Biology 101 Study Guide

Overview

This guide covers two fundamental processes in biology: photosynthesis and cellular respiration. At a high level, they are opposite processes. Photosynthesis captures and stores energy from sunlight in glucose molecules, while cellular respiration releases that stored energy to produce ATP, the cell's energy currency. Photosynthesis uses carbon dioxide and water to produce glucose and oxygen, whereas cellular respiration uses glucose and oxygen to produce carbon dioxide, water, and ATP.

Key Terms

Photosynthesis
The process occurring in chloroplasts where light energy is used to convert carbon dioxide and water into glucose (sugar) and oxygen.
Cellular Respiration
The process of breaking down glucose with oxygen to produce carbon dioxide, water, and a large amount of ATP (energy).
ATP
Adenosine Triphosphate, the main energy currency of the cell. Energy is released when a phosphate bond is broken.
Chloroplast
The organelle in plant cells where photosynthesis takes place.
Mitochondria
The "powerhouse of the cell," where the Krebs cycle and electron transport chain of cellular respiration occur.
Thylakoid
The membrane inside the chloroplast where the light-dependent reactions of photosynthesis happen.
Stroma
The fluid-filled space within the chloroplast where the Calvin cycle takes place.
RuBisCO
An enzyme used in the Calvin cycle to "fix" CO2 into sugar. It is noted as the most abundant protein on Earth.
Glycolysis
The first stage of cellular respiration, occurring in the cytoplasm. It is anaerobic (doesn't require oxygen).
Fermentation
An anaerobic process that occurs after glycolysis if no oxygen is present. Examples include lactic acid fermentation in muscles and alcohol fermentation in yeast.

Important Processes

Photosynthesis

Equation: 6CO2 + 6H2O + Light Energy → C6H12O6 (glucose) + 6O2

  1. Light-Dependent Reactions
    • Location: Thylakoid membrane (inside chloroplast).
    • Inputs: Light, Water (H2O).
    • Process: Chlorophyll absorbs light energy. Water is split (photolysis), releasing oxygen as a byproduct.
    • Outputs: ATP, NADPH (energy-carrying molecules).
  2. Calvin Cycle (Light-Independent Reactions)
    • Location: Stroma (inside chloroplast).
    • Inputs: ATP, NADPH (from light reactions), Carbon Dioxide (CO2).
    • Process: The enzyme RuBisCO "fixes" CO2. ATP and NADPH provide the energy to convert the fixed carbon into G3P, a sugar. Two G3P molecules combine to make one glucose.
    • Outputs: Glucose (or G3P), ADP, NADP+.

Cellular Respiration

Equation: C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + ATP (energy)

  1. Glycolysis
    • Location: Cytoplasm.
    • Inputs: Glucose.
    • Process: Glucose is broken down. This step does not require oxygen (anaerobic).
    • Outputs: 2 Pyruvate, a small amount of ATP.
  2. Krebs Cycle (Citric Acid Cycle)
    • Location: Mitochondrial matrix.
    • Inputs: Pyruvate (converted).
    • Process: Completes the breakdown of the sugar.
    • Outputs: NADH, FADH2 (energy-carrying molecules), CO2.
  3. Electron Transport Chain
    • Location: Inner mitochondrial membrane.
    • Inputs: NADH, FADH2, Oxygen (O2).
    • Process: Energy from NADH and FADH2 is used to create a proton gradient, which powers ATP synthesis. Oxygen acts as the final electron acceptor.
    • Outputs: The majority of ATP (approx. 34), Water (H2O).

Practice Questions

  1. What is the chemical equation for photosynthesis?
  2. Where in the cell does glycolysis occur?
  3. What are the two main stages of photosynthesis?
  4. Which process produces more ATP: glycolysis or the electron transport chain?
  5. What is the role of RuBisCO in the Calvin cycle?
  6. Why are most plants green?
  7. If a cell has no oxygen available, what process might occur after glycolysis?
  8. What are the primary inputs and outputs of the Krebs cycle?
  9. Explain the role of oxygen in cellular respiration. Where is it used and why is it important?
  10. Compare and contrast photosynthesis and cellular respiration in terms of their overall goal, location in the cell, and relationship with energy.

Answer Key

1. What is the chemical equation for photosynthesis?

6CO2 + 6H2O + Light Energy → C6H12O6 (glucose) + 6O2

2. Where in the cell does glycolysis occur?

In the cytoplasm.

3. What are the two main stages of photosynthesis?

The light-dependent reactions and the Calvin cycle.

4. Which process produces more ATP: glycolysis or the electron transport chain?

The electron transport chain produces the most ATP (around 34 molecules).

5. What is the role of RuBisCO in the Calvin cycle?

RuBisCO is the enzyme that "fixes" atmospheric carbon dioxide (CO2) into an organic molecule, starting the process of sugar creation.

6. Why are most plants green?

The pigment chlorophyll in their chloroplasts absorbs red and blue light for photosynthesis but reflects green light.

7. If a cell has no oxygen available, what process might occur after glycolysis?

Fermentation (e.g., lactic acid fermentation or alcohol fermentation).

8. What are the primary inputs and outputs of the Krebs cycle?

The primary inputs are derived from pyruvate, and the outputs are NADH, FADH2, and CO2.

9. Explain the role of oxygen in cellular respiration. Where is it used and why is it important?

Oxygen acts as the final electron acceptor in the electron transport chain. It is critical because without it, the chain would back up, and the majority of ATP production would stop.

10. Compare and contrast photosynthesis and cellular respiration in terms of their overall goal, location in the cell, and relationship with energy.

Goal: Photosynthesis's goal is to store energy in glucose. Cellular respiration's goal is to release energy from glucose to make ATP.
Location: Photosynthesis occurs in the chloroplasts. Cellular respiration occurs mainly in the cytoplasm and mitochondria.
Energy: Photosynthesis is an energy-storing process (endergonic). Cellular respiration is an energy-releasing process (exergonic).

Made with Kernl · see how