What is Life? Because there is no one universal definition for all life, it is therefore defined by the common characteristics that it shares.

1. Organization: Cells & DNA Living things are made up of one or more units called cells, the smallest units considered fully alive. Organisms consisting of only a single cell are called unicellular. Larger organisms, which contain many cells, are called multicellular Cells contain a universal genetic code called DNA.

2. Reproduction Because all individual organisms eventually die, reproduction is necessary for a species (a group of similar organisms) to survive. There are two basic kinds of reproduction: (A) sexual reproduction -- two cells from different individuals unite to produce the first cell of a new organism. (B) asexual reproduction -- a single organism produces offspring identical to itself.

3. Growth and Development During growth an organism goes through a cycle of change called development. As development continues organisms experience a process called aging. Aging causes organisms to become less efficient at the process of life. Eventually, the ability to reproduce ends and is followed by the end of the life span called death.

4. Obtaining and Using Material and Energy Living things obtain energy and materials from their environment to build the substances that make up their cells. They practice both anabolism (the process of synthesizing complex substances from simpler ones) and catabolism (the break down of complex substances into simpler ones) at the same time. The total sum of all chemical reactions in the body - the balance of anabolism and catabolism is called metabolism.

5. Responding to the Environment These responses can be rapid (e.g., a behavioral change) or slow (e.g., growth). Anything in the environment that causes an organism to react is called a stimulus. Examples of stimuli include light, temperature, odor, sound, gravity, heat, etc. The ability of organisms to react to stimuli is called irritability.

6. Homeostasis The process by which organisms respond to stimuli in ways that keep conditions in their body suitable for life is called homeostasis. In other words, homeostasis is the process by which organisms keep internal conditions constant despite changes in their external environments.

7. Taken as a group, living things evolve. Over generations, groups of organisms evolve, or change over time. Evolutionary change links all forms of life to a common origin more than 3.5 billion years ago.

Branches of Biology Biology is the study of life. A biologist is anyone who uses science to study life. Biology includes many different branches. The following is a small sample: Anatomy - The study of an animal’s structure (morphology). Botany - The study of plants. Cytology - The study of cells.

Branches of Biology Ecology - The study of the interactions of organisms with one another and their surroundings. Entomology - The study of insects. Ethology – The study of animal behavior. Herpetology - The study of reptiles and amphibians. Mycology - The study of fungi.

Branches of Biology Paleontology - The study of extinct organisms. Pathology - The study of diseases and disorders. Physiology - The study of the functions of living things. Virology - The study of viruses. Zoology - The study of animals.

Different types of biologists ask different types of questions. QUESTIONS AT THE MOLECULAR LEVEL: A molecular biologist, for example, may study thebasic chemical units of life. Or, they might study the effects of drugs on molecules in cells in order to understand why organisms react to those drugs as they do.

Different types of biologists ask different types of questions. QUESTIONS AT THE CELLULAR LEVEL A Cell biologist, for example, might study: The way normal cells become cancer cells. How a single cell divides and changes to form the different cell types in an adult.

Different types of biologists ask different types of questions. QUESTIONS AT THE MULTICELLULAR LEVEL For example: A Zoologist might study the changes within animals that tell them when to sleep, eat, or mate. A Paleontologist might try to explain how certain animals changed, or evolved, over time.

Different types of biologists ask different types of questions. QUESTIONS AT THE POPULATION LEVEL An ecologist might want to know how the following will affect nearby plant and animal life. The construction of a new road. The cutting down of forests. The use of pesticides.

Different types of biologists ask different types of questions. QUESTIONS AT THE GLOBAL LEVEL Some biologists take a worldwide view of biology and are concerned with organisms and their environment on a global scale. For example, Global ecologists, might try to estimate the effects on the Earth's climate of burning coal and oil.

Tools of a Biologist MICROSCOPY Two factors play an important role in microscopy: 1. Magnification is the comparison of the real size of a specimen with that of the one viewed under the microscope. 2. Resolution (resolving power) refers to the clarity of the specimen viewed under the microscope.

Tools of a Biologist COMPOUND LIGHT MICROSCOPE The most commonly used microscope. Cells and small organisms can be observed while they are still alive. Light microscopes are limited to about 1000 times magnification due to the limit of resolution.

Tools of a Biologist COMPOUND LIGHT MICROSCOPE Limit of resolution is the point of magnification beyond which images become blurry and lose detail. This occurs because light passing through a lens is scattered, making it hard to form a clear image.

Tools of a Biologist COMPOUND LIGHT MICROSCOPE For standard light microscopes, the limit of resolution is about 0.2 micrometers. A typical cell is about 10 micrometers across.

Tools of a Biologist ELECTRON MICROSCOPES These microscopes use a beam of electrons and magnets instead of light and lenses. They have a shorter wave length (0.2 nanometers) than a light microscope. Because of the high-energy particles involved, these microscopes cannot view living specimens.

Tools of a Biologist Transmission Electron Microscope (TEM)  TEM transmits a beam of electrons through a very thinly sliced specimen.  TEM can magnify objects up to 1,000,000 times.  The electron beam can also be used to expose photographic film to produce a permanent image of the specimen.

Tools of a Biologist Scanning Electron Microscope (SEM) SEM get their name from a pencil like beam of electrons that scans back and forth across the surface of a specimen. Electrons that bounce off the specimen are picked up by detectors that provide information to form a three-dimensional picture. SEM can magnify objects up to 300,000 times.

Tools of a Biologist PROBE MICROSCOPES A new class of microscopes d eveloped in the 1980s. They do not use lenses to produce images. These instruments trace the surfaces of a sample with a fine tip known as a probe. They are called scanning probe microscopes.

Tools of a Biologist PROBE MICROSCOPES Scanning probe microscopes have revolutionized the study of surfaces and have even made it possible to observe single atoms. Unlike electron microscopes, scanning probe microscopes do not require that specimens be placed in a vacuum.

Laboratory Techniques CENTRIFUGATION Used to study specific parts of a cell. 1st, cells are broken apart in a blender. 2nd, they are placed in a liquid in a tube. 3rd, the tube is inserted into a centrifuge.

Laboratory Techniques CENTRIFUGATION The centrifuge spins the tube up to 20,000 times per minute. This causes the cell parts to separate with the heaviest parts settling near the bottom and the lightest parts rising toward the top. A scientist can then remove the specific part of the cell to be studied by selecting the appropriate layer.

Laboratory Techniques MICROMANIPULATION With these techniques, special tools, that are so small they can be used only by looking through a microscope, are used to dissect, remove, insert, or manipulate specific parts of a cell. When parts are removed from the cell, it is also referred to as microdissection.

Laboratory Techniques CELL CULTURES They are used to obtain many identical copies of a particular type of cell. In this technique, 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.