Plants ORGANISING ANIMALS AND PLANTS Flashcards
What are epidermal tissues?
It covers the surface of plants and protects them. They often secrete a waxy substance that waterproofs the surface of the leaf.
What is palisade mesophyll tissue?
Tissue contains lots of chloroplasts for photosynthesis.
What is spongy mesophyll tissue?
Contains chloroplasts for photosynthesis but also has large air spaces and a large surface area to make the diffusion of gasses easier.
What are the xylem tubes?
They carry water and dissolved mineral ions from the roots up to the leaves.
What are the phloem tubes?
Carry dissolved food from the leaves around the plant. It transports the sugars made by photosynthesis from the leaves to the rest of the plant.
What is translocation?
The movement of dissolved sugars from the leaves to the rest of the plant.
What is the role of the stomata?
Stomata are small openings on the surface of the leaf. Carbon dioxide diffuses into the air spaces down a concentration gradient. At the same time, oxygen produced by photosynthesis is removed from the leaf by diffusion into the surrounding air. This maintains a concentration gradient for oxygen to diffuse from the cells to the air spaces in the leaf. Also, plants lose water vapour through the process of transpiration.
Describe transpiration.
Water moves into the roots from the soil by osmosis. This replaces the water constantly moving up the stream.
Water moves up from the roots into the stem through the xylem tubes.
Water moves up through the stem in the xylem tubes and into the leaves to replace the water lost by evaporation.
Water is lost by evaporation through the open stomata.
What factors effect transpiration?
Temperature
Humidity
The amount of air movement
Light intensity.
How does humidity effect the rate of transpiration?
Water vapour diffuses more rapidly into dry air than into humid air because the concentration gradient is steeper.
How does temperature effect the rate of transpiration?
The molecules move faster as the temperature increases so diffusion occurs more rapidly.
The rate of photosynthesis increases as the temperature goes up so more stomata will open up for gas exchange to take place.
What happens when the rate of evaporation increases in a plant?
The rate of transpiration increases.
What may happen to the plant if it loses water faster than it is replaced?
The plant may wilt. This is a protection mechanism against further water loss. The leaves collapse and hang down. This greatly reduces the surface area available for water loss by evaporation.
The stomata close which stops photosynthesis and risks overheating. However, this prevents most water loss and further wilting.
What is the size of the stomata controlled by?
Guard cells.
