Guided Study: Photosynthesis and Its Global Significance

Q1. True or false: A photoautotroph is a type of heterotroph that uses solar energy to produce sugars. If false, make it a correct statement.

Background

Topic: Types of Organisms and Energy Acquisition

This question tests your understanding of the difference between autotrophs and heterotrophs, and specifically what a photoautotroph is.

Key Terms:

• Autotroph: An organism that produces its own food from inorganic substances.

• Heterotroph: An organism that obtains its food by consuming other organisms.

• Photoautotroph: An organism that uses light energy to synthesize organic compounds from carbon dioxide.

Step-by-Step Guidance

1. Recall the definitions of autotroph, heterotroph, and photoautotroph.

2. Determine whether a photoautotroph is a type of heterotroph or autotroph.

3. If the statement is false, rephrase it to accurately describe a photoautotroph.

Try solving on your own before revealing the answer!

Final Answer:

False. A photoautotroph is not a heterotroph; it is an autotroph that uses solar energy to produce sugars.

Q2. A new bacterium is discovered in Lake Superior. Scientists are able to determine that these bacteria produce oxygen gas. What is likely to be true about these organisms?

Background

Topic: Oxygenic Photosynthesis

This question tests your understanding of the types of organisms that produce oxygen as a byproduct of photosynthesis.

Key Terms:

• Oxygenic photosynthesis: Photosynthesis that produces oxygen as a byproduct, typically performed by plants, algae, and cyanobacteria.

• Photoautotroph: Organism that uses light to synthesize food and often releases oxygen.

Step-by-Step Guidance

1. Recall which organisms perform oxygenic photosynthesis.

2. Consider what the production of oxygen gas indicates about the metabolic pathway used by the bacterium.

3. Relate this to the likely classification of the organism (e.g., photoautotroph).

Try solving on your own before revealing the answer!

Final Answer:

The bacteria are likely photoautotrophs and perform photosynthesis.

Q3. A plant’s leaves are the primary site of photosynthesis. A plant’s leaves would be expected to have a large amount of ____________.

Background

Topic: Plant Cell Structure and Photosynthesis

This question tests your knowledge of the organelles and molecules involved in photosynthesis within plant leaves.

Key Terms:

• Chloroplasts: Organelles where photosynthesis occurs.

• Chlorophyll: The pigment that captures light energy for photosynthesis.

Step-by-Step Guidance

1. Recall which organelle is responsible for photosynthesis in plant cells.

2. Think about what pigment is abundant in these organelles and why.

3. Fill in the blank with the most appropriate term.

Try solving on your own before revealing the answer!

Final Answer:

Chloroplasts (or chlorophyll could also be argued).

Q4. A student has been shrunk to fit inside the thylakoid space of a granum. How many layers of phospholipids would he or she need to cross through to get completely out of the mesophyll cell?

Background

Topic: Cell and Organelle Membranes

This question tests your understanding of the structure of plant cells and the membranes that separate different compartments.

Key Terms:

• Phospholipid bilayer: The basic structure of cell and organelle membranes.

• Thylakoid: Membrane-bound compartment inside chloroplasts.

• Mesophyll cell: The main photosynthetic cell in leaves.

Step-by-Step Guidance

1. Identify all the membranes the student would cross from the thylakoid space to the outside of the mesophyll cell.

2. Remember that each membrane is a phospholipid bilayer (2 layers).

3. List the sequence: thylakoid membrane, chloroplast envelope (inner and outer), plasma membrane, and cell wall (if applicable).

4. Count the total number of phospholipid layers (not just membranes).

Try solving on your own before revealing the answer!

Final Answer:

Eight layers of phospholipids.

Q5. Which of the following substances provides the majority of the atoms that make up the sugar produced by photosynthesis?

Background

Topic: Inputs and Outputs of Photosynthesis

This question tests your understanding of where the atoms in glucose come from during photosynthesis.

Key Terms:

• Photosynthesis equation:

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

• Carbon source: The origin of the carbon atoms in glucose.

Step-by-Step Guidance

1. Examine the molecular formula for glucose ($\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$).

2. Identify which reactant supplies most of the atoms in glucose.

3. Consider the roles of water and carbon dioxide in the process.

4. Choose the correct answer from the options provided.

Try solving on your own before revealing the answer!

Final Answer:

Carbon dioxide provides the majority of the atoms that make up the sugar produced by photosynthesis.

Q6. True or false: During photosynthesis, CO2 is split to release oxygen gas. If false, make it a correct statement.

Background

Topic: Source of Oxygen in Photosynthesis

This question tests your understanding of which molecule is split to release oxygen gas during photosynthesis.

Key Terms:

• Photolysis: The splitting of water molecules during the light reactions of photosynthesis.

• Oxygen gas ($\mathrm{O}_2$): The byproduct of water splitting, not CO2 splitting.

Step-by-Step Guidance

1. Recall the overall equation for photosynthesis and identify which molecule is split to release oxygen.

2. Determine if the statement is true or false based on your knowledge.

3. If false, rewrite the statement to make it correct.

Try solving on your own before revealing the answer!

Final Answer:

False. Oxygen gas is created as a result of splitting water ($\mathrm{H}_2\mathrm{O}$), not carbon dioxide ($\mathrm{CO}_2$).

Q7. Complete the following table that compares photosynthesis with cellular respiration.

Background

Topic: Comparison of Photosynthesis and Cellular Respiration

This question tests your ability to compare and contrast the two major energy processes in cells.

Key Terms:

• Reduction: Gain of electrons (e.g., CO2 is reduced in photosynthesis).

• Oxidation: Loss of electrons (e.g., glucose is oxidized in respiration).

• Exergonic: Releases energy (cellular respiration).

• Endergonic: Requires energy input (photosynthesis).

Step-by-Step Guidance

1. For each process, determine if CO2 is reduced or not.

2. For each process, determine if glucose is oxidized or not.

3. Classify each process as exergonic or endergonic.

4. Fill in the table accordingly, using your knowledge of the processes.

Try solving on your own before revealing the answer!

Final Answer:

Photosynthesis: CO2 is reduced (Yes), Glucose is oxidized (No), Endergonic (Yes), Exergonic (No). Cellular respiration: CO2 is reduced (No), Glucose is oxidized (Yes), Endergonic (No), Exergonic (Yes).

Q8. The Calvin cycle is also referred to as the light-independent reactions. Briefly explain why referring to the chemical reactions of the Calvin cycle as the light-independent reactions is only partially accurate.

Background

Topic: Calvin Cycle and Its Dependence on Light Reactions

This question tests your understanding of the relationship between the light reactions and the Calvin cycle in photosynthesis.

Key Terms:

• Calvin cycle: The set of chemical reactions that synthesize sugar from CO2, using ATP and NADPH.

• Light-independent: Reactions that do not require light directly, but may depend on products of light reactions.

Step-by-Step Guidance

1. Recall what the Calvin cycle requires to function (ATP and NADPH).

2. Determine where ATP and NADPH come from (light reactions).

3. Explain why the Calvin cycle is not truly independent of light, even though it does not use light directly.

Try solving on your own before revealing the answer!

Final Answer:

Although the Calvin cycle does not directly require light, it depends on ATP and NADPH produced by the light reactions, so it is only partially accurate to call it light-independent.