Biology:2014:CBSE:[DELHI]:Set-II

Water hyacinth (Eichhornia crassipes) is referred to as “Terror of Bengal”.

True breeding lines are a group of genetically identical homozygous organisms that produce offspring with stable traits for several generation on intercrossing.

(i) Polymorphic-nuclear leukocytes and monocytes

(ii) Macrophages

Fresh water snail and fish are the two intermediate hosts which the human liver fluke depends on to complete its life cycle so as to facilitate parasitisation of its primary host.

Stratification is the vertical distribution of different species occupying different levels. In a forest, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.

Zooplanktons enter diapauses, i.e., they undergo a period of suspended development to overcome unfavourable conditions.

Inheritable mutation and genetic drift cause DNA polymorphism. Mutations that arise in non- coding sequences have no effect on the reproductive ability of an individual. These mutations accumulate generation after generation and form the basis of polymorphism.

Eutrophication refers to the natural aging of a lake due to the increase in the amount of nutrients in the water. Human activities such as discharge of effluents from industries and sewage from homes accelerate the aging process resulting in accelerated eutrophication.

The exine and intine of pollen grains of angiosperms are made up of sporopollenin and cellulose respectively.

Exine is the outer layer of a pollen grain which is made up of a highly decay-resistant chemical called sporopollenin. Sporopollenin can withstand high temperature, strong acids, alkali and even cannot be degraded by any enzymatic activity. These characteristics of sporopollenin help the pollen grains to be preserved as fossils. Absence of sporopollenin in some portions of exine of pollen grains create germ pores through which pollen tube germinates.

 i.

ii. Test Cross