How do Organisms Reproduce

Ans. Zygote is located inside the ovule which is present in the ovary.

Ans. The DNA in the cell nucleus is the information source of making proteins.

The two basic events in reproduction are:

(i) Creation of a DNA copy

(ii) Additional cellular apparatus by the cell involved in the process.

Ans. Artificial methods of vegetative propagation like layering is used for growing jasmine plant.

Ans. An example of unisexual flower is papaya, water melon and of bisexual flower is hibiscus, mustard.

Ans. Testes produces sperms and ovary produces ova.

Ans. The method by which Spirogyra reproduces under favourable conditions is Fragmentation. This is an asexual mode of reproduction.

Ans. Plasmodium

Ans. Amoeba, Euglena, Lieshmania, Paramecium

Ans. Leaves

Ans. Regeneration: The process of getting back a full organism from its body parts is called regeneration.

The simple animals like Hydra and Planaria shows regeneration, i.e., if Hydra or Planaria somehow get cut into a number of pieces, then each body part can grow into a new complete organism.

Ans. Ovary is the part of female reproductive system. Its functions are:

(i) It secretes the female hormones called Oestrogen and Progesterone.

(ii) It also releases the female gamete called ovum for fertilisation.

(iii) It also releases ovum every month during menstrual cycle.

Ans. When a cell reproduces, its DNA makes the two copies, each divided cell getting one.

Ans. DNA copying is not perfectly accurate and the resultant errors are a source of variations in populations of organisms.

Ans. Sexually transmitted disease caused due to

(i) Bacterial infection is gonorrhoea and

(ii) Viral infection is AIDS (Acquired Immune Deficiency Syndrome)

These diseases can be prevented by responsible sexual behaviour such as use of condom during intercourse, etc.

Ans. DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA.

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Ans. The importance of DNA copying during reproduction are:

(i) It is responsible for the transmission of parental characteristics to the offspring’s.

(ii) During DNA copying in reproduction, the changes occur due to the inheritance of traits from both the parents. This leads to certain genetic variations, which are useful for the evolution of species over a period of time.

Ans. Regeneration is the ability of a fully differentiated organisms to give rise to new individual organisms from its body parts. More complex organisms cannot give rise to new individuals through regeneration because:

(i) Their body is highly complicated.

(ii) There are specific organs to do specific functions.

(iii) There is a labour division in the body of complex organisms.

(iv) Regeneration is carried out by specialised cells which are not present in complex organisms.

Ans. In vegetative propagation, new plants are obtained from the parts of old plants like stems, roots and leaves, without the help of any reproductive organ.

There are two ways of vegetative propagation:

(a) Natural Vegetative Propagation

(b) Artificial Vegetative Propagation

Natural Vegetative Propagation by leaves: The fleshy leaves of Bryophyllum bear adventitious buds in the notches along the leaf margin.

Artificial Vegetative Propagation

Grafting: In this method of reproduction, two plants of closely related varieties are joined together so that they live as one plant.

The portion of a plant that is grafted on the other plant is called scion, and the plant in which grafting is performed is called the stock.

This method is applied to improve variety of fruits like mango, apple, peas, citrus and guava.

Ans. The embedding of a fertilised mammalian egg (embryo) into the inner thick wall of the uterus (womb) where it will continue its development is called implantation.

Ans. It is a complex double-layered spongy vascular tissue in human female formed by the joint activity of maternal and foetal tissues in the wall of uterus that is meant for attachment, nourishment and waste disposal for the foetus.

Ans. The average duration of human pregnancy is 40 weeks or 280 days.

Ans. (a) The role of seminal vesicles and the prostate gland are as follows:

(i) Seminal vesicles produce seminal plasma which is in the form of fluid makes the transport of sperms smooth.

(ii) Prostate gland secretes prostatic fluid that keeps the sperms alive and helps them to swim vigorously.

(b) Two functions performed by testis in human beings are as follow:

(i) Formation of sperms takes place in testis.

(ii) They secrete the hormone testosterone which regulates the formation of sperms and brings changes in appearance of boys at the time of puberty.

Ans. Variations allow organisms to exist in diverse habitats or niches. If it is absence, then a species may remain restricted to a particular area. If this area gets drastically altered then, the species may be wiped out.

However, if some variations are present in few individuals, it would help them to colonise other habitats and survive. But, if variations are present in a single organism, there would be very little chance for it to survive and species is lost forever.

Hence, variation is beneficial to the species, but not necessary for the individuals.

Ans. When the colony of yeast is in water, it does not get nutrition. Sugar solution, on the contrary provides nutrition. As the yeast gets nutrition and thus energy, it grows and begins to produce buds. This is why colonies of yeast fail to multiply in water, but multiply in sugar solution.

