CBSE Class 10 Science How do humans reproduce Notes

CBSE Class 10 Science: How Do Organisms Reproduce? Notes

Chapter 8: How do organisms reproduce?

Reproduction

Reproduction is an integral feature of all living beings. The process by which a living being produces its own like is called reproduction.

Importance of reproduction

Reproduction is important for each species, because this is the only way for a living being to continue its lineage. Apart from being important for a particular individual, reproduction is also important for the whole ecosystem. Reproduction helps in maintaining a proper balance among various biotic constituents of the ecosystem. Moreover, reproduction also facilitates evolution because variations come through reproduction over several generations.

Types of reproduction

There are two main types, viz. asexual and sexual reproduction.

Asexual reproduction: When a single parent is involved and no gamete formation takes place, the method is called asexual reproduction. No meiosis happens during asexual reproduction.

Sexual reproduction: When two parents are involved and gamete formation takes place, the method is called sexual reproduction. Meiosis happens during gamete formation, which is an important step of sexual reproduction.

Intext questions (page 128)

What is the importance of DNA copying in reproduction?

Answer: The importance of DNA copying during reproduction is that: (i) it is responsible for the transmission of parental characteristics to the offspring, and (ii) it also leads to certain genetic variation.

Why is variation beneficial to the species but not necessarily for the individual?

Answer: Variations allow organisms to exist in diverse habitats or niches. In the absence of variations, a species may be restricted to a particular area. If this area gets drastically altered, due to various natural or man-made causes, the species may be wiped out. However, if some variations were present in a few individuals, these could colonize other habitats and survive. But if the variation is present in a single organism, there would be very little chance for the species to survive.

Asexual reproduction

Modes of reproduction used by single organisms

Modes of reproduction involving a single parent, without involving gametes, are known as asexual modes of reproduction. Organisms can reproduce asexually in many ways. Some of them are given here.

Fission

Binary fission: Most of the unicellular animals prefer this method for reproduction. These organisms reproduce by binary fission, especially when conditions are favourable, i.e. an adequate amount of food and moisture is available. Binary fission is somewhat similar to mitosis. The mother cell divides into two daughter cells, and each daughter cell begins its life like a new individual. The parent generation ceases to exist after binary fission. Amoeba is a very good example of an organism which reproduces by binary fission.

Multiple fission: When conditions become unfavourable, i.e. food, moisture, proper temperature, etc. are not available, this is the preferred mode of reproduction by unicellular organisms. The organism develops a thick coating around itself, called a cyst. The cyst helps the organism to tide over the bad phase. The nucleus divides into several nuclei and each daughter nucleus is surrounded by a membrane. All metabolic activities stop in the organism after cyst formation. When favourable conditions return, the cyst dissolves or breaks down, releasing the daughter nuclei. The daughter nuclei, in turn, grow into new individuals. Plasmodium and Entamoeba undergo a cyst stage when they are not in the body of their prime host, i.e. humans.

Fragmentation

In multicellular organisms with simple body organization, simple reproductive methods have been noticed. Reproduction by fragmentation is seen in filamentous algae, e.g. Spirogyra. In Spirogyra, the plant body breaks up into smaller fragments. Each fragment grows into a new individual.

Regeneration

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. Regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells.

Budding

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.

Vegetative propagation

Vegetative propagation is the ability of plants to reproduce by bringing forth new plants from existing vegetative structures without sexual reproduction. Some examples of vegetative propagation are given below.

Tuber of potato: The potato tuber is a modified stem. Many notches can be seen on the surface of a potato. These are called the 'eyes' of the potato. Each 'eye' of a potato can give rise to a new potato plant. Farmers utilize this capability of potatoes to grow potatoes more quickly, which is not possible by using the seeds of potato.

Modified roots of carrot and sweet potato: Carrot and sweet potato are examples of modifications of roots for food storage. These roots can give rise to new plants when kept under the soil.

