For example, plants can bend toward a source of light or respond to touch. Figure 1.2 A toad represents a highly organized structure consisting of cells, tissues, organs, and organ systems.
#BIOCHEMICAL EVIDENCE FOR EVOLUTION LAB 12 ANSWERS SKIN#
How these specialized cells come together to form organs such as the heart, lung, or skin in organisms like the toad shown in Figure 1. Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms in that their cells can be specialized to perform specific functions, and even sacrificed in certain situations for the good of the organism as a whole. These in turn make up cell components or organelles. Inside each cell, atoms make up molecules. Even very simple, single-celled organisms are remarkably complex. Organisms are highly organized structures that consist of one or more cells. When viewed together, these eight characteristics serve to define life. Properties of LifeĪll groups of living organisms share multiple key characteristics or functions: order, sensitivity or response to stimuli, reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing.
It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life.įrom its earliest beginnings, biology has wrestled with four questions: What are the shared properties that make something “alive”? How do those various living things function? When faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? And, finally-what biologists ultimately seek to understand-how did this diversity arise and how is it continuing? As new organisms are discovered every day, biologists continue to seek answers to these and other questions. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. What exactly is life? This may sound like a silly question with an obvious answer, but it is not easy to define life.
Biology is the science that studies life.
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