Ans. Multicellular organisms like filamentous algae (Spirogyra) and sea animal called sea anemone on maturation breakup into two or more small fragments or pieces. Each fragment subsequently grows to form a complete new organism. This type of asexual reproduction is known as fragmentation.

Two advantages of vegetative propagation are as follows:

(i) Vegetative reproduction is easier and faster methods of reproduction.

(ii) It is useful in those plants/animals, which cannot reproduce sexually.

Ans. Layering is a type of vegetative propagation e.g. lemon, rose, jasmine, strawberry, etc., can produce new plant by the process of layering.

Ans. The main difference between sexual and asexual reproduction involves the production and union of gametes in the process of fertilisation in sexually reproducing organisms which do not occur in asexual mode of reproduction.

Sexual reproduction is considered to be superior over asexual reproduction as it leads to variations, while asexual reproduction does not induce variations among progeny individuals.

Advantages of variations in individuals are

(i) It brings adaptation in individuals

(ii) It helps in the survival of species.

(iii) It is the basis of evolution.

Hence, the species that reproduce through sexual reproduction have better chances of survival.

Ans. The number of chromosomes in the female gamete would be same as that in the male gamete, i.e., it will have 24 chromosomes. The number of chromosomes in the zygote would be double the number present in the gamete and hence, it would be 48.

Ans. Pollination is transfer of pollen grains from anther to the stigma of a flower. It is of two types.

(i) Self-Pollination: Transfer of pollen from the stamens of a flower to the stigma of the same flower or on the stigma of other flower of the same plant.

(ii) Cross-pollination: Transfer of pollen from the stamens of a flower to the stigma of different flower of different plant of same species.

Ans. Stamens and carpels (pistils) are the reproduction organs lower, i.e., organs by which sexual reproduction in floral plants takes place.

Most plants have both male and female reproductive organs in the same flower and are known as bisexual flowers, e.g. lily, rose, etc., while others have either male or female reproductive parts in a flower known as unisexual flowers, e.g. papaya, water melon, etc.

Ans. Variations appear among the progeny formed by sexual reproduction due to the following reasons:

(a) Sexual reproduction results in new combination of genes that are brought together during the formation of gametes by meiotic divisions. (I and II)

(b) The combination of two sets of chromosomes, one between the homologous chromosomes arms set from each parent during zygote formation, leads to variation within a species.

A – Pollen grain

Ans. Pollen grain reaches part B, i.e., stigma by pollinating agents such as insects, wind, water, etc. This process is known as pollination.

Ans. Part C is pollen tube. It allows the passage for the male gametes to reach the ovary having female gamete for fertilization.

Ans. Part D, i.e., female gamete or egg cell that forms zygote after fertilisation.

Ans. Ovum is produced by ovaries which are paired, oval-shaped organs.

Ans. Oviduct or Fallopian tubes are the site of fertilisation. They have funnel-shaped opening near ovary and carry ova or egg from ovary to uterus.

Ans. Implantation refers to embedding of the embryo in the thick lining of uterus.

Ans. Ovary in females is responsible for the production of female gametes (ova) and also produces female sex hormones, i.e., oestrogen and progesterone.

Ans. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta.

This is a disc-like tissue which develops between the uterine wall and embryo. As mother eats, the food passes through the digestive system where it breaks down into small particles. These nutrients travel through the mother’s bloodstream and get exchanged with the bloodstream of foetus through placenta.

Ans. The umbilical cord contains blood vessels which supply blood between the foetus and the placenta.

Ans. Testes are located outside the abdominal cavity because sperm formation requires a lower temperature than the normal body temperature.

Ans. The ratio of chromosome number between egg and its zygote is 1:2. An egg is a female gamete and it has haploid number of chromosomes.

During fertilisation, it fuses with male gamete (also having haploid number of chromosomes) to form a zygote which now has diploid number of chromosomes.

Sperms and eggs are genetically different in terms of nature of sex chromosomes. The sperm contains either X or Y-chromosomes, whereas an egg will always have an X-chromosomes.

Ans. Two methods of contracting an STD other than the sexual contact are as follows

(i) Sharing needles with an infected person

(ii) Transfusion of STD unscreened blood

Ans. No, Copper-T does not prevent the transmission of sexually transmitted diseases. Copper –T only prevents implantation. The only safe method that can be used to prevent the 30 no transmission of sexually transmitted diseases is condoms.

Ans. Use of a condom is beneficial for both the sexes involved in a sexual act. It is because of the following facts:

(a) It prevents pregnancy which is not desired by a couple.

