Page 15 - E-Biology Sec.2 2024-2025 U1_Handy

L3: Excretion in plant

There is no specialized excretory system in plants as:

1- The accumulation of metabolic wastes in the plant cell is very slow as the
rate of catabolism in plants is much lower than that in an animal.

2- The plants reuse the catabolic wastes as CO2 & H2O in photosynthesis
and nitrogenous wastes in synthesis of proteins.

3- The metabolism in plants is based mainly on carbohydrates (less toxic)
rather than proteins.

4- In terrestrial plants, organic salts and acids are stored as insoluble
crystals in cytoplasm / vacuoles.

5- Some plants live in soils are rich in Ca, get rid of its excess by its
accumulation in the leaves and are expelled out (shed).

6- Plants get rid of the gases through stomata by diffusion or by their roots.
7- Plants get rid of the excess water by transpiration and guttation.

Guttation:

The excretion of water drops at the leaf’s tips in the early morning at the
end of spring.

It has a special system which may consist of 1 / many loose cells opening by
a hydathode (opened permanently)

Water drops aren’t pure, there may be deposited substances
after evaporation. “little amount of water drops”

Transpiration:
Water loss in the form of water vapor and it has 3 types.

14

Second Term