Unit 3 - movement in and out of the cell Flashcards
(13 cards)
Define diffusion
The net movement of particles from a region of of high concentration to a region of low concentration, down the concentration gradient.
Give 2 examples of diffusion
Movement of carbon dioxide and oxygen in leaves
Movement of carbon dioxide in the alveoli of the lungs
Which 5 factors affect diffusion and how?
- Temperature increase - particles gain kinetic energy and therefore diffuse faster.
- Higher concentration gradient - causes rate of diffusion to increase because there is a larger difference between the two areas, therefore diffusion has more drive
- Distance increase - decreases rate of diffusion because the particles need to travel farther
- Surface area increase - increases rate of diffusion because there is more space for the molecules to diffuse across
- Molecular size - larger molecules take longer than small molecules because they move slower
- Number of particles/volume - more particles, longer to diffuse
How does sa:volume ratio affect rate of diffusion (experiment + method + variables)?
IV: sa:volume ratio of agar cube (cm^2 to cm^3)
DV: rate of diffusion (how much time it takes for agar cubes to turn transparent, minutes)
CVs: temperature, volume & concentration of acid
1. Get agar cubes (which contain sodium hydroxide & phenolphtalein indicator) of side length 0.5, 1 & 2cm
2. Fill a beaker with 100ml dilute HCL
3. Put agar cubes into beaker, making sure they’re fully submerged and start the stopwatch
4. Make sure the temperaure remains constant by meausuring it at the start & finish
5. Stop the stopwatch when agar cube turns transparent (time necessary for HCL to diffuse into each cube turning colour from pink to colourless) & record it
A shorter distance (center of the cube is farther away from the semi-permeable membrane when the cube has a larger volume) means an increase in rate of diffusion, and the larger the surface area, the more space for the molecules to diffuse across. This means that the object with the shortest distance aka smallest volume and the largest surface area will have the fastest rate of diffusion. In other words, the greater the sa:volume ratio, the faster the rate. In the agar cube experiment, it was the acid outside that diffused into the cube, as it was high concentration outside and low inside. The smaller cubes had a higher sa:volume ratio because their surface are only grew by 4x while the volume grew by 8x.
When does diffusion stop?
Diffusion will stop when the concentration of the substance is equal in both areas, though the particles are still moving back and forth, it’s just that there in no net movement.
Define osmosis
The net movement of water particles from an area of high water potential to an area of low water potential across a partially permeable membrane.
Experiment: If a potato is placed in different concentrations of blackcurrant squash, what will happen to it?
DV: percentage change in mass of potatoes (measured using digital balance, %)
IV: concentration of blackcurrant squash (measuring cylinder)
CVs: time in solution, volume of potato slices
1. Measure and pour 10ml of blackcurrant squash of 0%, 20%, 40%, 60%, 80% & 100% into different boiling tubes
2. Cut out some potato chips, making sure they have the same dimensions to maintain volume
3. Weigh them on a digital balance and record their dry/original weight
4. Place a chip in each solution and start a timer for 15 mins
5. Remove chips from squash and dry them
6. Weigh them again, calculate the percentage change of mass
Potato will gain mass because the water/low concentration of squash will travel through it’s membrane into its cells and fill them up because the water potential outside the potato cells was higher than inside. Considered a hypotonic solution due to higher water potential.
At about 60% concentration, squash is considered isotonic solution, because it has very similar concentration to potato slices. Above 60%, potato slices will lose mass because water will flow out of its cells (the squash is a hypertonic solution due to its water potential being lower thain in the potato cells)
Name the 3 states of plant cells depending on whether they’re filled with water
Turgid - the plant cell is stiff because it gained water through osmosis. Turgor pressure is acting on its inelastic walls. Both the vacuole and the cytoplasm grew in size.
Flaccid - plant cell is less stiff, no longer helps support the plant. It’s turgor pressure decreased because it lost some water by osmosis, which also caused its vacuole and cytoplasm to shrink.
Plasmolysed - when a plant cell loses too much the water, the cytoplasm may pull away from the cell wall. The plant will likely die then.
Example of where osmosis occurs and could be dangerous in animals
Red blood cells that gain too much water could swell and burst
State the 3 types of solutions based on water potential in cell vs solution
Hypertonic - solution has lower water potential than cell, meaning that water will flow out of cell (it will shrink & become flaccid/plasmolysed)
Hypotonic - higher water potential in cell than solution, so cell will swell and potentially burst.
Isotonic solution - same water potential inside & outside cell. There will be no net movement of water particles.
Define active transport
The movement of particles through a cell membrane from an area of low concentration to an area of high concentration. It requires the energy released from respiration to function. Goes against the concentration gradient
Give 2 examples of active transport
In plants, active transport is seen when root hair cells absorb more nitrate ions from the soil, even though their concentration there is lower than inside the cell.
In animals, active transport is seen in the movement of glucose from the intestines into the blood. To get as much nutrients as possible, glucose is moved by active transport into the bloodstream after it becomes lower in concentration in the intestines than there.
What 3 things are required for active transport to happen?
Energy from respiration, semi-permeable membrane and a protein
