L1.1 Introduction to Cells and Microscopy

Kris Athomescience

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AUTHOR Kris Athomescience

CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2013 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: September 10, 2013

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Contents

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Contents 1

Cells

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2

Microscopes

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3

Organic Compounds

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C HAPTER

Chapter 1. Cells

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Cells

• Explain how cells are observed. • Define the three main parts of the cell theory. • Explain the levels of organization in an organism.

What are you made of? Cells make up all living things, including your own body. This picture shows a typical group of cells. But not all cells look alike. Cells can differ in shape and sizes. And the different shapes usually means different functions. Introduction to Cells

A cell is the smallest structural and functional unit of an organism. Some organisms, like bacteria, consist of only one cell. Big organisms, like humans, consist of trillions of cells. Compare a human to a banana. On the outside, they look very different, but if you look close enough you’ll see that their cells are actually very similar. Observing Cells

Most cells are so small that you cannot see them without the help of a microscope. It was not until 1665 that English scientist Robert Hooke invented a basic light microscope and observed cells for the first time. You may use light microscopes in the classroom. You can use a light microscope to see cells (Figure 1.1). But many structures in the cell are too small to see with a light microscope. So, what do you do if you want to see the tiny structures inside of cells? In the 1950s, scientists developed more powerful microscopes. A light microscope sends a beam of light through a specimen, or the object you are studying. A more powerful microscope, called an electron microscope, passes a beam of electrons through the specimen. Sending electrons through a cell allows us to see its smallest parts, even the parts inside the cell (Figure 1.2). Without electron microscopes, we would not know what the inside of a cell looked like. 1

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FIGURE 1.1 The outline of onion cells are visible under a light microscope.

FIGURE 1.2 An electron microscope allows scientists to see much more detail than a light microscope, as with this sample of pollen.

Cell Theory

Three scientists–Theodor Schwann, Matthias Jakob Schleiden, and later Rudolf Virchow–using microscopes much better than Hooke’s first microscope, developed the hypothesis that cells only come from other cells. For example, bacteria, which are single-celled organisms, divide in half (after they grow some) to make new bacteria. In the same way, your body makes new cells by dividing the cells you already have. In all cases, cells only come from cells that have existed before. This idea led to the development of one of the most important theories in biology, the cell theory. Cell theory states that: 1. All organisms are composed of cells. 2. Cells are alive and the basic living units of organization in all organisms. 3. All cells come from other cells. As with other scientific theories, many hundreds, if not thousands, of experiments support the cell theory. No evidence has ever been identified to contradict it. 2

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Chapter 1. Cells

Specialized Cells

Although cells share many of the same features and structures, they also can be very different (Figure 1.3). Each cell in your body is designed for a specific task. In other words, the cell’s function is partly based on the cell’s structure. For example: • Red blood cells are shaped with a pocket that traps oxygen and brings it to other body cells. • Nerve cells are long and stringy in order to form a line of communication with other nerve cells, like a wire. Because of this shape, they can quickly send signals, such as the feeling of touching a hot stove, to your brain. • Skin cells are flat and fit tightly together to protect your body. As you can see, cells are shaped in ways that help them do their jobs. Multicellular (many-celled) organisms have many types of specialized cells in their bodies. FIGURE 1.3 Red blood cells (left) are specialized to carry oxygen in the blood. Neurons (center ) are shaped to conduct electrical impulses to many other nerve cells. These epidermal cells (right) make up the “skin” of plants. Note how the cells fit tightly together.

Vocabulary

• cell: Basic unit of structure and function of a living organism; the basic unit of life. • cell theory: Scientific theory that all living things are made up of cells, all life functions occur within cells, and all cells come from already existing cells. • electron microscope: Microscope that uses a beam of electrons to magnify an object. • microscope: An instrument that uses lenses to produce magnified images of small objects. Summary

• Cells were first observed under a light microscope, but today’s electron microscopes allow scientists to take a closer look at the inside of cells. • Cell theory says that: – All organisms are composed of cells. – Cells are alive and the basic living units of organization in all organisms. – All cells come from other cells. Practice

