Understanding Photosynthesis and Cellular Respiration

Posted on Feb 9, 2026 in Biology

Photosynthesis and Energy Storage

  • Photosynthesis: A process that uses light energy to make glucose.
  • Overall Purpose: To store energy in glucose.
  • Equation: Carbon dioxide + Water + Light → Glucose + Oxygen

Chloroplasts and Pigments

  • Chloroplast: The organelle where photosynthesis occurs.
  • Chlorophyll: A pigment that absorbs light energy.

Light-Dependent Reactions

  • Inputs: Light, water, ADP, and NADP+.
  • Outputs: ATP, NADPH, and oxygen.
  • Role of Water: It is split to release oxygen.

The Calvin Cycle (Light-Independent)

  • Inputs: Carbon dioxide, ATP, and NADPH.
  • Outputs: Sugar (glucose).
  • ATP Becomes: ADP; NADPH Becomes: NADP+.

Key Energy Molecules

  • ATP: The main energy molecule of the cell.
  • ADP: The low-energy form of ATP.
  • NADP+: An empty electron carrier.
  • NADPH: An electron carrier loaded with energy.

Biological Properties of Water

  • Polarity: An uneven distribution of charge.
  • Cohesion: Water molecules sticking to other water molecules.
  • Adhesion: Water molecules sticking to other surfaces.
  • Capillarity: The upward movement of water.
  • Significance: Allows water to reach leaves for photosynthesis.

Leaf Cross-Section: Labels and Functions

  • Upper Epidermis: Protects the leaf and lets light in.
  • Palisade Mesophyll: The main site of photosynthesis.
  • Spongy Mesophyll: Facilitates gas exchange.
  • Air Spaces: Allow for CO&sub2; and O&sub2; movement.
  • Stomata: Pores where CO&sub2; enters and O&sub2; exits.
  • Guard Cells: Open and close the stomata.
  • Xylem: Transports water to the leaf.
  • Phloem: Transports sugar away from the leaf.

Cellular Respiration and ATP Production

Basics of Cellular Respiration

  • Cellular Respiration: The process that releases energy from glucose.
  • Overall Purpose: To make ATP.
  • Equation: Glucose + Oxygen → Carbon Dioxide + Water + ATP
  • Mitochondria: The organelle where most respiration occurs.

Stages of Cellular Respiration

Glycolysis

  • Location: Cytoplasm.
  • Oxygen Required: No.
  • Inputs: Glucose and ATP.
  • Outputs: Pyruvate and a (net +) small amount of ATP.

The Krebs Cycle

  • Location: Mitochondrial matrix.
  • Outputs: Carbon dioxide and electron carriers.
  • Carbon Dioxide Release: Occurs during the Krebs Cycle.

The Electron Transport Chain (ETC)

  • Location: Inner mitochondrial membrane.
  • Final Electron Acceptor: Oxygen.
  • Inputs: Electrons, oxygen, and hydrogen ions.
  • Outputs: ATP and water.
  • Role of Oxygen: Accepts electrons at the end of the ETC.

Aerobic vs. Anaerobic Respiration

  • Aerobic Respiration: Uses oxygen and produces a large amount of ATP.
  • Anaerobic Respiration: Occurs without oxygen and produces little ATP.
  • Fermentation: Allows glycolysis to continue without oxygen.
  • Lactic Acid Fermentation: Occurs in muscles.
  • Alcoholic Fermentation: Occurs in yeast.
  • ATP Comparison: Aerobic production is greater than anaerobic.

The Digestive System and Cellular Respiration

  • Purpose: To provide glucose for cellular respiration.
  • Mouth: Mechanical digestion and amylase production.
  • Esophagus: Moves food to the stomach.
  • Stomach: Uses acid and enzymes to break down food.
  • Small Intestine: Site of final digestion and absorption.
  • Large Intestine: Absorbs water.
  • Pancreas: Releases digestive enzymes.
  • Liver: Produces bile for fat digestion.
  • Absorption: The process where nutrients enter the bloodstream.

Macromolecules and Enzyme Function

Types of Macromolecules

  • Carbohydrates: Provide quick energy.
  • Lipids: Used for long-term energy storage.
  • Proteins: Provide structure and act as enzymes.
  • Nucleic Acids: Store genetic information.
  • Organic Compounds: Chemical compounds that contain carbon.

Enzymes and Chemical Reactions

  • Enzymes: Proteins that speed up chemical reactions.
  • Active Site: The specific region where a substrate binds.
  • Activation Energy: The energy needed to start a reaction.
  • Enzyme Denaturation: The loss of shape due to high temperatures.
  • Temperature Effect: Increases reaction rate until denaturation occurs.

Essential Chemical Processes

  • Hydrolysis: Breaking chemical bonds by adding water.
  • Dehydration Synthesis: Forming bonds by removing water.

Homeostasis and Membrane Transport

  • Homeostasis: Maintaining stable internal conditions.

Transport Across Cell Membranes

  • Diffusion: Movement from high to low concentration.
  • Osmosis: The diffusion of water.
  • Facilitated Diffusion: Passive transport using a protein.
  • Passive Transport: Movement that requires no energy.
  • Active Transport: Requires ATP to move substances against a gradient.
  • Why Diffusion Occurs: Particles move to reach equilibrium.
  • Why Osmosis Occurs: Water moves to balance solute concentration.
  • Why Facilitated Diffusion Occurs: Large or charged molecules need protein assistance.

Water and Solute Movement

  • Direction of Solute Movement: High → Low concentration.
  • Direction of Water Movement: Toward higher solute concentration.
  • Determining Water Movement: Water always moves toward the higher solute concentration.

Understanding Tonicity

  • Hypertonic Solution: Water leaves the cell, causing it to shrink; contains more solute.
  • Hypotonic Solution: Water enters the cell, causing it to swell; contains less solute.
  • Isotonic Solution: No net water movement occurs.

pH Levels and Buffers

  • Acid: A substance that releases H+ ions.
  • Base: A substance that releases OH− ions.
  • pH Scale: Ranges from 0 to 14.
  • Acidic: pH values below 7.
  • Neutral: pH value of 7.
  • Basic: pH values above 7.
  • Strength: The farther a value is from 7, the stronger the acid or base.
  • Buffers: Substances that resist changes in pH.

Ocean Acidification and the Carbon Cycle

  • Ocean Acidification: A decrease in ocean pH levels.
  • Cause: Increased levels of atmospheric CO&sub2;.
  • Effect: Harms corals and shell-building organisms.
  • Carbon Cycle: The movement of carbon through Earth’s systems.
  • Photosynthesis: Removes CO&sub2; from the atmosphere.
  • Cellular Respiration: Releases CO&sub2; into the atmosphere.
  • Emissions: Human activities that increase atmospheric CO&sub2;.