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STUDENT GUIDE
ACTIVITY #5: Cell Structure and Function
Not that large, but definitely in charge!
What are cells? You
may have learned in the past that they are the “building blocks of life”. Organisms
can exist as one single cell or contain billions of cells!
You learned in the last activity that photosynthesis takes places in the chloroplast
of a plant cell and that cellular respiration takes place in the mitochondria of both
plant and animal cells. Some cells have more parts (called organelles) that have
special functions as well. In this activity, you will look at some of these cell
structures and determine how the presence or lack of these structures is used to
classify cells as either prokaryotic or eukaryotic.
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What is the difference between a prokaryotic and eukaryotic cell?
Do all cells look alike?
What special functions do organelles serve?
GOALS: In this lab activity, you will…
 Observe the differences between prokaryotic and eukaryotic cells.
 Observe that cells take highly varied forms in different plants,
animals and microorganisms.
 Observe and identify distinct organelles which perform processes
necessary for survival.
MAIN IDEAS: The important concepts and skills covered in this activity are…
 Cells, or the products of cells, are the basic units of
structure and function in all living things.
 The two basic types of cells are prokaryotic and
eukaryotic which differ in their structure.
 Prokaryotic cells are found in bacteria. These cells have
rigid cell walls, a plasma membrane, and a single
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chromosome made of continuous loop of DNA. Prokaryotes do not
possess internal membrane-bound structure called organelles found in
cells of eukaryotes.
Eukaryotic cells are found in all protests, fungi, plants and animals. These
cells have a cell membrane, but may or may not have a cell wall.
Eukaryotic cells contain small internal membrane-bound functional parts
called organelles. The most notable organelle is the nucleus that
surrounds the chromosomes.
Other eukaryotic cell organelles and cell structures, each with a specific
function, include, but are not limited to: nucleoli, plasma membrane,
lysosomes, centrioles, mitochondria, endoplasmic reticulum, Golgi
apparatus, cytoplasm, chloroplasts, vacuoles, ribosomes, cilia and
flagella.
ACTIVITY OVERVIEW: A synopsis of this lesson is as follows:
This activity is designed to be an introductory lesson in cell structure and
function. Students will observe six microscope slides to examine the differences
between prokaryotic and eukaryotic cells, to examine the different types of
structures found in cells, as well as propose explanations for the functions of
these structures. Students will then observe an unknown cell specimen and
classify it based on their observations made during the first part of the lab.
CONTEXT: The concepts that we have been developing and how this activity
serves as the ‘next step’ can be explained as follows…
The next topic in the Chemical Biology Unit covers the basic chemistry
and biochemistry of life. After completing this activity, students will be ready to
learn how cells carry out a variety of chemical transformations such as cellular
respiration, photosynthesis and digestion, which allow conversion of energy from
one form to another, the breakdown of molecules into smaller units and the
building of larger molecules from smaller ones. It is at the cellular level that these
reactions take place.
CONNECTIONS
Scientific Content –
 In order to establish and maintain their complex organization and structure,
organisms must obtain, transform and transport matter and energy,
eliminate waste products, and coordinate their internal activities.
 Cells take highly varied forms in different plants, animals and
microorganisms. Structural variations among cells determine the function
each cell performs.
 Cells have distinct and separate structures (organelles), which perform and
monitor processes essential for survival of the cell (e.g. energy production,
waste disposal, synthesis of new molecules, storage of genetic material).
 The highly specific function of each organelle is directly related to its
structure.
 The cell of a unicellular organism performs all the functions to sustain life.
 The cells of most multicellular organisms are specialized to perform particular
life functions.
Scientific Process –
 There is no quantitative data collected in this activity. The students are asked
to use microscope skills and observational skills to identify cell parts as well
as to distinguish between prokaryotic and eukaryotic cells.
Math/Graphing –
 There are no math or graphing skills associated with this activity.
Think about it:
Take a look at your skin. It looks like one continuous sheet that covers your body.
