5.5.1 plant responses to environment

Question 1

abiotic components

Answer 1

components of an ecosystem which are non-living

Question 2

alkaloids

Answer 2

organic nitrogen-containing bases that have important physiological effects on animals eg. nicotine, quinine, strychnine & morphine

Question 3

biotic components

Answer 3

components of an ecosystem which are living

Question 4

pheromone

Answer 4

any chemical substance released by 1 living thing, which influences behaviour/physiology of another living thing

Question 5

tannins

Answer 5

phenolic compounds, located in cell vacuoles or in surface wax on plants

Question 6

tropism

Answer 6

a directional growth response in which the direction of the response is determined by the direction of the external stimulus

Question 7

3 types of stimuli

Answer 7

1. tannins
2. alkaloids
3. pheromones

Question 8

describe tannins (type of stimuli)

Answer 8

• toxic to microorganisms & larger herbivores
• leaves: found in upper epidermis & make leaf taste bad
• roots: prevent infiltration by pathogenic microorganisms

Question 9

describe alkaloids (type of stimuli)

Answer 9

• derived from amino acids
• scientists think they’re feeding deterrent in plants to animals (taste bitter)
• located in growing tips/flowers & peripheral cell layers of stems/roots

Question 10

describe pheromones (type of stimuli)

Answer 10

• chemicals
• released by 1 individual
• can affect physiology/behaviour of another

Question 11

name 4 types of tropism (directional growth responses)

Answer 11

1. phototropism
2. geotropism
3. chemotropism
4. thigmotropism

Question 12

describe phototropism

Answer 12

• shoots grow towards light
• enables photosynthesis

Question 13

describe geotropism

Answer 13

• roots grow toward pull of gravity
• anchors them in soil & helps them take up water
• water needed for support (keep cells turgid), as raw material for photosynthesis & help cool plant
• also minerals (eg. nitrate in water) needed for synthesis of amino acids

Question 14

chemotropism

Answer 14

• flower: pollen tubes grow down style (as attracted by chemicals) toward ovary where fertilisation occurs

Question 15

thigmotropism

Answer 15

• shoots of climbing plants (eg. ivy) wind around other plants/solid structures for support

Question 16

positive tropic response

Answer 16

if plant response towards stimulus

Question 17

negative tropic response

Answer 17

plant responds away from stimulus

Question 18

nastic responses

Answer 18

non-directional responses to external stimuli

Question 19

where are plant hormones produced

Answer 19

in cells in variety of tissues in plant

Question 20

what happens when plant hormones reach target cell

Answer 20

• bind to complementary receptors on plasma membrane
• specific hormones = specific shapes
• specific binding ensures hormones only act upon correct tissues

Question 21

what coordinates plant responses to external stimuli

Answer 21

plant hormones

Question 22

what can hormones influence

Answer 22

eg.
- cell division
- cell elongation
- cell differentiation

Question 23

hormone:
what’s its effect?

Answer 23

• promote cell division
• delay leaf senescence
• overcome apical dominance
• promote cell expansion

Question 24

hormone: abscisic acid
what’s its effect?

Answer 24

• inhibits seed germination & growth
• causes stomatal closure when plant stressed by low water availability

Question 25

hormone: auxins (eg. IAA)
what’s its effect?

Answer 25

• promote cell elongation
• inhibit growth of side-shoots
• inhibit leaf abscission (leaf fall)

Question 26

hormone: gibberellins
what’s its effect?

Answer 26

• promote seed germination & growth of stems

Question 27

hormone: ethene
what’s its effect?

Answer 27

• promotes fruit ripening

Question 28

how do hormones move around the plant

Answer 28

either:
- active transport
- diffusion
- mass flow in phloem sap or in xylem vessels