Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 4 (p. 74)

1. All living things have a cellular organization, respond to stimuli, have a metabolism, are able to reproduce themselves, regulate internal processes, and maintain homeostasis. Multicellular organisms also go through development to maturity. All of these characteristics are necessary for an entity to be considered to be "alive." However, these characteristics are not sufficient to define life. A genetic system is the sufficient condition of life.

2. The atmosphere of early earth contained N₂, CO₂, H₂O, NH₃, Ch₄, and maybe H₂. O₂ was absent. Then the atmosphere was reducing, now it is oxidizing as a result of several million years of photosynthesis.

3. RNA-worlders claim that without molecules capable of transmitting genetic information, proteins and other complex molecules could not have evolved successfully. Protein-firsters maintain that enzymes (proteins) would have had to exist for anything to replicate at all. The discovery of ribozymes and their apparently autocatalytic properties has therefore been very attractive to many theoreticians.

4. Coacervates are protein/lipid aggregations, have a quasi-lipid bilayer membrane, accumulate more organic materials inside themselves, and divide by "budding." They are not alive because they possess no known genetic material.

5. Prokaryotic organisms were probably the earliest known organisms, appearing about 3.5 billion years ago. They are mostly closely related to cyanobacteria.

6. The first eukaryotes known as fossils are 1.3 to 1.5 billion years old. Eukaryotes are thought to have evolved through the phenomenon of endosymbiosis.

7. The six kingdoms of life are the Archaebacteria (methanogens); Eubacteria (true bacteria); Protista (single-celled eukaryotes), Fungi (multicellular saprophytes such as mushrooms), Plantae (multicellular eukaryotic autotrophs such as trees, bushes, and flowers); and Animalia (multicellular eukaryotic heterotrophs such as jellyfish, spiders, sea cucumbers, fish, and birds).