pre-lab homework lab 1: intro to genetics. · biology 102 pcc, cascade 1 pre-lab homework lab 1:...

Biology 102 PCC, Cascade

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Pre-lab homework Lab 1: Intro to Genetics. Lab Section: Name:

1. Briefly explain the following terms in your own words. (You may use any resource you can find,

textbook, website, instructor..., but you need to try to use your own words!) .

• Cell:

• Nucleus:

• DNA:

• Gene:

• Genetic Disorder:

2. Write a short description of your background in biology. This could include what previous classes

you have had, any interesting experiences you have had that relate to biology, really anything that you

think is important and related to biology that would help us understand your background.

3. What are your goals for taking this class? (Why are you in this class? What do you hope to learn? Is

this class a prerequisite for other classes you need for a degree? Which ones?...)


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Lab 1: Issues in Genetics

Goals: After successfully completing this lab, a student will be able to:

• List characteristics of a topic that make it a good issue.

• Describe several contemporary issues involving genetics.

• Use the resources available at PCC to find information about issues.

Overview:

Throughout this term we will be working on a project to discuss different social issues that are

related to the topics which we will be covering. This first lab is designed to introduce you to some of

these issues and to help provide some of the structure and tools you will need for the rest of the terms

discussions. We will then watch a movie that should introduce you to some issues in modern biology

and give you a sense of some of the things that are being discussed this term. Finally we will review the

systems that PCC has available to you to access information for your project.

As your instructor introduces the idea of issues in biology try to answer the following questions:

1. What makes an issue different from some other topic that we cover in biology?

2. What are some issues that you (or your group) came up with while thinking about this term?


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3. Why do you think scientists sometimes have a hard time addressing issues when they are so

good at solving other problems in biology?

4. What is the role of non-scientists in the discussion of issues in biology?

5. Why is it important for even non-scientists to understand the basic concepts in biology when

they discuss these issues?

On the next page you will answer questions about a video on some of the current areas of research in

biology. While you watch the video and answer the questions think about how these topics relate to the

idea of issues in biology.


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Video Worksheet for "Gene Hunters” Name: _____________________________ A Passion for DNA

1. What did James Watson and his colleague Francis Crick discover?

2. Why was Watson and Crick's discovery so important? Gene Reader 3. How many “letters” are there in the human genome?

a) 3 b) 3 million

c) 3 billion d) 3 trillion

4. How much difference is there between any two humans' genomes?

a) none b) %10 difference

c) 100% difference d) 0.1% difference.

Fishing for Baby Genes 5. What does Nancy Hopkins hope to learn from Zebra fish?

6. How many genes does Hopkins think she's looking for?

a) 30,000 b) 2400

c) 16 d) 1

A Gene You Won't Forget 7. What skill does Tim Tully enhance genetically in fruit flies?

a) sense of smell b) ability to detect shocks

c) memory d) ability to see red.

8. How does Tim Tully’s experiment relate to studying for biology class? (just try to relate his findings

to your study habits!)


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Genes for Youth 9. What is special about Cynthia Kenyon's mutant strain of worms?

a) they live twice as long as normal

b) they are twice as big as normal

c) they reproduce twice as fast as normal

d) they move twice as fast as normal

10. What is one of the two ways Kenyon found to regulate the aging process in worms?

Bypass Genes on Trial 11. What does Jeffrey Inser hope the genes he inserts in his patients will do?

a) stop the growth of cancer cells

b) stimulate the growth of a new heart

c) act as a placebo

d) stimulate the growth of new blood vessels

12. Do you think this type of gene therapy is a good idea? Why? 13. Think about the topics that you saw in the video, what do you think is the most controversial topic

that was presented in the video? Why do you think it is controversial?


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Review of PCC’s electronic resources: In biology 101 you had a tour of the PCC library system that was designed to show you how to use the resources available to you. This short review is to remind you of these resources and to give you some ideas for how to find information about current issues in biology.

1. How can you access magazine articles online through the PCC library website?

2. What will you need to access this from home?

3. What other databases are available for you through the library?

4. What other options do you have for finding information about current issues in biology?

5. How can you access information and web links your instructor(s) post for you?


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Pre-lab homework Lab 2: Mitosis and the Cell Cycle. Lab Section: Name:

1.

