Which type of protein uses energy from ATP to transfer particles across membranes against a concentration gradient?
Correct Answer: \( \boxed{\mathbf{B}} \)
Pump proteins carry out active transport, moving substances across the cell membrane from a region of lower concentration to higher concentration. This process requires energy released from the breakdown of ATP, allowing particles to move against the concentration gradient.
Which molecule is paired with the component of the cell membrane that allows it to pass through the membrane?
| Molecule | Component of the cell membrane | |
|---|---|---|
| A | Insulin | Aquaporin |
| B | Glycogen | Channel protein |
| C | Oestradiol | Phospholipid bilayer |
| D | Carbon dioxide | Pump protein |
Correct Answer: \( \boxed{\mathbf{C}} \)
Oestradiol is a lipid-soluble (non-polar) molecule, so it can move directly through the phospholipid bilayer by simple diffusion without requiring transport proteins. Small non-polar molecules readily cross the membrane because of its hydrophobic interior. This makes option C the correct pairing.
The table shows the concentrations of potassium and sodium ions found inside and outside human cells.
| Ions | Intracellular | Extracellular |
|---|---|---|
| Potassium | 135 | 4 |
| Sodium | 10 | 145 |
What process best explains how these ion concentrations are maintained?
