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Basic science chapter Metals and Non metal Questions answer class 8
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 Q1) What is the importance of DNA copying in reproduction? Ans- DNA is the genetic material present in the cells of all organisms. The genetic information from,generation to generation is carried by DNA .It is therefore possible for the organism to produce organism of its own type due to DNA copying only. For the inheritance of traits of the parent,DNA copying is a must.DNA copying also brings about variation ,which forms the basis for the origin of new species. Q2) What are the changes seen in girls at the time of puberty? Ans: i) Enlargement of breasts with the darkening of skin of the nipples . ii) growth of hair in the genital region and in armpits occurs. iii) onset of menstruation . Q3) If a woman is using a copper-Twill it help in protecting her from sexually transmitted diseases(STD’s)? Ans- No,using copper-T will not protect a woman against catching STD.Copper-T is a device which will only guard her against pregnancy . Q4)Sexual reproduction is considered advantageous over asexual reproduction? Explain Ans Sexual reproduction ensures that large number of variations appear in the daughter organism constituting a population. This is made possible by the appearance of many new gene combinations which are contributed by the two parents. Sexual reproduction also ensures that the rate of appearance of new variations is speed up which is not achieved due to asexual reproduction. Q5) Mention the changes observed in flower after fertilization. Ans- a) ovary ripens and developed into fruit. b) ovules develop into seed. c) petals and sepals wither and drop. d)stigma, style and stamens dry up and fall off. Q6) Give the advantages of vegetative propagation. Ans- 1) it is much easier,lowcost,quicker method compared to sexual reproduction. 2) plants which produce non viable seeds or too few seeds or have lost the ability to produce seeds can be made to reproduce vegetatively to produce daughter organisms. 3) plants produced by vegetatively reproduction are genetically similar to the parent plant and show all the characteristics of the parent. Q7) What is placenta? Give the significance of placenta Ans-placenta is a disc like mass of nutritive tissue which develops on the inner wall of uterus where the fertilized egg is implanted. Placenta performs the following functions: 1)it provides all the nutrients such as glucose,proteins,minerals and vitamins to the foetus. 2)ti provides antibodies through the mother’s blood to the foetus.these antibodies provide immunity to the child after its birth against a number of diseases. 3)it also meets the oxygen requirement of the foetus and removes carbon dioxide and other metabolic waste generated in the body of the foetus. These metabolic wastes are ultimately removed and excreted by mother’s excretory system. Q8) Why is reproduction essential for a species? Ans Reproduction is necessary for species in order to increase their numbers otherwise it will become extinct. Q9) Name an organism which shows binary fission and another that shows multiple fission. Ans-binary fission-Amoeba, multiple fission-material parasite.e.,plasmodium Q10) Name a unicellular organism and also a multi-cellular organism that show budding process. Ans-Unicellular-yeast, multicellular-hydra. Q11)How do oral contraceptive pills prevent pregnancy? Ans-oral pills do not allow release of ovum from the follicle to occur, so fertilization does not take place. Q12)Which is the most effective contraceptive method which will not allow sexually transmitted diseases(STD’s) to spread? Ans-mechanical barrier by condoms, cervical caps, etc. Q13)Give one difference between zygote and embryo. Ans-Zygote is single celled fusion product of sperm and ovum. Embryo is a multicellular product produced by mitotic divisions from zygote. 14)How does the embryo derive nutrition after getting implanted in the walls of uterus? ans-the embryo derives nutrition after getting implanted in the walls of uterus through a disc like tissues called placenta which has villi like projections on embryo side and blood spaces on mother’s side. This enables transport of materials like amino acids,glucose and oxygen from mother to child. Q15)What happens if the ovum does not fertilized in female body? Ans-when the ovum does not get fertilized it lives for one day.As the preparations of the uterine lining are not needed any more, the lining breaks and comes out along with the unfertilized ovum through the vaginal path in form of blood discharge. This is known as menstruation as it happens once in a month and it lasts for 2-8 days. Q16)What is the function of seminal vesicles and prostate gland in the male body? Ans-they add their secretions to sperms in order to make the sperms lie in a fluid which makes their flow and transport easier and also provides nutrition to sperms. Q17)Why are pair of testes located outside the male body? Ans-the pairs of testes are located outside the body of the males because a temperature of 2-3 degrees C,less than the body temperature is required for production of sperms. Q18) Give example of two bacterial and two viral diseases which are transmitted through sexual contact? Ans-bacterial diseases-gonorrhoea and syphilis, viral diseases-AIDS and genital warts. Q19)What factors have lead to adoption of contraceptive methods? give at least four factors. Ans-factors are: 1)growing human population. 2)spread of sexually transmitted diseases like AIDS. 3)gap between children in a family so that both mother and child get proper nutrition. 4)maintenance of sexual health. Q20) How do sperms reach the female genital tract? where does fertilization and implantation of the embryo takes place. For how long does the embryo remain attached to uterine walls. Ans-sperms travel upwards through uterus to oviduct where they may meet an ovum and hence fertilize it. Fertilization takes place in oviduct to give rise to single celled zygote. The zygote divides to become multicellular embryo which gets fixed in uterus. The embryo remains attached in uterine walls throughout gestation period which is 40 weeks in humans. full post Chapter - 8 How Do Organisms Reproduce ?
