Page 128
1. What is the importance of DNA copying in reproduction?
Answer:
- It maintains the characteristics of species.
- It maintains the continuity of life.
- Characters of organisms are transmitted to their progeny.
- It produces variations in organisms.
2. Why is variation beneficial to the species but not necessarily for the individual?
Answer:
Consistent DNA copying maintains body design, helping the organism to use a particular niche. However, niches can change due to many reasons. If a niche is drastically altered, the population not suited to that niche is wiped out. Organisms with variations that enable survival can reproduce under varied conditions. Hence, variation is beneficial to the species but not necessarily to individuals.
Page 133
1. How does binary fission differ from multiple fission?
Answer:
| Binary Fission | Multiple Fission |
|---|---|
| Parent cell divides into 2 daughter cells. | Parent cell divides into many daughter cells. |
| No cyst formation. | A cyst is formed. |
| It generally occurs in favourable conditions. | It occurs in unfavourable conditions too. |
2. How will an organism be benefited if it reproduces through spores?
Answer:
Spores are surrounded by a thick layer to protect them in adverse conditions. Under favourable conditions, these spores start to grow again.
3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer:
Complex multicellular organisms have a very high degree of organisation and differentiation in their body. So, they cannot be reproduced from their cut body parts by the process of regeneration. For example, the cells in a finger cannot produce organs such as the brain, heart, eye, stomach, intestine, etc. So a complete organism will not be developed from a finger.
4. Why is vegetative propagation practised for growing some types of plants?
Answer:
It is practiced for growing plants which usually do not produce seeds or produce non-viable seeds.
5. Why is DNA copying an essential part of the process of reproduction?
Answer:
DNA is the information source for making proteins. If the information is changed, different proteins will be made, leading to changes in body designs. Therefore, the creation of a DNA copy is the basic event in reproduction.
Page 140
1. How is the process of pollination different from fertilisation?
Answer:
- Pollination: The transfer of pollen grains from the anther to the stigma of a carpel.
- Fertilisation: The fusion of the male gamete present in the pollen grain with the female gamete present in the ovule.
2. What is the role of seminal vesicles and the prostate gland?
Answer:
- Seminal vesicles and prostate gland secrete fluids which form a part of the semen. It acts as a medium for the movement of sperms.
- This fluid provides nutrition to sperms in the form of fructose, calcium, and some enzymes. It also protects the sperms from the acids present in the urethra.
3. What are the changes seen in girls at the time of puberty?
Answer:
- Hairs under armpits and pubic region.
- Mammary glands develop and enlarge.
- The hips broaden.
- Extra fat is deposited in hips and thighs.
- Development of fallopian tubes, uterus, and vagina.
- Menstrual cycle and menstruation.
- Feelings and sexual drives.
4. How does the embryo get nourishment inside the mother’s body?
Answer:
The embryo gets nutrition from the mother’s blood through the placenta. The placenta contains villi, which provide a large surface area for the transfer of glucose, oxygen, and other substances from the mother to the embryo.
5. A woman is using a copper-T. Will it help in protecting her from sexually transmitted diseases?
Answer:
Copper-T prevents conception but cannot prevent sexually transmitted diseases.