Chapter 4

Summary		Questions		Media Resources
4.1 All living things share key characteristics.
• All living things are characterized by cellular organization, growth, reproduction, and heredity. • Other properties commonly exhibited by living things include movement and sensitivity to stimuli.		1.  What characteristics of living things are necessary characteristics (possessed by all living things), and which are sufficient characteristics (possessed only by living things)?
4.2 There are many ideas about the origin of life.
• Of the many explanations of how life might have originated, only the theories of spontaneous and extraterrestrial origins provide scientifically testable explanations. • Experiments recreating the atmosphere of primitive earth, with the energy sources and temperatures thought to be prevalent at that time, have led to the spontaneous formation of amino acids and other biologically significant molecules.		2.  What molecules are thought to have been present in the atmosphere of the early earth? Which molecule that was notably absent then is now a major component of the atmosphere?		• Origin of Life Evolution/History of Life/Origin of Life •Origins by Shapiro •Miller-Urey Experiment •Miller-Urey Experiment Results
4.3 The first cells had little internal structure.
• The first cells are thought to have arisen from aggregations of molecules that were more stable and, therefore, persisted longer. • It has been suggested that RNA may have arisen before cells did, and subsequently became packaged within a membrane. • Bacteria were the only life-forms on earth for about 1 billion years. At least three kinds of bacteria were present in ancient times: methane utilizers, anaerobic photosynthesizers, and eventually O2-forming photosynthesizers.		3.  What evidence supports the argument that RNA evolved first on the early earth? What evidence supports the argument that proteins evolved first? 4.  What are coacervates, and what characteristics do they have in common with organisms? Are they alive? Why or why not? 5.  What were the earliest known organisms like, and when did they appear? What present-day organisms do they resemble?		•  Current Bubble Hypothesis
4.4 The first eukaryotic cells were larger and more complex than bacteria.
• The first eukaryotes can be seen in the fossil record about 1.5 billion years ago. All organisms other than bacteria are their descendants. • Biologists group all living organisms into six "kingdoms," each profoundly different from the others. • The two most ancient kingdoms contain prokaryotes (bacteria); the other four contain eukaryotes. • There are approximately 1020 stars in the universe similar to our sun. It is almost certain that life has evolved on planets circling some of them.		6.  When did the first eukaryotes appear? By what mechanism are they thought to have evolved from the earlier prokaryotes? 7.  What sorts of organisms are contained in each of the six kingdoms of life recognized by biologists?		•Key Events in Earth's History Evolution/History of Life/Key Events

•  Scientists on Science •  How Scientists Think •  Student Papers

•  Bioethics Case Studies •  General Biology Weblinks

• Essential Study Partner

• Multiple Choice Quiz