This doc contains in-depth notes about the topic diffusion, osmosis and active transport, which can be found in the IGCSE CIE & Edexcel syllabus, as well as the GCSE AQA, Edexcel & OCR syllabus. You'll find info about the full process, including factors, as well as a past paper Q.
CAMBRIDGE IGCSE BIOLOGY 2021 EDITION
Movement into and out of cells – (CLASS NOTES)
DIFFUSION
DEFINITION : Diffusion is the net movement of molecules and ions from a region of higher
concentration to a region of lower concentration down a concentration gradient as a result of
their random movement.
IMPORTANCE OF DIFFUSION :
Diffusion is important for living organisms as this is the process by which gases such as
oxygen and carbon dioxide are exchanged between the organism and the
environment.
By this process, solutes dissolved in water such as mineral ions and food molecules
enter into organisms and waste products such as CO2 and urea are excreted from an
organism into the environment.
DIFFUSION IN CELLS :
Oxygen diffuses from alveoli into red blood cells by diffusion.
Digested food molecules from ileum in small intestine are absorbed by diffusion into
the blood stream.
In kidneys some solutes are reabsorbed into the blood stream by diffusion.
DIFFUSION IN PLANTS :
In photosynthetic plants CO2 diffuses through stomata into leaves and oxygen along
with water vapors produced during photosynthesis diffuses out of the leaf through
stomata.
FACTORS THAT INFLUENCE THE RATE OF DIFFUSION :
1. Surface Area : The greater the surface area, the faster the rate of diffusion, because
more area is exposed and vulnerable to the surrounding environment.
2. Temperature : An increase in temperature causes the increase in kinetic energy that
molecules and ions possess. This enables them to move faster, so the process of
diffusion speeds up.
3. Concentration Gradient : The difference in concentration is known as the
‘concentration gradient’. The bigger the difference in concentration of a substance on
either side of a membrane, the faster it will tend to diffuse.
4. Distance : In plant cells, the cell wall is thicker. Thus, the rate of diffusion is slower. In
animals, when oxygen diffuses from the alveoli into red blood cells, it has to travel
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