Transport across the Cell Membrane

Question 1

Define facilitated diffusion.

Answer 1

• Larger molecules and charged particles (ions) diffuse through carrier proteins across the cell membrane
• It is a passive process
• It occurs down a concentration gradient (high to low)

Question 2

How does a carrier protein aid facilitated diffusion?

Answer 2

• Larger molecules attach to the carrier protein
• The protein then changes shape
• The protein then releases the molecule to the other side
• Carrier proteins are specific and only facilitate the diffusion of one specific molecule.

Question 3

How does a channel protein aid facilitated diffusion?

Answer 3

• Channel proteins form pores in the cell membrane for charged particles to diffuse through
• Channel proteins are specific and only facilitate the diffusion of one specific particle across the membrane.

Question 4

Define active transport.

Answer 4

• When a molecule attaches to a carrier protein, the protein changes shape and releases a molecule to the other side.
• This happens against the concentration gradient (low to high)
• Energy, from ATP, is used to carry out this process (active process)

Question 5

How does ATP used in active transport?

Answer 5

• It is produced by respiration
• It is an immediate source of energy in the cell
• ATP is hydrolysed (broken down) in the cell and energy is released
• Energy released is used to move molecule against the concentration gradient.`

Question 6

Describe the process of endocytosis.

Answer 6

• Large molecules can be surrounded by cell with section of its cell membrane
• Membrane pinches off to form vesicle inside cell containing ingested substance
• This process requires energy from ATP

Question 7

Describe the process of exocytosis.

Answer 7

• Substances need to be released from the cell by secretion
• Vesicles containing substances pinch off sacs on the Golgi apparatus and move towards the cell membrane.
• Vesicle fuses to cell membrane
• Substance can be secreted outside the cell or into the cell membrane
• This process requires energy from ATP

Question 8

What cell uses the process of endocytosis?

Answer 8

White blood cells (phagocytes) ingest micro-organisms and dead cells in order to destroy them.

Question 9

What substances can be secreted using exocytosis?

Answer 9

Examples: Digestive enzymes, hormones and lipids