Net movement of particles from an area of high to low concentration (down concentration gradient)
What does it mean by ‘net movement’?
Overall movement: particles can move in any direction, but generally speaking, most of the particles are moving in one particular direction, hence ‘net’ movement
State three factors that affect the rate of diffusion.
Concentration gradient, temperature, surface area
How does concentration difference affect the rate of diffusion?
Higher conc difference/Steeper conc gradient –> faster diffusion
Explain why a higher temperature results in faster diffusion.
More kinetic energy, particles move around more
Name a substance that diffuses into our cells for use.
Name a substance that diffuses out of our cells to be removed.
Carbon dioxide, urea
Name a structure in the body that is adapted to increase diffusion rate.
Net movement of water molecules down the water concentration gradient through a partially permeable membrane
A solution with a high water conc, but low solute conc
A solution with a low water conc, but high solute conc
What are partially permeable membranes?
Membranes that only allow some types of substances to pass through
What is an isotonic solution?
A solution with the same solute conc as the cell
What is a hypertonic solution?
A solution with a higher solute conc than the cell
What is a hypotonic solution?
A solution with a lower solute conc than the cell
If a cell is in a hypertonic solution, water will ___ (enter/leave) the cell.
If a cell is in a hypotonic solution, water will ___ (enter/leave) the cell.
What will happen to an animal cell if it is in a hypertonic solution?
Water leaves cell –> shrivelled
What will happen to an animal cell if it is in a hypotonic solution?
Water enters cell –> burst
Why do animal cells burst in hypotonic solutions?
No cell wall
What will happen to a plant cell if it is in a hypertonic solution?
Water leaves cell –> plasmolysed
What will happen to a plant cell if it is in an isotonic solution?
No net water movement –> flaccid
What will happen to a plant cell if it is in a hypotonic solution?
Water enters cell –> turgid
What does ‘plasmolysed’ mean?
The cell membrane becomes detached from cell wall
Why does the potato skin needs to be removed before putting the potato cylinders into the solutions?
Skin is impermeable
How do we calculate % change in mass?
(final mass - intial mass)/initial mass x 100
Define ‘active transport’.
Movement of particles against the concentration gradient (low to high) using energy in the form of ATP
Explain the importance of active transport in plants.
Root hair cells carry out AT to absorb mineral ions effectively in dilute soil
Explain the importance of active transport in animals.
Cells in gut lining does AT to absorb glucose effectively from the bloodstream
State one adaptations cells may have if they need to carry out active transport.
Lots of mitochondria for respiration for energy
How does active transport differ from diffusion and osmosis?
AT uses energy, D and O do not
State two differences beween diffusion and osmosis.
D: Any particles, does not need a membrane; O: Water specific, needs partially permeable membrane
State the relationship between size and surface area to volume ratio.
The bigger the size, the smaller the SA:V
Describe three adaptations of exchange surfaces.
Large SA, thin membrane/surface, ability to maintain high conc difference
How are alveoli adapted for efficient gaseous exchange?
Large SA, thin membrane (short diffusion distance), rich blood supply (maintain steep conc gradient)
How are plant roots adapted for efficient water and mineral absoprtion?
Large SA (root hairs), transpiration stream
How does stomata help maintain efficient gas exchange in leaves?
Allow gases to move in and out of leaf, maintaining steep concentration gradient