Energy for living things

• All living organisms must respire, meaning they produce energy from food
• Plants and some bacteria, lacking a digestive system, synthesize their own food using energy from the environment
• To respire, organisms need to burn fuel to produce energy; they obtain fuel to create energy from organic molecules like glucose
• Autotrophs can be classified into two groups:

  • Photoautotrophs: use sunlight to energize metabolic reactions
  • Chemoautotrophs: use energy from chemicals like hydrogen sulfide, sulfur, and ammonium to produce organic molecules via chemosynthesis
• Heterotrophs, like animals, obtain organic compounds by consuming other organisms
• Autotrophs produce organic molecules from inorganic molecules like carbon dioxide, water, ammonium, nitrates, and sulfites
• Heterotrophs consume other organisms to obtain carbohydrates, lipids, nucleic acids, and proteins, which can be broken down into monosaccharides, fatty acids, nucleotides, and amino acids, respectively
• Most autotrophs are photoautotrophs, like plants, cyanobacteria, and algae, while all known chemoautotrophs are simple prokaryotic organisms; animals, fungi, some bacteria, and protists are heterotrophic
• All organisms, whether autotrophs or heterotrophs, use food to produce energy through cellular respiration, which generates adenosine triphosphate (ATP)
• The energy released from the breakdown of glucose is used to make ATP.
• Cellular respiration purpose: break down high-energy compounds (e.g., glucose) to produce ATP, vital for all forms of life
• Cellular respiration occurs in two distinct forms: aerobic respiration and anaerobic respiration
• All cells require energy obtained from the breakdown of organic compounds via cellular respiration, resulting in the synthesis of ATP molecules to power cellular reactions
• Mitochondria play a role only in aerobic cellular respiration, with the formula: C6H12O6 + 6O2 → 6CO2 + 6H2O + 36-38 ATP
• Mitochondria have an outer membrane surrounding a highly folded inner membrane, creating a narrow intermembrane space and a mitochondrial matrix inside, aiding in the production of ATP
• Photosynthesis purpose: convert carbon dioxide, water, and light energy into oxygen, water, and glucose (food), occurring in chloroplasts of photoautotrophs
• Chloroplasts consist of inner and outer membranes, grana (stack of flattened sacs called thylakoids), and stroma, with chlorophyll absorbing light energy during photosynthesis
• Photosynthesis formula: 6CO2 + 12H2O + light energy → C6H12O6 + 6O2 + 6H2O
• Plants source carbon dioxide through stomata in leaves and water through root hairs, with photosynthesis primarily occurring in leaves with a large surface area to maximize light absorption
• After photosynthesis, products like glucose are used immediately for energy in cellular respiration, stored as starch, or used to form complex molecules like cellulose for cell walls