Remember to Keep Washing Your Hands!!! Even Though We Cannot Continue Regular Class It Is Super Important That WE STILL LEARN

Dear Students,

I hope that you all are doing great and that you are staying healthy!! Remember to keep washing your hands!!! Even though we cannot continue regular class it is super important that WE STILL LEARN. I listed below a couple different assignments for you guys to work on in our time apart. These assignments will all be posted on google classroom. The regular homework as well as the worksheets will also be given out by Mr. Dwyer.

1. Ck-12 Readings (on google classroom and in this packet) a. Read each article b. Take notes c. Define vocab words d. Answer article questions e. ***Watch any videos that are linked! **** 2. Khan Academy a. I will post a new assignment each week on Khan academy. Your job is to work through each lesson, watch videos, answer questions and take the unit assessments when they come up. IF YOU STRUGGLE, make sure to take notes on the videos, work through his examples. Also feel free to ask my any questions! 3. Worksheets a. I will post the Philadelphia School District Learning Resources, please complete these at your own pace! The packets are not intended to be done in one day or even a week, take your time!

If you need me for anything at all please email me at [email protected] or give me a call/text 610-551-3797!

Best, Ms. Mills

Name: Cell Division Notes: ➢ ➢ ➢ ➢ ➢

Vocabulary: ■ Binary Fission:

■ Cell Division:

■ Cytokinesis:

■ Daughter Cell:

■ Mitosis:

■ Parent Cell:

Review Questions: 1. Describe binary fission.

2. What is mitosis?

3. Contrast cell division in prokaryotes and eukaryotes. Why are the two types of cell division different?

www.ck12.org Chapter 1. Cell Division

CHAPTER 1 Cell Division

Learning Objectives

• Define cell division. • Explain binary fission. • Define mitosis and cytokinesis. • Contrast cell division in prokaryotes and eukaryotes.

Where do cells come from?

No matter what the cell, all cells come from preexisting cells through the process of cell division. The cell may be the simplest bacterium or a complex muscle, bone, or blood cell. The cell may comprise the whole organism, or be just one cell of trillions.

Cell Division

You consist of a great many cells, but like all other organisms, you started life as a single cell. How did you develop from a single cell into an organism with trillions of cells? The answer is cell division. After cells grow to their maximum size, they divide into two new cells. These new cells are small at ﬁrst, but they grow quickly and eventually divide and produce more new cells. This process keeps repeating in a continuous cycle. Cell division is the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells. How this happens depends on whether the cell is prokaryotic or eukaryotic. Cell division is simpler in prokaryotes than eukaryotes because prokaryotic cells themselves are simpler. Prokaryotic cells have a single circular chromosome, no nucleus, and few other cell structures. Eukaryotic cells, in contrast, have multiple chromosomes contained within a nucleus, and many other organelles. All of these cell parts must be duplicated and then separated when the cell divides. A chromosome is a coiled structure made of DNA and protein, and will be the focus of a subsequent concept.

Cell Division in Prokaryotes

Most prokaryotic cells divide by the process of binary fission. A bacterial cell dividing this way is depicted in Figure 1.1. Binary fission can be described as a series of steps, although it is actually a continuous process. The steps are described below and also illustrated in Figure 1.2. They include DNA replication, chromosome segregation, and finally the separation into two daughter cells.

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FIGURE 1.1 Binary Fission in a Bacterial Cell. Cell division is relatively simple in prokaryotic cells. The two cells are dividing by binary ﬁssion. Green and orange lines indicate old and newly-generated bacterial cell walls, respectively. Eventually the parent cell will pinch apart to form two identical daughter cells. Left, growth at the center of bacterial body. Right, apical growth from the ends of the bacterial body.

• Step 1: DNA Replication. Just before the cell divides, its DNA is copied in a process called DNA replication. This results in two identical chromosomes instead of just one. This step is necessary so that when the cell divides, each daughter cell will have its own chromosome. • Step 2: Chromosome Segregation. The two chromosomes segregate, or separate, and move to opposite ends (known as "poles") of the cell. This occurs as each copy of DNA attaches to different parts of the cell membrane. • Step 3: Separation. A new plasma membrane starts growing into the center of the cell, and the cytoplasm splits apart, forming two daughter cells. As the cell begins to pull apart, the new and the original chromosomes are separated. The two daughter cells that result are genetically identical to each other and to the parent cell. New cell wall must also form around the two cells.

