3 - Intermediate School Biology



3.5.2 Responses in the Flowering Plant

NOTES

A stimulus is anything that causes a reaction in an organism, or in any of its parts.

A response is the activity of the cell or organism as a result of the stimulus.

Growth regulation

The growth of a flowering plant can be controlled by external and internal factors.

Some external factors that regulate the growth of plants are light intensity, day length, gravity, temperature.

Among the principal internal factors that regulate these responses is the production of a series of chemicals called growth regulators in regions of the plant called meristematic regions.

Examples of meristematic regions: apical meristems e.g. root tip and shoot tip

Tropism: A tropism is a change in the growth of a plant in response to a stimulus.

Positive tropisms : Growth towards stimulus

Negative tropisms: Growth away from stimulus

▪ Phototropism: A change in the growth of a plant in response to light

▪ Geotropism: A change in the growth of a plant in response to gravity

▪ Thigmotropism: A change in the growth of a plant in response to touch

▪ Hydrotropism: A change in the growth of a plant in response to water

▪ Chemotropism: A change in the growth of a plant in response to chemicals

Tropisms allow plants to obtain more favourable growing conditions:

Phototropism

▪ Stem grows towards light

▪ More favourably positioned to photosynthesise.

Geotropism

▪ Roots grow towards gravity

▪ They can penetrate into the soil for better anchorage and absorption

Regulatory system:

Definition of a growth regulator, transport through the vascular system

▪ Growth Regulators are chemicals which control the growth of a plant.

▪ Produced in small amount in the meristems of plants

▪ Transported in the vascular tissue (xylem and phloem)

Different combinations of regulators bring about different effects.

The effects of regulators depend on their concentration i.e. the same regulator can have different effects at high or low concentrations.

Their effect depends on the location of the plant in which they are acting i.e. the same concentration of plant regulator can have opposite effects in the stem and root.

IAA (Indole Acetic Acid)

At low concentrations, IAA causes roots to grow. High concentrations inhibit root growth.

Low concentrations inhibit shoot growth. At high concentrations, IAA causes shoots to grow.

Different regulators interact in different ways. Some regulators support each other to produce a greater effect (Synerginism).

Others interfere with each other and their combination may have no effect (Antagonism )

e.g. Absissic acid causes dormancy in buds and gibberellins break the dormancy.

Some regulators promote growth e.g auxins are growth promoters

Others inhibit growth e.g ethane and abscisic acid are growth inhibitors

Note of information

Synthetic auxins (2,4- D) are commonly used as herbicides due to their differential effects on dicots and monocots.

The herbicide contains a greater concentration of auxin than the amount of auxin produced naturally naturally produced in the plant.

Dicots are killed by much lower concentrations than monocots.

Synthetic auxins are therefore used to control broad-leaved weeds (mainly dicots) on lawns and in cereal crops.

The weedkiller causes dicots to elongate so fast that they cannot sustain their own growth and die.

Describe any 4 methods of anatomical or chemical adaptation by which plants protect themselves from adverse external environments – anatomical/ structural or chemical e.g. heat shock proteins or stress proteins

Plants are subject to a range of potentially harmful environmental conditions such as

▪ Eaten by herbivore

▪ Infected with disease causing organisms

▪ Loss of water

▪ Overheating

To protect themselves, plants have a large number of adaptive features

Anatomical adaptations

▪ Enclosed by a physical barrier e.g. epidermis or bark

▪ Cuticle

▪ Thorns

▪ Shortage of water causes guard cells to shrivel, closes stomata, reduces loss of water

OR

Chemical adaptations

▪ Heat shock proteins surround enzymes, once temperature rises above 400C these help them maintain their shape.

▪ Stress proteins are produced in response to micro-organisms. They damage the micro-organism by attacking their cell walls. They can also stimulate nearby plant cells to respond to the micro-organism.

Contemporary Issue

Use of plant regulators: any 2 examples

Plant growth regulators can be produced outside of plants by artificial or synthetic methods.

1. Rooting powders

Contain a synthetic growth regulator such as NAA (naphtylacetic acid). This stimulates rapid root formation on stem cuttings.

