B3 - Exchange Systems in Plants Flashcards
How does carbon dioxide enter plants?
By diffusion into the stomata cells.
How do water and minerals enter plants?
Water and minerals are absorbed by the roots; water by osmosis, minerals by active transport.
What is transpiration?
Transportation is the loss of water vapour from the leaves of a plant.
What is the transpiration stream?
The transpiration stream is the continuous movement of water molecules from the roots to the leaves.
The roots absorb water by osmosis, the water molecules then travel up the stem in the xylem tubes and go into the leaves to replace the water lost by evaporation. The water is then lost by evaporation through the stomata.
When is transpiration at it’s highest?
Hot, dry and windy days.
Dry days - high concentration gradient between the leaves and the air.
Windy days - blows away the water molecules and keeps the concentration gradient high.
How are plants adapted for controlling water loss? (5 techniques)
Plants are adapted for controlling water loss in a number of different ways.
The WAXY CUTICLE is waterproof. No water from inside the plant can escape. It also allows the sun’s rays to bounce off which prevents evaporation.
STOMATA CAN BE CLOSED - guard cells can close the stomata (also stops carbon dioxide entering).
STOMATA ARE ON UNDERSIDE OF LEAF mainly as distinct from the top. The underside is cooler and there is no sunlight here.
PLANTS WILL WILT. Leaves will collapse down if it is not getting enough water. This reduces it’s surface area and decreases the rate of evaporation.
LEAVES ARE SMALLER - less stomata, less water escapes.
What happens to the plant if it loses water faster than it can be replaced in the leaves?
The leaves will wilt and collapse down. This reduces the surface area and so decreases the rate of transpiration.
How is a plant adapted for gas exchange? (2 ways)
It has thin leaves which increase the surface area for diffusion to occur. The distance the carbon dioxide to diffuse is kept as short as possible.
There are many air spaces within the leaf to make sure the carbon dioxide can come into contact with a large number of cells.
What factors affect the rate of transpiration? (4 factors)
Temperature of surroundings - the higher the temperature, the greater the rate of transpiration because the rate of evaporation and diffusion increases.
Light Intensity - the greater the light level the more transpiration because the plant will have it’s stomata open to take in lots of carbon dioxide.
Air Movement - The more air movement the faster the rate of transpiration because it creates a constant, steep concentration gradient as the water molecules are blown away from the plant.
Humidity - the more humid the conditions the lower the rate of transpiration is because there is a much more gradual concentration gradient for diffusion because the air is already saturated with water.
Why is transpiration important for plants?
It provides water to keep the plant cool.
It supplies the water to plant cells for photosynthesis.
It allows dissolved mineral ions to be transported around the plant.
It provides water for plant cells to remain turgid to stand upright and photosynthesise properly.
What doses a plant use magnesium for?
Needed to make chlorophyll.
What does a plant use nitrates for?
The production of amino acids to form proteins and grow.