Cell Division in Eukaryotes

Cell division is more complex in eukaryotes than prokaryotes. Prior to dividing, all the DNA in a eukaryotic cell’s multiple chromosomes is replicated. Its organelles are also duplicated. Then, when the cell divides, it occurs in two major steps:

1. The ﬁrst step is mitosis, a multi-phase process in which the nucleus of the cell divides. During mitosis, the nuclear membrane breaks down and later reforms. The chromosomes are also sorted and separated to ensure that each daughter cell receives a diploid number (2 sets) of chromosomes. In humans, that number of chromosomes is 46 (23 pairs). Mitosis is described in greater detail in a subsequent concept. 2. The second major step is cytokinesis. As in prokaryotic cells, the cytoplasm must divide. Cytokinesis is the division of the cytoplasm in eukaryotic cells, resulting in two genetically identical daughter cells.

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FIGURE 1.2 Steps of Binary Fission. Prokaryotic cells divide by binary ﬁssion. This is also how many single-celled organisms reproduce.

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Science Friday: The Axolotl: A Cut Above the Rest

The axolotl is an animal with the incredible ability to regenerate its legs. In this video by Science Friday, Dr. Susan Bryant discusses the research on how these animals are able to accomplish this amazing feat.

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Summary

• Cell division is part of the life cycle of virtually all cells. Cell division is the process in which one cell divides to form two new cells. • Most prokaryotic cells divide by the process of binary ﬁssion. • In eukaryotes, cell division occurs in two major steps: mitosis and cytokinesis.

Review

1. Describe binary ﬁssion. 2. What is mitosis? 3. Contrast cell division in prokaryotes and eukaryotes. Why are the two types of cell division different?

References

1. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation;Ed Uthman. CK-12Foundation;CK12;http:/ /web2.airmail.net/uthman/specimens/images/tvp.html . CC BY-NC 3.0;Public Domain 2. Zachary Wilson;Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. CK-12Foundation . CC BY- NC 3.0 3. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. CK-12Foundation . CC BY-NC 3.0

4 Prokaryotic Cell Division Notes: ➢ ➢ ➢ ➢ ➢

Vocabulary: ■ N/A

Review Questions: 1. What is asexual reproduction?

2. What is binary fission?

3. Describe the process of prokaryotic cell division.

4. What is division septum?

www.ck12.org Chapter 1. Prokaryotic Cell Division - Advanced

CHAPTER 1 Prokaryotic Cell Division - Advanced

• Describe the properties of cell division in prokaryotes.

How do bacteria reproduce?

Essentially, after replicating their DNA, they just grow and divide. As shown here, they grow larger and then split into two separate but genetically identical cells.

Cell Division in Prokaryotes

Prokaryotic organisms reproduce asexually by binary fission, a process that produces identical offspring (Figure 1.1). In asexual reproduction, a single parent produces genetically identical offspring. As prokaryotes do not have a nucleus, and have only one circular chromosome, they do not need to reproduce by the same mechanism as eukaryotic cells; mitosis does not exist in prokaryotic cells. Prokaryotic cell division is a much simpler process. In prokaryotic cell division, after the single chromosome is copied, the cell grows larger. Eventually the two chromosomes separate and move to opposite ends of the cell. Newly formed cell membrane then grows into the center of the cell, separating the two chromosomes, and forming two genetically identical daughter cells. Some eukaryotic organelles, such as mitochondria and chloroplasts, also divide by binary fission. Binary fission can be described as a series of steps, although it is actually a continuous process. The steps are described below and also illustrated in Figure 1.2. They include DNA replication, chromosome segregation, and finally the separation into two daughter cells.

• Step 1: DNA Replication. Just before the cell divides, its DNA is copied in a process called DNA replication. This results in two identical chromosomes instead of just one. This step is necessary so that when the cell divides, each daughter cell will have its own chromosome. • Step 2: Chromosome Segregation. The two chromosomes then attach themselves to different parts of the cell membrane. Segregation or separation of the chromosomes occurs as they move to opposite ends of the cell during the cell separation process. • Step 3: Separation. A new cell membrane starts growing into the center of the cell, and the cytoplasm splits apart, forming two daughter cells. New cell wall must also form around the two cells. This new developing

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cell walls between the cells is known as a division septum. As the cell begins to pull apart, the new and the original chromosomes are separated. The two daughter cells that result are genetically identical to each other and to the parent cell.

