Chapter 8: How do organisms Reproducer ?

Internal Questions and Answers

1. What is the importance of DNA copying in reproduction?

Answer: DNA copying is important in reproduction because it transfers genetic information from parents to offspring. It helps in maintaining the body design and characteristics of the species. Small variations produced during DNA copying also help organisms adapt to changing environmental conditions.

2. Why is variation beneficial to the species but not necessarily for the individual ?

Answer: Variations are beneficial to the species because they help some individuals survive under changing environmental conditions. These surviving individuals reproduce and ensure the continuity of the species. However, a variation may not always be useful or beneficial for an individual organism.

Internal Question and  Answers

1. How does binary fission differ from multiple fission?

Answer: The difference between binary fission and multiple fission :

Binary Fission	Multiple Fission
In binary fission, the parent cell divides into two equal halves (two daughter cells).	In multiple fission, the parent cell divides into many daughter cells simultaneously.
The nucleus divides only once followed by cytoplasmic division.	The nucleus undergoes repeated divisions before the cytoplasm divides.
Example: Amoeba, Paramecium, Leishmania.	Example: Plasmodium (malaria parasite), Amoeba during unfavorable conditions.

2. How will an organism be benefited if it reproduces through spores?

Answer: An organism reproducing through spores gets several advantages. Spores are produced in large numbers and can spread easily through air, water or animals. They have thick protective coverings that help them survive unfavourable conditions like heat and dryness. When conditions become suitable, the spores germinate and grow into new organisms, ensuring continuity of the species.

3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer: More complex organisms cannot reproduce through regeneration because their bodies are highly organised with specialised tissues and organs. Different cells perform specific functions and cannot easily divide to form a complete new organism. In such organisms, regeneration is mainly used for repair and healing of damaged body parts, not for producing new individuals.

4. Why is vegetative propagation practised for growing some types of plants?

Answer: Vegetative propagation is practised because it produces new plants quickly and preserves the desirable characteristics of the parent plant. It is useful for plants that do not produce viable seeds, such as banana, sugarcane and potato. The new plants grow faster, mature earlier and are genetically identical to the parent plant, ensuring better quality and uniformity in crops.

5. Why is DNA copying an essential part of the process of reproduction?

Answer: DNA copying, or DNA replication, is essential in the process of reproduction because it ensures that each new offspring receives an accurate and complete copy of the genetic information from the parent. This fidelity in DNA copying is crucial for maintaining genetic continuity and passing on inherited traits to subsequent generations.

Internal Question and Answer :

1. How is the process of pollination different from fertilisation?

Answer: The difference between pollination and fertilisation is:

Pollination	Fertilisation
It is the transfer of pollen grains from the anther to the stigma of a flower.	It is the fusion of male and female gametes (sperm and egg) to form a zygote.
It is a physical process.	It is a biological and genetic process.
It occurs in flowering plants (angiosperms) and gymnosperms.	It occurs in all sexually reproducing plants and animals.
Pollination is external and takes place on the stigma.	Fertilisation is internal and takes place inside the ovule.
It can be of two types: self-pollination and cross-pollination.	It does not have such types; it is simply the fusion of gametes.
Pollination is required for fertilisation to occur in seed plants.	Fertilisation depends on successful pollination.

2. What is the role of the seminal vesicles and the prostate gland?

Answer: The seminal vesicles and prostate gland are accessory glands of the male reproductive system. The seminal vesicles secrete a fructose-rich fluid that provides energy to the sperm and forms a major part of semen. The prostate gland secretes a thin, milky alkaline fluid that protects and activates the sperm. This alkaline nature helps neutralise the acidic medium of the female reproductive tract, improving sperm movement and survival.

3. What are the changes seen in girls at the time of puberty?

Answer: At the time of puberty, several changes are seen in girls due to hormonal changes in the body. The body grows taller and the hips become broader. Breasts begin to develop and hair starts growing in the armpits and pubic region. Sweat and oil glands become more active, sometimes causing pimples. The reproductive organs also mature, and menstruation begins. Emotional and mental changes are also noticed, such as mood swings and increased sensitivity. These changes show that the girl is growing into adulthood.

