Movement of Substances : Transport Processes Flashcards
what is diffusion?
- the random movement of particles from an area of high concentration to an area of lower concentration
why do all particles move randomly?
- all particles move randomly and in different directions all the time due to their kinetic energy
what does diffusion describe?
- the overall direction and speed of the movement
what is it called when over time, all of the particles will be equally distributed?
equilibrium
does equilibrium mean that the particles stop moving?
no!
describe the speeds and rates for diffusion and osmosis.
- diffusion and osmosis can happen at different speeds or rates
what are the four main factors which affect the rate of diffusion?
- temperature
- concentration gradient
- distance
- surface area : volume
how can temperature affect the rate of diffusion?
- at higher temperatures, molecules have more kinetic energy and so move faster
- therefore diffusion occurs faster
how does concentration gradient affect the rate of diffusion?
- if there is a very large difference in concentration between two areas, molecules will diffuse from the higher to the lower concentration quickly
- if the concentration gradient (difference) is small, diffusion will happen more slowly
how does distance affect the rate of diffusion?
- diffusion takes longer if the molecules have to travel further, molecules don’t travel in a straight line which slows the process
- therefore cells are small as smaller volume reduces distance
how does surface area: volume affect the rate of diffusion?
- a larger SA speeds up the rate of diffusion as there are more opportunities for the molecules to move, which is why surfaces such as alveoli in lungs are so large
- SA:V is more significant, as the two oppose each other: an efficient exchange surface has a surface area which is very large compared to the distance the molecules must travel
- SA:V is increased when structures are small
what do cells rely on for their function?
- diffusion
what is osmosis?
- a special type of diffusion
- it is only ever used to describe the movement of water molecules across a membrane
what is the definition of osmosis?
- osmosis is the net diffusion of free water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane
draw a diagram to represent and describe free water molecules.
one note page
draw a diagram to represent and describe partially permeable molecules.
one note page
what is water potential?
- a measure of the concentration of free water molecules in a solution
- pure water has a water potential of 0
- as a solute is added, water potential falls as there will be a lower concentration of free water molecules
- concentrated solutions have a very low water potential.
what are constantly moving in and out of cells?
- free water molecules
how do animal and plant cells react to being placed in different concentrations and why?
- they react differently
- this is because plant cells are placed in different solutions
what is an isotonic solution?
- when the solution outside the cell has the same water potential as inside the cell - no net movement
what is a hypotonic solution?
- when the solution outside the cell has a higher water potential then inside the cell - net movement of free water molecules into the cell
what is a hypertonic solution?
- when the solution outside the cell has a lower water potential then inside the cell- net movement of free water molecules out of the cell
draw a diagram to describe as to how an animal vs a plant cell would react in a hypotonic solution.
one note page
draw a diagram to describe as to how an animal vs a plant cell would react in an isotonic solution.
one note page
draw a diagram to describe as to how an animal vs a plant cell would react in a hypertonic solution?
one note page
what is active transport?
- active transport is used by organisms to transport substances against the concentration gradient
- in order to do this, the organism ends special carrier proteins in the cell membrane
- these use ATP to provide the energy to move the substances across the membrane against the concentration gradient
what is absorbed by active transport in the small intestine?
- glucose
how do plants use active transport?
- in their root hair cells
-to absorb mineral ions
define active transport.
- active transport is the movement of molecules from an area of low concentration to an area of high concentration using ATP
describe an experiment to demonstrate the relationship between surface area: volume ratio and the rate of diffusion.
- agar cubes of different sizes
- the cubes contain alkali and an indicator - they are placed in an acid
- as the acid diffuses into the cube it reacts with the alkali
- this neutralisation turns the indicator colourless
- the smallest (0.5cm length) cube becomes colourless quickest
describe an experiment to demonstrate the relationship between the concentration gradient and the rate of diffusion and osmosis.
- potato chips placed in sucrose or salt solutions of different concentrations
- osmosis will occur until the water potential of the tissue and the solution are the same
- which causes a mass change
- if the solution has a higher water concentration, water will move into the potato chip and the mass will increase
- if the solution has a lower water concentration, water will move out of the potato chip and the mass will decrease
- this method can be used to determine the water potential of the potato, if there is no change in mass, the concentration of the solution is the same as the concentration of the cytoplasm.
- by leaving the experiment for a short time , e.g. 20 minutes, you would be able to see that the potato chips in solutions where the concentration has the biggest difference to the cytoplasm will experience the biggest mass changes.
describe an experiment to demonstrate the relationship between concentration/temperature and the rate of diffusion.
- one note page
- visking tubing only allows small soluble molecules to pass through (e.g. glucose and water).
- therefore osmosis can occur
how else could you study the effects of osmosis?
- use thin sections of onion cells
- one note page
- the cells on the left are turgid - they are soaked in pure water
- the cells on the right are plasmolysed - they have been soaked in a concentrated salt or sugar solution
