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Plant responses Flashcards

1
Q

Stimulus

A

Anything that causes a reaction in an organism

eg: Light

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2
Q

Response

A

The activity of an organism due to a stimulus

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3
Q

Tropism

A

Plant growth response to a stimulus

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4
Q

When growth response is towards the stimulus it is

A

Positive

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5
Q

When growth response is away from the stimulus it is

A

Negative

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6
Q

Phototropism

A

change in plant growth in response to light

eg: stems grow toward light and are positively phototropic
eg: Roots grow away from light and are negatively phototropic

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7
Q

Geotropism

A

Change in plant growth in response to gravity
eg:
Roots are positively geotropic
- They grow down towards the pull of gravity in search of water
- Minerals and to anchor the plant
eg:
Stems are negatively geotropic
- They grow up and away from the pull of gravity

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8
Q

Chemotropism

A

Change in plant growth in response to chemicals
eg:
- Flowering plants
- Pollen tube grows down towards chemicals released
- Positively chemotropic
eg:
- Roots are negatively chemotropic to lead/zinc

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9
Q

Hydrotropism

A

Change in plant growth in response to water

eg: Roots grow down through the soil towards the water and so are positively hydrotropic

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10
Q

Thigmotropism

A

Change in plant growth in response to touch

eg: plants like ivy grow around any object they touch

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11
Q

Advantages of tropism

A
  • allow plants to obtain more favourable growing conditions
  • shoots are positively phototropic which allows increased photosynthesis
  • roots are positively geotropic which allows increased availability of soil water and anchorage
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12
Q

External factors

A

Light intensity, gravity, temperature and day length

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13
Q

Internal factors

A

Plant growth regulators

  • Auxins
  • Ethene and abscisic acid
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14
Q

Importance of light intensity for plant growth

A
  • Light energy is needed for photosynthesis

- Produces chlorophyll

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15
Q

Importance of gravity for plant growth

A
  • water and minerals

- anchorage

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16
Q

Importance of temperature for plant growth

A
  • affects the rate of enzyme action
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17
Q

Importance of day length for plant growth

A
  • Flowering and seed formation
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18
Q

Define Meristem

A

Region of a plant where cells are actively dividing by mitosis to produce new cells for growth

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19
Q

Name 2 types of meristem

A
  • Apical (primary)

- Lateral (secondary)

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20
Q

Apical meristem

A
  • Located at the tips of stems, roots and buds
  • responsible for growth in plant length
  • formation of leaves and axillary buds
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21
Q

Lateral meristem

A
  • Located along stems
  • responsible for the growth in width
  • produces secondary xylem and phloem
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22
Q

Define plant growth regulator

A

A chemical that controls the growth of a plant

eg:
- Auxins
- Ethene and abscisic acid

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23
Q

Define auxins

A

Plant growth regulators are known as growth promoters

24
Q

Natural occurring auxins are called

A

Indole-acetic acid/ IAA

25
Q

Auxin production sites include

A
  • Meristems eg: root tip, shoot tip

- Developing seeds

26
Q

Where is auxin transported?

27
Q

General functions of auxins include

A
  • Stem elongation and root growth
  • Side branching stems
  • Positive stem phototropism
  • Fruit development
28
Q

It is difficult to establish the exact role of plant growth regulators as

A
  • Active in small amounts

- Effect depends on concentration and where they are active

29
Q

State 2 ways in which growth regulators in plants are similar to hormones in animals

A
  • Made at one site and functions at another

- Chemical in nature and travel slowly

30
Q

Apical dominance

A
  • Auxin is produced in the apical meristems
  • transported in the phloem
  • High auxin concentrations inhibit axillary buds
  • apical bud is removed
  • axillary buds are stimulated to produce side branches
31
Q

Root and shoot growth

A
  • At low concentration auxin causes roots to grow

- At high concentration IAA causes shoots to grow

32
Q

Fruit formation

A
  • Developing seed produce auxin
  • Initiate fruit development by applying IAA to flowers before pollination
  • Develops seedless fruit
33
Q

Explain the mechanism of response by a plant to a named external stimulus

A
  • Light
  • Stem is exposed to light that is coming in one direction
  • Auxin diffuses down the shaded side of the stem
  • Unequal distribution of auxin as there is more on the shaded side
  • Cells on the shaded side elongate and grow faster on the shaded side which results in bending
34
Q

Abscisic acid

A

allows the plant to respond to harmful conditions

35
Q

Explain the 2 roles of abscisic acid

A
  • Triggers the closing of the stomata in dry conditions to conserve water
  • Promotes seed dormancy
36
Q

Ethene

A

Produced in ripe fruits and decaying leaves

37
Q

Explain 3 roles of Ethene

A
  • Ethene causes ripening of fruit
  • Stimulates leaf fall in autumn
  • Stimulates the production of more ethene
38
Q

