Class 10 Science Chapter 7 Important Questions

The process of reproduction is necessary for preservation and increase in population of a species. If the organism would not reproduce the species to which they belong would extinct once they are dead. In order to maintain the species an organism reproduces. Reproduction process is not necessary for an individual to live but necessary for perpetuation of its species.

Reproduction process is not essential for an individual. But it is very necessary for the continuity of the species. Reproduction performs following functions:
(i) In the process of reproduction one generation of living organism produce the next generation that’s why parents produce offspring like themselves. Thus, this process preserves a species and maintains community of the race.
(ii) Reproduction is also the means of increasing the population of a species.
(iii) Reproduction plays an important role in evolution by transmitting favourable variation from parents to offspring.

An offspring formed by a form of asexual reproduction or sexual reproduction involving fusion of gametes. In case of asexual reproduction, the offspring have subtle difference from their parents. In sexually reproducing organisms these difference is more pronounced as a result of genetic combination during meiosis.

The consistency of DNA replication during reproduction is important for the maintenance of body design features that allow an organism to use a particular ecological niche. However, DNA replication is not full-proof. It results in subtle variation which may be harmful or beneficial to the individual according to the ecological niche it occupies. The niches may also change any variation in an individual which makes it suitable for the niche would be beneficial for its survival. Variation is the basis of evolution.

Method of asexual reproduction are:
(i) Fission
(ii) Budding
(iii) Fragmentation
(iv) Spore formation and
(v) Vegetative propagation.

Organism which reproduce by:
(a) Budding: Hydra and Yeast.
(b) Fragmentation: Spirogyra and flatworm.
(c) Spore formation: bacteria, mucor, moss and fern.

The higher multicellular organism have differentiated structure and function unlike spirogyra in which all the cells are similar and independent units.

In complex organisms, reproductive tissues are entrusted with reproduction. The male and female gametes combine to form a zygote which by cell division and differentiation forms the individual. The zygote has all the genetic information to develop into a fully developed individual.

Multicellular organisms cannot simply divide cell by cell because
(i) Many multicellular organisms are not simply a random collection of cells. Specialised cells are organized as tissues and tissues are organized into organs which are placed at definite position in the body.
(ii) Each organ performs a specific function. In such a carefully organized situation cell division would be impracticable.

Asexual Reproduction: The type of reproduction in which only single parent is involved to produce offsprings exactly similar to the parents. In this type of reproduction, meiosis, gamete formation and gamete formation and gamete fusion does not take place. The cell division involved with asexual reproduction is mitosis.
The method involved in the in asexual reproduction:
(i) Fusion
(ii) Budding
(iii) Fragmentation
(iv) Spore formation
(v) Vegetative propagation

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 single leaf of a plant that helps in survival of the species.

Regeneration.
Basic features:
(i) Regeneration is carried out by specialized cells that proliferate and make large number of cells.
(ii) This mass of cell undergo differentiation to form various cell types and tissues.
(iii) These changes take place in an organized sequence referred to as development.

(a) (i) Hyphae
(ii) Sporangia
(b) (i) On maturing sporangia ruptures and release spores. Each spore contain 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.

Leishmania and Plasmodium reproduce by fission.
Difference: Leishmania reproduce by binary fission that occurs in definite orientation in relation to whip like flagella, forming two cells:
Plasmodium (malaria parasite) divides into many daughter cells simultaneously by multiple fission.

Unicellular organism such as bacteria simply spilt into two equal halves during cell division to produce two new cell individuals. Plasmodium divides into many daughter cells simultaneously. This proves that cell division is a type of reproduction in unicellular organisms.

(i) Potato
(ii) Ginger
(iii)Turmeric
(iv) Onion
(v) Banana and
(vi) Garlic.

Bryophyllum leaves bear buds in their notches along their margin. When a leaf falls, the buds come in contact of the soil and develop into plantlets. These plantlets later grow into new plants.

(i) Grafting
(ii) Cutting
(iii) Layering and
(iv) Tissue culture.

(i) Bougainvillea
(ii) Rose
(iii) Cactus
(iv) Sugarcane
(v) Pineapple.

(i) Orchids
(ii) Chrysanthemum
(iii) Asparagus.

