CBSE Notes-Heredity & evolution CLASS- X, Subject – Biology

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Assignment-Heredity & evolution CLASS- X, Subject – Biology

CBSE Notes-Heredity & evolution CLASS- X, Subject – Biology

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CBSE Notes-Heredity & evolution CLASS- X, Subject – Biology

In asexual reproduction, all the off springs are exactly identical to one another as well as to parents because of same genetic makeup.

In sexual reproduction the various off springs are similar to their parents but are notidentical to items or to one another because of genetic various except IDENTICAL TWINS.

• Identical Twins: grow from a single cell which splits after fertilization.Look alike

• Non Identical twins: Look less like they grow from 2 different fertilized cells & hence don’t have exactly same genetic material.

Heredity: The transmission of characters (traits) from the parents to their off springs is called Heredity.

Variation: The differences in the characters among the individuals of a species is called variation is necessity for organic evolution.
Both Heredity & variation are fundamental factors in the process of Evolution of an organism.

Genetics: The branch of biology which studies heredity & variation is called genetic.

Terms gene was coined by scientist – Johanssen in 1909.

Chromosomes: Chromosomes are thread like structures present in the nucleus of a cell which contain hereditary information of the cell. They are made up of DNA & proteins.

Dipoid Cell: A cell which has the full no. of chromosomes with two of each pair, is called a diploid us.

Hiploid Cell: A cell c half the no. of chromosomes with one of each pair e.g. gamete cell/sex cell.

Autosomes: All the chromosomes in a cell (except sex chromosomes) are called autosomes.

Karyotype: During metaphase stage of cell division, the chromosomes become shorter, thicker & can be seen very clearly.

In order to study the no. shape, size and type of chromosomes of an individual, thechromosomes during melaphase, are arranged acc to their length & position of centromere. Such an arrangement of chromosomes for the purpose of studying is called Karyotype.

Identifying a chromosome thru microscope, special staming technique called “Banding Technique” is used.Study of karyotype of an individual helps in the diagnosis of genetically disorders.

Down’s Syndrome: Any variation in the no. of chromosomes from the normal no or any change in the shape of chromosome during fertilization can lead to severe abnormality or disorder in the child after birth which are called Genetic / Heredity Disordere.g.

Down’s syndrome which is caused by interitance of an extra 21st chromosome. In this syndrome, full mental development does not take place.

Symptoms: Mental retardation, Flattened , nose, Defective ears, widely separated eyes, short & broad neck, protruding tongue, small & sturdy hands widely.

Gene: Gene is the unit of inheritance. Various genes are located in the chromosomes at fixed position genes are responsible for our characteristic features.

Chemically gene is a segment of a large polynucleotide molecule called de oxyribonucleic acid
DNA: Dexyribo nucleic acid DNA was first isolated by Frederick meisher from the nucleus of the pus cells.It is acidic in nature so the name is nucleic acid. DNA is a macromolecule/polymer which is made up of a large no. of smaller units called Nucleotide. So DNA is a polynucleotide.

Nucleotide is the basic structure unit of DNA.

Components of a Nucleotide:

1. a nitrogen containg base
2. a pentose sugar
3. a phosphate gp

Any one of nitrogen base pairs up only c a specific nitrogenous base of the opposite side. Such specific pairing is called COMPLIMENTARY PAIRING.

(Adenine) A pairs up c T (Thymine)
(Cytosome) C pairs up c G (Guanine)

DNA molecule is like that of a spiral staircase in which both the railing of the staircase are made of sugar & phosphate molecules alternative each other and held together by strong chemical bonds whereas the steps of the staircase are made of complimentary nitrogenous bases held together by weak bonds.

DNA structure established by Wastson & Crick in 1953.

Each helical turn of the DNA molecule has a length of 3.4 nm in which 10 nucleotide units are present.

Genetic Engineering: The technique for altering an organisms genetic make up inserting genes from other organism its chromosomes is called Genetic Engineering.

Sex Determination: The process by which the sex of a per is determined is called sex determination.
The Chromosomes which determine the sex of a person called sex chromosomes which areof 2 types X & Y.
                     XX combination is always found in females
                     XY combination is always found in males.