FIGURE 1.1 In binary ﬁssion, the single chromosome is copied and eventually separates into two separate chromosomes, the cell grows larger, and two identical cells form by the formation of new cell membrane (and cell wall) and the division of the cytoplasm.

Under ideal conditions, reproduction in bacteria is extremely efﬁcient, with some bacteria reproducing every 20 minutes. This makes bacteria an extremely effective tool for the molecular biologist. However, bacteria do not usually live in ideal conditions; otherwise, bacteria would grow and divide extremely rapidly, eventually covering the surface of Earth. Bacterial growth is limited by nutrients and water, predation, and by their own wastes.

FIGURE 1.2 Cell division is relatively simple in prokaryotic cells. The two cells divide by binary ﬁssion. Green and orange lines indicate old and newly-generated bacterial cell walls, respectively. Eventually the parent cell will pinch apart to form two identical daughter cells. Left, growth at the center of bacterial body, such as in Bacillus subtilis and E. coli. Right, apical growth from the ends of the bacterial body, such as in Corynebacterium diphtheriae.

2 www.ck12.org Chapter 1. Prokaryotic Cell Division - Advanced

Summary

• Binary ﬁssion is a form of cell division in prokaryotic organisms that produces identical offspring.

Review

1. What is asexual reproduction? 2. What is binary ﬁssion? 3. Describe the process of prokaryotic cell division. 4. What is division septum?

References

1. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. Steps of Binary Fission . CC BY-NC 3.0 2. Zachary Wilson. CK-12Foundation . CC BY-NC 3.0

3 Eukaryotic Cell Division Notes: ➢ ➢ ➢ ➢ ➢

Vocabulary: ■ N/A

Review Questions: 1. What is cell division?

2. What is cytokinesis and when does it occur?

3. Describe eukaryotic cell division.

4. When does cell division occur?

5. How many chromosomes do humans have?

www.ck12.org Chapter 1. Eukaryotic Cell Division - Advanced

CHAPTER 1 Eukaryotic Cell Division - Advanced

• Describe cell division in eukaryotes. • Explain the main differences between cell division in prokaryotic and eukaryotic cells.

Are these cells prokaryotic or eukaryotic?

Notice the nucleus. Eukaryotic cell division is more complicated than prokaryotic division because of this organelle. Having more than one chromosome and ensuring that all daughter cells receive a full compliment of chromosomes is no easy task.

Cell Division in Eukaryotes

Though cell division in all cells results in one cell becoming two cells, cell division in eukaryotic organisms is very different from that in prokaryotes, mainly because of the many chromosomes in the nuclei of eukaryotic cells. Cell division in eukaryotic organisms is necessary for development, growth, and repair of the organism. Just as in binary ﬁssion, eukaryotic cell division ensures that each resulting daughter cell receives a complete copy of the organism’s entire genome. Remember that all of an organism’s DNA must be present in each somatic, or body, cell. This DNA contains the information necessary for that cell to perform its functions, and to give that organism its traits. Therefore, prior to cell division, the eukaryotic cell’s complete genome must be copied, a process known as DNA replication, ensuring that each daughter cell receives a complete set of the genome. Prior to cell division, the cell’s organelles are also duplicated. Now the cell is ready to divide. Cell division occurs at the end of an eukaryotic cell’s cell cycle. Eukaryotic cell division occurs in two major steps:

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that each daughter cell receives a diploid number of chromosomes. In humans, that number of chromosomes is 46 (23 pairs). Mitosis is described in greater detail in Cell Cycle: Mitosis (Advanced). Because the DNA has replicated prior to mitosis, the two nuclei that result from mitosis are genetically identical. 2. The second major step is cytokinesis. As in prokaryotic cells, the cytoplasm must divide. Cytokinesis is the division of the cytoplasm in eukaryotic cells, resulting in two genetically identical daughter cells.

FIGURE 1.1 Shown are cells in various stages of their cell cycle. Numerous dividing cells are evident.

The formation of gametes, an organism’s reproductive cells, such as sperm and egg cells, involves a completely different method of cell division, called meiosis. This cell division ensures that each gamete receives a haploid number (half the amount) of chromosomes.

Summary

• Eukaryotic cell division involves mitosis and cytokinesis. • Eukaryotic cell division occurs at the end of the cell cycle.

Review

1. What is cell division? 2. What is cytokinesis and when does it occur? 3. Describe eukaryotic cell division. 4. When does cell division occur? 5. How many chromosomes do humans have?

