Hi all !
Could someone please explain to me electrochemical gradients (across the cell membrane)?
i don't understand it 
thankss 
If by electrochemical gradients you mean the processes of diffusion/facilitated diffusion, sure
Essentially, a substance will move from a region of high concentration to a region where it's low in concentration.
For example, imagine a cell surrounded by glucose molecules. Also imagine that the concentration of glucose outside of the cell (that is, the extracellular environment) is greater than the concentration inside the cell (that is, the intracellular environment). Now as you can imagine, there is now a difference in glucose concentrations between the inside and outside of the cell (or across the cell membrane, same thing really). This difference is called a
concentration gradient. When a concentration gradient exists, diffusion will inevitably occur.
Now, if we recall the definition of 'diffusion', we realise that glucose will move from its region of high concentration (outside the cell) to its region of low concentration (inside the cell). Hence, it will diffuse* across the cell membrane and into the cell, without the use of energy. Because of this, we say that diffusion is a passive process (does not require energy).
*To make things more confusing, glucose does not actually
simply diffuse across the cell membrane; rather it can only diffuse across a transmembrane protein embedded in the cell membrane. This is because glucose is a polar molecule, whereas the cell membrane (being composed of phospholipids) is largely non-polar. As polar substances can only dissolve in other polar substances, glucose cannot dissolve in the cell membrane and hence cannot cross it. The only molecules that can move across the membrane by
simple diffusion are small molecules such as H
2O and CO
2, as well as non-polar substances such as lipids, triglycerides etc.
Therefore glucose actually undergoes the process of
facilitated diffusion in order to pass through the plasma membrane. As this is also a form of diffusion, it too does not require energy. However, it does involve the use of transmembrane proteins such as channel proteins and carrier proteins.
I'll just end this here with a couple of definitions:
Diffusion: the movement of molecules from a region of high concentration to a region of low concentration, without the use of energy.
Facilitated diffusion: the movement of molecules from a region of high concentration to a region of low concentration, through specific transmembrane proteins (e.g. carrier/channel proteins) embedded in the cell membra
Actually have a couple of questions:
- Is there a neat list available somewhere of all the organelles visible through a light microscope?
Have you checked the notes section of AN? There are heaps of detailed notes that cover the entire course.
IIRC, the only organelles that cannot be viewed under a light microscope are ribosomes, Golgi body/apparatus/complex, smooth endoplasmic reticulum and lysosomes. But i think it really depends on the cell type.
- Does degenerate and redundant mean the same thing in relation to the nature of the genetic code?
Yes.
- Is parthenogenesis a form of sexual or asexual reproduction?
Asexual, although this is not required knowledge.
- What is the evolutionary reason in humans for 102 males being born every 100 females?
Not sure about this haha. Definitely don't need to know it.
Thanks
How much do we need to know about the actual structure and function of pathogens? I know we have to know quite a lot about the immune system but I'm not to sure how much we are required to know about e.g. bacteria or viruses ect...
You don't need to know much. Just the basic function (in the context of diseases and how they infect humans, to an extent) and in terms of structure, you'll need to be familiar with their appearance so as to recognise them in a question.
For example.
Bacteria:
-unicellular (usually)
-prokaryote
-no membrane-bound organelles
-no true nucleus
-single circular chromosomes
-can contain plasmids
-peptidoglycan cell wall
-has cell membrane
-asexual reproduction; binary fission
This is just a sample list.
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