Q 1. Sexual reproduction helps in evolution. How?
Solution
During Sexual reproduction gametes carrying genes of two parents fuse to develop a zygote. As there is mixing of genes present in gametes of two different individual. It leads to genetic variation which further helps in evolution.
Q 2. List any four reasons for vegetative propagation being practiced in the growth of some type of plants.
Solution
Reasons for adopting vegetative propagation:
(i) The plants grown by vegetative propagation usually needs less attention in their early years than the plants grown from seeds.
(ii)The plants are genetically similar.
(iii)It helps in producing those plants which either produce very few seeds or produce such seeds which are not viable. (iv) It can be used to produce plants that reach maturity and produce fruits and seeds faster.
Q 3. Describe the process of fertilization in flowering plants.
Solution
The process of fertilization in flowering plants is known as double fertilization. It takes place in the embryo sac. The steps of the process are stated below:
i. The pollen tube enters the egg apparatus, that contains one egg cell and two synergids.
ii. Release of two male gametes from the pollen tube takes place.
iii. One male gamete fuses with the egg cell (syngamy).
iv. The other male gamete fuses with the two polar nuclei present in the centre of embryo sac (triple fusion).
Q 4. Which organ of male reproductive system acts as thermoregulator?
Solution
Scrotum acts as thermoregulator.
Q 5. Why vegetative propagation is not a good method for production of new plants?
Solution
Vegetative propagation is not a good method for production of new plants because it includes overcrowding of seeds, shows no genetic variation and plants lose vigour.
Q 6. (a) Where is copper-T placed? (b) What will happen if the vas deferens in the male is blocked surgically?
Solution
(a)Copper-T is placed in the uterus to prevent pregnancy. (b)If the vas deferens in the male is blocked surgically, sperm transfer will be prevented and fertilization will not occur.
Q 7. Name the type of asexual reproduction in : (a) Planaria (b) Rhizopus (c) Spirogyra (d) Hydra
Solution
(a) Regeneration(b)Spore Formation (c ) Fragmentation(d) Budding
Q 8. Define variation in relation to a species. Why is variation beneficial to the species?
Solution
Variation means certain change which occurs in sexually reproducing organisms because of errors in DNA copying. Variations are beneficial for species because they give survival advantage even in the adverse environmental conditions.
Q 9. State two importance of DNA copying in reproduction.
Solution
DNA coping in reproduction leads to: (a) Transmission of characters from parents to offspring. (b) It leads to variations.
Q 10.
(a) Why it is said that sexual reproduction promotes diversity of characters in the offsprings?
(b) What are the barrier methods of birth control?
Solution
(a) It is because sexual reproduction results from the fusion of two gametes coming from two different and sexually distinct individuals. This leads to variation which is necessary for evolution.
(b) In barrier methods, physical devices such as condom, diaphragm and cervical caps are used. They prevent the entry of sperms in female genital tract during copulation.
Q 11. When we add a spoon of curd in warm milk it converts whole milk into curd. What is present in the curd? How it multiplies to convert milk into curd?
Solution
Curd consists of bacteria which reproduces by asexual reproduction. When curd is added in warm milk, an optimum temperature helps in the multiplication of bacteria and within few hours all the bacteria in curd makes identical copies by asexual reproduction and converts milk into curd.
Q 12. What are the advantages of sexual reproduction?
Solution
Advantages of sexual reproduction are:
(i) Sexual reproduction promotes diversity of characters in the offspring.
(ii) In sexual reproduction there are increasing opportunities for new combination of characters and therefore, it plays a prominent role in the origin of new species.
(iii) It leads to variation, which is necessary for evolution.
Q 13. How many eggs are produced every month by either of the ovaries in a human female? Where does fertilization taken place in the female reproductive system?
Solution
One egg is produced every month by one of the ovaries. Fertilization takes place in the fallopian tubes.
Q 14. Why organism belonging to same species looks similar to each other?
Solution
In a species, each cell consists of the same type of DNA and genes and has the same chromosome number. When the DNA passes to the next generation, the same morphology is retained in the new organism with little variations in features. So, individuals of a species look similar.
Q 15. Define the surgical methods used to prevent the conception.