2. Briefly describe the main occurrences in the 4 phases of mitosis (prophase, metaphase, anaphase and telophase). (Hint: include what happens to the nucleus, spindle fibers and chromosomes.)

• Prophase

• Metaphase

• Anaphase

• Telophase 3. On the back of this sheet briefly describe how we can estimate the length of time a growing onion

root tip cell spends in each of the phases of the cell cycle. (Hint: read lab exercise 3)

Interphase

Mitosis

Label the following stages of the cell

cycle:

• G1

• G2

• S

• Anaphase

• Metaphase

• Telophase

• Prophase


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Lab 2: Mitosis and the Cell Cycle


• Describe the major events of the cell cycle.

• Illustrate the process of nuclear division with models, words, and diagrams.

• Recognize cells in various stages of the cell cycle given pictures or descriptions.

• Explain the connection between checkpoints in the cell cycle and cancer.

Overview:

Cells go through a series of changes as they grow and age that are similar for all eukaryotic cells.

These changes are not always identical for all types of organisms but are similar enough to allow

scientists to generalize two main phases of a cells life the interphase during which there are no visible

changes to the nucleus and mitosis, or the M-phase, where the nucleus undergoes substantial changes

that culminate in the division of one nucleus into two. These phases can be subdivided and all together

make up a cells life cycle. (See Fig. 2.1)

The phases and their stages were initially named early on in the study of cell division and so the

names reflect what was observable to the earliest researchers. The interphase, that time in a cells life

where it is growing but there are no obvious changes in the nucleus, is actually made up of three

separate stages one of which contains crucial changes in the nucleus that are invisible with a light

G1

G2

S

T

A

M P

Figure 2.1: The Cell Cycle

The generalized cell cycle for

eukaryotic cells. The amount of time

spent in each phase of the cell cycle

depends on many factors including the

cell type and the conditions the cell is in.

In lab this week we will calculate the

length of each phase for cells in the

rapidly dividing root tip of an onion.


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microscope. The first stage, called G1 or Gap 1, is a time of growth for the cell (in fact some people like

to call G1 and G2 the growth stages since a lot of cell growth is going on during this time) the cell is

busy building more of its cellular components, organelles will increase in size (the rough and smooth

ER) or increase in number (the mitochondria) or both (the golgi body). The cytoplasm also increases in

volume and the entire cell increases in size. During this time the cell is actively monitoring both its

external and internal environments. When conditions are right both inside and outside the cell a decision

will be made to proceed to the next stage of interphase called S or the Synthesis stage. During this stage

each of the cells molecules of DNA are duplicated so that there are now two identical copies of each

DNA molecule inside the cells nucleus. These DNA molecules are wrapped around proteins and further

packed into structures called chromosomes so it is often said that the chromosomes duplicate during this

stage. While this phase involves dramatic changes in the amount of DNA in the nucleus it cannot be

detected by even the most sensitive of light microscopes. During this time a cell will continue to produce

mRNA and use it as a template to synthesize more proteins so that outside the nucleus the cell continues

on much as it does during the G1 phase. Once a cell has passed through the S stage it is committed to

dividing its nucleus, it just wouldn’t make any sense for a cell to spend all of those resources duplicating

its chromosomes and then not divide the nucleus, but nuclear division is not the next step in the cell

cycle. After S the cell enters a stage of interphase called G2, or the second Gap phase, during this phase

the cell continues to build proteins and other cellular components but there is change in the rate of

production of certain proteins as the cell prepares to enter into mitosis. At this point the cell once again

runs a series of checks with its internal environment to ensure that all is well prepared before it passes

out of interphase and into the process of nuclear division.

During mitosis the cells nucleus goes through a series of events that accomplish the task of dividing

the duplicated chromosomes into two groups and sorting them into two new nuclei. This process is

continuous, that is it is not broken into obviously distinct phases, but scientists studying the process

have, somewhat arbitrarily, divided this process into four phases. These phases, in order, are prophase,

metaphase, anaphase, and telophase. In most of the cells that we will examine these phases are followed

by the division of the rest of the cells components (its cytoplasm and associated organelles) which is

often called cytoplasmic division or cytokinesis. During lab this week you will spend some time

modeling the process of nuclear division then you will look at regions of plants and animals where large

numbers of cells are undergoing division and you will estimate the amount of time these cells spend in

each phase of cell division.


