Leaf Adaptations for Gas Exchange
- Gas exchange in plants occur through the leaf
- The leaf contains the following tissues:
- Epidermal tissue forming the outer boundary of the leaf
- Mesophyll tissue that make up the bulk of internal structure of the leaf
- Vascular tissue which transports substances between the leaf and the rest of the plant
Epidermis
- This is formed by a single layer of tightly packed cells
- The leaf has an upper and lower epidermis which protects the inner parts of the leaf
- The lower epidermis contains tiny pores called stomata (singular stoma)
- Each stoma is surrounded by two guard cells which controls the opening and closure of the pore
- When water moves into the guard cells they become turgid and change shape which opens the stomata
- They become flaccid when water is lost and this causes the stomata to close
- Stomata are the structures through which gas exchange occur in a leaf
- They allow for the diffusion of oxygen and carbon dioxide into and out of the leaf
- Each stoma is surrounded by two guard cells which controls the opening and closure of the pore
- The epidermis is often covered by a waxy layer called the cuticle
- This forms an impermeable barrier
Mesophyll tissue
- These are formed by parenchyma cells which contain chloroplasts
- This is where photosynthesis occurs in the leaf
- Two types of mesophyll tissue are found in the leaf:
- Palisade mesophyll forms a layer beneath the upper epidermis and contain many chloroplasts for maximum photosynthesis
- Spongy mesophyll contains large air spaces between the cells for gas exchange to occur
Vascular tissue
- Vascular tissue is arranged in vascular bundles and is responsible for the transport of substances around the plant
- Vascular bundles form the veins in leaves
- Xylem transports water and mineral ions from the roots to the leaves
- Phloem transports the products of photosynthesis from the leaves to other parts of the plant
Structure of a Leaf Diagram
The structure of a leaf has distinct layers each with their own function
Adaptations for gas exchange
- The leaf has several adaptations that facilitate gas exchange
Leaf Adaptations for Gas Exchange Table
Adaptation | Function |
Waxy cuticle | Prevents gases and water vapour from leaving through the epidermis so that gas exchange must occur through stomata. This allows gas exchange and water loss to be controlled |
Epidermis | Contain stomata for gas exchange. Most stomata are found in the lower epidermis where the temperature is lower. This reduces water loss |
Air spaces | Maintains a concentration gradient of gases between the air and spongy mesophyll cells by allowing movement of gases |
Spongy mesophyll | Increases the surface area for gas exchange |
Guard cells | Control gas exchange and water loss by opening or closing stomata |
Veins | Xylem vessels bring water to the leaf which is required for photosynthesis and transpiration. Photosynthesis requires carbon dioxide to diffuse into the leaf while transpiration involves the loss of water vapour |