Module 3: Section 3 - Transport in plants Flashcards
Why do multicellular plants need transport systems?
Because they have a small SA:V ratio so they cannot solely rely on diffusion as its too slow to meet their metabolic demand
What do xylems transport?
water and mineral ions up the plant only
What are the two types of transport systems involved in transport in plants?
-xylem and phloem
What does the phloem transport?
Sugars both up and down the plant
What is the structure of the root cross section?
- in the middle there is the xylem(looks like a cross)
-around it is the phloem
What is the structure of the stem cross section?
-the phloem and xylem are near the outside to provide some sort of scaffolding
-pith in the middle
-xylem is the part closest to the pith
-phloem is the section further from the pith
What is the structure of the root cross section?
- Xylem and phloem make up a network of veins which support the thin leaf
-the xylem is on top of the circular things
-the phloem is on the bottom of the circular things
What is the structure of the phloem?
-has companion cells
-has sieve tube elements
-joined by end to end walls
-made up of living cells
-has phloem fibres
-has phloem parenchyma
What are sieve tube element?
living cells which form the tube for transporting solutes through the plant
What is the structure of the xylem?
-elongated tube structures
-cells joined end to end
-dead cells
-has lignin for support and to stop them from collapsing inwards
-has pits where water and ions move out of
Do sieve tube elements have a nucleus?
no
Do sieve tube elements have a cytoplasm?
yes but very little
Why are companion cells there?
because sieve tube elements have a lack of a nucleus and other organelles so cannot survive on their own so companion cells carry out living functions for themselves and the sieve cells
How does water get from the soil to the xylem?
- water enters through the root hair cell and then passes through the root cortex, including the endodermis , to reach the xylem
How do you dissect plant stems?
-use a scalpel to thinly cut a transverse or longitudinal cross section of the stem
-Use the tweezers to place the cut sections in water
-transfer each section into a dish containing a stain
-rinse off sections with water
What are the pathways water travels to the roots?
-apoplast
-symplast
How does water move through the symplast pathway?
via osmosis
What happens when water in an apoplast pathway gets to the endodermis cells in the root?
The pathway is blocked by a waxy strip in the cell walls called casparian strip which means water has to take the symplast pathway
What happens in the apoplast pathway?
Water goes through the cell wall, as the walls are absorbent water can diffuse through them and water can carry solutes and move from an area of high hydrostatic pressure to low
What happens in the symplast pathway?
Water goes through the cytoplasm and the cytoplasm’s of the neighbouring cells connect through the plasmodesmata.
Why is the casperian strip being impervious to water a good thing?
water goes through the cell membrane which are partially permeable and can control whether or not substances in water get through
What is transpiration?
the evaporation of water from a plants surface, especially the leaves
How does light affect the rate of transpiration?
-the lighter it is the faster the rate of transpiration this is because the stomata opens when it gets light
How does the water move from the roots to leaves?
1)Water evaporates from the leaves
2) This creates tension, which pulls more water into the leaf
3)Water molecules are cohesive so when some are pulled into the leaf others follow. so the column of water moves up the xylem
What are the factors that affect the rate of transpiration?
-light
-temperature
-humidity
-wind
How does the temperature affect transpiration rate?
the higher the temperature the faster the rate of transpiration. This is as warmer molecules have more energy so they evaporate from the cells inside the leaf faster
How does humidity affect the rate of transpiration?
The lower the humidity the faster the rate of transpiration as the air around the plant is dry so the water potential gradient between the leaf and air is increased
How does wind affect the rate of transpiration?
- the windier the aster the rate of transpiration as air is blow away so there is less water molecules near the stomata, thus increasing the water potential gradient and thus the rate of transpiration
What is the function of pits in the xylem?
lateral movement of water
Describe and explain the precautions that need to be taken when setting up and using
the potometer?
-cut the stem underwater so no air can enter
-have apparatus underwater so no air bubbles that could block the xylem
-joints must be sealed tight to obtain a continuous column of water
what does the loading of the phloem consist of?
- sucrose diffuses across the leaf via the apoplast pathway
- protons are pumped out of companion cells using energy (ATP hydrolysis)
- sucrose is co-transported with protons by diffusion down their concentration gradiet into companion cells.
- sucrose move through plasmodesmata into sieve tube
- water potenial in sieve tube decreases due to this so water flows in via osmosis increasing hydrostatic pressure
what is transpiration pull?
the force that causes tension in the xylem due to water loss
this can be seen in transpiration as water is drawn upwards in the plant as a result of this force and cohesion
what is transpiration stream?
this is the continous movement of water up a plant
what are xerophytes?
‘dry plants’ these plants have structural ad physical adaptations that enable them to live in hot, dry OR cold (ice) conditions
what are adaptations of xerophytes?
adaptation -> why
minimum 3
- thick waxy cutile prevent water loss
- sunken stomata humid its reduce water vapour potential gradient
- reduced number of stomata
- reduced leaves smaller SA
- hairy/curly leaves traps water vapour so more humidity
- water storage succulents store H2O in roots/stems
- leaves loss in response to scarce water
- shallow roots to absorb water before evaporation occurs
- dormancy
what are hydrophytes?
Plants adapted to
live in freshwater or in
permanently saturated soil
what are adaptations of hydrophytes?
adaptation -> why
minimum 3
- Very thin or no waxy cuticle no need to conserve water
- Reduced structure no need to build structural
carbohydrates and proteins as
water can provide structure and
buoyancy - Many always-open stomata on upper surfaces
- Wide, flat leaves maximises klight absorption
- small roots
- Large surface area of stems
and roots under water maximises area for oxygen to
diffuse into submerged plants - air sacs enable floating
what are Aerenchyma and why are they useful in hydrophytes?
tissue with air spaces
Increases buoyancy of leaves and stems
forms a low-resistance internal pathway for
movement of oxygen to help with extreme
anoxic conditions in the mud
what is translocation?
the transport of organic compounds in phloem from sources to sinks
what are assimilates?
these are products of photosythesis that are transported
what does phloem unloading consist of?
- sucrose diffuses out of the phloem into sink cells
- cells convert sucrose into starch to maintain concentration gradient
- water follows by osmosis into cells or xylem maintaining pressure gradient
