Sexual Reproduction in Flowering Plants — BIOLOGY STD 12 Science — Question

What are the suggested reasons for population explosion ?

Biodiversity in living beings started about 3 billion years ago. Since then, new species are emerging on the earth and at the same time, their mass extinction is also taking place.
(a) How many phenomena of mass extinction have occurred on Earth and which extinction is in progress at present?
(b) How is the current phenomenon of extinction different from earlier occurrences and explain why.

Even though each pollen grain has two male gametes, why are at least 10 pollen grains and not 5 pollen grains required to fertilise 10 ovules present in a particular carpel?

Recently a baby girl has been reported to suffer from haemophilia. How is it possible? Explain with the help of a cross.

Males in whom testes fail to descend to the scrotum are generally infertile. Why?

Identify A, B, C and D in the given table:

Crop	Variety	Resistance to disease
A-	Himgir	Leaf rust
Cauliflower	Pusa Shubhra	B-
Brassica	Pusa Swarnim	C-
Cowpea	D-	Bacterial blight

Explain mechanism of pollination by water in fresh water plants.###Explain mechanism of pollination by water in Vallisneria.

Explain:

1. Stratification.
2. Leaching.

Give Diagrammatic representation of recombinant DNA Technology.

1. Select the homologous structures from the combinations given below:

1. Forelimbs of whales and bats.
2. Tuber of potato and sweet potato.
3. Eyes of octopus and mammals.
4. Thorns of Bougainvillea and tendrils of Cucurbita.

2. ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​State the kind of evolution they represent.