Page no- 114
1. What is the importance of DNA copying in reproduction?
Answer:
DNA (Deoxyribonucleic acid) is the genetic material found in all living cells. It carries hereditary information from parents to offspring, helping create organisms similar to their parents. DNA copying is necessary for passing traits, and small changes in it can lead to new species over time.
2. Why is variation useful for the species but not necessarily for the individual?
Answer:
Variation helps species survive sudden environmental changes, even if it doesn’t benefit every individual. For example, if the water temperature rises, some microbes may die while others survive due to variation. Thus, variation ensures the species continues even when individuals don’t survive.
Page no-119
1. How does binary fission differ from multiple fission?
Answer:
In binary fission, one cell divides into two equal halves — like in Amoeba and bacteria.
In multiple fission, one cell divides into many daughter cells at the same time — like in Algae and Plasmodium.
2. How is an organism benefited if it reproduces through spores?
Answer:
Spore reproduction has many benefits:
• Many spores are produced at once.
• Spores can spread far through air, reducing competition.
• Thick walls protect them from drying during harsh conditions.
3. Why can’t complex organisms give rise to new individuals by regeneration?
Answer:
Complex organisms cannot form new individuals by regeneration because their organs are highly specialized and interdependent. They can repair or regrow parts like skin or muscles but cannot form a complete new organism.
4. Why is vegetative propagation used for some plants?
Answer:
Vegetative propagation is used because:
• Some plants like banana and orange don’t have viable seeds.
• It’s quick, cheap, and reliable.
• It helps preserve good varieties and works where seeds fail to grow.
5. Why is DNA copying an essential part of reproduction?
Answer:
DNA copying ensures that genetic information is passed from parents to offspring. During reproduction, DNA makes a copy of itself along with other cell parts, and then the cell divides into two, each with the same DNA.
Page no -125
1. How is pollination different from fertilization?
Answer:
Pollination means transferring pollen from anther to stigma with help of wind, water, or insects.
Fertilization means fusion of male and female gametes inside the ovule, forming a zygote.
2. What is the role of the seminal vesicles and prostate gland?
Answer:
They produce fluids that help sperms move easily. These fluids provide nutrients like fructose and enzymes, making sperm active and mobile.
3. What changes are seen in girls during puberty?
Answer:
• Hair grows in the genital area and underarms.
• Breasts enlarge, and nipple skin darkens.
• Uterus and ovaries grow.
• Menstrual cycle begins.
• Pimples appear due to more oil in the skin.
4. How does the embryo get nourishment inside the mother’s body?
Answer:
After fertilization, the uterus lining thickens with more blood. The placenta, attached to the uterine wall, passes food and oxygen from the mother’s blood to the embryo and removes waste.
5. If a woman uses a Copper-T, will it protect her from sexually transmitted diseases?
Answer:
No. Copper-T only prevents pregnancy; it does not stop the exchange of body fluids. So it cannot protect against sexually transmitted diseases.
EXERCISE
1. Asexual reproduction takes place through budding in –
(a) Amoeba (b) Yeast (c) Plasmodium (d) Leishmania
Answer:
(b) Yeast
Yeast reproduces by budding, where a small bump grows on the parent cell. The nucleus divides, and one part enters the bud. Later, the bud separates to form a new yeast cell.
2. Which of the following is not a part of the female reproductive system?
(a) Ovary (b) Uterus (c) Vas deferens (d) Fallopian tube
Answer:
(c) Vas deferens
Vas deferens belongs to the male reproductive system. It carries sperm from the testis to the urethra for ejaculation.
3. The anther contains –
(a) Sepals (b) Ovules (c) Pistil (d) Pollen grains
Answer:
(d) Pollen grains
Anther holds pollen grains, which produce male gametes in flowering plants.
4. What are the advantages of sexual reproduction over asexual reproduction?
Answer:
• Offspring inherit traits from both parents.
• It ensures species survival through variation.
• Offspring adapt better to environmental changes.
• It helps improve genetic health.
5. What are the functions of the testis in humans?
Answer:
• Testes make sperms.
• They also produce testosterone, a hormone responsible for male sexual traits and maturity.
6. Why does menstruation occur?
Answer:
Every month, the uterus prepares for pregnancy. If no fertilization happens, the thickened uterine lining breaks down and comes out through the vagina as menstrual blood.
7. What are the different methods of contraception?
Answer:
• Natural method: Avoid intercourse during fertile days.
• Barrier method: Use condoms or diaphragms.
• Oral pills: Hormonal pills prevent ovulation.
• Devices & surgery: Use Copper-T or block tubes to stop egg or sperm movement.
8. How are the modes of reproduction different in unicellular and multicellular organisms?
Answer:
Unicellular organisms reproduce by fission or budding, forming new cells directly.
Multicellular organisms use special organs for reproduction — like flowers in plants or sexual systems in animals.
9. How does reproduction provide stability to species populations?
Answer:
Reproduction maintains the species by replacing dying individuals with new ones. It keeps population balance and helps species continue through generations.
10. Why do people adopt contraceptive methods?
Answer:
People use contraception to control population, avoid unplanned pregnancies, and prevent sexually transmitted diseases.