Rhizomes of ginger and turmeric: Rhizomes are examples of modified underground stems for food storage. These contain nodes, internodes and scaly leaves. When buried under the soil, the rhizomes produce new plants.

Leaf of Bryophyllum: Leaves of Bryophyllum have notches on the margin. If a leaf is put under the soil, small saplings grow from the notches on the leaf margin.

Artificial vegetative propagation: Man has used artificial vegetative propagation to grow many plants. This has enabled farmers and horticulturists to grow many plants in a shorter duration and has helped them to earn more profit. Artificial vegetative propagation has also helped in developing many new varieties of plants. Stem cutting, layering and grafting are the preferred means of artificial vegetative propagation.

Spore formation

Rhizopus produces hundreds of microscopic reproductive units called spores. When the spore case (also called sporangium) bursts, the spores spread into the air. These air-borne spores land on food or soil; under favourable conditions like damp and warm conditions, they germinate and produce new individuals. Most of the fungi like Rhizopus, Mucor etc., bacteria and non-flowering plants such as ferns and mosses reproduce by the method of spore formation.

Advantages of asexual reproduction

• The organism does not have to depend on another organism for carrying out reproduction, because only a single parent is needed.
• It takes less time than sexual reproduction and hence more offspring can be produced in a shorter time.
• The offspring are exact clones of their parent.
• Desirable characteristics can be easily incorporated into plants with artificial vegetative propagation.

Disadvantages of asexual reproduction

• As a single parent is involved, there is a negligible chance of variation.
• In most cases in simple organisms, the parent generation ceases to exist after asexual reproduction.
• Asexual reproduction cannot give rise to biodiversity, which is important for a healthy ecosystem.

Intext questions (page 133)

How does binary fission differ from multiple fission?

Answer: The differences are given below.

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

Answer: Spores are tiny, spherical, asexual reproductive bodies which, under favourable conditions like damp and warm conditions, germinate to produce new plants. They are covered by a hard protective wall, which enables the plant to survive unfavourable conditions.

Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer: Multicellular organisms cannot reproduce cell by cell because they are not a simple random collection of cells. In them, specialised cells are organized as tissues and tissues are organised into organs, which then have to be kept at different positions in the body. Cell-by-cell division would be impractical. Multicellular organisms, therefore, require more complex ways of reproduction.
Moreover, simple multicellular organisms possess a special type of tissue which has the potential to grow into a new organism, but complex multicellular organisms have no such specialised cells.

Why is vegetative propagation practised for growing some types of plants?

Answer: Vegetative propagation is used for growing certain plants which do not produce viable seeds. It is also used for growing plants bearing superior traits, because it produces genetically identical plants. It is also used for growing plants which require a longer time to grow and become mature. Plants which require a lot of care during the early stages of development are also grown by this method.

Why is DNA copying an essential part of the process of reproduction?

Answer: Chromosomes in the nucleus of a cell contain information for inheritance of features from parent to the next generation in the form of DNA. The DNA in the cell nucleus is the information source for making proteins. Therefore, a basic event in reproduction is the creation of a DNA copy for the next generation.

Sexual reproduction

Sexual reproduction in plants

Sexual reproduction is the process in which two components (male and female) are involved to produce offspring of their own kind. A bull alone cannot produce new calves; it needs a cow. A female sheep alone cannot produce new ones; it needs a male sheep. Both the sexes, male and female, are needed to produce new offspring.

Parts of a typical flower

A flower is a modified shoot with limited growth. Flowers vary in size, shape, structure and colour. The main parts of a flower are:

1. Calyx
2. Corolla
3. Androecium
4. Gynoecium

Androecium is the male part of a flower and gynoecium is the female part. Androecium is a group of stamens. Each stamen consists of a stalk called the filament and a small bag-like structure called the anther at the tip. The pollen grains are contained in the anther within the pollen sacs.

