Q1. Name the processes by which CO₂ and H₂O move in and out of the cell?

Solution

CO₂ and H₂O move in and out of the cell by the process of diffusion and osmosis respectively.

Q2. What will happen if:

(a) Ribosomes are removed from the cell.

(b) Golgi apparatus is removed from the cell.

Solution

(a) If ribososmes are removed from the cell, proteins will not be synthesized.

(b) If Golgi apparatus is removed from the cell, packaging of materials, synthesis of complex sugars and formation of lysosome will be adversely affected.

Q3. Distinguish between chloroplast and leucoplast with respect to their pigments and function.

Solution

Differences between chloroplast and leucoplast: Chloroplast  Leucoplast Green pigment Colourless pigment Helps in photosynthesis Helps in the storage of proteins and starch

Q4. Which cell organelles are called the powerhouses of the cell and why? Why is ATP called energy currency of the cell?

Solution

Mitochondria are called the powerhouses of the cell. During oxidation of food, a large amount of energy is released by mitochondria which gets stored in the form of energy-rich compound called adenosine triphosphate (ATP). This energy stored in the form of ATP is used for making new chemical compounds and for performing mechanical work, therefore ATE is called energy currency of the cell.

Q5. What will happen if plasma membrane ruptures or breaks down?

Solution

Plasma membrane is a selectively permeable membrane of the cell that maintains homeostasis, i.e. a constant internal composition of the cell. If it ruptures or breaks down, the constant internal composition of the cell will be lost and the cell will not be able to perform its basic functions. Such a cell with a ruptured plasma membrane gets killed.

Q6. What would happen to a cell if its nucleus is removed?

Solution

The nucleus controls all the metabolic activities of the cell. If the nucleus is removed from a cell, its protoplasm dries up and the cell dies. Therefore, the nucleus is paramount to a cell’s survival.

Q7. What did A. Leeuwenhoek discover in 1674?

Solution

In 1674, with the help of an improved microscope, A. Leeuwenhoek discovered the free-living cells in pond water for the first time.

Q8. State two reasons for plant cells to have a large central vacuole.

Solution

Plant cells have a large central vacuole because: (i) They help in maintaining the osmotic pressure of the cell. (ii) They store important substances like amino acids and proteins. (iii) They also store metabolic wastes of the cell.

Q9. Define diffusion.

Solution

Diffusion is the spontaneous movement of molecules from a region of high concentration to a region of low concentration.

Q10. Give one function each of the following nuclear parts: a) Nuclear pore b) Nuclear membrane c) Chromosomes

Solution

a) Nuclear pore: It allows the transfer of materials from inside the nucleus to the cytoplasm. b) Nuclear membrane: It gives a distinct identity to the nucleus by keeping its contents inside and separate from the cytoplasm. c) Chromosomes: They contain DNA, which carries the information necessary for constructing and organizing cells.

Q11. When can you call a single cell as an organism?

Solution

A single cell is called an organism when it carries out all the functions needed to sustain its life. Amoeba and bacteria are single-celled organisms.

Q12. List six functions of nucleus of a cell.

Solution

Functions of nucleus: (i) Nucleus has a double layer covering called nuclear membrane which has pores which allow the transfer of materials from inside the nucleus to its outside. (ii) It directs the chemical activities of the cell. (iii) It determines the way, the cell will develop and the form it will exhibit at maturity. (iv) It plays an important role in cell division. (v) It plays a central role in cellular reproduction. (vi) Nucleus has chromosomes which contain information for the inheritance of features from parents to the next generation.

Q13. What are cell organelles? Give four examples.

Solution

Within the cytoplasm of a cell, there are various minute but distinct structures which perform special functions. These structures are called cell organelles. Examples: Mitochondria, endoplasmic reticulum, golgi apparatus and ribosomes.

Q14. (a)Differentiate between: (i)Functions of RER and SER. (ii)Plasma membrane and cell wall. (b)What is endocytosis?

Solution

(a) (i) RER helps in protein synthesis whereas SER helps in the synthesis of fat molecules and detoxifies poisons and drugs. (ii) Plasma membrane is semi-permeable, flexible and made up of lipids and proteins. It is found in the animal cell as well as plant cell whereas cell wall is found only in plant cell. It is rigid in nature and made up of cellulose. (b) The ability of the plasma membrane to engulf food particles from the external environment is called endocytosis.

Q15. Name the three basic parts of a cell. Of these, which forms the outer boundary of the cell?

Solution

The three basic parts of a cell are cell membrane, cytoplasm, and nucleus. The cell membrane forms the outer boundary of the cell.

Q16. Differentiate between cell wall and cell membrane.

