- Can endo/exocytosis happen down as well as against the concentration gradient?
Endocytosis is from high to low. Just think about when pathogens are endocytosed by phagocytes, the pathogens are going from a high to low concentration. Also think about when Amoeba organisms absorbed water in bulk in their watery environment, obviously from high to low concentrations. Also, exocytosis typically occurs from high to low concentrations, such as when production of antibodies from plasma B cells is occurring, the antibodies are being produced at a rapid rate inside the cell and accumulating, and the exocytose outside the cell into the tissue. However, this knowledge is not required for VCE, just know that endo/exo are active transport and require energy (ATP)
- Can large hydrophobic molecules pass through the membrane?
No, not directly through the membrane, they are too large and hence can puncture the plasma membrane. Instead, they can endocytose through the membrane. However, small hydrophobic molecules such as alcohol can indeed pass through via simple diffusion.
- How much do I need to know about glycosisdic bonds?
Just know that glycosidic bonds are the bonds between the monomers of polysaccharides.
- Are all mono and disaccharides soluble in water?
Yes
- Is it correct to say starch and glycogen are slightly soluble in water but cellulose is hydrophobic?
No, because polysaccharides such as glycogen, cellular and starch are in fact not soluble in water, they are all hydrophobic. This is due to their structure and size.
- Are steroids a type of hormone? If so then aren't hormones generally made of proteins?
Yes, steroids are a type of hormone, also known as lipid-based hormones. No, there are two types of hormones:
1. Lipid-based hormones (hydrophobic hormones)
2. Protein-based hormones (hydrophilic hormones)
- I read somewhere that secretion is not a good way to describe the exocytosis of proteins as it should only be used for the exocytosis of wastes. What would be a more appropriate term to use instead?
Secretion typically refers to the process whereby something is synthesised and released. For example when an endocrine gland produces a hormone and secretes it into the blood stream. So, only if the cell has for example produced a protein via the Rough ER, then you can easily say that the proteins were secreted or exocytosed, either is fine. However, if the cell is 'excreting' wastes, then that is the better term to use.
- Is the following correct answer to a SAC question:
- Osmosis the net movement of water molecules from an area of high concentration of solute to an are of low concentration of solute. It is correct, but osmosis is ALWAYS the movement of water molecules ACROSS A MEMBRANE. That is a vital part that you have missed, the membrane part.
- Simple diffusion is the net movement of particles from a region of low concentration to a region of high concentration. Incorrect, a better structured answer would be: Simple diffusion is the net movement of particles from a region of high concentration to a region of low concentration, going along the concentration gradient. Simple diffusion is a passive form of movement. Also, in your definition, you wrote that it goes from low to high, please do not confuse this with active transport, diffusion is always high to low.
- Active transport is the movement of molecules with the help of ATP. (I tried not to say against the concentration gradient because of bulk transport) I like your thinking about the concentration gradient, but unfortunately in VCE Biology, you must include that active transport is the transport against the concentration gradient. As I said above, you are right in saying bulk transport is indeed from high to low, but for VCE just assume that it is not.
- Are all polypeptides proteins?
For VCE, yes assume that. But in reality, polypeptides are amino acid linkages that are <50 amino acids, whereas proteins are >50 amino acids, so technically, polypeptides are not proteins.
- Is it true that all proteins have a teritiary structure?
Yes, all functional proteins have a tertiary structure, because this level of structure determines the function of the proteins.