Gynoecium: Gynoecium is the female part of the flower and consists of the carpels. Gynoecium has three parts: (1) stigma, (2) style and (3) ovary. The ovary contains the ovules and each ovule carries within it an embryo sac, within which lies the egg cell or the female gamete.

The sexual reproduction in flowering plants involves (1) pollination and (2) fertilization.

1. Pollination

Transfer of pollen grains from the anther to the stigma is called pollination. Pollen grains are transferred mainly by wind, water and insects. They are called pollinating agents. Pollination is the first and important event in the development of the fruit and seed. Pollination is followed by fertilization.

Types of pollination

Pollination is of two types: (1) self pollination and (2) cross pollination.

Self pollination: Self pollination is also known as autogamy. The transfer of pollen grains from the anther of a flower to the stigma of the same flower or another flower of the same plant is known as self pollination.

Advantages of self pollination

• Self pollination is certain in bisexual flowers.
• Flowers need not depend on agents of pollination.
• There is no wastage of pollen grains.

Disadvantages of self pollination

• The seeds are fewer in number.
• Endosperm is minute. Therefore, the seeds produce weak plants.
• New varieties of plants cannot be produced, resulting in the degradation of the plant.

Cross pollination (allogamy): The transfer of pollen grains of a flower to the stigma of another flower of a different plant of the same species is called cross pollination or allogamy.

Advantages of cross pollination

• The seeds produced as a result of cross pollination develop, germinate properly and grow into better plants, i.e. cross pollination leads to the production of new varieties.
• More viable seeds are produced.

Agents of cross pollination

In order to bring about cross pollination, it is necessary that the pollen should be carried from one flower to another of a different plant. This takes place through the agency of animals, insects, wind and water.

Zoophily (pollination by insects, birds and animals): Birds, squirrels and insects are attracted to the bright petals of the flowers. These flowers are also large in size and have a sweet smell. Some of these flowers have nectar and a sweet scent. This is the most common of all methods of pollination. Pollination by birds is called ornithophily.

Anemophily (pollination by wind): The flowers pollinated by air are mostly small in size and without any attractive colour, smell and nectar. They produce a large number of pollen grains to make up for the wastage of pollen in transit. The pollen grains are dry and powdery, and hence are easily carried by the wind. Some pollen grains even have wings. Stigmas are large and protruding, even branched and feathery, e.g. maize. Flowers pollinated by wind are called anemophilous, e.g. grass and pine.

Pollination by water (hydrophily): This pollination takes place in water plants or plants that are adapted to a water habitat, e.g. Vallisneria. This pollination is known as hydrophily. The flowers are small and inconspicuous.

2. Fertilization

Pollination is the transfer of pollen grains from the anther to the stigma. Each pollen grain has protective walls called exine and intine. The outer wall, exine, is thick and has small pores called germination pores. The inner wall is thin and elastic.

Germination of pollen grain: If a pollen grain falls on a suitable stigma, it starts germinating. A mature pollen grain consists of two cells. The larger one is the vegetative cell and the smaller one is the generative cell. The vegetative cell starts growing and emerges through the germination pore. It develops through the style as a long tube known as the pollen tube. The generative cell gets into the tube and divides into two male gametes (sperms).

Process of fertilization: The pollen tube enters the embryo sac through the micropyle. At this time, the pollen tube bursts open, and the gametes released from the pollen tube enter the embryo sac. One of the gametes fuses with the egg, and the other fuses with the secondary nucleus. The fusion of a male gamete with the egg is known as fertilization. The fertilized egg is known as the zygote, which develops into the embryo.

Double fertilization: The other male gamete fuses with the secondary nucleus. The secondary nucleus is diploid in nature. The fusion of this nucleus with the second male gamete is known as triple fusion. The triple fusion nucleus is called the endosperm nucleus because it develops into the endosperm. Endosperm is a nutritive tissue meant for the development of the embryo. The process of fusion of a male gamete with the egg and the other gamete with the secondary nucleus is known as double fertilization.