Solution

  Cell membrane Cell wall 1. Cell membrane is thin and flexible. Cell wall is thick and rigid. 2. It is present in both plants and animals. It is present only in plants. 3. It is made up of lipids and proteins. It is made up of cellulose.

Q17. What is endocytosis? Give one example.

Solution

The flexibility of the cell membrane enables the cell to engulf food and other materials from its external environment. This process is called endocytosis. Example: Amoeba engulfs its food by endocytosis.

Q18. What will happen to red blood cells if they are placed in i. Hypotonic solution ii. Isotonic solution iii. Hypertonic solution

Solution

i. RBCs (Red Blood Corpuscles) will swell if they are placed in a hypotonic solution. The cells will gain water by osmosis (endosmosis). The cells might burst and rupture if they are placed in the hypotonic solution for a longer time. ii. RBCs (Red Blood Corpuscles) will remain the same if they are placed in an isotonic solution. No change will occur in the shape and size of the cells.  iii. RBCs (Red Blood Corpuscles) will shrink if they are placed in a hypertonic solution. The cells will lose water by osmosis (exosmosis).

Q19. How do substances like CO₂ and water move in and out of the cell?

Solution

CO₂ moves in and out of the cells by the process of diffusion which involves the movement of molecules from a region of higher concentration to a region of lower concentration across the cell membrane. Water moves in and out of the cells by osmosis which involves the movement of water through a semi-permeable membrane from a solution of a lower concentration of solutes to a higher concentration of solutes to which the membrane is relatively impermeable.

Q20. What is a cell? Why is cell called the structural and functional unit of life?

Solution

A cell is the basic structural and functional unit of living organisms. The cell is called the structural and functional unit of life because it maintains the structure of living organisms and performs all the life functions like intake of food materials, excretion, metabolism, and respiration.

Q21. What is plasmolysis? Give an example.

Solution

When a living plant cell loses water through osmosis, there is shrinkage or contraction of the contents of the cell away from the cell wall. This is known as plasmolysis. Example: Shrinkage of vegetables when kept in a salt solution.

Q22. Explain active transport.

Solution

Active transport is the pumping of molecules or ions across a membrane against their concentration gradient. It always involves the expenditure of energy, the source of which is ATP because materials are pumped against the concentration gradient.

Q23. Name a cell organelle which contains its own genetic material.

Solution

The cell organelles plastids and mitochondria have their own genetic material.

Q24. How does a cell membrane form a barrier and establish a connection with the adjacent cells?

Solution

The cell membrane forms the outer boundary of the cell and keeps the cell contents intact within the cell. In this way, it forms a barrier to the outside environment. At the same time, it allows only certain substances to enter and leave the cell. Thus, it keeps the cell connected with its environment.

Q25. (a) What is DNA? Where is it found?

(b) Name the functional segment of DNA.

Solution

(a) DNA is Deoxyribo Nucleic Acid which contains information necessary for constructing and organizing cells and the inheritance of features from one generation to another. DNA is found in the chromosomes.

(b) The functional segment of DNA is a gene.

Q26. Differentiate between plant cells and animal cells on the basis of:

a) Plastids

b) Vacuoles

c) Position of nucleus in cell

Solution

  Criteria Plant cells Animal cells

1. Plastids They are present in plant cells. They are absent in animal cells.

2. Vacuoles They are large sized in plant cells. They are small sized in animal cells.

3. Position of nucleus in cell The nucleus is towards the periphery of the plant cell. The nucleus is present in the centre of the animal cell.

Q27. Give four examples of animal cells showing different structures.

Solution

Examples of animal cells differing in their structures: Nerve cells Ovum Smooth muscle cells Fat cells

Q28. Name the plastid which stores starch, oils and protein granules.

Solution

Leucoplast is a type of plastid which stores starch, oil and protein granules.

Q29. State the technical term for a medium which has exactly the same solute concentration as the cell. Why does the size of the cell remain the same when placed in such a solution?

Solution

Isotonic solution has exactly the same concentration of solute as the cell. Water crosses the cell membrane in both the directions but the amount of water entering the cell is equal to the amount of water leaving the cell. As a result, there is no overall movement of water.

Q30. (a) List any three differences between a prokaryotic and eukaryotic cell.

(b) Write the composition of a chromosome. Name the part of the cell where it is formed.

Solution

(a) Differences between a prokaryotic and eukaryotic cell: Prokaryotic cell Eukaryotic cell

(i) It is small in size.

(ii) The nuclear region is not well-defined.

(iii) Single chromosome is found.

• It is large in size.
• (ii) The nuclear region is well-defined and is surrounded by a nuclear membrane.
• (iii) More than one chromosome is present.  

(b) A chromosome is composed of DNA and proteins. It is formed in the nucleus during cell division.