Describe how roots take up water and mineral salts by active and passive absorption.

Roots absorb water and minerals through two main processes: active absorption and passive absorption.

Passive absorption occurs when water moves into the root cells by osmosis. The water in the soil has a higher water potential than the root cells, so water moves from the soil into the root hair cells through the semi-permeable membrane. This process does not require energy and depends solely on the difference in water potential between the soil and the root cells.

Active absorption involves the active transport of minerals from the soil into the root cells against their concentration gradient. This requires energy in the form of ATP. Special carrier proteins in the cell membrane pump mineral ions (such as potassium, nitrate, and calcium) into the root cells. This decreases the water potential in the cells, and as a result, water enters the cells from the surrounding soil via osmosis. Active absorption is essential for the uptake of minerals like nitrogen, phosphorus, and potassium, which are necessary for plant growth.