C2 - Energy Transformations Summary

Energy Transformations

Energy Basics

• Cells need energy input (light or chemical).
• Autotrophs vs. heterotrophs.
• Energy is the capacity to do work.
• Energy transforms from one type to another.
• Law of Conservation of Energy: Energy isn't created/destroyed, only changes form.
• Cells convert chemical energy into usable forms for movement, synthesis, and stable intracellular environment.

Forms of Energy

• Chemical energy: Stored in bonds.
• Radiant (light) energy: From the sun for photosynthesis.
• Heat (thermal energy): Byproduct of molecule movement, increases kinetic energy.
• Kinetic energy: Energy of moving molecules.
• Cells need energy for:
  • Movement (cell and within):
  • Sperm, muscle contraction, chromosome movement (mitosis), secretion, endocytosis/exocytosis.
  • Growth, repair, reproduction, synthesis (DNA, protein, carbs, lipids).
  • Stable environment: Regulating water/solute balance, pH, temperature, oxygen, wastes.

Nutrition Types

• Autotrophic: Organisms make their own food, synthesizing organic molecules from inorganic ones.
  • Photo-autotrophs: Need light (plants, algae).
  • Chemo-autotrophs: Need chemical energy (some bacteria).
• Heterotrophic: Organisms eat others for organic molecules (consumers).
  • Herbivores: Eat producers (plants).
  • Carnivores: Eat other heterotrophs.
  • Omnivores: Eat both.

Photosynthesis

• Sun is the main energy source.
• Photosynthesis converts light energy to chemical energy.
• $6CO<em>2 + 6H</em>2O + \text{light energy} \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2$
• Sun's energy:
  • Heat
  • Light
• Photosynthetic autotrophs use sunlight energy to produce glucose.
• Chemosynthetic autotrophs oxidize chemicals.
• Photosynthesis uses light to create bonds in glucose.
• Calvin cycle: Enzyme-catalyzed steps.
• Eukaryotes use chlorophyll in chloroplasts.
• Prokaryotes: Chlorophyll on plasma membrane.
• Occurs in chloroplasts, abundant in leaf mesophyll.
• Palisade mesophyll maximizes light exposure.
• Cytoplasmic streaming increases efficiency.
• Lower epidermis has stomates (guard cells, pores).
• Stomates regulate water loss and gas exchange.
• Chloroplast structure:
  • Two membranes.
  • Thylakoids (sacs).
  • Grana (thylakoid stacks).
  • Stroma (fluid).
  • Thylakoids store chlorophyll.
• Two stages:
  • Light-dependent (grana).
  • Light-independent (Calvin cycle, stroma, glucose produced).
• Oxygen is a byproduct.
• Factors affecting photosynthesis: Light wavelength, temperature, light intensity, $CO_2$, water.

Cellular Respiration

• Energy can't be created/destroyed, only transferred.
• Energy stored in chemical bonds.
• Breaking down large molecules releases energy.
• Aerobic respiration: Complex molecules break down, releasing chemical energy from glucose to make ATP, regulated by enzymes.
• Two stages:
  • Glycolysis (cytoplasm): Glucose to 2 pyruvate, yields 4 ATP.
  • Citric Acid Cycle (mitochondria): 2 Pyruvate to 2 Acetyl CoA, 2 ATP to start cycle, produces intermediate products, ATP, $CO_2$.
  • Net gain: ~32 ATP per glucose.
• Aerobic respiration produces $6H<em>2O$ and $6CO</em>2$.
• Mitochondria have folded membranes for aerobic respiration steps, abundant in high-energy cells.

Fermentation

• Anaerobic alternative to aerobic respiration.
• Occurs when oxygen is limited.
• Releases less ATP (2 ATP) than aerobic respiration as glucose is not fully broken down.
• Occurs in cytoplasm only.
• Two types:
  • Alcohol fermentation (plants, yeast, some bacteria): $C<em>6H</em>{12}O<em>6 \rightarrow 2C</em>2H<em>5OH + 2CO</em>2 + \text{energy}$
    • Ethanol is toxic.
    • Used in wine making, brewing, baking.
  • Lactic acid fermentation (animals): $C<em>6H</em>{12}O<em>6 \rightarrow 2C</em>2H<em>6O</em>3 + \text{energy}$
    • Lactic acid is toxic.
    • Important for diving mammals and sprints.

Aerobic Respiration vs Fermentation

• Bigger molecules, more bonds = more stored energy.
• Breaking down molecules:
  • Some energy remains in products.
  • Some transferred to ATP.
  • Some lost as heat.
• Anaerobic respiration is less efficient (incomplete breakdown).

Energy and Bonds

• Energy required to break bonds, released when new bonds form.
• Chemical energy is potential energy.
• Stored in bonds between atoms.
• Bigger molecules store more energy.

ATP

• ATP formed from ADP and Pi.
• ATP to ADP + Pi releases energy.
• Breaking down large molecules converts stored chemical energy to ATP energy and releases heat.
• ATP is a renewable, soluble energy currency.
• ATP parts:
  • Adenine base.
  • 5-carbon sugar (ribose).
  • Three phosphate groups.
• ATP breaks down to ADP + phosphate, releasing energy.
• ATP/ADP cycle is continuous.
• Cellular reactions coupled to ADP/ATP inter-conversion.
• ATP needed for:
  • Growth, uptake, synthesis.
  • Cell division.
  • Movement.
  • Repair.
  • Reproduction.