Post-fertilization changes

• The ovule develops into the seed.
• The integuments of the ovule develop into the seed coats.
• The ovary enlarges and develops into the fruit.

Reproduction in human beings

Male reproductive system

The male reproductive system in human beings is composed of the following parts:

Testis: There is a pair of testes, which lie in a skin pouch called the scrotum. The scrotum is suspended outside the body, below the abdominal cavity. This helps in maintaining the temperature of the testes below the body temperature, which is necessary for optimum sperm production. The testis primarily serves the function of sperm production. Sperms are the male gametes. Apart from that, the testis also produces testosterone. Testosterone is also called the male hormone, as it is responsible for developing certain secondary sexual characters in boys.

Vas deferens: The vas deferens is the tube which carries sperms to the seminal vesicle.

Seminal vesicle: This is the place where sperms are stored. Secretions from the seminal vesicle and prostate gland add up to make the semen.

Penis: It is a muscular organ which serves the genito-urinary functions. The urethra works as the common passage for urine as well as for sperms.

Female reproductive system

The female reproductive system in human beings is composed of the following parts:

Uterus: This is a pear-shaped hollow muscular organ. The uterus is the place where the embryo gets implanted and develops into a newborn baby. The wall of the uterus provides safety and nutrition to the growing foetus.

Fallopian tubes: One fallopian tube comes out from each side at the top of the uterus. The fallopian tubes end in finger-like structures called fimbriae. Fertilization happens in the fallopian tube.

Ovary: There are two ovaries, one near each fallopian tube. The ovary produces the eggs or the female gametes. All the eggs are produced by the ovary when the female child is still in the womb. One egg matures in each ovulation cycle and is released from the ovary. The egg is caught by the fimbriae and transferred to the fallopian tube.

Vagina: The cervix (mouth of the uterus) opens into the vagina. The vagina is a muscular tube-like organ which serves as the passage for the sperms and also as the canal during child birth.

Puberty

Human beings are complex animals and hence there is a distinct phase in their life cycle which marks the onset and attainment of sexual maturity. This period is called puberty. It usually starts at around 10–11 years of age in girls and at around 12–13 years of age in boys. It usually ends at around the 18th year of age in girls and at around the 19th year of age in boys. Since the years during puberty end in 'teen', this phase is also called teenage.

Changes in boys during puberty: The boys suddenly grow in height dramatically. The voice becomes deep and the Adam's apple becomes prominent. Shoulders become broad and the body becomes muscular. Facial hair begins to grow. Hair also grows under the armpit and in the pubic region.

Changes in girls during puberty: The voice becomes thin. Shoulders and hips become rounded. Breasts get enlarged. Hair grows under the armpit and in the pubic region.

Sexual dimorphism: The physical dissimilarities in the male and female of a species which give them different appearances is called sexual dimorphism.

Secondary sexual characters: Features which highlight sexual dimorphism are called secondary sexual characters.

Menstruation: Menstruation is a trait which is unique to humans and some primates. During each ovulation cycle, the uterus prepares itself in anticipation of a possible pregnancy. The uterine wall develops an additional lining. When the egg is not fertilized, it gets disintegrated and so does the additional lining in the uterine wall. The fragments of disintegrated tissues are shed along with blood. This is observed in the form of bleeding through the vagina, which can last from 3 to 7 days. The whole sequence of events during an ovulation cycle is called the menstrual cycle. The bleeding which occurs for a few days is called menstruation. The first menstrual flow is called menarche and the last menstrual flow (which happens in the late 40s) is called menopause.

Reproductive health

Human beings are different from other animals because they have the power of thinking. They have to obey certain moral values and need to behave sensibly in most aspects of life. The beginning of puberty does not mean that a person is psychologically ready for the process of reproduction. For a human being, reproduction involves more than just producing an offspring. As any act of sex has the potential of fertilization, taking care of contraception becomes important. Moreover, the act of sex also has the potential of spreading many sexually transmitted diseases. Examples of STDs are gonorrhea, herpes, syphilis, AIDS and hepatitis B. AIDS and hepatitis B are incurable to date. Even the curable STDs are potentially dangerous, not only physically but also psychologically.

