Look for words that mean and and or to help determine which probabilities to multiply ( and) and which to add ( or). Proteins are long chains of polypeptides, and thus, so are enzymes. However, some enzymes contain parts that are not made up of proteins but assist the enzyme in its function. These are called coenzymes. Vitamins often act as coenzymes. The name of an enzyme usually reflects the name of the chemical on which the enzyme acts (that is, the chemical substrate). For example, an enzyme that acts on a fat (fat being the substrate) is called a lipase (remember, lip = fat). The nervous system consists of two main systems, the central nervous system (CNS) and the peripheral nervous system. The CNS is made up of the brain and spinal cord and sends out instructions. The peripheral nervous system contains the nerves that send the messages from the CNS to the rest of the body.

Homeostasis is the balance, or equilibrium, of the body. Regulation of all the body’s systems seeks to keep the body in homeostasis. Integumentary system: Serves as your first line of defense against infection. Made up of your skin (see Chapter 17).As you discover in Chapter 10, the amazing diversity of life on Earth helps ensure that life continues in the face of environmental change. Each type of organism plays a role in the environment, and each one is connected to the other. Green organisms such as plants combine energy and matter to make the food on which all life depends, herbivores eat plants, predators hunt prey, and decomposers such as bacteria and fungi recycle dead matter so it becomes available again to other living things. (For more on the interconnectedness of all living things on Earth, head to Chapter 11.)

Tiny holes called stomata in the surfaces of leaves open and close to allow plants to absorb carbon dioxide from the atmosphere and release oxygen. Scientific experiments help people answer questions about the natural world. To design an experiment: 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 Everything an organism’s body does happens because its cells make those actions happen, whether that organism is a single-celled E. coli bacteria or a human being made up of approximately 10 trillion cells.Discovery science: When scientists seek out and observe living things, they’re engaging in discovery science, studying the natural world and looking for patterns that lead to new, tentative explanations of how things work (these explanations are called hypotheses). If a biologist doesn’t want to disturb an organism’s habitat, he or she may use observation to find out how a certain animal lives in its natural environment. Making useful scientific observations involves writing detailed notes about the routine of the animal for a long period of time (usually years) to be sure that the observations are accurate. An enzyme is a protein used to speed up the rate of a chemical reaction. Because they regulate the rate of chemical reactions, they also are called catalysts. There are many, many, many different types of enzymes, because for each chemical reaction that occurs, an enzyme specific to that reaction must be made. Circulatory system: Transports materials throughout the body. Consists of your heart, blood, and blood vessels (see Chapter 15). different types of structures you'll see in some cells versus others, this right here is eukaryotic cell which we will talk more The Central Dogma of Genetics is that the genetic information stored in genes is first transcribed into messenger RNA (mRNA) and is then translated into protein. Transcription occurs in the nucleus of a cell and uses the sequence of a gene to create an mRNA transcript. Each gene is identified by transcription machinery and includes its regulatory sequences (promoter, enhancers, silencers), exons (the sequences that code for the protein product), introns (the intervening sequences located between the exons that do not code for protein product), and the sequences that signal the end of the gene (terminator sequence).

remember Systems thinking is an approach that seeks to understand the whole system by looking at the connections between the parts of the system. Systems thinking is a very powerful approach for solving complex problems because it makes people widen their perspective and consider many different components that could contribute to the situation. By taking a wider view and considering the big picture, people are more likely to identify how they can change a system to solve a problem.

Hypothesis-based science: When scientists test their understanding of the world through experimentation, they’re engaging in hypothesis-based science, which usually calls for following some variation of a process called the scientific method (see the next section for more on this). Modern biologists are using hypothesis-based science to try and understand many things, including the causes and potential cures of human diseases and how DNA controls the structure and function of living things. How DNA changes, how it’s passed from one living thing to another, and how it controls the structure and function of living things Defining what it means to be alive Of course, plants also have major differences from humans. Most importantly, they make their own food using carbon dioxide, water, and energy from the Sun, whereas humans have to eat other organisms to survive. As a byproduct of their food production, plants give off oxygen as waste. Humans gladly breathe oxygen in and return the favor by breathing out carbon dioxide that the plants can use to make food (see Chapter 5 for more on photosynthesis and respiration and how they lead to this gas exchange between humans and plants). Chapter 2 How Life Is Studied IN THIS CHAPTER is common to all cells is the notion of a ribosome, and this picture is full of ribosomes. All of these little dots right

Yet as humans draw more heavily upon the Earth’s resources, we’re putting stress on many other species and possibly driving them to extinction. The great lesson of biological evolution (a topic we cover in Chapter 12) is that not only do populations change over time but they’re also capable of going extinct. The challenge that humans face today is discovering ways to get what we need but still live in balance with the Earth’s various ecosystems. Getting Up Close and Personal with the Anatomy and Physiology of Animals Different kinds of food molecules enter cellular respiration at different points in the pathway. Cells break down simple sugars, such as glucose, in the first pathway — glycolysis. Cells use the second pathway, the Krebs cycle, for breaking down fatty acids and amino acids. membrane that separate it from the outside world. You see the membrane right over here. This is just a cross section. You could imagine aremember A system is a group of related parts that work together. As an example, consider your own body. You are a system. You have a boundary (your skin) that keeps all of you separate from the outside world. Within your body, you have many smaller systems like your nervous system or your cardiovascular system that work together so that your whole body functions. To truly understand how one of your organ systems works to help keep you healthy, we need to look not just at that system, but also how it interacts with the other parts of your body. Scientists are discovering more and more about DNA; they’re also developing tools to read and alter the DNA in cells (see Chapter 9). Chances are you’re already experiencing the impacts of scientists’ work with DNA, even if you don’t know it. Why? Because scientists use recombinant DNA technology to alter organisms used in food and medicines. This technology allows them to take genes from one organism and place them into the cells of another, changing the characteristics of the receiving organism. For example, scientists alter the cells of bacteria with human genes, turning them into tiny living factories that produce human proteins needed to treat diseases. Making the Connection between Ecosystems and Evolution remember The condition you alter in your experiment is your experimental variable. The changes you measure are your responding variables.