Study Materials

NCERT Solutions for Class 10th Science

 

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Chapter 8. How do Organisms Reproduce

Additional Questions With Solutions

 

 

 

Chapter - 8.  How do Organisms Reproduce?


Q1.What are the significances of reproduction?

Answer: 

.(i) continuation of life

(ii) perpetuation of species

(iii) replacement of individual

(iv) variation and transfer of variation.

Q2.Why do we find variations in the offspring of parents although they have taken birth from the same parents?

Answer: Variations are differences found in morphological, physiological and other traits of individuals belonging to the same organism, race or family. They develop due to

(i) faulty DNA replication

(ii) Crossing over

(iii) Chance separation of chromosome during separation

(iv) Chance combination during fertilisation

(v) Mutation.

Q3.Why variations are considered extremely important?

Answer: 

.(A) Pre adaptation -Variation function as pre adaptation to environmental changes like increase or decrease in temperature, drought, antibiotic resistance, pesticide resistance etc.

( B) Individuality- As variation provides individuality we recognise each other.

(C) Evolution-Provides raw material for evolution or formation of new species.

Q4.Differentiate between regeneration and fragmentation?

Answer: 

 Regeneration  Fragmentation

 1. This type of reproduction is seen in fully differentiated organisms. 

2. It is carried out by specialised cells, which proliferate and form mass of cells. From mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organise sequence. E.g.-Hydra, Planaria.

1. The type of reproduction is seen in multicellular organisms with relatively simple body organisation. 

2. No specialised cells involves in this process. E.g. Algae, Fungi, Bryophytes.

 


Q5.Why is regeneration not same as reproduction?

Answer: Because organisms would not normally depend on being cut up to be able to reproduce.

Q6.How will an organism be benefited if it reproduces through spores?

Answer: The spores are covered by thick resistant walls due to which they pass through unfavorable conditions of drought, high or low temperature. Being small they can disperse long distances by air.

Q7.Which part of plant is considered as the reproductive part? Draw the L.S of labeled diagram of reproductive part showing the male and female reproductive organ.

Flower. see text book diagram figure 8.7

Q8.Distinguish between self and cross pollination.

Answer:

Self pollination-It is the transfer of pollen grains from anther to stigma of same flower.

Cross pollination- It is the transfer of pollen grains from anther of one flower to stigma of another flower. The transfer is accomplished by an external agency like wind, water, insect or birds.

Q9.Differentiate pollination and fertilization.

Answer: 

Pollination-It is the transfer of pollen grains from anther to stigma and this process precedes fertilisation.

Fertilisation-It is the fusion of male and female gametes that occur after fertilisation.

Q10.Explain the post fertilization changes in flower.

Answer: 

The changes are as follows: 

(i) Zygote divides several times to form an embryo within ovule.

(ii) Ovule changes into seed having tough seed coat

(iii) Ovary changes into fruit.(iv)Sepal, petal, stamen, style and stigma shrivel and fall off.

Q11.What are the advantages of seed formation?

Answer: 

(i) Dormant embryo and tough seed coat best suited to pass through unfavorable seasons.

(ii) Easily dispersed to long distances as they are small and light.

(iii) As seeds remain dormant, so edible seeds can be stored for later use.

Q12.Give the labeled diagram of
a. Germination of pollen on stigma.
b. Seed Germination.
c. Structure of seed.

Answer: See text book diagram.

Q13.What are the similar changes observed in boys and girls at puberty?

Answers: The following similar changes observed in boys and girls at puberty. 

(i) Hair-Growth of hair in arm pits and genital area between the thighs.

(ii)Genital area- Becomes darker.

(iii) Body hair-Thinner hair on legs, arms and face.

(iv)Skin-Becomes oily, appearance of pimples mainly on face.

(v)Awareness of body- Children become conscious and aware of their own bodies as well as those of others.

Q14.What are the different changes that occur in boys and girls during puberty?

Answer: 

Girls- The changes occur in response to hormone estrogen.

(i) increase of breast size

(ii) darkening of skin nipples

(iii)beginning of menstruation

(iv)broadening of pelvis

(v) fat deposition on face, buttocks and thigh.

Boys- The changes occur in response to hormone testosterone.

