Download c.1.2_bot120_covill

Botany 120: Cell Lab
Lab Objectives
 To identify cell structures visible with a light microscope
 Identify and describe different types of plastids and their functions
 Identify and describe the structural and functional differences of parenchyma, collenchymas, and
scleranchyma cells
 Differentiate between plasma membrane, primary cell wall, and secondary cell wall in terms of
location and function
Introduction
Cells are the basic unit of all living things; they are the lowest level of biological organization that displays the
characteristics of living things. All activities performed by living organisms and all structures within living
things are due to cells or materials that cells make. There are two fundamental types of cells; prokaryotic and
eukaryotic. Prokaryotic cells are only found in Bacteria and Achaeans and will be examined in a future lab. All
other organisms—including plants are made of one or more eukaryotic cells. Eukaryotic cells are characterized
by their large size and the presence of a nucleus along with other membrane bound organelles. However,
many components of eukaryotic cells are not readily visible with a typical light microscope.
While plant cells possess the general characteristics shared by all eukaryotic cells—large size, nucleus, and
membrane bound organelles—they possess three specific structures missing in many other eukaryotic taxa.
These are: plastids, vacuole, cell walls. Although there are many specific types of plant cells each of which are
specialized for specific functions, plant cells can be divided into three basic types: parenchyma, collenchymas,
and schleranchyma.
In this lab you will examine a variety of plant cell types, view several more prominent cell parts (e.g., cell walls,
vacuoles, plastids), and consider how and why different plant cells have different structural characteristics.
This will include cells displaying a variety of plastids and comparing parenchyma, collenchyma, and
schleranchyma cells.
A. Paranchyma Cells
Paranchyma cells are the most common type of cell in plants. They are found in all parts of the plant
and are responsible for most of the metabolic activity of the plant (e.g. photosynthesis), repair of
damage, and storage of food (energy). Paranchyma cells are characterized by having thin cell walls
consisting only of a primary wall. You will look at several examples of parenchyma cells: tomato pulp
cell, elodea leaf cell, red onion cell, red bell pepper cell, and potato cells
1. Tomato Cells
Prepare a wet mount of a tomato cells. Using a scapel or razorblade, make a very thin slice of the
tomato. The large cells you see are parenchyma cells; not the thin cell walls. The thinness of the
cell wall is a reflection of the fact that parenchyma cells have only primary cell walls. As in many
cells, you cannot differentiate the cell wall from the plasma membrane because the thin plasma
membrane is pressed against the inside edge of the cell wall making the two structures
indistinguishable.
Draw some representative parenchyma cells seen in the tomato and label the cell wall, cytoplasm,
and nuclei if visible.
2. Elodea
Elodea is an aquatic freshwater plant that has leaves which are only several cells thick, allowing
you to clearly examine several cell structures. Remove a single leaf from an elodea plant make a
wet mount. These cells are another example of parenchyma cells designed for photosynthesis.
Use the high power lens locate and identify the following structures: cell wall, cytoplasm, and
chloroplast. Note that you may see the chloroplast moving within the cell, if so they will be circling
around the vacuole allowing you to get a sense of the location and extent of the vacuole.
Draw several representative elodea cells in the space provided on the worksheet being sure to
include and label the cell wall, chloroplast, cytoplasm, and vacuole. Answer the associated
questions.
3. Red Onion (Allium)
Onion bulbs are actually below ground modified leaves designed for food storage (more details in
a future lab). Prepare a wet mount by carefully peeling the dark, pigmented outer layer of the
leaf. You may need to use the scalpel to peel this layer off of the leaf. This pigmented later is the
epidermis of the leaf (more details in future labs) and is only a single cell thick. Keep in mind that
these are also parenchyma cells. The red color of this layer is caused by water soluble pigments
known as anthocyanins. The anthocyanins are stored within the cell’s vacuole which allows you to
easily determine the size of the vacuole. Look closely where two cells meet and you should be
able to differentiate the plasma membrane from the cell wall.
Draw several representative red onion cells in the space provided on the worksheet being sure to
include and label the cell wall, plasma membrane, cytoplasm, nucleus, and vacuole. Answer the
associated questions.
