Topic 3 - Movement in and out of a cell Flashcards
Diffusion
Diffusion is the movement of particles from an area of high concentration to an area of low concentration down a concentration gradient.** This process is positive - it does not require any energy.
Osmosis
Movement of water molecules from a high to a low concentration through a semipermeable membrane - it does not require any energy.
Active transport
Active transport is the movement of molecules or ions through a semi-permeable membrane against the concentration gradient, from an area of low concentration to an area of high concentration. This process is “active” because it requires the use of energy, which comes from aerobic respiration
The surface area:volume ratio problem
larger surface area = more rapid rate of diffusion
larger volume = larger quantity of materials needed
Surface area to volume ratio in an arctic fox
An organisms surface area to volume ratio influences the tendency to lose heat to the environment. Surface area to volume ratio is determined by an organisms shape. Explain
the reasons for the different shaped head of each fox described below: Arctic fox – Body temp = 37°C Environmental temperature = 0°C
Small ears, round head
Agar plates variables
Independent(what we change): Concentration of acid
Dependent(what we measure): Diameter of circle
Control(what we keep the same): Size of holes in plate, time
Small intestine -
What molecules are diffusing?
How are the structures adapted for diffusion?
The digestive food-from the food to our stomach
The villi are tiny finger shaped structures that increase the surface area. Some important parts in the villi are the wall just 1 cell thick, network of blood capillaries and internal structures called a lacteal.
Lungs and alveoli -
What molecules are diffusing?
How are the structures adapted for diffusion?
Oxygen- through our alveoli to our blood- to our whole body
Large surfaces area, thin walls, moist walls, permeable walls (always gases to pass through), blood supply system (oxygen away from lung CO2 to lung) and a large diffusion gradient (oxygen difference in our lungs and blood).
Fish gills -
What molecules are diffusing?
How are the structures adapted for diffusion?
Oxygen-from the water into the blood
Large surfaces area, blood capillaries, short distance required for diffusion and the gills are very efficient with ventilation
Plant roots -
What molecules are diffusing?
How are the structures adapted for diffusion?
Water- into a plant cell
Roots have hair cells like long fingers to extend the outer cell membrane and cell wall. Which increases the surface area available for water to diffuse into a cell
Plant leaves -
What molecules are diffusing?
How are the structures adapted for diffusion?
Carbon dioxide to diffuse into leaf through tiny pours
They have a spongy mesophylls layer inside to allow gases to move easily through the leaf, maintaining a steep concentration gradient. The leaf is very thin, creating a short diffusion pathway
How to calculated the % gain or loss in mass?
Final mass - initial mass = x
x
—————- =
initial mass
How can we determine osmosis?
This can be determined by measuring the change in mass and/ or length of the potato pieces. If the mass does not change then there has ben no movement of water and the solution is said to be isotonic – the same concentration as the potato.
Diffusion can be affected by:
Temperature: higher temperatures mean molecules have more kinetic energy, they mix faster and the rate of diffusion increases
- Surface area to volume ratio (SA:Vol): the larger this is the faster the rate of diffusion
- Concentration gradient: the greater the difference in
concentration (i.e. the ‘steeper’ the gradient) the faster
the rate of diffusion.
How can we test for diffusion?
Diffusion can be investigated using agar cubes
containing phenolphthalein. They change colour as acid diffuses in and this can then be measured to calculate a rate.
