Class X – How do Organisms Reproduce (PYQs) – Solutions

Ans. Reproduction

Ans. DNA is found in the nucleus.

Ans. DNA means deoxyribo nucleic acid. It lies in the cell nucleus, which is the source of information for making proteins and different proteins lead to different body designs.

Ans. DNA in the nucleus of a cell is the source of information for making proteins. The two basic events in reproduction are:

(i) creation of copy of DNA

(ii) creation of an additional cellular apparatus by cell then the DNA copies separate, each with its own cellular apparatus.

Ans. DNA copying will lead to variation in populations which helps in evolution of the species.

Ans. The cell uses biochemical reactions to make exact copies of DNA or genetic material.

Ans. Reproduction involves producing same kind of species from parents. The genetic information is passed to the offspring by DNA present in each cell. This DNA, which is replicated (copied) is responsible for the resemblance of parents with offsprings with same traits. New traits are passed on due to difference in copying, new variations may occur and new species may evolve.

Ans. (i) DNA is found in nucleus of cell, (ii) Genes are located on the chromosomes.

Ans. Deoxyribonucleic acid.

Ans. During the process of reproduction, transmission of DNA from parents to offspring takes place. Before reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides into two, these two copies are distributed equally between the two daughter cells so that similar amount and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency in the amount and type of DNA in the living organism of a particular species.

Ans. Reproduction is an energy consuming process which is not essential for the survival of an individual. But it is the most important characteristic of all living beings, because of the following reasons:

(i) Reproduction helps in increasing the number of members of a population.

(ii) By replacing the dead members with the new ones, it minimises the risk of extinction of a species.

(iii) It brings about variations in species, thus leading to their evolution.

Ans. Deoxy Ribonucleic Acid

Ans. It helps in synthesis of protein and transfer of genetic characteristics.

Ans. Proteins will be changed.

Ans. Body designs are similar due to DNA copying.

DNA cell nucleus carry information for synthesis of protein.

If DNA copying will not take place, then body design will change.

Ans. Buds arise from the notches in the leaf margins of Bryophyllum.

Ans. Each piece regenerates into new organism, planaria.

Ans. A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new plant. This process of reproduction is called fragmentation.

Ans. Hydra reproduces by budding. It is an asexual mode of reproduction.

Ans. Planaria and Hydra

Ans. Leishmania causes ‘kala-azar’. It reproduces by binary fission in a definite orientation.

Ans. Heredity

Ans. Evolution

Ans. Specialised cells called regenerative cells which can make large number of new cells.

Ans. Spore with a cell wall can survive even in adverse conditions. Large number of spores are produced in one sporangium. It is easily dispersed through wind as they are large in number and light in weight.

Ans. Under favourable conditions, spirogyra reproduces by a process known as fragmentation. This is an asexual method of reproduction.

Ans. Planaria reproduces by a process known as regeneration. It is a type of asexual reproduction in which if Planaria can be cut into any number of pieces, each piece grows into a new individual organism.

Ans. Plasmodium is a single celled organism which reproduces by the process of multiple fission. Multiple fission (i.e. breaking up of a single cell into many daughter cells) is an asexual mode of reproduction.

Ans. (i) Characteristics of parent plants are preserved.

(ii) Since these plants do not have viable seeds, therefore vegetative propagation is advantageous.

Ans. (i) Availability of nutrition (food),

(ii) moist place,

(iii) warmth,

(iv) dark place.

Ans. Regeneration

Ans. Spore formation

Ans. Fragmentation

Ans. Budding

Ans. Leaves of bryophyllum has adventitious buds or plantlets in the notches along the leaf margin. When buds fall on the soil, they develop into new plant under favourable conditions.

Ans. Binary fission, e.g. Fission in Amoeba

Elongation of cell and its nucleus is the first step.

Ans. Sequence (showing the four stages), the process of binary fission in Amoeba.

Ans. The process in which parent cell divides into several small and equal sized daughter cells, which grows into a new organism is called multiple fission.

The nucleus of a cell divides into large number of nuclei and cytoplasm separates, forming a membrane around it. All this occurs within a protective covering. Plasmodium exhibits multiple fission.

Ans. Regeneration is the ability to produce an organism from their body parts. Many fully differentiated organisms show ability to reproduce by regeneration. In hydra, if the body is cut into two or three pieces, the lower part will develop head while the upper part will develop rest of the body. If its cells are separated, hydra will reform its structure by regeneration.

Ans.

Ans. Each piece will regenerate into complete organism. Cells at the location of the site of cut or wound, forms a small ball of cells that will differentiate into new tissues and regenerate the missing parts of the cut piece of the planaria.

