CBSE Class 10 Biology How Do Organisms Reproduce Worksheet Set K

ONE MARK QUESTIONS

Question: When a cell reproduces, what happens to its DNA?
Answer: Its DNA first doubles up followed by its equal and accurate division between two daughter cells.

Question: How does the embryo get nourished inside the mother’s body?
Answer: The embryo grows inside the mother’s womb and gets nourishment from its mother’s blood through placenta. Placenta contains villi which connects the embryo with the mother’s blood. These villi provides a large surface area for glucose and oxygen to pass from mother to the embryo.

Question: Why is temperature of scrotal sac 2°C less than the body temperature?
Answer: Because testes require temperature 2°C less than the body temperature for the production of sperms.

Question: What are those organisms called which bear both sex organs in the same individual. Give one example of such organism.
Answer: Bisexual. For example: earthworm, leech, starfish, hibiscus, mustard. (Any one)

Question: How can the chromosomes be identified?
Answer: Chromosomes can be seen as thread like structure when cell is dividing.

Question: List two functions of ovary of human female reproductive system.
Answer: In human female, ovary contains thousands of eggs.
One egg is produced every month one of the ovaries. Ovary also secretes estrogens hormone for development of sexual characteristics at puberty.

Question: How does binary fission differ from multiple fission?
Answer: Binary Fission: An organism is divided into two individuals. Mitotic division takes place resulting in two identical individuals or daughter cells. e.g., Amoeba.
Multiple Fission: Mitotic division takes place. The nucleus divides repeatedly to form a number of equal sized and similar individuals, e.g., Plasmodium.

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 because:
1. Their body design is highly complicated.
2. There are specific organs to do specific functions.
3. There is a labour division in the body of complex organisms.
4. Exception is lizard, which can regenerate its tail.

Question: Why is DNA copying an essential part of the process of reproduction?
Answer:  DNA copying is needed because information stored in DNA is used to make protein.
Synthesis of different proteins will lead to altered body design. Thus, reproduction at its most basic level involves making copies of the blueprints of body design.

Question: Name the causative organism of the disease “Kalaazar”and its mode of asexual reproduction.
Answer: Leishmania, Binary fission.

Question: Regeneration is not possible in all types of animals.Why?
Answer: Regeneration is carried by specialised cells. The organisms which have those cells only can show regeneration.

TWO MARKS QUESTIONS

Question: “The chromosomal number of the sexually producing parents and their offspring is the same.” Justify this statement.
Answer: a. DNA copying is essential for formation of addition cellular apparatus, so that when DNA copies separate, each cell gets its own cellular apparatus.
b. The process of DNA copying results in variation each time. As a result, the DNA copies generated will be similar, but may not be identical to the original.

Question: State the importance of chromosomal difference between sperms and eggs of humans.
Answer: Eggs always contain same type of sex chromosomes (both X). Sperms contain X or Y sex chromosomes.
Thus, sperm containing X chromosome when combines with X chromosome of egg results in a female child.
Whereas sperm containing Y chromosome when combines with X chromosome of egg results in a male child.

Question: Why is vegetative propagation practised for growing Download more materials in free at : some types of plants?
or
Why is vegetative propagation practiced for growing some types of plant? List two plants which are grown by this method.
Answer: Advantages of vegetative propagation:
a. The plants bear flowers and fruits earlier than those propagated sexually.
b. Plants have lost capacity to form seeds hence they are propagated vegetatively. Such plants are genetically similar to parent plants and have all their characters.

Question: Why do we need to adopt contraceptive measures?
Answer: a. Contraceptive measures are needed to be adopted to prevent unwanted pregnancies.
b. To prevent sexually transmitted diseases.
c. Spacing between children.
d. For sound health of a mother.

Question: Draw labelled diagrams to illustrate budding in Hydra.
Answer: a. In sexual reproduction, fusion of male and female gametes takes place, these germ-cells/gametes contain half the number of chromosomes and by the fusion of these gametes the zygote is formed with full set of chromosomes.
b. When male and female gametes fuse at the time of fertilization, it restores the original number  of chromosomes (of the parent), ensuring the stability of species.