Reproductive health involves preventing the chances of STDs and preventing unwanted children. Reproductive health means a couple should be able to enjoy the reproductive phase of its life without taking the burden of a gigantic family.

Intext questions (page 140)

How is the process of pollination different from fertilisation?

Answer: The differences are given below.

What is the role of the seminal vesicles and the prostate gland?

Answer: Secretions from the seminal vesicles and prostate gland provide nutrition to the sperms and make their transport easier by providing a fluid medium.

What are the changes seen in girls at the time of puberty?

Answer: Changes seen in girls at the time of puberty are as follows:

1. Hair grows in the armpits and the pubic region.
2. Mammary glands (breasts) develop and the hips broaden.
3. The uterus, vagina and fallopian tubes enlarge and the pelvis widens. Menstruation and ovulation also start.

How does the embryo get nourishment inside the mother's body?

Answer: The embryo gets nutrition from the mother's blood with the help of a special tissue called the placenta. This is a disc-like tissue which develops between the uterine wall and the embryo. It has villi on the embryo's side of the tissue. On the mother's side are blood spaces which surround the villi. This gives a large surface area for oxygen and glucose to pass from the mother to the embryo.

If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Answer: No, copper-T does not prevent the transmission of sexually transmitted diseases. Copper-T only prevents implantation. The only safe method used to prevent the transmission of sexually transmitted diseases is the use of condoms.

Exercise questions (page 141)

Asexual reproduction takes place through budding in

1. amoeba.
2. yeast.
3. plasmodium.
4. leishmania.

Answer: (b) yeast. Asexual reproduction in Hydra and yeast takes place by budding.

Which of the following is not a part of the female reproductive system in human beings?

1. Ovary
2. Uterus
3. Vas deferens
4. Fallopian tube

Answer: (c) Vas deferens. It is a part of the male reproductive system in humans.

The anther contains

1. sepals.
2. ovules.
3. carpel.
4. pollen grains.

Answer: (d) pollen grains. The anther is the male reproductive part in plants. It contains pollen grains, the first cell of the male gametophyte.

What are the advantages of sexual reproduction over asexual reproduction?

Answer: There are a number of advantages of sexual reproduction over asexual reproduction. These include:

1. Sexual reproduction creates variations which are useful for ensuring the survival of the species and for species formation.
2. Two different individuals in a population would have quite different patterns of accumulated variations.
3. The desired phenotype can be promoted by sexual reproduction.

These advantages are not available with asexual reproduction.

What are the functions performed by the testis in human beings?

Answer: Functions of the testes: (i) they produce male sex cells, the sperms; (ii) they produce the male sex hormone testosterone.

Why does menstruation occur?

Answer: Menstruation occurs when the egg is not fertilised. Every month the uterus prepares itself to receive a fertilised egg, and to nourish the embryo its lining becomes thick and spongy. In case the egg is not fertilised, this lining breaks and is discharged out of the body through the vagina in the form of blood.

Draw a labelled diagram of the longitudinal section of a flower.

Answer: The parts of the flower and their functions are:

• Petals (corolla): brightly coloured; attract insects for pollination; the base contains the nectary which produces nectar.
• Sepals (calyx): protect the flower while in bud; generally green and serve to photosynthesize food.
• Receptacle (thalamus): the base of the flower to which all parts are attached. In some cases, after fertilization it becomes fleshy (apple).
• Pistil (carpel): the female reproductive part of the flower, known as the gynoecium. It comprises the stigma, style and ovary. The stigma is sticky and receives pollen during pollination. The style links the stigma to the ovary; it is an elongated tube through which pollen tubes grow. The ovary contains ovules (which contain the female gametes), which develop into seeds.
• Stamen: the male reproductive part of the flower, known as the androecium. It comprises the anther and filament. The anther is bilobed; each lobe contains two pollen sacs which produce pollen grains. The filament is the stalk of the stamen that supports the anther.

