Wednesday 16 December 2020

Chapter 8 How do Organisms Reproduce?


Chapter 8 How do Organisms Reproduce?

Question 1
Asexual reproduction takes place through budding in
(a) amoeba
(b) yeast
(c) plasmodium
(d) leishmania

(b) Yeast

Question 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

(c) Vas deferens

Question 3
The anther contains
(a) sepals
(b) ovules
(c) carpel
(d) pollen grains

(d) Pollen grains

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

(i) In asexual reproduction, the offspring are almost identical to their parent because they have the same genes as their parent. So, much genetic variation is not possible in asexual reproduction. This is a disadvantage because it inhibits the further evolution of the organism.
(ii) In sexual reproduction the offspring, although similar to their parents, are not identical to them or to one another. This is because the offspring receive some genes from the mother and some from the father. Because of the mixing of genes of mother and father in various different combinations, all of the offspring have genetic variations. In this way, sexual reproduction leads to a greater variety in population. This means that a species (animal or plant) can adapt quickly to changes in its surroundings. This is because there are always likely to be some individuals which are more suited to the changes than others, and these individuals will survive and reproduce themselves.

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

The functions of testes in humans are following :
(i) After the stage of adolescent, testes produce male gametes in the human males which are called sperms.
(ii) A hormone called testosterone is produced in testes. Testosterone controls the development of reproductive organs and secondary sexual characters.

Question 6
Why does menstruation occur?

If the ovum (or egg) does not get fertilised (due to non-availability of sperm in the female body) then the thick and soft inner lining of uterus is no longer needed and hence it breaks. So, the thick and soft inner lining of uterus along with the blood vessels and the dead ovum (or egg) comes out of the vagina in the form of blood called menstruation. Menstruation occurs after the interval of every 28 days and the time period between ovulation and menstruation is about 14 days.

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


Question 8
What are the different methods of contraception?

The different methods of contraception are as follow :
(i) Barrier method: In this method, condom, diaphragm and cervical caps are used. These prevent the entry of sperms in the female genital tract during sexual intercourse.
(ii) Chemical method: In this method a woman uses two kinds of pills (oral and vaginal pills). The oral pills are hormonal preparations which suppress the release of ovum in fallopian tube. These are called oral contraceptives. The vaginal pills/ creams are spermicidal. The chemicals in these spermicidal kill the sperms during their journey in the vaginal tract.
(iii) Intrauterine contraceptive devices: Intrauterine contraceptive devices such as copper-T are placed safely in the uterus by a skilled doctor. It prevents the sperms to reach the uterus.
(iv) Surgical method: In this method, a small part of vas deferens of male and fallopian tube of female is cut or tied by surgery. It is called vasectomy in males and tubectomy in females.

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


Reproduction mode in unicellular organisms

Reproduction mode in multicellular organisms

(i) A sexual reproduction takes place in unicellular organisms.

(i) Sexual reproduction takes place in multicellular organisms.

(ii) Only one organism is required in this method.

(ii) A male and a female both are required in this method.

(iii) No special cells are present for reproduction.

(iii) Special cells are present for reproduction.

(iv) No special organs are present for reproduction.

(iv) Special organs are present for reproduction located at the fixed position in the body.

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

The introduction of variations during reproduction provides stability to the populations of various species by preventing them from getting wiped out during adverse conditions. Reproduction also helps to generate copies of individuals which are suited to a particular environment.

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

The reasons for adopting contraceptive devices are as follow:

1.     To control the birth rate and prevent the increase in population.

2.     To reduce the adverse effects on mother’s body due to frequent pregnancy.

3.     To provide safety from sexually transmitted diseases.