B3.2 Plants

Question 1

Tropism definition

Answer 1

When plants detect stimuli in their environment and respond by growing in a particular direction

Question 2

Phototropism

Answer 2

= growing towards light

- as plant can photosynthesise more

Question 3

Gravitropism

Answer 3

= growing in same direction as gravity

- roots grow deeper, provides anchorage in soil, takes roots near water

Question 4

Auxin

Answer 4

Plant hormone, enables plant to grow towards/away from stimulus

• made in cells near tips of plant shoots/roots
• stimulates growth of shoot cells, inhibits growth of root cells

Question 5

Explain positive phototropism in plant shoots

Answer 5

• light hits 1 side of shoot tip
• auxin moves to other side of shoot, conc increases in unlit side
• cells elongate, increases length of unlit side so shoot bends towards light

Question 6

What happens when light falls evenly on shoot

Answer 6

• level of auxin evenly distributed throughout tip

- all cells in top grow at same rate so shoot grows straight

Question 7

Explain negative phototropism in plant roots

Answer 7

• shaded side contains more auxin
• auxin inhibits growth of root cells, so doesn’t grow as other side does
• root bends away from light

Question 8

Explain gravitropism in plants

Answer 8

1. Auxin spread evenly through tissue of young plant
2. In root & shoot, more auxin gathers on lower side (gravity)
3. Root grows more on side with least auxin (top), bends & grows down (positive gravitropism)
4. shoot grows more on side with most auxin(bottom), bends & grows up (negative gravitropism)
5. Auxins become evenly spread again

Question 9

Auxins

Answer 9

• stimulate growth by causing cell elongation

- regulate fruit development

Question 10

Ethene

Answer 10

• causes plant fruits to ripen by stimulating conversion of starch into sugars
• only one in gas state

Question 11

Gibberellins

Answer 11

• promote growth, stem elongation

- end dormancy period of seeds/buds, shoots/flowers open

Question 12

Killing weeds (using plant hormones)

Answer 12

• weed killers contain auxin
• makes weed grow too fast, rapid uncontrolled growth kills plant
• selective herbicide, kills bread-leaved plants, not narrow-leaved

Question 13

Promoting root growth (using plant hormones)

Answer 13

• rooting powder contains auxins
• gardeners cut off plant shoot, dip it into rooting powder & plant it
• after few days roots develop from cut stem, new roots anchor into soil, take up water & minerals

Question 14

Delaying ripening (using plant hormones)

Answer 14

• auxin sprayed onto fruit trees to delay ripening

- allows harvest to be collected at same time, prevent fruit dropping off trees early

Question 15

Ripening fruit (using plant hormones)

Answer 15

• ethene sprayed on fruit trees/plants so fruits ripen quicker
• allows fruit to be ready earlier in growing season

Question 16

Producing seedless fruit (using plant hormones)

Answer 16

• apply auxins to unpollinated flowers

- seeds produced after plant pollinated by insects/wind

Question 17

Controlling dormancy (using plant hormones)

Answer 17

• seeds remain dormant until conditions idea for growth
• prevents them germinating at end of summer so survive winter
• commercial growers spray plants with gibberellins/auxins, trigger seeds to germinate in winter