B8 - Transport in Plants T11 Flashcards
XYLEM
direction of transport:
cell living or dead:
cell walls made of:
adaptations:
what it transports:
cell wall thickness:
direction of transport: one way only - up (root to stem/leaf)
cell living or dead: dead hollow cells
cell walls made of: cellulose + lignin
adaptations: 1. no end walls 2. strengthened by lignin, waterproof
what it transports: minerals and water
cell wall thickness: very thick
PHLOEM
direction of transport:
cell living or dead:
cell walls made of:
adaptations:
what it transports:
cell wall thickness:
direction of transport: 2 ways
cell living or dead: living
cell walls made of: cellulose
adaptations: 1. holes in end walls so sucrose and amino acids move easily 2.no organelle
what it transports: sucrose and amino acids
cell wall thickness: usual thickness
Why is waterr needed in leaves?
- photosynthesis
CO2 + H2O -> C6H12O6 + O2 - cells remain turgid - plant is upright
Define transpiration
evaporation of water from leaves
Order how water and minerals move through xylem
- water vapour diffuses
Order how water and minerals move through xylem
- Water vapour diffuses through the air spaces in the mesophyll and out of the stomata
- More water vapour evaporates from the surface of mesophyll cells
- Water lost from the mesophyll cells is replaced by water from the xylem
- As water leaves the xylem if pulls up more water to replace it (transpiration pull)
- More water enters the xylem from the roots
- Water enters the root by osmosis in the root hair cells
Why does the lower epidermis have more stomata?
How are root hair cells adapted?
large SA:V
no chloroplasts - underground
What is transpiration
evaporation of water from the surface of a plant, consequence of gas exchange when stomata open
how transpiration works
Water also evaporates at the open stomata
● As water molecules are attracted to each other, when some molecules leave the plant
the rest are pulled up through the xylem
● This results in more water being taken up from the soil resulting in a continuous
transpiration stream through the plant
[6 marks]
Using a potometer to measure transpiration
- Cut a leafy shoot from a plant (e.g. Pelargonium) and plunge the cut stem into water.
- Immerse the whole of the potometer into the sink. Move it about until all the air bubbles come out.
- Put the stem into a large sink full of water and carefully cut off the bottom of the shoot under water with a sharp razor blade
- Put the shoot stem into the bung, grease the joint with plenty of petroleum jelly, then put the bung into the potometer.
- Make sure the tap is closed, then lift the whole ensemble out of the water.
- Leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water
Factors affecting transpiration:
increase in light intensity
increase in temperature
increase in air movement
increase in humidity
how increase in light intensity affects transpiration
This leads to an increased rate of photosynthesis, so more
stomata open to allow gaseous exchange to occur. This means
more water can evaporate, leading to an increased rate of
transpiration.
how increase in temperature affects transpiration
The molecules move faster, resulting in evaporation happening at a faster rate and therefore the rate of transpiration increases.
The rate of photosynthesis increases, meaning more stomata are open for gaseous exchange, so more water evaporates and the rate of transpiration increases
how increase in air movement affects transpiration
If more air is moving away from the leaf due to it being blown
away, then the concentration of water vapour surrounding the leaf will be lower. This will mean there will be a steeper concentration gradient resulting in diffusion happening faster. This will increase the rate of transpiration.