So it is the sperm (carrying either X or Y) which determines the sex of a child


Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of yrs. In which non species are provided.
Some import ants sources which provide evidence for organic evolution are

  • Fossils
  • Homologus organs
  • Analogus organs
  • Vestigial organ
  • Embryology

Homologus organ: Organs having similar basic structure & origin but different functions e.g. porelnubs of a frog, birds & man.

Analogous organs: The organs with different basic structure but have similar appearance & performs similar functions. e.g. wings of an insect & a bird.

Vestigial organs: Organs which are functionless useless but were functional in aucestors e.g. Vermiform appendix Nietuting membrame.
Embrgology: The study of the development of the embryo of an animal is called Embrgoloy.

Biogenetic law: It states chat “Ontogeny recapitulates Phylogeny” It means that during the development of the embryo of any organism, its complete evolutionary history is repeated.


1. Lamarckism 2. Darwinism 3. Synthetic Theory of Evolution

1. Lamarckism: It states

(a) The use & disuse of an organ by an organism leads to acquiring of variation in the features of that organ.
(b) These variations (acquired characters) are inherited by the offsprings. (c) This leads to evolution

This theory was criticsed by August weismann who ejected the idea of inheritance of acquired characteristics.

DARWINISM / Theory of Natural Selection

(a) All the species produce a large no of offsprings but population remains fairly constant due to struggle bt the members of same species & different species for food, space & mate

(b) This struggle eliminates the unfit individuals. (Survival of the fittest)

(c) This gives orgin to variations which pass into progeny & over a long period of time, leads to origin of new species.

Limitations: It could not explain how the variations arise.

Synthetic Theory of Evolution:

The most accepted theory these a days which says that “origin of species is based on the interaction of genetic variation & natural selection’.