Question: ‘Regeneration is not reproduction’. Justify this statement with reason.
Answer: When a piece is cut from an organism, it grows into complete organisms. Regeneration is carried out by specialized cells. It is not reproduction since most organisms would not be able to grow through pieces.

Question: Give reasons as to why the following processes are different from each other:
a. Fission in Amoeba and Plasmodium .
b. Binary fission and Fragmentation.
Answer: a. In Amoeba during binary fission the cell divides into two daughter cells while in Plasmodium multiple fission occurs, where the cell divides into many daughter cells. 
b. In binary fission, a cell divides into two daughter cells while in fragmentation, the body of a multicellular organisms divides into two or more Download more materials in free at : parts which grow further.

Question: a.List any two methods of asexual reproduction.
b. Explain how Spirogyra reproduces.
Answer: a. (i) Budding in Hydra and Yeast.
(ii) Spore formation in Fungi.
b. Spirogyra breaks up into smaller pieces upon maturation. These fragments grow into new individuals

THREE MARKS QUESTIONS

Question: What are sexually transmitted diseases? Name four such diseases. Which one of them damages the immune system of human body?
Answer: Sexually Transmitted Diseases (STDs) are the diseases which are spread by sexual contact from an infected person to a healthy person. They are caused by various microorganisms that live in warm and moist environments of the vagina, urethra, anus and mouth.
The four sexually transmitted diseases are:
(i) Gonorrhoea
(ii) Syphilis
(iii) Trichomoniasis
(iv) AIDS (Acquired Immune Deficiency Syndrome).
AIDS damages the immune system of human body.

Question: (a) Explain the terms: (i) Implantation (ii) Placenta
(b) What is the average duration of human pregnancy?
Answer: (a) (i) Implantation: The embedding of a fertilised mammalian egg (embryo) into the inner thick wall of the uterus (womb) where it will continue its development is called implantation.
(ii) Placenta: It is a complex double-layered spongy vascular tissue in human female formed by the joint activity of maternal and foetal tissues in the wall of uterus that is meant for attachment, nourishment and waste disposal for the foetus.
(b) The average duration of human pregnancy is 40 weeks or 280 days.

Question: Justify the following statements:
a. Variation is beneficial for the species over a period of time.
b. New offsprings produced are similar to their parents but not identical.
c. Binary fission is different in Amoeba and Leishmania.
Answer: a. Variations help a population in the process of natural selection and accumulation of adaptations in a population. It leads to evolution of a species.
b. Offspring, especially when produced sexually, have minor differences or variations among themselves hence they may not look identical. By virtue of them being from same species they look similar.
c. Binary fission in Amoeba is in any plane but in Leishmania it is in a fixed plane.

Question: What is the effect of DNA copying, which is not perfectly ccurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer: a. DNA copying leads to more variations in the offspring.
b. Sexually reproducing organisms have special lineage of cells which have only half the number of chromosomes as the parent cell.
c. When such germ cells fused, a new individual is formed with the same amount of DNA as that of parent.

Question: DNA content has the tendency to double itself during sexual reproduction due to combining of the genetic materials from the two parents. How the problem of DNA doubling can be solved to maintain the consistency of the genetic material throughout the species?
                                                            or“
The chromosome number of the sexually reproducing parents and their offsprings is the same”. Justify the statement.
Answer: DNA doubling is always followed by cell division. Due to this special cell division, gametes form with half the content of DNA and single set of chromosomes. These gamete fuse to form zygote on fertilization. Thus the characteristic number of chromosome and the normal DNA content for a cell is regained.
Thus the consistency of the genetic material throughout the species is maintained and for the same reason the chromosome number of the sexually reproducing parents and their offsprings is the same.

Question: A part of the male reproductive system is shown below. Study the diagram and answer the questions that follow.
a. Two part have been incorrectly labelled. Identify them.
b. Give the function of urethra.
c. Which hormone is released by testis?
Answer: a. Testis, penis.
b. Urethra serves as a common passage for both sperms and urine.
c. Testosterone.