References

1. Image copyright Dimarion, 2014. Live healthy red cells . Used under license from Shutterstock.com

2 Cell Cycle Notes: ➢ ➢ ➢ ➢ ➢

Vocabulary: ■ Cancer:

■ Cell Cycle:

■ Interphase:

■ Mitotic Phase:

■ Tumor:

■ DNA Replication:

Review Questions: 1. Identify the phases of the eukaryotic cell cycle.

2. What happens during interphase?

3. Define cancer.

4. Cells go through a series of events that include growth, DNA synthesis, and cell division. Why are these events best represented by a cycle diagram?

5. Explain how the cell cycle is regulated.

6. Why is DNA replication essential to the cell cycle?

www.ck12.org Chapter 1. Cell Cycle

CHAPTER 1 Cell Cycle

Learning Objectives

• Deﬁne the cell cycle. • List, in order, the phases of the cell cycle. • Summarize the phases of the eukaryotic cell cycle. • Explain control of the cell cycle. • Deﬁne cancer.

What is a cell’s life like?

The eukaryotic cell spends most of its "life" in interphase of the cell cycle, which can be subdivided into the three phases, G1, S and G2. During interphase, the cell does what it is supposed to do. Though cells have many common functions, such as DNA replication, they also have certain speciﬁc functions. That is, during the life of a heart cell, the cell would obviously perform certain different activities than a kidney cell or a liver cell.

The Cell Cycle

Cell division is just one of several stages that a cell goes through during its lifetime. The cell cycle is a repeating series of events that include growth, DNA synthesis, and cell division. The cell cycle in prokaryotes is quite simple: the cell grows, its DNA replicates, and the cell divides. In eukaryotes, the cell cycle is more complicated.

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The Eukaryotic Cell Cycle

The diagram in Figure 1.1 represents the cell cycle of a eukaryotic cell. As you can see, the eukaryotic cell cycle has several phases. The mitotic phase (M) actually includes both mitosis and cytokinesis. This is when the nucleus and then the cytoplasm divide. The other three phases (G1, S, and G2) are generally grouped together as interphase. During interphase, the cell grows, performs routine life processes, and prepares to divide. These phases are discussed below.

FIGURE 1.1 Eukaryotic Cell Cycle. This diagram represents the cell cycle in eukaryotes. The First Gap, Synthesis, and Second Gap phases make up interphase (I). The M (mitotic) phase includes mitosis and cytokinesis. After the M phase, two cells result.

Interphase

Interphase of the eukaryotic cell cycle can be subdivided into the following three phases, which are represented in Figure 1.1:

• Growth Phase 1 (G1): during this phase, the cell grows rapidly, while performing routine metabolic processes. It also makes proteins needed for DNA replication and copies some of its organelles in preparation for cell division. This phase is sometimes referred to as Gap 1. • Synthesis Phase (S): during this phase, the cell’s DNA is copied in the process of DNA replication. • Growth Phase 2 (G2): during this phase, the cell makes ﬁnal preparations to divide. For example, it makes additional proteins and organelles. This phase is sometimes referred to as Gap 2.

Control of the Cell Cycle

If the cell cycle occurred without regulation, cells might go from one phase to the next before they were ready. What controls the cell cycle? How does the cell know when to grow, synthesize DNA, and divide? The cell cycle is controlled mainly by regulatory proteins. These proteins control the cycle by signaling the cell to either start or delay the next phase of the cycle. They ensure that the cell completes the previous phase before moving on. Regulatory proteins control the cell cycle at key checkpoints, which are shown in Figure 1.2. There are a number of main checkpoints.

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• The G1 checkpoint, just before entry into S phase, makes the key decision of whether the cell should divide. • The S checkpoint determines if the DNA has been replicated properly. • The mitotic spindle checkpoint occurs at the point in metaphase where all the chromosomes should have aligned at the mitotic plate.

FIGURE 1.2 Checkpoints in the eukaryotic cell cycle ensure that the cell is ready to proceed before it moves on to the next phase of the cycle.

Cancer and the Cell Cycle

Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell’s DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor (see Figure 1.3). The rapidly dividing cells take up nutrients and space that normal cells need. This can damage tissues and organs and eventually lead to death.

MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/ﬂx/render/embeddedobject/223144

Further Reading

Reproductive Life Cycle

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FIGURE 1.3 These cells are cancer cells, growing out of control and forming a tumor.

