36 Resource Acquisition and Transport in Vascular Plants Flashcards
How were primitive plants anchored to the soil?
By the bas of the stem of by threadlike rhizoids
eventually roots developed
In what direction does water move in xylem?
In only one direction: root to leaf
In what direction do sugars move through the phloem?
Either way - its multidirectional
What does phloem carry?
Phloem spa which contains sugars etc.
Where does carbon dioxide enter and leaf the plant?
Gas exchange happens in both the leaves and the roots.
Not that in the leads there is a net entry of carbon dioxide and a net loss of oxygen. This is due to photosynthesis.
In the roots only respiration occurs so there is a net intake of oxygen from the soil and a net release of carbon dioxide into the soil
What is the principal factor that determines the size of a plant’s leaves?
Water availability: where water is plentiful many plants have large leaves to maximise photosynthesis.
In drier areas small leaves minimise water loss.
What is the arrangement of leaves on a stem called?
Phyllotaxy.
Why is phyllotaxy important?
As the shoot extends new leaflets form.
If the leaves are in the same place when looks at from above they would shade each other.
If the leaves were all on one side the stem would be unbalanced.
As the stem ascends what angle will the next leaf be from the previous? Why is this important?
Approximately 137.5º.
This is important as its prevents leaves shading each other.
If the angle was lower i.e. 30º the leaves wouldn’t shade each other but would the first few to develop will all be on one side and thus the stem will be unbalanced.
What indicates the extend of leaf coverage?
The ‘leaf area index’
What does the ‘leaf are index’ actually represent and thus how is it calculated?
It is the total leaf area of the plant divided by the total ground area. The total ground area is found by drawing a circle from the stem and increasing its radius so that the circle includes all of the plant.
Therefore the leaf index area represents the ‘efficiency’ of the arrangement of the leaves whilst also predicting how much it shades the ground below.
Can a plant have a ‘leaf area index’ greater than 1?
Yes, if there are multiple layers of leaves.
What is a the highest ‘leaf area index’ seen in nature?
They usually go as high as ‘7’ - any higher is frivolous.
As new leaves are added to the plant they shade the leaves below. What happens to these leaves?
Eventually these leaves will be so shaded that they perform more respiration than photosynthesis and thus are a net loss to the plant.
These leaves or even entire branches are removed by programmed cell death and are shed. This is called ’self-pruning’
What factor besides shading and height, can effect the amount of light hitting a leaf?
Its orientation i.e. horizontal or vertical.
How does orientation of a leaf effects the sunlight it receives. Therefore where is each orientation seen?
Horizontal leaves i.e. in trees are better at collecting light as they are perpendicular to the rays of sun. However as a consequence they shade the leaves below and the top leaves to be exposed to damagingly intense light.
Vertical leaves i.e. those of grass are parallel to the sun. This means that they do not shade the leaves below as much and thus the entire blade receives light. This prevents the top region from receiving a damagingly high intensity of light.
What are two ways a plants growth affects its ability to receive light?
Growing tall may allow it to extend above the canopy and thus receive direct sunlight.
A distinctly branching pattern can help it receive light by extending into gaps where there is little shading. It also maximises the surface area as viewed from above and thus increase the sun light it gets (even if that sunlight has gone through the canopy.)
Typically speaking, what types of plant grow taller and why? What is the exception
Eudicots and gymnosperms are generally taller as they have the strong anchoring taproots
Monocots generally not grow so tall as their fibrous roots provide less anchoring, The exception is palm tress which even as monocots, grow relatively tall.
What type of root system do gymnosperms have?
Taproots.
How is the growth of roots adapted to maximise nutrient acquisition?
They are highly branched to maximise to collect water form a large region.
They are also undergo hydrotropism and growth towards nitrates.
How is competition between roots prevented?
When they are near roots of a different plant but the same species they avoid growing in that direction.
Therefore they avoid infraspecific competition for water etc.
Besides roots hairs, what improves the efficiency of roots?
Most plants have symbiotic fungi called ‘mycorrhizae’ growing in the roots. These vastly increase the surface area.
Note that the mycorrhizae take in the water, then give it to the plant.
What structure of the mycorrhizae increases surface area?
As fungi they have a vast network of branching fibres called ‘mycelium’
It fibre of the mycelium is called a ‘hyphae’. It is the vast number of these thin hyphae that absorbs the water.
