Limiting water loss

Plants require a large leaf surface area for photosynthesis. However, a large surface area also means lots of water loss.

How plants can limit water loss:

1. They have a waterproof waxy cuticle on their leaves.
2. They have guard cells that can close stomata when needed.

Xerophytes

Xerophytes are plants adapted to living in dry environments with limited water availability. Without adaptations they would become desiccated (dry out) and die.

Key adaptations of xerophytes to reduce water loss:

1. Thick waxy cuticle - This reduces water loss through evaporation.
2. Rolling or folding of leaves - This encloses the stomata on the lower surface to reduce air flow and the evaporation of water.
3. Hairs on leaves - These trap moist air against the leaf surface to reduce the diffusion gradient of water vapour.
4. Sunken stomata in pits - These reduce air flow and the evaporation of water.
5. Small, needle-like leaves - These reduce the surface area across which water can be lost.
6. Water storage organs - These conserve water for when it is in low supply.

Structure of a typical leaf

The structure of a typical leaf allows for efficient gas exchange between the leaf and the surrounding air.

Some important structures include:

1. Upper epidermis with waxy cuticle - This reduces water loss from the leaf surface.
2. Air spaces - These are interconnecting spaces that run throughout the mesophyll layer.
3. Mesophyll cells - These are cells within the mesophyll tissue, located between the upper and lower epidermis.
4. Stomata - These are small pores surrounded by guard cells on the underside of leaves that can open and close.
5. Lower epidermis - This is the bottom layer of cells in a leaf that contains the stomata and guard cells.
6. Vascular tissue (xylem and phloem) - This transports water and nutrients.

Adaptations of leaf structures for gas exchange:

1. Air spaces - These provide a network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells.
2. Mesophyll cells - These are dispersed throughout the leaf, providing a large surface area across which gases can diffuse.
3. Stomata - These open when conditions are suitable for photosynthesis, allowing inward diffusion of carbon dioxide and outward diffusion of oxygen, and close to minimise water loss.