Horticulturalists use NAA to produce roots on cuttings more quickly than would normally be the case.

2. Tissue culture

In tissue culturing pieces of plant material are grown to form entire new plants.

If a piece of plant tissue is grown in a high auxin concentration, it will develop into a mass of similar, undifferentiated cells (called a callus).

By adding different concentrations of auxins, the mass of cells can be stimulated to form roots, shoots or an entire plant.

3. A synthetic auxin is used as a synthetic weedkiller ( 2,4-D)

4. Ethene is sprayed on fruit to promote ripening.

• Mandatory Activity

Investigate the effect of I.A.A. growth regulator on plant tissue.

Materials/Equipment

Radish seeds

IAA solution (0.01% w/v)

Distilled water

2 syringes (10cm3)

8 Graduated droppers

8 Small bottles

Thermometer

Beaker

Procedure

1. Label the petri dishes as follows: 102 ppm, 101 ppm, 1 ppm 10-1 ppm, 10-2 ppm, 10-3 ppm, 10-4 ppm, distilled water (control)

2. Label the bottles in the same way.

3. Using a syringe, add 10 cm3 of the IAA solution to the first bottle (0.01% w/v or 10-2 ppm).

4. Using the other syringe add 9 cm3 of distilled water to each of the next seven bottles.

5. Using a dropper, remove 1cm3 of the IAA solution from the first bottle and add it to the second bottle. Place the cap on the second bottle and mix.

6. Using a different dropper, remove 1 cm3 of solution from the second bottle and add it to the third bottle. Place the cap on the third bottle and mix.

7. Using a different dropper each time, repeat this serial dilution procedure for the fourth fifth, sixth and seventh bottles.

8. Discard 1cm3 of solution from the seventh bottle. Each bottle now contains 9 cm3 of solution.

9. Fit a circular acetate grid inside the lid of each dish.

10. Place five radish seeds along a grid line in each dish as shown.

11. Place a filter paper on top of the seeds in each dish.

12. Using the appropriate droppers, add 2cm3 of each solution to its matching dish. Use the dropper bulb to press gently on the damp filter paper, to reduce the trapped air.

13. Spread a piece of cotton wool, about 0.5 cm thick and the approximate area of the dish, on top of the filter paper in each dish to absorb the excess solution.

14. Add the remaining 8 cm3 of each solution to the cotton wool in the appropriate dish. Leave for a few minutes, until the cotton well absorbs all the solution.

15. Put the base of each dish in place and secure with a small piece of adhesive tape on either side.

16. Stand the dishes vertically on their edge, to ensure the roots grow down. Leave in the incubator for 2-3 days.

17. Measure the length of the roots and shoots of the seedlings in each dish by using the acetate grids and record.

18. Calculate the total length and the average length of the roots and shoots in each dish and record.

19. Estimate the percentage stimulation or inhibition of root and shoot growth in each dish using the following formula:

20. A graph should be drawn of percentage stimulation and inhibition of root and shoot growth against IAA concentration. Put IAA concentration on the horizontal axis.

21. Replicate the investigation or cross reference your results with other groups.

Results

Concentration of IAA (ppm) |Length of root

(mm)

Seed 1 |Length of root (mm)

Seed 2 |Length of root (mm)

Seed 3 |Length of root (mm)

Seed 4 |Length of roots (mm)

Seed 5 |Total length (mm) |Average length (mm) |Percentage stimulation or inhibition | |0 | | | | | | | | | |10-4 | | | | | | | | | |10-3 | | | | | | | | | |10-2 | | | | | | | | | |10-1 | | | | | | | | | |1 | | | | | | | | | |10 | | | | | | | | | |102 | | | | | | | | | |

Concentration of IAA (ppm) |Length of shoot

(mm)

Seed 1 |Length of shoot (mm)

Seed 2 |Length of shoot (mm)

Seed 3 |Length of shoot (mm)

Seed 4 |Length of shoot (mm)

Seed 5 |Total length of shoot

(mm) |Avg length (mm) |Percentage stimulation or inhibition | |0 | | | | | | | | | |10-4 | | | | | | | | | |10-3 | | | | | | | | | |10-2 | | | | | | | | | |10-1 | | | | | | | | | |1 | | | | | | | | | |10 | | | | | | | | | |102 | | | | | | | | | |

Conclusion/Comment

H.3.5.5 Auxins

NOTES

Auxin (Indole Acetic Acid)

Auxin (IAA) produced in the meristematic tissue in the tips of shoots, roots and buds.

