Which diagram shows the correct direction of net water movement between the four cells due to osmosis?
A. 
B. 
C. 
D. 
▶️ Answer/Explanation
Ans: A
Water moves from higher (less negative) to lower (more negative) water potential. In option A, water correctly moves from -22 kPa (highest) to -40 kPa (lowest), with intermediate flows between -36 kPa and -33 kPa. Other options show incorrect flow directions against the potential gradient.
Agar cubes can be used to demonstrate the effect on diffusion of changing the surface area to volume ratio. Three different agar cubes made using a coloured indicator solution were placed into a dilute acid that diffused into the cubes. As the acid diffused into the agar cubes, the colour of the indicator solution changed. The cubes had volumes of 1 cm, 2 cm, and 3 cm and were left in the dilute acid for 10 minutes. All other variables were kept the same. After 10 minutes, the agar cubes were removed from the dilute acid and cut in half. The cut surfaces were observed, and the results were recorded as diagrams. All diagrams were drawn to the same scale. The results for the 2 cm cube are shown.
▶️ Answer/Explanation
Ans: C
The 1 cm cube has a higher surface area-to-volume ratio, allowing the acid to diffuse completely, resulting in a full colour change. The 3 cm cube has a lower ratio, so diffusion is slower and only partial colour change occurs in the same time. The 2 cm cube (shown) exhibits an intermediate change, supporting option C as correct.
The diagram shows how an artificial partially permeable membrane was used to separate a 5% sodium chloride solution and a 10% sodium chloride solution in a beaker.
The two sides of the beaker were labelled R and S.
Which row correctly describes and explains what will happen in the half of the beaker labelled S?
▶️ Answer/Explanation
Ans: A
Since side S has a 10% NaCl solution (higher concentration) and side R has a 5% NaCl solution (lower concentration), water will move from R (lower solute concentration) to S (higher solute concentration) by osmosis. This will cause the volume in S to increase, and the NaCl concentration in S to decrease as it becomes diluted. Thus, option A is correct.
Sodium ions can enter cells across the cell surface membrane.
Which methods could be used by sodium ions to cross a cell surface membrane and enter a cell?
▶️ Answer/Explanation
Ans: B
Sodium ions (Na+) are charged particles and cannot passively diffuse through the hydrophobic lipid bilayer. They enter cells via:
- Active transport (against concentration gradient, using ATP and carrier proteins).
- Facilitated diffusion (down concentration gradient, through channel or carrier proteins).
Simple diffusion is not possible due to their charge and polarity. Thus, B is correct.