1. What is the main role of calcium ions in cell signaling?
A.
They act as a second messenger inside the cell
B.
They form the cell wall
C.
They store genetic information
D.
They digest proteins outside the cell
Correct Answer:
They act as a second messenger inside the cell
Explanation:
Calcium ions act as second messengers by carrying signals from activated receptors to target proteins inside the cell.
2. Which organelle is an important internal store of calcium ions in many animal cells?
A.
Nucleus
B.
Endoplasmic reticulum
C.
Ribosome
D.
Golgi vesicle
Correct Answer:
Endoplasmic reticulum
Explanation:
The endoplasmic reticulum stores calcium ions and can release them into the cytoplasm during cell signaling.
3. What usually happens to cytoplasmic calcium levels when a calcium signal is produced?
A.
They increase temporarily
B.
They remain permanently zero
C.
They become part of DNA
D.
They are immediately converted into glucose
Correct Answer:
They increase temporarily
Explanation:
A calcium signal commonly involves a temporary rise in cytoplasmic calcium concentration, which activates target proteins.
4. Which protein commonly binds calcium ions to help transmit a calcium signal?
A.
Calmodulin
B.
Hemoglobin
C.
Keratin
D.
Collagen
Correct Answer:
Calmodulin
Explanation:
Calmodulin binds calcium ions and changes shape, allowing it to regulate other proteins involved in cellular responses.
5. From where can calcium ions enter a cell to act as second messengers?
A.
The extracellular fluid
B.
The DNA molecule
C.
The cell wall only
D.
The nucleolus only
Correct Answer:
The extracellular fluid
Explanation:
Calcium ions may enter the cytoplasm from the extracellular fluid through calcium channels in the plasma membrane.
6. Why is a rise in cytoplasmic calcium useful for cell signaling?
A.
It can activate calcium-sensitive proteins
B.
It permanently stops all cell activity
C.
It destroys the plasma membrane
D.
It removes all proteins from the cell
Correct Answer:
It can activate calcium-sensitive proteins
Explanation:
Calcium binds to sensitive proteins such as calmodulin, helping start specific cellular responses.
7. What is the usual calcium concentration in the cytoplasm before a calcium signal?
A.
Relatively low
B.
Always higher than outside the cell
C.
Exactly equal to the concentration in bone
D.
Constantly increasing
Correct Answer:
Relatively low
Explanation:
Cytoplasmic calcium is normally kept relatively low, so a small increase can serve as a clear intracellular signal.
8. What helps remove calcium ions from the cytoplasm after a signal has ended?
A.
Calcium pumps
B.
Ribosomes
C.
DNA polymerase
D.
Cellulose fibers
Correct Answer:
Calcium pumps
Explanation:
Calcium pumps lower cytoplasmic calcium by moving calcium ions back into storage compartments or out of the cell.
9. Which event can directly trigger the release of stored calcium ions into the cytoplasm?
A.
Opening of calcium-release channels
B.
Copying of DNA
C.
Formation of a peptide bond
D.
Breakdown of the cell wall
Correct Answer:
Opening of calcium-release channels
Explanation:
When calcium-release channels open in an internal membrane, stored calcium ions enter the cytoplasm and act as a second messenger.
10. A temporary increase in calcium ions inside a cell can help regulate which type of process?
A.
Muscle contraction
B.
Formation of a bacterial capsule
C.
Digestion in the stomach lumen only
D.
Production of sunlight
Correct Answer:
Muscle contraction
Explanation:
Calcium ions can activate proteins that control muscle contraction, showing how calcium functions as an intracellular second messenger.
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