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7.1 Life Is Cellular 7.1 Life is Cellular Mrs. Baldessari Biology The key to every biological problem must finally be sought in the cell, for every living organism is, or at some time has been, a cell. E.B. Wilson, 1925 1 Cells are Us 2 Cells are Us Cilia on a protozoan Sperm meets egg 3 Lesson Overview Life Is Cellular THINK ABOUT IT What’s the smallest part of any living thing that still counts as being ―alive?‖ Can we just keep dividing living things into smaller and smaller parts, or is there a point at which what’s left is no longer alive? As you will see, there is such a limit. The smallest living unit of any organism is the cell. 4 Cells are Us A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells. There are about 200 different cell types in mammals (one of us). Red and white blood cells above vessel- forming cells. 5 nerve cell CELL SIZE • Smallest cell in the human body is the sperm cell • Largest cell in the human body is the egg cell 6 Most cells are small 1. Surface to volume ratio: cell has to be 2. The nucleus can small enough to get only control a – Waste out certain size cell – Nutrients in 7 Lesson Overview Life Is Cellular The Discovery of the Cell What is the cell theory? The cell theory states: - All living things are made up of cells. - Cells are the basic units of structure and function in living things. - New cells are produced from existing cells. 8 Early Microscopes • Prototypes were developed in the late 1500’s by European eyeglass makers • It was not until the mid-1600s that scientists began to use microscopes to observe living things. th Early compound microscope 17 century9 In 1665, Robert Hooke used an early compound microscope to look at cork • Observed that cork was made up of thousands of hollow chambers • Dubbed them cells since they looked like the monatsery’s tiny rooms called “cellula”. • Today we know that living cells are not empty chambers, but contain a huge array of working parts, each with its own function. 10 Anton von Leewenhoek • Late 1600’s- Dutch textile salesman • Created different types of microscopes FIRST person to OBSERVE and • Discovered over 5,000 types of DESCRIBE MICROSCOPIC microscopic life ORGANISMS and LIVING • Lenses were able to magnify up CELLS to 300X • . 11 Lesson Overview Life Is Cellular Early Microscopes Anton van Leeuwenhoek examined pond water and other things, including a sample taken from a human mouth. He drew the organisms he saw in the mouth—which today we call bacteria. 12 The Cell Theory • In 1838, German botanist Matthias Schleiden concluded: “plants are made of cells” • The next year, German biologist Schleiden Theodor Schwann stated that all: “Animals are made of cells” Schwann 13 Cell Theory In 1855, German physician Rudolf Virchow concluded that new cells could be produced only from the division of existing cells. 1. All living things are made of cells. 2. Cells are the basic unit of structure and function 3. New cells come from preexisting cells. *cells are different shapes and sizes based on their function 14 Lesson Overview Life Is Cellular Exploring the Cell How do microscopes work? Most microscopes use lenses to magnify the image of an object by focusing light or electrons. 15 A Sense of Scale and Abundance – Bacteria on the Head of a Pin 16 Exploring the Cell- 3 major types of microscopes1. There are 1) Light Microscope •Allows light to pass through a specimen and uses two lenses to form an image. •The first set of lenses, located just above the specimen, produces an enlarged image of the specimen. •The second set of lenses magnifies this image still further. •Because light waves are diffracted, or scattered, as they pass through matter, light microscopes can produce clear images of objects only to a magnification from 40 – 1,000 times depending on objective being used 17 Lesson Overview Life Is Cellular 1) Light Microscopes • magnification from 40 – 1,000 • Eyepiece magnifies 10X • Total magnification calculation: multiply the eyepiece by the objective being used. Example- eyepiece (10X) times low power objective (4X) = 40X • Used to magnify objects that light can pass through. • Uses slides 18 Dissecting Microscope • Magnifies 10 to 30 times • Eyepiece magnifies 10X • Objectives: 1X and 2X (3X) • Used to magnify objects that light cannot pass through • Used mostly by research scientists and jewelers • Advantage: objects are 3-D • Disadvantage: can’t view small objects 19 Lesson Overview Life Is Cellular Light Microscopes and Cell Stains A problem with light microscopy is that most living cells are nearly transparent, making it difficult to see the structures within them. Using chemical stains or dyes can usually solve this problem. Some of these stains are so specific that they reveal only compounds or structures within the cell. 20 Lesson Overview Life Is Cellular Light Microscopes and Cell Stains Some dyes