Download Cell Structure and Function Lab Report: Exploring Diffusion and Osmosis and more Lab Reports Cell Biology in PDF only on Docsity!
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Pre-laboratory Questions-answer in the space provided
- What does it mean for a substance to move down its concentration gradient?
When does a substance stop moving down its concentration gradient? Provide
an example.
A substance stops moving down its concentration gradient when it reaches equilibrium, from
an area of high concentration to low concentration. An example would be food coloring drops
into water as it disperses evenly.
- What does it mean to say that a membrane is selectively permeable? Explain
how the plasma membrane of the cell is selectively permeable.
To say that the plasma membrane is selectively permeable is saying it only allows some
molecules through. The membrane is composed of a phospholipid bilayer, which won’t let
certain harmful substances in to keep the overall health of the cell in good shape and
homeostasis in balance. It only allows essential molecules such as oxygen and nutrients to keep
the cell healthy and operating efficiently.
- How is osmosis similar to simple diffusion? How is osmosis different from simple
diffusion?
Osmosis is like diffusion in the sense that it works to make things even and equal on each side,
but they differ in how they function. Diffusion can work with other elements besides water
while osmosis cannot, and osmosis works with water molecules across a membrane in response
to higher concentrations of solutes, while diffusion works from high concentration to low.
Observations
Activity 1 Simple Diffusion
Data Table 1
Time (min)
Diameter, Potassium
Permanganate (mm)
Diameter, Methylene
Blue (mm)
Insert the photos of the Petri dish from Activity 1, with appropriate labels and figure
captions.
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Activity 2 Osmosis
Data Table 2
Treatment A Treatment B Treatment C
Solution in
dialysis tubing
20% sucrose 40% sucrose 20% sucrose
Solution in cup 20% sucrose 20% sucrose 40% sucrose
Initial volume
(V
i
) (mL) 7ml^ 7ml^ 7ml
Final volume
(V
f
) (mL) 7ml^ 10ml^ 5ml
Change in
volume
(V
f
−V
i
) (mL)
0ml 3ml -2ml
Percent change
in volume
(change in
volume/Vi) ×
Hypotonic,
isotonic,
or hypertonic
Isotonic Hypertonic Hypotonic
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Discussion Questions: Answer in the space provided.
- The molecular weight of potassium permanganate is 158 g/mol. The molecular
weight of methylene blue is 320 g/mol. Based on the information recorded in
Data Table 1, what can you conclude about the relationship between molecular
weight and diffusion?
My methylene blue was more concentrated due to having a little more on its side, which caused
a steeper concentration gradient, causing it to diffuse slower but with the most expansion
length in the end. Larger molecules should diffuse slower, but in this case, I believe the weight
caused it to spread faster. The Potassium Permanganate initially diffused fast due to its
lightweight molecules, but eventually, both subjects slowed in diffusion.
- In Data Table 2, what is the significance of a negative percent change in
volume?
There was a negative percent change in volume in that bag tube because it was a hypotonic
solution in a hypertonic solution, and the tube acted as a membrane, which caused water to flow
out of it into the more concentrated area.
- What would you predict if a person tried to stay hydrated by drinking seawater?
Their fluids would leave and cause dehydration very quickly. The saltwater is concentrated
compared to our PH level in the body, and our fluids would be trying to reach the saltwater
concentration, causing hydration to drop very quickly.
- Aquaporins are membrane proteins. Based on what you have learned of their
function, are aquaporins peripheral or integral membrane proteins?
Aquaporins are integral. They are encased in the cell membrane, and their main function is to
pass water and other molecules that it selects through. The peripheral has entirely different
functions and is on the surface of the cell membrane.
