Plant Transport Flashcards
Why do plants need transport systems?
Metabolic demands, size and SA:V
What are dicotyledonous plants?
(Dicots) are plants that make seeds. There are herbaceous dicots and woody dicots
What are herbaceous dicots?
Dicots with soft tissues and short lifespans
What are woody dicots?
Dicots with hard, lignified tissues and a long life cycle
What are the structures in herbaceous dicots?
Vascular system, vascular bundles; xylem and phloem
How are vascular bundles arranged in the stem of a herbaceous dicot?
Vascular bundles are around the edge to give strength and support
How are vascular bundles arranged in the root of a herbaceous dicot?
In the middle of the plant to help the plant withstand tugging strains from wind
How are vascular bundles arranged in the leaf of a herbaceous dicot?
In the midrib of the leaf to help support the structure of the leaf
What is the xylem?
A structure made of non-living tissue in plants
What is the function of the xylem?
Transporting water and mineral ions, support
How does the structure of the xylem support its functions?
Long, hollow columns with cells fusing end-to-end so water and mineral ions can flow continuously, lignified secondary walls for extra support, lignin in either circles or spirals to reinforce xylem vessels
What are xylem parenchyma?
Thick-walled packs around xylem vessels that store food and tannin (bitter chemical that prevents predatation)
What is the phloem?
Living tissue that transports organic solutes around the plant from the leaves
What is the function of the phloem?
Transport organic solutes (sugars) and amino acids for cellular respiration and synthesis of other molecules, can go in either direction
How does the structure of the phloem support its functions?
Sieve tube elements connected end-to-end to form a long hollow structure, sieve plates at the end of each cell with pores for substances to travel through, companion cells to provide the sieve tube element with regular functions, plasmodesmata between the companion cell and sieve tube element for substances to pass through, supporting tissues and fibers
Why is water needed in plants?
Maintain turgor pressure to support stems and leaves, cell expansion with that turgor, loss of water via evaporation, transport of mineral ions and products of photosynthesis via aqueous solutions, material for photosynthesis
What is the function of root hair cells?
Exchange surface where water is taken into the plant
How are root hair cells adapted to function?
Microscopic size can penetrate between soil particles, each microscopic hair has a large SA:V and there are thousands on each tip, each hair has a thin surface layer to decrease diffusion and osmosis time, concentration of solutes in cytoplasm maintain water potential gradient
How does water move across the root hair cell?
Symplast and apoplast
What is the symplast pathway?
The pathway where water travels via the cytoplasm and plasmodesmata of living plant cells. The root hair cell has a higher water potential than the living cell and therefore, by osmosis, water travels down the water potential gradient and the process continues
What is the apoplast pathway?
The pathway where water travels via the cell walls and intercellular spaces. As the water is moved into the xylem, more water is pulled into the apoplast pathway by cohesive forces that creates a continuous flow
What is the Casparian strip?
A band of waxy material at the endodermis that pushes water from the apoplast pathway into the symplast pathway
How is water transported into the xylem?
The water potential of the endodermal cells and cytoplasm is higher than the xylem, therefore the water molecules move into the xylem via osmosis. Once the water is in the vascular bundle the water is pushed back into the apoplast pathway to enter the actual xylem via osmosis which creates root pressure
What is root pressure?
Gives water a push up the xylem, not always a major factor in water movement from roots to leaves- this is an active process
Give evidence for root pressure
Some poisons (cyanide etc) affect the production of mitochondria and therefore ATP, therefore root pressure disappears. Root pressure increases with temperature, suggesting chemical reactions are involved. Same with oxygen levels.
What is transpiration?
Loss of water vapour from the leaves
What features of the plant are used in transpiration?
Waxy layer of leaves to prevent water loss, stomata with guard cells to open and close to prevent excessive water loss, xylem to transport the water, root hair cell to absorb water
What is the transpiration stream?
The constant flow of water from the roots out of the stomata on the leaves down the water potential gradient (via the xylem)
What is cohesion-tension theory?
When water moves from the soil in a continuous stream up the xylem via cohesive forces
State some evidence for cohesion-tension theory
Change in diameter of trees; transpiration is at its height during the day, so the tension is highest in the xylem therefore the tree shrinks in diameter
How do stomata effect the rate of transpiration?
Turgor driven shape changes to swell up to close to prevent water loss and relax to open to allow gas exchange
What factors affect transpiration?
Light, humidity, temperature, air movement and soil-water availability
What is a source?
Storage for sugars
What is a sink?
Growth areas that use the sugars from the sources
Name an example of a source
Leaves, stems, storage organs, food stores in seeds in germination
Name an example of a sink
Roots, meristems, any growth areas
What is translocation?
The process of a plant transporting organic substances from source to sink
How are organic substances translocated?
Passive and active phloem loading (via apoplast route)
How are organic substances translocated in the apoplast pathway?
From source to sink down the concentration gradient, from the companion cell into the phloem via active transport (hydrogen ions are active pumped into the phloem to transport sucrose down the concentration gradient with a transport protein)
How is sucrose unloaded from the phloem?
Via diffusion from the phloem into the surrounding cells
Suggest some evidence for translocation
Advances in microscopy, if mitochondria stop working in the companion cells translocation stops, flow of sugars in the phloem is 10000 times faster than it would be by diffusion alone
What are xerophytes?
Plants in very dry habitats that have adapted to the environment
What are some adaptations of xerophytes?
Thick waxy cuticle, sunken stomata, reduced number of stomata, reduced leaves, hairy leaves, curled leaves, succulents, leaf loss, root adaptations
What are hydrophytes?
Plants that live in aquatic habitats that have adapted to the environment
What are some adaptations of hydrophytes?
Very think/no waxy cuticle, many open stomata on the top of leaves, reduced structure, wide flat leaves, small roots, large surface arear of stems and roots, air sacs
