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
What may happen when a plant cell is placed in aver hypertonic solution?
Water moves out of cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from cell wall, causing cell to become plasmolysed
What is active transport?
The movement of molecules from a low concentration to a high concentration, against a concentration gradient, using energy from respiration
How do plant root hair cells use active transport?
Root hair cells use active transport to take up mineral ions from a lower concentration in soils. Ions such as magnesium and nitrates are required for healthy growth
How is active transport used to absorb the products of digestion?
Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration
Diffusion can’t always be used as sometimes there can be a lower concentration of sugar molecules in the gut than the blood so active transport is required to move the sugar to the blood against the concentration gradient
Describe osmosis practical
-peel the potato as potato skin can affect osmosis
-use cork borer to produce 3 cylinders of potato with the same diameter
-use a scalpel to trim the cylinders to same length (3cm)
-measure length of each cylinder using a ruler and mass of each cylinder using a mass balance
- place each cylinder into a test tube
- add 10cm cubed of a 0.5molar solution into first test tube
- add 10cm cubed of 0.25molar solution to second test tube
- add 10cm cubed of distilled water into third test tube. Use distilled water as it contains no dissolved substances
-leave cylinders
-remove potato cylinders and gently roll them on a paper towel to remove any surface moisture
- measure the length and mass of cylinders again
-calculate percentage change of mass and length
What are the variables in the osmosis experiment?
Independent- concentration of sugar solution
Dependent- the percentage change in mass
Control- volume of sugar solution, time left in solution, temperature, type of potato
Why do u calculate the percentage change in mass in osmosis practical?
As the potato cylinders had different start masses
What does it mean when the mass of the potato doesn’t change?
The sugar solution is the same concentration as the cell so no water moves in or out of
Why did the mass of the potato cylinders decrease?
As water moved out of the cell by osmosis through a partially permeable membrane because the concentration of sugar solution is greater than the concentration of sugar inside cells. This is a hypertonic solution
Why did the mass of the potato not change when the experiment was repeated using boiled pieces of potato?
The partially permeable membrane was damaged
