CBSE Class 10 Science How Do Organisms Reproduce VBQs Set 02

CASE-BASED QUESTIONS

The human immunodeficiency virus (HIV) targets the immune system and weakens people’s defence systems against infections. As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. Immunodeficiency results in increased susceptibility to a wide range of infections, cancers and other diseases that people with healthy immune systems can fight off. The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which can take from 2 to 15 years to develop if not treated, depending on the individual. The symptoms of HIV vary depending on the stage of infection. Though people living with HIV tend to be most infectious in the first few months after being infected, many are unaware of their status until the later stages. In the first few weeks after initial infection people may experience no symptoms or an influenza-like illness including fever, headache, rash or sore throat.

Question. (a) Do contraceptive pills prevent transmission of STD?
(b) Name one STD caused by bacteria.
(c) What happens when a person is infected by HIV? Or Mention two modes of transmission of HIV.

Answer: (a) No, contraceptive pills change hormonal balance to prevent pregnancy but do not act as a barrier against STDs.
(b) Syphilis or Gonorrhoea.
(c) HIV weakens the immune system, making the person susceptible to various infections. Or HIV can be transmitted via sexual contact with an infected person or through the transfusion of infected blood.

Reproduction is the process by which organisms increase their population. It is of two types – asexual and sexual reproduction. The rates of birth and death determine the size of human population. An expanding population makes it harder to improve everybody’s standard of living. If we look around us, we can identify that expanding population is the most important reason for poor living standards. The process of reproduction also introduces new variations. These variations introduce changes which enable species to survive in even adverse environment.

Question. (a) Give one advantage of asexual reproduction.
(b) Name two modes of reproduction used by single organisms.
(c) Write two significance of reproduction. Or What is the importance of variation in a species?

Answer: (a) It allows for rapid multiplication of the population from a single parent.
(b) Fission and Budding.
(c) Reproduction ensures the continuity of a species and introduces variations essential for evolution. Or Variations are useful for the survival of species over time, especially when environmental conditions change drastically.

The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population.

Question. (a) List two common signs of sexual maturation in boys and girls.
(b) Write two factors that determine the size of a population.
(c) What is the result of reckless female foeticide? Or Which contraceptive method changes the hormonal balance of the body?

Answer: (a) Growth of hair in armpits and pubic region.
(b) Birth rate and death rate.
(c) It leads to a skewed child sex ratio and imbalance in society. Or Chemical methods like oral pills.

Vegetative propagation refers to the development of new plants from vegetative parts (roots, stem or leaves) of an existing plant. It is generally preferred for growing those plants which cannot produce their seeds or those which produce non-viable seeds (or seeds with prolonged period of dormancy). It is cheaper, easier and more rapid method of propagation in plants than growing plants from their seeds.

Question. (a) Name the part of Bryophyllum where the buds are produced for vegetative propagation.
(b) Name the plant parts that are used in vegetative propagation.
(c) List two disadvantages of vegetative propagation. Or State what type of method is used for growing (i) jasmine plant (ii) rose plant

Answer: (a) Notches along the leaf margin.
(b) Roots, stems, and leaves.
(c) No genetic variation and loss of vigour over generations. Or (i) Layering (ii) Cutting or Grafting.

Ankita started feeling changes in her body and also observed similar changes taking place in all the girls of her class. She is curious to know about it. Her mother explained that changes are seen both in boys and girls. But in girls, the changes are more important as they become mothers to babies and the baby is carried in mother’s body for a long period and will be breast fed later.

Question. (a) How long the baby is carried in mother’s womb? Draw a diagram of human reproductive system and mark where the baby is carried in mother’s womb for a long time.
(b) What are some of the changes that are seen in girls but not in boys? Or Ankita also wants to know how does embryo get nutrition from mother’s blood?

Answer: (a) Approximately 9 months (Gestation period). The baby is carried in the Uterus.
(b) Broadening of hips, development of mammary glands (breasts), and onset of menstruation. Or The embryo gets nutrition through the placenta, a disc-like tissue embedded in the uterine wall.

QUESTIONS

Question. What is the importance of DNA copying in reproduction? 

Answer: DNA contains information for inheritance of characters from parents to the next generation. As a result of DNA copying, blueprints of body design are produced which passes from parents to the offsprings. Thus, DNA copying maintains the body features in different generations of a species. Sometimes DNA copying also creates variation which are useful for the survival of species over time.

Question. Why is variation beneficial to the species but not necessarily for the individual?

Answer: A species include a large number of individuals of the same kind. All the organisms of a species have similar body design and well adapted to a niche or place. If a variation arises in the individual, it may not be of much benefit to it; even this variation may lead to the death of the individual. But the variation may be beneficial if the species faces a drastically altered condition. In this condition, the population may be wiped out completely. But if some variations are there in few individuals of these populations, there could be chances for survival and thus, variation is beneficial for the species. For example, if there is a population of certain bacteria living in water which is neither hot or cold and if the temperature of water increases suddenly, then most of the bacteria living in that water would die. But some bacteria which are resistant to heat would be able to survive. However, if these variation were not there, then the entire species of bacteria would not have been survived.

