Cell membranes Flashcards
Facilitated diffusion
Channel/carrier proteins
Large/polar molecules
Complementary to substrate
Net movement of particles down a concentration gradient
Passive process
Aquaporins are protein channels that allow water to pass through the membrane
The cell membrane
Selectively permeable
Role of cholesterol
A lipid found within the bilayer
Not found in bacterial cell membranes
Make the membrane more rigid
Maintains shape
What affects the permeability of cell membranes
pH affects structure of enzymes and proteins
Buffer solutions can be used to control pH
Solvent concentration
The phospholipid bilayer is more permeable in acidic conditions
High temperatures increase permeability
Investigating cell membrane permeability
Beetroot often used because of coloured pigment
Use cork borer to collect samples of uniform diameter
Rinse in cold water to remove excess pigment that may have been released from broken cell membranes
Prepare dilution series of ethanol and distilled water
Place in test tubes for 10 minutes
Remove discs
Calibrate colourimeter using a cuvette of distilled water
Measure the absorbance of each solution
Plot a graph of concentration and absorbance
What is diffusion
The net movement of particles from an area of high to low concentration
It’s passive
What is a carrier protein
When a substance binds to a carrier protein it changes shape allowing the molecule to pass through
Factors affecting diffusion
The concentration gradient - the bigger the concentration gradient the fast the rate of diffusion
Higher temperature results in higher rate
The larger the surface area of the membrane the faster the diffusion rate
The thicker the exchange surface the slower the rate
The number of channel or carrier proteins
What is osmosis
The diffusion of water across a partially permeable membrane from a high (dilute) to low (concentrated) water potential
A partially permeable membrane allows water to pass through but not substances dissolved in water
The lower the water potential gradient the slower the rate of osmosis
What is active transport
Requires energy (ATP)
Movement of ions and molecules against a concentration gradient
Uses carrier proteins
Affected by surface area and number of carrier proteins
What is co-transport
Glucose and amino acids into the epithelial cells in the ileum
Sodium binds to sodium-glucose co transporter proteins allowing glucose and amino acids to be actively transported
