B3.1 gas exchange plants

monocots

1 seed leaf

single cotyledon

dicot

2 cotyledons

2 seed leaves

adaptions of leave for gas exchange

Hydrophobic so prevents water loss and dehydration in waxy cuticle 

Lots of chloroplasts to absorb sunlight in paliside layer

Xylem: water and mineral transport

Phloem: sugar, amino acids, hormone transport

stoma Regulates gas exchange with the guard cells (plural: stomata)

spongy mesophyll Air spaces allow space for gases to diffuse across locations

drawing

leave

consequence of gas exchange

Transpiration

process of transpiration

Water vapour is lost via the stomata as it diffuses down its concentration gradient into the atmosphere creating negative pressure in the xylem. This creates tension that further draws water up the xylem from the roots to the leaves.

transpiration facillitates 

Transpiration also facilitates:

Temperature regulation

Absorption of water and minerals from soil

measure of transpiration

estimates the volume of water absorbed by the plant over a set period of time.

Rate = volume of water absorbed

Time

by potometer

factors affecting rate of transpiration

Higher temperatures increase transpiration by increasing the rate of evaporation and the kinetic energy of water molecules.

High humidity decreases transpiration because it reduces the water concentration gradient between the inside of the leaf and the surrounding air, slowing down the diffusion of water vapor.

Higher light intensity leads to a higher rate of transpiration. This is because light causes the stomata to open for photosynthesis, and it also increases the temperature of the leaf.

Wind increases transpiration by removing water vapor from the air immediately surrounding the leaf, maintaining a steep concentration gradient.

stomatal density?

number of stomata in a particular unit of  area. stomata/mm2