Page 127 - Knowledge Organiser Yr9 24-25

Knowledge Base: Science B1: Cell Biology Year 9
6. Diffusion & surface area
6.1
What is diffusion?
The spreading out of particles of any substance in a gas or solution resulting in a net movement from an area of higher concentration to an area of lower concentration.
6.12
What is the benefit of single celled organisms having a large SA:V?
Sufficient transport of molecules into and out of the cell by diffusion.
6.13
Why do multicellular organisms require exchange surfaces and a transport system?
Small surface area to volume ratio, so cannot rely on diffusion alone.
6.14
Name four ways the effectiveness of an exchange surface can be increased.
• Having a large surface area.
• Thin membrane – to provide a short
diffusion path.
• Having an efficient blood supply
(in animals only).
• Being ventilated (in animals, for
gaseous exchange only).
6.15
Name four ways alveoli are specialised for diffusion.
Large SA (surface area), moist lining, thin walls, efficient blood supply.
6.16
Name two ways villi in the small intestine are specialised for diffusion.
Increased SA for quick absorption, efficient blood supply.
6.17
Name three ways leaves are specialised for diffusion.
Stomata for gas exchange, flattened shape, air spaces to increase SA.
6.18
Name four ways gills in fish are specialised for diffusion.
Filaments (large SA), lamellae (large SA), thin surface layer, blood flow.
6.19
Calculate the surface area of a cube with 1cm sides
SA = (length x width) x number of sides SA = (1cm x 1cm) x 6
SA = 6cm2
6.20
Calculate the volume of a cube with 1cm sides
Volume = length x width x height V = 1cm x 1cm x 1cm
SA = 6cm2
6.2 What is meant by net movement? The overall movement of particles.
6.3
What is meant by concentration gradient?
The difference in concentration between two regions.
6.4
Why is diffusion important to cells?
It allows substances to be transported in and out of cells.
6.5
Name two substances transported by diffusion in gas exchange.
Oxygen and carbon dioxide.
6.6
What is the name of the substance transported by diffusion from cells into blood plasma (for excretion in the kidney)?
Urea.
6.7
Name three factors which affect the rate of diffusion.
Difference in concentration (concentration gradient), temperature, surface area of membrane.
6.8
What effect will increasing the concentration gradient have on the rate of diffusion?
It will increase – due to the larger difference in concentration.
6.9
What effect will increasing the temperature have on the rate of diffusion?
It will increase- the particles have more energy so move around faster.
6.10
What effect will increasing the surface area of a membrane have on the rate of diffusion?
It will increase- more particles pass through at once.
6.11
Does a single celled organism have a large or small SA:V (surface area: volume ratio)?
Large.
6.21 Calculate the SA:V of the cube 6:1
6.22
Calculate the SA:V of a cube with 2mm sides, in its most simplest form
SA = (2x2) x6 = 24mm2 V = 2x2x2 = 8mm3
24:8 → simplified to 3:1
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