(i) slow growth of thick hair on face(moustaches, beard)

(ii) cracking of voice

(iii) enlargement of testes, scrotum, penis.

(iv) Erect of penis either in day dreams or at night.

Q15.Define Puberty?

Answer: The period when reproductive maturity begins to appear is called puberty.

Q16.Distinguish between primary and secondary sex organs?

Answer: 

(I) Primary sex organ-Sex organ which produce germ cells or gametes and sex hormones. Male-testes, females-ovaries.

(ii) Secondary sex organs-The sex organs which conduct and nourish the gametes.

Male-vasa differentia, penis, seminal vesicles, prostrate gland.

Female- fallopian tube, uterus, vagina

Q17.What are two important functions of testes and ovary?

Answer:

Testes-

(i) produce sperms

(ii) secrete hormone testosterone.

Ovaries-

(i) produce ovum

(ii) secrete hormone estrogen.

Q18.Why are human testes extra abdominal?

Answer: Testes are extra abdominal because it acts as thermo regulator keeping a temperature 1-3 degree Celsius below that of body, essential for development of sperm.

Q19.What are the functions of testosterone and estrogen?

Answer: 

Testosterone-Regulate sperm formation. Development of secondary sexual characteristics in males i.e., changes appear in boys at puberty.

Estrogen- Regulates ovum formation. Development of secondary sexual characteristics in females.

Q20.Distinguish between male and female germ cell.

Answer:

Male germ cell-

(i) smaller size

(ii) active and motile

(iii) contains genetic material in a tiny body and a long tail.

Female germ cell-

(i) bigger size

(ii) passive and nonmotile

(iii) contains nucleus and cytoplasm .Nucleus contains genetic material.

Q21.Where fertilization does takes place in case of human oviduct or fallopian tube?

Answer: Oviduct or fallopian tube

Q22.What is placenta? What is its function?

Answer: Placenta is a disc shaped structure which is the vital connection between fetus and mother. It provides glucose and oxygen from to embryo. It transfers waste of embryo to mother’s blood.

Q23.What happens when egg is not fertilized?

Answer: 

(i) Ovary releases one egg every month and the uterus prepares itself to receive the fertilised egg.

(ii) To receive the zygote its lining become thick, spongy for nourishing embryo.

(iii)If the egg is not fertilised, this lining is not needed any longer.

(iv) So the lining slowly breaks and comes out through vagina as blood and mucus, this is called menstruation.

(v) This cycle takes place every month and menstruation starts for 2-8 days.

Q24.The marriageable are of male and female is 21 years and 18 years respectively, the rule is made by government, although the sexual maturation take place in them earlier. Why?

Answer: Sexual maturation is a gradual process. It occurs while the general body growth is still going on. So sexual maturation does not mean that body and mind is ready for sexual acts and bringing up children.

Q25.What are the adverse effects of early marriage?

Answer: (i) Teen age couples cannot bring up their children.

(ii) Reproduction may affect the health of mother as well as child.

(iii) May bring deformity in children.

(iv)Young couple cannot peruse studies, nor can they have a carrier.

Q26.What is reproductive health?

Answer: It is the state of physical, mental and social fitness to lead a responsible, safe and satisfying reproductive life.

(i) It provides awareness regarding fertility regulating method.

(ii) Family planning.

(iii) Prevention of STD.

(iv) Manage disorders related to reproductive system by getting them treated at the earliest.

Q27.What are the various types of contraception?

Answer: Prevention of pregnancy is called contraception. The technique used in preventing the occurrence of pregnancy is called contraceptive devices.

(i) Mechanical Barrier method-It prevents the entry of sperm to uterus or reach to egg. E.g. condom (males), cervical cap (females), diaphragm.

(ii) Hormonal method-It changes hormonal balances, so that eggs are not released and fertilisation does not occur. These are oral pills.

(iii)Surgical method-It prevents passage of sperms in males and ova in females. It is of two types. (i) Tubectomy-In this oviduct is blocked by which ova cannot be released. (ii)Vasectomy- In this vasadeferntia of males is blocked. This prevents passage of sperms from testes to semen. Loop or copper T-It is placed in uterus of female which prevents fertilisation.

 

       

 

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