taxes and kinesis

Give three examples of tropisms plants have

Phototropism’s

Gravitropisms

Hydrotropisms

Define stimulus

A change in the external or internal environment of an organism

Define response

A conscious or unconscious reaction by an organism to a stimulus

Define receptor

A cell that requires signals from the stimulus and generate a response

Define kinesis

The random non-directional change in movement in an organisms response to a stimulus

Define taxis

The directional movements to a stimulus

Positive taxis means…

Towards the stimulus

Negative taxis means…

Away from the stimulus

Give the prefix for each stimuli- Light

Photo

Give the prefix for each stimuli- Water

Hydro

Give the prefix for each stimuli- Chemicals

Chemo

Give the prefix for each stimuli- Temperature

Thermo

Give the prefix for each stimuli- Oxygen

Aero

Give 2 differences in how shoots and roots respond to gravity and light (2 marks)

Shoots have positive phototropism while roots have negative phototropism

Shoots have negative gravitropism while roots have positive gravitropism

Explain how the plant shoots bend towards the sun as the sun moves across the sky

IAA diffuses towards the shaded side of the shoot

Increasing the concentration of IAA in the shaded side

This causes cells in the shaded side to elongate

Causing the plant to bend towards the sun

Shoots have positive phototropism causing them to bend towards the light.

Explain why and how roots grow downwards away from the light

IAA diffuses towards the shaded side of the root and inhibits cell elongation

This causes root cells on the light side to elongate more.

Causing the root to bend away from light.

This is negative phototropism.

Where is IAA found in?

The tips of roots and shoots

Explain how IAA promotes negative gravitropism in plant shoots (3 marks)

IAA diffuses from the upper side to the lower side of the shoot.

This causes the plant cells to elongate in the lower side and cause the shoot to bend upwards

Explain how IAA promotes positive gravitropism in plant roots (3 marks)

IAA diffuses to the lower side of the roots, inhibiting cell elongation in the cells on the lower side.

This causes cells in the upper side of the plant to elongate more.

This causes the root to bend towards gravity