cell membrane exam qs

Question 1

why is the model known as the fluid mosaic model

Answer 1

• it’s fluid because the phospholipid molecules move around
• it’s mosaic as the proteins float among phospholipids

Question 2

Name and describe five ways substances can move across the
cell-surface membrane into a cell

Answer 2

(Simple) diffusion of small/non-polar molecules down a
concentration gradient;
2. Facilitated diffusion down a concentration gradient via
protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via
protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;

Question 3

Use your knowledge of transport across cell membranes to suggest how
NHE3 does this.

Answer 3

Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;

Question 3

The movement of substances across cell membranes is affected by
membrane structure. Describe how.

Answer 3

Phospholipid (bilayer) allows movement of nonpolar/lipid-soluble substances;
Phospholipid (bilayer) prevents movement polar substances
Carrier proteins allow active transport; allow facilitated diffusion
Cholesterol affects fluidity

Question 4

Compare and contrast the processes by which water and inorganic ions
enter cells

Answer 4

Comparison: both move down concentration gradient;
2. Comparison: both move through (protein) channels in membrane;
3. Contrast: ions can move against a concentration gradient by active
transport