It conserves specific chromosome number of each species achieved across generations.
Enhances the genetic variability in the population of organisms from generation to generation. These variations are significant for the evolution process.
It produces gametes for sexual reproduction
Promotes crossing over. It introduces a new combination of variations or traits
Chromosomal mutations can occur due to abnormalities during meiosis. a few of these can be beneficial to organisms.

Question - 12 : -
Discuss with your teacher about

(i) haploid insects and lower plants where cell-division occurs.
(ii) some haploid cells in higher plants where cell-division does not occur.

Answer - 12 : -

i) Haploid insects where cell division occurs is drones of honey bee and lower plants are Spirogyra, Chlamydomonous, Pteridophytes. These haploid gametes are produced by them through mitosis and not meiosis.

ii) Spermatozoa and ova of higher animals and microspores of higher plants will not undergo cell division.

Question - 13 : - Can there be mitosis without DNA replication in ‘S’ phase?

Answer - 13 : -

During S phase, DNA synthesis or replication of DNA takes place. DNA replication is essential for cell division.

Without DNA replication, cell division will not take place.

Question - 14 : - Can there be DNA replication without cell division?

Answer - 14 : -

Yes, DNA replication can take place without cell division. In order to prepare for cell division, DNA replication is necessary. Cell division is the succeeding logical step that occurs post cell division.

Question - 15 : -
Analyse the events during every stage of cell cycle and notice how the following two parameters change

(i) number of chromosomes (N) per cell
(ii) amount of DNA content (C) per cell

Answer - 15 : -

i) Yes, DNA replication can take place in G1 phase of cell cycle. The number of chromosomes remain the same and each chromosome is formed from one chromatid. In the S phase, chromosome is formed by two sister chromatids joined at the centromere. Similar conditions continue in the G2 phase, while in M phase, sister chromatids separate and move to different cells. The number of chromosomes stays the same in mitosis.

ii) Amount of DNA content in the cell remains the same in G1 phase but in S phase it doubles as the DNA replication takes place. It remains double in G2 phase but halved in the M phase of the cell cycle.

Question - 16 : -
What are the factors affecting the rate of diffusion?

Answer - 16 : -

Diffusion is the passive movement of substances from a region of higher concentration to a region of lower concentration. Diffusion of substances plays an important role in cellular transport in plants. Rate of diffusion is affected by concentration gradient, membrane permeability, temperature, and pressure. Diffusion takes place as long as there is a difference between the concentrations of a substance across a barrier. However, diffusion stops, when the concentrations of the substance on either side of the barrier become equal. The permeability of a membrane affects the rate of diffusion. Diffusion rate increases as membrane permeability increases. Changes in temperature and pressure values also affect the diffusion of substances. Pressure plays an important role in the diffusion of gases as gases diffuse from a region of higher partial pressure to a region of lower partial pressure.

Question - 17 : -
What are porins? What role do they play in diffusion?

Answer - 17 : -

Porins are types of proteins which form pores of large sizes in the outer membranes of plastids such as chloroplast, mitochondria and the membranes in bacteria. They help in facilitating the passive transport of small-sized protein molecules.

Question - 18 : -
Describe the role played by protein pumps during active transport in plants.

Answer - 18 : -

In plant cells, active transport occurs against the concentration gradient, i.e., from a region of lower concentration to a region of higher concentration. The process of active transport involves specific protein pumps. The protein pumps are made up of specific proteins called trans-membrane proteins. These pumps first make a complex with the substance to be transported across the membrane, using the energy derived from ATP. The substance finally gets liberated into the cytoplasm as a result of the dissociation of the protein–substance complex.

Question - 19 : -
Explain why pure water has the maximum water potential.

Answer - 19 : -

Water potential quantifies the tendency of water to move from one part to the other during various cellular processes. It is denoted by the Greek letter Psi or Ψ. The water potential of pure water is always taken as zero at standard temperature and pressure. It can be explained in terms of the kinetic energy possessed by water molecules. When water is in liquid form, the movement of its molecules is rapid and constant. Pure water has the highest concentration of water molecules. Therefore, it has the highest water potential. When some solute is dissolved in water, the water potential of pure water decreases.

Question - 20 : -
Differentiate between the following:

(a) Diffusion and Osmosis
(b) Transpiration and Evaporation
(c) Osmotic Pressure and Osmotic Potential
(d) Imbibition and Diffusion
(e) Apoplast and Symplast pathways of movement of water in plants.
(f) Guttation and Transpiration.

Answer - 20 : -

(a) Diffusion andosmosis

Diffusion		Osmosis
1.	Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient.	1.	Osmosis is the process in which the diffusion of a solvent (water) occurs across a semi-permeable membrane.
2.	It can occur in solids, liquids, and gases.	2.	It occurs in the liquid medium.
3.	It does not require a semi-permeable membrane.	3.	It requires a semi-permeable membrane.

(b) Transpiration andevaporation

Transpiration		Evaporation
1.	It occurs in plants.	1.	It occurs from any free surface and involves living and non-living surfaces.
2.	It is a physiological process.	2.	It is a physical process.
3.	It occurs mainly through the stomatal pores on plant leaves.	3.	It is occurs through any free surface.
4.	It is controlled by environmental factors as well as physiological factors of plants such as root-shoot ratio and number of stomata.	4.	It is entirely driven by environmental factors.

(c) Osmotic pressure andosmotic potential

Osmotic pressure		Osmotic potential
1.	It is expressed in bars with a positive sign.	1.	It is expressed in bars with a negative sign.
2.	It is a positive pressure.	2.	It is a negative pressure.
3.	Its value increases with an increase in the concentration of solute particles.	3.	Its value decreases with an increase in the concentration of solute particles.

(d) Imbibition anddiffusion

Imbibition		Diffusion
1.	Imbibition is a special type of diffusion. In this process, water is absorbed by solids and colloids, causing an enormous increase in volume.	1.	Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient.
2.	It usually involves water.	2.	It involves solids, liquids, and gases.

(e) Apoplast andsymplast pathways of movement of water in plants

Apoplast pathway		Symplast pathway
1.	The apoplast pathway involves the movement of water through the adjacent cell walls of the epidermis and cortex. The movement of water is restricted at the casparian strips of the root endodermis.	1.	The symplast pathway involves the movement of water through the interconnected protoplasts of the epidermis, cortex, endodermis, and root pericycle.
2.	It is a faster process of water movement and water moves through mass flow.	2.	It is a slower process of water movement.

(f) Guttation andtranspiration

Guttation		Transpiration
1.	It occurs usually at night.	1.	It occurs usually during the day.
2.	Water is lost from the leaves in the form of liquid droplets.	2.	Water is lost from the leaves in the form of water vapour.
3.	It occurs through the vein endings of leaves.	3.	It occurs through the stomata.
4.	It is an uncontrolled process.	4.	It is a controlled process.

Free - Previous Years Question Papers

Chapter 10 Cell Cycle and Cell Division Solutions

Subscribe Now!