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Exercise 1: Modeling Mitosis with Pop Beads

In this exercise you will be modeling the movement of chromosomes through the four phases of

mitosis. To begin you will need to get a bag of pop beads from the instructor. These beads will be strung

together to represent chromosomes and you will then use them to demonstrate the stages of mitosis. In

humans there are 23 different types of chromosomes and each of your cells (except sperm or egg cells)

have two versions of each of these chromosomes for a total of 46 in each cell. In order to simplify the

number of chromosomes we have to deal with we will model mitosis in an organism with only two types

of chromosomes. To distinguish the two types apart we will use different lengths of chromosomes

represented by chains of pop beads strung together.

Procedures:

1. Count out your beads – you will need 38 red beads and 38 yellow beads to build your

chromatids. You will also need 8 of the magnetic “centromeres”

2. Assemble your large chromatids by building a chain of 4 red beads and a chain of 8 red beads

and joining these chains to a centromere. Now repeat this to produce another red chromosome

and then do the same thing with yellow beads to produce a total of 2 red and 2 yellow long

chromosomes. (see Fig. 2.2)

3. Assemble your small chromatids by building a chain of 3 red beads and a chain of 4 red beads

and joining these chains to a centromere. Now repeat this to produce another red chromosome

and then do the same thing with yellow beads to produce a total of 2 red and 2 yellow short

chromosomes. (see Fig. 2.2)

4. Once you have your chromatids assembled you can begin to model the stages of the cell cycle

using these pop-bead models.

Instructors initials:

Centromere

Figure 2.2 Your chromatids You will build 4 long (2 red and 2 yellow)

and 4 short (2 red and 2 yellow) chromatids.

Long chromatid

Short chromatid


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Exercise 2: Identifying cells in mitosis

In this exercise you will be using the microscope to identify cells in various stages of cell

division. We have two different types of prepared slides for you to use, onion root tips and whitefish

blastula, both of the slides contain a large number of cells that have been preserved at various stages in

the cell cycle. While each of your slides should have cells that show all the stages of cell division any

one cell is frozen in the stage it is in forever – think of each of the cells as a snapshot of one particular

time in the cell cycle. Your job will be to identify cells in each of the stages of mitosis

Procedures:

1. Get either the onion root tip (sometimes the slide will be labeled allum root tip) or the whitefish

blastula slide and focus on a region where there are cells with visible chromosomes.

Remember to always start on the lowest power and only after you are in focus on

this power swing in the next most powerful objective. At the higher powers only use

the fine focus to sharpen your picture to avoid cracking the slide.

2. Once in focus with the 10X objective (this will be a total of 100X magnification!) you should be

able to identify the nucleus of the cell. This part of the cell is really what you need to pay the

most attention to – especially at first as you try to distinguish cells undergoing division from

those still in interphase.

3. First find a cell that has a clear nucleus but no visible chromosomes (they would appear as thick

strands, almost wormlike) this is characteristic of a cell in interphase. Now sketch this cell in the

interphase in the first box of your sketches.

4. Now find a cell whose nucleus appears to be in prophase – if you can’t remember what to look

for try to remember the main occurrences you modeled in each of the phases in exercise one with

the pop beads. Now sketch this cell, label any structures you can see and list the main things that

you know are happening in this phase

5. Continue on finding cells in metaphase, anaphase, and telophase – sketch each cell, label your

sketch and list out what is happening during each phase.


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Exercise 3: Estimating the time spent in the phases of mitosis

Now that you are becoming proficient at identifying cells in all the different phases of the cell

cycle you can use this skill to develop an understanding of how long this process takes. For this exercise

you will be looking at a large number of cells and deciding which phase each cell is in. We can then use

this information to decide how long each of these phases lasts.

Procedures:

1. For this exercise it will help to work in teams of two. You will need the onion root tip slide from

your box so if one of your lab partners has the slide you should work with them.

2. Once again you need to focus in on the region of the root tip where cells are frozen in the

different stages of cell division. Now start identifying the phase of cell division of each of the

cells you look at and telling your lab partner so they can record the number of cells in each stage.

Once you have identified 25 cells trade jobs with your lab partner. After identifying 50 cells total

trade data with 3 other groups so you have a total of 200 cells identified.

Table 1: Number of cells in each phase of cell cycle.

