Ch. No. 12 The Life Cycle
Q1. Fill in the blanks.
1. The two main methods of reproduction are _____________ and ________________. (sexual reproduction, asexual reproduction)
2. The functional unit in a plant’s sexual reproduction is ____________. (flower)
3. The male reproductive part of a flower is _____________(stamen)
4. When the transfer of pollen from an anther to the stigma occurs in the same flower, the process is called ____________. (self pollination (autogamy))
5. ________ give rise to variety and diversity. (variation)
6. Hydra uses regenerative cells for reproduction in the process of _________. (budding)
7. Yeast reproduces by _____________. (budding)
8. During unfavourable conditions ___________ type of fission is seen in amoeba. (multiple)
9. A basic process in reproduction is the creation of a _____________ copy. (DNA)
10. _______________ is necessary to maintain the number of individuals of a species. (Reproduction)
Q2. Write the correlated terms:
1. Amoeba: Simple binary fisson : : Paramoecium: ______________(Transverse binary fission)
2. Planaria : regeneration : : Rhizopus : ________________(spore formation)
3. Root, stem, leaf : Vegetative propogation : : Flower : ______________(sexual reproduction)
4. Asexual reproduction : similarity : : Sexual reproduction : ____________ (diversity)
Q4. Explain the following terms.
1. Reproduction: - The fundamental characteristic of living things to produce new individuals of the same species, that is a new generation of the species from and existing individual is known as reproduction.
2. Vegetative propogation: -When new plants are produced from the vegetative parts like roots, stems, leaves and buds it is known as vegetative propagation.
3. Pollination:- The process of transfer of pollen grains from anther to stigma is called as pollination.
Q5. Write the functions of the following organs in reproduction.
1. Vagina
i. It provides the route for the menstrual blood to leave the body during menstruation.
ii. It is a pathway through which sperms enters into woman’s body.
iii. It is a pathway through which a baby comes out of the woman’s body during child birth.
2. Stigma
i. It receives pollen grains and on which pollen germinates.
3. Ovaries
i. Ovaries develop and release eggs into the oviduct.
ii. It secretes hormone estrogen.
4. Seminal vesicle and Prostate glands
i. Produce ejaculatory fluid which helps the sperm in transport and provides nutrition.
5. Uterus
i. It accommodates a growing foetus.
ii. It push the baby during labour.
Q6. Draw a well labeled diagram of: [refer to text book]
1. Longitudinal section of flower.
2. Binary fission in amoeba.
3. Spore formation in Mucor.
4. Human female reproductive system.
Q7. Answer the following.
1. What are the advantages of sexual reproduction over asexual reproduction?
Ans.
i. The offsprings produced by sexual reproduction are different from parents.
ii. Variations give rise to variety and diversity.
iii. Variation enables organisms to adapt and survive in the changing environment.
iv. It helps to prevent the complete extinction of animal and plant species.
2. Why does menstruation occur?
Ans.
i. A woman’s ovaries usually release one egg each month.
ii. When the egg is not fertilized, menstruation occurs to leave out the unfertilized egg along with blood and mucous from the uterus.
3. Describe sexual reproduction in plants.
Ans.
i. In plants, flower is the functional unit concerned with sexual reproduction.
ii. In a flower, the ovary produced female germ cell or egg and the pollen grains produces male germ cells.
iii. When the pollen lands on stigma, it germinates producing a pollen tube which grow downwards to reach ovary.
iv. Each pollen tube contains two male gametes and are released near the egg,
v. One male gamete fuse with the egg cell to form zygote.
vi. The second male gamete fuse with the secondary nucleus in the embryo sac to form endosperm. This is called as double fertilization.
vii. The zygote develops into embryo and the endosperm serves as nutritive tissue for the growing embryo.
4. Describe the modes of reproduction in unicellular organisms.
Ans. Binary fission, multiple fission and budding are the modes of sexual reproduction in unicellular organisms.
a. Binary fission: -
i. It is employed by most prokaryotes, some protozoa and some organelles within eukaryotic cells.
ii. In it, the living cell divides into two equal parts which have the potential to grow to the size of the original one.
b. Multiple fission: -
i. During unfavourable condition, the amoeba withdraws its pseudopodia and form a cyst.
ii. Inside the cyst, nucleus divides into many nuclei and as a result many daughter cells are formed.
iii. The cyst bursts to release the daughter cells during favourable condition.
c. Budding: -
i. Yeast reproduces by budding in which a small outgrowth is formed on the parental cell.
ii. The nucleus of the parental call divides and one daughter nucleus migrates into the bud. The bud increases in size separates and grows further.
5. Explain disadvantages of large family size.
Ans.
i. There is a strong relation between high national fertility rate and measures of poverty.
ii. As the population density increases, decrease in per capital income and natural resources takes place.
iii. General health goes down and creates an economical burden on the nation.
iv. Large families affect both the individual as well as the community life.
v. Economic pressure, mother’s poor health, children neglected at home, poor nourishing, malnutrition, insufficient medical care, lack of better education, etc., are some of the disadvantages of large family size.
Q8. Write short notes on the following:
1. Pollination: -
i. The process of transfer of pollen grains from anther to stigma is called as pollination.
ii. If this transfer of pollen occurs in the same flower or another flower of the same plant, it is known as self pollination.
iii. On the other hand, if pollen is transferred from one flower to the flower of another plant, it is known as cross pollination.
iv. The agents of cross pollination are wind, water or animals.
2. Regeneration: -
i. The capacity to regenerate is very high among some animals.
ii. They can reconstruct the entire body from the isolated body cells.
iii. Regeneration is carried out by specialized cells.
iv. These cells proliferate and make large number of cells which later developed into various cell types and tissues, and helps in production of new organism.
v. Eg. When Planaria is cut into many pieces, each piece develops into a whole Planaria. This process occurs only if the Planaria body gets cut up into pieces. But animals cannot wait to be cut to reproduce. So regeneration is not the same as reproduction.
3. Germination of seeds : -
i. After fertilization, the zygote divides several times to form an ambryo within the ovule.
ii. The ovule develops into a seed and ovary develops into the fruit.
iii. The seed contains the future plant. It develops into the seedling under appropriate condition. This process is known as germination.
4. Multiple fission: -
i. During unfavourable condition, the amoeba withdraws its pseudopodia, becomes almost round and secretes a hard covering called cyst.
ii. Inside the cyst nucleus divides into many nuclei by repeated division, follow by division of cytoplasm.
iii. As a result many daughter cells are formed.
iv. The cyst bursts to release the daughter cells during favourable condition.
5. Importance of variation.
i. Changes in ecological system, which are beyond our control like varying temperature, varying water level can wipe out the population species.
But, if variations in some individuals are suitable for new environment, there is a chance of survival of that species.