CBSE Class 10 Biology How Do Organisms Reproduce Worksheet Set B

Question. Some flowers of pumpkin and bottle gourd develop fruits whereas other flowers fail to develop fruits. What may be the possible reason?
Answer : Pumpkin and bottle gourd bear unisexual flowers. Some flowers are male and others are female. Male flowers do not develop fruits. They produce pollen grains. The female flowers posses carpels which develop fruits after fertilisation. Therefore, only female flowers develop fruits but not the males.

Question. (a) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run.
(b) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
Answer : (a) Prenatal sex determination was banned in India in1994. This was done to prevent sex selective abortion. It is being used to kill the normal female fetus. This killing of the unborn girl child is called female feticide which is reducing the number of girls drastically in some societies of our country. Due to reckless female feticide, male–female sex ratio is declining at an alarming rate. Its benefit in the long run is that the female-male ratio could be maintained for a healthy society.
(b) Bacterial diseases due to unsafe sex are gonorrhoea, syphilis. Viral diseases due to unsafe sex are AIDS, genital herpes.

Question. Name and explain in brief the four different methods of contraception.
Answer : Contraception literally means prevention of pregnancy.
Different methods for the prevention of pregnancy are as follow:
(i) Barrier methods in which a mechanical barrier such as condom, cervical cap or diaphragm is used for preventing the entry of sperms in the female genital tract or vagina. Thus,
sperms and egg do not meet and fertilisation is prevented from taking place.
(ii) Chemical methods of contraception are those in which release of eggs from the ovary can be prevented by the intake of pills by the female. The oral pills are hormonal preparations and are also termed as oral contraceptives.
(iii) Intra-Uterine Contraceptive Devices (IUCDs) are placed in the uterus to prevent pregnancy. These devices are very effective and popularly used by females. Copper-T and Lippes
Loop are examples of IUCDs. These devices are placed in the uterus by skilled personnel.
(iv) Surgical method : Contraception can also be brought about by surgically removing or tying a part of vas deferens (vasectomy) in the male and removing or tying a part of
fallopian tube (tubectomy) in the female. Surgery should be performed by well trained doctors under sterile conditions.

Question. What does HIV stands for? Is AIDS an infectious disease? List any four modes of spreading AIDS.
Answer : HIV stands for Human Immunodeficiency Virus. Yes, AIDS is an infectious disease. It is transmitted sexually or through exposure to contaminated blood.
Four modes of spreading AIDS are :
(i) Unprotected sex with an infected partner
(ii) Use of contaminated needle and syringes
(iii) Use of contaminated razors for shaving
(iv) Transfusion of infected blood or blood products.

Question. Answer the following. 

(a) What happens to the zygote after fertilisation in flowering plants?
(b) What is germination?
(c) Identify the labelled parts A, B and C of the given figure.
Answer : (a) After fertilisation, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off.
(b) Germination is the process included all changes that take place from the time when a dry, viable seed starts to grow when placed under suitable condition of germination
to the time when the seedling becomes established on the substratum.
(c) A – Plumule, B – Radicle, C – Cotyledon

Question. Give reasons for the following :
(i) Oral pills help in birth control.
(ii) Petals of flowers are variously coloured.
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.

Question. What is vegetative propagation? How does vegetative propagation take place in potato?
Answer : Vegetative propagation is the process of formation of the plant from vegetative propagules or units, such as stem, root, leaf, buds, etc. Tuber of potato is the swollen underground stem and bears number of nodes or eyes. Each eye bears one or many buds. New plants are produced from the buds on the eyes of the stem tuber.

Question. State two differences between budding in Hydra and budding in yeast.
Answer : Differences between budding in Hydra and budding in yeast are as follows: 

Question. List two functions each of the following parts of human female reproductive system.
(a) Ovaries (b) Fallopian tubes (c) Uterus
Answer : (a) Ovaries : (i) It produces ovum.
(ii) It secretes female sex hormone.
(b) Fallopian tubes : (i) It conveys the ovum from the ovary to the uterus.
(ii) It acts as site for fertilisation.
(c) Uterus : (i) It nourishes the fertilised ovum which develops into the fetus.
(ii) It holds the fetus till the baby is mature enough for birth.

Question. Reproduction is linked to stability of population of a species. Justify the statement.
Answer : Reproduction is the only means to ensure the continuity of a species. During reproduction, DNA passes from one generation to the next. Copying of DNA takes place with consistency but with minor variations. This consistency leads to stability of species. Hence, reproduction is linked to stability of a species population. By reproduction, organisms
produce large number of new individuals of their own kind out of which several get perished and only some survive.
These surviving organisms replace the naturally dying members of the population. Hence, the population as a whole is not affected and remains stable.

