Cell Biology- Cell Transport Flashcards
What is diffusion?
The net movement of particles from an area of high concentration to low concentration down a concentration gradient until equilibrium is met
What factors affect the rate of diffusion?
Concentration gradient- the greater the difference in concentration, the faster the diffusion because move particles are randomly moving down the gradient than are moving against it
Temperature- higher temp means particles move more resulting in more collisions so faster rate of diffusion
Surface area of membrane- greater the surface area, the more space for particles to move through, resulting in faster rate of diffusion
Give examples of substances transported by diffusion in the lungs and the kidney
Lungs- oxygen diffuses into blood from lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient
Kidney- urea diffuses from cells into blood plasma so it can be excreted in urine
How are single-celled organisms adapted for diffusion?
They have a large SA to volume ratio- maximises the rate of diffusion of molecules to meet the organism’s needs. Due to their low metabolic demands diffusion across surface of organism it’s sufficient enough to meet its needs
Why can’t multicellular organisms rely on diffusion alone ?
Because they have a small SA to volume ratio so surfaces and organ systems have a number of different adaptions that allows molecules to be transported in and out of cells
How is surface area to volume ratio calculated?
Sa= number of sides X(length Xwidth)
V= length X width X depth
Ratio = SA:volume
Give examples of exchange surfaces
Lungs-oxygen and co2 is across across the surface of millions of air sacs(alveoli
Small intestine- digested food is absorbed over the membrane of villi cells into bloodstream
Fish gills- each gill has plates where gill lamellae are which is where diffusion of gasses takes place (oxygen-blood co2-water) blood flows in one direction whilst water flows in the other
Roots- adapted to take up water and mineral ions - have root hair cells with large surface areas which project into the soil
Leaves- co2 diffuses through stomata for photosynthesis while o2 and water vapour move out through them
What factors increases the effectiveness of a gas exchange surface/ how are they adapted?
Large SA-increases surface that particles can move across e.g lungs have millions of aveoli, small intestine has microvilli, fish gills have lamellae, leaves have flattened shape
Thin membrane- short diffusion pathway
In animals, efficient blood supply- maintains concentration gradient
Ventilation- kept moist so substances diffuse faster
What is osmosis?
The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
What is meant when a solution is isotonic to a cell?
The concentrations of the external and internal solutions are the same
What is meant when a solution is hypertonic to a cell?
The concentration of the external solution is higher than the concentration of the internal solution
What is meant when a solution is hypotonic to a cell?
The concentration of the external solution is lower than that of internal solution
What may happen when an animal cell is placed in a very hypotonic solution?
Water moves into the cell causing it to burst
What may happen when an animal cell is placed in a very hypertonic solution?
Water moves out of the cell causing it to shrivel up
How do plant leaves and stems remain rigid ?
Turgor pressure- water moves in by osmosis causing the vacuole to swell and the cytoplasm to press against the cell wall