Question: (a) Explain the role of placenta in the development of human embryo.
(b) Give example of two bacterial and two viral sexually transmitted diseases. Name the most effective contraceptive which prevents spread of such diseases.
Answer: (a) Role of placenta in the development of human embryo: A special tissue develops between the uterine wall and the embryo (foetus) called placenta, where exchange of nutrients, glucose and oxygen takes place. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta. The development of the child inside the mother’s blood takes approximately nine months.
(b) Sexually transmitted diseases (STDs) transmitted by bacteria are:
(i) Gonorrhoea (ii) Syphilis
STDs transmitted by virus:
(i) AIDS (ii) Genital warts
The most effective contraceptive which prevents the spread of these diseases is by the use of mechanical barriers such as physical devices like condoms.

Question: What is AIDS? Which microbe is responsible for AIDS infection? State one mode of transmission of this disease. Explain in brief one measure for the prevention of AIDS.
Answer: AIDS is the Acquired Immune Deficiency Syndrome.
It is caused by a virus called Human Immunodeficiency Virus.
AIDS is transmitted by sexual contact with an infected person.
AIDS can be prevented by avoiding sexual contact with infected person or by using condom during sex.

Question: Mention one function each of the following parts with respect to the female reproductive system:
a. Vagina
b. Ovary
Answer: a. The uterus open into vagina through the cervix.The sperms enter through the vaginal passage during sexual intercourse.
b. One egg (female gamete) is produced every month by one of the ovaries.

Question: What happens when:
a. APlanaria is cut into three different pieces,
b. Leaf of the Bryophyllum with notches fall on the soil.
c. Testosterone is released in the male reproductive system.
Answer: a. Three new Planaria will form due to regeneration.
b. New plantlets will form from these buds helping the plant to propagate vegetatively.
c. The male shows masculine features and attains fertility. Sperm starts forming in testis.

Question: List any four reasons for vegetative propagation being practised in the growth of some type of plants.
Answer:
(i) Vegetative propagation is a cheaper, easier and more rapid method of propagation in plants than growing plants from their seeds.
(ii) Better quality of plants can be maintained by this method.
(iii) It results in propagation of those plants which do not produce viable seeds or produce seeds with prolonged period of dormancy.
(iv) The plants generated from vegetative means are more uniform and genetically similar to the parent stock.

Question: Differentiate between the following:
a. Placenta and uterus
b. Unisexual and bisexual flowers
c. Fertilization and germination
Answer: a. Placenta and uterus : The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta.
After fertilization, embryo gets attached to the walls of uterus.
b. Unisexual flowers contain either stamens or carpels. Bisexual flowers contain both stamens and carpels.
c. Fertilization and germination : The fusion of male gamete with female gamete leading to the formation of zygote is known as fertilization.
The growth of embryo (present in the seed) into seedling under appropriate conditions is known as germination.

Question: List and explain in brief three methods of contraception.
                                             or
List any four methods of contraception. How are they helpful to young couples?
Answer: Four methods of contraception:
a. Condoms
b. Copper-T
c. Diaphragm
d. Oral pills
All these help in family planning as it helps in keeping gap between two children. They help in proper utilization of family resources.

FIVE MARKS QUESTIONS

Question: Define the following processes:
a. Fertilization
b. Menstruation
c. Binary fission
d. Vegetative propagation
e. Regeneration
Answer: a. The fusion of male gamete with female gamete is known as fertilization.
b. Menstruation cycle takes place every month when egg is not fertilized. It lasts for about two to eight days and during this cycle the lining of uterus slowly breaks and comes out through the vagina as blood and mucus.
c. Binary fission is the splitting of nucleus into two daughter cells which can take place in any plane. It can be observed in Amoeba.
d. When vegetative part of a plant like the root, stem or leaves develops into new plant under appropriate conditions, it is known as vegetative propagation.
e. When body of an organism cuts into any number of pieces and each piece grows into a complete organism. This is known as regeneration. Hydra and Planaria reproduce through this process.

Question: List six specific characteristics of sexual reproduction.
Answer: Characteristics:
Two parents are involved,
Two dissimilar gametes are formed, gamete formation involves meiosis,Variations are produced, Occurs in all the higher and some of the lower organisms, Fertilization/fusion of gametes leading to zygote formation Slow.

Question: (A) Write the functions of the following parts in human female reproductive system:
(i) Ovary
(ii) Oviduct
(iii) Uterus
(B) Describe the structure and function of placenta.

