RHS Level 2 Certificate

Week 11 – Plant growth, development and control

Christmas Prize Quiz

Test conditions 30 minutes Ho! Ho! Ho!

Learning Outcomes

State what is understood by growth and development.

State that simple cell division produces growth and results in an increase in size.

Describe how competition for water, nutrients, light and space can influence growth.

Describe two examples of how auxin influences plant growth.

Describe what is meant by the term phototropism. Define the term: ‘photoperiodism’.

Review of growth

Takes place by mitosis At the meristems Meristems – vascular cambium,

cork cambium, apical meristem, pericycle

Growth and Development

Growth and development – what is the difference? Plant growth = increase in size. Plant development = maturation of plant, formation

of plant organs such as flowers etc.

Competition and growth

Key factors required for growth are sufficient light, water, nutrients, oxygen and carbon dioxide and suitable temperature.

Competition means these may not be available to plants

Use of plant spacing in horticulture to provide optimum conditions for growth

Competition may mean death or reduced size or yield

Plant Growth Regulators 1

Control the way in which plants grow. For example that roots grow downwards and shoots upwards.

Chemicals produced by the plant which control the speed and location of the division of cells and the differentiation of those cells once produced

Plant Growth Regulators 2

Auxin stimulates plant cells to increase in length especially near to stem and root tips. It also promotes fruit formation

Cytokinins promote cell division (mitosis) and delay the senescence of leaves.

Gibberellins promote cell division and elongation of the stem. They also promote flowering and bolting in ‘long day’ plants and seed germination.

Ethylene promotes ripening of fruit and senescence of leaves and flowers. Induces abscission of leaves in deciduous plants (the process of leaf fall).

Abscisic acid maintains dormancy in seeds and possibly in buds. It also is responsible for causing the closing of stomata

Auxin and tropisms

Tropisms are growth responses to external stimuli

Phototropism – plants grow toward the light Geotropism – may be positive (growth towards

gravitational pull) or negative (growth away) Thigmatropism – growth towards touch. Auxin migrates in the stem to cause cell

elongation that causes the above growth responses

Day length and growth

The growth responses of plants to the length of day light hours is called photoperiodism.

Triggers flowering, leafy growth, formation of bulbs and tubers etc in some species

Day Neutral plants are not affected by day length Short Day plants – flower when the day length is

short (night is long). Long Day plants – flower when the day length is long

(night is short)

Learning outcomes

State what is understood by growth and development.

State that simple cell division produces growth and results in an

increase in size. Describe how competition for water, nutrients, light

and space can influence growth. Describe two examples of how auxin influences

plant growth. Describe what is meant by the term phototropism. Define the term: ‘photoperiodism’.

Term Dates

Happy Christmas! Classes start again on the 13th

January Happy homework!