Use the sliding bar to zoom in on this animation to get an idea of the relative sizes of your cells. • Cell Size and Scale - The University of Utah at http://learn.genetics.utah.edu/content/begin/cells/scale/ 3

www.ck12.org 1. What is the average size of a grain of salt? 2. How big is an amoeba proteus? How big is a paramecium? Remember this relationship for when you study amoeba. 3. How big is a skin cell? How big is a red blood cell? Can you think of any problems that might exist if this relationship was reversed? Explain your thinking fully. 4. How big is an E. coli bacterium? How big is a mitochondrion? Remember this relationship for when you study endosymbiosis. 5. Are all cells the same size? Review

1. What type of microscope would be best for studying the structures found inside of cells? 2. What are the three basic parts of the cell theory? 3. According the cell theory, can you create a cell by combining molecules in a laboratory? Why or why not?

References 1. Image copyright Jubal Harshaw, 2010. . Used under license from Shutterstock.com 2. Dartmouth Electron Microscope Facility. . Public Domain 3. Red blood cells: Courtesy of the National Cancer Institute; Neurons: Image copyright Promotive, 2012; Epidermal cells: Image copyright A.R. Monko, 2012. . Red blood cells: Public Domain; Neurons and epidermal cells: Used under licenses from Shutterstock.com

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C HAPTER

Chapter 2. Microscopes

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Microscopes

• Describe how microscopes are used in the life sciences.

How can we see the details of bacteria? With the naked eye, bacteria just look like a slimy smear on a petri dish. How can we study them in more detail? The invention of the microscope has allowed us to see bacteria, cells, and other things too small to be seen with the naked eye.

The Microscope

Microscopes, tools that you may get to use in your class, are some of the most important tools in biology. A microscope is a tool used to make things that are too small to be seen by the human eye look bigger. Microscopy is the study of small objects using microscopes. Look at your fingertips. Before microscopes were invented in 1595, the smallest things you could see on yourself were the tiny lines in your skin. But what else is hidden in your skin?

Invention of the Microscope

Since ancient times people have created tools for magnification, but modern microscopy begain in the 17th century when Galileo Galilei made a compound microscope containing two lenses. In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork—the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells because they reminded him of the small rooms that monks live in. He published Micrographia in 1655, the first major publication of the Royal Society of London and the first scientific best-seller. Dutch scientist Antoine van Leeuwenhoek, in one of his early experiments, took a sample of scum from his own teeth and used his microscope to discover bacteria, the smallest living organism on the planet. Italian scientist Marcello Malphigi studed both plants and animals and contributed especially to our understanding of human anatomy and physiology. 5

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Timeline of Microscope Technology • c2000 BCE - The Chinese use water microscopes made of a lens and a water-filled tube to visualize the unseen. • Up to 612 BCE - The Assyrians manufacture the world’s oldest surviving lenses • 1590 - Dutch spectacle-makers Hans Jansen and his son Zacharias Jansen, claimed by later writers (Pierre Borel 1620 - 1671 or 1628 – 1689 and Willem Boreel 1591 – 1668) to have invented a compound microscope. • 1609 - Galileo Galilei develops a compound microscope with a convex and a concave lens. • 1619 - Cornelius Drebbel (1572 – 1633) presents, in London, a compound microscope with two convex lenses. • 1625 - Giovanni Faber of Bamberg (1574 - 1629) of the Linceans coins the word microscope by analogy with telescope. • 1665 - Robert Hooke publishes Micrographia, a collection of biological micrographs. He coins the word cell for the structures he discovers in cork bark. • 1674 - Anton van Leeuwenhoek improves on a simple microscope for viewing biological specimens. • 1863 - Henry Clifton Sorby develops a metallurgical microscope to observe structure of meteorites. • 1860s - Ernst Abbe discovers the Abbe sine condition, a breakthrough in microscope design, which until then was largely based on trial and error. The company of Carl Zeiss exploited this discovery and becomes the dominant microscope manufacturer of its era. • 1931 - Ernst Ruska starts to build the first electron microscope. It is a Transmission electron microscope (TEM) • 1936 - Erwin Wilhelm Müller invents the field emission microscope. • 1951 - Erwin Wilhelm Müller invents the field ion microscope and is the first to see atoms. • 1953 - Frits Zernike, professor of theoretical physics, receives the Nobel Prize in Physics for his invention of the phase contrast microscope. • 1967 - Erwin Wilhelm Müller adds time-of-flight spectroscopy to the field ion microscope, making the first atom probe and allowing the chemical identification of each individual atom. • 1981 - Gerd Binnig and Heinrich Rohrer develop the scanning tunneling microscope (STM). • 1986 - Gerd Binnig, Quate, and Gerber invent the Atomic force microscope (AFM) • 1988 - Alfred Cerezo, Terence Godfrey, and George D. W. Smith applied a position-sensitive detector to the atom probe, making it able to resolve atoms in 3-dimensions. • 1988 - Kingo Itaya invents the Electrochemical scanning tunneling microscope • 1991 - Kelvin probe force microscope invented.

