Figure 1.1 Life’s Calendar Origin of Life Oldest fossils Photo-synthesis evolves Multi- cellular organisms Eukaryotic cells evolve First land plants Coal-forming forests Insects abundant First mammals Dinosaurs dominant First birds First flowering plants Rise of mammals Abundant fossils of aquatic life First land animals First hominids

Figure 1.2 The Basic Unit of Life Is the Cell Membrane Haloferax mediterranei

Figure 1.4 The Tree of Life Life Number of known (described) species Estimated total number of living species BACTERIA 10,000 Millions 1,000– 1 million ARCHAEA 260 Life Chloroplasts 400,000– 500,000 270,000 Mitochondria Plants Protists Protists Protists 80,000 500,000– 1 million Protists Protists Protists 10 million– 100 million 1,300,000 EUKARYA Animals 98,000 1–2 million Fungi

Figure 1.5 DNA Is Life’s Blueprint One nucleotide DNA Gene DNA Protein

Figure 1.6 Biology Is Studied at Many Levels of Organization (Part 1) (A) Atoms to organisms Organism Large molecules, proteins, nucleic acids Cells Small molecules Atoms Cell specialization Tissues Water Oxygen Colonial organisms Methane Organs Carbon Hydrogen Organs systems Carbon dioxide Multicellular organism (leopard frog) Unicellular organisms

Figure 1.6 Biology Is Studied at Many Levels of Organization (Part 2) (B) Organisms to ecosystems Biosphere Ecosystem Community Population

Figure 1.7 Adaptations to the Environment (Part 1) (A) Dyscophus guineti

Figure 1.7 Adaptations to the Environment (Part 2) (B) Xenopus laevis

Figure 1.7 Adaptations to the Environment (Part 3) (C) Agalychnis callidryas

Figure 1.7 Adaptations to the Environment (Part 4) (D) Rhacophorus nigropalmatus

Figure 1.8 Scientific Methodology 1. Make observations. 2. Speculate, ask a question. Ask new questions. Form a hypothesis to answer the question. Revise your hypothesis. Make a prediction: What else would be true if your hypothesis is correct? Design and conduct an experiment that uses quantifiable data to test your prediction. Reexamine the experiment for uncontrolled variables. Use statistical tests to evaluate the significance of your results. Significant results support hypothesis. Results do not support hypothesis. Experiment repeated and results verified by other researchers.

Figure 1.9 Controlled Experiments Manipulate a Variable (Part 1) Exposure to atrazine during larval development causes abnormalities in the reproductive tissues of male frogs. Establish 9 tanks in which all attributes are held constant except the water’s atrazine concentration. Establish 3 atrazine conditions (3 replicate tanks per condition): 0 ppb (control condition), 0.1 ppb, and 25 ppb. Place Rana pipiens tadpoles from laboratory-reared eggs in the 9 tanks (30 tadpoles per replicate). When tadpoles have transitioned into adults, sacrifice the animals and evaluate their reproductive tissues. Test for correlation of degree of atrazine exposure with the presence of abnormalities in the gonads (testes) of male frogs.

Figure 1.9 Controlled Experiments Manipulate a Variable (Part 2) Atrophied testes Testicular oogenesis Oocytes (eggs) in normal-sized testis (sex reversal) Male frogs with gonadal abnormalities (%) Control Atrazine (ppb) Exposure to atrazine at concentrations as low as 0.1 ppb induces abnormalities in the gonads of male frogs. The effect is not proportional to the level of exposure.

Figure 1.10 Comparative Experiments Look for Differences among Groups (Part 1) Presence of the herbicide atrazine in environmental water correlates with gonadal abnormalities in frog populations. Based on commercial sales of atrazine, select 4 sites (sites 1–4) less likely and 4 sites (sites 5–8) more likely to be contaminated with atrazine. Visit all sites in the spring (i.e., when frogs have transitioned from tadpoles into adults); collect frogs and water samples. In the laboratory, sacrifice frogs and examine their reproductive tissues, documenting abnormalities. Analyze the water samples for atrazine concentration (the sample for site 7 was not tested). Quantify and correlate the incidence of reproductive abnormalities with environmental atrazine concentrations.

Male frogs with gonadal abnormalities (%) Figure 1.10 Comparative Experiments Look for Differences among Groups (Part 2) Atrophied testes Testicular oogenesis Atrazine level Atrazine (ppb) Male frogs with gonadal abnormalities (%) Site Reproductive abnormalities exist in frogs from environments in which aqueous atrazine concentration is 0.2 ppb or above. The incidence of abnormalities does not appear to be proportional to atrazine concentration at the time of transition to adulthood.