Plant Growth Substances

Hi have been given the following passage and questions to answer :

Synthetic auxins, such as 2,4-dichlorophenoxyacetic acid (2,4-D) have been used as weedkillers. This is useful because it is a selective herbicide which kills broad-leaved plants but not grasses.
Natural auxin (IAA) is actively transported into cells by a carrier protein molecule in the cell membrane and leaves the cells by facilitated diffusion through a different channel protein molecule. The importing protein will also work of 2,4-D. However the exporting protein cannot transfer 2,4-D back out of the cell.

What are the effects of auxins on root and shoot growth? (3 marks) - Done this.

Suggest how application of 2,4-D could kill a plant (3 marks)

Suggest an explanation for the selective action of 2,4-D (3 marks) - isnt this just whats quoted in the passage?

Explain how the structures of protein molecules enable channel proteins to be specific in the molecules which they allow through the membrane. (2marks)

Will be grateful for any help + will give rep.

Regards, Asad

Reply 1

iceman_jondoe

1. 2,4 D would increase the rate of cellular respiration and cause abnormal growth of internodes and rooting system, leading to death of the plant. It would soften the cell walls. The cells would become less turgid and take up more water, resulting in expansion of the cell. Due to the orientation of cellulose micro fibrils in the cell wall, cell elongation would occur in the longitudinal direction.
2. Selective action? well i know that auxins are absorbed much more effectively by broad-leaved (dicotyledonous) plants than by monocotyledons and are therefore particularly useful for removing broad-leaved weeds from monocotyledonous cultures such as lawns and wheat fields.

3. not sure what the last question is exactly saying...not sure if its referring to the hydrophillici properties of channels? allowing only water soluble substances to pass through

Reply 2

asadtamimi

Thanks a lot- tried repping you but it says i have to spreadmore reputation around before giving it to you again.

Sorry to bother you again but could you tell me where abscisic acid, ethene,auxins, gibberellins and cytokinis are produced. I have a table to fill in with their names, site of production and one main effect. I filled in all except site of production.

Reply 3

iceman_jondoe

Forgive my late reply as far as i am aware auxins are prodcued in the shoots and tips of plants and travel to OTHER areas of the plant to stimulate/inhibit growth,
The only info i have on gibberellins is that its from a fungus Gibberella fujikuroi growing on rice plants
Cytokinins are mostly extracted from seeds ( e.g. Zeatin from endosperm of maize/coconut ) where they seem to be involved in the growth of the embryo.
Ethene is a gas produced in small amounts by plants from the amino acid methionine.
Im not sure about abscisic acid..i THINK it might be produced in a similar way to auxins but dont quote me on it. Hope this helps :smile: