What is the importance of DNA copying in reproduction?
Answer
DNA copying has the following importance in reproduction:
- It maintains the characteristics of species.
- It maintains the continuity of life.
- From this, the characteristics and features of organisms are transformed to their progeny.
- It produces variations in organisms which is the basis of evolution of new species.
Why is variation beneficial to the species but not necessarily for the individual?
Answer
The various populations of organisms interact with many types of ecological niches. This is important for them to survive in given conditions. In case of any damage caused to the ecological conditions of the population, the population gets adversely affected. The organisms which are able to survive, may reproduce to develop a population which is adapted or suited to the varied conditions. Hence variation is beneficial to species, but not necessarily to individuals.
Page Number: 133
How is the process of binary fission different from multiple fission?
Answer
Binary fission | Multiple fission |
|---|---|
1. In this an organism divides into two similar organisms. | 1. In this an organism produces two or more organisms. |
2. A cyst or thick layer is not formed around the cell. | 2. A cyst or thick layer is formed around the cell. |
It generally occurs in favourable conditions Example : Amoeba, paramecium | 3. It can take place in unfavourable conditions too. Example: Malarial parasite. |
How will an organism be benefited if it reproduces through spores?
Answer
An organism is benefited by reproducing through spores because spores are surrounded by a thick wall that protects them in adverse conditions. When favorable conditions return, these spores begin to grow again. In this way, they successfully survive in unfavorable conditions.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer
For example, a dog is a complex multicellular organism which cannot be regenerated from its cut body part say, a cut tail. This is because the cells present in the cut tail of a dog cannot produce dog’s organs like heart brain, lungs, stomach, intestines and limbs, etc, needed for the making of a complete dog.
Why is vegetative propagation practised for growing some types of plants?
Answer
Vegetative propagation is practiced for growing plants that usually do not produce seeds or produce non-viable seeds.
Why is DNA copying an essential part of the process of reproduction?
Answer
DNA copying is an essential part of the process of reproduction so that the characteristics of the parent organisms are transmitted to their offspring, while also introducing variations. These variations enable organisms to adapt and survive in changing environments.
Page Number: 140
How is the process of pollination different from fertilisation?
Answer
Pollination | Fertilisation |
|---|---|
1. The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination. | 1. Fertilisation occurs when the male gamete present in pollen grain joins with the female gamete (or egg) present in ovule. |
2. It takes place by various pollinating agents. | 2. It takes place by natural or artificial means. |
What is the role of the seminal vesicles and the prostate gland?
Answer
- Both seminal vesicles and the prostate gland secrete fluids that form part of the semen. The fluid from seminal vesicles forms about 60% of semen, while fluid from the prostate gland forms about 30%. These secretions facilitate smooth sperm transport.
- This fluid protects sperms from acidic conditions in the urethra.
- It provides nourishment to sperms containing fructose, calcium, and specific enzymes.
What are the changes seen in girls at the time of puberty?
Answer
The various changes that occur in girls at puberty are:
- Hair grow under armpits and pubic region.
- Mammary glands (or breasts) develop and enlarge.
- The hips broaden.
- Extra fat is deposited in various parts of the body like hips and thighs.
- Fallopian tube, uterus and vagina enlarge.
- Ovaries start to release eggs.
- Menstruation (monthly periods) starts.
- Feelings and sexual drives associated with adulthood begin to develop.
How does the embryo get nourishment inside the mother’s body?
Answer
Inside the mother’s body, the embryo receives nutrition from the mother’s blood via a specialized tissue called the placenta. The placenta contains villi surrounded by blood spaces in maternal tissues, providing a large surface area for the transfer of glucose, oxygen, and other nutrients to the embryo.
A woman is using a copper-T. Will it help in protecting her from sexually transmitted diseases?
Answer
No, a copper-T is a contraceptive device designed to prevent implantation in the uterus. It does not protect against sexually transmitted diseases, which are transmitted through intimate fluid contact that a copper-T cannot prevent.
Textbook Chapter End Questions
Answer
Asexual reproduction takes place through budding in
- amoeba
- yeast
- plasmodium
- leishmania
Answer: (b) Yeast
Which of the following is not a part of the female reproductive system in human beings?
Answer
- Ovary
- Uterus
- Vas deferens
- Fallopian tube
(c) Vas deferens
Answer
The anther contains
- sepals
- ovules
- carpel
- pollen grains
Answer: (d) Pollen grains
What are the advantages of sexual reproduction over asexual reproduction?
Answer
- In asexual reproduction, offspring are virtually identical to the parent due to copying the same genetic material, resulting in minimal genetic variation. This lack of variation can be a disadvantage as it limits adaptive evolution.
- In sexual reproduction, offspring receive a combination of genes from both parents, creating unique genetic variations. This higher genetic diversity enables populations to adapt quickly to changing environmental conditions, increasing the chances of species survival.
What are the functions performed by the testis in human beings?
Answer
The key functions of the testes are:
- Production of male gametes (sperms) starting at puberty.
- Secretion of testosterone, a hormone that regulates male reproductive organ development and secondary sexual characteristics.
Why does menstruation occur?
Answer
If an egg is not fertilised, the thickened uterine lining is no longer required. It breaks down along with its blood vessels and passes out through the vagina as menstrual flow. This process recurs approximately every 28 days, occurring roughly 14 days after ovulation.
Draw a labelled diagram of the longitudinal section of a flower.
Answer
What are the different methods of contraception?
Answer
The primary contraceptive methods include:
- Barrier Methods: Condoms, diaphragms, and cervical caps block sperms from entering the female genital tract.
- Chemical Methods: Oral pills prevent egg release, while spermicidal creams or gels destroy sperm in the vagina.
- Intrauterine Devices (IUDs): Devices like Copper-T are inserted into the uterus by a doctor to prevent fertilization and implantation.
- Surgical Methods: Sperm or egg transport tubes are cut or tied via vasectomy (in males) or tubectomy (in females).
How are the modes for reproduction different in unicellular and multicellular organisms?
Answer
Reproduction mode in unicellular organisms | Reproduction mode in multicellular organisms |
|---|---|
(i) A sexual reproduction takes place in unicellular organisms. | (i) Sexual reproduction takes place in multicellular organisms. |
(ii) Only one organism is required in this method. | (ii) A male and a female both are required in this method. |
(iii) No special cells are present for reproduction. | (iii) Special cells are present for reproduction. |
(iv) No special organs are present for reproduction. | (iv) Special organs are present for reproduction located at the fixed position in the body. |
How does reproduction help in providing stability to populations of species?
Answer
Reproduction helps maintain population size by replacing individuals lost to age or mortality. Furthermore, subtle variations introduced during reproduction help species adapt to changing environments, preventing population extinction during adverse conditions.
What could be the reasons for adopting contraceptive methods?
Answer
Primary reasons for adopting contraceptive methods include:
- To control the birth rate and prevent the increase in population.
- To reduce the adverse effects on mother’s body due to frequent pregnancy.
- To provide safety from sexually transmitted diseases.