Solved EXERCISE 4 REVIEW SHEET Cell Membrane Transport | Chegg.com - Free Printable

Let's go through each question step by step based on the content of the image and general principles of biology and osmosis.

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4. Sac 4: Sucrose and Congo red dye suspended in distilled water

- Was there net movement of dye out of the sac?
Yes, because Congo red dye is a large molecule that cannot pass through the semipermeable membrane, but if it was initially inside the sac and the membrane allows small molecules to move freely, then any leakage or diffusion would depend on the membrane’s permeability. However, typically, Congo red dye is not able to cross the membrane, so no net movement out — unless the membrane is damaged or the dye is broken down. But assuming standard lab conditions (e.g., dialysis tubing), the dye stays inside. So:

✔ No, there was no net movement of dye out of the sac.

- Was there net movement of sucrose out of the sac?
✔ No, because sucrose is a large molecule and cannot pass through the semipermeable membrane (such as dialysis tubing) used in these experiments.

- Explanation:
The semipermeable membrane allows only small molecules (like water and ions) to pass through. Both sucrose and Congo red dye are large molecules and are too big to diffuse across the membrane, so they remain inside the sac.

- Test used to determine the movement of sucrose into the beaker:
A Benedict’s test (or similar test for reducing sugars) could be used. If sucrose were moving out, it would hydrolyze into glucose and fructose (reducing sugars), which can be detected by Benedict’s reagent turning brick red.

But since sucrose itself is non-reducing, and doesn’t pass through, no color change would occur in the beaker, indicating no sucrose moved out.

- Direction of net osmosis:
Water moves from an area of lower solute concentration to an area of higher solute concentration. Inside the sac, we have sucrose and dye dissolved → higher solute concentration than distilled water outside.

Therefore, net osmosis is INTO the sac (water moves from the beaker into the sac).

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5. What single characteristic of the semipermeable membranes used in the laboratory determines the substances that can pass through them?

✔ Molecular size (or more specifically, pore size of the membrane). Only molecules smaller than the pores can pass through.

In addition to this characteristic, what other factors influence the passage of substances through living membranes?

- Charge of the molecule
- Solubility in lipids (lipid-soluble substances pass more easily)
- Presence of transport proteins (for facilitated diffusion or active transport)
- Concentration gradient
- Temperature
- Hydrostatic pressure

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6. A semipermeable sac containing 4% NaCl, 9% glucose, and 10% albumin is suspended in a solution with the following composition: 10% NaCl, 10% glucose, and 60% albumin. Assume that the sac is permeable to all substances except albumin. State whether each of the following will (a) move into the sac, (b) not move, or (c) move out of the sac.

Let’s analyze each substance:

- Glucose:
Sac: 9%
Outside: 10%
→ Higher concentration outside → glucose will move into the sac? No! Wait: Higher concentration outside → glucose will move into the sac? Actually, no — diffusion goes from high to low. So glucose will move OUT of the sac.

✘ (c) move out of the sac

- Water:
Water moves via osmosis. Total solute concentration:
- Inside: 4% NaCl + 9% glucose + 10% albumin = ~23%
- Outside: 10% NaCl + 10% glucose + 60% albumin = ~80%

→ Much higher solute concentration outside → water will move out of the sac (into the beaker)

✔ (c) move out of the sac

- Albumin:
Membrane is not permeable to albumin → cannot move

✔ (b) not move

- NaCl:
Sac: 4%
Outside: 10%
→ Higher concentration outside → NaCl will move into the sac?

Wait: Diffusion is from high to low. So NaCl will move into the sac.

✔ (a) move into the sac

But wait: Is NaCl permeable? The problem says the sac is permeable to all substances except albumin, so yes, NaCl can move.

So:

| Substance | Direction |
|---------|-----------|
| Glucose | (c) move out |
| Water | (c) move out |
| Albumin | (b) not move |
| NaCl | (a) move in |

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7. The diagrams below represent three microscope fields containing red blood cells. Arrows show the direction of net osmosis.

We have three diagrams: (a), (b), (c)

Assuming:
- (a): Cells swelling → water entering → hypotonic solution
- (b): Cells normal → no net movement → isotonic
- (c): Cells shrinking → water leaving → hypertonic

Now answer:

- Which field contains a hypertonic solution?
✔ (c) — cells shrink due to water loss

- Which cells in this field are said to be?
✔ Crenated (shriveled)

- Which field contains an isotonic bathing solution?
✔ (b) — no change in cell shape

- Which field contains a hypotonic solution?
✔ (a) — cells swell, may burst (lyse)

- What is happening to the cells in this field?
✔ They are swelling and may lyse (burst) due to water entering.

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8. Define diffusion:

✔ Diffusion is the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. It is a passive process driven by the kinetic energy of molecules.

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9. What determines whether a transport process is active or passive?

✔ The energy requirement and direction relative to concentration gradient:

- Passive transport: Moves substances down their concentration gradient (high to low); no energy required (e.g., simple diffusion, facilitated diffusion).
- Active transport: Moves substances against their concentration gradient (low to high); requires energy (ATP) (e.g., sodium-potassium pump).

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10. Contrast phagocytosis and pinocytosis:

| Feature | Phagocytosis | Pinocytosis |
|-----------------------|----------------------------------------|----------------------------------------|
| Meaning | "Cell eating" | "Cell drinking" |
| Substance ingested| Large particles (e.g., bacteria, dead cells) | Fluids and dissolved solutes |
| Size of vesicle | Large vesicles (phagosomes) | Small vesicles |
| Occurrence | Primarily in white blood cells, macrophages | Occurs in most cells |
| Energy required | Yes (ATP) | Yes (ATP) |
| Type of process | Endocytosis | Endocytosis |

✔ Phagocytosis involves engulfing solid particles, while pinocytosis involves taking in extracellular fluid and dissolved molecules.

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Final Answers Summary:

4.
- Dye movement: No
- Sucrose movement: No
- Explanation: Molecules too large to pass through membrane
- Test: Benedict’s test
- Osmosis direction: Into the sac

5.
- Characteristic: Molecular size / pore size
- Other factors: Charge, lipid solubility, transport proteins, concentration gradient, temperature

6.
- Glucose: (c) move out
- Water: (c) move out
- Albumin: (b) not move
- NaCl: (a) move in

7.
- Hypertonic: (c)
- Cells: Crenated
- Isotonic: (b)
- Hypotonic: (a)
- Happening: Cells swell and may lyse

8.
- Diffusion: Movement from high to low concentration without energy.

9.
- Determined by whether it moves with or against concentration gradient and whether ATP is needed.

10.
- Phagocytosis: Engulfs solids; pinocytosis: engulfs fluids.

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