In reality, it consists of millions of different types of cells – squamous cells, basal
cells, and melanocytes to name a few. The average human body contains over
75 trillion cells, but many life forms exist as single cells that perform all the
functions necessary for life as an independent organism. Most cells are so small
that they cannot be seen without a microscope. Other cells, like frog eggs, can
be seen by the naked eye.
There are two major categories of cells: prokaryotic cells, which
lack a nucleus and membrane-bound organelles, and eukaryotic
cells, which DO contain a nucleus and DO contain membranebound organelles. Bacteria are prokaryotes. Organisms such as
animals, plants, fungi and protists are all eukaryotes.
In this investigation, you will observe several microscope slides to
examine the differences between prokaryotic and eukaryotic cells
and to propose explanations for their functions. You will also use
these differences to classify an
unknown
specimen.
Let’s Investigate:
1. Separate one layer from an onion quarter and hold it so that the concave
(curved inward) surface faces you. Snap it backward to separate the
transparent, paper-thin layer of cells from the outer curve of the scale.
2. Use forceps to peel off a small section of the thin layer, and lay it flat on a
microscope slide. Discard the rest of the onion piece. Trim the piece with a
scalpel if necessary, and smooth any wrinkles.
3. Add 1 or 2 drops of Lugol’s iodine solution and a cover slip.
4. Examine the first slide with low power and then with high power.
5. Sketch a few cells as they appear under high power. Label your sketch as
“Onion cells”. In the Data Table, write the name of the type of cell that you
examined. Describe the general shape of the cell in the space provided. Put a
check mark next to the cell structures you are able to observe.
6. Based on your observations, decide whether the cell is prokaryotic or
eukaryotic and record this in the Data Table.
7. Obtain a prepared slide of bacteria. The slide has three sections, each of
which contains a different species of bacteria.
8. Examine the slide with the low-power objective and then with the high-power
objective.
9. Sketch a few cells of each type of bacteria. Label your sketch. In the Data
Table, write the name of the type of cell that you examined. Describe the
general shape of the cell in the space provided. Put a check mark next to the
cell structures you are able to observe
10. Based on your observations, decide whether these cells are prokaryotic or
eukaryotic and record this in the Data Table.
11. Repeat steps 7 through 10 using prepared slides of human blood, paramecia,
Elodea cells and human fat cells (adipose tissue).
12. Repeat steps 7 through 10 using an unidentified prepared slide provided by
your teacher.
Sketches
1.
2.
4.
5.
7. Unknown
Data Table
3.
6.
Cell Structures
Chloroplasts
Vacuoles
Cytoplasm
Nuclear
membrane
Nucleus
Cell membrane
Shape
Cell Wall
Cell Type
Prokaryotic
or
Eukaryotic
Investigation Reflection:
1. Based on your observations, formulate a hypothesis to explain why cells
have different shapes and sizes.
2. What cell structures are common to all cells?
3. What parts of the plant cell were not present in the animal cell? What are
the functions of these plant-specific cell structures?
4. Formulate a hypothesis to explain the differences between plant cells and
animal cells.
5. What structural differences did you observe between the prokaryotic cells
and the eukaryotic cells? What do you think the functions of these
structures are?
6. What type of cell do you think the “unknown” slide represents, prokaryotic
or eukaryotic? Explain your reasoning.
Investigating Further…
A virus is a microscopic parasite that infects cells in
biological organisms. Viruses are also important to
the study of molecular and cellular biology because
they provide simple systems that can be used to manipulate and investigate the
functions of cells.
Research how viruses infect cells and what consequences a viral infection can
have on the organisms they infect.
Summary of Activity…
Based on your observations in this activity, explain why science textbooks
commonly compare a cell to a factory or an office. Include the following in your
summary:
 All of the cell parts (organelles) you identified in this activity.
Applying what you have learned…
Create another analogy for a cell other than a factory or an office as listed above.
Explain what insights you can draw from this analogy.