CBSE Class 10 Biology How Do Organisms Reproduce Worksheet Set J

Very Short Answer Type Questions :

Question. List two functions of ovary of human female reproductive system.
Answer: Two functions of Ovary:
(i) To produce female gamete / ovum.
(ii) To secrete female hormones / estrogen and progesterone.

Question. List two unisexual flowers.
Answer: Watermelon, papaya.

Question. Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual type of reproduction?
Answer: Fragmentation, Asexual → Single parent involved.
                           ↓ 
Breaking into 2 or more fragments

Question. Give reason for the statement— Since the ovary releases one egg every month, the uterus also prepares itself every month by making its lining thick and spongy.
Answer: It is required for nourishing the embryo if fertilization takes place and reaches the uterus.

 Question. Why is fertilization not possible without pollination?
Answer: Pollination allows pollen grains that produce male germ cell to reach the carpel which contain the female germ cell, egg.
Thus, fertilization which involves fusion of male and female germ cells can only occur after pollination.

Question. Newly formed DNA copies may not be identical at times. Give one reason. 
Answer: If there is an error in DNA copying or mutation, then newly formed DNA copies may not be identical at time.

Question. In the human female reproductive system where does fertilization occur?
Answer: Oviduct or Fallopian tube.

Question. What are those organisms called which bear both the sex organs in the same individual? Give one example of such organism.
Answer: Bisexual; For e.g., Hydra/Earthworm/Mustard/ Hibiscus.

Short Answer Type Questions :

Question. What happens when:
(a) Accidently, Planaria gets cut into many pieces?
(b) Bryophyllum leaf falls on the wet soil?
(c) On maturation sporangia of Rhizopus bursts?
Answer: (a) Each piece regenerates into new Planaria. 
(b) Buds called leaf buds at its notches develop into new plants. 
(c) It releases spores which germinate into new mycelium in moist conditions.

Question. How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations?
Explain with the help of suitable example.
Answer: (i) When organisms reproduce asexually, only mitotic divisions are involved and the chromosome number remains the same. 
(ii) During asexual reproduction, the DNA (in the chromosomes) or the cells involved are copied and then equally divided among the two daughter cells.
Thus, chromosome number remains unchanged. 
(iii) In sexual reproduction, organisms produce gametes through a special type of division called meiosis or reductional division, in which the original number of chromosomes is reduced to half.
These two male & female gametes fuse to form the zygote and the original number of chromosomes is restored.
(iv) In sexual reproduction, specialized cells / germ cells with only half the number of chromosomes are formed. When these germ cells from two individuals combine to form a new individual, the original chromosome number is restored. 
(v) Example: In humans, the parents (father and mother) each have 46 or 23 pairs of chromosomes.
In the gametes, the sperm has half the number of chromosomes i.e., 23 and the egg also has 23 chromosomes. When the sperm and the egg fuse, the zygote has 46 or 23 pairs of chromosomes.
Thus, the chromosome number remains constant.

Question. What is multiple fission? How does it occur in an organism? Explain briefly. Name one organism which exhibits this type of reproduction.
Answer: Multiple fission: The process of reproduction in which many individuals are formed or produced from the parent cell. 
In this process, the nucleus divides repeatedly to produce large number of nuclei. Each nucleus gathers a bit of cytoplasm around itself, develops a membrane around each structure.
Many daughter cells develop which on liberation grow into adult organism.
Plasmodium exhibits this type of fission.

Question. Explain the term “Regeneration” as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra. 
Answer: Regeneration: It is the ability of an organism to give rise to a new organism/individual from their body parts. 
Regeneration in Hydra:
(i) The body of Hydra by any means is cut into number of pieces. 
(ii) Each piece contains specialized cells. 
(iii) These cells, proliferate and make large number of cells. 
(iv) From this mass of cells, different cells undergo changes to become various cell types and tissues, which finally develops into a new organism.

Question. State the changes that take place in the uterus when:
(i) Implantation of embryo has occurred.
(ii) Female gamete/egg is not fertilised.
Answer: (a) When implantation of embryo has occurred, the uterine wall thickens and is richly supplied with blood to nourish the growing embryo. 
(b) The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.

Question. Write the functions of the following parts of human female reproductive system:
(i) Ovary, (ii) Fallopian tube (iii) Uterus.
Answer: (i) Ovary: Produces egg or female gamete, female sex hormone/ estrogen and progesterone.
(ii) Fallopian tube: Transfer of ovum to the uterus, site for fertilization 
(iii) Uterus: Site of implantation of zygote, development of embryo.

