CBSE Class 10 Science HOTs How Do Organisms Reproduce Set 05

VSA Type Questions

Question. What is implantation?
Answer: The attachment of fertilised ovum to the wall of uterus is called implantation.

Question. What does HIV stands for? Is AIDS an infections disease?
Answer: HIV stands for Human Immunodeficiency Virus. Yes, AIDS is an infections disease. It is transmitted sexually or exposure to contaminated blood.

Question. OR Which reproductive organ serves as a passage for menstrual flow?
Answer: Vagina serves as passage for menstrual flow.

Question. Name the parts of a bisexual flower that are directly involved in reproduction.
Answer: The parts of a bisexual flower that are directly involved in reproduction are stamens in males and pistil in females.

SA I Type Questions

Question. Write two differences between binary fission and multiple fission.
Answer: (i) Binary fission of the parent cell results in the formation of two small, nearly equal sized daughter individuals whereas multiple fission results in the formation of several daughter individuals.
(ii) In binary fission, the parent nucleus divides into two daughter nuclei while in multiple fission the parent nucleus divides into a number of daughter nuclei.

Question. List any four reasons for vegetative propagation being practised in the growth of some type of plants.
Answer: Four reasons for vegetative propagation being practised in the growth of some type of plants are as follows :
(i) The characters of the parent plants are preserved hence a good variety produced can be propagated by vegetative means.
(ii) The plants, which do not produce viable seeds or produce very few seeds, can be reproduced by this method, for example, banana, potato, grapes, sugarcane, rose, orange, etc.
(iii) It is an easier, quicker and cheaper method of propagation.
(iv) It is easier to get rid of pathogen from any part of plant by vegetative propagation.

Question. OR Mention the aims of reproduction.
Answer: The aims of reproduction are:
(i) It allows perpetuation of species.
(ii) It is the means of increasing the populations of a species.
(iii) It plays an important role in evolution by transmitting useful variations from one generation to another.

Question. Write down the functions of prostate gland and seminal vesicles.
Answer: Prostate gland - It secretes milky fluid which helps in the nourishment and mobility of sperms.
Seminal vesicles - Seminal vesicles produce an alkaline secretion containing fructose, hormone like prostaglandins and clotting proteins that are different from those in blood. Fructose is a source of energy for the sperm, prostaglandins stimulate uterine contractions and thus may help the sperm to be moved towards the fallopian tubes, where fertilisation takes place and clotting proteins help semen coagulate after ejaculation.

Question. How does the uterus prepares itself every month to receive and nurture the growing embryo? Where does fertilisation takes place in human females?
Answer: The uterus prepares itself every month to receive and nurture the growing embryo as the lining thickens and is richly supplied with blood to nourish the growing embryo. Fertilisation takes place in the oviduct or fallopian tube in females.

SA II Type Questions

Question. Why is variation so important?
Answer: Variation is so important because of the following reasons:
(i) Populations of organisms normally live and interact with definite kinds of ecological niches. If there is an alteration in the ecological conditions of such places, the population of organisms will get damaged and may be wiped out. The variants of the organisms, however, may have better chances of survival. The surviving individuals may reproduce and develop a kind of population which is suited to the changed niche.
(ii) It makes some individuals better fitted in the struggle of existence.
(iii) It helps the individuals to adapt themselves according to the changing environment.
(iv) It allows breeders to improve races of useful plants and animals for increase resistance, better yield, quicker growth and lesser input.
(v) Pre-adaptation caused by the presence of neutral variations are extremely useful for survival against sudden changes in environment, e.g., resistance against a new pesticide or antibiotic.
(vi) It constitute raw material for evolution.
(vii) It gives each organism a distinct individuality. (any three)

Question. Write a short note on tissue culture.
Answer: Tissue culture is a modern technique of vegetative propagation in which tissues from the growing tip of a plant are removed and placed in an artificial medium where they divide rapidly to form a small group of cells or callus which is again transferred to another medium containing hormones for growth and differentiation. The plantlets are then placed in the soil so that they can grow into mature plants. This technique is commonly used for ornamental plants.

Question. OR Give reasons for the following : (i) Oral pills help in birth control. (ii) Petals of flowers are variously coloured. (iii) Some plants are propagated only by vegetative methods.
Answer: (i) Oral pills contain the hormone estrogen and progesterone which check ovulation.
(ii) The petals of the flowers are coloured to attract pollinators for cross pollination.
(iii) The plants which are propagated only by vegetative methods either have lost the ability to produce viable seeds or do not produce seeds at all.

Question. What are sexually-transmitted diseases? How can the transmission of such diseases prevented?
Answer: The infectious (communicable) diseases, which are spread from an infected person to a healthy person by sexual contact, are called sexually transmitted diseases. These include bacterial infections such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS. Using a covering, called a condom, for the penis during sex helps to prevent transmission of many of these infections to some extent.