4. How does the embryo get nourishment inside the mother’s body?

Answer: The embryo receives nourishment inside the mother's body through the placenta. The placenta is a specialized organ that forms during pregnancy. It is connected to the embryo through the umbilical cord and facilitates the exchange of oxygen, nutrients and waste products between the mother's bloodstream and the developing embryo.

5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Answer: No, a copper-T intrauterine device (IUD) does not provide protection against sexually transmitted diseases (STDs). Copper-T is a form of long-acting reversible contraception that primarily works by preventing pregnancy. To prevent the transmission of STDs, it is important to use barrier methods such as condoms in addition to contraception methods like the copper-T.

Exercises of Chapter 8: How do organisms Reproducer ?

1. Asexual reproduction takes place through budding in

(a) amoeba.     (b) yeast.     (c) plasmodium.     (d) leishmania.

Answer:  (b) yeast.

[ In budding, a small outgrowth develops on the parent organism and grows into a new individual; this process is seen in yeast.]

2. Which of the following is not a part of the female reproductive system in human beings?

(a) Ovary      (b) Uterus      (c) Vas deferens     (d) Fallopian tube

Answer:  (c) Vas deferens.

[ Vas deferens is part of the male reproductive system, where it carries sperm from the testes, while the others are parts of the female reproductive system.]

3. The anther contains

(a) sepals.     (b) ovules.      (c) carpel.       (d) pollen grains.

Answer: (d) pollen grains.

[ The anther is part of the stamen in a flower and produces and contains pollen grains, which carry the male gametes. ]

4. What are the advantages of sexual reproduction over asexual reproduction?

Answer: Sexual reproduction leads to more variations in offspring because it combines DNA from two parents. These variations help species survive when the environment changes. In contrast, asexual reproduction produces identical copies, so if a disease or change occurs, all individuals may die. Thus, sexual reproduction helps species evolve and adapt better over time.

5. What are the functions performed by the testis in human beings?

Answer: The functions performed by the testes in human beings are:

(a) Production of male gametes called sperms.

(b) Secretion of the male hormone testosterone, which controls the development of secondary sexual characters.

6. Why does menstruation occur ?

Answer: Menstruation occurs because if the egg is not fertilised, the thick and spongy lining of the uterus, which was prepared to receive and nourish the embryo, is no longer needed. Therefore, the lining breaks down and comes out through the vagina as blood and mucous. This process is called menstruation.

7. Draw a labelled diagram of the longitudinal section of a flower.

Answer: The diagram of the longitudinal section of a flower:

8. What are the different methods of contraception?

Answer:  The different methods of contraception are:

(a) Barrier methods : use of condoms and diaphragms to prevent the meeting of sperms and egg.

(b) Chemical methods : use of oral pills and hormonal preparations to prevent ovulation.

(c) Intrauterine devices (IUCDs):  devices like Copper-T placed in the uterus to prevent pregnancy.

(d) Surgical methods:  vasectomy in males and tubectomy in females to block the transport of gametes.

9. How are the modes for reproduction different in unicellular and multicellular organisms?

Answer: The different modes of reproduction in unicellular and multicellular organisms are :

Unicellular Organisms	Multicellular Organisms
Reproduction occurs through simple methods like binary fission or budding.	Reproduction occurs through more complex methods involving specialised reproductive organs.
A single cell carries out all life processes including reproduction.	Different cells and tissues are specialised for reproduction.
Reproduction is generally faster.	Reproduction is usually slower and more complex.
Examples: Amoeba, Paramecium	Examples: Human beings, flowering plants

10. How does reproduction help in providing stability to populations of species?

Answer: Reproduction helps in providing stability to populations of species by producing new individuals and replacing those that die. It also helps in passing genetic information from one generation to the next, thus ensuring continuity of the species.

11. What could be the reasons for adopting contraceptive methods?

Answer: The reasons for adopting contraceptive methods are:

(i) To prevent unwanted pregnancies.

(ii) To control population growth.

(iii) To maintain proper gap between children.

(iv) To protect the health of the mother and child.

(v) To prevent sexually transmitted diseases such as AIDS.