Solution
Vasectomy: In this method, vas deferens in males is blocked that will, in turn, prevent the transfer of sperms. Tubectomy: In this method, fallopian tube is blocked to prevent the entry of ovum into the fallopian tube.
Q 16. “Variation is beneficial to the species but not necessarily for the individual”. Justify this statement.
Solution
Variation is useful for the survival of species in changed environmental situations. Some variations found in few individuals of a population, would lead for some chance for them to survive, rest will be wiped out.
Q 17. How sexual reproduction is better than asexual reproduction?
Solution
Sexual reproduction promotes diversity of characters in an offspring due to combinations of genes which can lead to variation whereas in asexual reproduction evolutionary change is not possible as only one parent is involved therefore no variation takes place.
Q 18. What happens when pollen grains get deposited on the stigma of a flower?
Solution
When pollen grains get deposited on the stigma of a flower, following changes take place: i. Pollen grains enlarge due to absorption of water. ii. They germinate to produce pollen tube that reaches the stigma through the style. iii. Formation of two non-motile male gametes takes place. iv. After reaching the ovary, pollen tube enters the ovule through the micropyle, so that fertilization can take place.
Q 19. Define the term ‘double fertilization in plants’. After fertilization name the part in each case which develops into (i) fruit and (ii) seeds. Where does vegetative propagation finds its application?
Solution
Double fertilization occurs when one male nucleus fertilizes with an egg cell to form a zygote cell and the other male nucleus fuses with two polar nuclei to cause triple fusion. As these two types of fertilizations takes place at the same time in the ovule of the plant, it is known as double fertilization. After fertilization:
(i) Ovary develops into a fruit.
(ii) Ovules develop into seeds. Vegetative propagation is used in methods such as layering or grafting to grow many plants like sugarcane, roses or grapes for agricultural purposes.
Q 20. Differentiate between male and female gamete.
Solution
MALE GAMETE FEMALE GAMETE It is small, motile with no food reserves. It is larger, non-motile with food reserves.
Q 21. Differentiate between menarche and menopause. Mention any three points.
Solution
Menarche Menopause
(i) It is the start of menstruation in human females.
(i) It is the stoppage of menstruation in human females. (ii) It occurs at the age of 10-12 years.
(ii) It occurs at the age of 50 years.
(iii) It marks the beginning of reproductive life in a human female.
(iii) It is the end of reproductive life in a human female.
Q 22. Where does fusion of male and female gamete take place in plants?
Solution
In plants, the fusion of male and female gamete takes place in the embryo sac.
Q 23. Name the sex hormones secreted by male and female sex organs in human beings. State one function of each.
Solution
Males – Testosterone – It controls the production of sperms. Females – Estrogen – It controls the production of ova.
Q 24. (a) Explain the process of regeneration in Planaria. (b) How is regeneration different from reproduction?
Solution
(a) Regeneration in Planaria: In Planaria, any part of the body which gets cut is capable of regeneration or developing into a complete organism. Regeneration is carried out by specialized cells which proliferate and make large numbers of cells. From these mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organized sequence referred to as development. (b) Regeneration Reproduction 1. It is a type of asexual mode of reproduction in which only single parent is involved.
1. In includes both sexual and asexual mode of reproduction in which either single parent or both the parents are involved respectively.
2. This mode of reproduction is dependent of the cut in an organism. 2. This mode of reproduction is independent of cut in an organism. Example – Planaria. Example – Sexual reproduction in humans.
Q 25. List three methods to limit the family size. State the principle involved in each.
Solution
(a) Barrier Method – It is based on the using a mechanical barrier which prevents the sperm from reaching the egg. (b) Chemical Method – It is based using certain chemicals which changes the hormonal balance of the body and prevents pregnancy. (c) Surgical Method – It is based on blocking of the male and female tract that transports the gametes, through surgery to prevent pregnancy.
Q 26. Write two examples each of sexually transmitted diseases caused by (i) virus, (ii) bacteria. Explain how the transmission of such diseases be prevented?