Question. Explain the process of spore formation in fungi. How is spore formation differ from budding?
Answer: Spore formation is the most common method of asexual reproduction seen in fungi and bacteria. During spore formation, a structure called sporangium develops from the fungal hypha. The nucleus divides several times within the sporangium and each nucleus with a bit of cytoplasm, develops into a spore. The spores are liberated and they develop into new hypha after reaching the ground. e.g., Rhizopus, Mucor and Penicillium.
Difference between budding and spore formation is as follows:
Budding: Process of asexual reproduction where bud develops as an outgrowth of body due to repeated cell division, e.g., Yeast, Hydra.
Spore formation: Spore formation is the process in which tiny bulb like structures called sporangia develop in organisms like Rhizopus.

LA Type Questions

Question. Answer the following. (a) What do you mean by puberty? (b) Mention the different changes that takes place in boys and girls during puberty. (c) Why does the body show sexual maturation at this stage?
Answer: (a) During adolescence, the rate of general body growth begins to slow down, reproductive tissues begin to mature. This period during adolescence is called puberty.
(b) During sexual maturity, hormonal changes take place in males and females, and under the influence of these hormones, secondary sexual characteristics are developed. Secondary sexual characteristics in males include deepening of voice, widening of shoulders, appearance of beard and moustache, growth of axillary and pubic hair, enlargement of external genital organs and formation of sperms. Secondary sexual characteristics in females include growth of axillary and pubic hair, widening of pelvis and hip, enlargement of breasts and initiation of menstrual cycle.
(c) There is a need for specialised cell types in multicellular bodies to carry out specialised functions. The creation of germ cells to participate in sexual reproduction is another specialised function. Human beings also develop special tissues for reproduction. However, while the body of the individual organism is growing to its adult size, the resources of the body are mainly directed at achieving this growth and the maturation of the reproductive tissue is not likely to be a major priority. So, during puberty maturation of reproductive tissues takes place to attain sexual maturity and the rate of general body growth slows down.

Question. (a) State the meaning of pollination and mention a distinguishing feature between self-pollination and cross-pollination. (b) How does fertilisation occur in flowers? Name the parts of the flower that develop into (i) seed and (ii) fruit after fertilisation.
Answer: (a) The process of transfer of pollen grains from anther of a flower to the stigma of the same flower or another flower of the same species is known as pollination. Self pollination occurs within a flower or between two flowers of the same plant while cross pollination occurs between two flowers of two different plants of the same species.
(b) Fertilisation, in plants, occurs when the male gamete present in pollen grain fuses with the female gamete (or egg) present in ovule. When a pollen grain falls on the stigma of the carpel, it bursts open and grows a pollen tube downwards through the style towards the female gamete in the ovary. Male gametes move down the pollen tube. The pollen tube enters the ovule in the ovary. The tip of pollen tube bursts and male gametes comes out of pollen tube. In ovary, the male gamete of pollen combines with the female gamete or egg present in ovule to form a fertilised egg.
After fertilisation, (i) ovule develops into seed, (ii) ovary develops into fruit.

Question. (i) Give reasons for avoiding frequent pregnancies by women. (ii) Explain the following methods of contraception giving one example of each: (a) Barrier method (b) Chemical method (c) Surgical method.
Answer: (i) Having pregnancies too frequently and giving child birth at quick succession reduce mother’s health and vitality and cause mental strain. Health of children is also affected due to nutritional deficiencies.
(ii) (a) Barrier method: These are physical devices to prevent the entry of sperm into the female genital tract during copulation. They also protect against sexually transmitted diseases e.g., condoms. Condoms are thin, strong rubber sheaths used by man to cover the erect penis. It is simple but effective and widely used contraceptive that has no side effects. It checks pregnancy by preventing deposition of semen in the vagina.
(b) Chemical method: Some common chemicals like foam tablets, jellies, pastes, creams and spermicides are used by females. These are placed in vagina. These chemicals adhere to the mucous membrane and immobilise and kill the sperms.
(c) Surgical method: Surgical methods include – Vasectomy and Tubectomy. Vasectomy is a small surgical operation performed in males. It involves removal of a small portion of the sperm duct (or vas deferens) by surgical operation. The two cut ends are then ligated (tied) with threads and this prevents the sperms from coming out. Tubectomy is done in females where oviducts are cut and cut ends tied with threads and therefore, passage of ova is prevented.

Question. Suppose there is no meiosis and the gametes are formed by mitotic divisions. What kind of situation do you expect under such circumstances?
Answer: Normally the two haploid gametes fuse to form one diploid zygote. The zygote develops into a mature organism. At maturity, the organism develops sex organs and gametes are formed from diploid cells by meiosis resulting in the formation of haploid gametes. This process continues generation after generation. Now if there is no meiosis at the time of gamete formation the gametes formed as a result of mitosis will be diploid. The two diploid gametes will fuse to form a 4n zygote which develops in tetraploid organism. Again this 4n organism will develop 4n gametes which fuse to form 8n zygote. The number of chromosomes will continue to double after each generation and a time will come when there will be only DNA on earth.