Chapter 32 - Plant Responses

Question 1

What is a stimulus?

Answer 1

Anything that causes a reaction in an organism

Question 2

What is a response?

Answer 2

The activity of a cell in reaction to a stimulus

Question 3

What four structures are needed for an organism to respond?

Answer 3

Hormonal system
Nervous system
Ability to move and grow
An immune system

Question 4

What kind of responses are plant responses?

Answer 4

Growth or changes in growth

Question 5

Why are plant responses different from animal ones?

Answer 5

Plants cannot move

They have no nervous system and instead use chemical coordination

Question 6

What are growth regulators?

Answer 6

Chemicals that control growth in a plant

Question 7

What are the internal factors of growth regulators?

Answer 7

Chemicals produced by a plant

Question 8

What are the external factors of growth regulators?

Answer 8

Light intensity - needed for photosynthesis, produces chlorophyll
Day length - causes plants to flower, seed, ferment
Gravity - roots grow down, shoots grow up
Temperature - affects rate of enzyme reactions

Question 9

What is a tropism?

Answer 9

A change in the growth of a plant in response to an external stimulus

Question 10

What is a positive tropism?

Answer 10

Growth towards stimulus

Question 11

What is a negative stimulus?

Answer 11

Grows away from stimulus

Question 12

What is the purpose of a tropism?

Answer 12

To help plants obtain the best growing conditions

Question 13

What are the 5 types of tropisms?

Answer 13

Phototropism 
Geotropism
Thigmotropism
Hydrotropism 
Chemotropism

Question 14

What is phototropism?

Answer 14

The change in growth of a plant in response to light
Positively phototropic - stems, to carry out more photosynthesis
Negatively phototropic - roots

Question 15

What is geotropism?

Answer 15

The change in growth of a plant in response to gravity
Positively geotropic - roots, anchor and absorb minerals
Negatively geotropic - stems

Question 16

What is thigmotropism?

Answer 16

The change in growth of a plant in response to touch

Positively thigmotropic - tendrils

Question 17

What are tendrils?

Answer 17

They respond to touch by wrapping around supporting structures
Ivy has tendrils

Question 18

What is hydrotropism?

Answer 18

A change in growth of a plant in response to water

Positively hydrotropic - roots, grow towards damp soil

Question 19

What is chemotropism?

Answer 19

Change in growth of a plant in response to chemicals
Positively chemotropic - roots, grow towards minerals
Negatively chemotropic - roots, grow away from acids or heavy metals

Question 20

Where are growth regulators produced?

Answer 20

The meristem

Question 21

How are growth regulators transported?

Answer 21

Vascular tissue

Question 22

Why are growth regulators difficult to study?

Answer 22

Active in small amounts
Opposite effects at high and low concentration
Effects depend on location
Interacts in different ways - combine, interfere, or no effect

Question 23

What are growth promotors?

Answer 23

Increase rate of growth

Question 24

What are the most known growth promotor?

Answer 24

Auxins

Question 25

What is the best known auxin?

Answer 25

IAA (indoleacetic acid)

Question 26

What is the function of IAA?

Answer 26

Made in Shoot Tips, young leaves, seeds
Causes stem and root to grow
Causes fruit formation

Question 27

What are growth inhibitors?

Answer 27

Decrease rate of growth

Question 28

What are the two best known growth inhibitors?

Answer 28

Ethene and abscisic acid (ABA)

Question 29

What is the function of ethene?

Answer 29

Gas made in plant nodes, ripe fruits, decaying leaves
Causes fruit to ripen, leaves to fall
Bananas exposed to ethene before being sent to shops stimulates ripening

Question 30

What is the function of abscisic acid?

Answer 30

Made in leaves, stems, root caps
Causes plants to respond to harmful conditions:
Stomata closes at night
Bud scales in winter
Inhibits seed germination until ready

Question 31

What are the 7 functions of auxins?

Answer 31

Stimulate stem elongation 
Stimulate root growth
Causes cells to form into different structures
Develop fruit
Inhibit side branches
Causes phototropism 
Causes geotropism

Question 32

What are the effects of auxins?

Answer 32

Tropisms
Allows cell walls to expand 
Apical dominance 
Fruit formation - IAA
Root growth - low concentration (used in root powders)

Question 33

Explain apical dominance?

Answer 33

If apex is present - no side branches
If apex is not present - side branches
Apical dominance - lateral buds do not develop due to inhibition
Lack of apical dominance - side branches form

Question 34

What 3 ways can growth regulators be used in industry?

Answer 34

Rooting powders
Tissue culturing
fruit ripening

Question 35

Explain rooting powders

Answer 35

Contains an artificially produced growth regulator (NAA)

Used to stimulate root growth in cuttings

Question 36

Explain tissue culturing

Answer 36

Piece of plant material growth in high auxin concentration

Question 37

Explain fruit ripening

Answer 37

Ethene ripens bananas

Question 38

What are two anatomical plant adaptations?

Answer 38

1. Epidermis - physical barrier (bark or cuticle), prevents water loss, entry of pathogens, thorns (cactus), stinging hairs (nettles)
2. Stomata - reduces water loss, close by shriveling of guard cells by the release of abscisic acid

Question 39

What are 2 chemical plant adaptations?

Answer 39

1. Heat shock proteins - allow a plant to function properly in high temperatures, normal proteins don’t work above 40°c
2. Phytoalexins - stress proteins produced when a plant is infected with micro organisms
   Attacks micro organisms, strengthens cell walls to stop infection, alerts outer plant cells

Question 40

How have plants in deserts adapted?

Answer 40

Spins for leaves
Stores water in stem 
Lighter colour 
Waxy leaves
Long root systems spread out wide and deep
Grow slowly