Transport across Cell membrane

name the similarities between the diagram of a cell membrane and the fluid mosaic model (4)

• both have a phospholipid bilayer

• both have hydrophobic tails pointing inwards

• both have hydrophilic heads pointing outwards

• both have protein

name the differences between the diagram of a cell membrane and the fluid mosaic model (4)

• fluid mosaic has carrier and channel proteins

• fluid mosaic has cholesterol

• fluid mosaic has glycoproteins

• fluid mosaic has glycolipid

draw the fluid mosaic model

name how substances can move across the cell membrane

• simple diffusion

• facilitated diffusion

• osmosis

• active transport

• co-transport

what is the role of ATP hydrolase in a K+ NA+ pump (2)

• releases energy

• to allow ions to be moved against a concentration gradient via active transport

how does the movement of Na+ out of the cell allow the absorption of glucose into the cell (2)

• maintains a conc gradient for Na+ in the cell

• so Na+ moves in via facilitated diffusion and brings glucose with it

explain the features of a cell specialised for absorption (4)

• folded membranes to increase the surface area

• large number of carrier and channel proteins to increase the rate of absorption via active transport and facilitated diffusion

• large number of mitochondria to release ATP for active transport

• membrane-bound digestive enzymes to maintain the concentration gradient

describe how the movement of substances across cell membrane is affected by the membrane structure (7)

• phospholipid bilayer allows the movement of nonpolar substances

• phospholipid bilayer prevents movement of polar substances

• carrier proteins allow active transport

• channel and carrier proteins allow facilitated diffusion

• number of channel and carrier proteins determine how much movement

• membrane surface area determines how much movement

• cholesterol affects permeability of the membrane

how is ATP used in co-transport (3)

• hydrolysis of ATP

• changes the shape of the protein

• and causes the release of molecule

compare the processes by which water and inorganic ions enter the cell (3)

• both move down the concentration gradient

• both move through channels in the membrane

• ions can move against a concentration gradient via active transport

contrast the process of facilitated diffusion and active transport (3)

• facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins

• facilitated diffusion does not use ATP whereas active transport does

• facilitated diffusion is down a conc gradient whereas active transport is against a conc gradient

explain how glucose is absorbed by the ileum cells (4)

• Na+ leaves the cell to enter blood via active transport through the sodium-potassium pump

• therefore the conc of Na+ in cell is lower than outside of cell

• this maintains a conc gradient for Na+ to diffuse into the cell through a simporter via facilitated diffusion

• glucose absorbed with Na+ via the Na+ and glucose co-transport protein via facilitated diffusion

why is a fluid mosaic model called that (2)

• fluid because the phospholipids and proteins can move around via diffusion

• mosaic because there is a scattered pattern of proteins within the bilayer

What is the function peripheral proteins

• Provide mechanical support

• Can connect to proteins or lipids to make glycoproteins and glycolipids

• Cell recognition as receptors

What is the function of integral proteins

Protein carriers or channel proteins involved in transport

What are protein channels

Tubes that fill with water to enable water soluble ions to diffuse

What are carrier proteins

Bind with larger molecules and change shape to transport them to other side

Why do we say that the membrane is partially permeable

As lipid soluble substances and very small molecules can diffuse across the membrane but larger molecules and water soluble molecules cannot

Define isotonic

Water potential in solution is same as cell

Define hypertonic

Water potential of solution is lower than cells

How does active transport work in the phospholipid bilayer

• Transport through carrier proteins

• Molecules bind to receptor complementary in shape on the protein

• ATP binds to carrier protein from inside cell and is hydrolysed into ADP + Pi

• This causes carrier protein to change shape and release molecule out of the other side of the

• Phosphate ions is then released and protein returns to original shape

Define hypotonic

Water potential of solution if greater than cells