How do Organisms Reproduce?

Intext Questions 1

Question 1

What is the importance of DNA copying in reproduction?

Answer

The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs. Therefore, the creation of a DNA copy is very important in reproduction.

Question 2

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

Answer

Variation is not necessary for an individual but it is very important for survival of a species. A population of reproducing organisms or a species are suited to a particular niche. If there is no variation among individuals of a species they can be easily wiped out in case of drastic change in niche. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Therefore, variations prevent the complete wiping out of species in adverse climatic changes in their niche.

Intext Questions 2

Question 1

How does binary fission differ from multiple fission?

Answer

Question 2

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

Answer

Some of the advantages of reproduction through spores formation are:

1. Spores are often small, lightweight, and easily dispersed by wind, water, or other external factors. This helps them to travel far distances to avoid competition for essential resources required for growth.
2. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
3. It helps the parent organism to conserve energy compared to the resources required for more complex reproductive structures (such as seeds or offspring).

Question 3

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

Answer

More complex organisms have high level of tissue differentiation and these tissues are highly specialized in their functions. The body has organ-system level of organisation. They can regenerate few damaged tissues but cannot regenerate organ or organ sysytem. Therefore, more complex organisms cannot give rise to new individuals through regeneration. Regeneration is only possible in lower and simple organisms that do not show complex cellular differentiation.

Question 4

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

Answer

Vegetative propagation is practised for growing some types of plants because:

1. Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
2. Such methods also make possible the propagation of plants such as banana, navel orange, rose and jasmine that have lost the capacity to produce seeds.
3. All plants produced are genetically similar enough to the parent plant to have all its characteristics. This result in uniformity in produce.

Question 5

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

Answer

The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs. Therefore, the creation of a DNA copy is an essential part of the process of reproduction.

Intext Questions 3

Question 1

How is the process of pollination different from fertilisation?

Answer

Question 2

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

Answer

The seminal vesicles and the prostate gland add their secretions along the path of vas deferens which makes transport of sperms easier and this fluid also provides nutrition to the sperms.

Question 3

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

Answer

The changes seen in girls at the time of puberty are:

1. Breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts.
2. Thick hair growth in armpit and genital area.
3. Begin to menstruate at around the time of puberty.

Question 4

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

Answer

The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo.

Question 5

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

Answer

Copper-T is an Intrauterine Device (IUD) which is placed in the uterus to prevent pregnancy. It cannot prevent sexually-transmitted diseases.

Exercises

Question 1

Asexual reproduction takes place through budding in

1. Amoeba
2. Yeast
3. Plasmodium
4. Leishmania

Answer

Yeast

Reason — Yeast can put out small buds that separate and grow further as an individual.

Question 2

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

1. Ovary
2. Uterus
3. Vas deferens
4. Fallopian tube

Answer

Vas deferens

Reason — Vas deferens is a part of male reproductive system.

Question 3

The anther contains

1. sepals
2. ovules
3. pistil
4. pollen grains

Answer

pollen grains

Reason — Anther contains pollen grains which has male gamete.

Question 4

What are the advantages of sexual reproduction over asexual reproduction?

Answer

Following are the advantages of sexual reproduction over asexual reproduction:

1. It creates variation in population. Variation in population prevents wiping out of any species.
2. It helps in evolution of species.
3. Variation may result in new species.

Question 5

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

Answer

The functions performed by the testis in human beings are:

1. The formation of germ-cells or sperms takes place in the testes.
2. Testes secretes the hormone - testosterone.

Question 6

Why does menstruation occur?

Answer

In females, the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if fertilisation had taken place. In absence of fertilised eggs this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation.

Question 7

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

Answer

Below labelled diagram shows the longitudinal section of a flower:

Question 8

What are the different methods of contraception?

Answer

The different methods of contraception are:

1. Barrier method (condom)
2. Intrauterine Devices like copper -T
3. Birth control pills
4. Surgical methods: Vasectomy, Tubectomy

Question 9

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

Answer

Unicellular organisms generally reproduce by asexual methods like budding, binary fission, multiple fission, fragmentation, spore formation. Variation is not common in their progeny.

On other hand, multicellular organisms can divide by sexual as well as asexual methods. For example, vegetative propagation in plants is a means of asexual reproduction while all higher animals reproduce sexually. Variation is seen in sexually reproducing organisms.

Question 10

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

Answer

Reproduction helps in providing stability to populations of species in following ways:

1. It maintains population by replacing the number of individuals lost due to death.
2. It helps the species population to survive by creating variations.
3. It helps in evolution of species due to selective adaptation.

Question 11

What could be the reasons for adopting contraceptive methods?

Answer

The reasons for adopting contraceptive methods are:

1. To avoid unwanted pregnancies.
2. To control population rise or birth rate.
3. To safeguard oneself against sexually transmitted diseases.