What are the different methods of contraception?

Answer: The different methods of contraception are:

1. Barrier methods: physical devices such as condoms and the diaphragm are used. Condoms are used by males by putting a rubber covering on the penis. They prevent sperms from meeting the egg.
2. Chemical methods: females use pills, oral pills and vaginal pills. The oral pills contain hormones which stop the ovaries from releasing the ovum. The vaginal pills contain chemicals called spermicides which kill the sperms.
3. Surgical methods: in males, a small portion of the sperm duct is cut by surgery and the cut ends are tied properly (vasectomy). This prevents the sperms from coming out. In females, a small part of the oviduct is cut and tied (tubectomy). This prevents the egg from entering the oviduct.

How are the modes of reproduction different in unicellular and multicellular organisms?

Answer: Unicellular organisms are made up of only a single cell, in which all the functions are performed by that single cell. So reproduction is done by simple, asexual methods. But in multicellular organisms various cells perform different functions, so the production of all these specialised cells/tissues is required, and simple methods of reproduction are insufficient.

How does reproduction help in providing stability to populations of species?

Answer: Reproduction leads to certain variations in the characteristics of the offspring. This may allow organisms to exist in diverse habitats and niches. Certain variations present in the individuals of a population may enable them to survive unfavourable conditions. Organisms with such favourable traits transmit the characters to their offspring, thereby providing stability to the population of a species.

What could be the reasons for adopting contraceptive methods?

Answer: The reasons for adopting contraceptive methods are: (i) to avoid frequent pregnancies, which in turn helps in population control; (ii) to prevent the spread of sexually transmitted diseases.

Question. DNA copying is necessary during reproduction because
(a) it leads to the transmission of characters from parents to offsprings
(b) it leads to variation
(c) it helps in survival of the species over time
(d) all of these.
Answer. D

Question. Which of the following is a sexually transmitted viral disease?
(i) Gonorrhoea  (ii) Syphilis
(iii) Warts         (iv) HIV-AIDS
(a) (i), (iii) and (iv)
(b) (ii) and (iv)
(c) (iii) and (iv)
(d) (i) and (ii)
Answer. C

Question. Unisexual flowers contain
(a) both stamen and carpel
(b) only stamen
(c) only carpel
(d) either stamen or carpel.
Answer. D

Question. Sexual reproduction is the mode of reproduction that
(i) depend on the involvement of two different gametes.
(ii) incorporates a process of combining DNA from two gametes.
(iii) gives better chances of variations as compared to asexual reproduction.
(iv) gives rise to genetically identical offspring.
(a) (i) and (ii)
(b) (i), (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (i), (ii) and (iii)
Answer. D

Question. Factors responsible for the rapid spread of bread mould on slices of bread are
(i) large number of spores
(ii) availability of moisture and nutrients in bread
(iii) presence of tubular branched hyphae
(iv) formation of round shaped sporangia.
Which of the above statements are true?
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer. C

Question. The number of chromosomes in parents and offsprings of a particular species remains constant due to
(a) doubling of chromosomes before zygoteformation
(b) halving of chromosomes during gamete formation
(c) doubling of chromosomes during gamete formation
(d) halving of chromosomes after gamete formation.
Answer. B

Question. Which of the following is not a vegetative propagule?
(a) Root
(b) Stem
(c) Leaf
(d) Seed
Answer. D

Question. Which of the following layers of uterus breaks off during menstruation?
(a) Epimetrium
(b) Myometrium
(c) Endometrium
(d) Perimetrium
Answer. C

Question. Select the correct match.
Organism Mode of reproduction
(a) Bryophyllum – Leaf bud
(b) Hydra – Binary fission
(c) Paramecium – Multiple fission
(d) Spirogyra – Vegetative propagation
Answer. A

Question. In humans, gestation is completed in
(a) 40 weeks
(b) 60 weeks
(c) 120 weeks
(d) 240 days.
Answer. A

Question. Why is cell division considered as a type of reproduction in unicellular organisms?
Answer. Cell division results in the formation of two daughter cells, i.e., it results in the production of more individuals of the organism like the process of reproduction.

