Biology Lab need done

Your third lab deals with cellular biology.  Remember that “the cell is the basic unit of life” and, therefore, you must become very familiar with cellular structure and function.  Eukaryotic cells contain a number of smaller units – organelles – each one of which has very specific jobs to do. You may think of a cell as a factory: 

The nucleus is the “administrative office” from which directions go out for production. The nucleus contains the genetic material. Then, there is the ribosomal, or rough, endoplasmic reticulum, the site of polypeptide production.  The smooth endoplasmic reticulum puts lipids together. The Golgi bodies are the packaging and storage sites, where polypeptides are put together into functioning proteins. Lysosomes are in charge of removing waste products. All of this work requires energy, which is produced by the mitochondria. You will find additional structures that also have specific functions.

Before you begin with any lab work, please read the Introduction section of your Lab Manual very carefully. The first cells to develop were the very small and quite simple prokaryotes. Fossils of such early cells have been found and they have been dated to over 3.8 billion years ago! This is almost a billion years after the earth first formed from solar dust. About two billion years later, the first eukaryotes appeared. Compare the two cell types very carefully in terms of their structure and function. On pages 40 and 43 (of your lab Manual), you will find a useful list of structural comparisons. You should be able to interpret the functional differences from this information!

Looking at eukaryotes, you will discover that there are significant differences between plant and animal cells, which are based on different functions. Plants photosynthesize, that is, they make the basic chemical energy – glucose – required for all metabolic functions from two inorganic substances: carbon dioxide (CO2) and water (H2O). Carefully look at all the physical differences between these two cell types and then interpret these differences in terms of ‘function’. In other words, there are good reasons for these differences, because plants and animals have different lifestyles with different needs.

Experiment 1: Identifying Cell Structure

After you have thoroughly familiarized yourself with the structure and function of cells, try to answer carefully and in detail the nine questions. (No materials required.)

Experiment 2: Direction and Concentration Gradients

In this experiment, you will test how the concentration of a solute will affect osmosis. A semi-permeable membrane is necessary for osmosis to occur, and cells have such membranes. Water is the actor in this scenario.

You will need the following items from your lab kit: 30% sucrose solution, 3 250ml Beakers, 4 15cm long each of dialysis tubing (it is flat!), 4 colored beads, and 8 small rubber bands. You will find the dialysis tubing, beads and rubber bands in a small plastic bag, labeled Cell Structure & Function – Osmosis. You will have to supply the water and a reliable watch. The plastic dialysis tubing is flat, and before you begin your work with the four pieces of tubing, you will have to soak them first in water, in order to open them. Simply follow the instructions and don’t hurry through this exercise – give yourself plenty of time!

Have fun with this lab and be sure to involve your family or friends!

UMUC Biology 102/103

Lab 3: Cell Structure and Function

INSTRUCTIONS:

· On your own and without assistance, complete this Lab 3 Answer Form electronically and submit it via the Assignments Folder by the date listed on your Course Schedule (under Syllabus).

· To conduct your laboratory exercises, use the Laboratory Manual that is available in the WebTycho classroom (Reserved Reading or provided by your instructor) or at the eScience Labs Student Portal. Laboratory exercises on your CD may not be updated.

· Save your Lab3AnswerForm in the following format: LastName_Lab3 (e.g., Smith_Lab3).

· You should submit your document in a Word ( or x) or Rich Text Format (.rtf) for best compatibility.

Experiment 1: Labeling (consult the Lab 3 Introduction for more details)

Bacteria: Nucleoid region, cell wall, plasma membrane, ribosomes, flagella

 

Protist: Macronucleus, micronucleus, plasma membrane, cytoplasm, contractile vacuole

 

Plant Cell: Nucleus, cell wall, plasma membrane, cytoplasm, chloroplast, mitochondria, vacuoles

 

Animal Cell: Nucleus, nucleolus, plasma membrane, cytoplasm, mitochondria, golgi apparatus, rough ER, ribosome

 

Questions

1. For each structure identified, do you think its location affects its ability to function? Why or why not? (Hint: those buried deep in the cell probably do different things than those closer to the cell membrane)

2. Draw a labeled diagram of a small section of the plasma membrane and briefly describe its structure and function.

3. Describe the differences between animal and plant cells.

4. Which of the following structures are present in both prokaryotic and eukaryotic cells?

5. Where is genetic material found in plant cells?

6. Mitochondria are the only organelles that contain their own DNA (circular) and have a double membrane. Why do you think this might be so?

