1. State the functions of xylem and phloem.
Xylem: specialised tissue in plants that transports water and inorganic ions from the root up to all the other parts of the plant
Phloem: specialised tissue in plants that transports food nutrients (e.g. glucose) from the leaves to other parts of the plant.
2. Identify the positions of xylem and phloem tissue.
3. Identify root hair cells, as seen under the light microscope, and state their functions.
Root hair cells are found at the end of young roots, their function is to help the plant absorb water and mineral ions from the soil via osmosis. They have large surface areas so they can maximise absorption.
4. Relate the structure and functions of root hairs to their surface area and to water and ion uptake.
As said above, root hairs have large surface areas for absorption of water and ions. The cell membrane is semi-permeable so only minerals and water can go through, but not necessarily go back out.
5. State the pathway taken by water through root, stem and leaf (root hair, root cortex cells, xylem, mesophyll cells).
1. There is a high concentration of salts in the cell sap of the root hair, but a low concentration in the soil.
2. By osmosis, water passes into the root hair from the soil.
3. The cell sap is now diluted by the water. Next to the root hair is the cells of the cortex. Osmosis occurs through the cells until the water reaches the xylem.
4. The xylem vessel transports the water up the xylem tube from root to stem through a process called capillary action*.
*capillary action = cohesion of hydrogen bonding and adhesion to cell wall --> this pulls up everything against the force of gravity
5. The water leaves the xylem and is absorbed by the cells in the leaves.
6. Investigate, using a suitable stain, the pathway of water through the aboveground parts of a plant.
7. Define transpiration as evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata.
So water is pulled up form the xylem, and is used for photosynthesis. Transpiration is when water evaporates from the leaves into the air. When the water has evaporated, more is needed to continue photosynthesis. The transpiration stream is the stream of water that is pulled up from the roots to the leaves, similar to how a drink is sucked up a straw.
8. Describe how water vapour loss is related to cell surfaces, air spaces and stomata.
Water in the mesophyll cells forms a layer on the surface of the cell. The water evaporates into the air spaces between the spongey cells. A high concentration of water is in the cells, so water diffuses out of the leaf through the stomata. The water lost is replaced by water from the xylem.
9. Describe the effects of variation of temperature, humidity and light intensity on transpiration rate.
temperature: the higher the temperature, the faster the rate of transpiration
humidity: the higher the humidity, the slower the transpiration --> this is because there is a lot of moisture in the air
wind speed: transpiration increases as wind speed increases
light intensity: the more light, the faster the transpiration --> this is because the stomata open in light for photosynthesis
water supply: the less the water, the slower the transpiration --> when there is less water, the stomata close up to conserve water
10. Explain the mechanism of water uptake and movement in terms of transpiration producing a tension (‘pull’) from above, creating a water potential gradient in the xylem, drawing cohesive water molecules up the plant.
Once water enters the xylem tubes in the roots, it flows to the stem, then the leaves. This flow is called the transpiration stream. The columns of water in the xylem tubes are prevented form breaking by strong cohesive forces between the water molecules.
11. Define translocation in terms of the movement of sucrose and amino acids in phloem; from regions of production to regions of storage OR to regions of utilisation in respiration or growth.
Translocation is the movement of manufactured food through the phloem tissue. Food in manufactured in the leaves. In younger plants, food is distributed to areas of growth while in older plants, it is transported to areas for storage e.g. roots in a potato plant. In all plants, food needs to be transported to the cells for respiration.
As said above, root hairs have large surface areas for absorption of water and ions. The cell membrane is semi-permeable so only minerals and water can go through, but not necessarily go back out.
5. State the pathway taken by water through root, stem and leaf (root hair, root cortex cells, xylem, mesophyll cells).
1. There is a high concentration of salts in the cell sap of the root hair, but a low concentration in the soil.
2. By osmosis, water passes into the root hair from the soil.
3. The cell sap is now diluted by the water. Next to the root hair is the cells of the cortex. Osmosis occurs through the cells until the water reaches the xylem.
4. The xylem vessel transports the water up the xylem tube from root to stem through a process called capillary action*.
*capillary action = cohesion of hydrogen bonding and adhesion to cell wall --> this pulls up everything against the force of gravity
5. The water leaves the xylem and is absorbed by the cells in the leaves.
6. Investigate, using a suitable stain, the pathway of water through the aboveground parts of a plant.
7. Define transpiration as evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata.
So water is pulled up form the xylem, and is used for photosynthesis. Transpiration is when water evaporates from the leaves into the air. When the water has evaporated, more is needed to continue photosynthesis. The transpiration stream is the stream of water that is pulled up from the roots to the leaves, similar to how a drink is sucked up a straw.
8. Describe how water vapour loss is related to cell surfaces, air spaces and stomata.
Water in the mesophyll cells forms a layer on the surface of the cell. The water evaporates into the air spaces between the spongey cells. A high concentration of water is in the cells, so water diffuses out of the leaf through the stomata. The water lost is replaced by water from the xylem.
9. Describe the effects of variation of temperature, humidity and light intensity on transpiration rate.
temperature: the higher the temperature, the faster the rate of transpiration
humidity: the higher the humidity, the slower the transpiration --> this is because there is a lot of moisture in the air
wind speed: transpiration increases as wind speed increases
light intensity: the more light, the faster the transpiration --> this is because the stomata open in light for photosynthesis
water supply: the less the water, the slower the transpiration --> when there is less water, the stomata close up to conserve water
10. Explain the mechanism of water uptake and movement in terms of transpiration producing a tension (‘pull’) from above, creating a water potential gradient in the xylem, drawing cohesive water molecules up the plant.
Once water enters the xylem tubes in the roots, it flows to the stem, then the leaves. This flow is called the transpiration stream. The columns of water in the xylem tubes are prevented form breaking by strong cohesive forces between the water molecules.
11. Define translocation in terms of the movement of sucrose and amino acids in phloem; from regions of production to regions of storage OR to regions of utilisation in respiration or growth.
Translocation is the movement of manufactured food through the phloem tissue. Food in manufactured in the leaves. In younger plants, food is distributed to areas of growth while in older plants, it is transported to areas for storage e.g. roots in a potato plant. In all plants, food needs to be transported to the cells for respiration.
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