4.5.4.1 Control and Coordination

Question 1

Why do plants produce hormones?

Answer 1

• plants produce hormones to coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism)
• hormones move from the place they are made to where they are needed in order to produce the appropriate response

Question 2

What do unequal distributions of auxin cause?

Answer 2

unequal distributions of auxin cause unequal growth rates in plant roots and shoots

Question 3

Tropism:

Answer 3

a growth response made by a plant in response to an external stimulus

Question 4

Geotropism/gravitropism:

Answer 4

• roots grow towards gravity (positively gravitropic/geotropic)
• shoots grow upwards away from gravity (negatively gravitropic)

Question 5

Phototropism:

Answer 5

shoots grow towards lights - positively phototropic

Question 6

Hydrotropism:

Answer 6

movement of root towards a source of water

Question 7

Haptotropism:

Answer 7

movement of particles of a plant (esp. tendrils) in response to touch of a stimulus

Question 8

What are tropisms caused by?

Answer 8

caused by unequal distribution of plant hormones (auxins)

Question 9

Where are auxins produced and what do they promote?

Answer 9

• auxins produced in tips of roots and shoots
• auxins diffuse away from where it was made and promote cell division and cell elongation on shaded side

Question 10

Survival benefits of tropisms shown in the images:

Answer 10

• phototropism
  
  • grow towards light → increased photosynthesis → increased growth
• gravitropism
  
  • roots grow downwards to absorb water and minerals
• haptotropism
  
  • can’t get nitrogen from soil as it is water-logged so get it from insect
  • sensitive to touch so can capture insects and digest them and get nitrogen from them

Question 11

When happens when the auxin distribution is equal in the shoots?

Answer 11

if the auxin distributions becomes equal on both sides of the shoot it grows straight in that direction

Question 12

Explain phototropism:

Answer 12

• auxins produced in tips of roots and shots → auxins diffuse from where it is made and promotes cell division and cell elongation on shaded side
• auxin molecules move to shaded side
• growth of stem cells caused by auxins will cause cells on shaded side to grow and elongate
• growth of stem cells will cause shaded side to grow and elongate causing plant to grow and bend towards light

Question 13

Why do plants bend towards light?

Answer 13

plant bends towards light → increase photosynthesis → increased sugars and starch made for respiration → increased energy by from respirations used for growth

Question 14

What do most plants show in terms of phototropism?

Answer 14

• most plants show positive phototropism as they grow towards the light source
• auxin, a hormone, moves to shaded side of shoot
• auxin stimulates cell division and elongation on shaded side of plant causing it to grow more
• this causes the shoot to bend toward the light
• the plant receives more light - photosynthesis occurs at a faster rate

Question 15

Explain geotropism/gravitropism in roots:

Answer 15

• auxin produced by root tip becomes unevenly distributed
• unequal distribution of auxin due to gravity
• auxins sink to bottom of root due to gravity
• auxin inhibits growth in roots which causes the part of the root without auxin to grow - causes roots to grow downwards

Question 16

What do most shoots show in terms of gravitropism?

Answer 16

• most shoots show negative gravitropism as they grow away from gravity
• if a shoot is horizontal, auxins sink to the lower side (due to gravity)
• the cells of the shoot grow more on the lower side due to the auxins causing cell division and elongation stimulating cells to grow more here
• this makes the shoot bend and grow away from the ground
• this beneficial as light levels are likely to be higher further away from the ground

Question 17

What do most roots show in terms of gravitropism?

Answer 17

• positive gravitropism as they grow towards gravity
• auxins sink to the lower side (due to gravity)
• the cells of the root grow more on the side with less auxins so it stimulates cells to grow on the upper side as auxins inhibit growth in roots
• this makes the root bend and grow downwards
• this is beneficial as it is more likely for they to be increased levels of water and nutrients lower down, provides stability for the plant

Question 18

Gibberellins:

Answer 18

hormones that are important to stimulate seed germination

Question 19

Ethene:

Answer 19

involved in cell division and the ripening of fruits