Q1)Name a bacteria found in human intestine?
Ans-coliform bacteria is found in human intestine.
Q2)Which is the easiest method to detect water pollution?
Ans-pH detection using the universal indicator.
Q3)A person lives near a forest.Enlist 4 items which he can get from forests to meet his daily needs.
Ans-food, fodder,fuel and medicinal plants.
Q4)Why are forest called “biodiversity hot spot”?
Ans-forest are rich in most of the species of flora and fauna.All species of plants like bryophyte,pteridophyta,ferns, gymnosperms,angiosperms and animal species from amoeba to man are found.
Q5)Name 4 substances that can be recycled.
Ans-glass,plastics,metals and paper.
Q6)What do you mean by the trm sustainable development?
Ans-Sustainable development means to meet the needs of present generation ,without foreclosing the options of future generation,to keep balance between development andenvironment.
Q7)How does mining lead to pollution?
Ans-mining causes pollution because the large amount of slag is discarded for every tonne of metal extracted in the earth.
Q8)”Coal and petroleum are converted forms of solar energy”.is this statement correct?
Ans-this is statement is correct because millions of years ago the raw material from which coal and petroleum are derived were daed and decayed plants , which when were living photosynthesized by solar energy.
Q9)Hydroelectric power is also an indirect form of solar
Ans-hydroelectric power is indirect form of energy, because the water which is stored in dams is rainwater and rainfall occurs due to evaporation of water from water bodies due to heat of the sun.
Q10)Writeatleast two ways by which people of ancient India managed water resources?
Ans-a)kulhs in Himachal Pradesh (b)khadins in rajasthan.
Q11)What will happen if loss of biodiversity occurs?
Ans-when loss of biodiversity will occur ,it will lead to ecological crisis, the foodcahins and food webs will get disturbed and resources will not be available for future generations.
Q12)What strategies should be adopted such that forest products are used and theenvironment also does not get disturbed?
Ans- a)reforestation and afforestation to remake forests.
b)not allowing monoculture of plants.
c)employment of local people for maintenance of forests .
d)killing of animals should be banned.Steps to create awareness among people to save the
endangered flora and fauna should be taken.
Q13)Besides conservation of wildlife and forest , suggest some ways which can improve ourenvironment.
Ans – a)water conservation , mainly fresh water.
b)use of coal and petroleum should be done judiciously as its sources are limited.
c)recyclable material such as paper, glass ,metals should be segregated from the
trash.Biodegradable trash should be used for bioenergy through fermentation and anaerobic
respiration to produce biogas.
d)oxides of sulphur and nitrogen should not be released into the atmosphere.
Q14)What is watershed management?what is its aim and what are the benefits?
Ans-watershed management is a scientific way of developing primary and secondary sources of water .Its main aim is to develop primary sources of land and water and use scientific methods to increase the biomass production as secondary sources so that no ecological imbalance occurs.They work on rejuvenating ancient and traditional way of water storage along with mega- projects like dams and reservoir
Q15)what you can do as an individual to reduce consumption of various nature resoources and help in environment conservation?
Ans a)follow 3 R’s(reduce,recycle, and reuse)
b)wastage of paper and water can be reduced .
c)extra food should be given to poor instead of throwing it.
d)plastic, polythene, metal cans can be recycled.e)wastage of electricity, petrol, diesel, LPG can be
1. What will be the effect of increase in the amount of CO2 in the atmosphere on the average temperature of the earth.
Ans. The average temperature of the earth will increase.
2. Why is it necessary to conserve our environment?
Ans Conservation of environment is required for preventing damage to environment and depletion of natural resources 3. Which of the following is the major constituents of biogas. CO2, H2, CH4, CO.
4.Which of the following pollutants of air would affect the capacity of blood in human bodies to absorb O2 from lungs . NO2 SO4,CO,CO2
5. Where was CHIPKO MOVEMENT started?
Ans: Reni in Garhwal.
6. What will be the result of presence of excess amount of CO2 in environment.
Ans.Green house effect.
7.What are the two major benefits of dams?
Ans. 1. Irrigation 2. To produce electricity.
8.What are kulhs?
Ans.Kulhs are age old concepts of water harvesting used in Himachal Pradesh.
9.List any two systems of water harvesting.
Ans Ponds and check dams
10 How is the increase in demand for energy affecting atmosphere?