What are the “compartments” of plant tissue?
The apoplast and the symplast
What is the apoplast and what is the symplast?
The apoplast is everything external to the plasma membrane of living cells. This includes cell walls, extracellular spaces and the interior of dead cells.
The symplast is the interior of the cells and thus consists of the cytosol of the living cells as well as the plasmodesmata that connect the cells.
What are the routes substance can take as they move through tissues?
The ‘apoplastic route’, the ’symplastic route’ and the ’transmembrane route’
What is the ‘apoplectic route’?
The solutes and water move exclusively through the apoplast i.e. through the cell walls and extracellular spaces.
What is the ’symplastic route’?
The solute/water moves exclusively through the symplastic route. This involves moving through to cytosol and the plasmodesmata.
What is the ’transmembrane route’?
The solute moves in and out of the cells and thus travels through both the apoplast and the symplast.
This is called the ’transmembrane route’ as it passes from the apoplast to the symplast and vice versa it must cross the plasma membrane.
How is membrane potential established in plants and how does this differ from animal cells?
In animal cells membrane potentials are established primarily by pumping Na+ (and potassium)
In plant cells such potentials are more commonly initiated through the movement of H+ ions
How does co-transport differ between plants and animals?
In plants H+ ions are typically actively transported then allowed to return, causing cotransport.
In animals the mechanism is the same but it is typically Na+ ions, not H+ ions, that are pumped.
What are some specific examples of cotransport in plants?
By pumping H+ ions against their concentration gradient plants are able to transport Nitrate ion and Sucrose into their cells.
What predicts what direction water will flow in?
‘Water potential’ which includes the effects both of solute concentration and physical pressure.
Water will move form a region of higher water potential to a region of lower water potential.
In what unit is water potential measured?
Megapascals (MPa)
What is the equation for water potential?
ѱ = ѱs + ѱp
where:
ѱ = water potential
ѱs = solute potential
ѱp = pressure potential
What does solute potential relate to?
The potential due to the solute concentration of a solution.
As solutes are added the solute potential decreases so that it is always either 0 (pure water) or negative in the case of a solution
What is solute potential also known as?
Osmotic potential
What does pressure potential refer to?
The physical pressure exerted on the solution.
It is positive if a positive pressure is applied to the solution i.e. a “push”
It is negative if a negative pressure is applied i.e. suction.
A solute is added to a solution on one side of a semipermeable membrane. In what direction will the water flow.
Towards the solution with the solute.
This is because its solute potential decreases and thus water moves form high water potential to low.
What happens if a plant cell is placed in a hyper osmotic solution?
It will lose water and plasmolyse as the cell wall detaches from the protoplast (cell’s living contents including the plasma membrane)
Do animal cells undergo plasmolysis?
No, this is because plasmolysis is technically the separation of the cell wall and the plasma membrane.
Since animals don’t have plasma membranes this is not possible.
What is the living part of the cell called, including the plasma membrane?
The protoplast.
What does ‘protoplast’ refer to?
The living content of the cell including the plasma membrane.
What channel facilitates the diffusion of water through the plasma membrane?
Aquaporins.
What affects the permeability of aquaporins?
Their permeability is decreased if the cytosolic Ca2+ levels drop.
If the cytosolic pH increases so does their permeability.
What is the general principle in which long distance transport occurs in a plant?
‘Bulk flow’ which is the movement of a liquid and its contents does to water potential differences.
This is opposed to each solute diffusion through the extracellular fluid individually.
What adaption of vascular structures allows water to flow through more easily?
Mature tracheids and vessel elements are dead cells and therefore have no cytoplasm, and the cytoplasm of sieve-tube elements is almost devoid of internal organelles.
What path does water in the soil take to the before entering the xylem. Why is this important?
The epidermis of the root hair cell is highly permeable to water and thus allow water, and dissolved solutes i.e. ions, to easily enter.
Once in the root it takes either a symplastic or apoplectic root. As it does this it passes through various cells of the cortex.
This flow enhances the exposure of the cells of the cortex to the soil solution, providing a much greater membrane surface area for absorption than the surface area of the epidermis alone. For example the cortex cells filter the water as it passes through them and therefore important solutes i.e. K+ ions are accumulated.