Phase Interphase Prophase Metaphase Anaphase Telophase Total

Your 25

Partners 25

Totals

Other #1

Other #2

Other #3

TOTALS


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3. Now you are ready to estimate the amount of time these cells spend in each different phase. In an

onion root tip the entire cell cycle take about 12 hours (depending on the plants health and where

you are looking in the root). We will use 12 hours as a rough estimate.

4. Calculate the percentage of time spent in each phase by counting the total number of cells in

each phase (total in interphase, in prophase… and so on) and dividing each by the total number

of cells you counted (this should be 200 if you have compared with 3 other groups).

5. Now multiply the percentage of time in each phase by the total time of the cell cycle ( about 12

hours) and this gives you an estimate of the time spent in each phase.

Table 2: Estimate of time spent in each phase of cell cycle.

Phase Interphase Prophase Metaphase Anaphase Telophase Total

% of cells in

each phase 100%

Time

estimate 12 hours

6. Most of the cells in your body are not dividing this quickly and so the total time may vary a lot

but the amount of time spent in Mitosis (that is in prophase, metaphase, anaphase and telophase)

is about the same as you see here.


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Pre-lab homework Lab 3: DNA Structure & Function Lab Section: Name:

1. Define the following terms in your own words. (Using your textbook, or any other resource, is ok just rephrase

the definitions in your own words!) • DNA:

• Ribose:

• Nucleotide:

• Base pairing:

2. The monomers of DNA are made up of smaller molecules joined together. These three smaller

molecules, a phosphate group, a sugar molecule and a base, are joined together to build the monomer.

Find a diagram in your textbook that shows these subunits and draw one of the monomers in the space

below. (you don’t need to label all the atoms just show the basic structure of the monomer)

3. How are the monomers of RNA different from those of DNA that you drew in question 2?

4. If all the monomers have the same basic structure (sugar, phosphate, base) then where is the variability that allows DNA molecules to store information? (Hint: read the lab!)


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Lab 3: DNA Structure & Function


• Describe the structure of DNA and how this structure allows replication.

• Demonstrate the process of DNA replication and transcription & translation

• Explain how changes in DNA structure can cause changes in protein structure.

Overview:

DNA is the molecule responsible for storing the information your cells need to make protein

molecules. These proteins then go on to control almost all the functions of you cells. So in many ways

DNA controls your cells. Because of this we will spend a lot of time thinking about DNA structure and

seeing how its structure can give it the properties it needs for its central role in all cells. As you know

DNA is a polymer made up of many nucleotides strung together in a long chain. These nucleotides all

have the same sugar and phosphate makeup but the attached base is variable. It is this variable base that

allows gives DNA’s structure the variability it needs to store information During the first part of the lab

we will be working on developing a good understanding of this structure of DNA. To do this we will use

a cardboard model of the nucleotides of DNA in order to build and replicate a short DNA molecule. We

will then be able to use this molecule as a template for transcription and translation while we work on

the next part of the lab which involves an experiment in gel electrophoresis. This is the process of

separating molecules based on their size and charge and is a common way to separate different sized

pieces of DNA for identification. In this weeks lab we will separate not DNA but different dyes but the

principles are the exactly the same. While we set up and run our gels we will continue to work with the

cardboard model of DNA this time to show transcription and translation. This should give us a on feel

for how information stored on DNA can be passed on into RNA and then used as a template for building

protein molecules. Finally we will see how an understanding of DNA and electrophoresis can be used in

a more practical way.


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Exercise 1: Modeling the structure and replication of DNA

In this exercise you will be modeling the structure of DNA using basic cardboard cutout pieces

to represent the nucleotide monomers of DNA. These pieces represent the sugar, phosphate, and base of

a nucleotide and come in four different versions to represent each of the four different types of bases (G,

A, T, & C).

Procedures:

5. To begin you will need to get a DNA modeling set from your instructor and sort the pieces out

into stacks representing each of the four types of nucleotides (see Fig. 3.1) – the pieces labeled as

tRNA and amino acids you should set aside we will use them for exercise 3.

6. Once you have sorted your nucleotides build a chain of nucleotides that reads

GATTACGCCGAC this represents ½ of a DNA molecule.

7. Now build the other half of your molecule by following the base pairing rules of A pairing with

T and G pairing with C.

8. This model now represents a molecule of double-stranded DNA. If this were a human

chromosome it would contain somewhere between about 50 and 250 million bases!