Summary

• The cell cycle is a repeating series of events that cells go through. It includes growth, DNA synthesis, and cell division. In eukaryotic cells, there are two growth phases, and cell division includes mitosis. • The cell cycle is controlled by regulatory proteins at three key checkpoints in the cycle. The proteins signal the cell to either start or delay the next phase of the cycle. • Cancer is a disease that occurs when the cell cycle is no longer regulated. Cancer cells grow rapidly and may form a mass of abnormal cells called a tumor.

Review

1. Identify the phases of the eukaryotic cell cycle. 2. What happens during interphase? 3. Deﬁne cancer. 4. Cells go through a series of events that include growth, DNA synthesis, and cell division. Why are these events best represented by a cycle diagram? 5. Explain how the cell cycle is regulated. 6. Why is DNA replication essential to the cell cycle?

References

1. Ed Uthman;User:Kelvinsong/Wikimedia Commons. http://web2.airmail.net/uthman/specimens/images/tvp. html;http://commons.wikimedia.org/wiki/File:Animal_cell_cycle.svg . Public Domain;CC BY-NC 3.0 2. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. CK-12Foundation;CK12 . CC BY-NC 3.0 3. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation;Ed Uthman. CK-12Foundation;http://web2.air mail.net/uthman/specimens/images/tvp.html . CC BY-NC 3.0;Public Domain 4. Ed Uthman. http://web2.airmail.net/uthman/specimens/images/tvp.html . Public Domain

4 180 in theirenvironments. Populations aresensitiveto changes UNIT 4 Unit Performance Task219 . Unit Review 217 . Unit Connections 216 . 212 . Forests ComeBack Thing Explainer:How 196 . Lesson 2:EcosystemDynamics 182 . Lesson 1:Population Dynamics Unit 4 and Change Ecosystems: Stability Ecosystems: Stabilityand Change

Pigeons were domesticated and bred by people thousands of years ago. Pigeons were often used as message carriers because of their ability to find their way home even over long distances. Today, however, the pigeon population has boomed and the birds are damaging buildings, statues, and landmarks. Cities often use wire and netting to keep the birds out and off of buildings. These devices cause the birds to move to a new location but don’t reduce the population. Some cities are looking into different forms of birth control to reduce the population to more manageable numbers.

Predict How do you think changes in population size can affect the composition and stability of an ecosystem?

DRIVING QUESTIONS

As you move through the unit, gather evidence to help you answer the following questions. In your Evidence Notebook, record what you already know about these topics and any questions you have about them. 1. How do scientists measure population and changes in population? 2. What causes populations and ecosystems to remain stable or to change over time? 3. What factors affect populations within an ecosystem? 4. How do modest or drastic changes in ecosystems affect ecosystem stability?

UNIT PROJECT

Go online to download the Unit Project Wetlands at Your Service Worksheet to help plan your project. Wetlands are ecosystems that have water at or near the soil surface at various times of the year. Examples of wetlands include marshes and swamps. Wetlands often form

©Milkovasa/Shutterstock along the boundaries of water features, such as lakes or rivers. How do wetlands help stabilize ecosystems and populations? Model your own wetland and investigate the services wetlands provide for humans and the ecosystem. How might the destruction

Image Credits: of wetlands change the composition of populations and ecosystems?

Unit 4 Ecosystems: Stability and Change 181 4.1 Population Dynamics

Many different species CAN YOU EXPLAIN IT? inhabit the Greater Yellowstone Ecosystem. FIGURE 1: About 500 wolves live in the Greater Yellowstone Ecosystem today. When first reintroduced to the ecosystem, there were only 31 wolves.

Gather Evidence As you explore the lesson, gather evidence for how populations interact in ecosystems.

Yellowstone National Park, located primarily in northwest Wyoming, is at the heart of the Greater Yellowstone Ecosystem. The rugged terrain and abundance of prey make this temperate ecosystem an ideal environment for wolves. However, due to aggressive eradication efforts in the 1800s and early 1900s, wolves were hunted to

the point that they were no longer present in the park. By 1926, the last wolf pack in (b) ©SBTheGreenMan/iStock/Getty Images Plus Yellowstone had been eliminated. The effect of such a change on an ecosystem was not well understood by scientists at that time. In 1995, a program began to reintroduce wolves into Yellowstone National Park. During the first several years in which the wolf population was restored, observational studies reported that the diversity of plant species increased, certain songbirds returned, and aquatic ecosystems within the park changed.

