Simple Diffusion`

[risingstar5]

which of the following is an example of simple diffusion through a membrane?

- the movement of H+ across the thylakoid membrane during photosynthesis
- the uptake of neurotransmitters by the postsynaptic membrane during the transmission of a nerve impulse
- the movement of oxygen in the alveoli across a cell membrane through the Na/K pump
- the movement of glucose across the body cell membranes and the cells of the liver, which stores it as glycogen

(i can't find the answer anywhere...)

[kiekyon]

simple diffusion, so
just pick the simplest one

[ajs]

- the movement of H+ across the thylakoid membrane during photosynthesis..........Active Transport (check the chemosmotic theory)

- the uptake of neurotransmitters by the postsynaptic membrane during the transmission of a nerve impulse........Simple diffusion

- the movement of oxygen in the alveoli across a cell membrane through the Na/K pump.....Oxygen moves by simple diffusion in the alveoli but not through the Na/K pump; this is a bit confusing.

- the movement of glucose across the body cell membranes and the cells of the liver, which stores it as glycogen.........Facilitated diffusion

[risingstar5]

oops... i misposted two of those

its either one of these

- the movement of oxygen in the alveoli across the epithelial membrane and into the bloodstream
or
- the uptake of neurotransmitters

[Poison]

The first.
Neurotransmitters are not taken by simple diffusion. They bind to the receptors and cause ion channels to open.

[ajs]

The first.
Neurotransmitters are not taken by simple diffusion. They bind to the receptors and cause ion channels to open.

Poison, the first is for sure not simple diffusion. Look up chemiosmotic theory

[Poison]

Movement of O2 is not simple diffusion? so what is it?
The movement is from high concentration to low.

Neurotransmitters bind to the membrane. If you are looking for a reference:

The neurotransmitters then diffuse across the synaptic cleft to bind to receptors. The receptors are broadly classified into ionotropic and metabotropic receptors. Ionotropic receptors are ligand-gated ion channels that open or close through neurotransmitter binding. Metabotropic receptors, which can have a diverse range of effects on a cell, transduct the signal by secondary messenger systems, or G-proteins.

From wikipedia:

http://en.wikipedia.org/wiki/Neurotransmitter

And I couldn't understand your point on chemiosmotic hypothesis. Can you explain please?

[kiekyon]

The first.
Neurotransmitters are not taken by simple diffusion. They bind to the receptors and cause ion channels to open.

agreed