Ans. Increased consumption of fossil fuels is releasing a lot of polluting gases some of which are causing Global Warming and producing acid rain
1.Write two advantages of classifying energy sources as renewable and non renewable.
1.A judicious use of non renewable energy source so as to prevent its depletion.
2. Increasing use of renewable energy source but not beyond its renew ability.
2. Why should we conserve forests? Suggest any two ways of conserving forests.
Ans.1.Forests provides us O2 which is required for living –Natural habitat, prevent soil erosion, and regulate water cycle.
2.They protect the soil, retain and regulate flow of rain water.
Conservation of forests:
1.afforestation and reforestation
2.Social forestry.
3.What are fossil fuels. Give two examples of fossil fuels.
Ans .Fossil fuels are energy yielding combustible substances that have been formed millions of years ago by compression and anaerobic heating of organic matter. Ex coal and petroleum.
4.Write the ecological functions of forests.
Ans .Forests regulate climate they help in retaining rain water and its storage they control soil erosion and occurance of floods.
5.What is chipko movement? How did this movement ultimately benefit the local populations and the environment.
Ans.It was a movement initiated by local people in Reni Village of Gharwal Region to oppose and protect trees in the forest.
6. How do the forests get depleted? What are its consequences?
Ans. Clearing forests for agriculture, roads canals, human habitation and building dams. Consequences: less rain fall, climatic change.
7 .Suggest any two measures for controlling Co2 levels in the atmosphere.
Ans. 1.Increased vegetation cover. 2. Using alternate sources of energy.
8 Why are Arabari forests of Bengal known to be good example of conserved forests.
Hint .Sal forests of south western districts of West Bengal regenerated with people participation.
Ans. Because villagers were involved in the protection of 1272 hectares of badly degraded sal forests. In return for help in protection villager,s were given employment in both silviculture and harvesting operations. 25% of final harvest was given to them and they were allowed fuel wood and fodder collection on nominal fee.
9.Why are environmentalists insisting upon sustainable natural resource management?Give any three reasons.
Ans. Equitable distribution, controlled exploitation, minimum wastage, disposal of waste.
10. Suggest any two ways of utilizing waste water.
Ans.1.Treated municipal water can be poured in irrigation channels for supply to crop fields. 2. Sewage sludge separated from waste water is a source of manure compost and bio gas
1. Briefly describe Ganga action plan.
Hint. Details of steps taken to reduce pollution.
2. Explain the methods of water harvesting
hint. check dams , khadins,kuhls etc of different states.
3. Quote three instances where human interventions saved the forests.
1. Silent valley(Kerala) 2. Garwal Himalayas. 3. Kelase Forests.:
4. T here are four main stake holders when it comes to forests and wild life Which among these should be the authority to decide the management of forest produce? Why?
HINT people, forest department, industrialists, wild life and nature enthusiasts.
People  living around the forest area
5. What is the importance of water harvesting.
Hint Importance in ground water recharging ,irrigation, drinking water supply
6. An environmentalist on your visit to your school suggested the use of three R‘s to save the environment.explain the three R‘s
Hint .Reduce Reuse Recycle.
7.What is meant by sustainable management? The environmentalists are insisting upon sustainable natural resources management?State four advantages.
Ans .It is controlling the use of resources in such a way so as to provide for its equitable and continuous availability not only to the present generation without any harmful impact on the environment.
Four advantages:
Equitable distribution, controlled exploitation,minimum wastage,disposal of waste
8 What is a dam? Write two main advantages and two illeffects of constructing a big dam
Ans. Dam is a large water reservoir built across a stream by holding back water during rainy seasons.
Advantages: prevention of floods, irrigation Ill effects. 1. Displacement of large people. 2. Ecological problems.
9. Why is replenishment of forests necessary?
Ans. 1. To maintain Ecological balance.
2. To prevent Soil erosion
3. To reduce the amount CO2 in atmosphere and check Global Warming.
4. To maintain rain fall.
5. They control occurrence of floods.
6. Provides habitat to animals.
10. List four changes you would incorporate in your life style in a move towards sustainable use of available resources.
Hint some changes in the life style