Ans. When spirogyra attains considerable length, it breaks into smaller fragments and each fragment grows into a new plant.

Ans. On maturation, sporangial wall breaks and spores are dispersed to grow into new individual. These spores are very light and easily dispersed by wind.

Ans. A bud is an outgrowth from the body part of parent due to repeated cell division at a specific site. These buds develop into new individuals, which detach from the parent body on maturation. In hydra, the cells divide very fast at a specific site as an outgrowth called bud. These bud develops into a small individual, while remaining attached to the parent. When it matures, it detaches from the parent body to exist as an independent organism.

Ans. When Planaria gets cut into many pieces, it will undergo a process known as regeneration due to which each piece will grow into a new planaria organism.

Ans. When bryophyllum leaf falls on the wet soil, the buds that are produced in the notches along the leaf will develop into new plants by the process known as vegetative propagation.

Ans. When the sporangia of Rhizopus bursts upon maturation, the spores present inside it spread in the open environment. Then, with the help of different agents, they are carried to different places and when they land on a favourable surface, they start growing and produce new organism.

Ans. Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from vegetative parts of the plants. It does not involve the production of seeds or spores for the propagation of new plants.

Two advantages of vegetative propagation are:

(i) Plants which do not produce seeds are propagated by this method, for example sugarcane, potato, etc.

(ii) Vegetative propagation is a cheaper, easier, rapid method of propagation in plants than growing plants from their seeds. For example, lilies grow very slowly and take 4 to 7 years to develop flowers when grown through their seeds, but flowers are produced only after a year or two when grown vegetatively.

Two disadvantages of vegetative propagation are:

(i) As there is no genetic variation, there is no chance of development of new and better varieties.

(ii) The vegetatively propagated plants are more prone to diseases that are specific to the species. This can result in the destruction of an entire crop.

Ans. Pollination: The process in which pollen is transferred from stamen to the stigma is called pollination.

Significance: After the pollen lands on suitable stigma, it needs to reach the female germ cells in the ovary where fertilisation takes place, zygot is formed. Zygot divides several times to form embryo with in ovule which develops a tough coat around it called seed coat and seed is formed. The ovary grows rapidly and ripens to form fruit.

Ans.

Ans. A mature spirogyra filament breaks into smaller fragments and each fragment grows into a new plant. This process of reproduction is called fragmentation.

Ans. Binary fission is a fission in which two daughter cells are formed of nearly equal size after replicating the genetic material of a single cell. Single-celled organisms like amoeba undergoes binary fission.

Ans. Fragmentation, Spirogyra

Ans. Multiple fission, Plasmodium

Ans. Budding, Yeast/Hydra

Ans. Spore formation, Rhizopus

Ans. Regeneration, Planaria

Ans. ‘A’ is Bryophyllum–Vegetative propagation; ‘B’ is Plasmodium–Multiple fission

Ans. Spores are covered with thick walls which protect them until they come into contact with a moist surface.

Ans. Budding and regeneration

Ans.

Ans. Multicellular organisms cannot reproduce by cell because they are not simple random collection of cells.

They have specialised cells, organised as tissues which are organised into organs.

Cell-by-cell division would be impractical (not practical).

Multicellular organisms require to use more complex ways of reproduction.

Ans. These are called hermaphrodites, e.g. earthworm and leech.

Ans. Fertilisation is the process in which pollen grain and egg fuse to form zygote. Pollination is the process of transfer of pollen grains from stamen to the stigma of carpel. It means that fertilisation is not possible without pollination.

Ans. Watermelon, Cucumber and Willows

Ans. (i) Special cell division involved in the process of gametes formation is the cause of variations.

(ii) Genetic material comes from two parents, which brings variations in offsprings.

Ans. (i) Testis produces sperms.

(ii) It produces testosterone hormone.

Ans. Sepals and petals are not directly involved in reproduction.

Ans. Chromosomes can be seen as thread like structure having specific shape when cell is dividing by which they can be identified.

Ans. Scrotal sac temperature is less by 2° because sperms are safe at a little lower temperature than body temperature. It is outside the body that is why it has lower temperature than body.

Ans. Pollen grains contain male gametes in plants and ovules contain female gametes.

Ans. Germination: Involves development of embryo into a seedling.

Fertilisation: It involves fusion of male with female gametes.

Ans. Diseases that spread through the sexual contact are called STDs

AIDS damages the body’s immune system.

Ans. When egg is not fertilised, blood and mucus comes out through vagina. This process is called menstruation.

Ans. The lining of uterus becomes thick and spongy by the action of progesterone to receive and nurture the development of embryo.

