SBI4U: Biochemistry UnitCellular Transport

Consolidation and Pre-Lab Questions

Use your textbook and the reading “Cellular Transport.pdf” (pp. 93-101) that is on the class website to help you answer the following questions. When you are finished complete the “Egg Lab”.

  1. What is the major barrier to substances crossing a biological membrane?
  1. Give an example of molecules that will and will not cross the cell membrane easily and explain why.
  1. Many substances move in and out of cells by a number of processes. The main mechanisms by which substances cross cell membranes are called active transport and passive transport. Outline the similarities and differences of these methods of cellular transport by completing the Venn-diagram below. The similarities are listed in the centre darker-shaded area, while the points unique to each form of transport are listed under their respective headings. Be sure to include the terms: concentration gradient, energy, ATP, transporter, pump.


Differences SimilaritiesDifferences

  1. Why is active transport an important cellular function? Explai9n using your understanding of concentration gradients.
  1. In what way is active transport an endergonic process?
  1. In your own words, explain why osmosis occurs when water molecules interact with solutes in the presence of a membrane that separates two solutions having different concentration of solutes (pg. 73).
  1. Define the terms hypertonic, isotonic, and hypotonic:

  1. Describe, using a diagram, how the movement of water is affected by osmotic pressure under the following conditions: 1) a hypertonic solution, 2) an isotonic solution, and 2) a hypotonic solution.
  1. Summarize the steps of the sodium-potassium pump.
  1. Why is it important for animal cells to maintain osmotic balance?


Investigating the Movement

of Substances across the Cell Membrane

Passive Transport is the movement of molecules across a cell membrane from an area of high to lower concentration (ie. with the concentration gradient) WITHOUT the use of energy.

Osmosis is important in biological processes where the solvent is water. It is a form of passive transport that plays a great role in the movement of substances across cellular membranes. The transport of water molecules and other molecules across biological membranes are essential to living organisms. Osmosis is defined as the movement of a solvent (ie. H2O) through a selectively permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).


Ms. Manning’s grade 12 biology students were studying osmosis one day. Like good little scientists, they were interested in bringing the theory of cellular transport to life in an experiment!

Ms. Manning performed an experiment using uncooked eggs placed into three different solutions to demonstrate the concept of osmosis. She explained that the outer egg membrane is a good model of a cell membrane because it is thin and flexible.

To obtain the outer egg membrane, Ms. Manning placed the three uncooked eggs into a beaker with vinegar in order to dissolve the hard shell. After 2 days (48 hours), she took the three eggs out of the vinegar beaker and measured the initial mass of each egg using the balance beam (see Table 1 for the results). She then placed the eggs into three different solutions (0%, 5%, 20% salt concentrations) and waited. After 45 minutes, she took the eggs out and measured the final mass of each egg using the balance beam (see Table 1 for the results).


Table 1. Initial and final mass of eggs placed in different salt solutions

Trial #1
Egg Number / Solutions / Initial Mass (g) / Final Mass (g) / Change in Mass (g) / % Change in Mass
1 / 0% Salt (Distilled Water) / 80.20 / 85.27
2 / 5% Salt (NaCl) / 85.46 / 79.18
3 / 20% Salt (NaCl) / 83.67 / 70.02

Table 2. Initial and final mass of eggs placed in different salt solutions

Trial #2
Egg Number / Solutions / Initial Mass (g) / Final Mass (g) / Change in Mass (g) / % Change in Mass
1 / 0% Salt (Distilled Water) / 81.28 / 86.56
2 / 5% Salt (NaCl) / 87.98 / 82.23
3 / 20% Salt (NaCl) / 86.75 / 72.15
  1. Calculate the change in mass (g) for each of the eggs placed in the three different solutions.

Change in mass=Final mass (g) – Initial Mass (g). Show your calculations (6 marks).

  1. Calculate the % change in mass using the formula:

Show your work (6 marks)

  1. Explain what it means when you have a positive % change in mass and a negative % change in mass. Include a diagram to explain the biological process of why either a positive or negative % change in mass in each condition was observed (Hint: think hypertonic and hypotonic) (5 marks).
  1. Using the data in Table 1 and 2, calculate the average % change in mass for the egg placed in the three different solutions (0%, 5%, 20% NaCl solution). Show you calculation and fill the values in Table 3 below. (3 marks)

Average mass difference for eggs in 0% salt solution / Average mass difference for eggs in 5% salt solution / Average mass difference for eggs in 20% salt solution
  1. Plot a graph to illustrate the average mass difference for eggs in the three different salt solutions. Use the graph paper provided on the next page. Remember to label all the axes, include a legend, and give the graph a meaningful and explicit title. (4 marks)
  1. What can you conclude about osmosis or passive diffusion across the cell membrane? Explain the relationship between the difference in the mass of eggs and the different concentrations of salt solution? (2 marks)
  1. What are three potential sources of error that Ms. Manning could have done that may have lead to inaccurate results? (3 marks)
  1. Ms. Manning wants to improve her laboratory procedures. List one suggestion you would give her to help her students better understand osmosis. (1 mark)

BONUS: Identify who the puppet character is on page 3  (1 mark)

**adapted from