Bioenergetics: Exchange and Transport in Plants

Bioenergetics: Exchange and Transport in Plants

Exchange and Transport in Plants: Overview

• Plants, unlike animals, do not have specialist exchange organs or a circulatory system. Instead, they rely on direct diffusion or active transport of substances into and out of their cells.
• Each plant organ (leaf, root, stem) has a specific function in the absorption or movement of water, ions and sugars.

Roots: Specialisation for Absorption

• The root hair cells of plants have long, thin outgrowths known as root hairs. These increase their surface area, enhancing absorption of water and mineral ions from the soil.
• Inside the roots, the xylem and phloem vessels transport these absorbed substances to other parts of the plant.

Stems: Support and Transport

• The stem provides support to the plant and holds leaves, flowers and fruits up to the light and air.
• The xylem vessels transport water and mineral ions from the roots up to the rest of the plant.
• The phloem vessels, on the other hand, distribute the sugars produced by photosynthesis from the leaves to all parts of the plant.

Leaves: Site of Photosynthesis and Gas Exchange

• Leaves are thin and flat with many chloroplasts, making them the main site of photosynthesis in most plants.
• Oxygen and carbon dioxide diffuse in and out of leaves through tiny pores called stomata, which can open and close depending on environmental conditions.

Transpiration: The Movement of Water Through Plants

• Transpiration is a process of water movement from the roots through the xylem to the leaf surface, where it eventually evaporates.
• The transpiration stream provides a force that draws water up the stem, supporting the absorption process in the roots.
• Factors that affect the rate of transpiration include light, temperature, wind, humidity, and soil water availability.

Translocation: The Movement of Sugars

• Translocation is the movement of sugars, such as glucose and sucrose, from leaves (where they are made) to other parts of the plant, e.g., roots, stems.
• Translocation takes place in the phloem vessels. It is an active process and requires energy.

The Importance of Minerals

• Essential minerals like nitrogen, potassium, and phosphorous are absorbed from the soil and contribute to the plant’s health.
• Nitrogen, for example, is required for protein synthesis, while potassium is important for enzyme function and stomata operation. Phosphorous aids in energy transfer within cells.