Solution
Sexually transmitted diseases by virus: Genital Herpes is caused by herpes simplex virus and AIDS is caused by HIV. Sexually transmitted diseases by bacteria: Gonorrhoea is caused by Nisseria gonorrhoeae and Syphilis is caused by Trepanoma pallidum Prevention of transmission of STD’s: i. Having sex with infected or any unknown person should be avoided. ii. Sharing of needles, syringes etc. must be prohibited. iii. The surgical and dental instruments should be sterilized properly before use. iv. Avoid blood transfusion from infected person. Blood should be tested before transfusion. v. Adedqate medical treatment should be provided to the pregnant woman to protect the child from getting infected.
Q 27. State any two function of human ovary.
Solution
Functions of human Ovary are: a. Production of female germ cells or eggs. b. Production of hormones.
Q 28. Why is it said that “sexual reproduction promotes diversity of characters in the offspring”?
Solution
It is because sexual reproduction results from the fusion of two gametes coming from two different and sexually distinct individuals. This leads to variation which is necessary evolution.
Q 29. State the role of seminal vesicles and prostate gland in the human body.
Solution
i. Seminal vesicles-It secretes alkaline secretions which lower the pH of semen and provide nourishment. ii. Prostate Gland -The secretions of these glands keep the sperm active and mobile.
Q 30. (a) How do the oral pills function as contraceptives? (b) The use of these pills may be harmful. Why?
Solution
(a) They function by changing the hormonal balance of the body. This prevents release of ova from the ovary and hence fertilisation does not occur. (b) Change in hormonal balance may cause some side effects.
Q 31. What is the main function of fallopian tubes?
Solution
The fallopian tubes act as a site for the fertilization of egg and sperm.
Q 32. Mention two functions of human testis.
Solution
i. They produce male germ cells i.e. sperms ii. They act as endocrine gland and secrete hormone testosterone which controls the secondary sexual characters in males.
Q 33. Leaves of Bryophyllum fallen on the ground produce new plants. Why?
Solution
It bears adventitious buds in the notches along the leaf margin. When the buds fall on the soil they develop into new plant under favourable conditions.
Q 34. Pre-natal sex determination has been prohibited by law. State two reasons.
Solution
(a) Indiscriminate female foeticide and desire for a male child. (b) Declining female-male sex ratio.
Q 35. A parasite reproduces by dividing its body into small pieces. Name the animal and explain the process.
Solution
Flatworm reproduce by the process of fragmentation. In this type of reproduction the body breaks up into two or more small fragments upon maturation and each fragment grows into new individual.
Q 36. List two basic differences between male and female germ cell.
Solution
Male germ cell Female germ cell (i) Smaller in size. (i) Bigger in size. (ii) It is motile. (ii) It is non – motile.
Q 37. How does the process of seed germination take place in plants? Describe in brief.
Solution
Seed germination – After the ovary ripens to form fruit, the petals, sepals, stigma, stamen, and style shrivel and fall off. The seed contains a future plant or embryo which develops into a seedling under appropriate conditions. This process is known as seed germination.
Q 38. Differentiate between : (a) Asexual and Sexual reproduction. (b) Plumule and Radicle (c) Pollination and Fertilization.
Solution
(a) Asexual reproduction Sexual reproduction It is a type of reproduction in which new organisms are produced from single parent. It is a type of reproduction in which new organisms are produced through gametes that are obtained from the male and female organism. (b) Plumule Radicle It is the part of the seed that develops into shoot. It is the part of the seed that develops into roots. (c) Pollination Fertilization It is the transfer of pollen (male gamete) from anther to stigma of the flower. It is the fusion of male and female gamete.
Q 39. How do potato plant and bryophyllum plants reproduce vegetatively?
Solution
Potato tuber has depressions called “eyes” on its surface. These eyes have vegetative buds in them which germinate to produce a new potato plant. Similarly, the fleshy leaves of Bryophyllum bear vegetative buds in the notches along the leaf margin. These buds germinate to form small plantlets which form new plants on being detached.
Q 40. State in brief the function of the following organs in the human female reproductive system: (a) Ovary (b) Fallopian tube (c) Uterus
Solution
(a) Ovary: It is a site of production of germ cells or eggs and is also responsible for the production of female hormones. (b) Fallopian tube: It transports the male sperm cells to the egg, provide a suitable environment for fertilization, and transport the egg from the ovary. (c) Uterus: It is the site for implantation of fertilized ova and also helps in the growth and development of the foetus.