NCERT Solutions for HOW DO ORGANISMS REPRODUCE of Class 10 Science
Question 1.What is the importance of DNA copying reproduction? Solution
Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprint for these designs should be similar. Thus, reproduction its most basic level will involve making copies of the blueprints of body design.
Question 2.Why is variation beneficial to the special but not necessarily for the individual? Solution
The DNA copies generating in a reproducing copies are similar, but may not be identical to the original. Some of these variations in the DNA copies do not lead drastic outcomes. These surviving cells are similar but substances different from each other. This inbuilt tendency is variation during reproduction cause to develop new species. So, variations are beneficial to the species but not necessarily for the individual. Question 3.How does binary fission differ from multiple fission? Solution Binary fission: Some unicellular organisms split into two halves to create two new individuals. This is called binary fission. Example: many bacteria and protozoa such as amoeba. Multiple fission: Some unicellular organisms like malarial parasite (plasmodium) divide into many daughter cells to form many new individuals. This process of fission is called multiple fission. Question 4.How will an organism be benefited if it reproduces through spores? Solution
The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow. Thus, it is benefited for the organisms like rhizopus to reproduces through spores. Question 5.Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration? Solution
ore complex organisms cannot reproduce by regeneration process because:
(i) Their body is highly complicated.
(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 specialized cells, which are not present in complex organisms. Question 6.Why is vegetative propagation practiced for growing some types of plants? Solution
Some plants bear no seeds. This method makes possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds. Vegetative propagation takes place only in those plants whose parts like root, stem and leaves have the property of propagation. By this process, we can reproduce the plants having more similar characteristics. Question 7.Why is DNA copying an essential part of the process of reproduction? Solution
DNA copying is a basic event in reproduction. Two copies are built in reproducing cells. These two copies need to separate from each others. One copy of DNA remains in the original cell and other copy need to have any organized cellular structure for maintaining life processes. So, DNA copying is accomplished by creation of an additional cellular structure. In this way, two copies are separated and two new cells are formed. Question 8.How is the process of pollination different from fertilization? Solution
Pollination: The process in which pollen grains are transferred from anther to the stigma of the flower is called pollination .In this process, no fusion of two cells takes place.
Fertilization: The process in which fusion of two cells (one male and other female) takes place to form zygote called fertilization. Question 9.What is the role of the seminal vesicles and the prostate gland? Solution The male reproductive system contains some gland like seinal vesicle and prostate gland. These glands are their secretions so that sperms remain a fluid. This fluid makes the transport of sperms easier. It also provides nutrition to the sperms. Question 10.What are the changes seen in girls at the time of puberty? Solution
(i) Breast size begins to increase.
(ii) The skin of nipples at the tip of the breast become dark.
(iii) Menstruation starts at this time. Question 11.How does the embryo get nourishment inside the mother’s body? Solution
After fertilization, zygote is formed which developed into embryo. The embryo is attached with uterus walls. This process is called implantation. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side there are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. In this way, embryo gets its nutrition. Question 12.If a woman is using a copper – T will it help in protecting her from sexually transmitted diseases? Solution
No, copper – T will not help in protecting her from sexually transmitted diseases. Question 13.What are the advantages of sexual reproduction over asexual reproduction? Solution
(i) Sexual reproduction promotes diversity.
(ii) It results in new combination of genes, i. e. causes genetic variations.
(iii) it plays a prominent role in the origin of new species. Question 14.What are the functions preformed by the testis in human beings? Solution
Testis is the main reproductive organ of male reproductive system. There are two testis located outside the abdominal cavity in scrotum. Scrotum lowers the temperature than the normal body temperature to activate the testis. Testis produce the germ cells or sperm. The sperms are the tiny bodies that consist of mainly genetic material and a long tail which helps them to move towards the female germ cell Question 15.Why does menstruation occur? Solution
If the egg is not fertilized, then it is lost after one day. The uterus prepares itself to receive a fertilized egg. The lining of uterus becomes thick and spongy. These lining slowly breaks and comes out through vagina as blood and mucous. This process is called menstruation. So, it takes place when no fertilization of egg takes place.
Question 16.What are the different methods of contraception? Solution there are various methods of contraception:
(i) Barriers: It prevents the sperm to reach near the egg. For example, condoms on the penis or similar coverings worn in the vagina can used for this purpose.
Intra uterine devices such as copper – T are also popular. However, they can cause side effects due to irritation of the uterus. It prevents implantation of embryo.
(ii) Chemicals: There are various chemicals or the pills which act by changing the hormonal balance of the body so that eggs are not released and fertilization cannot occur.
(iii) Surgical: If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, transfer of egg is prevented and no fertilization takes place. Question 17.How are the modes for reproduction different in unicellular and multicellular organisms? Solution
The unicellular organisms have only one cell. There are no separate tissues for reproduction. So, they can be reproducing by the process of fission (binary or multiple) or budding as in yeast.
The multicellular organisms contains various cells and separate systems, so they can reproduce by both sexual and asexual reproduction. Question 18.How does reproduction help in providing stability to population of species? Solution Population of organisms fill well defined places or niches in the ecosystem using their ability to produce. The rate of birth must be at par with the rate of death to provide stability to population of a species. And it is possible only by reproduction. Further, the consistency of DNA copying during reproduction is important for the maintenance body design features that allow the organism to use the particular niche. Reproduction is therefore linked to the stability of population of species. Question 19.What could be the reasons for adopting contraceptive methods? Solution Reproduction is the process by which organisms increase their population. But the size of the human population is a cause for concern for many people. This is because an expanding population makes it hard to improve everybody’s standard of living. It is the main reason for poor standards of living for many people. So balance the size of population, contraceptive methods adopted. Question 20.What name is given to primary sex organ? Solution
Gonads. Question 21.Name the male and female gonads. Solution Male gonads: Testis
Female gonads: Ovary. Question 22.What are the various parts of a carpel? Solution
(iii) Ovary. Question 23.Why do organisms reproduce? Solution
Reproduction is necessary to ensure the exist of any species. Question 24.Are the two cells formed in reproduction are identical? Solution The two cells are identical or not it depends on the copying reactions. No biochemical reaction is absolutely reliable. So, there are some variations in the copying of the DNA each time. SAs a result the DNA copies generated will the similar, but not be identical to the original. Thus, surviving cells are like, but subtly different from each other. Question 25.List the advantages of sexual reproduction. Solution Sexual reproduction has many advantages, for example:
1. There is always a possibility of diversity of characters in the offspring because the offspring is formed as a result of fusion of two gametes produced by two different individuals – the male and the female parents.
2. There is every opportunity for new combinations of characters.
3. It leads to variation which is so essential for evolution and the origin of new species. Question 26.How do the following organisms reproduce by asexual methods?
(a) Euglena(b) Spirogyra
(c) Ginger(d) Chrysanthemum
(e) Strawberry (f) Mango Solution (a) Euglena – Binary fission.
(b) Spirogyra – Regeneration.
(c) Ginger – Natural vegetative propagation by stems.
(d) Chrysanthemum – Artificial vegetative propagation by cutting.
(e) Strawberry – Artificial vegetative propagation by layering.
(f) Mango – Artificial vegetative propagation by grafting.
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