Question. Define reproduction. How does it help in providing stability to the population of species? 
Answer: Reproduction: It is a (biological) process by which new individuals of the same species are produced by the existing organisms. 
(i) Populations of organisms live in well-defined places called niches in the ecosystem using their ability to reproduce. 
(ii) Reproduction involves DNA copying which is the source of information for making proteins thereby controlling body design. 
(iii) These body designs allow the organism to use a particular niche for the stability of the population of a species.
(iv) (Minor) variations may also lead to the stability of the species.

Question. Distinguish between pollination and fertilisation.
Mention the site and the product of fertilisation in a flower.
Answer: Pollination: Transfer of pollen grains from stamen/anther to stigma. 
Fertilization: Fusion of male & female gamete (or germ cells) 
Site of fertilisation: Ovary/ Ovule 
Product: Zygote.

Question. What is carpel? Write the function of its various parts.
Answer: Female reproductive part of the plant. 
(i) Stigma: Receive pollen grains
(ii) Style: Passage for the growth of pollen tube
(iii) Ovary: Site for fertilization 

Question. What is sexual reproduction? List its four significance.
Answer: Two major processes namely formation of gametes and fusion of gametes constitute sexual reproduction. 
Significance–(i) Incorporates the process of combining DNA from two different individuals during reproduction.
(ii) Increases genetic variation.
(iii) Promotes diversity in the offsprings.
(iv) Plays a role in the origin of new species.

Question. Name the reproductive parts of an angiosperm.
Where are these parts located? Explain in brief the structure of its female reproductive parts.
Answer: (i) Stamen and Carpel.
(ii) Located in the flower. 
(iii) The female reproductive part is Carpel. It is made up of three parts–the bottom swollen part is ovary, middle elongated part is the style, terminal sticky part is stigma.

Question. Define the term pollination. Differentiate between self pollination and cross pollination.
What is the significance of pollination?
Answer: The transfer of pollen grains from the anther to the stigma of a flower is known as pollination.
The two types of pollination are:
(a) Self pollination: When the pollen grains from the stamens of a flower fall on the stigma of the same flower, then it is called self pollination.
(b) Cross pollination: When pollen grains from the stamens of a flower fall on the stigma of another flower, it is called cross pollination.
Significance of pollination:
(i) It is a significant event because it precedes fertilization.
(ii) It brings the male and female gametes closer for the process of fertilization.
(iii) Cross-pollination introduces variations in plants because of the mixing of different genes. These variations further increase the adaptability of plants towards the environment or surroundings.

Question. Name the two types of mammalian gametes. How are these different from each other? Name the type of reproduction they are involved in. Write the advantage of this type of reproduction.
Answer: Male gamete: sperm 
Female gamete: ovum/egg 
Sperms are motile and produced by male individual, ova/eggs are non-motile and produced by female individual. 
Type of reproduction is Sexual reproduction 
Advantage: Generates more variations

Question. What is reproduction? Explain two advantages of sexual reproduction over asexual reproduction.
Answer: Reproduction: It is a (biological) process by which new individuals of the same species are produced by the existing organisms.
Advantages of sexual reproduction:
(i) Leads to stability of population of species. 
(ii) Results in variations useful for the survival of species over time.

Question. Mention the total number of chromosomes along with the sex chromosomes that are present in a human female and a human male. Explain how in sexually producing organisms the number of chromosomes in the progeny remains the same as that of the parents.
Answer: Total number of chromosomes is 46. In human male, two sex chromosomes i.e., X or Y are present, while in human female, both sex chromosomes are X.
During sexual reproduction, a female gamete or egg cell fuses with a male gamete or sperm cell which are haploid to form zygote. Zygote is diploid (2n) which contains 46 chromosomes, 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

Question. State briefly the changes that take place in a fertilized egg till birth of the child in the human female reproductive system. What happens to the egg when it is not fertilized?
Answer: Changes in fertilized egg:
(a) Zygote/fertilized egg starts dividing.
(b) Implantation of zygote in the inner uterine wall.
(c) Embryo starts growing with the help of the placenta which results in the development of the child.
(d) Birth of a child as a result of rhythmic contraction of the muscles in the uterus. 
When egg is not fertilized, the inner lining of the uterus slowly breaks and comes out through the vagina as blood and mucous (Menstruation)

Question. What is vegetative propagation? State two advantages and two disadvantages of this method.
Answer: Vegetative propagation is a mode of asexual reproduction in which new plants are formed from roots, stems, leaves and buds of the individual vegetative parts of the plants. e.g., eyes of potato. 
Advantages:
(i) Offsprings are genetically identical and therefore useful traits can be preserved. 
(ii) It is a rapid and economical method. 
Disadvantages:
(i) New characters cannot be introduced. 
(ii) The disease of the parent plant gets transferred to the offsprings.

