These are revision notes/a summary about the Plant Tissues, Organs & Organs Systems Module from the Organisation Topic. This is for GCSE AQA Biology(triple science) Higher tier. They were made using the specification and CGP revision guide.
Organ systems
Transpiration Translocation
Happens through Xylem cells Sieve plates are at the end if the cell walls
- Transports water & minerals up the plant The phloem vessel has a companion cell
- only one direction connected by pores
- Cohesion between the water molecules
means water is continuously pulled upwards
Transpiration pull - how water is transported up the
xylem
Water molecules evaporate out the top sucking up
water molecules below
Xylem vessels are:
- Dead
- Narrow
- hollow cells
- strengthened by lignin (makes them
waterproof and elongates them)
Transpiration stream
- Movement of water from the roots up the
stem via the xylem
- To the leaves
- Where water evaporates via the stoma
Can measure transpiration by a potometer
Stoma control the gases that come in and out of
the leaf for photosynthesis
They are controlled by guards cells
→ they control opening & closing of stomata
In the day time they swell up with water through
osmosis which causes them to open up the stoma
and allow gas to pass through
Water vapour evaporates and leaves through the
stoma, if it is too hot too much water will leave and
Factors Affecting Transpiration: the plant will wilt and not have enough water to
Humidity - dryer the air the higher concentration survive
gradient, faster water diffuses
Airflow - removes water molecules surrounding leaf
so higher concentration gradient
Temperature - water evaporates faster
Light intensity - more photosynthesis so stoma open
to allow CO2 in so water escapes faster
Structure of the Leaf
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