Question. Label the parts ‘A’, ‘B’, ‘C’, ‘D’, ‘E’ and ‘F’ in the following figure. Assign the role played by ‘B’ and ‘F’. 

Answer : In the given figure,
A = Pollen grain
B = Pollen tube
C = Stigma
D = Style
E = Ovary
F = Ovule.
Role of B : Pollen tube acts as carrier of male gametes to the embryo sac.
Role of F : Ovule becomes seed after fertilisation.

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.

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. Differentiate between natural and artificial vegetative propagation in plants.
Answer : Differences between natural and artificial propagation in plants are as follows: 

Question. (a) List few disadvantages of vegetative propagation?
(b) What is placenta? Explain its functions in humans.
Answer : (a) Some disadvantages of vegetative propagation are:
(i) Plants produced by this technique possess less vigour.
(ii) They are more prone to diseases.
(iii) They show no genetic variations.
(b) Placenta is a specialised tissue between fetus and uterine wall of mother. It develops finger-like processes called villi, which grows into tissue of the uterus.
Functions of placenta are listed below :
(i) Provides nutrition
(ii) Helps in the exchange of gases such as oxygen and carbon dioxide
(iii) Helps in the excretion, that is the removal of nitrogenous waste material from the fetal blood to that of the mother
(iv) It secretes hormones such as estrogen and progesterone.
(v) Placenta provides protection by partitioning the blood of the fetus and the mother. Thus, unwanted materials such as germs cannot contaminate the blood of the fetus.
(vi) Acts as a storage of glycogen. This glycogen gets converted to glucose and fulfils the energy requirement of the fetus.

Question. What is the role of seminal vesicles and prostate glands?
Answer: Seminal vesicles and prostate glands are accessory reproductive organs. The secretion from seminal vesicles provides nourishment and motility to the sperms. Prostate
glands secretion neutralizes the acidic pH of vagina so that sperms can easily pass through vagina.

Question. Students were asked to observe the permanent slides showing different stages of budding in yeast under high power of a microscope.
(i) Which adjustment screw were you asked to move to focus the slides?
(ii) Draw diagrams in correct sequence to show budding in yeast.
Answer: (i) Fine adjustment screws were moved to focus the slides.
(ii) 

Question. Answer the following questions:
(i) Write the names of those parts of a flower which serve the same functions as the following do in the animals.
(a) Testis, (b) Sperm, (c) Ovary, (d) Egg
(ii) State the function of flowers in the flowering plants?
Answer: (i) (a) Testis – Anther; (b) Sperm – Pollen grains; (c) Ovary – Ovary; (d) Egg – Ovum
(ii) Flowers are the main organs of sexual reproduction. They contain the reproductive organs.

Question. What is the advantage of reproduction through spores in the case of Rhizopus?
Answer: Spores are highly resistant to adverse environmental conditions like drought, heat etc. They have a thick wall which protects them and on exposure to suitable conditions they
germinate and give rise to new individuals.

Question. State the basic requirements for sexual reproduction? Write the importance of such reproduction in nature?
Answer: The basic requirements for sexual reproduction are involvement of a father and mother, parents which will contribute the male and female gametes respectively. The gametes are haploid which are produced through meiosis which on fusion produce a zygote and normal diploid number of chromosome is restored in offsprings.
Importance of sexual reproduction:
(a) It involves variations in species.
(b) Two individuals are required one male and another female.
(b) Specialized cells called sex cells are involved in this type of reproduction.
(d) It promotes diversity of characters in offsprings.
(e) It results in recombination of genes thus increase chances of genetic variations.
(vi) It plays an important role in origin of new species.

Question. Distinguish between pollination and fertilisation. Mention the site and the product of fertilisation in a flower.
Answer: (a) The transfer of pollen grains from anther of a stamen to the stigma of a carpel is called pollination whereas fertilisation is the process when the male gamete present in
pollen grain joins the female gamete present in ovule.
(b) Pollination is an external mechanism whereas fertilisation is an internal mechanism which takes place inside the flower.
(c) Site of fertilization in flower is ovary. Product of fertilization in flower is Zygote.