Effect on Roots:

• Low concentrations, IAA causes roots to grow.

• High concentrations inhibit root growth.

Effect on Shoots

• At high concentrations, IAA causes shoots to grow.

• Low concentrations inhibit shoot growth.

Apical dominance

The apical bud of a stem makes IAA in concentrations too high to allow the growth of side buds further down.

If apical bud is cut off, auxins are removed and so the side buds grow.

H.3.5.6 Plant growth regulators and Animal Hormones (Extended study)

NOTES

Explanation of mechanism of plant response to any one external stimulus.

Coleoptile: protective sheath around the germinating shoots of grasses.

Used because

▪ response to light easy to observe

▪ Small

▪ Easy to grow in large numbers

External Stimulus: Light

Response: Shoot grows towards light: Phototropism. Brought about by auxins

• Auxins (IAA) loosen cell walls

• This allows them to expand and elongate.

• Auxins produced in the growth tips (meristems) of the stems.

Mechanism of response:

▪ Plant illuminated from one side

▪ Auxin moves away (diffuses) from the light towards the shaded side of the stem

▪ Greater auxin concentration on the shaded side

▪ Greater cell elongation on the shaded side

▪ Uneven elongation

▪ Stem bends towards light

[pic][pic]

-----------------------

Growth regulation

Tropisms: definition of the following:

Phototropism

Geotropism

Thigmatropism

Hydrotropism

Chemotropism

Examples of phototropism and geotropism

Regulatory system:

Definition of a growth regulator

Transport through the vascular system

Combined effect

Growth promoter and growth inhibitor

Name four methods of anatomical or chemical adaptation that protect plants.

Syllabus P. 37

Contemporary Issue

Use of plant regulators: any 2 examples

Mandatory Activity

Investigate the effect of I.A.A. growth regulator on plant tissue

Growth regulation

Some external factors that regulate the growth of plants are light intensity, day length, gravity, temperature.

Among the principal internal factors that regulate these responses is the production of a series of chemicals called growth regulators in regions of the plant called meristematic regions.

Give some examples of meristematic regions.

Tropisms:

Definition of the following:

Phototropism

Geotropism

Thigmatropism

Hydrotropism

Chemotropism

Emphasise the significance of phototropism and geotropism with

Regulatory system:

Definition of a growth regulator, transport through the vascular system

Different combinations of regulators bring about different effects.

Some regulators promote growth e.g auxins

Others inhibit growth e.g ethane and abscisic acid

Describe any 4 methods by which plants protect themselves from adverse external environments – anatomical/chemical e.g. heat shock, proteins or stress proteins

T.G. P. 66

Contemporary Issue

Use of plant regulators: any 2 examples

Mandatory Activity

Investigate the effect of I.A.A. growth regulator on plant tissue

8 Petri dishes

8 Filter papers

8 Circular acetate grids

Absorbent cotton wool

Disposable gloves

Adhesive tape

Incubator (250C)

Percentage stimulation/inhibition

= (Average length – average length of control) x 100

Average length of control

Study auxin as an example of a plant growth regulator under the headings of production site(s), function and effects

P40

Study auxin as an example of a plant growth regulator under the headings of production site(s), function and different effects

T.G. p

Plant growth regulator

Production site

Function

Effects

Auxin

(IAA)

Meristems of

Shoot

Root

Bud

Cell elongation

▪ Stem elongation

▪ Root growth

▪ Phototropism

▪ Geotropism

▪ Differentiation of vascular tissue

▪ Controls apical dominance

Explanation of mechanism of plant response to any one external stimulus.

P40

Explanation of mechanism of plant response to any one external stimulus.

P71

Summary

Auxins move away from the light.

Concentrate on the shady side.

More growth on this side

Bends towards light

[pic]

Thigmotropism

Types of Tropisms

Entire plants can be grown

Positioning of radish seeds

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download