Question. How does binary fission differ from multiple fission? 

Answer:
Binary fission:
(i) It is the division of the parent into two nearly equal sized daughter individuals.
(ii) Nucleus of the parent cell divides to form two nuclei.
(iii) Ameoba and Leishmania divide by binary fission.

Multiple fission:
(i) It is the division of the parent into many small daughter individuals.
(ii) Nucleus of the parent cell divides to form a number of nuclei.
(iii) Plasmodium and yeast divide by multiple fission.

Question. How will an organism be benefitted if it reproduces through spores?

Answer: There are some benefits for the organisms which reproduce through spore formation. They are given below:
(i) Reproduction through spores is a simple as well as faster mode of reproduction.
(ii) The spores are light in weight and thus, they keep floating in the air. This helps in the dispersal of the organism.
(iii) The spores are covered with thick layer which enable them to survive in the unfavourable conditions like extreme temperatures lack of food and water.

Question. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer: More complex organisms cannot give rise to new individuals through regeneration because:
(i) Simple organisms reproduce through regeneration as their entire body is made up of similar kind of cells whereas complex organisms have a very high degree of organisation in their body.
(ii) There are specific organs to do specific functions.
(iii) There is a labour division in the body of complex organisms.
(iv) Regeneration is carried out by specialised cells which are not present in complex organisms.

Question. Why is vegetative propagation practised for growing some types of plants?

Answer: Vegetative propagation is generally preferred for growing those plants which cannot produce their seeds or those which produce non-viable seeds (or seeds with prolonged period of dormancy).

Question. Why is DNA copying an essential part of the pro cess of reproduction? 

Answer: The process of reproduction results in the production of offsprings which resemble to their parents. This means during the reproduction there must be a transfer of the blueprint of the body design from parent to the offsprings. DNA copying is essential as it passes generic information from parents to offspring. It determines the body design of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and results in two copies of DNA. Out of these two copies, one copy is passed to the newly formed individual.

Question. How is the process of pollination different from fertilisation? 

Answer:
Pollination:
(a) It is the transfer of pollen grains from anther to the stigma of a flower.
(b) Pollination precedes fertilisation.
(c) Pollination carries the male gamete producing pollen grains to the female sex organ.

Fertilisation:
(a) It is the fusion of male and female gametes.
(b) Fertilisation occurs only after pollination when the pollen grain has germinated and sent the male gametes to ovule.
(c) Fertilisation brings about fusion of gametes.

Question. What is the role of the seminal vesicles and the prostate gland? 

Answer: (i) Seminal vesicles are a pair of thin-walled muscular elongated sac which secrete fluid for nourishment and smooth transport of sperms.
(ii) Prostate gland also produce fluid which is released in the urethra along with the secretion of seminal vesicles to make transportation of sperms easier and also provides nutrition.

Question. What are the changes seen in girls at the time of puberty?

Answer: At the time of puberty, the changes which are seen in girls are given below:
• Thick hair grows in armpits and in the pubic region.
• Mammary glands develop and begin to enlarge.
• The hips broaden.
• Fat is deposited in various parts of the body as thigh, hips and shoulders.
• Menstruation starts and the ovaries also start to release eggs.

Question. How does the embryo get nourishment inside the mother’s body? 

Answer: 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 uterine wall. The embryo receives the oxygen and nutrients from the mother’s blood through placenta. The waste materials produced by the embryo are also cleared away through placenta.

Question. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Answer: If a woman is using a copper-T, it will not help in protecting her from sexually transmitted diseases. STDs transmit due to exchange of body fluid and copper-T cannot prevent from exchanging body fluid.

NCERT EXERCISES

Question. Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.

Answer: (b) Yeast reproduces asexually by budding.

Question. 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.

Answer: (c) Except vas deferens, all others are parts of female reproductive system in human beings.

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

Answer: (d) Anther contains pollen grains.

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

Answer: Advantages of sexual reproduction:
(i) Sexual reproduction promotes diversity of characters in the offsprings.
(ii) The sexual mode of reproduction incorporates process of combining DNA from two different individuals during reproduction. It plays a prominent role in the origin of new species.
(iii) The genetic variations that arise as a result of sexual reproduction also provide wider adaptability to the offsprings which ensures survival advantage.

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

Answer: The functions performed by the testis in human beings are as follows:
(i) Formation of sperms takes place in testis.
(ii) It secretes the hormone testosterone which regulates the formation of sperms and brings about secondary sexual characters in boys at the time of puberty.

Question. Why does menstruation occur?

Answer: Menstruation is a process in which thick blood flows out in the form of vaginal bleeding. This process take place every month because every month an egg is received from the ovary and uterus prepares itself to receive the fertilized egg. Thus, the inner lining of the uterus gets thickened and is supplied with blood to nourish the embryo. If the egg is not fertilised, then the lining of the uterus breaks down slowly and gets released in the form of blood and mucous from the vagina.

Question. What are the different methods of contraception?