Animals multiply asexually by a number of methods like binary fusion, multiply fission, budding gemmules, fragmentation and spores or cysts.
(i) Binary fission: It is found in multicellular animals like Amoeba, Paramoecium, Euglena etc. After attaining an optimum size, the adult individual undergoes a simple division into two daughter cells of equal size. It consists of division of the nucleus followed by cleavage of cytoplasm into equal parts, each having a daughter nucleus. Binary fission can occur in any place in Amoeba. It is longitudinal in Euglena and transverse in Paramoecium. The organism undergoing binary fission are almost immortal since they never grow old but divide to form two young offspring after attaining the adult size.
(ii) Multiple fission: The mode of asexual reproduction is found in unicellular animals or protozoans example Amoeba, Plasmodium, Monocystis. The nucleus of the parent cell undergoes repeated division to produce a number of daughter nuclei. The cytoplasm cleaves around each nucleus simultaneously to form a number of daughter cells or individuals inside a parent cell. Ultimately under favourable conditions parent cell membrane ruptures and daughter individual are released. Sometime the daughter cell derived from a multiple fission develop resistant coverings to produce spores. The process is called sporulation. In others the parent cell develops a cyst, wall around before undergoing multiple fission. Both the process is known in amoeba. As in binary fission, the parent individual disappears during the formation of daughters in multiple fission.

Single celled Amoeba reproduces by the asexual method known as binary fission that’s why during division, Amoeba splits into two equal halves. The splitting of the two cells during binary fission can take place in any plane.
During binary fission of Amoeba nuclear division starts first followed by appearance of a constriction in the cell membrane. As the nuclear division completes, constriction deepen and divides into two parts, each containing one nucleus. Finally, two independent daughter Amoeba are formed.

Advantages of vegetative reproduction are
(i) This is a very useful method of multiplying plants which do not produce seeds.
(ii) This is an easier and quicker method of propagation than from seeds. For example, lilies produce flowers within one or two years when grown vegetative. They produce flower in 4-7 years when grown seeds.
(iii) Vegetative propagation methods are useful in preservation of the desired parental characters in the offspring it is not possible by seeds as they are blended with the characteristics of both the parents.

To grow plants by cutting rather than from seeds is a method of artificial asexual reproduction. It has the following advantages:
1. It is the only method of reproduction in seedless plants.
2. We get a fully matured plants in a very short time.
3. It is a short cut method for rapid multiplication.
4. It helps to preserve the type of character that a plant breeder desires.
5. It is very easy and economical method for the multiplication of ornamental plants.

The modes of reproduction that depend on the involvement of two individuals before a new generation can be created is called sexual reproduction.

Variability in a race appears due to:
(i) Recombination as a result of crossing over in meiosis.
(ii) Chance separation and coming together of homologous chromosomes, during gametogenesis and fertilization.
(iii) Chromosomal aberrations or mutations: All these changes occur only in sexually reproducing plants. In vegetative propagation the new plants are formed by somatic division of cells and they would be similar to parts of the parent plant formed during normal growth and development that also involve somatic divisions. Hence plants propagated vegetatively are usually like the parents.

Vegetative Propagation: The mode of reproduction in which plant part like the root, stem and leaves develop into new plants under appropriate conditions is called vegetative propagation.
It is used in case of
(i) When the plant/plants which do not produce seeds such as rose, banana, etc.
(ii) When we want to produce young plants genetically similar enough to the parent plants.
Uses:
Plants raised by vegetative propagation can bear flower and fruits much earlier. Thus we can obtain yield much earlier than those produced from seeds, like in mango.

In asexual reproduction very little variation occur within generation. Asexual reproduction has a lesser significance for evolution of species.
Asexual reproduction involve only a single individual. It does not require two sexes. Sexual reproduction involves two different individuals, male and female sexes. The offspring is produced due to fission of male and female gametes.

Meiosis is a type of cell division that occurs in the reproductive cells of an organisms to form gametes which has half the DNA component of the parent. When the male and female gametes fuse to form the zygote the DNA is restored to the normal complement.

When a flower contains stamens or carpels is said to be unisexual.
Examples: Papaya and watermelon
When a flower contains both stamens (male) and carpel(female) are said to be bisexual.
Examples: Hibiscus and mustard.

The transfer of pollen grains from anther to stamen 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 lie 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.

The process of fusion of one male gametes with that of a female gametes(egg) is known as fertilization.

Germination: The development of the embryo contained in the seed into seedling under favourable condition is called germination.
Fertilization: The fusion of male germ cell with the female gamete is known as fertilization.

After pollination, pollen grain start germination on the stigma. The inline of the pollen grain develops pollen tube through germ pores of the exiles. The pollen tube pierce through tissue of the style and reaches up to ovule in the ovary. By this time pollen tube comes to possess two male gametes or sperms, formed from the generative nucleus. Generally, the tip of the pollen tube enters the embryo sac of the ovule through micropyle. The two male gametes along with the contents of the pollen tube are emptied into one of the synergids. From synergids one male gametes migrate to the egg cell and fuses with it to form the zygote which give rises to embryo. The other male gametes fuse with the secondary nucleus; this fusion-mass develops into the endosperm.

