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.

What is meant by moving 'down a concentration gradient'?

e.g. oxygen moving from blood into a body cell

Moving from where the substance is more concentrated to where it is less concentrated.

e.g. oxygen moves from blood (high oxygen) into the cell (low oxygen).

Name three factors that affect the rate of diffusion.

The concentration gradient (difference in concentration), the temperature, and the surface area of the membrane.

True or false? Diffusion is the movement of particles in one direction only.

False. Particles move randomly in all directions; diffusion is the net movement down the concentration gradient.

True or false? Cooling a cell increases the rate of diffusion into it.

False. At lower temperatures particles have less energy and move more slowly, so diffusion is slower.

Name two substances that move into or out of animal cells by diffusion.

Oxygen (into the cell) and carbon dioxide (out of the cell). Urea is also accepted.

What is osmosis?

The net movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane.

True or false? A red blood cell placed in pure water will burst.

True. Water moves into the cell by osmosis down a concentration gradient, so the cell swells and bursts (lyses).

What happens to a plant cell placed in a concentrated salt solution?

Water moves out by osmosis through the partially permeable membrane, so the cell loses mass and becomes plasmolysed (shrinks).

What are the steps to investigate osmosis in potato tissue?

e.g. using sucrose solutions of $0.0$, $0.2$ and $0.4$ mol/dm$^3$

1. Cut potato chips of equal size, blot them dry and record the initial mass of each.
2. Place one chip in each sucrose concentration for the same time, keeping temperature and volume of solution the same.
3. Blot dry, reweigh and calculate the percentage change in mass for each concentration.

What are the steps to calculate the percentage change in mass of a potato chip?

e.g. initial mass $5.0$ g, final mass $6.0$ g

1. Change in mass = final − initial: $6.0 - 5.0 = 1.0$ g
2. Divide by the initial mass: $1.0 \div 5.0 = 0.2$
3. Multiply by 100: a $20\%$ gain in mass (a negative answer is a loss).

On a graph of percentage change in mass against sucrose concentration, what does the point where the line crosses the x-axis (0% change) show?

The concentration that is the same as the concentration inside the potato cells, so there is no net movement of water by osmosis.

What is active transport?

The movement of substances across a membrane against a concentration gradient (from low to high concentration), using energy from respiration.

Where does the energy for active transport come from?

Respiration in the cell (which takes place mainly in the mitochondria).

How do root hair cells take up mineral ions from the soil?

By active transport — ions move against the concentration gradient into the cell, using energy from respiration.

True or false? Root hair cells absorb water from the soil by active transport.

False. Water enters root hair cells by osmosis; only mineral ions are taken up by active transport.

Which of diffusion, osmosis and active transport are passive (need no energy from respiration)?

Diffusion and osmosis are passive and move substances down a concentration gradient; only active transport requires energy.

Give one example of active transport in the human digestive system.

Glucose is absorbed from the small intestine into the blood by active transport, even when the blood glucose concentration is higher.