IB Biology HL - Plants - Gas Exchange in Plants

waxy cuticle

covers the epidermis cells, reduces evaporation

epidermis

protection for mesophyll cells, transparent so light can reach mesophyll cells (photosynthesis)

spongy mesophyll

increases surface area for gas exchange, surrounded by air spaces 

air spaces

facilitate the diffusion of gases between the surrounding atmosphere and the mesophyll cells 

stomata

pores which allow gases to enter and exit the leaf

veins/vascular bundles

provide structural support for the leaf, contain xylem and phloem tissue

xylem

transports water and minerals from the roots

phloem

transports nutrients up and down the plant

diagram of a leaf (drawing)

transpiration

the movement of water through a plant, and its evaporation through the stomata of the leaves

transpiration + concentration

water diffuses from the high concentration of water particles within the air spaces of the spongy mesophyll to the low concentration of water particles in the atmosphere

light intensity (factors affecting transpiration)

as light intensity increases, more stomata open. If there are more open stomata, then more water can diffuse out of the leaf, increasing the rate of transpiration

temperature (factors affecting transpiration)

as the temperature increases, the water particles gain kinetic energy, and move faster. Faster moving water particles diffuse through the stomata of the leaf at a faster rate. Additionally, higher temperatures increase the rate of evaporation, which also increases the rate of transpiration

humidity (factors affecting transpiration)

as humidity increases, the concentration of water outside the leaf increases. This decreases the concentration gradient between the inside and outside of the leaf.  Water particles will diffuse slower, resulting in a slower rate of transpiration

air flow (factors affecting transpiration)

as air flows past the leaf, it moves water vapour away from the leaf, reducing the concentration of water outside the stomata of a leaf. This increases the concentration gradient, resulting in an increase in the rate of transpiration

stomatal density