Transport in and out of cells Flashcards
What is diffusion?
The movement of particles in a gas or a liquid from an area of high concentration to an area of low concentration
What factors affect the rate of diffusion?
- distance
- surface area
- concentration gradient
- temperature
What increases the rate of diffusion?
- decreased distance
- increased surface area
- increased concentration gradient
- increased temperature
What are examples of diffusion?
- oxygen and co2
- urea
- food molecules
- oxygen and co2 diffusing during gas exchange in lungs, gills and plant leaves
- urea diffuses from cells into the blood plasma for excretion by the kidney
- digested food molecules from the small intestine diffuse into the blood
Why do single-celled organism have a relatively large surface area: volume ratio?
allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
Why do multicellular organisms need a transport system?
As size increases, SA/V ratio decreases.
surface area is no longer big enough to supply the needs of the body - needs to be sped up to move materials in and out of the organism
How are exchange surfaces adapted for maximised effectiveness?
- have a thin membrane, so substances have a short distance to diffuse
- large surface area so lots of a substance can diffuse at once
- Exchange surfaces in animals have a rich blood supply as it maintains the concentration gradient
- ventilation occurs too speed up gaseous exchange
- surfaces are moist - substances can dissolve and diffuse across cell membrane faster
How are alveoli are specialised to maximise the diffusion of O2 and CO2?
- enormous surface area
- moist lining for dissolving gases
- very thin walls
- a good blood supply
How are the small intestine specialised for the absorption of digested food.
- there are millions of villi which increases the surface area so digested food is absorbed much quickly to the board
- they have a single layer of surface cells
- they have a very good blood supply to assist quick absorption
How are the leaves in plants adapted to make photosynthesis happen easily?
- underneath the leaf is an exchange surface and covered with stomata where diffuses gases in and out
- flattened shape increases the surface area available to make diffusion more effective
- walls of the cell inside the leaf form an exchange surface
- air spaces (spongy mesophyll) inside the leaf increase the area available for gas exchange
How are the gills in fish adapted for the exchange in gills?
- each gill is made up of gill filaments which increases surface area for exchange of gases
- gill filaments covered in lamellae which further increases the surface area
- lamellae have lots of blood capillaries to speed up diffusion
- gills have a thin surface layer of cells which minimise diffusion distance
- blood and water flow in opposite directions through the lamellae which maintains a large concentration gradient between the water and the blood
- concentration of oxygen in the water is higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood
What is osmosis?
Diffusion of water molecules from a dilute to a more concentrated solution through a partially permeable membrane down a concentration gradient
What does a partially permeable membrane do?
Allows small water molecules to pass through but not large solute molecules
What happens when a red blood cell is placed in pure water?
Water moves into cell by osmosis and bursts
What happens when a cell is placed in a liquid the same concentration?
No net movement of water by osmosis
