plant responses

Question 1

why do plants respond to their environment?

Answer 1

-avoid abiotic stress
-maximise photosynthesis
-avoid herbivory

Question 2

similarities between plant and mammals hormones

Answer 2

hormones bind to specific and complementary receptors
act on several tissues
only need small conc to have an effect
may switch gene on or off

Question 3

differences between plant and mammals hormones

Answer 3

IN PLANTS produced by many tissues
IN MAMMALS produced by endocrine gland

IN PLANTS move in xylem/phloem or cell to cell
IN MAMMALS move in blood

IN PLANTS act on most tissues and in cell where produced
IN MAMMALS act on few specific target tissues

Question 4

seed germination

Answer 4

seed starts germinating by absorbing water
water activates in embryo to start making gibberellins
this activates genes to make enzymes that hydrolyse food store
food used to respire and make ATP for building roots and shoot

Question 5

which hormone is antagonistic with gibberellins

Answer 5

ABA abscisic acid

Question 6

how do we know gibberellins are responsible?

Answer 6

mutant varieties of seeds dont have gene that codes for gibberellins and do not germinate

if gibberellin biosynthesis inhibitors are applied, seeds dont germinate

Question 7

gibberellins and stem

Answer 7

affects length of internodes (regions between leaves on stem)
less gibberellins means smaller stem- better to adverse weather

Question 8

types of meristems

Answer 8

APICAL tips of root and shoots making them grow longer
LATERAL BUD buds that could form a side shoot
LATERAL circular band makes rots and shoots wider
INTERCALARY between nodes to help shoot get longer

Question 9

positive geotropism in unilateral light

Answer 9

-tip of shoot produces auxin
-auxin diffuses down from the shoot tip or moves down by active transport
-higher auxin conc on the shaded side of the stem
-auxin causes cell wall loosen and cell elongation
-shoot bends towards the light

Question 10

apical dominance

Answer 10

high conc of auxins suppress growth of lateral shoots
growth in a main shoot stimulated by auxin made at the tip
down the stem conc of auxin decreases

Question 11

what happens when apical shoot is removed?

Answer 11

-auxin production stops
-apical dominance stopped
-lateral buds develop
-side shoots grow
-plant become bushy

Question 12

what is tropism?

Answer 12

directional growth of plants determined by direction of an external stimulus

Question 13

what is positive tropism?

Answer 13

growth towards stimulus

Question 14

what is negative tropism?

Answer 14

growth away from stimulus

Question 15

phototropism

Answer 15

shoots grow towards light (positive)
roots grow away from light (negative)

Question 16

geotropism

Answer 16

shoots grow away from gravity (negative)
roots grow towards gravity (positive)

Question 17

hydrotropism

Answer 17

roots grow towards water

Question 18

chemotropism

Answer 18

growth of pollen tubes to an ovary

Question 19

thigmotropism

Answer 19

growth towards solid structures to gain support

Question 20

growing in the dark

Answer 20

-plants grow more rapidly in the dark
-to grow upwards rapidly to reach light in order to photosynthesise
-auxin not destroyed by the light
-more present in the dark
-causes cell elongation

-evidence they gibberellins are responsible for extreme cell elongation of stems

Question 21

suggest how hormones alter a plants growth in response to overcrowding by other plants?

Answer 21

auxin causes positive phototropism
plant shoot bends towards light
plant grows taller
climbing plants climb up and over other plants
thigmotropism
roots grow towards water minerals and gravity

Question 22

geotropism in shoots investigation

Answer 22

uses rotating drum known as a clinostat
plant grown so the stimulus is applied evenly to all sides of the plant and root
shoot grows straight

Question 23

geotropism in roots investigation

Answer 23

seeds in the petri dish
petri dishes stuck to the wall and dishes rotated at 90 at intervals
geotropic response seen

Question 24

name some abiotic stresses

Answer 24

changes in days length
cold and heat
lack of water
excess water
high winds
changes in salinity

Question 25

leaf loss in deciduous plants

Answer 25

loose all their leaves and remain dormant until days lengthen and temperature rises in winter less sunlight so less heat energy less photosynthesis not enough glucose to maintain leaves and produce chemicals from chlorophyll to stop then freezing also makes the tree less likely to blow over

Question 26

plant senescense

Answer 26

1. cytokinin inhibit senescensing by making leaf a sink for nutrients 2. in autumn cytokinin production drops senescening begins 3. auxins usually supports cells in abscission zone senescensing reduces auxin production 4. low auxin means increased production of ethene ethene causes increase in cellulase enzymes to break down cell walls in abscission zone petiole and stem separate

Question 27

what is deposited un the cells after leaf loss and why?

Answer 27

fatty material deposited in cells ether side of the separation layer prevents entry of pathogens

Question 28

what happens when a plant freezes

Answer 28

if cells freeze their membranes are disrupted and they die cytoplasm of plants cells and the vacuolar sap contains solutes solutes lowers freezing point of water in the cell polysaccharides amino acids sugars and protein

Question 29

preventing freezing in plants

Answer 29

genes responsible for the chemicals that make the plants frost resistant are activated in response to sustained decrease in temperature with a reduction in day length ABA

Question 30

stomatal closure and ABA

Answer 30

open stomata= cool the plants as water evaporates from the cells in leaves in transpiration close stomata= reserve water roots provide early warning of water stresses through ABA

Question 31

stomatal closure and ABA

Answer 31

1. water levels fall and plant roots make ABA 2. ABA transported to leaves 3. ABA binds to specific shaped receptors on plasma membranes of guard cells 4. causes Ca2+ ion channels to open and Ca2+ ions enter into the guard cells 5. causes K+ ions along with NO3- and Cl- to leave the guard cell increases water potential 6. water moves out of guard cell by osmosis to surrounding cells less flacid stomata closes

Question 32

herbivory

Answer 32

process by which herbivores eat plants

Question 33

physical defences

Answer 33

- thorns, barbs, spikes - spiney leaves, hairy leaves - stings - fibrous tissue - inedible tissue

Question 34

tannins

Answer 34

part of a group of chemicals called phenols bitter taste to put off animals eating leaves toxic to insects bind to enzymes in saliva tea and red wine rich in tannins

Question 35

alkaloids

Answer 35

bitter tasting nitrogenous compounds many acts as drugs include caffeine ( toxic to fungi and insects) nicotine (toxin produced in roots of tobacco plants stored in vacuoles) morphine and cocaine

Question 36

terpenoids

Answer 36

form essential oils toxic to insects and fungi pyrethrin produced by chrysanthemums interferes with insect nervous system citronella produced by lemon grass repels insects

Question 37

VOCs volatile organic compounds

Answer 37

-act like pheromones between themselves and other organism especially insects -usually made when plant detects an attacks by insects - through chemicals in insect saliva -if cabbage is attacked by greenfly, signal attracts wasp -when spider mites attack apple trees VOCs are produced which attract predatory mites to destroy -types of wheat seedlings produce VOCs when attacked by aphids VOCs repel other aphids from the plant