9. To replicate this molecule split the molecule in half by separating the base pairs. Now use each

of these chains of nucleotides as a template for a new molecule by once again following the base

pairing rules (A-T, G-C).

10. Compare each of the resulting molecules to each other – they should be identical.

Figure 3.1: Nucleotide models

The four different types of nucleotides are represented by four different shapes in this model.

A

C

T

G


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Exercise 2: Modeling Transcription and Translation

In this exercise you will be using your DNA model from Exercise 1 to serve as a template for

making a mRNA transcript and then using tRNA molecules to decode the information on the mRNA and

put together a short chain of amino acids. This would normally occur on ribosomes but for now we will

ignore them.

Procedures:

1. Start with one of the double-stranded molecules of DNA you created in exercise 1 (the other

molecule you can “digest” into nucleotides for use in creating your mRNA). This DNA should

have the sequence G-A-T-T-A-C-G-C-C-G-A-C

2. Now pull apart the two halves of your DNA molecule – one half of this molecule will be copied

into mRNA (we call this the sense strand) while the other half is not used (we call this the anti-

sense strand). You need to copy the strand that starts G-A-T-T-A... (the top strand in the above

molecule) to insure that you will have the correct mRNA sequence. Remember though that in

RNA molecules the letter T is replaced by the letter U - so the base pairing rules are actually, A-

U, T-A, C-G, G-C.

3. This mRNA molecule now represents a set of instructions for the order of amino acids needed

for a protein. We now need to decode this information.

4. Find the four tRNA molecules and connect them to the four amino acid molecules in your kit.

5. Now match up the tRNA with the appropriate codon on the mRNA.

6. Notice how this puts the amino acids into a specific order controlled by the order of bases in the

mRNA – changing the order in the mRNA may change the amino acid order in the protein.

G-A-T-T-A-C-G-C-C-G-A-C : : : : : : : : : : : : C-T-A-A-T-G-C-G-G-C-T-G


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Exercise 3: Kiwi DNA Extraction: (modified by Dr. Jennifer Schramm from procedure found at: www.exploratorium.edu (©2000))

Although we cannot see individual molecules of DNA at the molecular level, we can isolate

large quantities of DNA by breaking open large numbers of cells. The goal of this laboratory exercise is

for you to see, touch and feel DNA. Scientists in biotechnology and research laboratories perform

essentially the same technique you are performing today to study DNA in action.

How this procedure works:

1. Mashing: this process breaks down the cell walls of the kiwi

2. Extraction solution: this solution contains detergent and salt and water. A. The detergent breaks down membranes. What cell membranes need to be broken to release

DNA?

B. DNA carries a negative charge and is therefore very soluble in water, so when the cells are broken open, the DNA goes into solution.

C. The salt (NaCl) breaks down into ions in the water. Postively charged sodium ions (Na+) are attracted to and bind the negatively charged DNA molecules. This makes the DNA molecules neutral, so they clump together.

3. Ethanol: DNA is not soluble in ethanol. When ethanol is added to the solution, the DNA can no longer stay in solution and forms a precipitate.

Procedures:

1. You will share an ice water bath with the other group at your lab bench. Create the ice water bath by placing ice and water into a dishpan. The pan should be approximately one-third full.

2. Obtain one kiwi. Peel the kiwi and cut it into chunks. Use a balance to measure 30 g of kiwi. Thoroughly mash the measured kiwi with a fork. Place the mashed kiwi into a 200 ml beaker.

3. Add DNA extraction solution to the beaker containing the mashed kiwi. The total volume of the kiwi and the extraction solution should be twice the volume of the kiwi alone.

4. Place the beaker containing the kiwi and DNA extraction solution into a 60°C water bath.

5. Let the mixture sit in the water bath for 15 minutes.

6. Transfer the beaker to your ice water bath for 5 minutes.

7. While your DNA extraction is cooling, set up the filtration system. Place a funnel over a clean 500 ml beaker. Insert a coffee filter into the funnel.


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8. Pour your cooled extraction solution into your filtration system. It may take several minutes for all the liquid to pass through the filter.

