CBSE Class 10 Science Sexual Reproduction in Plants and Animals Worksheet Set 15

Answer: In amphibians fertilisation is external and takes place in water. In reptiles it is internal and takes place inside the female body.

Teacher's Note:
1. Syngamy means fusion of gametes.
2. Animals living in water usually release gametes into water.

Answer: 1. Male and female release mature gametes at the same time.
2. A very large number of gametes are released into the water so that some of them meet.

Teacher's Note:
1. Many gametes are lost in water.
2. Large numbers raise the chance of fertilisation.

Answer: (b) pollen grain on stigma and ovule. The pollen tube grows from the pollen grain on the stigma to the ovule.

Teacher's Note:
1. The tube grows from the stigma towards the ovule.
2. A longer style needs a longer pollen tube.

Answer: (d) (ii) and (iv). Flowers are the sexual organs of flowering plants and give fruits after fertilisation; they are not always bisexual or present in all plants.

Teacher's Note:
1. Flowers occur only in flowering plants.
2. Some flowers are unisexual.

Answer: (b) genetic material comes from two parents of the same species. Offspring get genes from two parents, giving more variation.

Teacher's Note:
1. Two parents contribute different genes.
2. Gamete fusion mixes the genetic material.

Answer: (c) (i), (ii) and (iii). Sexual reproduction needs two gametes, fertilisation and a zygote, and gives offspring that are not clones.

Teacher's Note:
1. Clones arise from asexual reproduction.
2. Sexual reproduction always involves fertilisation and a zygote.

Answer: Yes, the zygote, embryo and adult body cells have the same (diploid) number because body cells form by mitosis from the zygote. Over generations the number is kept constant because gametes are made by meiosis, which halves the number, and fertilisation restores it.

Teacher's Note:
1. Gametes carry half the chromosome number.
2. Zygote = male gamete + female gamete.

Answer: 1. The male produces sperms and the female produces eggs (ova).
2. A sperm fuses with an egg in fertilisation to form a zygote.
3. The zygote divides repeatedly to form an embryo.
4. The embryo grows and develops into a new individual.

Teacher's Note:
1. Sperm is small and motile while the egg is large with stored food.
2. Fertilisation can be internal or external.

Answer: 1. Stamens make pollen grains containing male gametes.
2. Carpels make ovules containing female gametes (egg cells).
3. Pollen is transferred to the stigma (pollination).
4. A male gamete fuses with the egg in the ovule (fertilisation) to form a zygote.
5. The ovule becomes a seed, which grows into a plant. Wheat and sunflower are examples.

Teacher's Note:
1. Pollination comes before fertilisation.
2. Seeds form from the fertilised ovules.

Answer: Gametes are formed by a special division (meiosis) that halves the chromosome number. At fertilisation the two gametes fuse and the original number is restored in the zygote.

Teacher's Note:
1. Without halving, the number would double each generation.
2. Each gamete contributes half the genetic material.

Answer: (a) 1 : 2.
(b) A gamete is a haploid sex cell (sperm or egg), while the zygote is the diploid cell formed when a sperm fuses with an egg.
(c) In the fallopian tube (oviduct).

Teacher's Note:
1. The zygote has the full chromosome number.
2. It is the first cell of the new individual.

Answer: Unisexual flowers contain only stamens or only carpels, for example papaya and watermelon. Bisexual flowers contain both stamens and carpels, for example hibiscus and mustard.

Teacher's Note:
1. Stamen is the male part and carpel is the female part.
2. A flower with both parts is called complete in sex organs.

Answer: The pollen grain on the stigma grows a pollen tube through the style to the ovule in the ovary. The male gamete travels down the tube and fuses with the egg to form a zygote.

Teacher's Note:
1. Pollen tube growth is guided by chemicals from the ovule.
2. Fertilisation takes place inside the ovule.

Answer: The petals, sepals and stamens wither and fall, the ovary grows into the fruit, and the ovules inside become seeds.

Teacher's Note:
1. The zygote becomes the embryo within the seed.
2. The seed is the start of a new plant.

Answer: (a) A is the carpel (pistil), with stigma, style and ovary.
(b) The ovary (ovules).
(c) B is the stamen and its top is the anther.
(d) B is male and A is female.

Teacher's Note:
1. Anthers hold pollen grains.
2. The stigma receives the pollen.

Answer: Pollination is the transfer of pollen from the anther to the stigma, whereas fertilisation is the fusion of the male and female gametes. Fertilisation occurs in the ovule inside the ovary and its product is the zygote.

Teacher's Note:
1. Pollination can be self or cross.
2. Fertilisation needs the pollen tube.

Answer: The carpel remains intact and can still receive pollen from another flower by cross-pollination. After fertilisation the ovary develops into a fruit.

Teacher's Note:
1. Removal of stamens does not stop the female part from working.
2. Pollen can come from a different flower.