Question

The physical process involved in the release of molecular oxygen from leaves is
A. Diffusion
B. Transpiration
C. Osmosis
D. Capillarity

Answer 1

Diffusion is a slow process and is not dependent on a living system.
Diffusion is very important to plants since it is the only means for gaseous movement within the plant body.

Complete answer:
Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature, and pressure.
1. The diffusion rate depends on the size of the substances; obviously smaller substances diffuse faster.
The diffusion of any substance across a Membrane also depends on its solubility in lipids, the major constituent of the membrane. Substances soluble in lipids diffuse through the membrane faster.
Substances that have a hydrophilic moiety find it difficult to pass through the membrane; their movement has to be facilitated.
2. Membrane proteins provide sites at which such molecules across the membrane.
3. They do not set up a concentration gradient: a concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins. This process is called facilitated diffusion.
4. It allows cells to select substances for uptake. It is sensitive to inhibitors that react with protein side chains. The proteins form channels in the membrane for molecules to pass through.
Some channels are always open; others can be controlled.
5. Some are large, allowing a variety of molecules to cross. The porins are proteins that form large Pores in the outer membranes of the Plastids, mitochondria, and some bacteria allowing molecules up to the size of small proteins to pass through.
6. Some carriers or transport proteins allow diffusion only if two types of molecules move together.
7. In a symport, both Molecules cross the membrane in the same direction; in an antiport, they move in opposite directions.
8. Active transport uses energy to transport and pump molecules against the concentration gradient.
Active transport is carried out by specific Membrane-proteins.
9. Hence different proteins in the membrane play a major role in both active as well as passive transport. Pumps are proteins that use energy to carry substances across the cell membrane.

So, the correct answer is “Option A ”.

Note: Plants obtain a variety of inorganic elements (ions) and salts from their surroundings, especially from water and soil. The movement of these nutrients from the environment into the plant as well as from one plant cell to another plant cell essentially involves movement across a cell membrane. Transport across the cell membrane can be through diffusion, facilitated transport, or active transport.