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If you have any questions or are uncertain about anything to do with the course, then this is the place to get help.
I will try and respond to your query as soon as possible, although I strongly encourage you all to try and answer each others questions first.


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biol 3 faq(nsfaq)


Q. what is the difference bettween exocytosis, endocytosis, endergonic and exergonic?
A. Both endocytosis and exocytosis are forms of bulk transport, that is movement of materials (either into or out of the cell) that are too big to pass through the cell membrane or protein channels. Endocytosis occurs when the cell forms a vesicle around an external substance which pinches off from the membrane and moves into the cells cytoplasm. Both phagocytosis and pinocytosis are examples of endocytosis. Exocytosis occurs when a vesicle formed within the cell fuses with the cell membrane and releases its content into the extracellular environment.
Endergonic is a term that describes a reaction that requires an input of energy to occur, e.g. reactions where larger molecules are built out of smaller ones (anabolic reaction). An exergonic reaction is one that has a net release of energy, e.g. a large molecule is broken down into smaller ones (catabolic reaction).
to summarize: endocytosis moves substances into the cell, exocytosis moves substances out of the cell. endergonic reactions use up energy and exergonic reactions release energy.


Q. also, what is the difference between phagocytosis and pinocytosis? (i get very confused)
A. The difference between pinocytosis and phagocytosis is that pinocytosis engulfs water and/or liquids from the extracellular fluid where as phagocytosis engulfs solids from the extracellular fluid. Both processes engulf substances from outside of the cell. However, pinocytosis is specifically the engulfing of fluids.

The above questions have been really well answered. GR, are you happy with these explanations? Just one other thing to be aware of in relation to endergonic and exergonic. Pretty much all reactions require some input of energy, so exergonic means that overall there is energy released as a result of the reaction whereas for endergonic, overall there is a an extra amount of energy needed. VM


Q.When the body has damaged tissue (due to injury- or something other than when the body is susceptible to bacterial infection) is inflammation triggered by the release of histamines still?
A. Yep, histamines are released and contribute to the process of inflammation. Other chemicals are also released such as cytokines. VM

Q. What is the production and differentiation between B cells due to?
A. "Due to"? Are you referring to what is the stimulus? If so, a particular B cell requires an interaction with a antigen that matches its immunoglobulin receptor. More importantly that B cell will only begin to clone itself (reproduce) and differentiate into plasma and memory cells when it gets a signal from a helper T-cell after it has bound to its matching receptor/antigen complex. VM

Q. What is polarisation/depolarisation referring to?
A. These two terms refer to the state of a neuron. In a resting state, the neuron is polarised. An action potential involves the nerve cell becoming depolarised. In other words, the resting state means the cytosol of nerve cell is negative with respect to the interstitual fluid. An action potential is generated when a stimulus being strong enough causes this to be reversed so that the cytosol (inside the cell) is now positive and the interstitual fluid (outside the cell) is negative. After the action potential has occurred the nerve cell needs to restore the resting conditions (ie become polarised again). Maybe the diagrams I have drawn below will help. VM
resting_neuron.pngexcited_neuron.png

Q. In regards to plants and stomata, are there stomata present for each group of plant cells? or; how else are they structurally organised?
A. Not sure what you mean by group of plant cells. Stomata are generally located on the underside of a leaf but also exist on the upperside and on stems. remember that stomata are not actual cells or structures but rather an opening created by a pair of guard cells changing their shape. VM

Q. What exactly is involved in blood clotting?
A. There are quite a number of things that can happen, if you go into blood clotting in detail. Given that it is in the study design under a dot point, this means you need to know something about it. So, you tell me what you know and I will repsond to that. VM

Q. Can steroidal hormones every be harmful to the cell in the way of switching genes on or off?
A. Not under normal conditions and everything is working as it should. Cells will not release hormones unless they are needed and sometimes the effect on a target cell could be to turn on or off a particular gene but this isn't harmful, otherwise it woudln't happen. It's only when things go wrong that responses can be harmful or if something else interferes with the normal functioning. VM

