Scientific experiments help people answer questions about the natural world. To design an experiment: Angiosperms (or flowering plants) have vascular tissue and produce both flowers and seeds. Scientists divide the most familiar flowering plants into two groups based on the number of cotyledons they contain in their seeds: tip You can calculate the averages for numerical data and create graphs that illustrate the differences, if any, between your two groups.

Responding variables: The factor you measure is the responding variable (also called a dependent variable). Report your results, being sure to explain your original ideas and how you conducted your experiment, and describe your conclusions. 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 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.Gymnosperms (also known as conifers) have vascular tissue and produce cones and seeds, but they don’t produce flowers. 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. Skeletal system: Provides support, helps with movement, and forms blood cells. Made up of your bones (see Chapter 14). Digestive system: Takes up nutrients and water and eliminates wastes. Made up of your stomach, intestines, liver, and pancreas (see Chapter 16). 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.)

Respiratory system: Brings in oxygen and expels carbon dioxide. Made up of your lungs and airways (see Chapter 15). 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.small thing, this cell. "Surely they are simple," but they're actually fairly complex RNA and protein structures, that Set up your experiment, being careful to control all the variables except the experimental variable.