Plant transport Flashcards
Describe the role of plasmodesmata in transport in plants
Transport of, water / sucrose / amino acids / organic substances / ions /minerals /
salts / lipids / hormones / ATP, (from cell to cell / between cells) without crossing, membranes / walls. This is movement is through the symplast pathway.
EXAMPLES: companion cell to (phloem) sieve tube (element / cell), between mesophyll cells
mesophyll cell to companion cell, cortical cell to cortical cell / across cells of the cortex
cortical cell to endodermal cell, endodermal cell to, pericycle cell / xylem / phloem
Explain why the rate of water uptake by the leafy part of the plant will not be the same as the rate of transpiration.
Water taken up may not all be lost in transpiration
Water is used in photosynthesis, hydrolysis reactions, maintaining turgidity and is necessary for cell elongation.
State two environmental conditions, other than temperature, which will affect the rate of water uptake of a leafy twig.
humidity; wind (speed); air movements; light intensity; (air) pressure
Transpiration is sometimes described as an ‘inevitable consequence of gas exchange’ in
plants. Explain this statement.
Stomata (must be) open for, gas exchange / uptake of carbon dioxide for photosynthesis
Water vapour, diffuses out, via (open) stomata
Most transpiration occurs when stomata are open
Describe and explain how the structure of xylem vessels is suited to their function.
Transport of water and mineral ions.
Elongated cells to form tubes for transport.
No end walls
Hollow so more space for greater volume to flow (minimal resistance)
Cellulose lining so hydrophilic, allowing for adhesion of water molecules.
Lignified prevents collapse and waterproofs.
Pitted walls allow lateral movement of water.
What’s the name of the ion that diffuses through carrier proteins with sucrose into companion cells phloem tissue?
Hydrogen
Explain the need for transport systems in plants.
large (size / volume / organism) so a smaller surface area
diffusion (alone), not enough / too slow (to supply needs)
surface too far from the centre of a plant
distances too far to supply required nutrients
plants require, supplies in bulk / mass flow
Plants require a xylem and phloem. A xylem to transports water (and mineral ions) and a phloem to transports assimilates.
State four differences between transport systems in mammals and in plants.
Plants have xylem and phloem. Mammals have arteries, veins and capillaries.
Plants do not have a pump. Mammals have a heart.
Plants do not have a circulation. Mammals have a double circulation.
Plants have pits and plasmodesmata. Mammals have a closed circulation.
Plants have living and dead cells. Mammals have just living cells.
Plants do not transport respiratory gases, whereas mammals do.
Plants have a slow rate of flow, mammals have a faster rate of flow.
Explain how cellulose is a suitable material for the cell walls of plants.
Cellulose cell wall is permeable
There are many gaps between fibres which allow passage of water
Cellulose is strong which allows it to withstand (turgor) pressure.
In plants, assimilates are transported in phloem sieve tube elements by a process known as translocation. Explain how assimilates that arrive in the phloem sieve tubes from mesophyll cells can be translocated to other parts of the plant.
Assimilates lowers water potential which causes water to enter by osmosis. This increased volume increases hydrostatic pressure. Assimilates (sucrose), leave at the sink and lower the hydrostatic pressure at the sink. This results in mass flow down a pressure gradient.
List three adaptations, which are characteristic of xerophytic plants.
stomata in pits, no stomata on upper surface, few stomata, hairs, thick (waxy) cuticle, thick walled epidermal cells, several layers of upper epidermis.
Describe the process of transpiration in plants
loss of water vapour from, leaves / aerial parts of the plant
water evaporates from, walls / surface, of mesophyll cells into air spaces
water vapour diffuses through open stomata (to atmosphere) down a water potential gradient
Suggest the advantage of complex plasmodesmata between cells in leaves.
Increased movement of assimilates.
There are more (symplast) pathways
e.g. of complex plasmodesmata - from companion cell into sieve tube (elements) / when loading sucrose into phloem
State what is meant by transpiration
Loss of water vapour from leaves / aerial parts of plant.
plus one from:
• evaporation of water, from surface of spongy mesophyll cells / into air spaces.
• diffusion of water vapour, out / to atmosphere.
• movement / diffusion, out through open stomata.
• water vapour moves out down the water potential gradient.
State one way in which transpiration differs from translocation.
transpiration involves only water. It involves evaporation/ diffusion and movement out to (external) environment / loss from leaves. Its affected by external factors such as humidity, light , wind speed and temperature. It occurs in one direction / from air spaces through stomata. Finally, ATP not required.
Translocation involve assimilates and involves (hydrostatic) pressure gradients. Translocation involves transport in phloem from source to sink. ATP is used (to enable loading of sucrose into phloem sieve tube).
Explain the effect of stomatal aperture on rates of transpiration in non-moving and moving air.
Increasing width of stomatal aperture allows more water vapour to diffuse out.
Intercellular air spaces in leaf have high water potential.
In moving air, air does not remain around the leaf. Water potential gradient is maintained.
Explain how hydrogen bonding is involved in the movement of water in the xylem.
Adhesion of water to cellulose (of xylem vessels). This occurs because of the polar, property of cellulose (fibres). There is cohesion between water molecules which maintains a column of water (transpiration pull).
Describe the function of phloem sieve tubes.
Transport of assimilates from source to sink, through translocation and mass flow
Explain how the structure of the walls of xylem vessel elements are adapted to their functions.
lignin for, waterproofing and support to prevent inward collapsing.
cellulose for adhesion of water.
pits for lateral movement of water.
rings / spirals, for, extension / growth.
Explain how sucrose moves into the companion cell, and then moves from the companion cell into the sieve tube element.
Protons moved out by active transport through proton pump (moved out against concentration gradient). This creates a, proton gradient. Protons go into the, cell wall (apoplast). Protons enter cells by facilitated diffusion by cotransporter proteins. Sucrose is transported into (companion) cell together with protons. Sucrose enters against concentration gradient. Sucrose concentration increases in companion cell. Sucrose then diffuses into sieve tube (element) through plasmodesmata.
State what is meant by a sink.
growing / storage area
examples of part of plant that stores / growing root / shoot tip / bud / flower / maturing leaf / tuber / fruit / seed
