Explain the general process of vision.
After light enters the eye it passes through the retina where there are light sensitive receptors (cones and rods). These receptors activate when hit by light. They then send signals down the optic nerve into the brain. The signals travel along a path through the lateral geniculate nucleus (LGN, a bundle of cell bodies located in the Thalamus) and terminate in the visual cortex (located in the occipital lobe of the brain). When the signal reaches the cell bodies in the visual cortex the neurons are activated and the brain processes the pattern of signaling into the image that reflected the light in the first place!
What is an Enzyme and why is it important?
An enzyme is a protein that exists within a cell. There are many types of enzymes and they are present in various cell types. An enzyme can be a small protein or a multi-subunit complex forming a large protein. Enzymes perform many functions in cells. They are important in lowering the activation energy of a reaction so it will occur more readily. Some reactions will not take place unless an enzyme is present to "catalyze" the reaction. Enzymes will not be altered from their original form during the reaction, at the end of the reaction they will return to the same state that they were in at the start.
Name two ways a molecule can travel across a cell membrane. Give specifics as to how and why such a molecule would use such mode of transportation.
1) Active transport. This form of transportation will take energy as the molecule will not readily cross the membrane (this can be due to size or charge of a molecule/ ion). A pump will be present in the membrane that will attach to the extracellular molecule and pass it through the lipid bilayer of the cell and into the cell itself. A common type of pump is the NA/K ATP-ase which uses ATP to pump potassium (K) into the cell and sodium (NA), this is a crucial pump in order for cells to create electrical gradients. 2) Passive transport. This form of transportation does not take energy. It does however require a channel in the membrane for a molecule to flow through. The molecule will flow through the channel due to concentration or electric gradients (the force causing these molecules to move is termed the electrochemical gradient).