After pollination and fertilization, following change occur in a flower:
(i) The petals, stamens, style and stigma of the flower fall off.
(ii) Generally sepals dry up and hold the ovary.
(ii) The ovules confined in the ovary develop into seeds.
(iii) The ovule confined in the ovary develop into seeds.
(iv) The ovary develops into fruit. Sometimes the ovary well may harden as in poppy. Sometime ovary wall becomes fleshy and succulent as in tomato or plums.

The males shows the growth of public hair, beards and mustaches, deepening of voice, occasional penis enlargement and erection. The females show development of breasts, darkening of nipples, menstruation and growth of public hair.

The creation of organ germ cells to participate in sexual reproduction is a specialized function of an animal. While the body of the organism is growing into an adult, the resources of the body are mainly concentrated towards this growth maturation of reproductive tissue is not a major priority. As the rate of general body growth begins to slow down, reproductive tissues begin to mature. This period during adolescence is called puberty.

Male reproductive organs: Reproductive system of male human body consist of the following organs:
(a) Testes: There is a pair of oval testes present in the scrotum. They descend into the scrotum at the time of birth. The approximate size id 4 × 3cm and each weight about 12 g. In the testes sperms are produced.
(b) Epididymis: It is the portion which is closely attached to the posterior side of each testis. It receives and store the sperms produced by the testes.
(c) Vas deferens: From each epididymis a tube of whitish colour arises. The tube is known as vas deferens. The sperm pass through it.
(d) Seminal vesicle: The epididymis is connected by the seminal vesicle by vas deference. The seminal vesicle is in pair of small sacs situated at the base of urinary bladder above the prostate gland. They join each other to form ejaculatory duct. Seminal vessel secretes a viscous fluid which forms most of the part of semen. It also lubricates the passing through which the sperm travel. This fluid also protects the sperm from the acids normally present in the urethra and female reproductive duct.
(e) Prostate gland: It is a billowed glandular mass embracing the urethra. In man two prostate glands fuse to form only one. It produced prostatic fluid which is discharged into urethra through more than two dozen fine ducts. There is more secretion during secretion act when they are forced to eject by contraction of muscular and elastic tissues.
(f) Urethra: It is a tube starting or arising at the urinary bladder. It passes through the penis to the tip of the gland penis. The urethra of the male functions both for the passage of sperms and urine.
(g) Penis: The penis is the copulatory organ of male for the transfer of sperms to the female reproductive tract. It is about 3” long in the flaccid condition. It is highly muscular organ having erectile tissue and vascular spaces. Under excitement these vascular space is filled with blood and provide additional rigidity. The enlarged tip of the penis is known as glans penis. It is most sensitive part and it is protected by a sheath of skin called the prepuce.

Role of seminal vesicle and prostate gland.
Along the path of the vas deference these glands add their secretion so that the sperms are now in a fluid which makes their transport easier and this fluid also provides nutrition to sperm.

(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 sperms.
(b) Testes produce sperms and male hormone testosterone.

The female reproductive parts consist of the following:
(a) A pair of ovaries,
(b) fallopian tubes,
(c) Uterus,
(d) Vagina,
(e) Vulva.
(a) Ovaries: The paired ovaries lie on either side of the uterus or lower part of the abdominal cavity. Each ovary is 3cm long bean shaped with the size of unshelled almond. The function of the ovary is to produce eggs and hormones notable estrogens and progesterone.
(b) Fallopian tubes: These are the two tubes attached to the uterus one on either side. Each tube is about 10-12 cm in length. The fallopian tube provides for the eggs to pass into the uterus by ciliary actions. It is the site fertilization.
(c) Uterus: It is a pear shaped hollow muscular organ situated between the urinary bladder and the rectum. It receives the fallopian tubes on either side of uterus and is capable of undergoing great enlargement. Uterus contains developing young and expels it y muscular contraction at birth. It is the site of development of young one.
(d) Vagina: It is a short, wide collapsible muscular tube about 9cm long. It connects cervical canal at the upper end with external genitalia at the lower end. Vagina internally lined by a much folded epithelial layer. In virgins’ orifice of a vagina is partially closed by a membrane called hymen. Vagina secretes acidic fluid which provides first hindrance in the movement of sperms towards uterus. The function of vagina is to receive penis and its ejaculated semen to act as lower part of birth canal and to duct for menstrual flow.
(e) Vulva: Vulva or the female external ganitalis consist of pubis, labia majora, labia minora-clitoris, urinary meatus and vaginal orifice. Pubis is covered with hair at maturity; labia majora are two folds of skin containing hair, sweat glands, labia minora are small akin folds lying internal to labia majora. Labia minora does not contain hair, sweat and sebaceous glands. At the upper junction of labia minora folds is present clitoris. It is formed of small erectile tissue and covered by prepuce. Below the clitoris lies opening of urethra called urinary meatus.

In girls, (i) breast size begins to increase with darking of the skin of the nipples at the tips of breast.
(ii) They begin to menstruate at around this time.

