PRELIMINARY STAGE 2023
St. Louis SHS: 52 points
Ola Girls SHS, Kenyasi: 28 points
St. Joseph SHS: 18 points
ROUND 4 - TRUE OR FALSE
PREAMBLE
A plasmolyzed cell can be de-plasmolyzed by:
1. Placing it in isotonic solution.
ANSWER: FALSE
EXPLANATION:
In an isotonic solution there is no net movement of water, so the cell stays plasmolysed.
2. Placing it in a saturated solution.
ANSWER: FALSE
EXPLANATION:
A saturated solution is strongly hypertonic, so the cell loses even more water.
3. Placing it in pure water or a hypotonic solution.
ANSWER: TRUE
EXPLANATION:
De-plasmolysis requires net water movement back into the cell, which only occurs in a hypotonic solution (or pure water) where the external water potential is higher than the cell's.
Isotonic solutions cause no net movement, and a saturated (hypertonic) solution would cause further plasmolysis.
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PRACTICE QUESTIONS
PREAMBLE 1
A plant cell placed in a concentrated sugar solution:
1. Loses water by osmosis.
ANSWER: TRUE
EXPLANATION:
The solution has a lower water potential.
2. May become plasmolysed.
ANSWER: TRUE
EXPLANATION:
The cytoplasm pulls away from the wall.
3. Bursts.
ANSWER: FALSE
EXPLANATION:
The cell wall prevents bursting; the cell shrinks.
PREAMBLE 2
A red blood cell placed in the given liquid bursts:
1. Pure water.
ANSWER: TRUE
EXPLANATION:
Water enters until the cell bursts (haemolysis).
2. Concentrated salt solution.
ANSWER: FALSE
EXPLANATION:
The cell shrinks and becomes crenated.
3. A very dilute salt solution.
ANSWER: TRUE
EXPLANATION:
Water enters by osmosis.
PREAMBLE 3
In a plasmolysed cell:
1. The cell membrane has pulled away from the cell wall.
ANSWER: TRUE
EXPLANATION:
The protoplast has shrunk.
2. The space between the wall and the membrane is filled with the outside solution.
ANSWER: TRUE
EXPLANATION:
The cell wall is fully permeable.
3. The vacuole is larger than normal.
ANSWER: FALSE
EXPLANATION:
The vacuole shrinks as water is lost.