What is the apoplast pathway
Water moves through the gaps between the cellulose microfibres in the cell wall
What is the symplast pathway
Water moves through the cytoplasm and the plasmodesmata in the cell wall
What is the vacuolar pathway
Water moves from vacuole to vacuole
What is the Casparian strip
An impermeable band of suberin across the cell walls of the endodermal cells blocks the apoplast pathway and pushes the water into the symplast
What is the vascular system in the root called
Vascular stele
What is the vascular system in the stem called
Vascular bundle
What are the three plant macronutrients
Nitrogen, phosphorus, potassium
How is nitrogen taken into the plant
Nitrogen is absorbed as dissolved ammonium or nitrate ions into the apoplastic stream by diffusion. The ions are absorbed into the symplast pathway by active transport
How are root hair cells adapted for absorption
Thin cell walls
Large SA:V ratio
Large number of mitochondria
Large sap vacuole
What are mycorrhizae
Fungi that grow around plant roots to increase the surface area for absorption. The plant supplies the fungi with sugars
How is water taken up the xylem
Root pressure
Cohesion and adhesion in the transpiration stream
Capillarity
How does root pressure work
Plants take up ions, lowering the water potential and drawing water in causing positive hydrostatic pressure forcing water upwards
What are the transport cells in phloem
Sieve tube cells
What is the sieve plate
Contains tiny holes at the end of the sieve tube allowing sugar solution to pass through
What is the role of a companion cell
Regulate the metabolism of the sieve tube cell and load and unload sugar from the phloem
Which part of the phloem and xylem vessels provides strength
Sclerenchyma cells and fibres
What is the role of tracheids
heavily strengthened, conducting cells
What is the role of parenchyma cells
Storage/packing cells
What is the role of vessels in plants
Conducting vessels
How are vessel elements is plants adapted to their function
Large diameter cells offer low water resistance and allows rapid uptake of water
Describe the vascular tissue in leaves
A system of veins resistant to tearing
Describe the effects of the following on transpiration:
Temperature
Air movement
Humidity
Light intensity
Temperature: Increased temperature increases the kinetic energy of water molecules and as such increases the rate of transpiration
Air movement: Increased air movement causes recently removed water to move far away from the stomata, increasing the concentration gradient and increasing the rate of transpiration
Humidity: High levels of humidity decrease the concentration gradient between the inside of the leaf and the air around the leaf, decreasing the rate of transpiration
Light intensity: High light intensity causes the stomatal opening to open more, allowing more water out and increasing the rate of transpiration
How do you set up a potometer correctly
Keep leaves dry
Set up apparatus underwater
Cut shoot underwater
Ensure all joints are airtight
Describe translocation
Movement of sugars from their source to their sink via the phloem
What is a source and what is a sink
source: site of the photosynthesis of the sugars
sink: where the products of photosynthesis may be used for growth or storage
How are substances transported between the companion cells and the sieve tube cells
Plasmodesmata
Describe the ringing experiments to prove translocation
Bark was removed in a ring around a tree, thus removing the phloem. No sugar was then found below the site of the ring, proving the sugars are transported in the phloem to the whole plant
Describe how aphids have been used to prove translocation
Aphids have hollow, needle-like mouthparts called a stylet. The stylet is inserted directly into the sieve tube allowing the aphid to feed on the sugary sap. The stylet can be cut off (using a laser) leaving it attached to the plant (it forms a useful micropipette). Sap exuding from the stylet is collected and analysed. Analysis shows that the sap contains the products of photosynthesis – sucrose and amino acids.
Describe how radioactive labelling can be used to prove translocation
Carbon dioxide labelled with radioactive carbon is supplied to an illuminated plant leaf. The radioactive carbon is fixed in the sucrose produced by photosynthesis and is translocated to other parts of the plant. This radioactive carbon in the sucrose can be traced using autoradiography
Describe the mass flow hypothesis
When sugar is made at the source the water potential becomes more negative and water passes into the source cells by osmosis.
As water enters the source cells, hydrostatic pressure increases forcing sugars and other products of photosynthesis into the sieve tubes – phloem sieve tubes are loaded.
Mass flow occurs along the sieve tubes to the sink, the products of photosynthesis are forced along by the flow of water from a high to a low hydrostatic pressure.
Hydrostatic pressure will be lower at the sink because sugars are stored as starch or are used for respiration; this reduces the water potential.
Water passes from the sink cells to the xylem to be returned to the source.
Name arguments against the mass flow hypothesis
The rate of translocation is 10,000 times faster than it would be if the substances were moving by diffusion.
Sieve plates with tiny pores act as a barrier impeding flow.
Sucrose and amino acids move at different rates and in different directions in the same phloem tissue.
Phloem tissue has a high rate of oxygen consumption, and translocation is stopped when a respiratory poison such as potassium cyanide enters the phloem.
Companion cells contain numerous mitochondria and produce ATP, but the mass flow hypothesis fails to suggest a role for the companion cells.
Describe how the waterlily is adapted to its environment
it is a HYDROPHYTE and so is surrounded by water. Therefore, it has a poorly developed xylem structure as it doesn’t need to transport much water. The stomata are on the top of the lilypad because the underside is submerged. It also has little to no waxy cuticle as water loss is not an issue, and large air spaces in the spongy mesophyll for buoyancy
Describe how marram grass is adapted to its environment
it is a XEROPHYTE and is surrounded by little water. The plant features rolled leaves, sunken stomata, a thick waxy cuticle and hairs to trap water vapour, all the reduce water loss.
Describe mesophytes
Mesophytes flourish in habitats with adequate water supply.
Most plants of temperate regions are mesophytes.
Most crops are mesophytes.
Close stomata during the night to decrease water loss.
Shed leaves in the winter to survive unfavourable times e.g. frost.
Underground organs survive winter e.g. bulbs.
Annual mesophytes (plants which flower, produce seed and die in the same year) survive the winter as dormant seeds.