Hint 1: Where else do we see circular DNA?)

Hint 2: What do you know about the relative age of eukaryotic cells?)

7. How is the structure of the plant’s cellulose-based cell wall related to its function?

8. Defects in structures of the cell can lead to many diseases. Pick one structure of a eukaryotic cell and develop a hypothesis as to what you think the implications would be if that structure did not function properly.

9. Using books, articles, the internet, etc. conduct research to determine if your hypothesis was correct.

Experiment 2: Directions and Concentration Gradients

Table 2: Water Movement

 

 

 

 

 

 

Initial Volume	Sucrose %	Prediction: Will water move in or out?	Final Volume
Bag #1 10 mL
Bag #2 10 mL
Bag #3 10 mL
Bag #4 10 mL

Questions

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

2. Which bag increased the most in volume? Why?

3. What does this tell you about the relative tonicity between the contents of the bag and the solution in the beaker?

4. What would happen if bag 1 is placed in a beaker of distilled water?

 

TYPE YOUR FULL NAME:

37

The Cell

Lab 3
Cell Structure & Func on

38

39

Lab 3: Cell Structure & Func on

Introduc on

A cell is the fundamental unit of life. All living organisms originate from a single cell. Some remain as a
single cell, while others become mul cellular (like you!). Though most cells are di cult to see with
the naked eye, using the microscope, cytologists have iden ed many of their features. These range
from the characteris cs of the outer membranes, to internal structures such as the nucleus and mito
chondria and have become the founda on for what is now known as “cell theory”.

Cell theory states:

All cells are generated from previous cells
All cells pass on their gene c informa on
All living things are made of cell(s)
Energy metabolism occurs inside cells
The chemical make up of cells is similar

Although all organisms are made up of cells, not all cells are iden cal. Prokaryotes and eukaryotes are
two structurally di erent types of cells.

Prokaryotes are the most primi ve and basic organisms, and span the taxonomic classes of
bacteria and archaea. They lack a membrane bound nucleus and membrane bound organelles
(specialized structures). The term prokaryote comes from the La n words “pro” (before) and
“karyote” (nucleus).

Eukaryote are much more complex organisms with two characteris cs that set them apart
from prokaryotes: a de ned nucleus and membrane bound organelles. The term “eukaryote”
comes from the La n words “eu” (true) and “karyote” (nucleus). Pro sts, fungi, plant and ani
mal cells are all eukaryo c cell(s).

Concepts to explore:

What is a cell?
Prokaryotes
Eukaryotes

Cell structure
Func on of cell structures
Di usion
Rare of Di usion

Cytologists are scien sts who
study cells. The study of the
cell is known as cytology.

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Lab 3: Cell Structure & Func on

Prokaryotes Eukaryotes

Bacteria and archaea (both prim
i ve cells) are the only prokary
otes

Are very small (.1μm to 2μm)

Reproduce asexually. This
means sexual reproduc on is
absent, and there is li le gene c
varia on between genera ons

Have simple cellular components

Are capable of living almost any
where and o en thrive in harsh
condi ons

Are unicellular

2 Billion years younger than pro
karyo c cells

Great biological diversity

All mul cellular organisms are
eukaryotes

Signi cantly larger than most
prokaryo c cells

More complex shapes and inter
nal structure than prokaryotes

Some are capable of capturing
light energy (chloroplasts in
plant cells and cones and rods of
the eye)

Figure 1: A prokaryo c cell showing
some of the major structures

Nucleoid (nucleus-like) Region

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Lab 3: Cell Structure & Func on

Both prokaryotes and eukaryotes have a plasma membrane (also known as the cell membrane) that
separates the cellular content from the external environment. This structure is o en referred to as a
phospholipid bi layer, as it is composed of two layers of lipids with proteins oa ng between these lay

Figure 2: Major structures of eukaryotes; Top: an animal cell; bo om le : a plant cell; Bo om right: a para
mecium.