Points to remember Read Solved Sample paper Read Important questions Read NCERT Questions Solved Download File Two marks questions solved Download File Three marks questions solved Download File Solved CBSE Test paper Download File important guess questions Download File CBSE Questions_banks Download File HOW WE DO REPRODUCE Notes Download 1. What is soil?
2. Name what type of soil is it, According to their size? (a) Greater than 2 mm in diameter (b) 0.005–0.05 mm in diameter 3. What is the last stage in the formation of soil? 4. What are the factors which influenced the formation of soil? 5. What is the composition of soil? 6. Which type of soil is classified as residual soil? Give example. 7. The soil at a given place was found to consist of sandstones, clay, shale and limestone. What type of soil is it and how it might have formed? 8. Mention all possible composition of soil. 9. Name physical and chemical properties of Soil. 10. Write a short note on A–horizon and B–horizon. 11. Write a short note on transported soils. 12. What are the main causes for the erosion of soil? 13. How will you demonstrate that the vegetation prevents erosion of SOIL SOLUTIONS 1. Soil forms the outer most layer of land on the earth. Its thickness on the earth’s surface ranges from a few millimeters to 3 – 4 meters. 2. Soil with particle size greater than 2 mm in diameter is gravel; that with particle size varying from 0.005 mm to 0.05 mm is known as silt. 3. The addition of organic matter from dead and decomposed plants and animals is the last stage in the formation of soil. 4. The formation of soil is influenced by climate, vegetation, parent materials and time factors to a great extent. 5. Generally soil contains fine particles of rock, humus, air and water. 6. The soil which remains at the place of its formation is called residual soil. The residual soil may be red or black or even laterite. 7. The soil containing sandstone, clay, shale’s and limestone is known as mountainous soil. This type of soil is found in depression and valley basins or an gently inclined slopes. It is probably formed by weathering. 8. The soil is made up of mineral particles, organic matter, solutions of various inorganic salts in water, air and living organism. 9. The physical properties of soil include its texture, structure, colour, porosity, water holding capacity and presence of soil organism. The chemical properties, like acidity and alkalinity of the soil, have a relation with the type of vegetation and crops grown on it. Temperature may affect biological, physical and chemical composition of soil. 10. The soil is arranged in two or more layers or horizons. The upper most layer is generally dark in colour, as it is rich in minerals and humus. This layer is soft, porous and can retain more water. It is called the top soil or the A–horizon. The next layer has lesser amount of humus or organic matter, iron oxide and more minerals. This layer is generally harder and more compact and is called the B–horizon or the middle layer. 11. The soil which settles at other places as a result of its transportation by gravity, flowing water, wind and glacier is called transported soil. Transported soil is further classified into various types depending upon their mode of transportation. Various types of transportation soil are alluvial type and sandy soil. 12. Erosion of soil is natural process. It is as old as the earth itself. Erosion involves the movement of soil from one place to another. It may be due to the flowing water or wind. Now a day, the rate of soil erosion is very high due to increase in the activities of humans. The rate of soil erosion is higher in region with high population density, mainly due to increase in the agricultural activities. Continuous cultivation of land by only one type of crop further adds to the loss of soil fertility. Deforestation, floods and overgrazing are some other main causes for the erosion of soil. The forest fires and even deep ploughing of land for crops also lead to soil erosion. 13. Water and wind, take away the top layer of the soil, where there is no vegetation or poor vegetation. The tree, grasses and hedges hold the soil in place. This can be mode clear by the following activity. Take two trays or baskets. Fill them with garden soil. Grow grass or some cereal in one of them and water it properly for a few days. Now keep both the trays in a slightly inclined position by placing a brick below their one side. Let allow the water to fall on both the trays. we will find that the water that flows from the tray with vegetation contains fewer amounts of soil particles in it. This is due to the fact that the roots of plants bind the soil and do not allow it to flow with water. |
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