Download Lab 5: Cells and Their Organelles

Lab 5: Cells and Their Organelles
Objectives
Identify cells under a microscope, identify different Kingdoms
Identify the major parts of a cell and its organelles
Be able to prepare wet mounts
Be able to stain cells
Draw models of cells observed
Introduction
All living things are composed of cells, the smallest units of life. Cells are composed of
structures called organelles, and organelles are in turn made of biomolecules. All
bacteria are prokaryotes, plants and animals are eukaryotes. In general, all eukaryotic
cells have three parts: cytoplasm, nucleus and plasma membrane. Eukaryotic cells
perform all the same functions as prokaryotic cells, but in addition have specialized
functions that they perform in membrane enclosed organelles. Plant cells, in addition to
containing all the components of animal cells also contain extra structures such as cell
wall, vacuole and plastids.
In this lab you will examine different prokaryotic and eukaryotic cells under the light
microscope. The cells you view will differ in size. You should be able to estimate their
dimensions in microns (1mm = 1000 microns).
Methods:
Part I: Observation of Prokaryotic cells.
Bacteria are so small that they are difficult to see under a light microscope. They can be
divided into three categories based on their shape: round (cocci), rod shaped (bacilli)
and spiral (spirilli). It is also possible to determine if flagella (for motility) are present.
Examine the prepared bacterial slides. Fill in the table below.
Name of Bacterium (example)
Shape (biological terminology)
Part II: Observation of Plant cells
Prepare a wet mount of a plant cell (as demonstrated). Prepare wet mounts of leaves
provided. Examine this preparation under the light microscope. Draw a typical cell you
observe. Scientific drawings, labeled.
Plant cells contain many organelles. In addition to the nucleus and cell wall; plant cells
contain many different types of plastid. The type of plastids found depend on what
organ of the plant the sample is taken from (roots, leaves, and stems). You may be
familiar with chloroplasts, a type of plastid involved in photosynthesis that stores the
light-absorbing pigment, chlorophyll. Plastids are primarily storage organelles for
various types of molecules, including pigments, sugars etc.
Draw a typical plant cell here.
Prepare a wet mount of onion tissue. Use very thin layer. It should be translucent. Add
a drop of acetocarmine dye to the onion section. This dye will stain the cytoplasm and
the nucleus red, leaving the vacuoles clear.
Draw a typical onion cell here.
Prepare a wet mount of potato tissue. Potato cells contain leucoplasts (a plastid) these
are small oval organelles that store starch. These may be found in the leaves, stem or
roots of many types of plants.
Leucoplasts store starch, in order to see them we will stain the sample. Add 2-3 drops
of Lugol’s stain to one edge of the coverslip of your wet mount. Wick the stain under
the coverslip with a Kimwipe, by touching the fibers of the Kimwipe to the opposite
edge of the coverslip.
Examine your slide under the scope.
Draw a typical potato cell here.
Part III: Observation of Animal Cells
Obtain a clean toothpick and gently but firmly scrape the flat end against the inside of
your cheek. Transfer the material to a clean slide and prepare a wet mount. Draw some
Methylene Blue dye under the coverslip and view your cells (look 40x).
Draw a typical cheek cell here. Accurately label all organelles observed.
Discussion Questions:
1. Compare the differences between bacterial and animal cells that you observed in lab
today. In your answer address size, organelles and the organization of genetic material.
2. What specific structures were observed in the plant leaf cell?
3. Which visible organelles were present in plant but not in animal cells?
4. What is the value of staining a sample?
5. Would you be able to distinguish a plant cell from an animal cell under a microscope
without staining?