NCERT Solutions for Class 10 Science Chapter 8

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NCERT Solutions for Class 10 Science Chapter 8

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Important Questions with Answers From Board Papers

How do Organisms Reproduce?

Question 1:
What is the importance of DNA copying in reproduction?
Answer 1:
DNA found in chromosomes in the nucleus of the cell has the information to create proteins which lead to body design of an organisms. If the organisms are to make exact copies of themselves, the DNA should replicate to make an exact copy of itself. DNA replicate in the cell with the help of various enzymes and this is accompanied by division of the basic unit of every organism, i.e., the cell.

Question 2:
What are sexually transmitted diseases? Name an STD which damages the immune system of human body.
Answer 2:
The sexually act is very intimate connection of bodies and thus many diseases can be sexually transmitted. These include bacterial infections like gonorrhoea and syphilis and viral infection like warts and HIV-AIDS (Human Immunodeficiency Virus-Acquired Immuno Deficiency Syndrome). HIV-AIDS causes damages to the immune system of human body.

Question 3:
Why is variation beneficial to the species but not necessarily for the individual?
Answer 3:
Variations are useful for the survival of species in changed environmental situations. For example, if a population of reproducing organisms were suited to a particular niche (well defined place of abode) and if the niche is drastically changed, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, if there is a population of bacteria living in temperate waters and if water temperature increases by global warming, most of bacteria would die. But few a variants resistant to heat would survive and grow further. Variation is thus useful for the survival of species over time.

Question 4:
What are the three categories of contraception methods? Write briefly about each.
Answer 4:
The methods used for regulation of child birth are:
(i) Barrier method: In this method physical devices like condoms, cervical cap and diaphragm are used to prevent sperms to reach up to the ovum.
(ii) Chemical method: In this method specific drugs are used by females. These drugs may be (a) oral pills or (b) vaginal pills. Oral pills mainly contains hormones and are called oral contraceptives. They disturb hormonal balance so that eggs are not released and fertilised.
(iii) Intrauterine contraceptive devices (IUCDs): ICUD like copper-T is placed safely in the uterus by skill doctor. ICUDs prevents implantation of the fertilized ovum inside the uterus.
(iv) Surgical method: this method is applicable to both male and female. In males, a small portion of vas deferens and the fallopian tube in female is surgically removed or ligated (tied). It is known as vasectomy in males which prevents release of sperms from the testes. In females, it is called tubectomy.

More Questions for Exams

Question 1:
“Multicellular organisms cannot divide cell by cell.” List two reasons to justify this statement.
Answer 1:
Multi cellular organisms cannot simply divide cell by cell because:
(i) Many multi cellular organism are not simply a random collection of cells. Specialised cell are organised as tissues and tissues are organised into organs which are placed at a definite position in the body.
(ii) Each organ performs a specific function/functions.
In such a carefully organised situation, cell by cell division (for reproduction) would be impracticable.

Question 2:
Describe menstrual cycle.
Answer 2:
The uterus develops thick and spongy lining to receive fertilised egg. When the egg is not fertilised, uterine lining slowly break and comes out as blood and mucous. This cycle takes place roughly every month and is known as menstrual cycle (menstruation).

Question 3:
Name the plant that reproduces through leaves. List two advantages of this way of reproduction.
Answer 3:
Bryophyllum
Advantages:
(i) Many buds are produced in the notches along the margin of a single leaf. Each leaf-bud of Bryophyllum produces a plant.
(ii) The plants from the buds are exactly similar to the parent plant.
(iii) A large number of young plants are produced by a single leaf of a plant that helps in survival of the species.

Question 4:
Give functions of the following organs of the human male reproductive system.
(a) Scrotum (b) Testes
Answer 4:
(a) Testes are placed in scrotum which are located outside the abdominal cavity. It keeps the temperature lower than the normal body temperature that is required for the formation of sperm.
(b) Testes produce sperm and male hormone testosterone.

Questions for March 2018-19 Exams

Question 1:
Define the process of fragmentation in some organisms. Which category of organisms are involved in this process? Give one example.
Answer 1:
Fragmentation: The mode of reproduction of simple multicellular organisms in which body simply breaks up into smaller pieces upon maturity and each piece or fragment grows into a new individual is called fragmentation. The relatively simple multicellular organisms which are simply a random collection of cells are involved in fragmentation type of reproduction. Example: Spirogyra.

Question 2:
What is the role of seminal vesicle and the prostate gland?
Answer 2:
Role of seminal vesicle and Prostate gland.
Along the path of the vas deferens, these glands add their secretions so that the sperms are now in a fluid which makes their transport easier and this fluid also provides nutrition to sperms.

Question 3:
(a) Name the following:
(i) Thread like non-reproductive structures present in Rhizopus.
(ii) ‘Blob’ that develops at tips of the non-reproductive threads in Rhizopus.
(b)Explain the structure and function of the structures released from the ‘blobs’ in Rhizopus.
Answer 3:
(a) (i) Hyphae
(ii) Sporangia
(b) On maturity sporangia ruptures and release spores. Each spore contains a nucleus and cytoplasm enclosed in a thick wall for protection.
Function: Spores disperse far and wide. Each spore grows into new Rhizopus when come in contact of moist surface and other suitable conditions.

Question 4:
Differentiate between pollen gains and ovule?
Answer 4:
Pollen grain produces male germs-cell (male gamete) in the plants. The ovule contains a female gamete (female germ cell or egg).

Question 5:
What is pollination? List the modes of pollination and define each of them?
Answer 5:
The transfer of pollen grains form anther of stamen to stigma is called pollination. The transfer of pollen from the anther of one flower to the stigma of another flower of a different plant of the same species is called cross pollination. In this case, pollen grains of the same flower do not pollinate its stigma. In cross pollination, the transfer of pollen grains may take place through some agency like wind, insect, bird, water, mammals etc.
Transfer of pollen from the anther of a flower to the stigma of the same flower or a flower on the same plant is called self pollination.


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