(i) Condoms on the penis or similar converging worn in the vagina.
(ii) Loop or Copper-T placed in the uterus.

The uterus develop thick and spongy lining to received fertilized egg. When the egg is not fertilized, uterine lining slowly breaks and comes out as blood and mucous. This cycle take place roughly every month and is known as menstrual cycle.

(i) Ovary: Produces eggs and female hormone sex hormone.
(ii) Fallopian tube: Carries ovum and site of fertilization of the egg.
(iii) Uterus: Receives fertilized egg and nurture the growing embryo.
(b) (i) Scrotum: Provides lower temperature than the normal body temperature to facilitate sperm formation by the testes.
(ii) Testes: They produce male gametes and male hormone.
(iii) Vas deference: It is a tube which carries sperms from the testes to the tube coming from urinary bladder.

Sexual reproduction requires the fusion of male gamete and female gametes. This is brought about by the two individuals joining theirs bodies together for internal transfer of gametes. To participate in the process of mating the state of sexual maturity of one must be identified by individual. The changes occur during puberty are signals a special apparatus for the sexual act, such as the ability of the penis to become erect.

The sperms enters through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg. The sperm may fuse with the egg and form a zygote which is fertilized egg. The zygote gets implanted in the lining of the uterus and starts to divide. The mother body is designed to undertake the development of the child for which the uterus prepares itself every month to receive and nurture the growing child.

The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is disc shaped tissue which is embedded in the uterine wall. Placenta contain villi on the embryo side of the tissue and blood space on mother side surrounding the villi. This provide a large surface area for food and oxygen to pass from mother to the embryo and waste product from embryo to mother. The development of the child in the uterus take place for about nine months after which the child is born as a result of rhythmic contraction of the muscles of the uterus.

The ovary releases one egg every month and the uterus prepares for the launching of the zygote by thickening its walls. If the egg is not fertilised, the uterine lining slowly breaks down and comes out through the vagina as blood and mucus. This cycle takes place roughly every month and is known as menstruation and lasts for about two to eight days.

Role of hormones secreted by the gonads are to
(i) regulate the formation of sperm and ovum.
(ii) maintain the structure and function of accessory sex organs.
(iii) help in developing secondary sex characters such as deepening of voice, growth of facial hair in males, development of mammary glands in females.

The method used for regulation of child birth are:
(i)Barrier method: In this method physical devices like condom, cervical cap and diaphragm are used to prevent sperm to reach up to the ovum.
(ii) Chemical method: In this method specific dugs are used by females. These drugs may be oral pills or vaginal pills. Oral pills mainly contain hormones and are called oral contraceptives. They disturb hormonal balance so that egg is not released and fertilised.
(iii) Intrauterine contraceptives devices: IUCD like copper T is placed safely portion of vas deference and the fallopian tube in female is surgically removed or ligated. It is known as vasectomy in males which prevents release of sperms from the testes. In females it is called tubectomy.

Animal Plant
(i) Testis Anther
(ii) Ovary Ovary of the carpel
(iii) Eggs Egg present in ovule
(iv) Sperm Pollen grain in the anther

The sexual act is very intimate connection of bodies and thus many diseases can be sexually transmitted. These include bacterial infections like gonorrhea and syphilis and viral infection like warts, COVID-19 and HIV-Aids (Human Immunodeficiency Virus Acquired Immuno Deficiency Syndrome). HIV-Aids causes damage to the immune system of the human body.

Human Immunodeficiency Virus Acquired Immuno Deficiency Syndrome is a lethal and fatal disease caused by the HIV virus. The virus enters the body mainly through sexual contact with infected person, blood transfusion and by an infected mother to the foetus. The virus destroys the White blood cells in humans and makes the body very susceptible to the other diseases. Thus a person could die of common cold if he infected with the HIV-Aids is incurable as of today. With increasing number of people in India getting infected by the virus the human resources of India are depleting. The disease is destroying families and is also a socioeconomic hazard other than a health hazard.

Sexually transmitted diseases:
(i) Gonorrhoea or Syphilis
(ii) Aids/Warts
STD mainly spread through sexual act.
Symptoms:
(i) Lesions, irrigation or inflammation in the mucous membrane of urogenital tract.
(ii) Loss of body immunity or defensive system to fight against infections.

Method of contraception:
(i) Mechanical Barrier: Use of condoms on the penis and similar converging worn in the vagina
(ii) Chemical method: Use of oral pills by females.
(ii) Intrauterine Contraceptive Devices: Use of loop or Copper T.
The use of contraception method helps:
To avoid frequent pregnancies which have a very adverse effect on the body and mind of the mother. Only a healthy mother can take care of its family properly.
In controlling the size of the family and pace of birth of children. It helps in developing children properly and maintaining the living standard.