Plant Cell

42

Lab 3: Cell Structure & Func on

ers. The proteins in the structure are responsible for carrying out the majority of the func ons speci c
to the membrane and impart a selec vity to certain materials that can pass through the membrane.
Many cells within the prokaryo c and eukaryo c families have cell walls outside the cell membrane hat
help to protect them and provide support (note: animal cells and protozoa do not have cell walls). Un
like the cell membrane, this barrier is not selec ve and does not allow materials to pass through easily.
Prokaryo c cells have a thick, rigid cell wall composed of amino acids and sugars (pep doglycan), but
the cell wall composi on within eukaryotes varies (e.g., fungi cell walls include a polysaccharide called
chi n while plants exhibit cell walls with the polysaccharide cellulose).

In all cells, the plasma membrane encases the cytoplasm (also called cytosol), which is a semiliquid, gel
like substance that is the founda on of the cell. Within the cytoplasm of eukaryo c cells, a number of
membrane bound organelles exist to provide speci c func ons within the cell. Prokaryotes do not have
these specialized bodies to compartmentalize the intercellular func ons and are therefore everything
is free oa ng within the cell. As you examine the structures of prokaryotes and eukaryotes in Figures
1 and 2, you will note these di erences.

Some Organelles Found in Eukaryotes:

Nucleus: Houses the gene c content (DNA) of the cell.

Nuclear Envelope: An outer membrane that surrounds the nucleus.

Nuclear Pores: Holes in the nuclear envelope that permit communica on between the internal
nuclear environment and the cytoplasm.

Nucleolus: (plural: nucleolus) A part of the nucleus that is made of RNA, Protein and Chroma
n and manufactures RNA and ribosomes.

Ribosomes: Ribosomes are large molecules found in all living cells. Ribosomes are responsible
for catalyzing protein forma on during transla on. A strand of mRNA docks onto a ribosome
molecule and the correct amino acids are then recruited to the ribosome to create a protein.

Mitochondrion: (plural: mitochondria) The “power plant” of the cell. They are a membrane
bound organelle (inner and outer membrane) with their own circular DNA, and make ATP
(energy) for the rest of the cell.

Endoplasmic Re culum (ER): A series of membranes extending throughout the cytoplasm that
can be peppered with ribosomes (rough ER) or not (smooth ER) and is the site of protein syn
thesis within a cell.

Golgi Apparatus: (also called the Golgi Body) A series of a ened sack like bodies that process
es the cell’s proteins and lipids before they are released to their nal des na on.

Peroxisomes: Contain enzymes that help the cell destroy toxins.

Lysosomes: A sack of enzymes found within the cell that aid in the diges on of food into usa
ble products for the cell.

Cytoskeleton: The “skeleton” found in all eukaryo c cells that provides shape to the cell while
also enabling it to move. It consists of three parts:

1. Micro laments: Small strands that help the cell resist tension. Think of it as a piece of wire.

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Lab 3: Cell Structure & Func on

2.Intermediate laments: Anchors the organelles in the cell and provide addi onal stability.

3.Microtubules: Small hollow tubes that help the cell maintain its shape, move things around
within the cell and form other key structures.

Centriole: Barrel shaped structures that help make cilia and agella. They also play a key role
in cell division.

Cilia: Small “hairs” on the outside of the cell. They help the cell move and are sensory recep
tors.

Flagella: The structure of eukaryo c agella is far more complex than prokaryo c agella as
the consist of mul ple laments. They provide mobility by rota ng back and forth, they help
transport uids and serve as sensory receptors.

Chloroplast: Think of them as the plant version of mitochondria. The main di erence is that
they take light energy and convert it to mechanical energy.

Vacuole:Membrane bound “sacs” that provide storage and provide transporta on within the
cell (excre on, secre on).

Vesicle: Plays a similar role to vacuoles, but are smaller.

Structure Prokaryo c Cell Eukaryo c Cell

Nucleus No Yes

Plasma Membrane Yes Yes

Cell Wall Yes Yes (in most cells)

Cytoplasm Yes Yes

Flagella and Pili Occasionally
Flagella Occasionally

Pili No
Cilia No Occasionally

Glycocalyx Occasionally Occasionally

Cytoskeleton No Yes

Endoplasmic Re culum No Yes

Mitochondria No Yes

Golgi Apparatus No Yes

Chloroplast No In plants and many pro sts

Ribosome Yes Yes

Lysosome No Yes

Peroxisome No Yes

Vacuole and Vesicle No Yes (in most cells)

Prokaryo c vs. Eukaryo c Cells

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Lab 3: Cell Structure & Func on

