Transport in Plants Flashcards
Define transpiration.
The loss of water due to evaporation from a plant through the stomata.
Is transpiration an active or passive process?
Passive.
How does humidity affect the rate of transpiration?
Higher humidity increases the water potential outside the plant, flattening the water potential gradient, so less transpiration takes place.
How does temperature impact the rate of transpiration?
Higher temperatures give more energy to water vapour on the outside of the plant, so it will move away, steepening the water potential gradient and increasing rate of transpiration.
How does light intensity impact the rate of transpiration?
The higher the light intensity, the more photosynthesis will occur in the plant, meaning more CO2 is needed, so the stomata open to let in, simultaneously allowing water to be lost by transpiration.
How does air movement impact the rate of transpiration?
The more the air moves, the more water vapour will be moved away from the plant, decreasing the water potential outside the plant and steepening the gradient, so rate of transpiration will increase.
Describe the structure of xylem vessels.
.Made of dead tissue,
.Walls are lignified, to strengthen them,
.Cells are hollow with no cytoplasm,
.Have pits- areas without lignin where water can move out into cells.
What is the function of the xylem?
To transport water and dissolved ions upwards.
Define vascular bundle.
Section in the middle of a plant root which contains the phloem and xylem.
How do water and ions move into a plant root?
Inside root hair cells are many ions, which means the water potential is lower than on the outside, so water moves into the roots through osmosis, carrying dissolved ions with it.
Define cohesion tension theory.
Water molecules are bonded by hydrogen bonds, so water moves as one continuous, unbroken column through the xylem. This is know as the transpiration pull/stream.
What part of the plant is the main site of gas exchange?
Spongy mesophyll.
What part of the plant is the main site of photosynthesis?
Palisade mesophyll.
Describe how water moves from the xylem to the palisade mesophyll.
.Higher WP in xylem than palisade cells,
.Water diffuses down WP gradient into cytoplasm or cell walls of other cells through plasmodesmata,
.Eventually reaches palisade cells.
Define translocation.
The process by which organic molecules and some mineral ions are transported between sources and sinks of a plant.
Define source of a plant.
The location in a plant where a resource us taken up, eg. leaves for glucose and roots for water.
Define sink of a plant.
The location where a resource is used up, eg. roots/flowers/seeds for glucose.
Describe a feature of companion cells.
They are high in mitochondria, which produce the necessary ATP to pump hydrogen ions out to create the hydrogen ion gradient.
Define mass flow.
Movement of a bulk of substances through a channel in a given time.
Why does mass flow happen in translocation?
There is high hydrostatic pressure at the source, and low hydrostatic pressure at the sink, so mass flow occurs down the pressure gradient.
How do aphids demonstrate evidence for translocation?
They feed off plants by putting their stylet into the stem. Higher volume of sucrose comes out lower on the stem, closer to the source, which is what is expected with translocation.
