What is the name of the reproductive process which involves (i) two parents (ii) only one parent?
(i) The reproductive process which involves two parents is called sexual reproduction. In this process, both the male and the female genders are required for producing the new generation.
(ii) Asexual reproduction in the process of reproduction, where only one parent is involved. This means that an individual organism is capable of generating new generation.
Name the agencies through which cross-pollination take place.
The transfer of pollen grains, in flowering plants, from one flower to another, is called cross-pollination. The agencies which carry out cross-pollination are wind, water and animals.
Give one word for each phrase:
(i) A sexually transmitted disease caused by a virus.
(ii) The reproductive organ cut and ligated for male sterilisation.
(iii) The biological end of a full term gestation.
(iv) The type of disease to which Trichomoniasis belongs.
One word for each given phrase is as follows:
(i) HIV-AIDS
(ii) Vas deferens
(iii) Parturition
(iv) Sexually transmitted protozoan disease.
Leaves of Bryophyllum fallen on the ground produce new plants whereas the leaves of rose do not. Why?
The leaves of Bryophyllum have notches on their margins, which produce buds. When these leaves fall on the ground, the buds develop into a new plant by process of vegetative reproduction, under favourable conditions.
The leaves of rose don’t have this property. They don’t produce any buds over them and hence cannot produce new plants by vegetative reproduction. Instead, the stems and branches of rose plant are used for the purpose.
‘Grafting is a common method of obtaining a superior plant from two different plants’. Explain.
Grafting is a technique of horticulture which uses the property of vegetative reproduction for cultivation of new plants. In grafting, the desirable characters of two or more plants are combined to produce a new and better plant. The shoot of one plant (called scion) is joined by vascular combination, to the root (called rootstock) of another plant. Some branches or buds of different plants can also be combined with the scion. This process has many benefits like:
•Plants raised by this method produce flowers and fruits earlier than those grown by seeds
•This method helps in growing plants that have lost their capacity to produce seeds.
•Plants produced are genetically similar to parent plant, and thus have all the desirable characters in them.
How do the ornamental plants propagate? Mention the method of propagation for the following:
(i) Jasmine (ii) Rose
(iii) Bougainvillea (iv) Hibiscus
The ornamental plants propagate by vegetative reproduction methods. These include layering, budding, cutting, grafting, etc.
The method of propagation of given plants is :
(i) Jasmine - layering
(ii) Rose – cutting
(iii) Bougainvillea – layering
(iv) Hibiscus- layering
Justify the statement ‘Primary sex organs control the growth, function and maintenance of secondary sex organs’.
Primary sex organs are those organs of reproductive system, which directly participate in the process of reproduction. In humans males, the primary sex organs are testes, and in females, the primary sex organs are ovaries. Apart from producing sperms and ovum, these organs also release some reproductive hormones, namely, testosterone (from testis) and oestrogen and progesterone (from ovaries), which control the growth, function and maintenance of other reproductive system organs, like epididymis, vas deferens (in males) fallopian tube and uterus (in females), also called the secondary sex organs. Hence primary sex organs control the growth, function and maintenance of secondary sex organs.
Why is it said that ‘sexual reproduction promotes, diversity of characters in the offsprings’?
The DNA replication processes, though precise are not absolutely accurate and thus mistakes can be made. These mistakes in DNA copying mechanism result in variations in the population, which are necessary for the survival of individual in a population. This process of creating variations speeds up in sexual reproduction. Here, two individuals of a population, with different patterns of accumulation of variations, interact and participate in producing a new generation. These variations are unique. Thus, the diversity in characters of offsprings is promoted in sexual reproduction.
What causes joining up of stock and scion in grafting? Name one positive trait that the plant contributing scion should have and one positive trait that the plant contributing the stock should have.
The combining up of vascular compartments of scion and stock cause joining of the two parts in grafting.
The plant contributing scion should be able to produce flowers and fruits quicker than those plants which are planted through seeds.
The plant contributing root stock should be able to keep the plant more resistant to diseases and pests.
“DNA copies generated will be similar, but may not be identical to the original.” Explain.
The DNA copying mechanism, also called the DNA replication processes, are highly precise, but they are not completely accurate. Each time when the DNA is copied, some changes or mistakes might take place in formation of the new DNA strand. These mistakes account for the variations that occur amongst the individuals in a population. In sexual reproduction, these changes increase in rate of occurrence due to involvement of two individuals with different patterns of accumulation of variations. The variations hence created, are unique in nature. Thus, the DNA copies generated are similar, but not identical to the original.