Q. It is my understanding that phagocytes are a type of WBC and that there are several different types of phagocytes. But wouldn't that mean that a phagocyte is the SAME as a white blood cell, or are there white blood cells that aren't phagocytes?
A. Phagocytes are WBC that can engulf substances (carry out phagocytosis) BUT not all WBC are phagocytes, eg the lymphocytes. VM

Q. I'm confused. When an allergen enters the body, Is it the release of histamine FROM mast cells which trigger an increased blood flow? or is it the release oh histamine TO mast cells which then trigger a release of another substance which results in increased blood flow?
A. When an allergen enters the body, antibodies to that allergen are produced and that's fine, nothing bad happens. But if the antibodies attach to mast cells, then the next time an allergen enters the body and attaches to the antibodies on the mast cell, the mast cell releases histamine which increases blood flow. So your first statement was right, histamine released from mast cells triggers increased blood flow. Jappelboom
Well answered, just remember that the histamine that is released by mast cells travels to the walls of the capillaries and causes vasodilation. VM

Q. A final clarification: Do T helper cells and B cells have receptors that fit with self cell markers - the MHC class 1 markers? Do they then interact with one and do nothing because it is recognised as self. A simple 'yes' will suffice if this is correct.
A. Ndio, oui, si, ano, ja, dah, ken. VM

Q. What do plant cells do in terms of exocytosis and endocytosis in relation to the cell wall. Do vesicles form like normal and just pass through the pores of the cell wall? Or does the cell wall surround the vesicle as well (don't think so, but not sure)?
A. As far as I know they also have these processes, the cell wall would not be part of them doing this. the cell wall has pores for substances to pass through and I would expect this is the case for exocytosis and endocytosis. I don't know of plant cells carrying out phagocytosis, as the cell wall would not allow this to happen and plant cells don't move around the plant, as they have no blood for them to move through. Plants cells have connections between them called plasmodesmata that allow substances to pass form one cell to another without actually leaving the cell. I will mention these next lesson. VM

Q. Is there any structural difference between globular proteins and fibrous proteins that enables them to be characterised into the two groups?
A. The main difference is that globular tend to be aqueous (ie water soluble) whereas fibrous are insoluble. This makes sense in that fibrous mainly form structural elements and therefore they need to be able to stay separate form water, otherwise they would just dissolve into it. VM

Q. Also, in regards to proteins in the cell membrane, i am under the impression that they fit within the globular protein category, but then the fibrous proteins are proteins which make up cell structure. So, is it a grey area or do these proteins fit into one definite category?
A. Yes you are right with your first statement. Fibrous proteins have a structural role in that they make up microtubules which form the cytoskelton fo a cell, or they form muscle contractile elements. Even though you could say, that the globular proteins are a structural component of a plasma membrane, their function is not structural but rather regulatory (ie assist certain substances to pass across the membrane). VM

Q. Is it worth knowing what microscopes do what. Light microscopes and electron microscopes and stuff like that. Should we know how powerful they are and what they pick up? Also i'mnot coming to period zero coz i have my hebrew oral in the morning and i need some shluff. jappel
A. it would be assumed knowledge and not directlty examinable.you should know that a light microscope doesn't provide the same detail as an electron microscope. to see most organelles in any detail requires an electron microscope. VM

Q. I'm doing a (stupid) TSFX exam (2009); A question asked what effect a decrease in CO2 levels (in the blood) would have on the pH. The answer is;
A decrease in carbon dioxide would cause the blood to become more acidic so there will be a decrease in pH. BUT, i was under the impression that INCREASED CO2 blood levels caused a decrease in pH (therefore being more acidic not more alkaline). Am i missing the point, or is the answer simply wrong?
A. This question should be put in the exam revision page. That page is designated for specifically dealing with any practise exam questions. Anyway, I think the exam is wrong and what you have written above is correct. VM

Q. Is chlorophyll not a protein?
A. I mentioned this in the course notes. It is not a protein. ie it is not made up of a chain of amino acids. It's chemical structure does not really fit into any of the four main groups we have looked at. VM

Q. Is there a second messenger when a steroidal hormone binds to a receptor in the cytosol? My guess is no.
A. And you are right. There is no need for one as the steroid hormone can bind with a receptor in the cell and that hormone-receptor complex can then directly lead to a cellular response. But be aware that just because there is no real second messenger there is still signal transduction involved. VM