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BIOL 1102 Exam Two
Water Balance
| Question | Answer |
|---|---|
| Why do plants need water | photosynthesis - water is split to release an e- to replace the one in the reaction center chlorophyll molecule that enters the light reactions, interior of plant cells and compartments are filled with water, plants take up mineral nutrients |
| How does CO2 diffuse in water rather than air | CO2 diffuses 10,000 times more SLOWLY in water than it does air |
| Where must chloroplasts be on the plants based on CO2 | to assimilate a lot of CO2 in photosynthesis, chloroplasts must be near air spaces |
| What happens if chloroplasts are exposed directly to air? | will lose too much water and potentially die |
| What is transpiration | water is passively transported into the roots and then into the xylem |
| What causes water molecules to form a column | cohesion and adhesion |
| What is the xylem | tube shaped cells that water transpires through |
| Where does water move to after the xylem | into the mesophyll cells, evaporates from the leaf surface and leaves the plant by diffusion |
| Where does water fully exit from | the stomata - pores in the leaves through diffusion |
| What are the two types of xylem cells | tracheids and vessels |
| What are tracheids and vessels made of | hardened lignin and are dead at maturity |
| What are tracheids | long, thin cells with tapered cells, water moves from cell to cell through pits along their length |
| What are vessel elements | wider, shorte, thinner-walled, less tapered than tracheids |
| How does water move through xylem | using negative pressure - it is sucked up, not pushs |
| What is the cohesion-tension theory | water is a polar molecule, when one water molecule is lost, another is pulled along |
| What is cohesion | the ability of like molecules to stick together |
| What is adhesion | the ability of dissimilar molecules to stick together |
| What is cavitation | when a plant cannot supply its xyelm with adequatewater so instead of being filled with water, the xylem gets an air bubble/embolism |
| What conditions can lead to cavitation | hottest part of the day, freezing conditions |
| Why does freezing conditions lead to cavitatioon | solubility of gas in ice is very low, gas comes out of solution when the water in the xylem freezes |
| How do pits in the xylem adapt to minimize cavitation | pits in xylem allow water to move laterally from cell to cell |
| How do plates in between xylem adapt to minimize cavitation | trap air bubbles in the cells |
| How do tracheids adapt to minimize cavitation | tracheids have narrower diameters compared to vessels and avoid cavitation because the column of water in a cell with a narrow diameter is better able to resist bubble formation |
| What is cutin | waxy coatng that consists of a protein |
| How is are leaf surfaces affected by cutin | surface of leaves is relatively impermeable due to cutin |
| How do plants balance CO2 uptake and water loss | controlling the opening and closing of stomata |
| When is the stomata open | during the day when light is available for photosynthesis |
| What is the stomata closed | during night when CO2 uptake is not necessary, closed to prevent water loss |
| How does light affect the stomata | blue light receptors in the plasma membrane of the guard cells sense light -> from the cells that accumulate K+ and become turgid -> causing stomata to open |
| How does CO2 depletion affect the stomata | stomata opens in response to depletion of CO2 as a result of photosynthesis |
| How does an internal clock of plants affect the stomata | stomata opens in response to an internal clock with a 224 hour cycle |
| How does drought stress affect the stomata | drought stress can cause stomata to close |
| What hormone do root leaves produce in response to water deficiency | abscisic acid (ABA) |
| What does ABA signal | signals guard cells to close stomata |
| How does low relative humidity affect the stomata | increases humidity gradient between the interior spaces of the leaf (100% saturated) and the air -> open stomata |
| How does wind affect the stomata | wind removes a boundary layer of moist air -> increases the humidity gradient between t |
| How do ocotillo adapt to reduce water loss | stems are leafless most of the time |
| How do cactus adapt to reduce water loss | hairs create a boundary layer, columnar shape reduces surface area |
| How does oleander adapt to reduce water loss | has stomata in deep crypts, crypts have hairs called trichomes, leaves have a thick waxy cuticle |
Created by:
goldengalleon