Guided Study for BIOL&213: History of Life, Phylogeny, Prokaryotes, and Protists

Q1. How long have humans been on earth, relative to other multicellular eukaryotes?

Background

Topic: Geologic Time and Evolutionary History

This question asks you to interpret geologic time scales and compare the duration of human existence to that of other multicellular eukaryotes.

Key Terms:

• Geologic Time Scale: A system of chronological dating that relates geological strata to time.

• Multicellular Eukaryotes: Organisms with complex cells containing a nucleus, made up of more than one cell.

Step-by-Step Guidance

1. Review Figure 25.8 in your textbook, focusing on both the 1-hour timer analogy and the horizontal timeline.

2. Identify when multicellular eukaryotes first appeared on the timeline.

3. Locate the point at which humans appear on the same timeline.

4. Compare the relative lengths of time that multicellular eukaryotes and humans have existed.

Try solving on your own before revealing the answer!

Q2. When do you think photosynthetic organisms first appeared?

Background

Topic: Evolution of Photosynthesis

This question tests your understanding of the timeline for the appearance of photosynthetic organisms in Earth's history.

Key Terms:

• Photosynthetic Organisms: Organisms that convert light energy into chemical energy via photosynthesis.

Step-by-Step Guidance

1. Review the geologic time scale in your textbook, focusing on the earliest evidence for photosynthesis.

2. Identify which organisms are believed to be the first to perform photosynthesis (hint: cyanobacteria).

3. Find the estimated time (in billions of years ago) when these organisms first appeared.

Try solving on your own before revealing the answer!

Q3. What are stromatolites? Based on the fossil record, how long ago did the first ones form?

Background

Topic: Early Life and Fossil Evidence

This question focuses on stromatolites as evidence for early life on Earth.

Key Terms:

• Stromatolites: Layered structures formed by the activities of certain prokaryotes, especially cyanobacteria.

• Fossil Record: The preserved remains or traces of organisms from the remote past.

Step-by-Step Guidance

1. Define what stromatolites are and how they are formed.

2. Consult your textbook or class notes for the age of the oldest known stromatolite fossils.

3. Express this age in billions of years ago (bya).

Try solving on your own before revealing the answer!

Q4. Write a simple, balanced equation that summarizes photosynthesis.

Background

Topic: Photosynthesis

This question tests your ability to recall and write the chemical equation for photosynthesis.

Key Formula:

• The general balanced equation for photosynthesis is:

$6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2$

Step-by-Step Guidance

1. Recall the reactants (inputs) and products (outputs) of photosynthesis.

2. Write the chemical formulas for carbon dioxide, water, glucose, and oxygen.

3. Balance the equation so that the number of atoms of each element is the same on both sides.

Try solving on your own before revealing the answer!

Q5. How did cyanobacteria contribute to the ‘Oxygen Revolution’?

Background

Topic: Evolution of Oxygen in Earth's Atmosphere

This question explores the role of cyanobacteria in increasing atmospheric oxygen.

Key Terms:

• Cyanobacteria: Photosynthetic prokaryotes that were among the first organisms to produce oxygen via photosynthesis.

• Oxygen Revolution: The period when oxygen began to accumulate in Earth's atmosphere.

Step-by-Step Guidance

1. Review how cyanobacteria perform oxygenic photosynthesis.

2. Explain how the oxygen produced by cyanobacteria accumulated in the atmosphere over time.

3. Consider the impact of this oxygen increase on Earth's environment and other organisms.

Try solving on your own before revealing the answer!

Q6. What happened to many prokaryotic organisms as a result of rising oxygen levels, and why?

Background

Topic: Oxygen Toxicity and Evolutionary Consequences

This question examines the effects of increased atmospheric oxygen on early prokaryotes.

Key Terms:

• Prokaryotes: Single-celled organisms without a nucleus (includes bacteria and archaea).

• Oxygen Toxicity: The harmful effects of oxygen on organisms not adapted to it.

Step-by-Step Guidance

1. Recall which prokaryotes were present before the rise of atmospheric oxygen.

2. Explain why oxygen can be toxic to some organisms.

3. Describe what happened to prokaryotes that could not tolerate oxygen.

Try solving on your own before revealing the answer!

Q7. What is the difference between a eukaryote and a prokaryote?

Background

Topic: Cell Structure and Classification

This question tests your understanding of the fundamental differences between prokaryotic and eukaryotic cells.

Key Terms:

• Prokaryote: Cell lacking a nucleus and membrane-bound organelles.

• Eukaryote: Cell with a nucleus and membrane-bound organelles.

Step-by-Step Guidance

1. List the main structural features of prokaryotic cells.

2. List the main structural features of eukaryotic cells.

3. Compare and contrast these features, focusing on the presence or absence of a nucleus and organelles.

Try solving on your own before revealing the answer!