Stomata and mineral transport

Where are stomata found?

On the lower side of the leaf mainly

What are stomata used for?

The exchange of gases and controlling water loss

When are stomata open and closed?

Stomata are surrounded by guard cells which open them in the day and close the pores at night (or sometimes also in periods of drought)

How do stomata open and close?

Potassium pumps in the epidermal cell membranes actively transport potassium ions into the guard cells. ATP has already been produced by the guard cells through photosynthesis. The potassium ions convert stored starch into malate so the water potential is lowered and water enters by osmosis. Guard cells become turgid. The inner wall is thicker than the outer wall which makes it inelastic so the pairs of cells curve away from each other and the pore opens

How is rate of transpiration measured?

With a photometer

How do minerals enter a plant?

Through the root hairs by a combination of diffusion and active transport

What factors affect rate of mineral uptake?

Oxygen concentration, water logging of soil, temperature, presence of inhibitory respirators

How does oxygen concentration impact the rate of mineral uptake?

Oxygen is needed for aerobic respiration to give energy for active transport

How does the waterlogging of soil impact the rate of mineral uptake?

There are fewer air spaces so less oxygen is present, so less ATP can be synthesised and there will be less energy for active transport

How does temperature impact the rate of mineral uptake?

It affects the rate of diffusion and affects enzymes needed for respiration

How does the presence of inhibitory respirators impact the rate of mineral uptake?

It affects the electron transport chain in the respiration pathway

Give an example of an ion being taken up into a plant

Nitrogen enters as nitrate ions and ammonium ions which diffuse along the concentration gradient into the apoplast stream, but then enter the symplast by active transport against the concentration gradient and then flows via the plasmodesmata into the cytoplasmic stream. At the endodermis, all ions must be taken up actively to bypass the casparian strip, which allows the plant to selectively take up ions at this point. This lowers the water potential in the xylem, causing water to be drawn through the endodermis. This produces a positive hydrostatic pressure inside the xylem, forcing water upwards. This is known as root pressure