2A- Exchange of substances

Completely made

Why is having a large surface area to volume ratio good?

Organisms that have a small surface area to v ratio require a further distance for gases to move and require a specialised system in order to provide adequate gas exchange

Name 3 features of an effective gas exchange surfaces

1. Large surface area (folded membranes in mitochondria)

2. Thin walls (capillary walls)

3. Steep concentration gradient (a good blood supply provides a constant flow of oxygen)

What is ficks law

What is the structure of a cell membrane?

• Phospholipid bilayer

• Glycoproteins and glycolipids

• Channel and carrier proteins

• Cholesterol

What is meant by the fluid mosaic model?

Fluid: the phospholipids can easily move around and embed new proteins

Mosaic: the random association of proteins within the membrane

Describe freeze-fracture

Freezing the cell membrane and then breaking it apart →fracturing it down the middle → results show smooth mosaic on inside.

Describe plant protein

Lectins are labelled with ferritin (visible under electron microscope) → showed membranes are asymmetrical

Describe mouse cells

• Fusing mouse cells with human cells, specific membranes were labelled

• 1 min after - protein in the same position

• 40 min - complete intermixing

• showed proteins diffuse through membranes and proved they’re fluid

What is facilitated diffusion

The movement of polar, particles from a high to lower concentration through a channel or carrier protein

Define active transport

The movement of particles from low to higher concentration which requires energy in the form of ATP, also requires a carrier protein.

What is endo/exocytosis?

Endocytosis: Cell membrane forms a vesicle and engulfs the molecule (proteins + lipids etc)

Exocytosis: Vesicle fuses with the cell membrane releasing the molecules (Enzymes + hormones)