plant responses recap.

Question 1

give 3 examples of how plants increase survival by responding to changes in their envi

Answer 1

• if they sense a change to direction of light, they will grow towards it to max photosynthesis
• they are gravitropic and thus roots + shoots will grow in right direction
• climbing plants have sense of touch so they can find things to climb + reach the sunlight.

Question 2

what do plants respond to ?

Answer 2

herbivory + abiotic stress.

Question 3

state 2 chemical defences plants can used against herbivory

Answer 3

alkaloids

tannins

Question 4

what do alkaloids do?

Answer 4

• have bitter taste, noxious smells + some have poisonous characteristics that deter + kill herbivores.
  eg Tobacco plants produce the alk nicotine in response to tissue damage -> v v poisonous to many insects.

Question 5

what do tannins do?

Answer 5

• taste bitter + in some herbivores (ie sheep + cattle) they can bind to proteins in their guts making the plant hard to digest.

Question 6

what are pheromones?

Answer 6

these are signalling chemicals that produce in other organisms eg alarm pheromones

Question 7

how can plants use pheromones to defend themselves against herbivory.

Answer 7

• alarm pheromones released into the air in response to herbivore grazing. This will cause nearby plants that detect these chemicals to start making chemical defences such as tannins.

Question 8

how does the Mimosa pudica defend itself against herbivory.

Answer 8

• response to touch
  if a single leaflet of Mp is touched the signal is sent across the whole leaf , causing it to quickly fold up. It is thought that this could help protect Mp against herbivory in a variety of ways , eg may knock off any small insects feeding on the plant and it may scare off animals trying to eat it.

Question 9

give an example of how some plants can survive by responding to abiotic stress ?

Answer 9

some plants produce antifreeze proteins in response to v v cold envis,
eg carrots, the antifreeze proteins bind to ice crystals, lowering their freezing point (ie <0) so more ice crystals are prevented from growing + accumulating.

Question 10

what is a negative control?

Answer 10

• a control used to check that only the independent variable (one ur changing) iss the only thig nhaving an effect on the dependant variable

Question 11

why are the tips removed before the experiments begin?

Answer 11

• auxin is produced in the shoot tip only so by removing the shoot tip, any effect of auxin is due to the added auxins of experiment.

Question 12

suggest why glucose is added aswell as the hormone in the tropism experiments.

Answer 12

• to provide energy for growth (via respiration + production of ATP in oxidative phosphorylation)

Question 13

explain how ethene makes plants/ fruits ripen?

Answer 13

• ethene breaks down the cell walls and chlorophyll in plants and converts starch to sugars (glucose).

Question 14

suggest a commercial advantage of being able to pick and transport tomatoes before they are ripe?

Answer 14

• plant will not be damaged in transport as its hard + unripe

Question 15

drought conditions stimulate the production of ABA , how does this help plants to survive when there is little water available(2m)

Answer 15

• ABA triggers stomatal closure.

- This helps plants to survive as less water is lost through transpiration.

Question 16

how does ABA cause stomatal closure?

Answer 16

• ABA binds to a receptor on a guard cell.
• this binding causes Ca2+ ions to be released from the vacuole into the cytol
• the increased conc of Ca2+ ion cytosol will cause other ion channels to open, these ion channels allow ions to leave the guard cells , raising the water potential of the cells (ie high water conc) and so water moves by osmosis out of cells down water potential gradient.
  when the water leaves the guard cells, they become more flaccid and the stomata close.

Question 17

how are auxins + cytokinins used commercially?

Answer 17

Auxins 
- rooting powder, growing seedless fruit
- low conc prevent leaf + fruit growth 
- high conc promotes fruit drop. 
Cytokinins 
- prevent yellowing of lettuce leaves 
- promotes shoot growth

Question 18

how are giberellins + ethylene used commercially?

Answer 18

GIB
- delay senecence in citrus 
elongation of apple + grape stalks, 
brewing beer for malt production 
ETHENE
- speed up ripening 
- promotes lateral growth 
- promotes fruit drop