4. Red Bell Pepper
Obtain a piece of red bell pepper. Using a scalpel peel the outer skin off the bell pepper and make
a wet mount. View the slide on high power. The best place to view is often along the edge of the
cut material.
In some situations plastids contain pigments other than chlorophyll. Carotenoids are a class of
red, yellow, and orange pigments and plastics containing carotenoids are called chromoplasts.
Chromoplasts are common in tomatoes and other fruit that become red (or orange or yellow) as
they ripen. In these situations, the plastids contain chlorophyll in the unripe fruit and as the fruit
ripen carotenoids replace the chlorophyll within the plastid. Chromoplasts can also be responsible
for red, orange, and/or yellow colors in leaves and flowers.
Draw several representative red bell pepper cells in the space provided on the worksheet being
sure to include and label the chromoplast, cell wall, and cytoplasm. Answer the associated
questions.
5. Potato
Potatoes are underground stems modified for storage (technically a tuber, more on this in a future
lab). The primary way plants store nutrients for future use is as starch (also known as amylose).
Starch is stored in plastids known as amyloplasts.
Using a scapel or razorblade, make a very thin (almost transparent) section of potato, place it on
slide and add one or two drops of iodine. Iodine turns amylose (starch) a dark purple color
allowing you to see the amyloplasts. View the slide on high or mid power and identify the cell
wall, plasma membrane, and amyloplast.
Draw several representative potato cells in the space provided on the worksheet being sure to
include and label the amyloplast, cell wall, and cytoplasm. Answer the associated questions.
B. Collenchyma Cells
Collenchyma cells are elongated (i.e., long and thin in shape), they have irregularly thickened
secondary cell walls that allow they to provide structural support. They are alive at maturity and are
used in areas that need rigid support such as stems and leaves
Using a razor blad, make a thin, almost transparent, section of celery stem and use it to make a wet
mount. Look deep to the outer curve of the stem where the “ribs” are to find the collenchyma cells.
Draw the collanchyma cells in the space provided and label the secondary cell walls and cytoplasm.
Answer associated questions.
C. Scleranchyma
Schlerenchyma cells have uniformly thickened secondary cell walls. Unlike parenchyma and
collenchymas cells, scleranchyma cells are dead at maturity, but the lignified secondary cell walls are
unaffected by the death of the cell and continue to provide support to plant structures. There are two
type of scleranchyma cells: fibers and sclerids. Fibers are long, thin and provide support to plant
structures. They are commercially important as they are used for cloth/fabric and natural ropes.
Sclerids are small and often irregular in shape, they can serve as attachment points for other cells and
give some fruit (such as pears) their gritty texture.
Make a wet mount of pear pulp (use a razor blade to make the thinnest possible section). On mid or
high power, locate the sclerids (a.k.a. stone cells). You may notice that there are often parenchyma
cells organized in a geometric pattern around the sclerids.
Draw a representative sclerid and label the secondary cell wall. Answer associated questions.
CELL LAB WORKSHEETS
NAME:
DIAGRAMS
Tomato
Red Onion (Allium)
Potato
Elodea
Red Bell Pepper
Collenchyma
Scleranchyma
additional material indicated by instructor
QUESTIONS:
1. Name three structures unique to plant cells.
2. What are the names of the three types of plastids seen in the cell lab and state the function of each.
3. Do plant cells have mitochondria? Why/Why not?
4. If the only plastids in a flower were chromoplasts, could the flower make its own food? Explain.
5. Do all plant cells have chloroplast? Explain.
6. What type of plastid would you most likely be found in each of these plant parts?
a. Stem specialized for food/energy storage
b. Green leaf
c. Turnip root
d. Bright red flower
e. Orange leaf
7. How does the diameter of collanchyma, scleranchyma, and parenchyma cells compare?
8. Compare and contrast parenchyma, collenchyma, and schleranchyma cells in terms of their cell wall,
diameter, functions, and if they are living or dead at maturity.
9.
Create a diagram of a cell including all major plant organelles (use chloroplast as the representative
plastid), label each structure and include a single phrase function for each labeled part.