Plant cell organisation Flashcards
Phloem
- transport food (dissolved sugars)
- made of elongated living cells with small pores to allow cell sap to flow through
- transport goes in both directions
- Process called translocation.
Xylem
- transport water and minerals from roots to stem and leaves.
- made of dead cells with no end walls
- hollow inside
- walls made of lignin—> able to withstand pressure changes as water moves up the plant.
What is a transpiration stream?
When stomata opens, plants lose water vapour from them, it diffuses from a high conc in plant to low conc outside,
Water evaporates from the surface of the leaves, so more water is pulled up throug the xylem vessels from the roots.
How can aphids kill a plant?
Aphids are plant pests, they push their sharp mouthparts straight into the phloem and feed on the sugary cell sap. If too many of them attack at once, they can kill a plant by taking all its food.
How can movement through xylem be demonstrated?
- place leafy celery stalk in water containing coloured dye.
- after a few hours, slice the stem into pieces.[
- there will coloured marks where the water&dye has moved through the xylem.
Why are young trees particularly vulnerable to damage by animals?
Because phloem is found in a ring just underneath a bark, if a complete ring in bark is eaten, the transport in the phloem stops and tree dies.
Why is transport of water important?
- water is needed for photosynthesis to make glucose
- plant needs water to hold itself upright
- when there is enough water in cells, due to the pressure the cytoplasm pushes against cell walls, provides support for young plants.
Gas exchange in plants.
CO2 diffuses from a high conc in air to a low conc inside cells.
O2 made in photosynthesis diffuses from a high conc in plant to low conc outside.
What affects transpiration rates?
light intensity
temp
air flow
humidity
Light Intensity
the brighter the light, the greater the rate.
This is cz stomata closes as it gets dark because photosynthesis doesn’t happen in the dark so they don’t need to stay open for gas exchange, so at night, very little water escapes.
Temp
the higher the temp, faster the rate.
When temp is high, water particles have more more energy to diffuse and evaporate.
Air flow
the better the flow near leaf, faster the rate.
- if air flow is fast, the water particles are just swept away, this maintains low conc of water vapour in the air so diffusion happens quickly.
Humidity.
drier the air around leaf, faster the rate.
Why would the mean water uptake be higher on a hot day than on a cold day?
On a hot day, more water lost, more and faster transpiration, so more water is taken up by the roots to replace the water loss.
Why do root hair cells contain lots of mitochondria?
Because they need to undergo active transport, they need energy for active transport, to get the mineral ions from low conc in the soil to high conc in the roots. Most energy is released from respiration in mitochondria.
