coordination in plants and invertebrates

Why is this plant growing to one side?

How would it benefit from this behavior?

What happens inside the plant to produce such a behavior?

Plants grow when the tips divide producing more cells then the cells start to elongate.

Plant cells produce a hormone-like chemical called Auxins that affect cell growth.

P.S. Auxin is a greekword which means to

increase.

Lets try to understand how Auxins work from these experiments.

1 , 2 and 3 are diagrams of the same plant shoot but at different times during the experiment.

Use this experiment’s result to figure what causes a shoot to grow to one side.

Which part of the shoot causes response to light?

Tip of shoot

If cut the shoot grows straight.

What is the nature of auxins?

Chemical.

It can diffuse through gelatin block, not through mica

What changes do they cause to plant shoot cells?

Grow faster, bent towards light.

As shown by Control, shoot covered by transparent cap and gelatin block.

When are auxins most active? light or dark?

In dark

When tip was covered grows faster.

Unlike animals plants respond slower, by growing, this is called tropism.

Growing towards light is positive phototropism while growing away is negative phototropism.

Shoots grow toward light to place their leaves in the best conditions for photosynthesis and their flowers for pollination and seeds for dispersal.

Roots grow away from light, to find soil to attach to, and absorb minerals and water.

Auxins stimulate growth of shoot cells, but inhibit growth of root cells.

.

Phototaxis,

chemotaxis and

hydrotaxis.

The response of small invertebrates by moving towards or away from light, chemicals and humidity.

A choice chamber is used to investigate invertebrate behavior towards light/dark conditions and humid/dry conditions.

Many woodlice are used to avoid errors due to chance, to get more reliable results.

Humid/dry

Dark/light

Invertebrates usually prefer moist conditions, can you explain why?

What word is used to describe that response?

To avoid drying out and to find food.

Positive hydrotaxis

Invertebrates usually prefer dark conditions. Can you explain why?

What word is used to describe that response?

To hide from predators, and avoid drying out.

Negative phototaxis.