Chapter 16 -plant hormones

Question 1

Ways hormones alter plant’s growth in response to overcrowding?

Answer 1

Auxin:

• plants will grow taller + will climb up over the other plants
• roots will grow towards water + minerals
• phototropism will cause shoots to bend towards the light

Question 2

How hormones alter growth if top of plant shoot eaten by animal?

Answer 2

• less auxin
• apical dominance stopped
• lateral buds develop
• side shoots grow
• plant becomes bushy

Question 3

Mechanism of phototropism?

Answer 3

• apical shoot produces auxin
• unilateral light causes lateral movement of auxin to shaded side from lit side
• greater auxin conc on shaded side
• auxin causes cell wall loosening + thus cell elongation
• bc H+pumped into cell wall
• low pH allows enzymes to work
• binds broken within cellulose in wall

Question 4

Similarities in action of plant + animal hormones in cell signalling?

Answer 4

• hormone binds to receptor

- may involve switching genes on + off

Question 5

Why plants are more able to form natural reproductive clones through asexual reproduction than animals?

Answer 5

• plant cells are totipotent
• retain ability to differentiate though its whole life
• most animal cells not totipotent
• meristematic tissue in plants contain totipotent cells

Question 6

Tropism?

Answer 6

Directional growth response of a plant

Question 7

Signalling molecule that enables plants to respond to environmental change?

Answer 7

Hormones

Question 8

Plants that lose their leaves seasonally?

Answer 8

Deciduous

Question 9

Why plants need to be able to respond to their environment?

Answer 9

• protect themselves against herbivory
• avoid abiotic stress
• maximise photosynthesis

Question 10

Why all lettuce seeds keeps at 25c during experiment testing hormones?

Answer 10

• fair test
• so temp doesn’t affect results
• temp affects enzyme activity

Question 11

Commercial uses?

Answer 11

• selective weed killer
• rooting powder
• controls ripening
• controls fruit dropping

Question 12

Insecticide absorbed by roots + leaves. How transported to fruits?

Answer 12

• in phloem by translocation

- in xylem by transpiration

Question 13

Why controls are necessary?

Answer 13

-show response without treatment

Question 14

Why both plants + animals need to be able to respond to changes in their environment?

Answer 14

• counter abiotic stress
• avoid being eaten
• access resources

Question 15

What type of tropism do shoots show?

Answer 15

• positive phototropism

- negative geotropism

Question 16

Why type of tropism do roots show?

Answer 16

• negative phototropism

- positive geotropism

Question 17

How is IAA transported?

Answer 17

In the phloem

Question 18

Apical dominance?

Answer 18

vertical growth is dominant over lateral growth

Question 19

How to control conc of CO2?

Answer 19

Burn paraffin

Question 20

How to control temp in greenhouse?

Answer 20

Use heaters

Question 21

How to control light in greenhouse?

Answer 21

Use glass windows

Question 22

How this result can be identified as an anomaly?

Answer 22

Repeat test

Question 23

Do sieve tube elements contain chloroplasts?

Answer 23

Yes

Question 24

Limiting factor?

Answer 24

The factor that will determine the rate when at low level

Question 25

Why plant leaf described as organ?

Answer 25

• similar plant cells form a tissue. Tissue carries out specific function
• diff tissues form an organ. Organ carries out specific function.

Question 26

Role of IAA?

Answer 26

Cell elongation

Question 27

How auxin causes cell elongation?

Answer 27

• auxin molecules bind to specific receptor sites in plant cell membrane Activating process which pumps H+ ions into cell wall spaces, lowering pH to 5
• this is the optimum pH for the enzymes that break down bonds between cellulose microfibrils, so they slide past each other easily
• walls remain flexible allowing cells to stretch and grow

Question 28

Why do trees lose their leaves?

Answer 28

• amount of photosynthesis that can take place decreases as day length decreases + temp decreases so amount of glucose produced decreases
• amount of glucose needed for respiration to maintain leaves through the winter + produce chemicals of prevent freezing damage increases
• becomes more efficient to lose their leaves + become dormant until temp + day length increases

Question 29

Abscission?

Answer 29

• falling light levels
• decreases conc of auxin
• leaves produce ethene
• ethene initiates gene switching in abscission zone at base of leaf stalk
• causes production of new enzymes
• digest + weaken cell walls in outer layer
• vascular bundles sealed off
• fatty material deposited in cells
• this layer form protective scar when leaf falls preventing pathogen entry
• cells in separation zone respond to hormonal cues by retaining water + swell
• more strain on outer layer
• further abiotic processes finish
• strain too much + leaf separates leaving meat waterproof scar