Q5 of 70 Page 92

Why do submerged plants receive weaker illumination than exposed floating plants in a lake?

Submerged plants are underwater plants. These plants receive weaker illumination because the sunlight reaches the plant by passing through deep water. Floating plants are exposed to high intensity sunlight because they float on the surface of the water. Sunlight directly reaches the plant.


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3

Why do all the freshwater organisms have contractile vacuoles whereas majority of marine organisms lack them?

 4

Define heliophytes and sciophytes. Name a plant from your locality that is either heliophyte or sciophyte.

 6

In a seashore, the benthic animals live in sandy, muddy and rocky substrata and accordingly developed the following adaptations.

a. Burrowing


b. Building cubes


c. Holdfasts / peduncle


Find the suitable substratum against each adaptation.


 7

Categorise the following plants into hydrophytes, halophytes, mesophytes and xerophytes. Give reasons for your answers.

a. Salvinia


b. Opuntia


c. Rhizophora


d. Mangifera