CBSE Class 10 Science Chapter-8 How do Organisms Reproduce? Important Questions – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 8 – How do Organisms Reproduce? prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Chapter-8 How do Organisms Reproduce? Important Questions
CBSE Class 10 science Important Questions Chapter 8 – How do Organisms Reproduce?
3 Mark Questions
1. What changes occur in girls and boys in the age group of 10 -14 years?
Ans. Changes in males (boys)
1) Widening of shoulder.
2) Deepening of voice
3) Appearance of beard and moustaches
4) Growth of sex organs
Changes in females (girls)
1) Widening of pelvis and hips.
2) High pitch voice.
3) Growth of auxiliary and pubic hair
4) Initiation of menstrual cycle.
5) Growth of mammary glands.
2. Describe sexually transmitted diseases (STDs) and mention the ways to prevent them.
Ans. Those infectious diseases which are spread by sexual contact called sexually transmitted diseases (STDs)
Methods for prevention of STDs
a) The people should be educated about various STDs
b) Extra – marital relations should be avoided
c) Sex without proper precaution should be avoided
d) High standard of moral education should be give to the people.
3. Name the surgical methods of birth control in human males and females respectively.
Ans. Surgical methods of birth control are –
a) Castration – Removal of testes from the body of a male
b) Ovariectomy – Removal of ovaries from the body of a female
c) Vasectomy – small pieces of both the vas deferens are cut and removed.
d) Tubectomy – Small pieces of both the fallopian tubes are removed.
e) Laparoscopy – Fallopian tubes are blocked with the help of an instrument called laparoscope
4. What are the essential requisites for sexual reproduction?
Ans. Essential requisites for sexual reproduction are –
a) Transfer of germ cells – Specialized germ – cells have to fuse together, which can happen by either of the following modes –
(i) External release of germ cells – In flowering plant
(ii) Internal transfer of germ cells – In animal cells.
Requirement of special organs –
For example –
a) An erectile organ called penis
b) Organs which can carry the baby for long period
5. What is micropropogation? Mention its advantages.
Ans. Micropropagation – It is a type of artificial vegetative propagation in which an isolated plant part is cultured under aseptic conditions with proper nutrient medium. Advantages of micropropagation.
a) It is a quick method of multiplication of plants.
b) Virus free plants are produced by this method from virus infected plants
c) It can overcome seed dormancy
6. Mention the events taking place when the ovum is fertilized in fallopian tube till it is implanted in the uterus of human female.
Ans. After fertilization, the zygote starts dividing by repeated mitotic divisions called cleavage. In about 4 -5 days after fertilization, zygote becomes a multicellular structure called blastocyst. The blasto cyst gets attached to the lining of uterus is called implantation.
7. What are the post fertilizational changes in the flower?
Ans. Post – fertilization changes in flowers are –
a) The sepals, petals and stamens wither off
b) Style and stigma degenerate
c) Ovary develops into fruit
d) Ovules grows into seed
e) Integuments of the ovule act as seed coats.
f) Fertilized egg gets converted into embryo which bear plumule, radicle and cotyledons.
g) Fertilized polar nuclei form endosperm which may or may not be consumed during seed development.
8. What are the major factors responsible for population explosion?
Ans. Reason for population explosion –
(i) Better medical facilities – Better medical facilities have resulted in fall of death rate.
(ii) Lack of education and awareness – This is a major factor since people become prey to ignorance
(iii) Religions – For some people, family planning is against the norms set by their religion.
(iv) Control over epidemics – Various medical technologies has made it possible to fight against epidemics.
(v) Sanitary conditions – There is a lot of improvement in sanitary conditions which led to increase in population.