Although prokaryo c cells do not have a nucleus, they do have DNA. The DNA is a closed loop and ex
ists freely in an unorganized manner within the cytoplasm, in an area known as the nucleoid region.
They can also have a slime coa ng, called the glycocalyx, which is used to protect the cell and enable it
to a ach to surfaces (such as teeth and lungs). Prokaryotes also have ribosomes to facilitate the pro
duc on of proteins. All cells, prokaryotes and eukaryotes, must have a means to regulate nutrients and
wastes, and also require a supply of energy to exist. Metabolic ac vi es such as photosynthesis and
respira on can be carried out by both cell types. In eukaryotes, photosynthe c ac vity ini ates in the
chloroplasts, while in prokaryotes it occurs in the thylakoid.

Regardless of the cell type or structure, di usion of
molecules is almost always a factor. Molecules are
constantly in mo on due to the kine c energy pre
sent in every atom. This energy results in the net
movement of molecules from areas of high concen
tra on to areas of low concentra on, or di usion
(Figure 3). If uninhibited, this movement will con n
ue un l equilibrium is reached and the molecules are
uniformly distributed.

The rate of di usion depends on the medium used,
size of the molecule, and polarity of molecule. Be
cause the medium will not change in a biological sys
tem, the di usion rate is usually dictated by molecu
lar characteris cs. Small, non polar molecules ex
hibit a higher rate of di usion than large, charged
ones.

The direc on of di usion depends on concentra on gradients, heat and pressure. The concentra on
gradient is the change of molecular density over a given area. Temperature and pressure typically re
main constant in biological systems, making the concentra on gradient the best indicator of direc on
ality. In general, molecules will move towards areas of lower concentra ons.

Figure 3

Di usion through a semi permeable membrane

(lipid bilayer)

45

Lab 3: Cell Structure & Func on

Experiment 1: Iden fying Cell Structures

View the slide pictures and images below, paying a en on to detail, and note the di erent characteris
cs of prokaryotes and eukaryotes. On each picture, label the parts indicated if they are visible. If you

can not see them, draw and label them where they would be located.

Bacteria: Nucleoid region, cell wall, plasma membrane, ribosomes, agella

Pro st: Macronucleus, micronucleus, plasma membrane, cytoplasm, contrac le vacuole

Figure 3

Figure 4

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Lab 3: Cell Structure & Func on

Figure 6

Figure 5

Plant Cell: Nucleus, cell wall, plasma membrane, cytoplasm, chloroplast, mitochondria, vacuoles

Animal Cell: Nucleus, nucleolus, plasma membrane, cytoplasm, mitochondria, golgi apparatus, rough
ER, ribosome

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Lab 3: Cell Structure & Func on

Ques ons

1. For each structure iden ed, do you think its loca on a ects its ability to func on? Why or
why not? (Hint: those buried deep in the cell probably do di erent things than those closer
to the cell membrane)

2. Draw a labeled diagram of a small sec on of the plasma membrane and brie y describe its
structure and func on.

3. Describe the di erences between animal and plant cells.

4. Which of the following structures are present in both prokaryo c and eukaryo c cells? Plas
ma membrane, Golgi apparatus, DNA, lysosomes and peroxisomes, cytoplasm

5. Where is gene c material found in plant cells?

6. Mitochondria contain their own DNA (circular) and have a double membrane. What explana
on for this observa on can you come up with?

(Hint 1: Where else do we see circular DNA?)
(Hint 2: What do you know about the rela ve age of eukaryo c cells?)

7. How is the structure of the plant’s cellulose based cell wall related to its func on?

8. Defects in structures of the cell can lead to many diseases. Pick one structure of a eukaryo c
cell and develop a hypothesis as to what you think the implica ons would be if that structure
did not func on properly.

48

Lab 3: Cell Structure & Func on

9. Using books, ar cles, the internet, etc. conduct research to determine if your hypothesis was
correct.

Experiment 2: Direc on and Concentra on Gradients

In this experiment, we will inves gate the e ect of solute concentra on on osmosis. A semi permeable
membrane (dialysis tubing) and sucrose will create an osmo c environment similar to that of a cell.
Using di erent concentra ons of sucrose (which is unable to cross the membrane) will allow us to ex
amine the net movement of water across the membrane.

