plants and tropisms

Question 1

what is a positive tropism

Answer 1

when plants grow towards a stimulus

Question 2

what is a negative tropism

Answer 2

when plants grow away from a stimulus

Question 3

what is the response to gravity known as

Answer 3

gravitropism

Question 4

what is positive gravitropism

Answer 4

when plants grow towards the force of gravity (eg toward roots)

Question 5

what is negative gravitropism

Answer 5

growth away from gravity (eg towards roots)

Question 6

what is the response to light known as

Answer 6

phototropism

Question 7

what is positive phototropism

Answer 7

growth towards light

Question 8

what is negative phototropism

Answer 8

growth away from light

Question 9

how must shoots grow

Answer 9

upwards
away from gravity
towards light
so that leaves are able to absorb sunlight

Question 10

how must roots grow

Answer 10

downwards into the soil
away from light and towards gravity
in order to anchor the plant and absorb water and minerals from the soil particles.

Question 11

what does this say about roots tropic responses

Answer 11

roots have a negative phototropic response and a positive gravitropic response

Question 12

what does this say about shoots tropic responses

Answer 12

shoots are negatively gravitropic and positively phototropic

Question 13

what is auxin

Answer 13

Plants respond to stimuli by producing a growth hormone called auxin which controls the direction of growth of roots or stems

Question 14

how do plants control their growth

Answer 14

chemically

Question 15

where is auxin mostly produced

Answer 15

Auxin is mostly made in the tips of the growing stems and roots

Question 16

how does auxin travel

Answer 16

through diffusion
high concentration in shoot tips down the shoot to an area of low concentration

Question 17

where does auxin stimulate growth

Answer 17

Auxin stimulates the cells behind the tip to elongate
the more auxin there is the faster they will elongate

Question 18

what is the part of the plant in which auxin grows the most called

Answer 18

Only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation. This part of a shoot is called the meristem.

Question 19

when light shines on a plant where does the auxin form

Answer 19

auxin forms in the shaded region (the side where light is not shone) making the cells on that side grow faster and longer
this unequal growth causes the shoot to bend and grow in the side of the light

Question 20

how does auxin affect gravitropism in shoots

Answer 20

Gravity modifies the distribution of auxin so that it accumulates on the lower side of the shoot
As seen in the phototropic response, auxin increases the rate of growth in shoots, causing the shoot to grow upwards
negative phototropism

Question 21

how does auxin affect gravitropism in roots

Answer 21

In roots, higher concentrations of auxin results in a lower rate of cell elongation
The auxin that accumulates at the lower side of the root inhibits cell elongation
As a result, the lower side grows at a slower rate than the upper side of the root
This causes the root to bend downwards

Question 22

Explain how auxins control the growth response of seedlings

Answer 22

auxins made in tip diffuse down the stem auxins collect in the side away from the light, greater elongation in the side in the dark

Question 23

explain the role of auxins in phototropism

Answer 23

auxin stimulates cell elongation, auxin accumulates on shaded side which causes bending on non-shaded side