Biology Essentials For Dummies

Introduction

Life is all around you, from invisible microbes and green plants to the other animals with whom you share the Earth. What’s more, these other living things aren’t just around you — they’re intimately interconnected with your life. Plants make your food and provide you with oxygen, microbes break down dead matter and recycle materials that all living things need, and insects pollinate the plants you rely on for food. Ultimately, all living beings rely on other living beings for their survival.

What makes biology so great is that it allows you to explore the interconnectedness of the world’s organisms and really understand that living beings are works of art and machines rolled into one. Organisms can be as delicate as a mountain wildflower or as awe-inspiring as a majestic lion. And regardless of whether they’re plants, animals, or microbes, all living things have numerous working parts that contribute to the function of the whole being. They move, obtain energy, use raw materials, and make waste, whether they’re as simple as a single-celled organism or as complex as a human being.

Biology is the key you need to unlock the mysteries of life. Through it, you discover that even single-celled organisms have their complexities, from their unique structures to their diverse metabolisms. Biology also helps you realize what a truly miraculous machine your body is, with its many different systems that work together to move materials, support your structure, send signals, defend you from invaders, and obtain the matter and energy you need for growth.

About This Book

Biology Essentials For Dummies takes a look at the characteristics all living things share. It also provides an overview of the concepts and processes that are fundamental to living things. We put an emphasis on looking at how human beings meet their needs, but we also take a look at the diversity of life on planet Earth.

Conventions Used in This Book

To help you find your way through the subjects in this book, we use the following style conventions:

Italics highlight new words or terms that are defined in the text. They also point out words we want to emphasize.

Also, whenever we introduce scientific terms, we try to break the words down for you so that the terms become tied to their meanings, making them easier to remember.

Foolish Assumptions

As we wrote this book, we tried to imagine who you are and what you need in order to understand biology. Here’s what we came up with:

You’re a high school student taking biology, possibly in preparation for an advanced placement test or college entrance examination. If you’re having trouble in biology class and your textbook isn’t making much sense, try reading the relevant section of this book first to give yourself a foundation and then go back to your textbook or notes.

You’re a college student who isn’t a science major but is taking a biology class to help fulfill your degree requirements. If you want help following along in class, try reading the relevant sections in this book before you go to a lecture on a particular topic. If you need to fix a concept in your brain, read the related section after class.

Icons Used in This Book

We use some of the familiar For Dummies icons to help guide you and give you new insights as you read the material. Here’s the scoop on what each one means.

Remember The information highlighted with this icon is stuff we think you should permanently store in your mental biology file. If you want a quick review of biology, scan through the book reading only the paragraphs marked with Remember icons.

Tip This symbol offers pointers that help you remember the facts presented in a particular section so you can better commit them to memory.

Beyond the Book

In addition to what you’re reading right now, this book comes with a free access-anywhere Cheat Sheet. To get this Cheat Sheet, go to www.dummies.com and search for Biology Essentials For Dummies Cheat Sheet by using the Search box.

Where to Go from Here

Where you start reading is up to you. However, we do have a few suggestions:

If you’re currently in a biology class and having trouble with a particular topic, jump right to the chapter or section featuring the subject that’s confusing you.

If you’re using this book as a companion to a biology class that’s just beginning, you can follow along with the topics being discussed in class.

Whatever your situation, the table of contents and index can help you find the information you need.

Chapter 1

Exploring the Living World

IN THIS CHAPTER

Bullet Identifying the characteristics of living things

Bullet Introducing the three main types of living things

Bullet Organizing living things into groups

Bullet Valuing the diversity of life on Earth

Bullet Observing the world like a scientist

Biology is the study of life, as in the life that covers the surface of the Earth like a living blanket, filling every nook and cranny from dark caves and dry deserts to blue oceans and lush rain forests. Living things interact with all these environments and each other, forming complex, interconnected webs of life.

In this chapter, we give you an overview of the big concepts of biology. Our goal is to show you how biology connects to your life and to give you a preview of the topics we explore in greater detail later in this book.

Living Things: Why Biologists Study Them, What Defines Them

Biologists seek to understand everything they can about living things, including

The structure and function of all the diverse living things on planet Earth

The relationships between living things

How living things grow, develop, and reproduce, including how these processes are regulated by DNA, hormones, and nerve signals

The connections between living things and their environment

How living things change over time

How DNA changes, how it’s passed from one living thing to another, and how it controls the structure and function of living things

Remember An individual living thing is called an organism. All organisms share eight specific characteristics that define the properties of life:

Living things are made of cells that contain DNA. A cell is the smallest part of a living thing that retains all the properties of life. In other words, it’s the smallest unit that’s alive. DNA, short for deoxyribonucleic acid, is the genetic material, or instructions, for the structure and function of cells.

Living things maintain order inside their cells and bodies. One law of the universe is that everything tends to become random over time. According to this law, if you build a sand castle, it’ll crumble back into sand over time. Living things, as long as they remain alive, don’t crumble into little bits. They constantly use energy to rebuild and repair themselves so that they stay intact.

Living things regulate their systems. Living things maintain their internal conditions in a way that supports life. Even when the environment around them changes, organisms attempt to maintain their internal conditions; this process is called homeostasis. Think about what happens when you go outside on a cool day without wearing a coat. Your body temperature starts to drop, and your body responds by pulling blood away from your extremities to your core in order to slow the transfer of heat to the air. It may also trigger shivering, which gets you moving and generates more body heat. These responses keep your internal body temperature in the right range for your survival even though the outside temperature is low.