Materials

30% Sucrose solu on

4 15 cm Pieces dialysis tubing**

3 250 mL Beakers

8 Rubber bands

Concepts to explore:

Water*

Watch*

*You must provide

**Cut to exact length

Note:

Dialysis tubing can be rinsed and used again if you make a mistake.

Dialysis tubing must be soaked in water before you will be able to open it up to create the
dialysis “bag”. Follow the direc ons for the experiment, beginning with soaking the tubing
in a beaker of water. Then, place the dialysis tubing between your thumb and fore nger
and rub the two digits together in a shearing manner. This should open up the “tube” so
you can ll it with the di erent solu ons.

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Lab 3: Cell Structure & Func on

Procedure

1. Submerge the four pieces of dialysis tubing into a 250 mL beaker
lled with 100 mL of water for at least 10 minutes.

2. A er 10 minutes, remove one piece of tubing from the beaker.
On one end (not the whole tube), gently twirl the tubing into a
long, thin cylindrical piece that is able to t into the hole of the
yellow bead.

3. Insert the long cylindrical end of the tube into the center hole in
the yellow bead. Once it is through, pull the cylindrical end un l
there is about 1.5 to 2 cm of tubing extending beyond the bead

4. Take the extra tubing you just pulled through the bead and fold it back over the bead, towards
the remaining, non folded tube. Place a rubber band above the bead and around the extra
tubing as to be sure no solu on can leak out of the tube (see Figure 4).

To test that no solu on can leak out, add a few drops of water and look for water leakage.
Make sure you pour the water out before con nuing to the next step.

5. Repeat steps 2 4 with the three remaining dialysis tubes, using each of the three remaining
bead colors (Figure 5).

6. Table 1 provides a dis nc on as to what bead belongs to which tube. Using a 10 mL graduated
cylinder, measure and ll the appropriate dialysis bag with the designated concentra on of su
crose solu on (3%, 15% or 30%) by adding the volumes of sucrose and water listed in Table 1.

Figure 4: Fold the bag un l
you have a piece narrow
enough to be threaded

through the bead.

Figure 5: Beads help to secure the ends of the dialysis bags and iden fy each one.

50

Lab 3: Cell Structure & Func on

7. Rinse the outside of the bags with water to remove any remaining sucrose.

8. Pour 150 mL of the stock sucrose solu on (30%) into the 250 mL beaker (beaker #1). Using the
graduated cylinder, measure 20 mL of the stock sucrose solu on and 180 mL of water to cre
ate a 3% sucrose solu on and place it into the 250 mL beaker (beaker #2).

9. Place bags #1 3 (red, blue, yellow) into beaker 2 and bag #4 (green) into beaker 1 (Figure 6).

10. In Table 2, predict whether water will ow in or out of each dialysis bag.

11. Allow the bags to sit for one hour. While wai ng, dump out the water in the 250 mL beaker
that was used to soak the dialysis tubing in step 1. We will use this in the last part of the ex
periment.

12. A er allowing the bags to sit for one hour, remove them from the beakers.

Bead Color Bag Number Stock Sucrose Solu on Water

Yellow Bag #1: 30% sucrose 10 mL 0 mL

Red Bag #2: 15% sucrose 5 mL 5 mL

Blue Bag #3: 3% sucrose 1 mL 9 mL

Green Bag #4: 3% sucrose 1 mL 9 mL

Table 1: How to Make a Serial Dilu on of Sucrose

Figure 6: The
dialysis bags
are lled with
varying con
centra ons of
sucrose solu
on and placed
in one of two
beakers.

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Lab 3: Cell Structure & Func on

13. Carefully open the bags, no ng that o en mes the tops may need to be cut as they tend to
dry out. Measure the solu on volumes of each dialysis bag using the empty 250 mL beaker.
Record your data in Table 2.

Ques ons

1. For each of the bags, iden fy whether the solu on inside was hypertonic, hypotonic or isotonic in
comparison to the beaker solu on it was placed in.

2. Which bag increased the most in volume? Why?

3. What does this tell you about the rela ve tonicity between the contents of the bag and the solu
on in the beaker?

4. What would happen if bag 1 is placed in a beaker of dis lled water?

Ini al Volume Sucrose % Predic on: Will water move in or out? Final Volume

Bag#1 10 mL

Bag #2 10 mL

Bag #3 10 mL

Bag #4 10 mL

Table 2: Water Movement

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