Class 10 Biology Chapter 3 - How do Organisms Reproduce Important Questions 

Most Important Questions:- 

Question 1.

Newly formed DNA copies may not be identical at times. Give one reason. 

Answer:

When a cell reproduces, DNA replication occurs which results in formation of two similar copies of DNA. The process of copying the DNA leads to some variations each time. As a result, the DNA copies produced are similar to each other but sometimes may not identical.

Question 2 

When a cell reproduces, what happens to its DNA? 

Answer:

When a cell reproduces, DNA replication occurs which forms two similar copies of DNA..

Question 3.

How do Plasmodium and Leishmania reproduce? Write one difference in their mode of reproduction. 

Answer:

Plasmodium and Leishmania reproduce by the process of fission which is an asexual mode of reproduction. Plasmodium reproduces by multiple fission. About 1000 daughter cells are produced by the multiple fission of a Plasmodium. Leishmania reproduces by the process of binary fission. In Leishmania, the splitting of parent cell takes place in a definite plane (longitudinally) with respect to flagellum at its end to produce two daughter cells.

Question 4.

List two advantages of practising vegetative propagation in plants. Select two plants raised by this method from the list given below : Banana, Gram, Pea, Rose, Tomato, Wheat .

Answer:

Two advantages of the vegetative propagation of plants are:

•Any desirable features of the parent plant can be replicated in the new plants.

•Flowers and fruits can be grown in a shorter time as compared to the plants grown from seeds. The two plants raised by this method are banana and rose.

Question 5 .

Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival – the one reproducing asexually or the one reproducing sexually? Give reason to justify your answer. 

Answer:

Difference between asexual and sexual mode of reproduction is as follows :

Asexual reproduction:

•Gametes are not formed hence fertilisation does not take place.

Sexual reproduction:

•Gametes are always formed and fertilisation takes place to form a zygote.

Species reproducing sexually has a better chance of survival as variations occur only during the sexual reproduction. Variations increase the chances of survival of an individual by making them more fit. Selection of variations by environmental factors forms the basis of evolution.

Question 6.

What happens when

(a) accidently, Planaria gets cut into many pieces-

(b) Bryophyllum leaf falls on the wet soil

(c) on maturation sporangia of Rhizopus bursts? 

Answer:

(a) When Planaria accidently gets cut into many pieces then its each piece grows into a complete organism. This is known as regeneration.

(b) When the Bryophyllum leaf falls on the wet soil, the buds present in the notches along the leaf margin develop into new plants. This is known as vegetative propagation.

(c) The sporangia of Rhizopus contain cells or spores that can eventually develop into new Rhizopus individuals when it bursts on maturation.

Question 7.

Which contraceptive method changes the hormonal balance of the body?

Answer:

Chemical contraceptive method changes the hormonal balance of the body.

Question 8.

Write two factors that determine the size of a population. 

Answer:

The rate of birth and death in a given population will determine the size of a population.

Question 9.

Why In Plants fertilisation is not possible without pollination? 

Answer:

The process of pollination in plants ensures that male gametes bearing structure called pollen comes in contact with the female reproductive structure of the plant. Once the male and female gametes are in close vicinity, they fuse and fertilisation is accomplished. Hence, fertilisation cannot take place without pollination.

Question 10.

No two individuals are absolutely alike in a population. Why? 

Answer:

No two individuals are absolutely alike in a population because sexual reproduction promotes diversity of characters in the offspring by providing genetic variation.

Question 11.

State the changes that take place in the uterus when:

(a) Implantation of embryo has occurred.

(b) Female gamete/egg is not fertilised. 

Answer:

(a) Implantation is the close attachment of the blastocyst (young multicellular embryo) to the uterine wall. It is fullowed by a number of developmental changes in the thickened wall of uterus. An intimate connection between the fetal membrane and the uterine wall called placenta is formed. This is a disc which is embedded in the uterine wall. The placenta serves as the nutritive, respiratory and excretory organ of the fetus.

(b) When the female gamete/egg is not fertilised, this lining is not needed any longer. So, the lining slowly breaks and comes out through vagina as blood and mucus. This cycle takes place every month and is known as menstrual cycle.

Question 12

List any two steps involved in sexual reproduction and write its two advantage. 

Answer:

The two main steps involved in sexual reproduction are:

•Formation of male and female gametes.

•Fusion of a male gamete with a female gamete to form a new cell called zygote by the process of fertilisation.

The two important advantages of sexual reproduction are:

•It promotes diversity of characters in the offspring through genetic variations.

•It plays an important role in continuous evolution of better organisms that may lead to the origin of new species.