Let's go through each question one by one and solve them with explanations based on the principles of
osmosis and
cellular tonicity.
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Question 1:
> Based on this diagram below, what would happen to the shape of red blood cells if they were bathed in sea water that is rich in solutes or has a higher osmolarity than the cell itself?
Answer:
✔ d. They would appear shrunken or crenated
####
✔ Explanation:
- Sea water is
hypertonic relative to the inside of red blood cells (RBCs), meaning it has a
higher concentration of solutes than the cytoplasm of the RBC.
- In a
hypertonic solution, water moves
out of the cell by osmosis to balance the solute concentration.
- As water leaves the red blood cell, it
shrinks and becomes
crenated (shrunken and spiky).
- This is shown in the first diagram labeled
"Hypertonic", where water exits the cell (green arrows pointing out), and the cells look wrinkled/shrunken.
> 🔹 So,
option d is correct.
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Question 2:
> Based on this diagram, what would happen to the shape of the red blood cells if they were placed in pure tap water?
Answer:
✔ b. They would enlarge and potentially burst
####
✔ Explanation:
- Pure tap water is
hypotonic compared to the inside of red blood cells — it has
lower solute concentration.
- Water will move
into the cell by osmosis to equalize the concentration.
- The red blood cells absorb water and
swell up.
- Since RBCs
do not have a rigid cell wall (unlike plant cells), they can
burst when too much water enters — this process is called
hemolysis.
- This is illustrated in the
"Hypotonic" diagram, where water enters the cell (yellow arrows pointing in), and the cells swell.
> 🔹 So,
option b is correct.
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Question 3:
> How does water move across the cell membrane in osmosis?
Answer:
✔ b. Passive diffusion
####
✔ Explanation:
- Osmosis is the movement of
water across a selectively permeable membrane from an area of
low solute concentration to an area of
high solute concentration.
- It occurs
without energy input (i.e., no ATP required), so it’s a form of
passive transport.
- Water moves
down its concentration gradient through
aquaporins (water channels) or directly through the lipid bilayer.
- This is
not active transport, nor does it involve pumps (which require energy).
>
✘ Why not others?
> -
a. Active transport – requires energy; used for moving substances against their gradient.
> -
c. Through pumps – like Na⁺/K⁺ pump; these are active and not involved in osmosis.
> -
d. Active diffusion – not a real term; diffusion is always passive.
> 🔹 So,
option b is correct.
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✔ Final Answers:
1.
d. They would appear shrunken or crenated
2.
b. They would enlarge and potentially burst
3.
b. Passive diffusion
These answers reflect fundamental concepts of
osmosis,
tonicity, and
cellular membranes.
Parent Tip: Review the logic above to help your child master the concept of cell membrane and tonicity worksheet.
