what is the function of stomata?
- preform gas exchange in plants
- take in co2
- responsible for transpiration that pulls water through plants
what is the stoma?
microscopic pore
what are guard cells?
two cells that flank the stoma opening and control the diameter of the opening and therefore the rate of transpiration and the uptake of CO2
what are the steps involved in the guard cells opening?
- Cells use active transport to pump potassium (K) inside, and build a gradient
- Water moves into cells by osmosis (water go to where there is more solute)
- Water movement causes guard cells to become turgid, and because of their bean shape and microfibrils this causes the cells to bow outward and the diameter of the hole between them increases
- Allows for gas exchange to happen
what are the steps involved in the guard cells closing?
- Cells stop actively pumping K inside, and it diffuses back out (because solute wants to be in equilibrium)
- the water also moves out of the cells when there is less solute (water wants to be where there is higher solute)
- Causes guard cells to become flaccid, and decreases/closes the diameter of the hole between guard cells
- Stops gas exchange and water loss from happening
what are crypts?
in some leaves, stoma are found in dugouts, this protects the guard cells from wind and from drying out
what triggers the stoma opening and closing?
Light levels, CO2 depletion, and internal clock
what effect do environmental stresses have on stoma? what are examples of these?
-may cause stomata to close at abnormal times, such as:
Drought (water deficiency), high temperatures, and wind
what does leaf orientation have an affect on? what are the types of orientation, what do they increase/decrease, what types of environments would you find these in?
-Can affect the rate of transpiration and photosynthesis in plants. Trade off of maximizing light capture and minimizing
Horizontal leaves → will receive more direct sunlight, therefore increasing rate of photosynthesis, but also will heat up more, increasing the rate of transpiration. more beneficial in shaded environments
Vertical leaves –> will receive less sun, and therefore have a lower rate of both transpiration and photosynthesis. more beneficial in sunny environments.
what is a cuticle?
waxy layer covering the epidermis of a plant
what is the purpose of a cuticle?
protects the plant from pathogens and pests, but mostly prevents water loss. it prevents water from transpiring out of the surface of the plant, and instead directs transpiration to the stomata
what does the thickness of a cuticle reveal?
-provides info about a plants ability to retain water and therefore its natural habitat
what kind of cuticles might be on plants in a hot/dry climate vs a cold/moist climate vs aquatic?
hot/dry: -cuticle will be much thicker cold/moist: -much thinner, may only have cuticle on side of leaf aquatic: may have no cuticle
when are stomata open/closed, why?
Typically open during the day and close at night (to minimize water loss while plant is not photosynthesizing)
what might effect stomata density/stomata placement?
-stomata density and placement are affected by its habitat. the more stomata that a plant has, the faster it will lose water from transpiration, therefore plants in hot/arid climates typically have fewer stomata. stoma also more commonly found in crypts to further protect them
where are stomata located and in what density in salal, succulents, duckweed, and elodea?
SALAL -very few on top -very large amount on bottom because of horizontal orientation, being on the bottom slows the rate of which they would dry out than if they were easy to access by sunlight SUCCULENTS -fewer amounts on both top and bottom -typically in crypts DUCKWEED: -some on top -very few on bottom because they are floating plants ELODEA: none.
what is the density of stomata in aquatic/floating plants? why? how are their stomata effected?
fully aquatic plants have no stomata. this is because they do not need to preform gas exchange with the air, they diffuse O2 and CO2 from the water.
- floating plants only have stomata on the top side of their leaves, as they cannot preform gas exchange with the air on the bottom side.
- because these plants are not scared of drying out as they always have access to water, they stomata remain open all the time (also why they may have no cuticle, or only cuticle on one side)
how do you calculate the density of stomata?
- Need to know the area of field of view (at 400x)(radius of field of view is 0.2mm) 3.14r2 → 3.14(0.2mm)2 → 0.1256mm2
- Average # of stomata in field of view/area of field of view
Eg. 4/0.1256 = 31.85
what is the function of leaf veins?
provide support for leaf and transport water/ minerals (xylem) and sugar (phloem)
what are mesophyll cells? how many layers are in mesophyll, what are they called?
ground tissue (parenchyma) cells found in the leaves of plants that are specialized for photosynthesis.
- 2 layers:
1. Palisade Mesophyll
2. Spongy Mesophyll
where is the Palisade Mesophyll located? what is its structure, what is its main function?
- typically only one layer of these cells, located near the surface of the leaf just under the epidermis
- arranged in an organized fashion, elongated cells perpendicular to epidermis
- main sites of photosynthesis in the leaf
where is the spongy Mesophyll located? what is its structure, what is its main function?
- spongy mesophyll located under palisade mesophyll
- cells with large spaces in between
- still some photosynthesis occurring; large spaces allow carbon dioxide to move around the leaf
- also allows the plant to bend and move in the wind (which itself helps move gases around the leaf’s cells)
which cells exchange gases with the air in leaves?
the mesophyll cells, as these preform photosynthesis and need co2 to do so
