CELLULAR TRANSPORT

A sugar enters a cell by diffusion. Which of the following does not affect the rate of diffusion of the sugar?

• temperature

• cell surface area to volume ratio

• concentration of the sugar outside the cell

• oxygen concentration in the cell

Which of the following is true about active transport?

• it does not need energy

• it involves carrier proteins in the cell membrane

• it produces ATP

• it moves substances from a high to a low concentration

The girl sitting two rows ahead of you put on too much perfume this morning. Is this diffusion, osmosis or active transport?

• diffusion

• osmosis

• active transport

What is diffusion?

• The spreading out of particles in a solution or gas from an area of higher concentration to an area of lower concentration.
• The spreading out of particles in a solution or gas from an area of lower concentration to an area of higher concentration.

How is the rate of diffusion affected by higher temperature?

• Increases (particles have more kinetic energy so they are faster)
• Decreases (particles have less kinetic energy so they are slower)

How is the rate of diffusion affected by the size of the concentration gradient?

• Increases as the size of the concentration gradient increases. (the difference in concentration of a substance from another area - the greater the difference the greater the rate)
• Decreases as the size of the concentration gradient increases. (the difference in concentration of a substance from another area - the greater the difference the lower the rate)

How does the surface area of the cell membrane affect the rate of diffusion of substances in and out of the cell?

• Increases as the surface area of the cell membrane increases (because the bigger the surface area of the cell membrane, the more particles can move across it at the same time)
• Decreases as the surface area of the cell membrane increases (because the bigger the surface area of the cell membrane, fewer particles can move across it at the same time)

Give TWO examples of substances transported by diffusion in the body.

• Oxygen and carbon dioxide between blood and the lungs during gas exchange.
• Urea diffuses from cells into the blood plasma (urea is a waste product that is excreted by the kidneys)
• Mineral ions from soil to root hair cells

What is osmosis?

• The diffusion of water molecules from a dilute solution to a higher concentrated solution through a partially permanent membrane.
• The diffusion of water molecules from a concentrated solution to a lower concentrated solution through a partially permanent membrane.

How does osmosis occur?

• A dilute solution contains more water molecules than a concentrated solution. A partially permanent membrane only allows small molecules through such as water but larger molecules e.g. sugar cannot pass through.
• A dilute solution contains fewer water molecules than a concentrated solution. A partially permanent membrane only allows large molecules through such as water but larger molecules e.g. sugar cannot pass through.