9. What are the advantages of vegetative propagation?
Ans. Advantages of vegetative propagation –
a) It is a rapid, cheap and easy method of reproduction for the multiplication of plants
b) Genetically identical plants (clones) are produced by this method
c) Superior quality fruits or flowers can be produced by grafting.
d) Disease free plants can be produced by this method
e) Early flowering and fruit formation
10. Describe any 3 methods of asexual reproduction
Ans. Methods of asexual reproduction –
a) Primary fission – It is a type reproduction in which one parent organism divides into two new organisms. Firstly nucleus divide and then division of cytoplasm takes place.
b) Spore formation – A spore is a small microscopic structure with a thick wall. Spores are formed in a structure called sporangium. Nucleus inside sporangium divides repeatedly and produces many nuclei. Each nucleus is surrounded by cytoplasm and called spore.
c) Fragmentation – It is the breaking of an organism into two or more parts upon maturation, each of which grows to form a new individual.
11. What changes occur in ovaries during menstrual cycle?
Ans. Change occurs in ovaries during menstruation
a) 1 – 4 days – Corpus luteum degenerates. The ovary starts preparing for the maturation of a new follicle.
b) 5 – 13 days – Ovarian follicle develops to optimum. Estrogen secreted by ovaries causes thickening of uterine wall.
c) 14 day – Egg gets released from the ovary. It enters the fallopian tube, known as ovulation.
d) 15 to 28 days – After releasing the egg, the follicle part produces corpus luteum which produces progesterone. If pregnancy has not occurred, corpus luteum degenerates corpus luteum. This restarts menstrual cycle once again.
12. Describe budding in yeast, a fungus
Ans. a) It is a type of asexual reproduction in which an outgrowth (bud) is formed on the parent organism due to single cell division.
b) The bud gradually grows in size and gets detached form the parent body.
c) Detached bud develops into an adult organism, similar to the parent.
13. What is the importance of reproduction?
Ans. Importance of reproduction –
a) Maintenance of the existence – Organisms are maintaining their existence on the earth since their origin, million year ago, only because of reproduction.
b) Preservation of species – Species (a group of similar organisms) are preserved because of reproduction. It is possible because reproducing organisms produce new individuals which are very similar to themselves.
c) Role in evolution – some variations is produced in the new organisms during reproduction which play an important role in evolution.
14. How are spores produced in sporangium of Rhizopus?
Ans. a) A spore is a small microscopic structure with a thick wall.
b) Spores are generally formed in a structure called sporangium which reassembles formed in a structure called sporangium which resemble blob on – a – stick.
c) Sporangia are formed at the tip of erect fungal hypha.
d) In each sporangium, a nucleus divides several times producing a large number of nuclei. Nuclei get surrounded by a little cytoplasm and develop into thick – walled cells or spores.
e) The wall of sporangium breaks to release the spores in air.
f) On germination in the presence of moist surface, each spore gives rise to a new organism.
15. Diagrammatically represent binary fission in amoeba
Ans.
16. Draw a flow chart showing various types of reproduction with examples.
Ans.
17. What is grafting? Why is it used in horticulture practices?
Ans. In grafting, cutting of a plant stem is attached to another rooted plant. The cutting of stem which is grafted on the other plant is scion and the rooted plant on which the cutting is grafted is called stock. The scion and stock are placed one over other and tied in such a way that there is no gap between them. The cambium activity takes place among them and they get joined. Grafting is used in plants which do not produce extensive roots.
18. What are the different methods of contraception?
Ans. Different methods of contraception are –
a) Barrier method – In this method, a device used to prevent the entry of sperms in the female genital tract example – Condom, Diaphragm, Cervical caps.
b) Chemical method – In this method certain drugs (containing hormones) are used by the females. These drugs are avaiblabe in the form of pills. There are two kinds of pills commonly used for preventing pregnancies – oral pills and vaginal pills or creams.
c) Intrauterine contraceptive devices (IUCD’S) – IUCD like copper – T is placed in the uterus – IUCD prevent implantation of the fertilized ovum inside the uterus.
19. What is AIDS? Name its causal organism. Mention its symptoms.
Ans. AIDS is a sexually transmitted disease. Its full form is acquired immune deficiency syndrome. It is a viral disease, caused by human immune deficiency virus. Its symptoms are-
a) Destroys the immune system of body.
b) Persistent cough and fever.
c) Body attacked by other diseases like pneumonia, TB and certain cancers.