Answer: (A) (i) Ovary → They produce egg for fertilisation.
→ Produce the reproductive harmones (Oestrogen & Progesterone).
(ii) Oviduct → It transfer the female gamete (egg) from the ovary.
→ It is the site of fertilization.
(iii) Uterus → Implantation of the zygote.
→ Nourishment of developing embryo.
→ Helps in placenta development.
(B) Structure of Placenta: Placenta is a special tissue connection between embryo and uterine wall. It acts as an endorine gland.
Functions of Placenta:
(i) It possess Villi that increase the surface area for absorption of nutrients.
(ii) Waste substances produced by embryo are removed through placenta into mother’s blood.
(iii) Facilitate passage of nutrition and oxygen to embryo from mother through blood.

Question: (A) Describe the role of prostate gland,seminal vesicle and testes in the human male reproductive system.
(B) How is the surgical removal of unwanted pregnancies misused?
(C) Explain the role of oral contraceptive pills in preventing conception.
Answer:
(A) Prostate glands and seminal vesicle : add their secretions so that the sperms are in a fluid and it makes their transport easier and also provides nutrition.Testes secrete testosterone which brings about changes in the appearances in the boys at the time of puberty.
(B) Female foeticides/illegal sex selected abortion of female foeticide.
(C) Interfere in release of egg and eggs are not released.

Question: (A) Define vegetative propagation. List its two methods.
(B) Why is this mode practised for growing some types of plants?
(C) Explain the process of budding in Hydra with the help of labelled diagrams.
Answer: (A) Vegetative propagation is a method of asexual reproduction in some higher plants in which a new plant develops from the vegetative parts of a plant such as root,stem or leaf.
Two methods are:
(1) From root as in Dahlia, sweet potato.
(2) From stem as in ginger, potato, onion.
(3) From leaf as in Bryophyllum
(4) Cutting as in grapes.
(5) Layering as in guava
(6) Grafting as in lemon

Question: What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Answer: Chromosomes: thread like structures made up of DNA found in the nucleus.
The original number of chromosomes becomes half during gamete formation.
Hence, when the gametes combine, the original number of chromosomes gets restored in the progeny. (or same thing explained in the form of a flow chart).

Question: (A) Write the functions of the following parts of the human male reproductive system:
(i) Testis (ii) Vas deferens (iii) Urethra (iv) Prostate
(B) List any two common pubertal changes that appear in human males. 
Answer: (A) The functions of the various parts of the human male reproductive system are given below:
(1) Testis: The formation of germ-cells or sperms takes place in the testes.
It secretes the male hormone, called testosterone, which regulates the formation of sperms and brings about changes in appearance in boys at puberty.
(2) Vas deferens: It is a long tube which arises from each testes and carries sperms into organs called seminal
vesicles, where the sperms get nourished and stored.
(3) Urethra: It is a common passage for both urine and spermatic fluid. The vas deferens unites with a duct coming from the urinary bladder to form urethra.
(4) Prostate: It is a gland that secretes an alkaline fluid which gives lubrication and nutrition for the sperm.
(B) Common pubertal changes appearing in human males:
(1) Growth of thicker hair in armpits and genital area between the thighs.
(2) Growth of thinner hair on legs and arms.
(3) Skin becomes oily and pimples develop.
(4) There is thick hair growth on the face.
(5) Cracking of voice.
(6) Penis occasionally gets erect and enlarged.

Question: a. Write the function of following parts in human
female reproductive system: (i) Ovary (ii) Oviduct (iii) Uterus
b. Describe in brief the structure and function of placenta.
                                               or
Write the functions of the following in human female reproductive system: Ovary, oviduct, uterus How does the embryo get nourishment inside the mother’s body? Explain in brief.
Answer: a. Functions of Ovary, oviduct, uterus Functions of Ovary
(i) Production of female hormone, oestrogen and progesterone.
(ii) Production of female gamete / egg /germ cell.
Functions of Oviduct:
(i) Transfer of female gamete from the ovary.
(ii) Site of fertilization.
Functions of Uterus:
(i) Implantation of Zygote/ embryo.
(ii) Nourishment of developing embryo.
b. Placenta is a special disc like tissue embedded in the mother’s uterine wall and connected to the foetus / embryo.
Placenta provides a large surface area for glucose and oxygen/nutrients to pass from the mother’s blood to the embryo/ foetus.