Transport in Plants

Introduction and Overview

Transport in plants involves the movement of water, minerals, and sugars to different parts of the plant.

Water and Mineral Transport

Water and minerals are transported through a tissue known as the xylem.
Water is mainly absorbed by the root hair cells due to the high concentration of minerals in their cytoplasm.
This procress is known as osmosis, the movement of water from an area of higher concentration to an area of lower concentration through a partially permeable membrane.
To reach the xylem, water must pass through the root cortex, either through the cells (symplastic pathway) or between the cells (apoplastic pathway).
Once in the xylem, the minerals and water form a weak solution known as xylem sap, which is transported up the plant due to transpiration pull.

Sugar Transport

The movement of sugars is facilitated through a tissue known as the phloem.
Sugars are produced in the leaves during photosynthesis, then are actively transported to all parts of the plant via the phloem in a process known as translocation.
This transport process requires energy in the form of ATP.

Stomata and Guard Cells

Stomata are tiny openings on the surface of leaves that allow for the passage of water, oxygen, and carbon dioxide.
They are guarded by two specialised cells known as guard cells.
Guard cells can change shape to open or close the stomata in response to various signals such as light, humidity, and carbon dioxide concentration.

Factors Affecting Plant Transport

Light intensity: Higher light intensity can increase the rate of photosynthesis, thus increasing sugar production and consequently translocation.
Air temperature: A higher air temperature may speed up the rate of transpiration by increasing water evaporation.
Wind speed: Higher wind speeds can increase the rate of transpiration by removing water vapour from around the leaves and maintaining a high humidity gradient.
Humidity: Lower humidity increases the water potential gradient between the leaf and air, thus increasing the rate of transpiration.
Water availability: Plants may close their stomata in response to drought conditions to prevent water loss.

Importance of Plant Transport

Transport systems in plants ensure distribution of water, minerals, and sugars to all parts of the plant which is crucial for their growth and survival.
Transpiration provides a cooling effect maintaining optimal temperatures within the plant.
It also maintains the turgidity (rigidity) of plant tissues, providing the plant with the structure required for photosynthesis to occur.
The movement of water also drives the flow of sap in the xylem, thereby aiding in the distribution of minerals and nutrients.