Types of Microscopes

Some modern microscopes use light, as Hooke’s and van Leeuwenhoek’s did. Others may use electron beams or sound waves. Researchers now use these four types of microscopes: 6

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Chapter 2. Microscopes

1. Light microscopes allow biologists to see small details of a specimen. Most of the microscopes used in schools and laboratories are light microscopes. Light microscopes use lenses, typically made of glass or plastic, to focus light either into the eye, a camera, or some other light detector. The most powerful light microscopes can make images up to 2,000 times larger. 2. Transmission electron microscopes (TEM) focus a beam of electrons through an object and can make an image up to two million times bigger, with a very clear image. 3. Scanning electron microscopes (SEM) (Figure 2.1) allow scientists to find the shape and surface texture of extremely small objects, including a paperclip, a bedbug, or even an atom. These microscopes slide a beam of electrons across the surface of a specimen, producing detailed maps of the surface of objects. 4. Scanning acoustic microscopes use sound waves to scan a specimen. These microscopes are useful in biology and medical research.

FIGURE 2.1 A scanning electron microscope.

Vocabulary

cell: Basic unit of structure and function of a living organism; the basic unit of life. light microscope: Tool that uses lenses to focus light in order to make things appear larger. microscope: Tool used to make things that are too small to be seen by the human eye look bigger. microscopy: The technology for studying small objects using microscopes. scanning acoustic microscope: Tool that uses sound waves to study a specimen too small to be seen with the naked eye. • scanning electron microscope (SEM): Tool that sends a beam of electrons across the surface of a specimen, producing detailed maps of the shapes of objects. • transmission electron microscope (TEM): Tool that focuses a beam of electrons through an object, magnifying it. • • • • •

Summary

• A microscope is a tool used to make things that are too small to be seen by the naked eye look bigger. • Types of microscopes include light microscopes, transmission electron microscopes (TEM), scanning electron microscopes (SEM), and scanning acoustic microscopes. 7

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Use the resources below to answer the questions that follow. • Using a microscope at http://www.youtube.com/watch?v=bGBgABLEV4g (4:01) 1. How should you carry a compound optical microscope? 2. What procedure should you use when seeking to use the most powerful optical lenses? Review

1. What is the purpose of a microscope? 2. Who invented the first compund microscope? 3. Who are three 17th century scientists that extensively studied the microscopic world?

References 1. Image copyright WH Chow, 2012. Scanning Electron Microscope (SEM) machine in cleanroom. Used under license from Shutterstock.com

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C HAPTER

Chapter 3. Organic Compounds

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Organic Compounds

• Describe the four main classes of organic molecules that are the building blocks of life.

What makes up a healthy diet? A healthy diet includes protein, fats, and carbohydrates. Why? Because these compounds are three of the main building blocks that make up your body. You obtain these building blocks from the food that you eat, and you use these building blocks to make the organic compounds necessary for life. Organic Compounds

The main chemical components of living organisms are known as organic compounds. Organic compounds are molecules built around the element carbon (C). Which organic molecules do you recognize from the list below? The four main types of macromolecules found in living organisms, shown in Table below, are: 1. 2. 3. 4.