Solved Assignment-Heredity and evolution CBSE X Biology

CBSE GUESS Solved-Heredity and evolution CBSE X Biology
Q1)Define evolution.
Ans-It a slow gradual process which occurs due to cumulative effects of adaptations and helps it to survive in a better way.
Q2)How are fossils helpful in developing evolutionary relationships?
Ans: Fossils forms a connecting link between groups of organisms.
Q3)Cat’s paw ,human hand and horse’s legs-are these organs homologous or analogous? Give reason
Ans- They are homologous organs as they are of same origin performing different functions.origin is forearm modified.
Q4)Wings of bird and wings of insect-are these organs homologous or analogous?give one suitable season to support your answer.
Ans-They are analogous organs as both have developed from different origin and perform same function of flying.
Q5)Give one difference between eyes and eye spot.Which animal possesses eye spots?
Ans-eyes are well developed organs helping to form an image, but eye spots just enable the animal
to distinguish between day light and darkness.e.g. planaria and euglena possess eye spots
Q6) Give one difference between artificial selection and natural selection.
Ans-Artificial selection is that in which man selects the beneficial gene and modifies it according to his requirement whereas in natural selection nature selects the advantageous gene and helps it to multiply.
Q7) What is true- humans have evolved from chimpanzees or humans and chimpanzees both have evolved from a common ancestor?
Ans- Both have evolved from a common ancestor because both are existing today .man has not replaced chimpanzees.
Q8)What is the mechanism behind the expression of a particular trait?explain briefly.
Ans – The mechanism behind the expression of trait is the presence of a functional gene.When gene is functional it is capable of producing a hormone or enzyme which helps in expression of that trait.But sometimes genes get altered and become non-functional,then the enzyme is not produced and the trait does not get expressed.
Q9) What will happen to the expression of a particular trait if agene get altered?
Ans – When gene gets altered the corresponding enzyme is not produced,hence the hormone related to it is not produced and the particular trait does not expressed.there are chances that instead a disease maybe seen due to altered gene
Q10)What are various ways by which genes can enter a population?
Ans. The various way are
a) GENE MIGRATION is gene flow which occurs when some members of main population migrate to other areas and may not come back .this is geographical isolation.
b) GENETIC DRIFT -is change in gene frequency due to chance or accident and not by natural selection.
c) NATURAL SELECTION-is a process in which better quality genes sekected by nature are allowed to multiply.
d) MUTATIONS arise suddenly- they are sudden changes in the gene inherited by offsprings for atleast 4-6 generations.
Q11) How will new species arise in case:
a) Two sub-populations are separated due to a huge mountain in between them?
b) A small population of individuals gets drifted away from the main land due to sea?
Ans. New species will arise;
a) The huge mountain acts as a geographical barrier and the members of the two sub-population will not be able to mate with one another due to this mountain .this will keep mating within the members of their own sub-population and hence two new species will arise.
b) when the small population gets drifted away from main land by sea,here also chances are that there may be some kind of gene flow between the partly separated populations,but if the two populations do not meet, chances are that two new species would arise.
Q12) Only advantageous variations help in the evolution of an organism giving rise to a new species.expalin with the help of an example.
Ans.This is because the advantageous variations are selected by nature and allowed to multiply or propogate fast to increase their members.because such variations help an individual to survive in a better manner in changing environment the population increases.this can be explained as under
A- EVOLUTION OF EYE which has occurred bit bt bit and not in one step.even the rudimentary eye was advantageous to Planaria or Octopus even though a clear image was not formed as in humans still it gave a fitness advantage.
B-EVOLUTION OF WING-earlier feathers were formed to provide warmth to the body,later these feathers helped in flying.
1. What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering?
Ans. The organisms that contain a segment of foreign DNA are known as transgenic organisms.The complimentary property of the nucleotides of the most powerful tool in genetic engineering.
2. Explain how the sex of the child is determined at the time of conception in human beings.
Ans. Male human beings have XY sex-chromosomes and female human beings have XX sex-chromosomes. If a sperm carrying x-chromosome fertilizes with the ovum, then sex of the baby will be female. If a sperm carrying y-chromosome fuses with the ovum, the sex of the baby will be male.
3. By comparing the similarity of nucleotide sequences in DNA of different kinds of organisms, evolutionary relationships can be established.
a) Arrange the following according to their evolutionary closeness (You may use your knowledge of classification also) Cockroach, mango tree, gorilla, fish.
b) Whose DNA among the following do you think is most similar to that of humans.
Ans. a) cockroach – fish – gorilla b) Gorilla
4. Mention the ways by which variant genotypes are produced in organism?
Ans. a) gene mutation b) Crossing over c) Hybridization
5. In human beings blue eye colour is recessive to brown eye colour . If a brown eyed man has a blue eyed mother then find
a) What are the possible genotypes of his father?
b) What is the genotype of the man and his mother?
Ans. BB , Bb B. Man: Bb, mother: bb
6. What are fossils? Of what interest are fossils to the evolutionary biologists?
Ans. A fossil is the remnant or impression of an organism that lived in the Remote past. Use of Fossils
a)Phylogeny , the evolutionary history can be reconstructed from the fossils.
b) The fossil record has helped in building the broad historical sequence of biological evolution.
1. a) Who isolated DNA for the first time from pus cells?
b) Why is DNA called polynucleotide?
c) Name two purine nitrogenous bases found in a DNA molecule.
Ans. a) F.Meishcer, named it nuclein.
b)DNA is called polynucleolide because it is a polymer or long chain of nucleolide.
c)Purine:- Adenine and Guanine.
2. a) Who put forward the double helical model of DNA?
b) What are the three chemically essential parts of nucleotides constituting a DNA?
Ans. a) Watson and Crick.
b)Nucleotide constituting –DNA Nitrogen bases (Purines and Pyrimidines), Pentose sugar(Deoxyribose sugar) and a phosphate molecule.
3.Guinea pig having black colour when crossed with guinea pig having same colour produced 80 offspring, out of which 60 were black and 20 were white. Now,find out:
a)What is the possible genotype of the guinea pigs?
b)Which trait is dominant and which trait is recessive?
c)What is this cross called as and what is its phenotypic ratio?
Ans.a) Bb x Bb b)Black is dominant and white is recessive.
c)Monohybrid cross, phenotypic ratio=3:1
4.Write a brief account on salient points of Lamarck‘s theory. Who disproved this theory?
A. Lamarckism
1.The use and disuse of an organ leads to acquiring of change in the features of that organ.
2. These changes are inherited by the offspring.
3. Favourable variations result in evolution of new species. August Weisman.
5. Distinguish between acquired and inherited traits giving one example of each.
Ans .
Acquired traits
1) A trait (or characteristic) of a organism which is ‗not inherited‘ but develops in response to the environment is called an acquired trait.
(2) The acquired traits of an organism can not be passed on to its future generations. e.g. low weight‘ of beetle, cut tail‘ of a mouse.
Inherited traits
1) A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait.
2) The inherited traits of an organism are passed on to its future generations. e.g. red colour of beetles, fur coat of guinea pigs.
1. a. What is genetics?
b. Give the common name of plant on which Mendel performed his experiments.
c. What for did Mendel use the term factors and what are these factors called now.
d. What are genes? Where are the genes located?
Ans. A. The branch of biology that deals with the study of heredity and variation.
b. Garden pea – Pisum sativum.
c. The units of inheritance of characters. These factors are now called as genes.
d.Gene is a hereditary unit, a segment of DNA. It is located on a chromosome at a particular locus or position.