Living things respond to signals in the environment. If you pop up suddenly and say Boo! to a rock, it doesn’t do anything. Pop up and say Boo! to a friend or a frog, and you’ll likely see him or it jump. That’s because living things have systems to sense and respond to signals (or stimuli). Many animals sense their environment through their five senses just like you do, but even less familiar organisms, such as plants and bacteria, can sense and respond. For example, during the process of phototaxis, plants direct their growth toward areas where they have access to light.

Living things transfer energy among themselves and between themselves and their environment. Living things need a constant supply of energy to grow and maintain order. Organisms such as plants capture light energy from the sun and use it to build food molecules that contain chemical energy. Then the plants, and other organisms that eat the plants, transfer the chemical energy from the food into cellular processes. As cellular processes occur, they transfer most of the energy back to the environment as heat.

Living things grow and develop. You started life as a single cell. That cell divided to form new cells, which divided again. Now your body is made of approximately 100 trillion cells. As your body grew, your cells received signals that told them to change and become special types of cells: skin cells, heart cells, liver cells, brain cells, and so on. Your body developed along a plan, with a head at one end and a tail at the other. The DNA in your cells controlled all these changes as your body developed.

Living things reproduce. People make babies, hens make chicks, and plasmodial slime molds make plasmodial slime molds. When organisms reproduce, they pass copies of their DNA onto their offspring, ensuring that the offspring have some of the traits of the parents.

Living things have traits that evolved over time. Birds can fly, but most of their closest relatives — the dinosaurs — couldn’t. The oldest feathers seen in the fossil record are found on a feathered dinosaur called Archaeopteryx. No birds or feathers have been found in any fossils that are older than those of Archaeopteryx. From observations like these, scientists can infer that having feathers is a trait that wasn’t always present on Earth; rather, it’s a trait that developed at a certain point in time. So, today’s birds have characteristics that developed through the evolution of their ancestors.

Meet Your Neighbors: Looking at Life on Earth

Life on Earth is incredibly diverse, beautiful, and complex. Heck, you could spend a lifetime exploring the microbial universe alone. The deeper you delve into the living world around you, the more you can appreciate the similarities between all life on Earth — and be fascinated by the differences. The following sections give you a brief introduction to the major categories of life on Earth (called domains, as we explain in the upcoming section "Organizing Life into Smaller and Smaller Groups: Taxonomy").

Unsung heroes: Bacteria

Consisting mostly of single-celled organisms, bacteria are prokaryotic, meaning they lack a nuclear membrane around their DNA. Most bacteria have a cell wall made of peptidoglycan: a hybrid sugar-protein molecule.

Remember Most people are familiar with disease-causing bacteria such as Streptococcus pyogenes, Mycobacterium tuberculosis, and Staphylococcus aureus. Yet the vast majority of bacteria on Earth don’t cause human diseases. Instead, they play important roles in the environment and health of living things, including humans. Photosynthetic bacteria make significant contributions to planetary food and oxygen production, and E. coli living in your intestines make vitamins that you need to stay healthy. So when you get down to it, plants and animals couldn’t survive on Earth without bacteria.

Generally speaking, bacteria range in size from 1 to 10 micrometers (one millionth of a meter) in length and are invisible to the naked eye. Along with being nucleus-free, they have a genome that’s a single circle of DNA. They reproduce asexually (meaning they produce copies of themselves) by a process called binary fission.

Bacteria have many ways of getting the energy they need for growth and various strategies for surviving in extreme environments. Their great metabolic diversity has allowed them to colonize just about every environment on Earth.

Bacteria impersonators: Archaeans

Archaeans are prokaryotes, just like bacteria. In fact, you can’t tell the difference between the two just by looking, even if you look very closely using an electron microscope, because they’re about the same size and shape, have similar cell structures, and divide by binary fission.

Until the 1970s, no one even knew that archaeans existed; up to that point, all prokaryotic cells were assumed to be bacteria. Then, in the 1970s, a scientist named Carl Woese started doing genetic comparisons between prokaryotes. Woese startled the entire scientific world when he revealed that prokaryotes actually separated into two distinct groups — bacteria and archaea — based on sequences in their genetic material.

The first archaeans were discovered in extreme environments (think salt lakes and hot springs), so they have a reputation for being extremophiles (-phile means love, so extremophiles means extreme-loving). Since their initial discovery, however, archaeans have been found everywhere scientists have looked for them. They’re happily living in the dirt outside your home right now, and they’re abundant in the ocean.

Because archaeans were discovered fairly recently, scientists are still learning about their role on planet Earth, but so far it looks like they’re as abundant and successful as bacteria.

A taste of the familiar: Eukaryotes

Unless you’re a closet biologist, you’re probably most familiar with life in eukaryotic form because you encounter it every day. As soon as you step outside, you can find a wealth of plants and animals (and maybe even a mushroom or two if you look around a little).

On the most fundamental level, all eukaryotes are quite similar. They share a common cell structure with nuclei and organelles, use many of the same metabolic strategies, and reproduce either asexually or sexually.

Despite these similarities, we bet you still feel that you’re pretty different from a carrot. You’re right to feel that way. The differences between you and a carrot are what separate you into two different kingdoms. In fact, enough differences exist among eukaryotes to separate them into four different kingdoms:

Animalia: Animals are organisms that begin life as a cell called a zygote that results from the fusion of a sperm and an egg. The fertilized egg then divides to form a hollow ball of cells called a blastula. If you’re wondering when the fur,