Topic 3: Mass Transport In Plants Flashcards
Define transpiration
Transpiration us the loss of water vapour from the stomata by evaporation
Describe how four different factors affect the rate of transportation
1: light intensity => there is a positive correlation between light intensity and transpiration. This is because the higher the light intensity, the more stomata that open and so provide a larger surface area for evaporation
2: temperature => positive correlation between temp and transpiration. The more heat there is the more kinetic energy, and therefore faster moving molecules.this increases evaporation
3: humidity => negative correlation. The more water vapour in the air, the more positive the water potential is outside of the leaf. This reduces the water potential gradient and therefore reduces evaporation.
4:wind => positive correlation. The windier it is, the more humid air containing the water vapour that is blown away. This maintains the water potential gradient, increasing evaporation
Describe how water moves up the xylem (5 marks)
- Water vapour evaporates out of the stomata on leaves. This loss in water volume creates a lower pressure.
- When this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to negative pressure)
- Due to the hydrogen bonds between water molecules (they’re cohesive) this creates a long continuous colum of water with the xylem
- Water molecules also adhere to the walls of the xylem which helps to pull the water upwards -> transpiration pull
- As this column of water is pulled up the xylem it creates tension, pulling the xylem in to become narrower
What is the function of the phloem?
Phloem is the tube responsible for the transport of organic substances in plants, such as sugars
Describe the structure of sieve tube elements
Living cells
Contain no nucleus
Very few organelles
–>makes the cell more hollow and so provides less resistance to the flow of sugars
Describe the structure of companion cells
As the sieve tube elements have few organelles, they depend on companion cell for resources
The companion cell provides ATP required for active transport of organic substances
Describe the source to dink mass flow hypothesis
Sucrose lowers the water potential of the source cell. This causes water to enter by osmosis. This increases the hydrostatic pressure in the source cell.
The respiring cell is using up sucrose, and therefore it has a more positive water potential. Therefore water leaves the sink cell by osmosis. This decreases the hydrostatic pressure in the sink cell.
This results in the source cell having a higher hydrostatic pressure than the sink cell, so the solution is forced towards the sink cell via the phloem
Describe the process of translocation
- Photosynthesis occurring in the chloroplasts if leaves creates organic substances, eg.sucrose
- This creates a high concentration of sucrose at the site of production, therefore sucrose diffuses down it’d concentration gradient into the companion cells via facilitated diffusion.
- Active transport of H+ occurs from the companion cell into the spaces sitting the cell walls using energy
- This created a concentration gradient and therefore the H+ move down their concentration gradient via carrier proteins into the sieve tube elements.
- Co transport of sucrose with the H+ ions occurs via protein co transporters to transport the sucrose into the sieve tube elements
- This increase of sucrose in the sieve tube element lowers the water potential, so water enters the sieve tube elements from the surrounding xylem vessels via osmosis. The increase in water volume in the sieve tube element increases the hydrostatic pressure causing the liquid to be forced towards the sink.
- Sucrose is used in respiration at the sink ot stored as insoluble starch. More sucrose is actively transported into the sink cell, which causes the water potential to decrease. This results in the osmosis of water from the sieve tube element into the sink cell (some water also returns to the xylem). The removal I’d water decreases the volume in the sieve tube element and therefore the hydrostatic pressure decreases.
- The movement of soluble organic substances is due to the difference I’m hydrostatic pressure between the sourcexand sink end of the sieve tube element
Describe the proccess of tracing
Involves radioactively labelling carbon.
Plants are provided with only radioactively labelled carbon dioxide and over time this is absorbed into the plant and used in photosynthesis to create sugars which all contain radioactively labelled carbon.
Thin slices from the stems are then cut and placed on the xray film that turns black when exposed to radioactive material
Explain how tracing provides evidence of translocation
When the stems are placed on the xray film the section of the stem containing the sugars turn black, and this highlights where the phloem are and shows sugars are transported in the phloem
Describe ringing experiments
A ring of bark and phloem is peeled and removed off a tree trunk
Explain how ringing experiments provide evidence of translocation
The result of removing the phloem is that the trunk swells above the removed section
Analysis of the liquid in this swelling shows it contains sugar. This shows that when the phloem is removed, the sugars can’t be transported and so proves the phloem transports sugars
What is a taxes response?
A simple response in which an organism will move its entire
body towards a favourable stimulus or away from an
unfavourable stimulus.
What is a kinesis response?
When an organism changes the speed of movement and the
rate it changes direction.
Name 3 stimuli that simple organisms respond to
by taxes and kinesis
light
moisture
chemicals
