4.2 Cell Transport Mechanisms Flashcards
why can gases diffuse directly into cells of small organisms?
they have short diffusion distance from outside and inside organs
large surface area to volume ratio
low metabolic demands
name the three chemical components of a cell
lipids- phospholipids and cholesterol
proteins
carbohydrates
how and why do bilayers form?
phospholipid bilayers form due to the hydrophobic tail of the phospholipid and hydrophilic head. this simple lipid bilayer allows fat, soluble organic molecules to pass through
why is it called the fluid mosaic model?
fluid lipid bilayer with a mosaic of proteins, glycoproteins and glycolipids floating on it
give the function of integral proteins
main transport system of membrane that can form permanent pores or other transport mechanisms (e.g carrier proteins)
give the function of peripheral proteins
can be enzymes that regulate transport
give the function of glycoproteins
often act as antigens- are important for cell recognition or act as receptors for hormones
name two things that proteins in cell membrane can do
form channels and carriers for passage of substances
can act as specific receptor molecules
give 4 key pieces of evidence for the fluid mosaic model
- monolayer of phospholipids is found to be 2x larger than cell surface area
- microscope images show proteins sticking out of cell surfaces
- some water-soluble substances pass in + out of cells- evidence of channels
- ionic + polar molecules do not pass through membranes but lipid-soluble molecules do
name the three types of passive transport
diffusion
facilitated diffusion
osmosis
describe active transport and give two examples
movement of substances across membrane of cells using ATP
e.g exocytosis- movement of large molecules through vesicle formation out cells
endocytosis - movement of large molecules through vesicle formation into cells
when would facilitated diffusion be used?
when specific substances like large molecules with strong charges need to be moved into the membrane down a concentration gradient
describe the process of facilitated diffusion
- amino acids are carried across the membrane in protein carriers of specific shape
- the protein carriers change shape + the molecule is passed into the cell
- the protein carrier returns to its original shape which allows more molecules to enter
what is a gated channel?
a channel that only opens when a specific molecule is present
does facilitated diffusion occur up or down a concentration gradient?
it can only occur down the concentration gradient
define osmosis
net movement of water molecules from an area of high concentration to an area of low concentration through a semi-permeable membrane
what is an isotonic solution?
solution with the same osmotic concentration as the cell
what is a hypotonic solution?
solution with a lower osmotic concentration than the cells so water moves in
what is a hypertonic solution?
solution with a higher osmotic concentration than the cells so water moves out
what happens if too much water enters a cell?
cell bursts - osmotic lysis
what happens if too much water leaves a cell?
cell shrinks - plasmolysis (in hypertonic solutions)
describe how pressure potential increases in a plant cell
the rigid nature of cellulose cell wall stops plant cells from bursting
if the surrounding fluid is hypotonic to the cytoplasm, water enters the cells via osmosis
as the cytoplasm swells, it generates hydrostatic pressure
the inward pressure of the cell wall on cytoplasm increases to oppose the entry if water - this is pressure potential
define turgor
state of a plant cell when solute potential that causes water to move into the cell by osmosis is balanced by the force of the cell wall pressing on the protoplasm
what happens when water leaves the cell?
turgor is lost and incipient plasmolysis occurs
define water potential
a measure of the potential for water to move out of a solution by osmosis
why does pure water have the highest water potential?
the water molecules will always move from pure water to any solution on the other side of the membrane
what is the maximum water potential (wP of pure water)?
0 - all other solutions will have a negative value for water potential because they have a lower concentration of water molecules
define osmosis in terms of water potential
net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
define turgor pressure
the hydrostatic pressure caused by cell contents pushing against the cell wall
how does turgor pressure increase?
- water moves into cell via osmosis and protoplasm swells
- as water continues to move into the cell, hydrostatic pressure is exerted by cell wall against cell contents
- turgor pressure increases until osmotic force pulling water into the cell is balanced by turgor pressure opposing entry of water
does turgor pressure have a positive or negative value? how can it be measured?
usually has a positive value
can be measured directly using a pressure probe
define osmotic potential
a measure of the potential of a solution to cause water to move into the cell across a partially permeable membrane
does osmotic potential have a positive or negative value? explain why.
pure water has the highest osmotic potential of 0 so all other solutions must have a lower osmotic value which is negative
define osmosis in terms of osmotic potential
net movement of water molecules from an area of high osmotic potential to low osmotic potential through a partially permeable membrane
when turgor pressure + osmotic potential are equal…
- cell is at full turgor
- water potential of cell is 0
give the equation to determine water potential of a cell
water potential = turgor pressure + osmotic potential
describe the role of ATPase in active transport
it catalyses the hydrolysis of ATP, breaking one bond and forming two more to provide energy needed by carrier in membrane or to release transported substances
name two things needed for active transport to occur
a carrier protein that spans the whole membrane
energy from ATP
define active transport
movement of substances into or out of the cell using ATP produced during respiration
describe the process of active transport
- proteins act as carriers that are specific to molecule being transported in one direction (against concentration gradient)
- release of energy from ATP hydrolysis causes change in carrier protein shape that moves molecules across membrane
- protein carrier returns to original shape to allow more molecules to enter
give 4 pieces of evidence for active transport
- only occurs in living cells
- rate of active transport depends on temperature and CO2 concentration
- cells that carry out a lot of active transport have lots of mitochondria
- poisons that stop respiration/prevent ATPase from working also stop active transport
give two similarities of endocytosis and exocytosis
- both are possible because of fluid nature of the membrane
- both are active processes, requiring energy from ATP
explain endocytosis
substance needed to be transported is englufed and move in by phagocytosis
explain exocytosis
intracellular vesicle fuses with cell membrane and ejects contents that need transporting