(b) It saves both the partners from sexually transmitted diseases like AIDS, etc

Ans. Oral contraceptives are the hormonal pills which are taken by the females after their menstruation ends up. It is taken for 21 days daily. It changes the cyclic events of ovulation, etc. So, mature ovum is not available for fertilisation.

Ans. Sex selective abortion means if the foetus is female, it is killed and extracted. This creates an imbalanced in the society by disturbing the sex ratio.

Ans. Ways to avoid pregnancy are called contraceptive methods. It includes a number of ways such as

(i) Mechanical barrier, e.g condom

Mechanical Barrier: There are number of methods that create barrier between sperm and egg

Some of them are as follows

Condom: It is fine rubber balloon – like structure worn over the penis during sexual intercourse. Semen is collected in it and not discharged into the vagina. This method also prevents the spread of STDs like AIDS, syphilis, etc.

Diaphragms or Caps: It can be fitted in the cervix of a woman to prevent semen from reaching the fallopian tube.

 (ii) Drugs (oral pills for females)

(iii) IUCD, e.g. copper – T

(iv) Surgical method for permanent contraception.

Ans.  A bisexual flower has the male as well as female reproductive organs. If the young stamen (i.e., male unit) is removed artificially, the flower still has its pistil (i.e., female unit) intact. Therefore, cross-pollination can occur.

When the pollen grains from the anther of another flower are transferred to the stigma of this flower with the help of pollinating agents such as insects, bees, wind and water, it causes cross-pollination. After the pollen grains fail on stigma, the next step is fertilisation, followed by formation of fruits and seeds.

Ans. All the living organisms need energy for the survival and growth. This energy is obtained from various life such as nutrition, excretion and respiration processes.

Thus, these phenomena are essential for the survival of an individual. Compared to these life processes, reproduction is not essential for survival of an individual.

It is basically important for continuity of the generation of an organism or species as DNA copying during reproduction helps to produce similar individuals as their parents to maintain stability of a species.

(a) Planaria – Regeneration

(b) Hydra – Budding

(c) Rhizopus – Sporulation

Ans. The leaves of Bryophyllum bear vegetative adventitious buds which on separation can give rise to new plants.

Ans. The transfer of pollen grains from the anther of the stamen to the stigma of a flower is termed as pollination. There are two types of pollination.

(i) Self-pollination: The pollen from the stamen of a flower is transferred to the stigma of the same flower or another flower on the same plant.

(ii) Cross-pollination: The pollen from the stamen of a flower is transferred to the stigma of another flower of different individual of the same species.

The pollen grains can be transferred by various agents like wind, water, insects and animals. As soon as the pollen lands on suitable stigma, it reaches the female germ cells in ovary. This occurs via pollen tube.

The pollen tube grows out of the pollen grain, travels through the style and finally reaches the ovary where it fuses with female gamete (ovule) to give rise to zygote. Hence pollination is followed by fertilisation in plants.

Ans.

The site of fertilization is ovule in the ovary.

The product of fertilization is a zygote.

Ans. Stamens and carpels are the reproductive parts of a flower.

• Stamen is the male reproductive part of the flower.
• Anther is a bilobed structure containing two pollen sacs present at tip of stamen. These produce pollen grains that are yellowish in colour.
• Carpel (Pistil) is the female reproductive part, which is present in the centre of the flower.

It comprises of three parts

(i) Stigma: It is the terminal part of carpel which may be sticky. It helps in receiving the pollen grains during pollination.

(ii) Style: It is the middle elongated part of carpel. It contains ovules having an egg cell (female gamete)

Fertilisation is the process of fusion of male germ cells with the female gametes. It gives rise to a zygote. As soon as the pollen lands on suitable stigma, it reaches the female germ cells in ovary. This occurs via pollen tube. The pollen tube grows out of the pollen grain, travels through the style and finally reaches the ovary.

Ans. Placenta is extremely essential for foetal development because it helps in nutrition, respiration, excretion, etc., of the foetus through the maternal supply.

Blocking of vas deferens prevents passage of sperms, hence, there is no fertilisation so it prevents pregnancy.

Wind acts as a pollinating agent because it helps in transfer of light weighted pollen grains from anther to stigma of a flower.

Condoms prevent entry of sperms into vagina, hence be prevents pregnancy.

If Fallopian tube is blocked, sperm and egg do not meet or fuse and fertilisation does not take place.

Ans. Reproductive health is a state of physical, emotional, mental and social well-being in relation to sexuality.

Significance of reproductive health in a society.

(i) It prevents the spread of various Sexually Transmitted Diseases (STDs)

(ii) Proper medication and check-ups will help in the production of healthy children.