Chapter 2: Biology as a Science 2-1 Characteristics of Living Things

Characteristics of Living Things We can state that all living things Are made up of one or more units called cells Reproduce Grow and develop Obtain and use energy Respond to their environment

Living Things Are Made Up of Cells Each cell is a collection of living matter enclosed by a barrier that separates the cell from its surroundings Most cells can perform all the functions we associate with life Organisms consisting of only a single cell are called unicellular Most of the organisms you are familiar with are multicellular Contain hundreds, thousands, even trillions of cells or more Cells are not found in nonliving matter unless that matter was once alive Wood

Living Things Reproduce Living things can produce new organisms of the same type Because all individual organisms eventually die, reproduction is necessary if a group of similar organisms is to survive Two basic kinds of reproduction Sexual reproduction requires that two cells from different individuals unite to produce the first cell of a new organism Asexual reproduction occurs when a single organism reproduces without the aid of another Some single-celled organisms divide in two to form two organisms

Living Things Grow and Develop All living things are capable of growth During growth, most living things go through a cycle of change called development The single cell that starts an organism’s life divides and changes again and again to form the many varied cells of an adult organism As development continues, organisms experience a process called aging During aging, an organism becomes less efficient at the process of life The ability to reproduce comes to an end For virtually all organisms, death is the inevitable end of the life span of every individual Death is a process of change that separates living and nonliving things

Living Things Obtain and Use Energy Living things obtain energy from their environment and use it to grow, develop, and reproduce All organisms require energy to build substances that make up their cells Any process in a living thing that involves putting together complex substances from simpler substances is called anabolism The final breakdown of complex substances into simpler ones, usually resulting in the release of energy, is called catabolism Living things must practice both of these at the same time The total sum of all chemical reactions in the body – the balance of anabolism and catabolism – is called metabolism

Living Things Respond to Their Environment Anything in the environment that causes an organism to react is called a stimulus Light, temperature, odor, sound, gravity, heat, water, and pressure The ability of living things to react to stimuli is known as irritability In general, living things respond to stimuli in ways that improve their chances for survival The process by which organisms respond to stimuli in ways that keep conditions in their body suitable for life is called homeostasis Homeostasis refers to an organism’s ability to maintain constant or stable conditions that are necessary for life

Chapter 2: Biology as a Science 2-2 Biology: The Study of Life

Biology: The Study of Life Biology is the science that seeks to understand, explain, and even control the living world Biology advances by observing the world, asking questions, and forming hypotheses that can be tested by experiment A biologist is anyone who uses the scientific method to study living things

Branches of Biology Contains many branches, or divisions Examples: Zoology Microbiology Botany Paleontology

Questions at the Molecular Level Molecular biologists may study the basic chemical units of life Molecular geneticists investigate the workings of DNA, the molecule that controls heredity and directs all the activities of the cell Other researchers might study the effects of drugs on molecules in cells in order to understand why entire organisms react to those drugs as they do

Questions at the Cellular Level Cell biologists might study the way normal cells become cancer cells when exposed to radiation or to the chemicals found in cigarette smoke Might try to explain how a single cell divides and changes to form all the cell types in an adult organism Other cell biologists might study how cells communicate with nearby cells

Questions at the Multicellular Level Goes beyond individual cells Study changes in animals, evolution, etc.

Questions at the Population Level Interested in groups of organisms that make up populations and how these populations interact with their environment

Questions at the Global Level Takes a more worldwide view of biology and are concerned with organisms and their environment on a global scale Biologists are both studying and trying to preserve the wonderful things that are alive on planet Earth – not just for their own use, but for the use of those who will live on this planet after us

Tools of a Biologist Use a wide variety of tools Graduated cylinders Balances Computers To study small organisms, researchers have developed several kinds of microscopes Microscopes are instruments that produce larger-than-life images, pictures, or even videotapes

The Compound Light Microscope Most commonly used microscope Make it possible to observe many kinds of cells and small organisms while they are still alive To view – Object is placed on a microscope slide and covered with a cover slip It is then placed on the stage of the microscope so that light passes through it into the lenses of the microscope Lens at the bottom = objective lens Lens at the top = ocular lens Because both lenses are used to form an image, it is properly known as a compound light microscope

Limits of Resolution There are limits to what can be seen with the compound light microscope As the magnification is increased, more and more detail can be seen – up to a certain point Beyond this point, called the limit of resolution, objects get blurry and detail is lost For standard light microscopes, the limit of resolution is about 0.2 micrometers

Using a Compound Light Microscope Many specimens are stained before they are observed under a microscope Stains are used to color cells or parts of cells to make them clearly visible Because many stains kill living cells, special types of light microscopes that do not require staining are used to observe living specimens Each uses a different property of light rays to improve the clarity of the image Phase contrast microscope Dark field microscope Nomarski microscope

Electron Microscopes In the 1920s physicists in Germany realized that electromagnets could bend streams of electrons They used these electromagnets to build electron microscopes The limit of resolution of electron microscopes is about 1000 times finer than the light microscope Transmission electron microscopes (TEMs) – shine a beam of electrons at a sample and then magnify the image onto a fluorescent screen and the bottom of the microscope Scanning electron microscopes (SEMs) – beam of electrons scans back and forth across the surface of a specimen; electrons that bounce off the specimen are picked up by detectors that provide the information to form an image on a television screen

Limitations of Electron Microscopes Extremely useful but do have serious drawbacks Specimens must be placed inside a vacuum and cut into very thin slices Specimens must be completely dried out before they are placed in the vacuum Living cells cannot be observed in the electron microscope – they are killed by the sample-preparation processes

Probe Microscopes Developed in the 1980s Do not use lenses to produce images Trace the surfaces of a sample with a fine tip known as a probe Have revolutionized the study of surfaces and have even made it possible to observe single atoms Specimens do NOT need to be placed in a vacuum

Laboratory Techniques of a Biologist In addition to staining, the following techniques are also used in the laboratory Centrifugation Micromanipulation Cell cultures

Centrifugation Involves placing cells in a blender to break them apart Cell fractionation The broken bits of cells are then placed in a liquid in a tube The tube is inserted into a centrifuge, which is a device that can spin the tube up to 20,000 times per minute While spinning, the cell parts begin to separate – with the heaviest parts setting near the bottom of the tube A scientist can then remove the specific part of the cell to be studied by selecting the appropriate layer

Micromanipulation Another technique to remove parts of a cell is called micro-dissection, which is a form of micromanipulation Special tools that are so small they can be used only by looking through a microscope are used to dissect, remove, insert, or otherwise manipulate specific parts of a cell

Cell Cultures Sometimes scientists want to study a particular kind of cell but to do so they need large numbers of that exact cell To obtain a cell culture, a single cell is placed in a dish that contains the nutrients the cell needs The cell is allowed to reproduce so that in time an entire population is grown from that single original cell