Cell Processes and Transportation

Transport Across a Cell Membrane

There are two types of transport across a cell membrane: Passive Transport and Active Transport
Passive Transport: The movement of substances across the plasma membrane without the expenditure of energy (ATP)
- Requires a small amount of energy (Think of running downhill- there is less energy required because gravity makes it easier for you to run)
Active Transport: The movement of substances across the membrane ^^against^^ their concentration gradients. These processes ^^require the cell to expend energy (ATP)^^
- Requires a ^^larger amount^^ of energy (Think of running uphill- there is more energy required because you are working against gravity)

Passive Transport

There are three types of passive transport:
1. Diffusion: The movement of molecules from an area of high concentration to an area of low concentration (moves down the concentration gradient on its own)
  1. High to Low
2. Facilitated Diffusion: The movement of molecules from a high concentration to an area of low concentration with the help of membrane proteins (moves down the concentration gradient with help from a protein)
  1. Usually requires the help of integral proteins (channel and carrier proteins)
  2. High to low
3. Osmosis: The movement of water from an area of low solute concentration to an area of high solute concentration
  1. Water is still moving down its own concentration gradient (High to Low), but it moves up the solute concentration gradient (Low to High)
Concentration Gradient: A difference in the concentration of molecules across a space.
- Say there are more molecules of a substance in one place than another. Those molecules want to move to an area where there aren’t as many molecules of that substance. This movement is known as moving down a concentration gradient (High to Low). Moving in the opposite direction is known as moving up a concentration gradient (Low to High).
There are three types of osmosis:
1. Hypertonic: The solute concentration outside of the cell is higher than the concentration of solute inside of the cell
  1. Because the solute concentration outside the cell is greater, water starts to leave the cell to get to the solute outside. Because of this, the cells start to shrink and shrivel up.
  2. ==Crenation==: A hypertonic occurrence in an animal cell
  3. Ex. A ==freshwater== fish would not survive in a ==saltwater== environment because the water would start leaving the fish’s cells- this would cause the cells to shrivel up, killing the fish.
  4. %%Plasmolysis%%: A hypertonic occurrence in a plant cell
  5. When plants are placed in hypertonic solutions, the cell %%pulls away%% from the cell wall
  6. Ex. A strawberry becomes juicier when coated in sugar. This is because %%water is leaving the strawberry’s cells%% and shrinking them.
  7. Neither animal cells nor plant cells benefit from this process.
2. Hypotonic: The solute concentration inside of the cell is greater than the concentration of solute outside of the cell
  1. Because the solute concentration inside the cell is greater, water starts entering the cell to get the solute inside. Because of this cells can increase in size and burst.
  2. ==Cytolysis==: A hypotonic occurrence in an animal cell
  3. When too much water enters the animal cell, ==the cell can burst== due to the increased amount of pressure
  4. Ex. A ==saltwater== fish would not survive in a ==freshwater== environment because the water would start entering the fish’s cells- this would cause the cells to swell up, killing the fish.
  5. %%Turgor Pressure (Turgidity)%%: A hypotonic occurrence in a plant cell
  6. Slight pressure is put against the cell wall, but %%the cell does not burst%%.
  7. The plant cell %%appears “chubby” or swelled up%%
  8. Ex. When a flower is placed in %%pure water%%, it can stand up properly. This is because water is entering the plant’s cells, causing them to increase in size. If there is not enough turgor pressure, flowers can start to wilt.
  9. %%Plant cells greatly benefit%% from this process, but on the other hand, ==animal cells do not==.
3. Isotonic: The solute concentration is equal on both the inside and outside of the cell
  1. Because the solute concentration is equal, there is a net movement of water between the inside and the outside of the cell, and water moves in both directions.
  2. ==Equilibrium==: An isotonic occurrence in an animal cell
  3. %%Flaccid%%: An isotonic occurrence in a plant cell
  4. ==Animal cells greatly benefit== from this process, while %%plant cells remain neutral%%.

Active Transport

There are three types of active transport:
1. Exocytosis: The movement of substances ^^out of the cell^^
  1. Usually, this is the movement of ^^larger substances through vesicles^^
  2. These vesicles fuse with the plasma membrane and release their contents into the ^^external environment^^
2. Endocytosis: A process in which ^^cells ingest substances^^ from the external environment ^^with the help of energy (ATP)^^
  1. The cell membrane folds in, forms a pouch, and ^^pinches off to form a vesicle^^
  2. Phagocytosis: The movement of larger particles
  3. “Cell ^^Eating^^”
  4. Pinocytosis: The movement of fluids
  5. “Cell ^^Drinking^^”
3. Cell Pumps: “Pumps” that move substances ^^against their concentration gradient^^
  1. Substances bind to a carrier protein, which transports the substances across the membrane ^^with the help of energy (ATP)^^
  2. The best-known cell pump is the Sodium-Potassium Pump
  3. Most cells need a higher concentration of ^^sodium outside the cell^^ and a high concentration of ^^potassium inside the cell^^, which is why these pumps function to move around these substances as needed
  4. For every ^^three Sodium^^ molecules, there are ^^two Potassium^^ molecules (3Na:2K)
Vesicle: A small organelle that holds waste, food, and water. It is meant for transport but it is similar to the vacuole