IIITn Diffusion Flashcards
Give 3 examples of molecules that diffuse
Some of the substances transported in and out of cells by diffusion are:
oxygen and carbon dioxide in gas exchange
urea from cells into the blood plasma for excretion in the kidney
How are the lungs in mammals adapted for exchanging materials?
Alveoli increase the surface area
The alveoli wall is only one cell thick (reduces the diffusion distance)
The lining of the alveoli is moist (to increase the diffusion of oxygen and carbon dioxide across the membrane)
Alveoli are covered in capillaries to ensure gases diffuse in and out of the blood efficiently
How do you calculate the volume of a cube?
volume = height x width x depth
remember to include the units e.g mm3 or cm3
Give 3 examples of molecules that can diffuse across cell membranes
Carbon dioxide
Oxygen
Carbon monoxide
Urea
How are gills in fish adapted for exchanging materials?
Gills have many gill filaments (to increase the surface area)
Gills are thin (to reduce the diffusion distance)
Gills have a good blood supply (to maintain a high concentration gradient)
Water continually runs over the surface of the gills (to maintain a high concentration gradient)
Give 4 ways in which the effectiveness of an exchange surface can be increased
- having a large surface area
- having a membrane that is thin,
- having a short diffusion path
- animals have an good (‘rich’) blood supply
- ventilating their gas exchange surfaces
Describe the pattern of movement of molecules that are diffusing
Random
How do you calculate the surface area of a cube?
Remember a cube has 6 faces!
The surface area of each face = height x width
If all faces are the same then multiply this by 6
If the faces differ in sizes i.e. it is an oblong rather than a cube 2 faces will have one surface area and 4 faces will have a different surface area
Remember to add units: e.g. mm2 or cm2
Define the term diffusion
The movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient across a partially permeable membrane i.e. from a concentrated to dilute solution. Diffusion usually occurs until an equilibrium is reached.
Give 3 factors that INCREASE the rate of diffusion
LARGER difference in concentrations (STEEPER concentration gradient)
HIGHER temperature
INCREASED surface area of the membrane
DECREASED the diffusion distance
Why can’t multi-cellular organisms use diffusion to obtain their nutrients and remove their wastes?
They have low surface area to volume ratios
The speed of diffusion is too slow to meet their nutrient demand - hence they develop a specialised circulatory system
How is the surface area to volume ratio (SA:volume) related to the size of an organism?
Large animals have a small SA:volume
Small animals have a large SA:volume
Single -celled organisms have a very large SA:volume
Is diffusion an active or passive process?
Passive - it does not require any energy input
The molecules that diffuse possess kinetic energy and this causes them to move
Label the diagram