Predict How might the reintroduction of wolves into Yellowstone National Park (t) ©Michael H Spivak/Moment/Getty Images; have caused both direct and indirect changes in populations of so many other species within their ecosystem? Image Credits:

182 Unit 4 Ecosystems: Stability and Change EXPLORATION 1

Population Density and Dispersion

If you have ever traveled from a rural area to a city, you may have noticed a change in FIGURE 2: Cities have dense population density. Cities have more dense populations, while rural areas have more human populations. widely dispersed, or scattered, populations. Species populations are measured in a similar way. What can we learn from population data?

Population Density

You may be familiar with the term density in the context of matter. It is the amount of matter in a given space. Population density is very similar: it is the number of individuals living in a defined space. When scientists such as wildlife biologists observe changes in population density over time, one of the things they study is whether the causes are due to environmental changes or natural variations in the life history of the species. The biologists use this information to decide whether it is necessary to make changes to maintain a healthy population. One tool that biologists can use to make this decision is to calculate the ratio of Collaborate With a individuals living in an area to the size of that area. partner, discuss whether Population density is calculated using the following formula: the area where you live has a dense or dispersed population. Explain number of individuals __ population density area (units2) = your reasoning. To calculate this ratio for the deer herd shown in Figure 3, a biologist would first determine the size of the herd’s territory. Then the scientist would count all of the individuals in that population within the defined area.

Math Connection A scientist and her team counted 200 individual deer in an area of 10 square kilometers. 1. What is the population density? ©Robert Harding/Wendy Connett/Getty Images;

(t) 2. Ten years later, scientists return to the same area and find that the population density has declined to 5 deer per square kilometer. What might a decrease in the density of a deer population tell scientists about the habitat in the area? Image Credits:

Lesson 1 Population Dynamics 183 Population Dispersion

You may have noticed that people tend to separate themselves in different ways— some hang out in large groups, some gather in twos and threes, while others prefer to be alone. There are also patterns in the way different populations of other organisms separate themselves. Figure 4 shows three main patterns of population dispersal: clumped, uniform, and random. Clumped dispersion occurs when resources are spread unevenly within an ecosystem. Individuals gather into groups where resources are available. Clumped dispersion helps protect individuals from predators and makes finding a mate easier. Uniform dispersion occurs when individuals of the same species must compete for limited resources and territory. Random dispersion is the least common pattern of distribution. It occurs when resources are evenly distributed within an ecosystem. In plants, this type of dispersion often occurs when seeds are scattered by wind or water, resulting in seeds being dropped randomly. The seeds will only sprout if conditions are right, which increases the randomness of the distribution.

FIGURE 4: Population Dispersion Patterns

Analyze Why might a population exhibit uniform dispersion? Think about why having a defined space might be beneficial.

a Clumped dispersion b Uniform dispersion c Random dispersion

Model Draw a diagram showing an overhead view of a population with each type of dispersion: clumped, uniform, and random.

Measuring population size over a large area may seem like an impossible task. Sometimes, a complete count of every individual can be done, particularly if the species lives in an enclosed area. However, what if you needed to count a very large population over many square kilometers? In this case, biologists can use a variety of sampling techniques to estimate the size of a population. One method scientists use to measure the size of a population of animals is the mark–

recapture technique. Biologists capture individuals within a population, tag them, and ©Moment/Stoneography/Getty Images; (c) then release them. After a period of time, a second sample is captured, and biologists look for and count the tagged individuals as well as any newly-captured animals. They may also fit animals with radio collars or GPS devices to track their movements. Another method is called quadrat sampling, in which ecologists use quadrats— typically square or rectangular grids of a known size—to collect data about population ©Rich Carey/Shutterstock;

numbers in an ecosystem. Quadrat sampling works best with species that do not (l) move, such as plants and corals. Image Credits:

184 Unit 4 Ecosystems: Stability and Change Hands-On Lab FIGURE 5: Quadrat sampling is most often used to survey Quadrat Sampling populations of plants.

Use a quadrat sampling method to collect data about population numbers.

Predict Does quadrat sampling provide an accurate estimated of a population size within a defined area?

PROCEDURE 1. Obtain a quadrat frame. Measure, calculate, and record the area of the quadrat on a piece of paper or in your notebook. MATERIALS 2. Stand at the edge of the area you will sample and randomly throw your quadrat. • calculator Make sure your quadrat does not overlap with another. • meterstick