Chapter 4 transport across cell membranes

Question 1

What is a cell surface membrane

Answer 1

It is a membrane that surrounds cells and is the boundary between cytoplasm and the environment

Question 2

What is the cell surface membrane made out of and what are the properties of this material that makes it suitable for the cell surface membrane

Answer 2

It is made from phospholipids and proteins forming a phospholipid bilayer The
Hydrophilic (water liking) head pointing inwards -> cell cytoplasm
Hydrophilic heads pointing outwards -> fluid which surrounds all cells

Question 3

What are the components of the fluid mosaic model

Answer 3

Phospholipids
Cholesterol
Intrinsic (integral)proteins
Extrinsic (peripheral) proteins
glycolipid/glycoprotein

Question 4

what are the functions of the cell surface membrane

Answer 4

To allow lipid soluble molecules to enter and leave the cell
Prevent water soluble molecules entering and leaving the cell
Make the membrane flexible

Question 5

what is the function of cholestrol in the cell surface membrane

Answer 5

Restrict movement in membraneto ensure that water and mineral ions cannot leak out of the cell at high temperatures.

Question 6

what is the function of glycoprotein in the cell surface membrane

Answer 6

They are made up of a carbohydrate covalently bonded to a protein.
act as recognition sites
helps cells to attach to eachother to form tissues
allows cells to recognise eachother (so lymphocytes dont attack the hosts cells)

Question 7

what is the function of glycolipid in the cell surface membrane

Answer 7

They are made up of a carbohydrate covalently bonded to a lipid.
act as recognition sites
helps cells to attach to eachother to form tissues
help to maintain the stability of the cell surface membrane

Question 8

What are the two types of proteins in a cell surface membrane

Answer 8

Intrinsic proteins and extrinsic proteins

Question 9

What are the features of extrinsic proteins

Answer 9

On the surface or only partly embedded in it
- Mechanical support to the cell
- Act as cell receptors (for molecules such as hormones)

Question 10

what are the features of intrinsic proteins

Answer 10

Intrinsic proteins:
Completely span the membrane
- Act as carriers to transport water soluble material across the membrane.

Question 11

Why is the cell surface membrane model described as fluid and mosaic

Answer 11

Fluid - the phospholipids can move relatiive to eachother
Mosaic - the proteins can vary in size and shape

Question 12

Picture of the fluid mosaic model of a cell surface membrane

Answer 12

Question 13

What is diffusion

Answer 13

Diffusionis the net movement of molecules from an area of higher concentration to an area of lower concentration.

Question 14

What is a concentration gradient

Answer 14

When the concentration of a particular molecule is greater in one area than another.

Question 15

What is the equation for ficks law

Answer 15

Rate of diffusion = (Surface area x concentration gradient)/ diffusion distance

Question 16

What is facilitated diffusion

Answer 16

Facilitated diffusion describes the passive transport of molecules across a membrane, with the help oftransmembrane proteins.

Question 17

When does facilitated diffusion occur

Answer 17

It occurs when a molecule cannot pass through the plasma membrane because of theirpolarity or charge.​

The transmembrane proteinsshieldthese molecules from the hydrophobic coreof the membrane

Question 18

What are the two types of intrinsic proteins

Answer 18

Channel and carrier proteins

Question 19

What is the difference between carrier and chanell proteins

Answer 19

Channel proteins only transport ions and molecules down the concentration gradient, which does not require any energy. Carrier proteins only consume energy to transport substances against the concentration gradient. No energy is used to transport substances down the concentration gradient.

Question 20

What is the defenition of osmosis

Answer 20

The passive movement of water from an area of less negative water potential to an area of more negative water potential across a partially permeable membrane

Question 21

What is water potential and what are the units

Answer 21

Water potential is a measure of how freely water molecules can move
The units are kPa and pure water has a water potential of 0

Question 22

What is an isotonic solution

Answer 22

Anisotonic solution=equalwater potential to that within the cell.

Therefore, water moves in both directions inside and outside of cell

Question 23

What is a hypertonic solution

Answer 23

Ahypertonic solution= more negative water potential outside the cell than inside.

Water moves out,shrinkingthe cell and making it shrivel up.

Question 24

What is a hypotonic solution

Answer 24

Ahypotonic solution= more negative water potential inside of the cell.

In animal cells -swellsup and can potentiallyburst.
In plant cells - maintains it in aturgidstate

Question 25

What is active transport

Answer 25

The movement of particles from an area of low concentration to an area of high concentration using a carrier protein and ATP

Question 26

What are the steps in active transport

Answer 26

ATP required
ATP binds to carrier protein
ATP is hydrolysed into ADP and releases energy
Allowing one carrier protein to change shape
Molecule can move through

Question 27

When is active transport used

Answer 27

Used for large or charged molecules such as glucose or urea

Question 28

What is co-transport

Answer 28

Using the concentration gradient of one molecule to drag through another molecule.
Two molecules moving through a transmembrane proteintogether.

Question 29

What are the steps in co-transport

Answer 29

1 Sodium ions are actively transported out of epithelial cells, by the sodium-potassium pump, into the blood. This takes place in one type of protein-carrier molecule found in the cell-surface membrane of the epithelial cells.
2 This maintains a much higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells.
3 Sodium ions diffuse into the epithelial cells down this
concentration gradient through a different type of protein carrier (co-transport protein) in the cell-surface membrane. As the sodium ions diffuse in through this second carrier protein, they carry either amino acid molecules or glucose molecules into the cell with them.
4 The glucose/amino acids pass into the blood plasma by facilitated diffusion using another type of carrier.