An Introduction to Life on Earth

1. 1 An Introduction to Life on Earth 0

2. Chapter 1 At a Glance What Is Life?

3. 1.1 What Is Life? Biology comes from the Greek words “bio” meaning “life” and “logy” meaning “the study of.” Organisms share common characteristics that, taken together, define life. Organisms: Acquire and use materials and energy Actively maintain organized complexity (made of cells) Perceive and respond to stimuli Grow Reproduce Have the capacity to evolve, collectively Homeostasis

4. 1.1 What Is Life? The cell is the basic unit of life It is separated from its surroundings by a membrane It encloses a variety of structures and chemicals in a fluid environment

5. Figure 1-1 The cell is the smallest unit of life nucleus cell wall plasma membrane organelles

6. 1.1 What Is Life? Organisms acquire and use materials and energy Materials and energy are required for organisms to maintain organization, to grow, and to reproduce Important materials (minerals, water, & other simple chemical building blocks) are acquired from the air, water, soil, and bodies of other living things Organisms use energy continuously to sustain themselves

7. Figure 1-2 Properties of life Antennae and eyes: living things respond to stimuli Gut: living things acquire nutrients Eggs: living things reproduce

8. 1.1 What Is Life? Organisms acquire and use materials and energy (continued) Organisms obtain energy in two ways, coming directly or indirectly from the sun Photosynthesis is the process by which plants and some single-celled organisms capture sunlight Other organisms consume energy-rich molecules in the bodies of other organisms

9. Figure 1-3 The flow of energy and the recycling of nutrients

10. 1.1 What Is Life? Organisms actively maintain organized complexity Living things use energy on a continuous basis to self-sustain Cells pump chemicals in and out for appropriate chemical reactions to occur Organisms maintain relatively constant internal conditions or homeostasis

11. Figure 1-4 Organisms maintain relatively constant internal conditions

12. 1.1 What Is Life? Organisms perceive and respond to stimuli and maintain homeostasis Organisms sense and respond to internal and external environmental stimuli Sensory organs in animals can detect and respond to external stimuli such as light, sound, chemicals, etc. Internal stimuli in animals are perceived by stretch, temperature, pain, and chemical receptors Plants and bacteria respond to stimuli as well (e.g., plants grow toward the light, and bacteria move toward available nutrients in a medium)

13. 1.1 What Is Life? Organisms grow Every organism becomes larger over time Plants, birds, and mammals grow by producing more cells to increase their mass Bacteria grow by enlarging their cells; they divide in half to reproduce after genetic material is copied Growth involves the conversion of acquired materials to molecules of the organism’s body

14. 1.1 What Is Life? Organisms reproduce Organisms reproduce by dividing in half, producing seeds, bearing live young, and laying eggs Organisms give rise to offspring of the same type The parent’s genetic material (DNA) is passed on to the offspring, creating continuity of life

15. Figure 1-6 Organisms reproduce Panda with its baby Dividing Streptococcus bacterium Dandelion producing seeds

16. Figure 1-7 DNA

17. 1.1 What Is Life? Organisms, collectively, have the capacity to evolve Evolution is the process by which modern organisms descended, with modifications, from preexisting forms of life Changes in DNA within populations occur over the course of generations, which results in evolution Populations are groups of the same type of organism living in the same area

18. 1.2 What Is Evolution? Evolution explains the diversity of life on Earth Evolution provides an explanation for the similarities found among different types of organisms Chimpanzees and people have various physical features in common DNA of humans differs from that of chimpanzees by less than 5%

19. Figure 1-8 Chimps and people are closely related