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Plant responses Flashcards

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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

Study These Flashcards
A

Plant growth regulators are known as growth promoters

24
Q

Natural occurring auxins are called

Study These Flashcards
A

Indole-acetic acid/ IAA

25
Auxin production sites include
- Meristems eg: root tip, shoot tip | - Developing seeds
26
Where is auxin transported?
Phloem
27
General functions of auxins include
- Stem elongation and root growth - Side branching stems - Positive stem phototropism - Fruit development
28
It is difficult to establish the exact role of plant growth regulators as
- Active in small amounts | - Effect depends on concentration and where they are active
29
State 2 ways in which growth regulators in plants are similar to hormones in animals
- Made at one site and functions at another | - Chemical in nature and travel slowly
30
Apical dominance
- 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
Root and shoot growth
- At low concentration auxin causes roots to grow | - At high concentration IAA causes shoots to grow
32
Fruit formation
- Developing seed produce auxin - Initiate fruit development by applying IAA to flowers before pollination - Develops seedless fruit
33
Explain the mechanism of response by a plant to a named external stimulus
- 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
Abscisic acid
allows the plant to respond to harmful conditions
35
Explain the 2 roles of abscisic acid
- Triggers the closing of the stomata in dry conditions to conserve water - Promotes seed dormancy
36
Ethene
Produced in ripe fruits and decaying leaves
37
Explain 3 roles of Ethene
- Ethene causes ripening of fruit - Stimulates leaf fall in autumn - Stimulates the production of more ethene
38
Plant regulators
- Fruit ripening | - Production of seedless fruits
39
Plant adaptations for protection
- Thorns | - Epidermis
40
To investigate the effect of IAA on plant tissue using radish seeds
- 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
Safety precaution
Ethanol is flammable so use away from the heat source and wear safety goggles to avoid irritation to the eyes
42
Compare the results you obtained in the experiment and in the control
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
The formula for root and shoot growth
Average length-Average length control/ average length control
44
How to prepare a serial dilution
- 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
What is auxin
Plant growth regulator
46
With regard to auxins state i) precise location in plants where they are produced ii) One example of an inhibitory function
i) Meristematic tissue | ii) Apical dominance prevents the growth of side branches
47
How does an unequal concentration of auxin in the elongation zone affect the growth of either a shoot or a root
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
Suggest what could cause an unequal concentration of auxin in a shoot or a root
ii) Shoot: difference in light direction | root: gravity
49
State 2 uses in horticulture of auxins or related compounds
ripening fruit | seedless fruit
50
Give an example of i) a growth regulator that promotes growth ii) A growth regulator that inhibits the growth
i) Auxin | ii) Ethene
51
Name the plant you used when you investigated the effect of a growth regulator on plant tissue
Raddish
52
Describe how you carried out the investigation
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
Give a safety precaution that you carried out the investigation
Ethanol is flammable- keep away from heat | Wear safety goggles to avoid eye irritation
54
Results of the experiment
Low concentration of IAA promoted root growth | High concentrations of IAA promoted shoot growth
55
What is the effect on the root of an auxin concentration?
Inhibition
56
Give 2 examples of uses of synthetic auxins
- Tissue culture | - Fruit formation
57
Describe 3 methods used by plants to protect themselves from adverse external environments
- Thorns - Heat shock proteins - Leaf fall

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