Topic 4.1 Cell transport mechanisms Flashcards
What are the 3 main types of passive transport?
- diffusion
- facilitated diffusion
- osmosis
Define passive transport
a transport that takes place as a result of concentration, pressure or electrochemical gradients and involves no energy from a cell
Define active transport
the movement of substances into or out of a cell using ATP produced during cellular respiration
Name the 3 active transport mechanisms
1) endocytosis
2) exocytosis
3) active transport
Define diffusion
the movement of the particles in a liquid or gas down a concentration gradient from an area of high concentration to an area of low concentration
Define facilitated diffusion
diffusion which takes place through carrier proteins or protein channels
Define osmosis
the movement of solvent molecules down a concentration gradient
Define endocytosis
the movements of large molecules into cells through vesicle formation, uses energy
Define exocytosis`
the movement of large molecules out of the cell by fusing the vesicle with the cell surface membrane, requiring ATP
What molecules are transported by facilitated diffusion?
- substances with strong positive or negative charges
- large molecules
Define osmotic concentration
a measure of the concentration of solutes in a solution that have an osmotic effect
What is an isotonic solution?
a solution in which the osmotic concentration of solutes is the same as that in the cells
What is an hypertonic solution?
a solution in which the osmotic concentration of solutes is higher than that in the cell contents
Define a hypotonic solution
a solution in which the osmotic concentration of the solutes is lower than that in the cell
Define pressure potential
a measure of the inward pressure exerted by the plant cell wall on the protoplasm of the cell, opposing the entry of water by osmosis. usually has a positive value
What is turgor?
the state of a plant cell when the solute potential causing the water to be moved into the cell by osmosis is balanced by the force of the cell wall pressing on the protoplasm
Define incipient plasmolysis
the point at which so much water has moved out of the cell by osmosis that turgor is lost and the cell membrane begins to pull away from the cell wall as the protoplasm shrink
What is plasmolysis?
the situation where a plant cell is placed in a hypertonic solution when so much water leaves the cell by osmosis that the vacuole is reduced and the protoplasm is concentrated and shrinks away from the cell wall
Define water potential
a measure of the potential water has to move out of a cell by osmosis
Define turgor pressure
a measure of the inward pressure exerted by the plant cell wall on the protoplasm of the cell as the cell contents expand and press outwards, a force which opposes the entry of water by osmosis
What is osmotic potential?
a measure of the potential of a solution to cause water to move into the cell across a partially permeable membrane as a result of dissolved solutes
Give the equation to determine water potential of a cell
water potential of cell= turgor pressure + osmotic potential
Is the value of osmotic potential always positive or negative
always negative
What happens when too much water enters an animal cell?
the cell bursts
What happens when too much water leaves an animal cell?
the cell shrivels
Which solution has the highest water potential?
pure water, value of 0
Which solution has the highest osmotic potential?
pure water
What is the trend in osmotic potential?
the greater the solute concentration of a solution, the lower/more negative the osmotic potential
What are carrier proteins?
proteins that move a substance through the membrane in active transport
What metabolic poison stops mitochondria from working?
cyanide
Define phagoctosis
the active process when a cell engulfs something relatively large such as a bacterium and encloses it in a vesicle
What is pinocytosis?
the active process by which cells take tiny amounts of extracellular fluid into vesicles
State the evidence for active transport (4 reasons)
1) active transport only takes place in living, respiring cells
2) the rate of active transport depends on the temperature and oxygen concentration. affecting the rate of respiration and production of ATP
3) many cells known to carry out lots of active transport contain large numbers of mitochondria- site of aerobic respiration and ATP production
4) poisons that stop respiration or prevent ATPase also stop active transport. e.g. cyanide prevents synthesis of ATP during respiration and active transport. however, if ATP is artificially added, active transport starts again
