Diffusion Vs Osmosis Vs Active Transport (gcse Biology)

A good understanding of diffusion, osmosis, and active transport is required to achieve the top marks, so here`s a breakdown filled with what you need to know for each one. There is a direct comparison between diffusion and active transport at the end

This is aimed towards AQA exam takers, but the notes will be useful for all GCSE students. Everything taken is from the specification, which can be found here: https://filestore.aqa.org.uk/resources/biology/specifications/AQA-8461-SP-2016.PDF

DIFFUSION:

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration until evenly distributed.

You must be aware of the factors that effect the rate of diffusion, as well as what adaptations organisms may have to increase their rate of diffusion.

Factors that effect the rate of diffusion are:

Concentration Gradient - the higher the concentration gradient between the two sides of the membrane, the greater the rate of diffusion

Temperature - The hotter it is, the more energy the molecules have so they move faster. This means the rate of diffusion increases

Surface Area - The greater the surface area of the membrane, the greater the rate of diffusion.

Adaptations of organisms for better diffusion:

Having a large surface area

A thin membrane, to decrease the diffusion distance

Having an efficient blood supply and being well ventilated (as this maintains a steep concentration gradient)

OSMOSIS:

Osmosis is the movement of water from a dilute solution to a concentrated solution across a partially permeable membrane.

That`s all you need to know for factual recall with osmosis, but you must also be able to calculate % change in masses as well as plot and interpret graphs related to osmosis.

ACTIVE TRANSPORT:

Active transport is the movement of substances from a dilute solution to a concentrated solution (against a concentration gradient), using energy from respiration.

Students should be aware that plants absorb minerals via active transport, and animals absorb sugar in the gut via active transport.

COMPARISON:

This is important as the specification explicitly says students should be able to compare diffusion, osmosis and active transport

1. Osmosis is the movement of water, while diffusion and active transport involve the movement of other molecules

The rest of the comparison will be between just diffusion and active transport

1. Diffusion occurs down a concentration gradient, Active transport occurs against a concentration gradient
2. Diffusion requires no energy, Active transport requires energy from respiration

I hope you understood everything in this article!! Remember, it`s very important to be very comfortable with all 3 of diffusion, osmosis, and active transport, as well as to remember everything in this article since questions get asked on these 3 topics almost every year. If you have any questions (about this article or any other questions) don`t hesitate to ask!!

Good luck!