Week 3 Experiment Answer Sheet Please Submit To The Week 3 E

Week 3 Experiment Answer Sheetplease Submit To The Week 3 Experiment D

Summarize the results regarding the presence (+) or absence (-) of glucose and protein in the dialysis bag and beaker in Table 2 below (4 pts):

In the initial testing, the dialysis bag contained both glucose and protein, indicated by the positive results for glucose (green Benedict’s test) and protein (violet Biuret test). The beaker water initially showed no glucose (blue Benedict’s test) and no protein (clear Biuret test). After 60 minutes, the dialysis bag still showed the presence of glucose and protein, indicating they did not diffuse out significantly, while the beaker water showed the appearance of glucose (green Benedict’s test), but still no protein, suggesting glucose diffused out, but proteins did not pass through the membrane.

Explain the movement or lack of movement of protein and glucose across the dialysis bag membrane (4 pts):

Glucose molecules, being small (molecular weight of 180 g/mol), readily diffused through the semi-permeable dialysis membrane from the bag into the surrounding water, driven by concentration gradients. Proteins, being large molecules with a molecular weight of 10,000 g/mol, could not pass through the membrane, so they remained inside the dialysis bag. Initially, glucose was inside the bag, and some diffused out over time, but proteins remained confined due to size exclusion.

Which solution, that in the bag or that in the beaker, is hypotonic compared with the protein solution (2 pts)?

The beaker water is hypotonic relative to the protein solution inside the dialysis bag; the protein solution has a higher solute concentration.

What factors affect the movement of molecules across a semipermeable membrane? Which factor plays the greatest role in biological systems (4 pts)?

Factors affecting molecular movement include concentration gradient, molecule size, temperature, and membrane permeability. Among these, the concentration gradient is the most critical factor in biological systems, driving passive diffusion of molecules across membranes.

Briefly explain what active transport is and how it differs from passive transport, especially in terms of concentration gradients (4 pts):

Active transport is the movement of molecules across a cell membrane against their concentration gradient, requiring energy typically in the form of ATP. In contrast, passive transport involves the movement of molecules down their concentration gradient without energy expenditure, relying on diffusion or facilitated diffusion processes.

Experiment 3 Exercise 2: Osmosis - The Movement of Water across a Membrane

Definitions of terms in relation to solute concentration outside vs inside the cell:

• Hypotonic: The solution outside the cell has a lower solute concentration compared to inside the cell.
• Isotonic: The solute concentration is equal inside and outside the cell.
• Hypertonic: The solution outside the cell has a higher solute concentration than inside the cell.

What concentration of salt is isotonic to animal cells (1 pts)?

Approximately 0.9% saline (NaCl) solution is isotonic to animal cells.

When cells are in isotonic solution, is there movement of water into or out of the cell? If so, describe this movement (3 pts).

In isotonic solutions, water movement into and out of the cell occurs at equal rates, resulting in no net change in cell size or shape.

Describe the net movement of water molecules when cells are placed in a hypotonic solution. Explain why water moves this way (3 pts).

In hypotonic solutions, water molecules tend to move into the cell because the extracellular fluid has a lower solute concentration than the cell’s interior, creating a concentration gradient that favors water influx.

What happens to an animal cell when placed in a hypotonic solution (2 pts)?

The animal cell swells and may burst (lyse) due to excessive water inflow.

What happens to plant cells when placed in a hypotonic solution? What accounts for the difference in outcomes between animal cells and plant cells (3 pts)?

Plant cells swell but generally do not burst because the cell wall provides structural support, preventing excessive expansion. Animal cells lack a cell wall and are more prone to lysis.

Describe the net movement of water molecules when cells are placed in a hypertonic solution. Explain why water moves this way (3 pts).

Water moves out of the cell into the hypertonic solution because the extracellular environment has a higher solute concentration, creating a gradient that favors water efflux.

Compare and contrast what happens to plant and animal cells when placed in a hypertonic solution. Be sure to use proper terminology (4 pts).

Animal cells shrink and become shriveled (crenate), while plant cells experience plasmolysis—where the cell membrane pulls away from the cell wall—due to water loss.

Explain why salt might make a good weed killer (3 pts).

Salt creates a hypertonic environment around the plant roots, causing water to leave plant cells, leading to dehydration, cell death, and ultimately, plant killage.

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