Question. Name the two reproductive parts of a bisexual flower which contain the germ cells. State the location and function of its female reproductive part.
Answer: Stamen and carpel are the two reproductive parts of a bisexual flower which contain the germ cells. Carpel- the female reproductive part is located at the centre of a flower. Carpel has three parts, the tip part is stigma which is sticky and receives the pollen grains, style is long and middle part through which pollen tube from pollen grains travel to reach ovary. Ovary is the swollen, bottom part of carpel which contains the female gametes where fertilisation occurs.

Question. Answer the following questions:
(i) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions.
(ii) Name the parts of the human female reproductive system where fertilisation occurs.
(iii) Explain how the developing embryo gets nourishment inside the mother’s body?
Answer: (i) Testes produces sperms as well as secretes a hormone in human males. The hormone secreted by testes is testosterone and its functions are:
(a) It stimulates sperm production.
(b) It stimulates development of secondary sexual characters in males.
(c) It involves the development, maturation and functioning of male accessory sex organs.
(ii) Fallopian tubes are the site of fertilisation in the human female reproductive system.
(iii) A specialised tissue called placenta connects developing foetus with uterine wall of mother that provides nutrients from mother to child. Placenta is formed by interlocking of finger
like projections called villi which provides a large surface area for diffusion of nutrients like glucose and respiratory gases like oxygen from mother. Carbon dioxide gas and metabolic
wastes released by foetus are removed by placenta.

Question. What are different methods of contraception?
Answer: The methods or devices used to prevent fertilisation and implantation are referred to as contraceptive methods. Some of the methods are:
(a) Barrier methods: Use of condoms in male and diaphragms in female prevents the entry of sperms into uterus.
(b) Chemical methods: Use of various hormonal pills prevents the release of egg from ovary. They cause a change in menstrual cycle thus delaying ovulation.
(b) IUCDs: Use of IUCDs devices like copper-T which is fitted inside uterus that prevents implantation of embryo into the wall of uterus.
(d) Surgical methods: Tubectomy is done in female where a small portion of oviducts are removed and ligated to prevent the entry of egg from ovaries. Vasectomy is done in males
where a small portion of vas deferens is cut and ligated preventing passage of sperms.
(e) Natural methods: To avoid copulation around the time of ovulation.

Question. What could be the reasons for adopting contraceptive method?
Answer: The reasons for adopting contraceptive method are:
(a) Preventing unwanted pregnancies to control population growth.
(b) It protects from sexually transmitted diseases like AIDS, Syphillis etc.
(b) Proper health of mother and child can be maintained by preventing frequent pregnancies.
(d) Sufficient gap between the offsprings, which ensures the proper health of the mother and child.

Question. What happens when:
(i) Planaria gets cut into two pieces.
(ii) A mature Spirogyra filament attains considerable length.
(iii) On maturation sporangia burst.
Answer: (i) Each piece regenerates into a new Planaria.
(ii) When a mature Spirogyra filament attains considerable length it breaks into two or more fragments and each fragments grow into a new individual.
(iii) On maturation when sporangia burst, spores are liberated and they are dispersed. On getting a suitable substratum and under favourable conditions each spore germinates into new
mycelium.

Question. (i) Wet a slice of bread, and keep it in a cool, moist and dark place.
(ii) Observe the surface of the slice with a magnifying glass.
Record your observations for a week.
Answer: A white cottony mass appears on the moist bread which later becomes black to produce sporangiosphores which contain spores in them. This is called Rhizopus or bread mould.

Question. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer: Complex organisms have highly and well developed tissue and organ system to perform a particular function. There is division of labour in the body of complex organisms. Their body is highly complicated and the tissue and organ system are highly differentiated and are made up of different kinds of cells. So, it is very difficult for complex organisms to give rise to new individuals through regeneration, which is seen in simple organisms like Hydra, Planaria etc.

Question. List four points of significance of reproductive health in a society.
Name any two areas related to reproductive health which have improved over the past 50 years in our country.
Answer: Significance of reproductive health in a society are:
(a) It helps in controlling population growth.
(b) It helps in preventing the transmission of sexually transmitted diseases like syphilis, AIDS etc.
(b) It helps in family planning.
(d) It helps in knowing the suitable age for marriage and giving birth to child so that the mortality rates of mother and new born child can be reduced. The two areas related to reproductive health which have improved over the past 50 years in our country are less mortality rate in new borns and mother.

Question. What is the importance of DNA copying in reproduction?
Answer: DNA copying is necessary as parents transmit their characters to offsprings through DNA. Due to this, the offsprings resemble in some of the features with their parents. But DNA copying also produces some variations in the offsprings that helps them to adapt to the changing environment.

Question. Why does the body show sexual maturation at puberty?
Answer : 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.