Lab Report: Understanding Passive Transport - Diffusion and Osmosis

Passive transport processes, such as diffusion and osmosis, play a crucial role in the movement of molecules across cellular membranes. This lab aims to explore these phenomena and their impact on various biological systems. The experiment involves four parts: Part A investigates the movement of molecules in a dialysis bag; Part B explores osmosis using different solutions; Part C examines water potential in potato cells, and Part D observes the effects of salt on onion cells.

Part A: Dialysis Bag Experiment

1. Calculations:
   • No specific calculations are involved in this part.
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2. Results and Observations:
   • Record the initial and final color of the starch solution in the bag and the beaker.
   • Note any changes in glucose presence.

Part B: Osmosis with Different Solutions

1. Calculations:
   • Calculate the initial and final mass of each dialysis bag.
   • Determine the change in mass for each bag.
2. Results and Observations:
   • Record the molarity of solutions in dialysis bags.
   • Observe changes in mass after submersion in water.

Part C: Water Potential in Potato Cells

1. Calculations:
   • Calculate the initial and final mass of potato cylinders.
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   • Determine the change in mass for each set of potato cylinders.
2. Results and Observations:
   • Observe and record any changes in the mass of potato cylinders.
   • Compare results between regular and sweet potatoes.

Part D: Effects of Salt on Onion Cells

1. Calculations:
   • No specific calculations are involved in this part.
2. Results and Observations:
   • Record observations of the onion cell under normal conditions.
   • Observe and describe changes in the cell after adding salt and subsequent water flooding.
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In Part A, the color change in the bag and the beaker indicates the movement of molecules. This suggests the occurrence of diffusion and possibly osmosis. In Part B, changes in the mass of dialysis bags indicate osmotic movement of water. The molarity of solutions in the bags is crucial for understanding the osmotic potential.

In Part C, the change in mass of potato cylinders provides insight into water potential. The comparison between regular and sweet potatoes allows for understanding variations in cellular structures. In Part D, the effects of salt on onion cells demonstrate how osmotic pressure can impact cell morphology.

This lab provides valuable insights into passive transport mechanisms, emphasizing diffusion and osmosis. The observations and calculations help in understanding the principles governing these processes. The variations seen in different parts of the experiment underscore the importance of these mechanisms in maintaining cellular balance.

To enhance the experiment, consider additional variables such as temperature and concentration gradients. Further exploration of different solutes and membrane types could deepen the understanding of passive transport. Additionally, repeating the experiment with variations in time intervals may provide a more comprehensive perspective on the kinetics of diffusion and osmosis.

Future research could focus on the molecular aspects of passive transport, including specific transport proteins involved. Investigating the impact of environmental factors on diffusion and osmosis in various organisms would broaden the applicability of the findings.

Part A. Data table (Diffusion)

Part B. Data table (Osmosis)

Part A:

1. The change in the bag's color confirms that glucose is leaving the bag, and the entry of IKI is validated by testing the beaker, which reveals the presence of glucose in it.
2. The movement of IKI from the beaker to the bag, leading to a color change, aims to equalize concentrations inside and outside the bag. Glucose moves out of the bag to balance solute concentrations.
3. Refer to the graph for detailed information.
4. The substances involved include water molecules, IKI molecules, glucose molecules, and membrane pores. Starch molecules cannot pass through the dialysis tubing due to their size.
5. If the initial setup includes glucose and IKI inside the bag with water and starch in the beaker, glucose and IKI will move out of the bag, equalizing concentrations. Starch, being too large, cannot enter the bag.
6. The purpose of easily opening dialysis tubes and ensuring their cleanliness.
7. Sucrose, being larger than glucose, cannot pass through the dialysis tubing.
8. The test was essential to confirm the presence of glucose in the beaker.

Part B:

1. The sucrose molarity in the bag determines water movement, affecting the mass change. For instance, a 0.2M solution causes water to enter, resulting in a 4.2% mass increase.
2. The bag expands when submerged, requiring space for expansion.
3. Percent change in mass calculates the mass increase due to water addition, attempting to equalize concentrations.
4. Placing bags in a 0.4M solution would lead to varied mass changes. Distilled water-filled bags' mass would decrease, while 0.4M bags would remain unchanged. Higher sucrose concentrations would lead to mass increase.

Part C:

1. Refer to the graph for details.
2. Osmotic pressure calculation yields -8.6 bars for regular potatoes.
3. Dehydration lowers water potential in potato cores as water evaporates.
4. If a plant cell has lower water potential, it becomes hypertonic and gains water from the hypotonic environment.
5. Spraying plants with water helps maintain turgidity and prevents dehydration.
6. Excessive fertilizer leads to cell hypertonicity, causing wilting.
7. The 0.5M sucrose solution was used in the experiment.

Throughout the lab, errors such as weighing with the cover on, incomplete tying of dialysis bags, and insufficient drying may have occurred. Despite these, the data collected is considered reasonably accurate.

Discussion: The lab observed passive transport, disproving the hypothesis about starch diffusion but confirming hypotheses about water movement in parts B and C. The addition of salt to onions showcased cell hypertonicity and subsequent recovery with water.