
(b) Nucleolus and nucleus
The Nucleus is the main control center of the cell containing chromosomes. The Nucleolus is a small spherical body inside the nucleus concerned with ribosome production.
(c) Centrosome and chromosome
The Centrosome is an organelle in animal cells that initiates cell division. Chromosomes are thread-like structures in the nucleus composed of DNA that carry hereditary information.
(d) Cell wall and cell membrane
The Cell wall is a non-living, rigid outer layer made of cellulose found in plant cells, and is freely permeable. The Cell membrane is a living, thin, flexible semi-permeable membrane found in all cells (inner to cell wall in plants).
(e) Plant cell and animal cell
A Plant cell has a cell wall, plastids, and large vacuoles, but no centrosome. An Animal cell lacks a cell wall and plastids, has small/temporary vacuoles, but possesses a centrosome.
(f) Prokaryotes and eukaryotes.
Prokaryotes (e.g., bacteria) have a primitive nucleus without a nuclear membrane and lack membrane-bound organelles. Eukaryotes (e.g., plants, animals) have a well-defined nucleus with a nuclear membrane and possess organelles like mitochondria.

5. Mention three features found only in plant cells and one found only in animal cells.
Found only in Plant cells:
1. Cell wall
2. Plastids (Chloroplasts, etc.)
3. Large prominent vacuoles.
Found only in Animal cells:
1. Centrosome.

6. Why are the cells generally of a small size?
Cells remain small to maximize their surface area to volume ratio. This ensures efficient diffusion of nutrients into the cell and metabolic wastes out of the cell. It also allows for rapid communication between different regions of the cell.

D. LONG ANSWER TYPE

1. What is the cell theory? Who propounded it and when?
The Cell Theory states that:
1. The cell is the smallest unit of structure of all living things.
2. The cell is the unit of function of all living things.
3. All cells arise from pre-existing cells.
It was proposed by Schleiden and Schwann in 1839. (Rudolf Virchow added the third point later in 1858).

2. Mention any three differences between a living cell and a brick in a wall.
1. Growth: A living cell grows and divides; a brick does not grow.
2. Metabolism: A living cell performs metabolic activities (respiration, digestion); a brick does not.
3. Reproduction: A living cell can reproduce (arise from pre-existing cells); a brick cannot produce new bricks.

3. Name the plastid and pigment likely to be found in the cells of:
(a) petals of sunflower
Plastid: Chromoplast. Pigment: Xanthophyll (yellow).
(b) ripe tomato
Plastid: Chromoplast. Pigment: Carotene (red).
(c) skin of green mango
Plastid: Chloroplast. Pigment: Chlorophyll (green).
(d) cells of potato.
Plastid: Leucoplast. Pigment: None (colourless/white).

4. State the major functions of the following:
(a) Plasma membrane: Regulates entry and exit of substances (selectively permeable); separates cell contents from surroundings.
(b) Ribosome: Site of protein synthesis.
(c) Lysosome: Intracellular digestion; destroys foreign substances and old organelles ("suicide bags").
(d) Mitochondria: Release energy (ATP) through cellular respiration ("power house").
(e) Golgi apparatus: Synthesis and secretion of enzymes, hormones, etc.
(f) Cytoplasm: Site of chemical reactions (metabolism); contains organelles.
(g) Asters of centrosome: Initiate and regulate cell division; form spindle fibres.
(h) Chromosomes: Carry genetic characters (genes) from parents to offspring.
(i) Glycogen granule: Food storage in animal cells.
(j) Vacuoles: Store water, food, pigments, and wastes; provide turgidity to plant cells.

5. Match the items in column 'A' with those in column 'B'

Correct Matching:
(a) Vacuoles — (iii) Covered by tonoplast
(b) Nucleolus — (v) Forms RNA
(c) Lysosomes — (i) Intracellular digestion
(d) Anthocyanin — (iv) Dissolved in the cytoplasm (Note: Accurately, it is dissolved in cell sap).
(e) Cristae — (ii) Respiratory enzymes (Cristae are in mitochondria where respiratory enzymes function).

6. Fill in the blanks:
(a) Lysosome secretes 40 types of digestive enzymes.
(b) Centrosome is surrounded by microtubules, located near the nucleus.
(c) Very thin flexible, living membrane which is differentially permeable, is called Plasma membrane (or Cell membrane).
(d) More than 1000 chromosomes are found in the nucleus of certain insects.
(e) Genes are hereditary units.
(f) Leucoplast is a plastid which stores starch.

E. STRUCTURED/APPLICATION/SKILL TYPE

1. Given below are the sketches of two types of cells A and B.
[Note: Diagram A shows an animal cell (no cell wall, centrioles present). Diagram B shows a plant cell (rigid wall, large vacuole)].

(a) Which one of these is a plant cell? Give reason in support of your answer.
Figure B is the plant cell. Reason: It possesses a distinct cell wall and a large central vacuole, which are characteristic features of plant cells.

(b) List the cell structures which are common to both the types.
Common structures: Cell membrane, Cytoplasm, Nucleus (nuclear membrane, nucleolus, chromatin), Mitochondria, Endoplasmic Reticulum, Ribosomes, Golgi bodies.

(c) Name the structures found only in plant cells and those found only in animal cells.
Only in Plant Cell (B): Cell wall, Plastids (Chloroplasts), Large Vacuole.
Only in Animal Cell (A): Centrosome (Centrioles).