Photosynthesis

[Primarygun]

How do carbon dioxide and oxygen diffuse into a leaf?

My book said that they first dissolve into a layer of water then diffuses into the cell membrane.

Why don't they just move into the cell ?

And is active transport only for those molecules which can pass through the cell membrane?

[Ophiolite]

How do carbon dioxide and oxygen diffuse into a leaf?

My book said that they first dissolve into a layer of water then diffuses into the cell membrane.

Why don't they just move into the cell ?

The cells are surrounded by water in the intercellular spaces. The gases have to dissolve in this water in order to enter the cells. The same water is exiting the plant through the stomates and evaporating. So, the evaporation controls the ascent of sap carrying minerals and other nutrients from the root system, and provides an entrance for gases into the cells.

That's it in a chloroplast. Is that what you were getting at?

[Guest HaReLdNkUmAr]

Osmosis

[Sorcerer]

Osmosis is the diffusion of water from a hypotonic solution to a hypertonic solution across a semipermiable membrane...... in this case then no, since we are dealing with O2 and CO2, not H2O......

 

From what I can remember its passive diffusion of the gases into the water through the stomata. O2 isn't so important for a plant because it is produced as a byproduct of photosynthesis, 6CO2 + 6H2O ------> C6H12O6 + 6O2..... from memory thats the basic equation, the oxygen comes from the splitting of water and the carbon dioxide is used to make the sugar.

[Firedragon52]

From what I can remember its passive diffusion of the gases into the water through the stomata. O2 isn't so important for a plant because it is produced as a byproduct of photosynthesis, 6CO2 + 6H2O ------> C6H12O6 + 6O2..... from memory thats the basic equation, the oxygen comes from the splitting of water and the carbon dioxide is used to make the sugar.

you got it, but don't forget the energy in the form of sunlight.

6CO2 + 6H2O + energy --> 6O2 + C6H12O6

http://www.wcsscience.com/photosynthesis/page.html

 

...I know I'm nitpicking...

[Sorcerer]

yeah, that goes over the arrow.......... hv /\/\/\/\->

 

Its way more complex that that anyway, it involves an electron transport chain and multiple intermediates.

[hyebeh]

well, the carbon dioxide and the oxygen will eventually have to be dissolved because most everything happens in an aqueous environment in life.

[Sorcerer]

The oxygen was never gaseous in the first place though.

[Primarygun]

Is there something to enchance the rate of oxygen gas into aqueous solution by the cell?

[Sorcerer]

The oxygen was produced in aqueous solution by the above reaction, if plants absorbed more oxygen from the air than they produced then we would all suffocate.

[Primarygun]

Which of the following is the least important for plant and oragnism?

Osmosis, diffusion , active transport.

[Sorcerer]

.....none......osmosis and diffusions are simply governed by the laws of physics, the plant uses active transport to counter these. All are necessary in order to maintain an offset equilibrim...... which is part of my definition of life.

[Primarygun]

I am not certain about the physical meaning in the osmosis.

I am quite confused with the word water potential .

[Ophiolite]

Imagine you have a container, divided in two by by an impermeable sheet. On one side of the sheet is fresh water, on the other side salt water. Nothing much happens. Now remove the sheet. Water molecules will now tend to move from the side where the concentration of water is highest - the fresh water - to the side where the water concentration is lowest - the salt water. In the same way the salt ions will tend to move from the area of high concentration (of ions) to the area of low concentration (of ions). After some time the concentration of ions will be the same throughout.

 

Now repeat the experiment, but with a sheet that is semi-permeable. In this case it will allow water molecules to pass through, but prevent the passage of salt ions. Both the water and the ions 'want' to cross the barrier, but only the water molecules can do so.

 

Water potential is a measure of how strongly the molecules 'want' to cross. The water potential is a way of quantifying that tendency. It is measured in pressure units. Water moves from a high water potential to a low water potential, Pure water has a water potential of 0, the highest possible, and all solutions have water potentials less than this.

 

Does that help make it any clearer?

[Primarygun]

Ya Certainly better.

I still have a question.

Isn't the pressure by the sugar solution area more than the pure water?

It has a higher density

[Sorcerer]

Hmm good question... not sure what the answer is, but heres a guess.

 

Water and sucrose solution are not the same, pressure is related to density only when the substance in question is constant. For instance if you compressed some water, thus increasing its density its pressure would increase also, but the comparison between the two solutions makes no sense.

[Primarygun]

Really troublesome question....

[MolecularMan14]

true, but I would assume what was stated in #16 where the substance would be diffused from an area of high concentration to that of a lower concentration. That's basically what diffusion is.

 

Edit** What the what?! this is post number 100,000?! crossing fingers for the arcade!

[Sorcerer]

Let me try again. If you compressed pure water you would increase its density and its pressure. If you compressed sucrose solution you would increase its density and its pressure. The density and the pressure of each of these solutions is therefore proportional.

 

However if you have two solutions and they are both of different densities and they contain different substances the proportional property of density to pressure is lost, this property only holds when the substance is kept constant.

 

For instance mercury and water are both at the same pressure, 1 atm, but mecury is more dense.

[Sorcerer]

Mind you I always hated physics.

[chadn]

How do carbon dioxide and oxygen diffuse into a leaf?

My book said that they first dissolve into a layer of water then diffuses into the cell membrane.

 

They do are "dissolved" into water via the PCR or photsynthetic carbon reduction cycle. Its also known as the C3 cycle. Maybe you've heard of C3 and C4 plants? The C3 or PCR cycle occurs in all higher plants, the C4 cycle simply has some additional steps that make it more efficient.

 

The gist of the PCR cycle is that CO2 enter through the stomata where it reacts with a 5-carbon molecule known as ribulose biphosphate (RuBP for short). This forms two 3-carbon acids called 3-phosphoglycerate (3-PGA for short), which are now part of the solution with water. 3-PGA is then converted to triose phosphate and used in other reactions throughout the cell.

[chadn]

Crap, this site doesnt have any edit options, that 1st sentence should be:

 

The CO2 is "dissolved" into water via the PCR ..........

[Sayonara]

You can't edit because you have not validated your account using the link in the email you received on signup.

[Primarygun]

Dissolve to form carbonic acid?

[chadn]

Dissolve to form carbonic acid?

 

Your words, not mine, hence the reason why I put quotation marks around the word dissolve. You said that your book says CO2 "dissolves" into a layer of water. Dissolve is not at all the correct word to use.