This document is a specification for the Pearson BTEC Level 3 National Extended Diploma in Applied Science. It outlines the content, structure, and assessment of the qualification, which covers key science concepts in biology, chemistry, and physics, as well as optional units covering topics such a...
Btec applied science unit 5 biology
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Unit 5 class notes- External
L/O-
Identify specific parts within a cell membrane
Explain the “Fluid mosaic model’ of membrane structure.
Link concentration gradients to a biological process
List key factors affecting the rate of diffusion
Define what facilitated diffusion is
Model of membrane structure
Lipids provide fluidity
Proteins give a patchwork (mosaic) appearance
Molecules move about
Question: Explain why the model for membrane structure is known as the fluid mosaic model (3
marks)
The membrane structure is known as the fluid mosaic model as the phospholipid molecules can
move freely and lipids provide fluidity. The proteins are distributed throughout the membrane in
evenly and in a mosaic pattern. The agreed structure is based upon experimental and chemical
evidence and so is classed as a model.
Channel Proteins-
Allows movement of some large, hydrophilic molecules directly across the membrane
The movement will be down a concentration gradient by diffusion.
Pores- allows a specific ion through
May be ‘gated’ open or closed
Carrier proteins-
Actively move substances across membrane (example-plant roots- use energy from ATP)
Specific shape to allow specific molecules to fit in
Changes shape to allow molecules across membrane
Diffusion-
Diffusion is a movement of molecules from a region of high concentration to a region of lower
concentration down a concentration gradient.
Diffusion occurs because the particles are free to move, so once they move due to kinetic
energy; The particles collide and start to spread out.
There is no energy from the cell needed.
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“Passive”.
Tendency to spread out away from high concentration if they are not contained.
Increasing the rate of diffusion-
1. Higher temperature for more kinetic energy)
2. Bigger concentration gradient for more molecules on one side of membrane)
3. Mixing (stirring) for more movement of molecules
4. Greater surface area – Red blood cells are biconcave, alveoli in lungs, microvilli in small
intestine
5. Shorter distance/ thickness
6. Smaller molecules
Particles that can diffuse
Lipid based molecules (Fat soluble, can diffuse through phospholipids including steroid
hormones)
Very small molecules and ions (such as CO2, O2 which fit between phospholipids and some
water will diffuse even though they are polar/charged).
Why do we have cholesterol in the membrane?
We have cholesterol as it reduces the permeability in the cell membrane.
More cholesterol means less movement of the phospholipid bilayer.
Provides some eukaryotic cell membrane stability- fits between fatty acid tails
Completes the hydrophobic barrier
Prevents water and ion movement
Learning objectives-
- Compare active transport with facilitated diffusion
- Draw Endocytosis and Exocytosis
- Recap Osmosis and apply new definition using Water potential
Active transport
Active transport is a movement of molecules or ions across membranes, using ATP to drive protein
‘pumps’- If substance is moved in opposite direction than it would move by diffusion or more quicker
than by diffusion, so for example- moving magnesium ion from soil against concentration gradient
by roots for chlorophyll manufacture.
Osmosis is a process which uses a spontaneous network of solvent molecules through a partially
permeable membrane from a less concentration solution to a more concentrated solution.
Solute is a component of a solution present in smaller amount than the solvent.
A solvent is a substance that dissolves a solute, resulting in a solution.
A solution is a mixture dissolved in another substance
‘Free’ water molecules
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