# Biology, Answering the Big Questions of Life/Introduction

Previous < Up > Next : Index
* EASY

## The Science of Life

Biology is the science that studies Life.
When we look at the world around us we see life. We ourselves are living creatures living in a world full of other living organisms. This world is full of complex and beautiful living things. But how do they work? What are they made of? Why do they do what they do?
The science that studies life and tries to answer these questions is called Biology. Everyone should learn biology because life is not only around us, it is within us. It is something that we experience every day, every moment. To study Biology is to learn about ourselves. Who we are. What we are. Why we are.
In this textbook we will ask the big questions of life and try to find the answers. $^1$
Questions like:
Feel free to browse this book, or read it straight through. It covers the information that you might cover in an introductory College Biology course and more. So let's be curious and investigate life.

### How do we know what we know?

When we are first learning about the world, we learn by asking. We ask our parents, other adults, and older children. This is how we learn to read. This is how we learn the names of things. We ask someone called an authority who tells us the answer.
But there is another way to learn about the world. We can ask questions and try to answer them ourselves through observation and deduction. We can lift a rock to see the earthworm that lives under it.

### What is Science?

Science is a way of finding out about the world by asking questions and trying to answer them by testing and observing. By devising experiments and looking at the results, we can get closer to the truth about how the world works. If experiments do not support one explanation, we find a new one.
Scientists believe that direct observation trumps authority. If the facts do not support a belief, we discard it in favor of one that the evidence does support. So scientific ideas are always in flux changing as our understanding of the world changes.

### How do you do Science?

Scientists find out about the world by experimenting and interpreting the results. This way of testing is sometimes formalized into something called The Scientific Method.
In the Scientific Method one begins with a question.
Scientific Method
* Ask a Question.
* Make a Hypothesis (an educated guess).
* Devise an Experiment (one where you've made predictions).
* Perform the Experiment and view the Results.
* Come to a Conclusion about what it means.
* If the hypothesis is not proven, go back to step 2 and make a new hypothesis.
These simple steps allow scientists to build up a body of proven facts about the universe and how it works. When a hypothesis has been proven by many, many experiments, we can call it a scientific theory. Some useful and well proven scientific theories are called natural laws.
    Click here to go to Theories page -->

## What is Life?

There isn't just one thing that separates living things from nonliving things. A cat moves but so does a car. A tree grows bigger, but so does a cloud. A cell has structure, but so does a crystal. In fact if you ask someone how to tell living things from nonliving things, many people would be at a loss. They would say, "You just know".
Defining life is complicated. Biologists define life by listing characteristics that living things share. Something that has all of the characteristics of life (not just one or two) is considered to be alive.

### What characteristics do living things share?

An individual living creature is called an organism. There are many characteristics that living creatures share.
Living organisms ...
* Respond to environmental changes.
* Grow and develop.
* Can reproduce and have offspring.
* Use energy and have a complex chemistry (metabolism).
* Maintain themselves in a stable state (homeostasis).
* Are built of structures called cells.
* Evolve biologically.

#### Respond to environmental changes

If you step on a rock, it will just lie there, but if you step on a turtle, it may move or even snap at you. Living things know what is going on around them, and respond to changes in the environment. In other words, living organisms are capable of responding to stimuli.

#### Grow and develop

A seed may look like a pebble, but under the right conditions it will sprout and form a seedling that will grow into a larger plant. Growth refers to the process by which the organism increases in size and the number of cells increases. In other words, growth produces more or larger cells. Development, on the other hand, is a change in specific structures. For example, a fertilized egg develops specialized structures such as organs.

#### Can reproduce and have offspring

Living things make more organisms like themselves. They reproduce sexually or asexually (cloning). Whether the organism is a rabbit, or a tree, or a bacterium, life will make more life.

#### Use energy and have a complex chemistry (metabolism)

A flower has a complicated and beautiful structure. So does a crystal. But if you look closely at the crystal, you see no change. The flower, on the other hand, is transporting water through its petals, producing pigment molecules, breaking down sugar for energy, and undergoing a large number of other chemical reactions that are needed for living organisms to stay alive. We call the sum of the chemical reactions in a cell its metabolism.
As another example, humans, Homo sapiens, eat to fuel their cells. The food they consume provides cells with chemical energy.

#### Maintain themselves in a stable state (homeostasis)

A human body has a temperature of about 98.6 degrees Fahrenheit (or approximately 37 degrees Celsius). If you step outside on a wintery morning, the temperature might be below freezing. You, however, don't just become an ice cube. You shiver and eat and do what you have to do to keep your body temperature the same. Living organisms keep themselves in a stable state. This is called homeostasis.

#### Are built of structures called cells

If you look closely at any organism you can see that it is made of structures called cells. Organisms that are very different such as ferns, and fish, and elephants all look very similar at the level of the cell. All living organisms are made of one or more cells.

#### Evolve biologically

Biological evolution refers to the change of inherited characteristics within a population over generations. Organisms often adapt to their environment which causes, in the long run, their characteristics to evolve.

## More about Biology

Wikipedia: Portal:Biology
Previous < Up > Next : Index
* EASY