Thursday, December 13, 2007


Nov. 29 - Concept check 28.1

Dec. 1 - Concept check 28.2 - 28.8 & Concept check 27.1 - 27.5

Dec. 8 - Concept check 29.1 - 29.4 & Concept check 30.1 - 30.4

Dec. 9 - Concept check 31.1 - 31.5

Dec. 10 - Concept check 24.1 - 24.3 & Concept check 26.1 - 26.6

Monday, December 10, 2007

Concept 26.6

Q1: Which kingdoms in Whittaker’s five- kingdom system include organisms now in the domain Eukarya?

A1: Protista, Plantae, Fungi, Animalia

Q2: Based on Figure 26.22, explain why the kingdom Monera is no longer considered a valid taxon?

A2: Monera included both bacteria and archaea, but archaea are more closely related to eukaryotes than to bacteria.

Concept 26.5

Q1: How does the division of function differ for single-celled and multicellular organisms?

A1: A single-celled organism must carry out all of the functions required to stay alive. Most multicellular organisms have many types of specialized cells, and life functions are divided among specific cell types.

Q2: In what way is “Cambrian explosion” a good description of the early part of the fossil record of animal history? What is meant by the metaphor of a “long fuse” for the Cambrian explosion?

A2: Fossils of most major animal phyla appear suddenly in the first 20 million years of the Cambrian period. Molecular clocks suggest that many animal phyla originated much earlier.

Concept 26.4

Q1: What evidence supports the hypothesis that mitochondria preceded plastids in the evolution of eukaryotic cells?

A1: All eukaryotes have mitochondria or genetic remnants of these organelles, but not all eukaryotes have plastids.

Q2: How is a eukaryotic cell like a chimera?

A2: The chimera of Greek mythology contained parts from different animals. Similarly, a eukaryotic cell contains parts form various prokaryotes; mitochondria from one type, and bacterium, plastids from another type, and a nuclear genome from parts of the genomes of these endosymbionts and at least one other cell.

Concept 26.3

Q1: What do fossilized stromatolites suggest about the evolution of prokaryotes?

A1: Prokaryotes must have existed at least 3.5 b.y.a, when the oldest fossilized stromatolites were formed.

Q2: The first appearance of free oxygen in the atmosphere must have triggered a massive wave of extinctions among the prokaryotes of the time. Why?

A2: Free oxygen attacks chemical bonds and can inhibit enzymes and damage cells. Some organisms were able to survive in anaerobic habitats, however.

Concept 26.2

Q1: Your measurements indicate that a fossilized skull you unearthed has a carbon-14/ carbon-12 ratio about ¼ that of the skulls of present-day animals. What is the approximate age of the fossilized skull?

A1: 22,920 years (four half-life reductions)

Q2: Based on Table 26.1, how long did prokaryotes inhabit Earth before eukaryotes evolved?

A2: About 1,300 million years, or 1.3 billion years.

Concept 26.1

Q1: What hypothesis did Miller and Urey test in their experiment?

A1: The hypothesis that conditions on the early Earth could have permitted the synthesis of organic molecules from inorganic ingredients.

Q2: Why was the appearance of protobionts surrounded by membranes likely a key step in the origin of life?

A2: In contrast to random mingling of molecules in an open solution, segregation of molecular systems by membranes could concentrate organic molecules, and electrical charge gradients across the membrane could assist biochemical reactions.

Q3: What is ribozyme?

A3: A ribozyme is an RNA molecule that catalyzes a chemical reaction