plant exam qs Flashcards
Describe how the apparatus should be set up to ensure that valid measurements can be made. (8)
1 cut shoot under water (to stop air entering xylem vessels);
2 cut shoot at a slant (to increase surface area);
3 check apparatus is full of water / is air bubble free / no air locks;
4 insert shoot into apparatus under water
5 remove potometer from water and ensure airtight / watertight,
joints around shoot;
6 dry leaves;
7 keep conditions constant;
8 allow time for shoot to acclimatise;
9 measure per unit time;
explain how hairs around the stomata affect rate of transpiration (3)
trap, moisture / water vapour;
reduces the water potential gradient as air surrounding leaf is more humid;
so transpiration rate is reduced;
why do large plants need a transport system? (3)
surface area relative to volume too small/AW;
diffusion too slow/AW; idea of speed needed
distance too great/some cells deep in body/not all cells in contact with
environment/AW; R large if unqualified
insufficient/AW, oxygen/(named) nutrient, supplied/(named) waste removed;
idea of linking (named) areas; look for ‘from…’ ‘to…’ with an
implication of organs, not just ‘all over body’
(may be,) more (metabolically) active/AW/, homoiothermic;
transpiration
transpiration is the loss of water, vapour/by evaporation;
why does a photometer not give you a direct value for transpiration? (3)
transpiration is the loss of water, vapour/by evaporation;
(apparatus) measures water uptake;
to replace loss;
assumes all uptake is lost/AW; ora some may be used
explanation of how some uptake may be used e.g. used to regain
turgor/used in photosynthesis;
uptake by detached shoot may not be same as whole plant/AW;
how does temperature increase rate of transpiration
temperature increased;
more KE/energy;
more evaporation/faster diffusion;
how does light intensity increase rate of transpiration
light (intensity) increased; stomata opened (wider); allowed more water vapour out/AW; must be linked to stomatal point above temp increase linked to light;
how does humidity increase rate of transpiration
humidity dropped/air less saturated;
internal spaces c. 100% saturated;
steeper water potential gradient;
how does wind speed increase rate of transpiration
wind (increased);
removed, saturated air/diffusion shells;
steeper water potential gradient;
adaptations of root hair cells for uptake of water
large surface area (to volume); low water potential; thin wall / short diffusion path; uncutinised / permeable / unlignified / AW; rapid, growth / replacement; large no; long; many mitochondria;
how does water move from soil to xylem? (6)
1 osmosis in correct context;
look for across membrane, or, into / out of, cell / root
2 moves down a water potential gradient;
3 most negative / lowest, in the xylem;
4 (uptake of) ions / minerals / solutes, into xylem / root hair;
5 tension in xylem / transpiration pull / cohesion-tension;
relate to pathway in root
6 (moves) via the cell walls;
7 (moves) via, cytoplasm / vacuoles;
8 passage via the plasmodesmata; look for linking cytoplasm /through wall
9 Casparian strip / suberin / waxy / fatty, blocks,
cell wall route / apoplast; A waterproof
10 water, crosses membrane / enters, cytoplasm / vacuole / symplast;
11 AVP; e.g. pits in xylem / passage cells /aquaporins /
protein channels / capillarity in cell wall (spaces)
name the adaptations of xylem vessels
lignified walls
no cytoplasm
no end walls
pits
large lumen
what does lignin help with ?
(allows) adhesion / waterproof / stops collapse (under tension);
rings / spirals / thickening;
prevents collapse (under tension);
what does the lack of cytoplasm in xylem help with?
less resistance to flow / ease of flow / AW / more space (linked to
lack of contents);
what does the lack of end walls in xylem help with?
continuous tube;
less resistance to flow / ease of flow;
what do pits in xylem allow?
lateral movement / get round air bubbles / supplies(water) to cells or
tissues / water in or out;
role of sieve tube elements and companion cells in the transport of carbohydrates (3)
1 sieve elements end to end or sieve plates perforated;
2 companion cells metabolically active / have many mitochondria / produce ATP / release energy;
3 (active) loading into, companion cell;
4 ref to proton pump;
5 ref to co-transporter;
6 role of plasmodesmata;
7 sieve element has few organelles for ease of flow
8 ref to, unloading mechanism / (hydrostatic) pressure gradient;
Explain how, at different times, the same plant root may be a source or a sink. (2)
source when root converts starch into sugars;
sink when root stores starch or uses carbohydrate for respiration growth;
high hydrostatic pressure makes it a source and low hydrostatic pressure a sink;
when loading it is a source and when unloading a sink;
explain how mass flow of materials between the source and the sink would be brought about
water will enter source; by osmosis; down a water potential gradient; increase in (hydrostatic) pressure; as source / sink cannot expand; force solution along (tube to sink);
State one piece of evidence for the involvement of an active process in transport of sugars
ATP involved / respiration involved / many mitochondria in companion
cells / reduced by metabolic inhibitors / oxygen dependent / temperature
dependent / loading against a concentration gradient
Describe an active mechanism which could possibly be involved in the transport of sugars from sources to sinks.
loading, into companion cell / from transfer cell / into sieve tube /
into phloem – implied;
H ions / protons, pumped out of, companion cell / sieve tube / phloem;
diffuse back in with sucrose;
protein carrier / co-transporter;
possible active unloading by reverse mechanism;
explain how transpiration results in water moving up a plant stem
loss of water from mesophyll; cell walls; more drawn from, cytoplasm / cell; cohesion of water molecules; hydrogen / H, bonds; water under tension / ref to hydrostatic pressure gradient implied; via, symplast / apoplast / vacuoles; (water from) xylem / xylem vessels; ref to water potential gradient;