Plant regulators

A
  • Fruit ripening

- Production of seedless fruits

39
Q

Plant adaptations for protection

A
  • Thorns

- Epidermis

40
Q

To investigate the effect of IAA on plant tissue using radish seeds

A
  • Prepare a stock solution of IAA
  • (because IAA doesn’t easily dissolve in water)
  • Use serial dilution to prepare different concentrations oF IAA
  • Fit a graphed acetate grid inside the lid of a petri dish and place 5 radish seeds along with one of the grid lines (using 5 seeds allows for non-germination in some seeds)
  • Add IAA as follows:
    . Place a filter paper on top of the seeds
    . Use a clean pipette to add 2cm of IAA @ 100mg/l
    . Cover with cotton wool and add the remaining IAA solution
  • Apply the base of the petri dish and tape out
  • Repeat for remaining IAA concentrations
  • Stand all Petri dishes vertically on their edges and incubate for 3 days at 25C (stand vertically to ensure roots grow down and shoots grow up if dishes are placed flat shoots and roots grow in a curved manner)
  • Prepare a control:
  • add distilled water only to seeds no IAA
  • Measure growth in each petri dish:
  • Use an acetate grid to measure the length of shoots and roots of each seed
  • Calculate the average of shoot and root length
  • Compare with the growth in control dish
41
Q

Safety precaution

A

Ethanol is flammable so use away from the heat source and wear safety goggles to avoid irritation to the eyes

42
Q

Compare the results you obtained in the experiment and in the control

A

In the test plates:
- a low concentration of IAA promoted root growth
- Higher concentrations of IAA promoted shoot growth
In the control plate
- There was little or no growth of shoots and roots

43
Q

The formula for root and shoot growth

A

Average length-Average length control/ average length control

44
Q

How to prepare a serial dilution

A
  • Label 8 Petri dishes A to H
  • Pipette 10ml of the stock solution of IAA into dish A
  • Using a clean pipette, place 9ml of distilled water into each of the dishes B to H
  • Use the serial dilution procedure outlined below to produce a range of IAA solutions in Petri dishes B to G
  • Dish H will serve as a control
  • Using a clean pipette each time and stirring to mix the contents, transfer 1ml of IAA solution from dish A to B, B to C, C to D, D to E, E to F, F to G
  • Do not transfer any IAA solution to dish H, which is the control with distilled water only
  • Remove 1ml of solution from dish G and dispose of it down the sink
45
Q

What is auxin

A

Plant growth regulator

46
Q

With regard to auxins state

i) precise location in plants where they are produced
ii) One example of an inhibitory function

A

i) Meristematic tissue

ii) Apical dominance prevents the growth of side branches

47
Q

How does an unequal concentration of auxin in the elongation zone affect the growth of either a shoot or a root

A

i) Root: Higher auxin concentration results in lower rate of cell division, less growth
Shoot: Higher auxin concentration results in a higher rate of cell division, more growth

48
Q

Suggest what could cause an unequal concentration of auxin in a shoot or a root

A

ii) Shoot: difference in light direction

root: gravity

49
Q

State 2 uses in horticulture of auxins or related compounds

A

ripening fruit

seedless fruit

50
Q

Give an example of

i) a growth regulator that promotes growth
ii) A growth regulator that inhibits the growth

A

i) Auxin

ii) Ethene

51
Q

Name the plant you used when you investigated the effect of a growth regulator on plant tissue

52
Q

Describe how you carried out the investigation

A

1) Prepare a stock solution of IAA
2) Use serial dilution to prepare different concentrations of IAA
3) Fit graphed acetate grid to a petri dish
4) Add 5 radish seeds along with one of the grid lines
5) Add IAA as follows
- place a filter paper on top of the seeds
- Use clean pipette add 2cm3 of IAA
- Cover with cotton wool
- Add remaining IAA
6) Apply a base of the petri dish and seal shut
7) Repeat for other IAA concentrations
8) Stand dishes vertically
9) Incubate for 3 days at 25C
10) Prepare a control with distilled water only no IAA
11) Measure growth in each dish

53
Q

Give a safety precaution that you carried out the investigation

A

Ethanol is flammable- keep away from heat

Wear safety goggles to avoid eye irritation

54
Q

Results of the experiment

A

Low concentration of IAA promoted root growth

High concentrations of IAA promoted shoot growth

55
Q

What is the effect on the root of an auxin concentration?

A

Inhibition

56
Q

Give 2 examples of uses of synthetic auxins

A
  • Tissue culture

- Fruit formation

57
Q

Describe 3 methods used by plants to protect themselves from adverse external environments

A
  • Thorns
  • Heat shock proteins
  • Leaf fall

Biology (21 decks)

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