Fermentation, Photosynthesis, and Cell Division: Study Guide

Fermentation

Overview of Fermentation

Fermentation is an anaerobic metabolic process that allows cells to generate energy without oxygen. It is essential for certain organisms and occurs in various forms, producing different end products.

• Alcohol Fermentation: Converts pyruvate into ethanol and carbon dioxide, regenerating NAD+ for glycolysis.

• Lactic Acid Fermentation: Converts pyruvate into lactic acid, also regenerating NAD+.

Key Reactions:

• Alcohol Fermentation: $2\ \text{Pyruvate} \rightarrow 2\ \text{CO}_2 + 2\ \text{NAD}^+ + 2\ \text{Ethanol}$

• Lactic Acid Fermentation: $2\ \text{Pyruvate} \rightarrow 2\ \text{Lactic Acid}$

Applications:

• Bread and alcohol production (alcohol fermentation)

• Yogurt production and muscle metabolism (lactic acid fermentation)

Key Terms:

• Oxygen debt: The amount of extra oxygen required after physical exercise to restore pre-exercise conditions.

• Facultative anaerobe: Organisms that can survive with or without oxygen.

• Obligate anaerobe: Organisms that cannot survive in the presence of oxygen.

Example: Human muscle cells perform lactic acid fermentation during intense exercise when oxygen is scarce.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

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

Light-Dependent Reactions

• Occur in the thylakoid membranes of chloroplasts.

• Convert light energy into chemical energy (ATP and NADPH).

• Involve Photosystem II and Photosystem I, Electron Transport Chains, and ATP Synthase.

Light-Independent Reactions (Calvin Cycle)

• Occur in the stroma of chloroplasts.

• Use ATP and NADPH to fix carbon dioxide into glucose.

• Key enzymes: Rubisco (catalyzes CO2 fixation), RUBP (ribulose bisphosphate, CO2 acceptor).

Pigments and Light Absorption

• Chlorophyll a and b: Main pigments absorbing light for photosynthesis.

• Carotenoids: Accessory pigments that absorb additional wavelengths.

• Absorption spectrum: Graph showing the wavelengths of light absorbed by pigments.

• Electromagnetic spectrum: Range of all possible light wavelengths; visible light is used in photosynthesis.

Example: The green color of leaves is due to chlorophyll reflecting green light while absorbing red and blue wavelengths.

Cell Division

Overview of Cell Division

Cell division is the process by which cells reproduce, essential for growth, repair, and reproduction. In eukaryotes, it includes mitosis and cytokinesis; in prokaryotes, binary fission.

Binary Fission

• Simple division in prokaryotes (e.g., bacteria).

• DNA replicates, and the cell splits into two identical cells.

Cell Cycle Phases

• Interphase: Period of cell growth and DNA replication; includes G0, G1, S, and G2 phases.

• G0: Resting phase; cells not actively dividing.

• G1: Cell growth.

• S: DNA synthesis (replication).

• G2: Preparation for mitosis.

Mitosis Stages

• Prophase: Chromatin condenses into chromosomes; spindle fibers form.

• Metaphase: Chromosomes align at the metaphase plate.

• Anaphase: Sister chromatids separate and move to opposite poles.

• Telophase: Nuclear envelopes reform; chromosomes decondense.

Cytokinesis

• Division of the cytoplasm, forming two daughter cells.

• In plants: Cell plate forms.

• In animals: Cleavage furrow forms, involving actin and myosin filaments.

Cell Cycle Regulation

• Checkpoints: G1, G2, and M checkpoints ensure proper division.

• Density-dependent inhibition: Cells stop dividing when crowded.

• Anchorage-dependent inhibition: Cells must be attached to a substrate to divide.

• Apoptosis: Programmed cell death, important for development and homeostasis.

Stem Cells and Cancer

• Stem cells: Undifferentiated cells; pluripotent (can become any cell type) vs. multipotent (limited range).

• Benign tumor: Non-cancerous growth.

• Malignant tumor: Cancerous, invasive growth.

• HELA cells: Immortal human cell line used in research.

Example: The Onion cell lab is commonly used to observe stages of mitosis in plant cells.

Term	Definition	Example/Application
Alcohol Fermentation	Conversion of pyruvate to ethanol and CO2	Bread, beer, wine production
Lactic Acid Fermentation	Conversion of pyruvate to lactic acid	Yogurt, muscle cells during exercise
Photosystem II	Protein complex in thylakoid membrane; initiates light reactions	Splits water, releases O2
Rubisco	Enzyme that fixes CO2 in Calvin Cycle	Carbon fixation in plants
Binary Fission	Simple cell division in prokaryotes	Bacterial reproduction
Pluripotent Stem Cell	Can become any cell type	Embryonic stem cells
Multipotent Stem Cell	Can become a limited range of cells	Adult stem cells

Additional info: Academic context and definitions have been expanded for clarity and completeness. Table entries have been logically grouped and inferred for study purposes.