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
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 carbondioxide 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.
Q21)How do variations help a genera to evolve?
Ans-variations are better for a species rather than an individual because the variationsenable the organism to survive competently in changing environment. When these variationsare passed to many organisms of same species it helps the new species to originate, asvariations occur in their DNA which is the genetic material and controls entire metabolism.
Q22)What is the need for DNA to replicate during the process of reproduction?
Ans-the need for DNA to replicate is due to the DNA being an important molecule which controls all metabolism of the body by producing proteins. No parent can give its own genetic material, needs to replicate and get transferred to the germ cell which will carry the information. When germ cells of two parents fuse to give rise to zygote.
Q23)What are the basic principles for contraception? Explain at least 3 principles with example of the device used?
Ans-the basic principles are;
i)not allowing the sperm to unite with ovum-MECHANICAL barrier,e.g.condoms,cervical caps.
Ii)not allowing the ovum to be released-CHEMICAL barriers,e.g. oral pills.
iii)creating a block in a path of ovum or sperm-SURGICAL barriers,e.g.vasectomy on males and tubectomy in females.
iv)preventing pregnancy by not allowing implantation to take place by copper-T and loops.
Q24)Why must pollination occur before fertilization? How is pollination different from fertilization? What does a pollen contain inside?
Ans-pollination must occur before fertilization as it has to reach the male gametes present in pollen grain which will germinate to form a pollen tube and carry the male gametes to the ovum. Pollination is different from fertilization Because here the pollen grain with its male gametes just reaches the stigma, whereas fertilization of male gamete to ovum results in formation of diploid zygote which is the foundation of new generation.
Q25)Give differences between asexual and sexual modes of reproduction.
Ans-asexual reproduction
1.only one parent is involved to form an offspring. does not lead to variations.
3.generally occurs in unicellular organisms ,plants and sponges, like hydra
4.exact replicas of parents produced –can be called clones.
Sexual reproduction
1.two parent male and female are involved to give rise to an offspring. gives rise to variations.
3.occurs in higher animals which are multicellular and well developed.
4.theoffsprings are not exact replicas,they differ from their parents.
Q26)What is vegetative propagation? Give examples of plants which can be propagated by their: a)stems b)roots c)leaves
Ans-vegetative propagation is a method of reproduction in higher plants in which their vegetative parts are capable of giving rise to new plants .vegetative propagation can be natural or artificial.
2.roots- banana, asparagus
3.leaves- Bryophyllum
Q27)Give the functions of the following A)ovaries b)testes c)uterus d)vas deferens e)fallopian tube
Ans: a)ovaries produce ovum; once every month alternatively. they produce estrogen and progesterone hormone.
b) testes produce sperms and testosterone hormone.
c) uterus walls become thick to help in attachment of embryo,i.e.,implantation to occurs.
d)vas deferens- help to carry sperms from testes to seminal vesicles.
e) fallopian tube-fertilization tube- fertilization occurs here as sperms travel to reach vum.
Q28)what is binary fission?
Ans)Many bacteria and protozoa simply split into two equal halves during cell division. This process is called binary fission. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.
Q29) what is multiple fission? Name the organism that shows this mode of reproduction.
Ans)Some single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously.This process is called multiple fission.
Q30) Define fragmentation?
Ans)In multi-cellular organisms with relatively simple body organisation,simple reproductive methods can still work. Spirogyra, for example,simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.
Q31) Define regeneration?
Ans)Many fully differentiated organisms have the ability to give rise to new individual organisms from their body parts. That is, if the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as regeneration
Q32)Explain budding in Hydra.
Ans) Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
Q33) How does bryophyllum multiply asexually?
Ans)Buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.
Q34)Explain the reproduction in Rhizopus.
Ans) In Rhizopus,the tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals.The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.