Question. How regeneration is carried out?
Answer. Regeneration is carried out by specialised cells which proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues.

Question. Name any two type of asexual reproduction.
Answer. (i) Fragmentation (ii) Budding

Question. Name the parts of a bisexual flower that are not directly involved in reproduction.
Answer. The parts of a bisexual flower that are not directly involved in reproduction are : sepals (calyx), petals (corolla) and thalamus.

For question numbers 41-50, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Both assertion and reason are true, and reason is correct explanation of the assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Assertion is false, but reason is true.

Question. Assertion : In human male, testes are extra abdominal and lie in scrotal sacs.
Reason : Scrotum acts as a thermoregulator and keeps testicular temperature lower by 2°C for normal spermatogenesis.
Answer. A

Question. Assertion : Vagina acts as copulation canal and fertilisation canal both.
Reason : Insemination occurs in vagina of female.
Answer. D

Question. Assertion : One pollen mother cell forms four microspores.
Reason : Microspores are formed due to reduction division.
Answer. B

Question. Assertion : Regeneration cannot be regarded as reproduction.
Reason : Most organism would not normally depend on being cut up to be able to reproduce.
Answer. A

Question. Assertion : Spores of Rhizopus can survive under extreme climatic conditions.
Reason : Spores are the reproductive parts in Rhizopus.
Answer. B

Question. Assertion : Contraceptive pills can cause side effects in females.
Reason : They prevent pregnancy by blocking the incoming sperms.
Answer. C

Question. Assertion : Male gametes are motile.
Reason : They are free-living diploid cells.
Answer. C

Question. Assertion : Corolla is a floral part.
Reason : It helps in pollination.
Answer. B

Question. Assertion : The uterine line in human females becomes thick and spongy every month.
Reason : The lining breaks and comes out through the vagina as blood and mucus if fertilisation does not occur.
Answer. B

Question. Assertion : Gametogenesis is the production of gametes through the meiosis.
Reason : In oogenesis polar bodies are formed.
Answer. B

Question. How Spirogyra reproduces?
Answer. Spirogyra reproduces through the fragmentation process.
Fragmentation is the mode of reproduction in which parent body breaks into two or more fragments and each fragment develops into a new individual. It is a method of
reproduction in many filamentous algae, mycelial fungi and thalloid bryophytes.

Question. How do insects help in pollination?
Answer. In entomophily (insect pollination), when an insect visits a flower for nectar, the pollen grains get deposited on the body of insect. When this insect visits another flower, some of the pollen grains stick to stigma of another flower. This leads to pollination.

Question. Why do multicellular organisms use complex way of reproduction?
Answer. In multicellular organisms, cells are organised into specialised groups; tissues, organs or organ systems, each of which occupy specific locations in the body. In such an organised condition cell-by-cell division would be impossible.
Hence, multicellular organisms need complex methods of reproduction.

Question. Describe the role of prostate gland, seminal vesicle and testes in the human male reproductive system.
Answer. Prostate glands - Secretion of the prostate gland nourishes and activates the spermatozoa to swim.
Seminal Vesicles - They produce an alkaline secretion which forms 60% of the volume of semen. Alkaline nature of the removal fluid helps to neutralise the acidic environment of the male urethra as well as that of female reproductive tract which otherwise would inactive and kill sperms.
Testes are responsible for producing sperm and secreting male sex hormones e.g., testosterone.