Cell membranes and transport.

Question 1

Function of the cell membrane.

Answer 1

• Controls what enters and leaves the cell.
• Takes up nutrients and other requirements.
• Secretes chemicals.
• cell recognition (distinguishes neighbouring cells).

Question 2

Structure of the cell membrane.

Answer 2

DIAGRAM.
Extrinsic proteins.
Glycolipids.
Channel proteins.
Cholesterol.
Phospholipid= hydrophilic phosphate head facing outwards on each side of the bi layer, hydrophobic fatty acid tail facing inwards against the other tail in the middle of the bi layer, away from water.
Glycoprotein.
Carrier proteins.
Intrinsic protein.
Whole thing called a phospholipid bi layer.

Question 3

Functions of separate structure in the membrane.

Answer 3

Extrinsic proteins-
On either surface of the bi layer, provides structural support and forms recognition sites by identifying cells and receptor sites for hormones attachment, enzymes.
Intrinsic proteins-
Extend across both layers of phospholipid bi layer. Some are carriers, transporting water- soluble substances across and others allow active transport of ions across, by forming channels.
Glycolipids/proteins-
Projection formed from carbohydrates molecules (calyx). Attached to phospholipid= glycolipid cell –>cell recognition, hormone receptors.
Carb layer around membrane= glycocalyx.
Cholesterol (animal)-
Make membrane more ridgid/stable/ control rigidity.

Question 4

Fluid mosaic structure.

Answer 4

• Not joined or bound.
• Free to move around relative to each other.
• Different size proteins scattered throughout.
• Moving throughout in fluid motion (random protein distribution).

Question 5

Permeability of the membrane.

Answer 5

Lipid-soluble:
Vit A, small molecules can dissolve in the phospholipid and diffuse across the membrane.
Lipid-soluble molecules move through the cell mem more easily that water-soluble ones.
Water-soluble:
Glucose, polar molecules and ions.
Cannot readily diffuse through the phospholipids and must pass through intrinsic protein molecules.
These form water-filled channels across the membrane.
As a result, the cell-surface mem is selectively permeable to water and some solutes.
Aquaporins for water molecules (channel proteins).

Question 6

Simple diffusion definition.

Answer 6

Passive transport (no energy), high concentration to low concentration through phospholipid bi layer (down concentration gradient).

Question 7

Facilitated diffusion definition.

Answer 7

Uses transport proteins (channel and carrier). Down the concentration gradient (passive), large molecules &/or charged.
Rate is limited by number of transport proteins.

Question 8

Active transport definition.

Answer 8

Transport molecules across concentration gradient (low to high concentration).
Uses carrier proteins (only transport proteins that can change shape and push a molecule across the membrane).
Active process that requires energy (ATP).

Question 9

Facilitated diffusion process.

Answer 9

Pores lined with polar groups.
Channels can open and close depending on the cells needs.
The molecules attach to a binding site.
The carrier protein then changes shape to release the molecule on the other side of the membrane.

Question 10

Active transport process.

Answer 10

Molecule binds to the centre of the carrier protein.
Uses energy to change shape then deposit molecule on the other side of the membrane.

Question 11

Co-transport definition.

Answer 11

A type of facilitated diffusion by which 2 substances are simultaneously transported across a membrane by the same carrier protein.

Question 12

Co-transport process.

Answer 12

Sodium and glucose move into and bind to the carrier protein.
The carrier protein changes shape and releases sodium and glucose on the other side of the membrane.

Question 13

Factors affecting rate of diffusion.

Answer 13

-Larger surface area= greater rate of diffusion. More space for molecules to diffuse across the membrane.
Higher surface area:volume ration(higher)= higher rate.
-Concentration gradient:
Greater=greater rate of diffusion. More molecules on 1 side= more rapidly molecules move across membrane.
-Thickness of exchange surface/cell membrane/distance of travel which diffusion takes place:
Thinner membrane/shorter distance= more molecules diffuse in a given time/quicker/less distance/faster rate.
Higher temp=higher kinetic energy=higher rate of diffusion.
Smaller molecules=diffuse faster than larger molecules.
Fat soluble(non-polar)(no charge) molecules diffuse faster across the membrane than water-soluble(have charge).

Question 14

Fick’s law.

Answer 14

Rate of diffusion is proportionate to surface area(diff in conc)/thickness of gas exchange surface.

Question 15

Endocytosis definition.

Answer 15

• Bulk transport of substances into a cell.
• Active process that uses energy/ATP.
• Occurs when material is engulfed by extensions of plasma membrane and cytoplasm, surrounding it, making a vesicle.

Question 16

Phagocytosis definition.

Answer 16

• Uptake of solid material that is too large to be taken in by diffusion or active transport.
  More detail in notes.

Question 17

Pinocytosis definition.

Answer 17

• Uptake of liquid by the same mechanism, although the vesicles produced are smaller.

Question 18

Exocytosis definition.

Answer 18

• Process which substance may leave cell.
• After transported through cytoplasm in a vesicle.
• Which fuses with cell membrane.
• Digestive enzymes are often secreted this way.
  Process happens from the Golgi body.

Question 19

Things essential for all these to occur.

Answer 19

• Membrane has to change shape.
• Requires energy.
• Active processes using ATP from respiration.
  Fluidity is essential for these processes to occur.