give off light of a particular color when viewed under specific wavelengths of light, a property called fluorescence. Fluorescent dyes can be attached to specific molecules and can then be made visible using a special fluorescence microscope. Fluorescence microscopy makes it possible to see and identify the locations of these molecules, and even to watch them move about in a living cell. 21 Lesson Overview Life Is Cellular 2) Electron Microscopes Light microscopes can be used to see cells and cell structures as small as 1 millionth of a meter. To study something smaller than that, scientists need to use electron microscopes. Electron microscopes use beams of electrons, not light, that are focused by magnetic fields. Electron microscopes offer much higher resolution than light microscopes. There are two major types of electron microscopes: transmission and scanning. 22 Electron Microscope -Two types: Transmission and Scanning • Uses electrons to illuminate objects • Can magnify from 30,000 to 9 million times • Mostly large institutions have them • Costly to own and maintain • Can only be used to look at dead specimens • Used for cytology, forensics, and virology 23 Lesson Overview Life Is Cellular Transmission Electron Microscopes Transmission electron microscopes make it possible to explore cell structures and large protein molecules. Because beams of electrons can only pass through thin samples, cells and tissues must be cut first into ultra thin slices before they can be examined under a transmission electron microscope. Transmission electron microscopes produce flat, two- dimensional images. 24 • Transmission Electron Microscope •TEM- thin slices need to be made to have clear images, images are 2-D •Useful for studying internal structures 25 Lesson Overview Life Is Cellular Scanning Electron Microscopes In scanning electron microscopes, a pencil-like beam of electrons is scanned over the surface of a specimen. Because the image is of the surface, specimens viewed under a scanning electron microscope do not have to be cut into thin slices to be seen. Scanning electron microscopes produce three- dimensional images of the specimen’s surface. 26 •SEM- samples do not need to be cut, are in 3-D • Useful for studying external structure 27 Lesson Overview Life Is Cellular Electron Microscopes Because electrons are easily scattered by molecules in the air, samples examined in both types of electron microscopes must be placed in a vacuum in order to be studied. Researchers chemically preserve their samples first and then carefully remove all of the water before placing them in the microscope. This means that electron microscopy can be used to examine only nonliving cells and tissues. 28 General info about cells • Cells come in a variety of shapes • Range in size from microscopic bacteria to giant amoeba Mycoplasma pneumoniae Chaos carolinensis – Giant amoeba, 29 approximately 1mm in length General info about cells c. All contain DNA d. All have a cell membrane- an outer, flexible barrier Cell membrane Nucleus- containing DNA 30 Two Main Categories of Cells a. Eukaryotes- have cells that enclose their DNA in a nucleus b. Prokaryotes- cells that do not enclose their DNA in a nucleus 31 Lesson Overview Life Is Cellular Prokaryotes and Eukaryotes How are prokaryotic and eukaryotic cells different? Prokaryotic cells do not separate their genetic material within a nucleus. In eukaryotic cells, the nucleus separates the genetic material from the rest of the cell. 32 Prokaryotes and Eukaryotes • Organisms whose cell contain a nucleus and other membrane bound organelles are called EUKARYOTES • Organisms whose cells never contain (or lack) a nucleus and other membrane bound organelles are called PROKARYOTES 33 A rat liver cell (with color enhancement to show organelles) 34 It’s Crowded In There An artist’s conception of the cytoplasm - the region of a cell that’s not in the nucleus or within an organelle. 35 It’s Crowded In There A micrograph showing cytoskeleton (red), ribosomes (green), and membrane (blue) 36 Two Fundamentally Different Types of Cells 37 Lesson Overview Life Is Cellular Prokaryotes and Eukaryotes Cells fall into two broad categories, depending on whether they contain a nucleus. The nucleus is a large membrane-enclosed structure that contains the cell’s genetic material in the form of DNA. The nucleus controls many of the cell’s activities. 38 Lesson Overview Life Is Cellular Prokaryotes and Eukaryotes Eukaryotes are cells that enclose their DNA in nuclei. Prokaryotes are cells that do not enclose DNA in nuclei. 39 Prokaryotes • Are generally smaller than eukaryotic cells • Have no nucleus • Carry out all of life’s processes • Ex: bacteria Bacillus anthracis 40 Eukaryotes a. Are generally larger and more complex than prokaryotes b. Contain dozens of membrane bound structures that are specialized c.
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