20. Explain vegetative reproduction through layering. Give examples.
Ans. It is a type of artificial vegetative reproduction in which a branch of the parent plant is buried in the soil. The portion of the branch which is in contact with the soil produces roots and this rooted branch is called layer. Layer is then detached form the parent plant which acts as a new plant. Example – Jasmine.
21. What is the importance of DNA copying in reproduction?
Ans. DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are the information source for making protein. If information is different, different protein will be made that lead to altered body design.
22. Why is variation beneficial to the species but not necessarily for the individual?
Ans. Variations are useful for the survival of species in changed environment situations. If a population of reproducing organism were suited to a particular niche and if the niche is drastically altered the population could be wiped out. However, some variations are present some species will survive. Thus, variation is useful to species but not the individual.
23. How does binary fission differ from multiple fissions?
Ans. Difference between binary fission and multiple fission:
24. Can you think of reasons why more complex organism cannot give rise to new individuals through regeneration?
Ans. The reason is that complex organisms are not merely random collection of cells. Specialized cells are organized in them as tissues are organized in organs. These organs have to be placed at definite positions in the body. So, regeneration is not possible in multicellular organism.
25. Why is vegetative propagation practiced for growing some types of plants?
Ans. (i) Plants raised by vegetative propagation can bear flower and fruits earlier than those produced from seeds.
(ii) Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds.
(iii) All plants produced by this method are genetically similar enough to the parent plant to have its all characteristics.
26. Why is DNA coping essential part of the process of reproduction?
Ans. DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are the information source for making protein. If information is different, different protein will be made that lead to altered body design.
27. How does the embryo get nourishment inside the mother’s body?
Ans. 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 wall of uterus. It contains finger-like projections villi on the embryo’s side of the tissue. On mother’s sides are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass the mother to the embryo and waste products from embryo to mother.
28. Why does menstruation occurs.
Ans. When in human female if the egg is not fertilized, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilized egg.
Thus, its lining becomes thick and spongy. This would be required for nourishing the embryo if had fertilized. However, this lining is not required any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes roughly every month and is known as menstruation.
29. Draw a labeled diagram of the longitudinal section of a flower.
Ans.
30. What are the different methods of contraception?
Ans. Various methods used for regulation of child birth can broadly categories as:
(i) Barrier methods: In this method, physical devices such as condom, diaphragm, cervical cap and copper-T are used.
(ii) Chemical method: use of spermicidal jelly by woman, oral pills and vaginal pills.
(iii) Surgical method: In surgical method, a small portion of vas deferens in male and the oviduct of female, is surgically removed or ligated. It is called vasectomy in male and Tubectomy in females.
31. What could be the reasons for adopting contraceptive methods?
Ans. The sexual act always has the potential to lead to pregnancy. Pregnancy will make major demands on the body and the mind of the woman and if she is not ready for it, her health will adversely affected. Therefore, adopting contraceptive methods are essential. Some contraceptive methods like condom also prevent spread of STDs and lethal diseases like HIV-AIDS.
32. Producing individuals by parents consume a lot of energy. So, why should an individual organism waste energy in the process, it does not need to stay alive?
Ans. Reproduction, unlike other life processes is not essential to maintain the life of an individual organism. But it is essential for providing stability to the population of species.
Maintaining the species is essential for maintaining balance in nature.
33. Blue prints of body design are stored in the DNA. Why?
Ans. The chromosomes present in the nucleus of a cell contain information for inheritance of features from parents to next generation in the form of DNA molecule. The DNA is the information source for making proteins. Thus, blueprints of the body design are stored in the DNA.
34. Why is variation beneficial to the species but not necessary for the individual?
Ans. Variation is beneficial to the species as it enables a species for its survival. A favourable variation makes an organism to live better in a changed environment and an unfavourable variation will not. So it is not necessarily true that a variation is beneficial to the individual always.
35. What is the advantage of reproduction though spores in the case of Rhizopus?
Ans. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
