Movement of Substances Into & Out of Cells Flashcards
All 18 cards in this deck
What is diffusion?
The net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient. It is a passive process.
Name two substances that move into or out of cells by diffusion.
Oxygen and carbon dioxide (also urea and some glucose).
State three factors that increase the rate of diffusion into a cell.
A steeper concentration gradient, a higher temperature, and a larger surface area of membrane.
True or false? Diffusion and osmosis are passive, so they do not need energy from respiration.
True. Only active transport requires energy from respiration.
What is osmosis?
The movement of water molecules from a dilute solution (high water concentration) to a concentrated solution (low water concentration) through a partially permeable membrane.
True or false? A red blood cell placed in pure water will shrink.
False. Water moves into the cell by osmosis, down the concentration gradient, and the cell bursts (lyses).
Why do plant cells not burst when placed in pure water?
They have a cell wall, which is strong/rigid and provides support; the cells become turgid as water enters the vacuole.
What happens to plant cells placed in a concentrated salt solution?
They lose water by osmosis through the partially permeable membrane, so they shrink, lose mass and become plasmolysed.
What is active transport?
The movement of substances across a membrane against a concentration gradient (from low to high concentration), using energy from respiration.
Which sub-cellular structure supplies the energy used in active transport?
The mitochondria, which release energy by respiration.
Give one example of a substance absorbed by active transport.
Mineral ions into root hair cells (also glucose absorbed from the small intestine into the blood).
What are the steps to investigate osmosis in potato tissue?
e.g. using distilled water and a concentrated sugar solution- Cut potato cylinders of the same size, blot dry and record the starting mass.
- Place one cylinder in each solution for the same time at the same temperature — e.g. one in distilled water, one in concentrated sugar solution.
- Blot dry, reweigh and work out the percentage change in mass.
What is the equation for percentage change in mass?
percentage change in mass = (final mass − starting mass) ÷ starting mass × 100
On a graph of percentage change in mass against solution concentration, what does the point where the line crosses the x-axis show?
The concentration at which there is no change in mass — it is the same as the concentration inside the potato cells.
In the potato osmosis core practical, why must each potato cylinder be blotted dry before it is reweighed?
To remove solution from the surface, which would otherwise add to the mass and make the mass change wrong.
True or false? Taking repeated readings at each concentration and calculating a mean makes the results of the potato osmosis investigation more reliable.
True. Repeats and a mean reduce the effect of anomalous results.
True or false? Starch and proteins can diffuse through cell membranes.
False. They are too large to pass through the membrane; only small molecules, such as glucose and oxygen, can diffuse across.
What is a partially permeable membrane?
A membrane that lets small molecules such as water pass through but stops larger ones such as sucrose.