Marine iguanas experience biggest problem as far as their diet is concerned. this is because 'they feed on sea plant that have high concentration of salts since plants living in this region are poor osmoregulators. in addition, when they are feeding, they may take in water which usually has high salt concentrations. to survive these harsh condition, marine iguana has salt gland located in the nostrils. these glands have several secretory tubules and each of the tubules has an epithelial lining with specialized cells that have the ability to transport salt from the body outside. to perform this function effectively, large amount of energy is required and as a result these cells have high numbers of mitochondria.
It's harder to find one of the many genes involved in a polygenic trait vs the only gene involved in a discrete trait.
When something needs to be transported against its concentration gradient, or a molecule is too big to simply diffuse through a membrane, active transport has to be used. So active transport requires energy (ATP).
Examples:
1. Antiport pumps: transport one substance in one direction while transporting another substance the other way. An example of this is the sodium-potassium pump.
2. Symport pumps - uses a substance that wants to move from an area of high concentration to low concentration and carries another substance against its concentration gradient. An example of this is the sodium-glucose transport protein
3. Endocytosis - large amounts of extra cellular fluid can be taken into a cell - needs ATP to bind proteins in the cell membrane and causes them to change their shape...which eventually causes the surrounding of the fluid to be brought in (a vesicle).
4.exocytosis - opposite of above
Ed happens because of Problems with blood flow