What is a seed? How does it help in reproduction in plants?
The zygote, after fertilisation in plants, divides several times to form an embryo, which is the future plant. This embryo is enclosed inside the ovule. The ovule, gradually hardens and develops into a small, tough and persistent structure, which encloses the embryo, called the seed.
This seed, when under favourable conditions of soil, water and air, develops into a seedling, a process known as germination. This germinated seedling further is involved in the development of new plant. This way, the seed helps in reproduction.
Fertilisation is possible if ovulation has taken place during middle of the menstrual cycle. Give reasons.
Fertilisation is the process of union of the sperm and the ovum inside the female reproductive tract. The site of fertilisation in humans is the junction between ampulla and isthmus of the fallopian tube. Thus, for fertility, it is necessary that the ovum be present at this site, when the sperm reaches and has not crossed it. As the release of ovum from the ovaries takes place between 11th to 16th day of menstrual cycle, which is roughly the middle of the cycle, the chances of ovum being present in fallopian tube at that time is high. Hence, fertilisation is possible when ovulation occurs, in the middle of menstrual cycle.
What changes are noticed on sexual maturity of human beings?
The changes that occur in humans on sexual maturity are collectively referred to as secondary sexual characters. Some of these changes are common to both the genders, whereas some changes occur specific to one gender.
The changes common to both sexes are:
1. Growth of thick hair in armpits and genital area.
2. Darkening of armpits and genital area.
3. Growth of thin hair on arms, legs and face.
The changes occurring in girls:
1. Enlargement of breasts
2. Darkening of the area of nipple
3. Beginning of menstruation.
The changes occurring in boys are:
1. Appearance of thick hair on face.
2. Cracking of voice.
3. Enlargement and erection of penis.
How can the reproductive health be maintained and sexually transmitted disease (STDs) be prevented?
Reproductive health can be maintained mainly by spreading awareness regarding the process of reproduction, and promoting safe sexual habits. Introduction of sex education in schools, use of birth control measures, prevention of sexual abuse and sex-related crimes will also help in maintaining reproductive health.
Sexually transmitted diseases can be prevented by use of condoms and avoiding sex with multiple partners.
What is meant by tissue culture? How this technique is performed? In which area this technique is finding its application?
Tissue culture is a technique of growing new plants from cells or tissue from the growing tip of already existing plant, in an artificial medium. The process of tissue culture is as follows:
1. Cells or tissue from the growing tip of a plant are removed or separated.
2. These cells are placed in an artificial medium, where they divide to form a group of cells called callus.
3. The callus is then transferred to a medium, which has hormones for growth and differentiation.
4. This results in growth of small plantlets, which are then placed in the soil to grow into mature plants.
This technique is finding it’s application in the propagation of ornamental plants, or for growth of plants from a single parent, in disease-free condition.
Name two bacterial diseases which are sexually transmitted. Name their causal organisms, symptoms and preventive measures.
Two bacterial, sexually transmitted diseases are gonorrhoea and syphilis.
Gonorrhoea
It is caused by Neisseria gonorrhoeae. Symptoms, if produced include burning with passage of urine, discharge from penis or vagina, pain in the pelvic region. The disease can be prevented by the use of condoms during sex or having sex with only one, uninfected partner.
Syphilis
It is caused by Treponema pallidum species. Symptoms include the presence of a firm skin ulcer, without pain or itching. This disease can be prevented by use of condoms.
Due to heavy rise in demand for tea in international market and simultaneous incentive given by government on tea plantation, a tea company wants to go for a large-scale expansion of its tea plantation in Assam. To implement the project, the company need a large number of sapling and a huge motivated work force.
(a) What is the best option for the company to arrange large number of sapling?
(b) What are the minimum facilities that the company should provide to its workers?
(c) What additional step can the company take to motivate the workers to put extra effort into successful expansion of the plantation?
(a) The best option for the company to arrange large number of saplings is by vegetative reproduction, through cutting of tea plant, or by tissue culture methods.
(b) The company must provide adequate salary to its workers. They must be made to work only for fixed hours, which can be rotatory in nature, healthy working environment must also be provided.
(c) The incentives received from cover can be distributed amongst the workers, their working environment can be made happy and healthy so as to motivate them to put extra efforts. They can be made a part of planning and management, where their ideas and opinions can be valued.