Transport in Cells Flashcards

All 45 cards in this deck

What is diffusion?

The spreading out of particles of a substance in solution, or of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.

What is meant by 'net movement' in diffusion?

Particles move in both directions, but overall more move from the higher concentration to the lower concentration.

Which two gases are exchanged by diffusion in gas exchange?

Oxygen and carbon dioxide.

Which waste product diffuses from cells into the blood plasma for excretion by the kidney?

Urea.

True or false? Diffusion requires energy from respiration.

False. Diffusion is a passive process; particles move down the concentration gradient without energy from respiration.

What is a concentration gradient?

The difference in concentration of a substance between two areas.

Name the three factors that affect the rate of diffusion.

The concentration gradient, the temperature, and the surface area of the membrane.

How does a steeper concentration gradient affect the rate of diffusion?

The rate of diffusion increases.

How does increasing the temperature affect the rate of diffusion?

The rate increases, because particles have more kinetic energy and move faster.

How does the surface area of a membrane affect the rate of diffusion across it?

The larger the surface area, the faster the rate of diffusion.

True or false? Particles stop moving across a membrane once the concentrations on both sides are equal.

False. Particles still move both ways, but there is no net movement.

How does a shorter diffusion distance (thinner membrane) affect the rate of diffusion?

The rate of diffusion increases.

What are the steps to calculate the surface area to volume ratio of a cube-shaped model organism?

e.g. a cube of side $2$ cm

1. Find the surface area: $6\times2\times2=24$ cm$^2$
2. Find the volume: $2\times2\times2=8$ cm$^3$
3. Divide surface area by volume and write as a ratio: $24:8=3:1$

What is the relationship between the size of an organism and its surface area to volume ratio?

As size increases, the surface area to volume ratio decreases.

Why can a single-celled organism rely on diffusion alone across its surface?

It has a relatively large surface area to volume ratio, so enough molecules can be transported in and out to meet its needs.

Why do multicellular organisms need exchange surfaces and a transport system?

They have a small surface area to volume ratio and long diffusion distances, so diffusion across the body surface is too slow to meet their needs.

List the four features that increase the effectiveness of an exchange surface.

Large surface area; thin membrane (short diffusion path); efficient blood supply (in animals); being ventilated (for gas exchange in animals).

How is the small intestine adapted for exchanging materials?

It is very long with villi and microvilli giving a large surface area, a thin wall and a good blood supply.

How are fish gills adapted for exchanging materials?

Many gill filaments covered in lamellae give a large surface area, with thin surfaces and a rich blood supply; water flows over them constantly.

How are plant roots and leaves adapted for exchanging materials?

Root hair cells give roots a large surface area for water and mineral ions; leaves are flat and thin with internal air spaces for gas exchange.

What is osmosis?

The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

What is a partially permeable membrane?

A membrane that lets small molecules such as water through but not larger solute molecules.

Which way does water move by osmosis when a cell is placed in a solution more concentrated than its contents?

Water moves out of the cell, so the cell loses mass.

True or false? In osmosis, water moves from a concentrated sugar solution to a dilute sugar solution.

False. Water moves from the dilute solution to the concentrated solution.

True or false? Osmosis only moves water molecules, not solutes.

True. Only water moves across the partially permeable membrane in osmosis.

Why does an animal cell burst in pure water but a plant cell does not?

Water enters both by osmosis, but the plant cell has a cell wall that withstands the pressure.

What are the steps of the required practical investigating the effect of salt or sugar solution concentration on plant tissue?

e.g. potato cylinders in a range of sugar solutions

1. Cut equal-sized potato cylinders, blot dry and record the starting mass of each.
2. Place one in each concentration of solution for the same set time.
3. Remove, dry the surface with a paper towel, reweigh and calculate the percentage change in mass.

In the osmosis required practical with potato in salt solution, what is the independent variable?

The concentration of the salt solution.

Why are potato pieces dried with a paper towel before being reweighed in the osmosis practical?

So that only the mass of the potato is measured, as surface liquid would make the mass higher.

Name two variables that must be controlled in the osmosis required practical.

Any two of: volume of solution, time left in solution, temperature, size/shape of the potato pieces.

On a graph of percentage change in mass against solution concentration, what does the point where the line crosses zero tell you?

The concentration of the solution equal to the concentration inside the plant cells, where there is no net movement of water.

What are the steps to calculate the percentage change in mass of plant tissue?

e.g. starting mass $2.5$ g, final mass $2.7$ g

1. Find the change in mass: $2.7-2.5=0.2$ g
2. Divide by the starting mass: $0.2\div2.5=0.08$
3. Multiply by 100: $8\%$ increase

Why is percentage change in mass used rather than change in mass in the osmosis practical?

The pieces may have slightly different starting masses, so percentages allow a fair comparison.

What is active transport?

The movement of substances from a more dilute solution to a more concentrated solution (against the concentration gradient), using energy from respiration.

Where does the energy for active transport come from?

From respiration (in the mitochondria).

How are mineral ions absorbed into plant root hair cells from very dilute soil solutions?

By active transport, against the concentration gradient, using energy from respiration.

Why do plants need to absorb mineral ions such as nitrate ions?

For healthy growth — e.g. nitrate ions are used to make amino acids and proteins.

How are sugar molecules absorbed from the gut when the blood already has a higher sugar concentration?

By active transport, against the concentration gradient; the sugar is then used for cell respiration.

True or false? Cells carrying out a lot of active transport usually contain many mitochondria.

True. Mitochondria release the energy from respiration needed for active transport.

Which of diffusion, osmosis and active transport can move a substance against its concentration gradient?

Active transport only.

Which transport process moves only water molecules?

Osmosis.

True or false? Osmosis and diffusion both require energy from respiration, but active transport does not.

False. Diffusion and osmosis are passive; only active transport requires energy from respiration.

Name the process by which water is absorbed into plant root hair cells.

Osmosis.

Which process moves oxygen from the air in the lungs into the blood?

Diffusion, down the concentration gradient.

True or false? In the osmosis required practical, a potato piece that gained mass must have been in a solution more concentrated than its cell contents.

False. Mass is gained when the solution is more dilute than the cell contents, so water moves into the cells by osmosis.