Question. (a) Mention the role of the following organs of human male reproductive system:
(i) Testis; (ii) Scrotum; (iii) Vas deferens;
(iv) Prostate glands.
(b) What are the two roles of testosterone?
Answer: (a) (i) Testis: To produce male gametes / sperm or male hormone / testosterone.
(ii) Scrotum: To provide optimal temperature to testis for the formation of sperms.
(iii) Vas deferens: To deliver the sperms to the urinary bladder.
(iv) Prostrate glands: To secrete the fluid which provides nutrition and medium for transport of sperms.
(b) (i) Regulates formation of sperms, (ii) Brings about the changes in boys during adolescence.

Question. What is placenta? Write any two major functions of placenta
Answer: Placenta: A disc shaped organ or special tissue in the uterus of pregnant mammal, nourishing and maintaining the foetus through the umbilical cord.
Functions of Placenta:
(i) Provides large surface area for glucose and oxygen to pass from mother to the embryo.
(ii) Removal of waste generated in the developing embryo into the mother‘s blood.

Question. State the basic requirement for sexual reproduction? Write the importance of such reproductions in nature.
Answer: Formation of male and female gametes, fusion of gametes/syngamy. In Sexual reproduction, new individual is formed. 
Importance: Combination of DNA from two different individuals lead to increase in genetic variation in the organism. 
This leads to diversity in the population which helps in natural selection.

Question. What are the functions of testis in the human male reproductive system? Why are these located outside the abdominal cavity? Who is responsible for bringing about changes in appearance seen in boys at the time of puberty?
Answer: Functions of testis:
(i) Produce sperms.
(ii) Produces male hormone/ testosterone. 
These are located outside the human body, as sperms need lower temperature than the normal body temperature to mature. 
Testosterone.

 Question. What is contraception? Name any two methods.
How does the use of these methods have a direct effect on the health and prosperity of a family?
Answer: (i) Contraception: Any method which prevents conception/ pregnancy is called contraception. 
(ii) Barrier Method, Chemical Method, Surgical Method. 
(iii) Health of women (mother) is maintained, Parents can give more attention to their children/ family, More resources may be made available for improvement of standard of living. (or any other relevant point)

Long Answer Type Questions :

Question. (a) Write the functions of following parts in human female reproduction system:
(i) Ovary, (ii) Oviduct, (iii) Uterus
(b) Describe in brief the structure and function of placenta. 
Answer: (a) (i) Ovary: Releases egg / female gamete/ovum, Releases oestrogen/female hormones.
(ii) Oviduct: Transportation of ovum/egg/ from ovary to the uterus/Site of fertilization.
(iii) Uterus: Development of embryo/foetus.
(b) Placenta: It is disc like tissue embedded in uterine wall which contains villi on the embryo side of the tissue and blood space on mother side.
Function of placenta: Provides nourishment to embryo from mother’s blood / Removal of waste from embryo to mother’s blood.

Question. (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions.
(b) Name the parts of the human female reproductive system where fertilisation occurs.
(c) Explain how the embryo gets nourishment inside the mother’s body. 
Answer: (a) Testes 
Testosterone 
Functions of Testosterone:
(i) Formation of sperms
(ii) Development of secondary sexual
characters 
(b) Fallopian Tubes/Oviduct
(c) Placenta, a special disc-like tissue embedded in the mother’s uterine wall and is 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 developing embryo/foetus.

Question. (a) Suggest any two categories of contraceptive methods to control the size of human population which is essential for the prosperity of a country.
Also explain about each method briefly.
(b) Name two bacterial and two viral infections each that can get sexually transmitted.
(c) List two advantages of using condom during sexual act. 
Answer: (a) Methods of contraception:
(i) Barrier method or mechanical method/ Condom/ Diaphragm, to prevent the meeting of sperms and ova.
(ii) Chemical method/ Oral pills: Changes the hormonal balance of the female partner so that the eggs are not released.
(iii) Surgical method: To block the vas deferens in males/ vasectomy or the fallopian tube (oviduct) in females/ tubectomy, to prevent the transfer of sperms or egg and hence no fertilization takes place.
(b) Bacterial infections: Syphilis and Gonorrhea Viral infections: Human papilloma virus (HPV), HIV
(c) (i) Prevents meeting of sperm and ova
(ii) Protects against sexually transmitted diseases

Question. What is sexual reproduction? Explain how this mode of reproduction give rise to more viable variations than asexual reproduction? How does this affect the evolution?
Answer: When male and female organisms are involved in producing young ones, is known as sexual reproduction / Gametes from two organisms of opposite sex must fuse to produce young ones. 
Gametes (germs cells) produced are the products of meiosis / due to combining of DNA from two individuals, this results in mixing of characters and causes variations. 
In asexual reproduction, single parent produces young ones. There is no mixing of characters.
More variations help in the process of evolution.
Helpful variations accumulate over time and produce new species and result in evolution.