Funtion of xylem
Transports water and minerals up the plant
-From the roots to the stem and leaves
Function of phloem
Transport of sucrose and amino acids in both directions
- From the leaves to every cell
Structure of xylem
Thick walls with lingin
No cell contents (dead hollow cell)
Cells joined end to end with no cross walls to form al long continous tube
Why do plants need water?
Plants need water for photosynthesis, for cooling, transport of minerals and nutrients from the soil into the plant
Where does water enter the plants
From the soil to the roots, by osmosis. It enters the root hair cells.
Function of root hair cells
Absorption of water (osmosis) and active transport of ions
Adaptations of root hair cells
- large surface area -> increases the uptake of water and mineral ions
- large vacuole -> for storage of water - mitochondria -> for active transport
Pathway of water
Soil -> root hair cells -> root cortex cells -> xylem vessel -> travels in the xylem up the stem -> into palisade mesophyll cells
What is transpiration
The loss of water vapour from plant that leaves by evaporation
What is water needed for in plants
- it is a recatant for photosynthesis
- to mantain turgor pressure in cells, supports the plant
Water evaporation (transpiration)
Water evaporates from the surface of mesophyll cells in the leaf to form water vapour. This moves through air spaces and diffuses out the leaf via stomata
The transpiration pull (7)
1) evaporation and diffusion of water occurs from the leaves
2) shortage of water from the leaf
3) more water is drawn into the leaf from the xylem to replace this lost water
4) there are forces of attraction between water molecules, holding them tigether (water has conesive forces)
5) water is pulled up the xylem from the roots
6) water is drawn up from the roots
7) there is a contant transpiration pull of water through the plant
How does leaf structure increase water loss?
- Leaves are adapted for photosynthesis and diffusion of gases
- This means that the mesophyll layer has a large surface area for diffusion of gasses, but also means more water can evaporate out the leaf
How do guard cells influence water loss?
- Gurad cells can change the diameter of the stomata to control water loss
-> the smaller the stomata, less water lost
-> the greater the number of stonata, the more water is lost
Factors that affect transpiration rate
Temperature
Humidity
Wind speed
Factors that affect transpiration rate: temperature
- More kinetic energy
- Faster diffusion/transpiration
Factors that affect transpiration rate:
Humidity
The higher the humidity, the more H2O around leaf -> slower transpiration
Lower concentration gradient
Factors that affect transpiration rate:
Wind speed
- Faster/higher speed -> faster transpiration
-> because wind sweeps evaporated water away
-> and higher concentratin gradient
What is translocation
The movement of sucrose and amino acids through the phloem from a source to a sink
What is a source
Any part of the plant which releases sucrose or amino acids
What is a sink
1) where sucrose and amino acids are stored
2) sucrose or amino acids are used up in respiration or growth
Are the concentration of solutes higher at the source or the sink
Concentration of solutes are higher at the source than the sink
Plants can be both sources and sinks: sources
- Plants growing -> leaves are photosynthesising
- Amino acids are made in the roots the transported to developing roots, flowers, leaves, seeds
Plants can be both sources and sinks: sinks
- Winter -> storage in roots, tubers and bulbs
- Reproductive structures and stems during growth
- Newly growing leaves in spring, when they are fully grown they become sources again