Ans. Hibiscus, Mustard

Ans. Seminal vesicle: It holds the liquid that mixes with sperm to form semen.

Prostate gland: It secretes fluid adding upto the semen and contains enzymes and other substances. It also provides nutrition to the sperms, in the form of fructose and calcium. It protects sperms.

Ans. (i) The inner uterine wall becomes thick.

(ii) More blood vessels develop in its lining.

Ans. Ovaries contain thousands of immature eggs at the time of birth. Some of these eggs start maturing when girls attain puberty. One egg is produced every month by one of the ovaries.

Ans. Testes –> vas deferens –> urethra –> penis and then opens to outside.

Ans. Sperms are motile (movable) and have X or Y chromosomes whereas eggs are non-motile and have X chromosome only.

The sperms can reach to egg for fertilisation because these are motile. Chromosomes in them help in determination of sex of a new born child.

Ans.

Ans. (i) To prevent unwanted pregnancies.

(ii) To prevent STD (Sexually Transmitted Diseases).

(iii) To have proper gap between two children.

(iv) To control population.

(v) To have sound health.

Ans.

Ans. Formation of sperms takes place in testes.

Ans. Prostate gland contributes fluid to the semen

Ans. (i) Testosterone regulates formation of sperms.

(ii) The appearance of secondary sexual characteristics at puberty like beard, genital hair, change in voice is due to testosterone.

Ans. The three techniques which prevent pregnancy are:

(i) Barrier method, (ii) Chemical method (iii) Surgical method

Chemical methods are not for males.

The use of contraceptive has a direct effect on the health and prosperity of the family.

(i) To avoid unwanted pregnancy–if the woman is not physically or mentally prepared to bear a child her health gets adversely affected.

(ii) Contraception allows the parents to space the birth of two children and helps in family planning.

(iii) This way they can decide how many children to have and allows them to bring them up properly especially in case of limited resources.

Ans. ‘A’ is anther. It contains pollen grains.

‘B’ is style. It allows growth in pollen tube up to the ovary from the stigma.

‘C’ is ovary. It contains ovules.

Ans. (i) Barrier method: Condom is placed on the erect penis of male before sexual intercourse. In female, a thin rubber disc is placed in the vagina, which covers the opening of cervix.

(ii) Oral pills: Birth control pills can be taken to prevent pregnancy.

(iii) Surgical methods: Use of Copper-T in females, surgically implanted at the opening of the cervix, prevents entry of sperms.

Vasectomy in males, tubectomy in females can also help in population control. In vasectomy, sperm ducts are cut. In tubectomy, oviducts are tied, blocked or cut. Sperms cannot reach the ova and thus pregnancy is avoided.

Ans.

Ans. Structure of placenta: It is a special disc like tissue embedded in mother’s uterine wall and connected to the foetus/embryo.

Functions of placenta: It provides a large surface area for glucose and oxygen/nutrients to pass from mother’s body to the developing/developed embryo/foetus and also helps in passing the waste from the foetus/embryo to the mother’s body.

Ans.

Ans. Sperm formation takes place at a lower temperature than body temperature therefore testes are located outside the body and its temperature is 2°C below the body temperature.

Functions of Testes:

Endocrine Function: The production of testosterone hormone.

Exocrine Function: The production of sperms.

Ans. (i) Two parents are involved

(ii) Two dissimilar gametes are formed

(iii) Variations are produced

(iv) Occurs in higher and some of lower organisms

(v) Fertilisation is needed for zygote formation

(vi) It is a slow process.

Ans. (i) Ovary: It produces ova and female sex hormones.

(ii) Fallopian tube: It is the site of fertilisation and transfer of female gamete from the ovary.

(iii) Uterus: Implantation of zygote and it keeps foetus till complete development.

Ans. (i) Scrotum: It protects testes.

(ii) Testes: It produces sperms.

(iii) Vas deferens: It delivers sperms from testes to urethra.

Ans.

Ans. The basic requirements for sexual reproduction to take place are involvement of two parents and fusion of their haploid gametes. In the sexual reproduction, a new individual is formed by the fusion of two haploid gametes, one from the male parent and the other from the female parent. Since the new individual formed is diploid in nature, the gametes must be formed by meiosis, so that chromosome number can be reduced to half. When fusion of gametes occurs, the two nuclei of these two gametes fuse and the chromosome number is restored to normal. The zygote, thus formed is diploid in nature.

Importance of sexual reproduction:

Sexual reproduction involves fusion of male and female gametes coming from both the parents. The fusion of these gametes results in genetic variations in the offsprings. This way sexual reproduction promotes diversity of characters in offsprings by providing genetic variations. These genetic variations, thus lead to evolution of species as well as allow the organisms to become better adapted in the changing environment.

