Transport in Plants Flashcards
What are the functions of the xylem?
It transports water and dissolved mineral salts from the roots to the rest of the plant.
It also provides mechanical support for the plant.
How is the xylem adapted for its function?
Empty lumen with no protoplasm -> reduced resistance to flowing water
Walls thickened with lignin -> hard and rigid -> prevents collapse of xylem
How is the phloem adapted for its function?
Numerous mitochondria in companion cells -> energy needed for active transport of sugars
Holes in sieve plates -> rapid flow of manufactured food
What is translocation?
Translocation is the transport of food substances such as sugars and amino acids in plants.
How does water enter a plant?
Each root hair is a fine tubular outgrowth of an epidermal cell. The sap in the root hair cell is relatively concentrated with sugars and salts; thus it has a lower water potential than the soil solution. Water enters the root hair by osmosis, diluting the cell sap. The cell sap of the root hair now has a higher water potential than that of the inner cells, hence it moves to the next cell via osmosis. The process continues until the water enters the xylem vessels.
How do root hairs absorb ions or mineral salts?
Active transport against a concentration gradient - energy comes from cellular respiration
Diffusion when the concentration in the soil solution is higher than that of the root hair cell
What is transpiration?
Transpiration is the loss of water vapour from a plant, mainly through the stomata of the leaves.
What is a transpiration pull?
Transpiration pull is a suction force which pulls water up the xylem vessels, caused by the evaporation of water from the leaves.
How does water move from the xylem to the plant’s surroundings?
Water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces. It evaporates from the thin film and moves into the intercellular air spaces. Water vapour accumulates near the stomata, then diffuses through the stomata to the drier air outside the leaf. This decreases the water potential of the cell sap, and as a result, the mesophyll cells begin to absorb water by osmosis. These cells, in turn, remove water from the xylem vessels, resulting in a transpiration pull.
Why is transpiration important to a plant?
- Transpiration pull draws water and mineral salts from the roots to the stems and leaves.
- Evaporation of water removes latent heat of vaporisation, cooling the plant and preventing it from being scorched by the sun.
- Water transported to the leaves can be used for photosynthesis, turgidity, and to replace water lost by cells.
What factors affect the rate of transpiration?
Humidity - More humid, more water vapour, less transpiration
Wind or air movement - Stronger wind, more transpiration
Temperature of air - Higher temperature, more transpiration
Light - Higher light intensity, wider stomata, more transpiration
