Chapter 7: Cell Structure and Function Photo Credit: © Quest/Science Photo Library/Photo Researchers, Inc. Copyright Pearson Prentice Hall

7.1 Life is Cellular Objectives State the cell theory Describe how different types of microscopes work Distinguish between prokaryotes and eukaryotes

The Discovery of the Cell The invention of the microscope led to the discovery of the cell. Jansenn’s microscope, 1595 Leeuwenhoek’s microscope, 1673 Hooke’s microscope, 1670 Copyright Pearson Prentice Hall

The Discovery of the Cell Early Microscopes In 1665, Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material. It seemed to be made up of thousands of tiny, empty chambers. Hooke called these chambers “cells.” Copyright Pearson Prentice Hall

The Discovery of the Cell At the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things, including a sample taken from a human mouth. The microscope revealed a world of tiny living organisms. Pond water Bacteria in mouth Copyright Pearson Prentice Hall

The Discovery of the Cell The Cell Theory In 1838, Matthias Schleiden concluded that all plants were made of cells. In 1839, Theodor Schwann stated that all animals were made of cells. In 1855, Rudolph Virchow concluded that new cells were created only from division of existing cells. These discoveries led to the cell theory. Copyright Pearson Prentice Hall

The Discovery of the Cell The cell theory states: All living things are composed of cells. Cells are the basic units of structure and function in living things. New cells are produced from existing cells. Copyright Pearson Prentice Hall

Exploring the Cell Most microscopes use lenses to magnify the image of an object by focusing light or electrons.

Light Microscopes and Cell Stains A typical 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 of about 1000 times.

Light Microscopes and Cell Stains Another 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.

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 they 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.

Copyright Pearson Prentice Hall Exploring the Cell Electron Microscopes Electron microscopes reveal details 1000 times smaller than those visible in light microscopes. Electron microscopes use beams of electrons, not light, that are focused by magnetic fields. Electron microscopy can be used to visualize only nonliving, preserved cells and tissues. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Exploring the Cell Transmission electron microscopes (TEMs) Specimens must be cut into ultra-thin slices because electrons must pass through it. TEMs are used to study cell structures and large protein molecules. Flat, two-dimensional images are produced. TEM image of an ebola virus Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Exploring the Cell Scanning electron microscopes (SEMs) Beams of electrons scan over the surface of specimens. SEMs produce three-dimensional images of a specimen’s surface. SEM image of a neuron Copyright Pearson Prentice Hall

Prokaryotes and Eukaryotes Cells come in a variety of shapes and sizes. All cells: are surrounded by a barrier called a cell membrane. at some point contain DNA. Copyright Pearson Prentice Hall

Prokaryotes and Eukaryotes Cells are classified into two 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. nucleus cell membrane Copyright Pearson Prentice Hall

Prokaryotes and Eukaryotes Eukaryotes are cells that enclose their DNA in nuclei. Prokaryotes are cells that do not enclose DNA in nuclei. Copyright Pearson Prentice Hall

Prokaryotes and Eukaryotes Prokaryotic cells have genetic material that is not contained in a nucleus. Prokaryotes do not have any membrane-bound organelles. Prokaryotic cells are generally smaller and simpler than eukaryotic cells. Bacteria are prokaryotes. Copyright Pearson Prentice Hall

Prokaryotes and Eukaryotes Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell. Eukaryotic cells are generally larger and more complex than prokaryotic cells. Eukaryotic cells generally contain dozens of structures and internal membranes. Plants, animals, fungi, and protists are eukaryotes. Copyright Pearson Prentice Hall