3.3 Plant Transport Flashcards
Why do plants need a transport system?
Because of their large size, high metabolic rate, and SA:V
What is the function of xylem tissues?
To transport water and mineral ions up the plant, and provide structural support to stems etc.
What is the function of phloem tissue?
To transport sugars/ solutes in solution up and down the plant from source to sink
Which plant vascular tissue is made from dead cells and which alive?
Xylem- Dead
Phloem- Living
Why do xylem cells have no end walls?
To make uninterrupted tube for water flow in a column
Xylem cells are supported by _____.
Lignin
How is lignin deposited on xylem vessel walls, and why?
In spirals or rings to allow flexibility and growth space
How does water move out of xylem vessels?
Through pits with no lignin
What are parenchyma?
Living cells which act as packing tissue between xylem vessels to support and separate them
What is sap made of?
Sucrose dissolved in water
What does phloem tissue consist of?
Sieve tube elements and companion cells
What are sieve plates?
End sieve tube element walls with many holes to allow assimilates through
Why do sieve tube elements have no nucleus, little cytoplasm and organelles?
To allow space for mass flow of sap to go through them
Why does a plant root need a lot of support?
To push through the soil and to anchor the plant
How are vascular tissues arranged in a root?
Xylem in an X in the middle with phloem around it
What is cambium?
Meristem cells that can produce vascular tissue
What is a vascular bundle?
Xylem, phloem and cambium
How is plant vascular tissue arranged in stems?
Vascular bundles found around outer edge of stem, with xylem inside and phloem outside with cambium in the middle
Why are vascular bundles found around the outer edge of the stem?
To provide strength, support and flexibility
How are xylem and phloem arranged in a plant leaf vein?
Xylem on top of phloem
What is the middle part of a leaf called?
Central midrib
Why do you cut a plant cross section (for examination) as thinly as possible?
To allow max light to pass through so structures are clear under light microscope
Why do you place a thin plant cross section in water before examining?
To prevent drying out
How do you stain a plant specimen cut thinly?
Place in dish containing stain for 1 min, then remove and rinse with water
What is a potometer used for?
To measure rate of water uptake of a plant and estimate the transpiration rate
Why do we set up a potometer underwater?
To ensure no air bubbles enter apparatus
How do you ensure that no air enters the xylem from a cut stem?
Cut it underwater
Why do we cut the stem at an angle?
To maximise SA in contact with water
What can you do to ensure a potometer experiment is fair?
Dry leaves before starting, allow time for plant to acclimatise before starting,ensure plant is healthy
How does water enter the roots of a plant?
Drawn in my osmosis, down water potential gradient
Cellulose cell walls are fully ________ permeable.
Water
Plant cells are joined together by _______________.
Plasmodesmata- cell channels
What is the symplast pathway?
Water travels through the living cell parts (cytoplasm, vacoule)
How does water move through the symplast pathway?
Osmosis
What is the apoplast pathway?
Water travels through the non living cell parts (cell walls)
Water can carry dissolved mineral ions and salts through the ________ pathway.
Apoplast
How does water move through the apoplast pathway?
Mass flow ( not osmosis as no membranes crossed, moves by pressure gradient )
The _______ pathway is used more because it provides the least resistance.
Apoplast
What is the Casparian strip and what does it do?
A waxy strip that forces water to take the symplast pathway
Why is the Casparian strip useful?
Water must pass through the symplast pathway which has a partially permeable membrane which can control entry of substances.
________ and ________ help water move up the transpiration stream against gravity.
Cohesion and tension
How is tension made in the transpiration stream?
Water evaporates at the top creating suction and a pressure gradient, pulling water up towards the leaf
Why is cohesion useful?
Water molecules stick together by hydrogen bonds and follow each other up the transpiration stream, making an uninterrupted column of water
What is adhesion?
Water molecules stick to xylem vessel walls
What is transpiration?
A side effect of gas exchange, the loss of water vapour from the top of the plant
Why is transpiration a side effect of gas exchange?
Stomata must be open for gas exchange but in the process let out water vapour
In what ways is transpiration vital to a plants survival?
Transports mineral ions up the plant, maintains cell turgidity, supplies water for photosynthesis, helps maintain temperature.
Why does light intensity increase transpiration rate?
When light, stomata are open for photosynthesis gas exchange, when dark stomata are normally closed
Why does temperature increase transpiration rate?
- Higher temp increases evaporation of water rate
- Diffusion rate increases
Why does humidity decrease transpiration rate?
More water in air decreases water vapour potential gradient
Why does wind increase transpiration rate?
Water vapour blown away from stomata so water vapour potential gradient steeper
How does water move through xylem?
Mass flow in transpiration stream
What is root pressure?
When water is drawn into the root by osmosis pressure builds up forcing water into xylem and up the stem
What is translocation?
The movement of dissolved substances to where they’re needed through phloem tissue
Translocation requires _______ from ___.
Energy from ATP
In what direction does translocation occur?
From source to sink,down a concentration and pressure gradient.
Why are sugars transported as sucrose?
As its soluble and metabolically inactive so it doesn’t get used up during transport
How do enzymes maintain the concentration gradient at the sink end?
By converting the assimilate to something else at the sink, e.g. sucrose to starch
What is active loading?
Active transport used to move substances into companion cells and sieve tubes against a concentration gradient
How does active loading work?
H+ are pumped out companion cell creating conc gradient, then H+ and solute bind to a cotransport protein and re-enter cell by facilitated diffusion.
How does mass flow in phloem work?
High hydrostatic pressure at source end, low hydrostatic pressure at sink end creating pressure gradient for sap to travel down.
What does a waxy cuticle do?
Reduces water lost from top of leaf by evaporation
Why are stomata found on the underside of leaves?
To prevent evaporation of water from direct sun heating
Why do deciduous plants lose their leaves in the winter?
Because water may be frozen (unavailable) or it may be too cold for photosynthesis
What is a xerophyte?
A plant adapted to live in dry conditions
What is the main concern for a xerophyte?
Losing water through transpiration and being unable to replace it
What are the two examples of xerophytes?
Cacti and marram grass
Why does marram grass have its stomata in sunken pits with hairs?
Shelter stomata from wind, traps humid air, reduces water loss
Why does marram grass have a dense spongey mesophyll?
Little air gaps to reduce SA for evaporation
Why do xerophytes have a long tap root?
To take advantage of any rain and to get the maximum amount of water possible
Why do cacti have ribs and flutes?
Because they store water in their stems and they need to expand when full of water
Why do xerophytes try to have a low water potential inside cells with a high salt content?
To reduce water vapour potential gradient between cells and outside air
Why do cacti have spines?
Reduce SA for evaporation of water, and to prevent being eaten by predators
Why do cacti have a green stem?
To carry out photosynthesis
What are hydrophytes?
Plants adapted to living in water
What is the main concern of a hydrophyte?
Oxygen availability for submerged tissues and keeping affloat
Why do hydrophytes need to stay affloat?
So that the leaves can access sunlight for photosynthesis
Why do hydrophytes have lots of large air spaces in the leaf?
To keep affloat and be a supply of oxygen
Why do hydrophytes have stomata on upper leaf surface?
So they can be exposed to air for gas exchange
Why do hydrophytes leaf stems have large air spaces?
To help with buoyancy and to allow oxygen to quickly diffuse to roots and submerged parts of the plant for respiration.
