Responses in plants

What is any condition that affects plant growth called?

A stimulus.

What is IAA?

An important auxin that's produced in the tips of shoots and roots in flowering plants.

What happens if there is a high concentration of auxins in shoots?

Auxins stimulate growth in shoots but high concentrations inhibit growth in roots.

How do plants respond to stimuli?

By regulating their growth.

How do plants increase their chances of survival?

By responding to changes in their environment.

What does this result in?

Different parts of the plant having different concentrations of IAA.

What are plants' growth affected by?

Environmental conditions.

What causes a plant to produce auxins?

Environmental stimuli like gravity, light and water.

What is the only auxin I need to know about?

Indoleacetic acid (IAA).

Why does it move and how?

It's moved around the plant to control tropisms; it moves by diffusion and active transport over short distances, and via the phloem over long distances.

What happens if the tip of a shoot is removed?

No auxin will be available and the shoots stop growing.

Where does cell division occur?

Only in meristems.

When do plants get taller?

Only when cells in meristems elongate following cell division. After this, cells differentiate into their final form.

Interpreting experimental data about IAA

Pages 76 and 77

What are the types of tropisms?

Phototropism, hydrotropism and geotropism.

Where are plant growth factors produced and where do they move to?

Produced in the growing regions of the plant, for example, shoot and root tips, and they move to where they're needed in the other parts of the plant.

Describe how shoots and roots show this?

Shoots are negatively gravitropic and grow upwards, whereas roots are positively gravitropic and grow downwards.

Describe how shoots and roots show this?

Shoots are positively phototropic and grow towards light, whereas roots are negatively phototropic and grow away from light.

What do plants use to respond to directional stimuli?

Specific growth factors; these are hormone-like chemicals that speed up or slow down plan growth.

What do plants need to grow?

Sunlight, air supply, water and mineral nutrients.

What is tropism?

The response of a plant to a directional stimulus (a stimulus coming from a particular direction). Or it's a growth movement in response to a stimulus.

What does this cause?

The uneven distribution of IAA means there's an uneven growth of the plant.

What are auxins and what do they control?

They are chemicals that diffuse from the growing regions of plants to other tissues and they control tropisms.

What are the differences between plant growth and animal growth?

- Many plants can continue growing throughout their lifetime. - Most plant growth occurs by cell elongation, not cell division. - Growth in plants only occur in certain tissues. - Many plant cells retain the ability to differentiate into any cell type. This is why cuttings can be used to create new plants.

Give some examples of this:

- They sense the direction of light and gravity towards it to maximise light absorption for photosynthesis. - They can sense gravity , so their roots and shoots grow in the right direction. - Climbing plants have a sense of touch, so they can find things to climb and reach the sunlight.

Give examples of this:

Example: phototropism IAA moves to the more shaded parts of the shoots and roots so there's uneven growth. Shoots: IAA concentration increases on the shaded side , cells elongate and the shoot bends towards the light. Roots: IAA concentration increases on the shaded side , growth is inhibited so the root bends way from the light. Example: gravitropism or geotropism IAA moves to the underside of shoots and roots , so there's uneven growth. Shoots: IAA concentration increases on the lower side , cells elongate so the shoot grows upwards. Roots: IAA concentration increases on the lower side, growth is inhibited so the root grows downwards.

What are the growth of shoots and roots controlled by?

Group of hormones called auxins.

What is a negative tropism?

Growth away from a stimulus.

What happens when auxins are produced in the shoots, how do they move and why?

Growth factors called auxins are produced in the tips of the shoots and diffuse backwards to stimulate the cell just behind the tips to elongate; this is where cell walls become loose and stretchy, so the cells get longer.

What is gravitropism (geotropism) ?

Growth of a plant in response to gravity.

What is phototropism?

Growth of a plant in response to light.

What is a positive tropism?

Growth towards the stimulus.

What do hormones produced by plants control?

Growth, flowering and fruit ripening.