Ans. When the implantation has occurred in uterus of the mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo.

Ans. If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more required, it will slowly break down and come out through the vagina as blood and mucus known as menstruation which lasts for about two to eight days.

Ans. The four main steps involved in sexual reproduction are:

(i) In the first stage of sexual reproduction, meiosis process occurs and the number of chromosomes reduces from diploid (2n = 46) to haploid (n = 23) for each gamete.

(ii) In the second stage, there is transfer of male gametes into the female body.

(iii) In the third stage, the two gametes will fuse together after fertilisation, a single male gamete will fuse with a female gamete. i.e. fertilisation process takes place.

(iv) After fusion of male and female gametes, they form a zygote, in which the number of chromosomes is restored to diploid (2n = 46).

The two main advantages of sexual reproduction are:

(i) There are more variations, which leads to better adaptability of the offsprings in the environment.

(ii) Promotes the diversity in the characteristics of offspring, because it results by fusion of gametes.

Ans. ‘A’ is stigma, ‘B’ is pollen tube, ‘C’ is ovary and ‘D’ is egg cell (female germ cell).

Ans. Pollination is a process of transfer of pollen grains from the anther of stamen to the stigma of carpel. It is necessary for fertilisation by sexual reproduction.

Ans. When male gamete and egg fuse together to form zygote, it is called fertilisation. It takes place in ovule. After that the ovule develops a tough coat and is gradually converted into seed.

Fruit: The ovary grows rapidly and ripens to form a fruit after ovule has been fertilised.

Ans. Egg develops in ovary.

Ans. Fertilisation takes place in fallopian tube.

Ans. The fertilised egg gets implanted in uterus.

Ans. The inner uterus lining becomes thick to receive the zygote and is supplied with blood and nutrients to nourish the embryo.

Ans. The inner uterus lining breaks and released in the form of blood and mucus through vagina.

Ans. Significance of reproductive health in society are:

(i) Prevent STD (Sexually Transmitted Disease)

(ii) Advantages of small family

(iii) Less mortality among new borns

(iv) Reduces cases of maternal mortality

Two areas of Improvement are:

(i) Family planning.

(ii) Decrease in STD cases.

Ans. (i) Formation of sperms and change in appearance.

(ii) Thick hair growth on face stet and pubic region and change in voice.

Ans. A tube grows out of the pollen grain and travels through the style to the ovary.

Ans. Zygote is formed i.e. fertilisation takes place.

Ans. Each piece grows into new organism

Ans. Buds may fall on the soil and change into new organism.

Ans. Two causes of human population explosion are:

(i) Reduced mortality rate due to better medical facilities.

(ii) Desire for male child.

(iii) Less awareness of birth control methods.

(iv) Illiteracy and poverty.

Methods to check population explosion are:

(i) By using contraception methods.

(ii) Awareness among people of the advantage of small family.

Ans. The organ that produces sperms as well as secretes male hormone is testis. The hormone secreted by it is testosterone. Its important functions are as follows: It stimulates sperm production. It stimulates the development of secondary sexual characters in males like growth of beard hairs, low pitch voice, etc. It involves in the development, maturation and functioning of the male accessory sex organs like vas deferens and seminal vesicles

Ans. In human female reproductive system, the process of fertilisation takes place in one of the fallopian tubes.

Ans. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. Placenta is a vascular membranous organ that connects the developing foetus to the uterine wall of the mother. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The placenta draws nutrients and oxygen, which it supplies to the foetus, from the maternal circulation. In turn, the placenta receives carbon dioxide and wastes of foetal metabolism and discharges them into the maternal circulation for disposal.

Ans. (i) Fallopian Tube/Oviduct

 (iii) Vagina

(ii) Uterus

Vagina

(b) Why do more and more people prefer to use condoms? What is the principle behind use of condoms?

Ans. People prefer use of condoms as it prevents STDs/gives privacy to the user. Condoms help create a mechanical barrier preventing meeting of sperms and ovum.

88. (a) List three different categories of contraception methods.

Ans. (i) Barrier method, (ii) Oral pills, (iii) Use of copper-T, (iv) Vasectomy in males, tubectomy in females.

Ans. • It is because female foeticide is increasing.

• It leads to unbalanced sex ratio i.e., more males, less females.

On long run, it will help in maintaining healthier (equal) sex ratio.

It will save mothers from illegal medical termination of pregnancy and health issues.

Ans. Gonorrhoea and syphilis are bacterial infections. Warts and HIV-AIDS are viral infections.