Proteins. Carbohydrates. Lipids. Nucleic Acids.

Carbohydrates

Carbohydrates are sugars and starches. An important role of carbohydrates is to store energy. Glucose (Figure 3.1) is an important simple sugar molecule with the chemical formula C6 H12 O6 . You get the carbohydrates you need for energy from eating carbohydrate-rich foods, including fruits and vegetables, as well as grains, such as bread, rice, or corn. Proteins

Proteins are molecules that have many different functions in living things. All proteins are made of amino acids that connect together like beads on a necklace (Figure 3.2). There are only 20 common amino acids needed to build proteins. Like the letters of the alphabet, these amino acids can form in thousands of different combinations. Proteins can differ in both the number and order of amino acids. It is the number and order of amino acids that 9

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FIGURE 3.1 A molecule of glucose, a type of carbohydrate.

determines the shape of the protein, and it is the shape (structure) of the protein that determines the unique function of the protein. Small proteins have just a few hundred amino acids. The largest proteins have more than 25,000 amino acids. FIGURE 3.2 Amino acids connect together like beads on a necklace. MET, ASN, TRP, and GLN refer to four different amino acids.

Many important molecules in your body are proteins. Examples include enzymes, antibodies, and muscle fiber. Enzymes are a type of protein that speed up chemical reactions. They are known as "biological catalysts." For example, your stomach would not be able to break down food if it did not have special enzymes to speed up the rate of digestion. Antibodies that protect you against disease are proteins. Muscle fiber is mostly protein (Figure 3.3). It’s important for you and other animals to eat food with protein, because we cannot make certain amino acids on our own. You can get proteins from plant sources, such as beans, and from animal sources, like milk or meat. When you eat food with protein, your body breaks the proteins down into individual amino acids and uses them to build new proteins. You really are what you eat!

Lipids

Have you ever tried to put oil in water? They don’t mix. Oil is a type of lipid. Lipids are molecules such as fats, oils, and waxes. The most common lipids in your diet are probably fats and oils. Fats are solid at room temperature, whereas oils are fluid. Lipids are needed to make the protective outer membrane of all cells. Animals use fats for long-term energy storage and to keep warm. Plants use oils for long-term energy storage. When preparing food, we often use animal fats, such as butter, or plant oils, such as olive oil or canola oil. 10

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Chapter 3. Organic Compounds

FIGURE 3.3 Muscle fibers are made mostly of protein.

Nucleic acids

Nucleic acids are long chains of nucleotides. Nucleotides are made of a sugar, a nitrogen-containing base, and a phosphate group. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two main nucleic acids. DNA is a double-stranded nucleic acid. DNA is the molecule that stores our genetic information. The single-stranded RNA is involved in making proteins.

Vocabulary

• • • • • • • • • • •

amino acid: Small molecule used to build proteins. carbohydrate: Organic compound such as sugar and starch that provides an energy source for animals. deoxyribonucleic acid (DNA): Nucleic acid that is the genetic material of all organisms. enzyme: Protein that speeds up chemical reactions. glucose: Simple sugar molecule with the chemical formula C6 H12 O6 . lipid: Organic compound that is insoluble in water and includes fats, oils, and waxes. nucleic acid: Organic compound that can carry genetic information. organic compound: Compound built around the element carbon. protein: Organic compound composed of amino acids and includes enzymes, antibodies, and muscle fibers. ribonucleic acid (RNA): Single-stranded nucleic acid involved in protein synthesis. starch: Storage carbohydrate in plants.

Summary

• Living organisms are comprised of organic compounds, molecules built around the element carbon. • Living things are made of just four classes of organic compounds: proteins, carbohydrates, lipids, and nucleic acids.

Review

1. What are the four organic compounds that make up living things? 2. What are examples of lipids? 3. What are examples of proteins? 11

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References 1. Image copyright Vasilyev, 2010. . Used under license from Shutterstock.com 2. CK-12 Foundation - Sam McCabe. . CC-BY-NC-SA 3.0 3. Image copyright YorkBerlin, 2012. . Used under license from Shutterstock.com

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