Coordination in plants 2018

Coordination in plants 2018

1. Coordination and response Do they feel what we feel?

2. Coordination in plants 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?

3. Basic information about plant growth 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 greek word  which means to increase .

4. Lets try to understand how Auxins work from these experiments .

5. Why do plants grow bent to one side? 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.

6. Answer these questions, giving a reason for each of your answers. 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.

7. Phototropism: is the response of plants to light by growing towards or away from it. 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.

8. Gravitropism: is the response of plants by growing away from or towards gravity pull . Can you explain why and how this potted plant is growing as shown in the photo? The second photo shows several seeds that were allowed to germinate in different positions. Describe the pattern shown by the growth of both the shoot and root. Explain how is this behavior useful to a growing plant. .

9. Plant shoot and root tips produce auxins that diffuse to the tissue behind the tip. In a horizontal lying shoots cells more auxins will accumalate on the lower side of the shoot due to the pull of gravity. Cells that receive more auxins will grow faster causing the shoot to bend and grow upwards. This is response is called negative gravitropism . The same idea applies to horizontal roots but cells receiving more auxins will grow slower, causing the root to bend and grow downwards. This response is called positive gravitropism .

10. A clinostat or a rotating drum can be used to eliminate the effect of gravity. The seedlings or the potted plant is fixed to a surface that rotates slowly several times. The radicles as shown here by the diagram have grown horizontally. This can be explained by auxins never staying in one place for long, all cells have received the same amount of auxins . So all the cells grow at the same rate, thus the radicals grow straight.