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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. Chapter 2: Biology as a Science
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Biology: The Study of Life

9. 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

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

11. 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

12. 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

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

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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

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

24. 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

25. 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

26. 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