Tropisms

Question 1

What is tropism?

Answer 1

-when plants respond via growth to a stimuli
-can be + or -

Question 2

What are the 3 factors plants respond to?

Answer 2

-light, gravity and water

Question 3

What is a plants response controlled by?

Answer 3

-specific growth factors eg. IAA

Question 4

What is IAA?

Answer 4

-type of auxin that controls cell elongation and root growth inhibition

Question 5

What is phototropism?

Answer 5

-when the shoot grows towards light to enable them to photosynthesise

Question 6

What is geotropsim?

Answer 6

-roots grows towards the pull of gravity
-provides them with anchorage with the soil and helps take up water for PS

Question 7

What is chemotropism?

Answer 7

-occurs when pollen tubes are attracted by chemicals and grow down the style towards ovary

Question 8

What is thigmotropism?

Answer 8

-shoots of climbing plants can wind around other plants and structures to gain support

Question 9

What happens with uneven growth?

Answer 9

-caused by uneven distribution of auxins
-response to a particular stimulus

Question 10

What is positive phototropism in shoots?

Answer 10

-unilateral light causes auxins to move laterally to the shaded side
-auxins increase elasticity of cell wall
-more elastic cells absorb more water and grow towards the light

Question 11

What is negative phototropism in roots?

Answer 11

-auxins don’t increase the elasticity of the cell wall
-causes roots to elongate on the lighter side
-root bends away

Question 12

What is negative geotropsim in shoots?

Answer 12

-auxins diffuse from upper side to lower side
-it will grow up if vertical
-it will bend up if horizontal

Question 13

What is positive geotropism in roots?

Answer 13

-more auxins = less root growth
-top part grows faster
-ensures roots grow downwards to absorb water and minerals

Question 14

What is negative geotropsim in roots?

Answer 14

-more auxins = more shoot growth
-bottom parts grow faster
-ensures shoots grow upwards for more light = more PS

Question 15

How were chemicals messenger shown to exist?

Answer 15

-when a shoot tip was placed on agar block
-auxin diffuses from tip into agar
-those with blocks stimulated growth

Question 16

What is the mechanism of an auxin?

Answer 16

1. active transport of H ions into cell wall by an enzyme in membrane
2. low pH in wall allows expansins to work
3. breaks bonds in cellulose and H ions disrupt H bond
4. cellulose gets less rigid = expand

Question 17

What happens to a plant when a lightproof cover is placed on tip?

Answer 17

-no growth

Question 18

What happens when a barrier of mica is placed the illuminated side?

Answer 18

-movement of chemical down shaded side
-bends towards light

Question 19

What happens when a mica barrier is inserted on the shaded sided?

Answer 19

-movement of chemical down shaded side is prevented by mica
-no growth

Question 20

What happens when the tip is removed and a gelatinous block is inserted and the tip is replaced?

Answer 20

-movement of chemical down shaded side
-bends towards light

Question 21

How can geotropism be investigated?

Answer 21

-control plant is spun slowly in a clinostat
-the root will bend downwards as the upper side of root has elongated more

Question 22

What is etiolation?

Answer 22

-plants grow abnormally long due to not enough light