Answer: The different methods of contraception are:
(i) Mechanical Barrier Methods: In these methods, physical devices such as condoms, diaphragm and cervical caps are used. These devices prevent the entry of sperms in the female genital tract during copulation, thus acting as a barrier between them.
(ii) Chemical Methods: In these methods, specific drugs are used by females, which are of two types — oral pills and vaginal pills. It contains hormones which stop the ovaries from releasing ovum into the Oviduct. These pills act by changing the hormonal balance of the body, so that eggs are not released and fertilisation cannot occur.
(iii) Use of Intra Uterine Contraceptive Devices (IUCDs): Copper-T is very effective in preventing pregnancy. It prevents implantation in the uterus. It is placed safely inside the uterus by a doctor or a nurse.
(iv) Surgical Methods: In these methods, a small portion of vas deferens in male and the fallopian tube in female is surgically removed or tied. It is called vasectomy in males and tubectomy in females. If the vas deferens in male is blocked, sperm transfer will be prevented and if the fallopian tube in the female is blocked, the egg will not be able to reach the uterus, thus fertilisation will not take place.

Question. How are the modes of reproduction different in unicellular and multicellular organisms?

Answer: The modes of reproduction are different in unicellular and multicellular organisms. The unicellular organisms have only one cell. There is no separate tissue for reproduction. So, they can reproduce by the process of fission, i.e. binary or multiple fission, or by budding as in Yeast. The multicellular organisms contain various cells and separate system for reproduction, so that they can reproduce by both sexual and asexual methods.

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

Answer: Reproduction helps in providing stability to populations of species because it helps living organisms to produce new individuals that resembles to the parents. The process of reproduction also introduce new variations. These variations introduce changes which enable species to survive in even adverse environment.

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

Answer: Contraceptive methods are adopted for the following reasons.
(i) For preventing unwanted pregnancy: Childbirth affects the health of a woman. So, there should be a gap between the two issues and contraceptives are used to prevent and delay the unwanted pregnancy.
(ii) For preventing STDs: Condom is used to prevent the transmission of fatal diseases like AIDS which transmits through sexual act

SELECT NCERT EXEMPLAR PROBLEMS

Question. In the list of organisms given below, those that reproduce by the asexual method are (i) banana (ii) dog (iii) yeast (iv) Amoeba
(a) (ii) and (iv)
(b) (i), (iii) and (iv)
(c) (i) and (iv)
(d) (ii), (iii) and (iv)

Answer: (b) (i), (iii) and (iv)

Question. In a flower, the parts that produce male and female gametes (germ cells) are:
(a) stamen and anther
(b) filament and stigma
(c) anther and ovary
(d) stamen and style

Answer: (c) anther and ovary

Question. Offspring formed by asexual method of reproduction have greater similarity among themselves because: (i) asexual reproduction involves only one parent (ii) asexual reproduction does not involve gametes (iii) asexual reproduction occurs before sexual reproduction (iv) asexual reproduction occurs after sexual reproduction
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)

Answer: (a) (i) and (ii)

Question. Characters transmitted from parents to offspring are present in:
(a) cytoplasm
(b) ribosome
(c) Golgi bodies
(d) genes

Answer: (d) genes

Question. Characters that are transmitted from parents to offspring during reproduction show:
(a) only similarities with parents
(b) only variations with parents
(c) both similarities and variations with parents
(d) neither similarities nor variations

Answer: (c) both similarities and variations with parents

Question. A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that:
(a) they reproduce asexually
(b) they are all unicellular
(c) they reproduce only sexually
(d) they are all multicellular

Answer: (a) they reproduce asexually

Question. Vegetative propagation refers to formation of new plants from:
(a) stem, roots and flowers
(b) stem, roots and leaves
(c) stem, flowers and fruits
(d) stem, leaves and flowers

Answer: (b) stem, roots and leaves

Question. During adolescence, several changes occur in the human body. Mark one change associated with sexual maturation in boys.
(a) Loss of milk teeth
(b) Increase in height
(c) Cracking of voice
(d) Weight gain

Answer: (c) Cracking of voice

Question. In human males, the testes lie in the scrotum, because it helps in the:
(a) process of mating
(b) formation of sperm
(c) easy transfer of gametes
(d) All of the options

Answer: (b) formation of sperm

Question. Which among the following is not the function of testes at puberty? (i) formation of germ cells (ii) secretion of testosterone (iii) development of placenta (iv) secretion of estrogen
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)

Answer: (c) (iii) and (iv)

Question. The correct sequence of organs in the male reproductive system for transport of sperms is:
(a) testis \( \to \) vas deferens \( \to \) urethra
(b) testis \( \to \) ureter \( \to \) urethra
(c) testis \( \to \) urethra \( \to \) ureter
(d) testis \( \to \) vas deferens \( \to \) ureter

Answer: (a) testis \( \to \) vas deferens \( \to \) urethra

Question. Which among the following diseases is not sexually transmitted?
(a) Syphillis
(b) Hepatitis
(c) HIV - AIDS
(d) Gonorrhoea

Answer: (b) Hepatitis