UMUC Biology 102 / 103 Lab 3: Cell Structure And Function

Cell Structure and Function

Post-Lab Questions

1.    Label each of the arrows in the following slide image:

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2.    What is the difference between the rough and smooth endoplasmic reticulum?




3.    Would an animal cell be able to survive without a mitochondria? Why or why not?

4.    What could you determine about a specimen if you observed a slide image showing the specimen with a cell wall, but no nucleus or mitochondria?


5.    Hypothesize why parts of a plant, such as the leaves, are green, but other parts, such as the roots, are not. Use scientific reasoning to support your hypothesis.


Post-Lab Questions

Experiment 2: Osmosis – Direction and Concentration Gradients

Data Tables and Post-Lab Assessment

1.    For each of the tubing pieces, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the beaker solution in which it was placed.


2.    Which tubing increased the most in volume? Explain why this happened.



3.    What do the results of this experiment this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker?


4.    What would happen if the tubing with the yellow band was placed in a beaker of distilled water?


5.    How are excess salts that accumulate in cells transferred to the blood stream so they can be removed from the body? Be sure to explain how this process works in terms of tonicity.


6.    If you wanted water to flow out of a tubing piece filled with a 50% solution, what would the minimum concentration of the beaker solution need to be? Explain your answer using scientific evidence.

7.    How is this experiment similar to the way a cell membrane works in the body? How is it different? Be specific with your response.

Sample Answer

UMUC Biology 102/103 Lab 3: Cell structure and function ANSWER KEY


Question 1

A – Chromosome

B – Nucleus

C – Cytoplasm

D – Cell wall

Question 2

The rough endoplasmic reticulum contains ribosomes attached to its outer membrane therefore it is able to carry out the role of packaging and synthesis of proteins while the smooth endoplasmic reticulum does not contain any ribosomes attached to its surface and its main role is synthesis and storage of steroids and lipids.

Question 3

An animal cell cannot survive without mitochondria. The main role of mitochondria is to carry out oxidative phosphorylation that yields energy and hence without it, animal cells would perish due to insufficient energy supply.

Question 4

I could determine that the specimen is prokaryotic and also a bacterial cell. This is because the major characteristic of prokaryotic cells is the absence of cell organelles such as the nucleus and mitochondria.

Question 5

Leaves are typical green in color due to the presence of chloroplasts that contain a green coloring pigment known as chlorophyll that captures sunlight and thereby facilitates photosynthesis while other parts such as the root are not green. This is because roots are found under the ground surface and are not exposed to direct sunlight thereby, they don’t require factors that facilitate photosynthesis such as the green coloring pigment known as chlorophyll.


Question 1

In comparison to the beaker solution in which the tubing pieces were placed, the following are the results;

Tubing 1 – hypotonic

Tubing 2 – hypotonic

Tubing 3 – isotonic

Tubing 4 – hypertonic

Question 2

The first tubing piece had a higher increase in volume. This is because the solution inside the tubing is hypotonic indicating that molecules of water move into the tubing through osmosis and increase its volume. Volume in tubing 1 is greater than that of a similar hypotonic solution in tubing 2 due to greater concentration of sucrose molecules in tubing 1.

Question 3

The results indicate that water that is found in the solution that is adjacent to the tubing’s travels through a semi-permeable membrane to reach a region of higher concentration of solutes inside the tubing piece.

Question 4

If the tubing that is marked with a yellow band is placed inside water, it would increase in volume. This is due to the fact that the contents inside the tubing piece have a higher concentration of solute molecules as compared to the distilled water which has no solute molecules and hence water molecules will move inside the tubing piece through osmosis.

Question 5

Excess salts that gather together in cells are transported to the blood stream through osmosis. They are first absorbed into the blood stream and transported to the kidney. When in the kidney cells, the salts make them hypertonic to surrounding regions and this triggers osmosis. Water molecules then move into the hypertonic region thereby increasing tonicity in the kidney. The water mixes with the excess salt to form a solution known as urine that is later excreted.

Question 6

The minimum concentration in the beaker needs to be 51%. This is because water molecules usually move from a region of higher concentration of solute molecules to a region of lower concentration of solute molecules through and across a semi-permeable membrane through a process known as osmosis.

Question 7

This experiment has a similarity factor when compared with the functioning of a cell membrane because both the tubing piece and the cell membrane act as semi-permeable membranes that allow for the movement of water or fluid particles but not ions or solute molecules.

The difference comes in whereby the tubing pieces in the experiment can withstand varying concentrations of water molecules while when the cell membrane of erythrocytes can’t withstand high amounts of fluid and they burst open through or lyse.

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