8: Transport in plants Flashcards
What is the function of xylem
the transport of water and mineral ions and support
What is the function of phloem
The transport of sucrose and amino acids
What is the structure of xylem vessels? How does it help its function?
- thick walls with lignin -> allows system to withstand the strong pressures which occur during water transport
- no cell contents -> more water content = more space for water transport
- cells joined end to end with no cross walls to form a long continuous tube -> constant flow of water
What are root hair cells function?
adapted for efficient water uptake by having a LARGE SURFACE AREA = increases rate of osmosis into the root, also have a THIN WALL = diffusion distance is shortened
What does the large surface area of root hairs do?
It increases the uptake of water and mineral ions
What is the pathway taken by water through the root, stem and leaf?
Root hair cells > root cortex cells > xylem > mesophyll cells
What is transpirtation?
The loss of water vapour from leaves
Where does water evaporate from the surfaces of the mesophyll cells into?
They evaporate into the air spaces and then diffuse out of the leaves through the stomata as water vapour
How water vapour loss related to the large internal surface are provided by the interconnecting air spaces between mesophyll cells and the size & number of stomata?
- mesophyll cells = moist cell walls, that line the air spaces inside the leaf. water evaporates from this large internal surface so the air spaces become saturated with water vapour
- stomata = generally more water vapour in the air spaces than in the outside air. the more stomata = the higher the rate of transpiration
Explain the mechanism by which water moves upwards in the xylem
It is a transpiration pull that draws up a column of water molecules held together by forces of attraction between molecules
Explain the effects on the rate on transpiration of the factors:
a - temperature
b - wind speed
c - humidity
a - temperature is higher = water evaporates more easily
b - more wind speed = rate of transpiration increases (water vapour gets blown away)
d - high humidity = decreases the rate of transpiration as there is more moisture in the air that the plant can take in
Explain how and why wilting occurs
The water vapour exits the plant VIA the stomata. Water helps maintain plant structure by keeping cells turgid. If the plant loses too much water which is not replaced, it begins to wilt as water moves OUT of the cells & turgor pressure decreases.
What is translocation?
The movement of sucrose and amino acids in phloem from SOURCES to SINKS
What are sources?
Sources are parts of the plant that RELEASE sucrose or amino acids (e.g. leaves during summer)
What are sinks?
Parts of the plant that use or store sucrose or amino acids (e.g. tubers in summer)
