Cellular Energetics: Energy, Metabolism, Photosynthesis, and Respiration

Cellular Energetics

Thermodynamics in Biology

Thermodynamics governs how energy is transferred and transformed in biological systems. The first law states that energy cannot be created or destroyed, only changed in form. The second law states that every energy transfer increases the disorder (entropy) of the universe.

• First Law of Thermodynamics: Energy is conserved. Example: Chemical energy in glucose is converted to ATP during cellular respiration.

• Second Law of Thermodynamics: Energy transformations increase entropy. Example: Heat released during metabolism increases disorder.

Catabolic and Anabolic Reactions

Metabolic reactions are classified as either catabolic (breaking down molecules) or anabolic (building molecules).

• Catabolic Reactions: Break down larger molecules into smaller ones, releasing energy. Example: Cellular respiration.

• Anabolic Reactions: Build larger molecules from smaller ones, requiring energy input. Example: Photosynthesis.

• Diagram Analysis: Diagrams showing molecules being broken down with energy release represent catabolic reactions; those showing molecules being built up with energy input represent anabolic reactions.

Endergonic and Exergonic Reactions

Biological reactions are also classified by their energy changes.

• Exergonic Reaction: Releases energy; products have less free energy than reactants. Example: Hydrolysis of ATP.

• Endergonic Reaction: Requires energy input; products have more free energy than reactants. Example: Synthesis of ATP from ADP and Pi.

• Graphical Comparison: Exergonic reactions show a downward slope in free energy; endergonic reactions show an upward slope.

ATP Structure and Function

ATP (adenosine triphosphate) is the primary energy currency of the cell.

• Structure: ATP consists of adenine (A), ribose (B), and three phosphate groups (C).

• Energy Release: Breaking the terminal phosphate bond releases energy for cellular work.

• ATP Cycle: ATP is regenerated from ADP and Pi in energy-requiring processes.

Component	Label
Adenine	A
Ribose	B
Phosphate Groups	C

Key Equations:

• ATP Hydrolysis: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• ATP Synthesis: $\text{ADP} + \text{P}_i + \text{energy} \rightarrow \text{ATP} + \text{H}_2\text{O}$

Photosynthesis

Overview and Light Reactions

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Light Dependent Reactions: Occur in the thylakoid membranes; convert light energy to chemical energy (ATP and NADPH).

• Light Independent Reactions (Calvin Cycle): Occur in the stroma; use ATP and NADPH to fix carbon dioxide into glucose.

• Electron Transport: Electrons flow through photosystems, generating ATP and NADPH.

• Photosystem I & II: Absorb light at different wavelengths to energize electrons.

• ATP Synthase: Enzyme that synthesizes ATP using the proton gradient.

Chlorophyll and Accessory Pigments

Photosynthetic pigments absorb light energy for photosynthesis.

• Chlorophyll a: Main pigment; absorbs mainly blue and red light.

• Chlorophyll b, Beta-Carotene, Xanthophyll: Accessory pigments; broaden the range of light absorption.

• Stroma: Fluid-filled space in chloroplasts where the Calvin cycle occurs.

Pigment	Function
Chlorophyll a	Main photosynthetic pigment
Chlorophyll b	Accessory pigment
Beta-Carotene	Accessory pigment
Xanthophyll	Accessory pigment

Cellular Respiration

Stages of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose.

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate, producing ATP and NADH.

• Krebs Cycle (Citric Acid Cycle): Occurs in mitochondria; oxidizes acetyl-CoA, producing ATP, NADH, and FADH2.

• Oxidative Phosphorylation (Electron Transport Chain): Occurs in the inner mitochondrial membrane; uses NADH and FADH2 to generate ATP.

• Fermentation: Occurs when oxygen is absent; regenerates NAD+ and produces lactic acid or ethanol.

Key Equations:

• Overall Respiration: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{energy}$

Endotherms and Ectotherms

Organisms are classified by how they regulate body temperature.

• Endotherms: Maintain constant body temperature using metabolic heat (e.g., mammals, birds).

• Ectotherms: Rely on environmental heat sources (e.g., reptiles, amphibians).

Type	Temperature Regulation	Examples
Endotherm	Internal metabolic heat	Mammals, birds
Ectotherm	External environment	Reptiles, amphibians

Photosynthesis and Respiration Investigations

Experimental Design and Analysis

Experiments can be used to investigate photosynthesis and respiration rates.

• Chromatography: Separates pigments to analyze photosynthesis.

• Respiration Rate: Measured by CO2 production or O2 consumption in germinating beans.

• Environmental Factors: Temperature, pH, and sugar concentration affect respiration rates.

Graphical Data Interpretation

Graphs are used to analyze experimental results, such as optimum temperature for yeast respiration or percent dry weight of plant organs over time.

• Optimum Temperature: Determined by the highest rate of bubble production in yeast respiration experiments.

• Plant Growth Analysis: Graphs show changes in root, stem, leaf, and reproductive organ mass during the growing season.

Key Vocabulary

• Photosynthesis: Conversion of light energy to chemical energy in plants, algae, and some bacteria.

• Cellular Respiration: Process of extracting energy from organic molecules.

• Enzyme: Protein catalyst that speeds up chemical reactions.

• Endergonic: Reaction requiring energy input.

• Exergonic: Reaction releasing energy.

• Autotroph: Organism that produces its own food.

• Heterotroph: Organism that consumes other organisms for food.

• Chloroplast: Organelle where photosynthesis occurs.

• Mitochondrion: Organelle where cellular respiration occurs.

• Fermentation: Anaerobic process producing ATP and byproducts like ethanol or lactic acid.

Additional info: Some definitions and explanations were expanded for clarity and completeness. Diagrams and tables were interpreted and recreated based on context.