CBSE Class 7 Science Advanced Biology Reproduction in Plants Long Answer Questions Set 01

Long Answer Questions

Question 1. Explain the main parts of a flower.
Answer:
A typical flower has four whorls.
Calyx: green, leaf-like sepals at the base; protects the bud.
Corolla: brightly coloured petals.
Stamen (androecium): male part, with an anther that holds pollen grains and a filament that holds the anther up.
Pistil (gynoecium): female part with stigma, style and ovary; the ovary contains ovules where the egg develops.

In simple words: Sepals, petals, stamens and the pistil are the four parts.

Teacher's Note:
1. Learn the labelled diagram.
2. Name the male and female whorls clearly.

Question 2. Dispersal mechanism is governed by structure of plant. Explain with suitable example.
Answer:
Seeds must move away from the parent plant to get space, so their structure suits a method of dispersal.
Water: seeds that float, as in water lily and coconut.
Wind: very light seeds, as in dandelion.
Animals and birds: fleshy fruits that are eaten and seeds that pass out, or seeds with hooks that stick to the animal's body.
Ballistic: fruits that burst and throw out seeds, as in gorse.
In simple words: Floating seeds use water, light seeds use wind, hooks use animals, bursting fruits throw seeds.

Teacher's Note:
1. Pick an example for each mode.
2. Seed structure decides the method.

Question 3. A seedling is growing without cotyledons. What is the probable effect this could have on its development?
Answer:
Cotyledons store the food needed by the growing embryo. Without them the seedling gets no stored food in the early stage, so its development will be poor or stunted.
In simple words: No stored food means weak growth.

Teacher's Note:
1. Cotyledons are the seed leaves that hold food.
2. Plumule takes food from them.

Question 4. Why do we observe that there are certain offsprings that are identical to their parents as in case of Amoeba, Hydra, etc.?
Answer:
Amoeba and Hydra reproduce asexually. Only one parent is involved and no gametes fuse, so the offspring are exact copies (clones) of the parent.
In simple words: One parent copies itself, so the young ones are identical.

Teacher's Note:
1. Asexual reproduction gives clones.
2. Sexual reproduction gives variation.

Question 5. It is observed that pollens of wheat plant are light in weight. Why?
Answer:
Wheat is wind pollinated. Light, dry pollen is easily blown by wind and has a better chance of reaching the stigma of another plant.
In simple words: Light pollen floats in the air easily.

Teacher's Note:
1. Wind pollinated flowers make a lot of pollen.
2. Rice, maize and grass are other examples.

Question 6. A particular flower is brightly coloured and secretes nectar. The flower also secretes certain smell to attract insects. What can be inferred about its mode of pollination?
Answer:
Colour, nectar and scent attract insects, so the flower is insect pollinated. The pollen sticks to the insect's body and is left on the stigma of the next flower it visits.
In simple words: Bright, sweet-smelling flowers are for insects.

Teacher's Note:
1. Rose and marigold are examples.
2. Wind pollinated flowers are small and dull.

Question 7. If a seed is provided with adequate water and oxygen, but without suitable temperature and enough light, will it continue to grow?
Answer:
No. A seed needs water, a suitable temperature and oxygen to germinate. If the temperature is not suitable, it will not germinate or grow properly.
The answer key also says light is needed. In fact most seeds germinate without light; light is needed later by the green seedling for making food.
In simple words: Without the right temperature the seed will not grow.

Teacher's Note:
1. Remember the three conditions for germination.
2. The missing temperature is enough to stop growth.