| What are the 2 types of active transport in root uptake? | direct: protein pumps move ions against a gradient
indirect: proton pumps expel H+ ions into the soil
displaces the cations which diffuse back into the root |
| What are the organic molecules that plants make? | glucose and starch |
| How are mineral ions up taken in the roots? | actively transported = causes absorption of water by osmosis |
| What are the layers in the leaf called? and what are the functions of each layer? (3) | upper palisade mesophyll = tightly packed w many chloroplasts (light absorption)
lower spongy mesophyll = loosely packed with air spaces near stomata = increase gas flow
vascular bundles between layers (xylem and phloem) |
| What are the 2 types of root systems? | fibrous roots = thin and very spread out (increases SA for absorption)
tap roots = penetrating w lateral branches (deeper reservoirs of water) |
| how is water uptake controlled by the casparian strip in roots? (4) | absorbed by ROOT EPIDERMIS
diffuses across CORTEX towards CENTRAL STELE
pumped across CASPARIAN STRIP that is impermeable
= controls uptake rate |
| What are vascular bundles? what are they used for? | xylem and phloem is used for transporting materials |
| What does xylem transport? | water = transpiration |
| what does phloem transport? | nutrients (source to sink) = active translocation |
| What is transpiration? | loss of water vapor from stems and leaves due to gas exchange |
| What are the steps of transpiration? (5) | light energy converts water in the leaves into vapor
water vapor is lost through evaporation
new water is absorbed from the soil through the roots
= P difference in leaves and roots
water flows up stem (xylem) in mass flow along the pressure gradient |
| How does evaporation cause transpiration? (3) | some light that is absorbed becomes heat = water becomes vapor in spongy mesophyll
vapor diffuses out of stomata and is evaporated = tension forces
negative hydrostatic P = draws new water out of xylem |
| How is water taken up into the root? | it is taken up through osmosis when mineral ions are actively transported into the roots |
| What is mass flow? | movement of fluid down a pressure gradient (roots - leaves)
leaves = lower pressure bec of evaporation
roots = higher pressure bec of osmotic uptake |
| What is capillary action? | water rising through tubes against gravity due to cohesive and adhesive forces |
| What is cohesion? (4) | water molecules stick together (hydrogen bonding)
bw 2 particles of the same substance
water is polar and can form H bonds through intermolecular bonding
= water molecules can be pulled up the xylem in a continuous stream |
| What is adhesion? (6) | when water molecules stick to the xylem wall (polar associations)
bw 2 particles of different substances
xylem wall + water are both polar
= as water moves up by capillary action, pulls inward on the xylem to create more tension |
| What are the features of the xylem? (7) | inner lining of dead cells fused into a continuous tube
vessel element / tracheid
hollow to enable water movement
cell walls have thickened cellulose
reinforced w/lignin = provides structural stability
outer layer is perforated (pores) to facilitate water movement
indents and pits |
| Why is the movement of water a passive process? | bec the cells are dead and happen in one direction only |
| Which part of the plant regulates the transpiration rate? | stomatal pores on the leaf's underside |
| How do stomata close? | when the guard cells beside it loses turgor and becomes flaccid
= by cellular signals in response to external triggers |
| How can transpiration be modelled? (3) | capillary tubing
filter paper
porous pots |
| How does capillary tubing model transpiration? (4) | water can flow in narrow spaces against gravity = capillary action
bec of cohesive forces and adhesion to the walls
thinner tube . less dense fluid = higher the liquid will rise |
| How does filter paper model transpiration? (3) | absorbs water bec of cohesive and adhesive properties
= similar to how water moves up the xylem
paper and xylem wall are both made of cellulose |
| How does porous pots model transpiration? (3) | semi permeable containers
water loss is similar to evaporation of water in the leaves
if an airtight seal is used = negative P = More liquid |
| What are potometers used for? | used to measure the transpiration rate by measuring the distance travelled by an air bubble every minute |
| Why is not all the water lost to transpiration? | a small amount is used in photosynthesis and to maintain the turgidity of the plant |
| What factors increase transpiration rate? (3) | light = opens stomata for photosynthesis = more water vapor lost
temp = increases evaporation = more water loss in leaves
wind = more air flow removes water vapor = more diffusion |
| How can all the factors affecting transpiration rate be tested with a potometer? (4) | light = diff distances from a lamp
temp = heaters / heated water baths
wind = fans to circulate air around the plant
humidity = plastic bags with diff levels of vapor |
| What are xerophytes? | desert plants they have higher rates of water loss bec of high temps increasing evaporation rate |
| How are xerophytes adapted to conserve water? (4) | thick waxy cuticles = prevents water loss from leaf surface
low growth and small leaves = small SA
rolled leaves with stomata in pits = traps WV
CAM physiology = stomata closed during the day |
| What are halophytes? | saltmarsh plants that have low levels of water uptake bec of high salinity in the soil reducing osmosis rates |
| How are halophytes adapted to conserve water? (4) | cellular sequestration = separating ions and salts in vacuoles
tissue partitioning= concentrating salts into specific tissues
root level exclusion = root structured to exclude salt
salt excretion = glands to eliminate salt |
| When is the hormone ABA released in plants? (6) | when a plant begins to wilt from water stress
the dehydrated mesophyll cells release ABA
= causes K to flow out from guard cells = reduces water P
= loses turgor
= stomata closes bec the guard cells become flaccid
= blocks opening |
| What are tracheids? | tapered cells that exchange water through pits = slower water transfer rate |
| What are vessel elements? | end walls are fused to form a continuous tube = faster water transfer |
| How are minerals taken up in plants? | 1) fertile soil has negatively charged clay particles for cations to attach to
2) passively diffuses into the roots
3) indirect active transport = H+ ions are released by proton pumps in the roots
4) these ions displace the positive ions from the clay = diffuse into the root along a gradient
5) anions can bind to the H+ ions and be reabsorbed with the proton |
| How is water taken up from the roots? | follows the mineral ions with mass flow through osmosis to a region of higher solute concentration |
| What is the symplastic and apoplastic pathways? | the way water moves towards the xylem
symplastic = cytoplasm
apoplastic = through cell wal |
| How is the cytoplasm of the cells connected for water to pass through? | plasmodesmata |
| At what point can the water not cross in the apoplastic pathway? | when it reaches the casparian strip = transferred to the cytoplasm |
