D it allows all substances to enter & exit the cell.
The Geologic time scale makes it easier to see the age of rock layers
Answer:
1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
Explanation:
Stabilizing Selection
This type of natural selection occurs when there are selective pressures working against two extremes of a trait and therefore the intermediate or “middle” trait is selected for. If we look at a distribution of traits in the population, it is noticeable that a standard distribution is followed:
Example: For a plant, the plants that are very tall are exposed to more wind and are at risk of being blown over. The plants that are very short fail to get enough sunlight to prosper. Therefore, the plants that are a middle height between the two get both enough sunlight and protection from the wind.
Directional Selection
This type of natural selection occurs when selective pressures are working in favour of one extreme of a trait. Therefore when looking at a distribution of traits in a population, a graph tends to lean more to one side:
Example: Giraffes with the longest necks are able to reach more leaves to each. Selective pressures will work in the advantage of the longer neck giraffes and therefore the distribution of the trait within the population will shift towards the longer neck trait.
Disruptive Selection
This type of natural selection occurs when selective pressures are working in favour of the two extremes and against the intermediate trait. This type of selection is not as common. When looking at a trait distribution, there are two higher peaks on both ends with a minimum in the middle as such:
Example: An area that has black, white and grey bunnies contains both black and white rocks. Both the traits for white and black will be favored by natural selection since they both prove useful for camouflage. The intermediate trait of grey does not prove as useful and therefore selective pressures act against the trait.
Answer:
Active transport:
- requires energy
- molecules move from low to high concentration sides
- Na+ and K+ move by active transport
Simple diffusion:
- molecules move from high to low concentration sides
- molecules pass between lipids
- small non-polar and polar molecules
Facilitated diffusion:
- molecules move from high to low concentration sides
- involves channel proteins
- move large molecules
Explanation:
- Simple Diffusion is the pathway of only small molecules that freely move through the membrane by momentary openings produced by the lipids' movements. Diffusion is a slow process that requires short distances and pronounced concentration gradients to be efficient. An example of diffusion is osmosis by which water is the transported molecule.
- Facilitated diffusion is the transport of hydrophilic molecules that can not freely cross the membrane. Channel protein and many carrier proteins are in charge of this transport. When uncharged molecules cross the membrane, they do it according to their concentration gradients, going from the more concentrated side to the lower concentrated one. When ions need to cross the membrane, the process depends on an electrochemical gradient. Glucose is an example of a hydrophilic protein that gets into the cell by facilitated diffusion.
Simple diffusion and facilitated diffusion are both passive transport processes because they only depend on electrochemical gradients, so they do not need any energy to occur.
- Active transport is the transport of molecules that move against the electrochemical gradient, so it does need energy to happen. Molecules move from the lower concentration side to the higher concentration side of the membrane. Carrier proteins are in charge of active transport. The needed energy might proceed from the ATP molecules or the membrane's electric potential. An example of molecules moved by active transport are the Na and K.