B7 Transport Flashcards
What are the two types of transport vessels in plants?
-Xylem vessels
-Phloem vessels
What is the function of xylem vessels?
Xylem vessels transport water and minerals from the roots to the stem and leaves.
What is the function of phloem vessels?
Phloem vessels transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non photosynthesising regions in the roots and stem.
What are root hair cells? Where do they grow?
Root hair cells are single-celled extensions of epidermis cells in the root. They grow between soil particles and absorb water and minerals from the soil.
How does water enter a root hair cell?
Water enters the root hair cell by osmosis. This is because the soil around it has a high water potential than the cytoplasm of the root hair cell.
Why is the root hair significant?
The root hair increases the surface area of the cells significantly. The large surface area is important as it increases the rate of absorption of water by osmosis and mineral ions by active transport.
What is the pathway taken by water?
root hair cell → root cortex cells → xylem → leaf mesophyll cells
How to investigate water movement in plants?
The pathway can be investigated by placing a plant into a beaker of water that has had a stain added to it. After a few hours, the leaves of the celery will turn the same colour as the dyed water, proving that water is being taken up by the celery. However, only certain area of the stack is stained the colour of the water showing that water is being carried in specific vessels through the stem - xylem vessels.
How is water transported from the roots to the leaves?
Water is transported from the roots to leaves by traveling up the xylem. This is to replace the water that has been lost due to transpiration.
What is transpiration?
Transpiration is the loss of water vapour from plant leaves by evaporation of water as the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata.
What is capillary action?
Capillary action is the forces that cause water to travel up a hollow tube on its own. Capillary action consists of two forces – cohesive force (the property of water molecules that make them stick to each other) and adhesive force (the property causing water molecules to stick to other things).
How does water move upwards in the xylem vessel?
As water vapour evaporates from the mesophyll cell surface and leaves the leaf, a sucking force is created. This means that there is less water pressure at the top than the bottom, creating a hydrostatic pressure gradient, and hence, a water potential gradient. This draws water up the xylem.
Describe the effects of variation of temperature on transpiration rate
The higher the temperature, the greater the transpiration rate, because water vapour molecules will have more kinetic energy and hence move out of the leaf faster.
Describe the effects of humidity on transpiration rate
The higher the humidity of the air outside the leaf relative to the air inside the leaf, the lower the transpiration rate. This is because water usually diffuses down a concentration gradient, but if the air outside is already saturated with water, there is more likely to be a net movement of water into the leaf (providing the stomata are open) rather than out.
What is translocation?
Translocation is the transport of sucrose and amino acids in the phloem from regions of production to regions of storage or use. They can be used in respiration or growth.
What direction of flow is there in the xylem?
One way from roots to leaves.
What direction of flow is there in the phloem?
In all directions.
What is the transpiration stream?
The transpiration stream is the upward movement of water through the xylem vessels.
What is transpiration pull?
Transpiration pull draws water upwards in the transpiration stream. This is because when water is lost by transpiration, more water is drawn upwards to replace it. This upward pull is known as transpirational pull.
What does cohesion do in the transpiration stream?
Cohesion is the force that makes water molecules stick to each other. The forces of attraction exert a pull on the molecule below pulling it upwards in a continuous pull.
What is the circulatory system?
The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow of blood.
What is a closed system?
A closed system means that the blood is always contained in the vessels and just continually makes loops throughout the system.
