OCR A-level Biology- biological membranes

what does it mean if a substance is hydrophilic

a substance that attracts water

what does it mean if a substance is hydrophobic

a substance that repels water

what is a phospholipid made of

a hydrophilic phosphate head and a hydrophobic fatty acid tail

what is the approximate thickness of a cell surface membrane

7-10nm

what is the role of cholesterol

to regulate membrane fluidity and allow fat soluble molecules to cross the bilayer

what is the role of glycolipids

to aid membrane stability and help cells attach to one another

what is the role of glycoproteins

to act as recognition sites and act as antigens

what is a channel protein

a protein that allows ions and small polar molecules to pass through pores in the membrane

what is a carrier protein

a protein that changes shape allowing larger molecules to pass through the membrane

what effect does increasing temperature have on a phospholipid bilayer and why

increasing temperature increases the kinetic energy of the phospholipids and breaks the weak intermolecular forces, additionally channel proteins denature, the permeability of the membrane increases

what is the effect of solvents on he membrane structure and why

solvents disrupt the bilayer causing kinks/bends by bonding to the components this increases permeability

what processes require the membrane to be fluid

diffusion of substances/fusing of membranes/cells moving and changing shape

what is dffusion

he net movement of particles down a concentration gradient

what is facilitated diffusion

diffusion across selectively permeable protein cannels within a plasma membrane

how does membrane thickness affect the rate of diffusion

an increased membrane thickness increases the diffusion distance and this decreases the rate of diffusion

how does SA:V ratio affect diffusion distance

an increased surface area to volume ratio increases the rate of diffusion

how does the concentration gradient affect the rate of diffusion

increasing the steepness of the concentration gradient the faster the rate of diffusion

how does temperature affect the rate of diffusion

increasing the temperature increases the kinetic energy of the particles causing them to vibrate more and increasing the rate of diffusion

what is active transport

the movement of ions/atoms from an area of lower concentration to an area of higher concentration, against a concentration gradient which requires energy in the form of ATP

what is bulk transport

the active transport of large molecules

what is endocytosis

the movement of a substance into the cell

what is exocytosis

the movement of a substance out of the cell

what is osmosis

the movement of water from an area of high concentration of water to an area of low concentration of water across a selectively permeable membrane

what is the water potential of pure water and the units

0Kpa

what happens when an animal cell is hypertonic

water moves out by osmosis and the cell becomes shrivelled

what happens when a plant cell is hypertonic

water moves out by osmosis and the cell becomes plasmolysed where the plasma membrane detaches from the cell wall

what happens when an animal or plant cell is isotonic

there is no net movement of water

what happens when an animal cell is hypotonic

water moves into the cell by osmosis and the cell bursts (lysis)

what happens when a plant cell is hypotonic

water moves into the cell by osmosis and it becomes turgid where the plasma membrane pushes against the cell wall