Question

in developing countries, contamination of food and water from cholera is a serious problem. cholera is a disease caused by the bacterium vibrio cholerae. cholera causes severe diarrhea, which leads to the loss of large amounts of water per day. cholera works by releasing a toxin that attaches to the lining of the digestive system. this toxin causes the release of sodium and chloride ions into the intestinal lumen (space inside the intestines).

1. explain how the release of sodium and chloride ions leads to a loss of water from the body.
2. given that intestinal cells have sodium - glucose cotransporters, explain why doctors administer a sodium - glucose solution to patients recovering from cholera.
3. the image to the left illustrates a portion of a neuron. identify the process occurring in this image.

exocytosis

1. the image to the right illustrates a portion of a white blood cell. identify the process occurring in this image.

endocytosis

Explanation:

• Question 8: When sodium ($\text{Na}^+$) and chloride ($\text{Cl}^-$) ions are released into the intestinal lumen, they increase the solute concentration there. According to the principle of osmosis, water moves from an area of lower solute concentration (inside the body cells/tissues) to an area of higher solute concentration (intestinal lumen). So, water moves out of the body cells and into the intestinal lumen, leading to water loss from the body.
• Question 9: Sodium - glucose cotransporters in intestinal cells can transport sodium ions ($\text{Na}^+$) and glucose into the cells simultaneously. When doctors administer a sodium - glucose solution, the sodium ions can be transported into the cells along with glucose via these cotransporters. This helps to increase the sodium concentration inside the cells. Since water follows sodium (due to osmosis), it also helps in re - absorbing water back into the body, counteracting the water loss caused by cholera.
• Question 10: In the image of the neuron portion, the process is exocytosis. Exocytosis is a process where vesicles inside the cell fuse with the cell membrane and release their contents (such as neurotransmitters in neurons) outside the cell.
• Question 11: In the image of the white blood cell portion, the process is endocytosis. Endocytosis is a process where the cell membrane invaginates (folds inwards) to engulf substances (such as pathogens in the case of white blood cells) and form vesicles inside the cell.

Answer:

• Question 8: Water moves out of body cells (by osmosis) into the intestinal lumen (due to higher solute concentration from $\text{Na}^+$ and $\text{Cl}^-$), causing water loss.
• Question 9: Sodium - glucose cotransporters take in $\text{Na}^+$ and glucose. $\text{Na}^+$ uptake helps re - absorb water (as water follows $\text{Na}^+$ by osmosis).
• Question 10: Exocytosis
• Question 11: Endocytosis