9. When filtration is complete dispose of the coffee filter in the garbage can.

10. Swirl the solution in your beaker. Immediately after swirling, transfer 5 ml of that solution into a test tube.

11. Use a plastic pipette to layer 10 ml of cold ethanol on top of your solution in the test tube.

12. Let the solution sit for 2 minutes.

13. A white gelatinous precipitate will form between the alcohol layer and the water layer (extraction solution). The white stuff is clump of DNA from the cells of the kiwi. Use a glass pipette to suck up your DNA and transfer it to a dish. The DNA is safe to touch!

14. Clean up! All materials in this laboratory can be disposed of in the garbage or down the sink.

Questions:

1. Compare the DNA you extracted in this laboratory to your own DNA. What are the similarities? The differences?

2. Your precipitated DNA contains both nucleic acids and proteins. Where do the proteins come from? (Hint: Think about how DNA is arranged inside a cell.)

3. The nucleus of every human cell contains approximately 2 meters of DNA. A typical adult human contains 60 trillion cells (60,000,000,000,000). The distance from the Earth to the Moon is 380,000 km. If the DNA of a single human were laid end to end, how close would it get to the moon?


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Exercise 4: Electrophoresis

One of the common techniques used in modern biology is gel-electrophoresis. This technique

relies on the fact that charged molecules will be attracted to oppositely charged electrical current and

that small molecules can move more quickly through complex polymers than large ones can.

Procedures:

1. Locate the gel rig on the counter at the side of the room. The lab prep staff has poured an

agarose gel and set it into the rig. This gel, made of a substance similar to jello, has small

chambers called wells in the middle of the gel (see Fig. 3.2) into which you will load samples

of molecules that we will then separate based on their size and charge.

2. Load the gel using the micro-pipette. Your group will be assigned one known molecule and

one unknown mix of molecules to load.

3. Once all 5 different dyes and all mixes have been loaded the gel will be submersed in a fluid

that conducts electricity and then the entire gel will be electrified. *caution high voltage*

Don’t touch the running gel rig!

4. After running you need to determine what molecules were present in your unknown mixture.

wells

Positive pole

Negative pole

Negatively charged molecules

Positively charged molecules

Larger molecules

Smaller molecules

Figure 3.2: Gel set up

Your gel has wells down the middle where you load samples. These samples migrate toward poles with a charge that is the opposite of the sample. Smaller molecules move faster than larger ones.


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Exercise 5: DNA fingerprint interpretation

One of the ways that electrophoresis is used is to separate pieces of DNA of various sizes. By

taking DNA from any individual and cutting it with enzymes that recognize specific base sequences you

can generate a number of DNA pieces of various sizes. Once separated on a gel these different pieces

will generate a set of bands representing the different sized DNA molecules. If you cut the DNA in a

region that is highly variable then different people will likely give different banding patterns allowing

you to determine where the DNA came from. In practice a large number of different variable regions are

compared to insure a match doesn’t happen just by chance.

Background:

Imagine you are a biologist in a small town called in to help solve a crime. Someone has been

sneaking into the local grocery store at night and stealing suckers. Luckily the thief always eats a

sucker at the store and leaves behind the stick that is covered with saliva and quite a few cells from

the thief’s cheek. After a little work you have managed to isolate DNA from these sticks and after

cutting them up you run them out on a gel and generate the following banding pattern.

Figure 3.3: DNA Fingerprinting Part I

In addition to the DNA from the Crime scene you

were able to get DNA samples from 5 suspects that you

cut and ran in the lanes labeled A – E.

After examining the data you call the police

chief and tell her... (What do you tell her?)

Lollypop DNA

Suspect DNA A B C D E


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Several years ago scientists used DNA fingerprinting similar to this to compare the DNA from

people known to be related to Thomas Jefferson to the DNA of people descended from one of

Jefferson’s slaves named Sally Hemmings. The information generated led the scientists to conclude

that one of Sally’s sons had been fathered by Jefferson but that her other son had not. This study was

complicated by the thought that perhaps one of Jefferson’s nephews had been both boys father. Why

would it be more difficult to use this sort of information to distinguish between people who are

closely related?

Lollypop DNA

Suspect DNA F G H I J

Figure 3.4: DNA Fingerprinting Part II

The Police Chief then brings you a new set of DNA

samples taken from some of the criminals that she has

in custody for other crimes.

After examining the data you call the police

chief and tell her... (What do you tell her?)

pre-lab homework lab 1: intro to genetics. · biology 102 pcc, cascade 1 pre-lab homework lab 1:...

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