Cells as the Basis of Life

Cell - The basic unit of life that coordinates activities to form colonial and multicellular organisms.

Prokaryotic Cell - A simple cell lacking a nucleus and membrane-bound organelles (e.g., bacteria).

Eukaryotic Cell - A complex cell with a nucleus and membrane-bound organelles (e.g., plant and animal cells).

Organelles - Specialized structures within a cell that perform specific functions.

Animal Cell Components:

• Nucleus - Contains DNA and controls cell activities.

• Cytoplasm - Gel-like substance where chemical reactions occur.

• Cell Membrane - Controls what enters and exits the cell.

• Mitochondria - Produces energy (ATP); powerhouse of the cell.

• Ribosomes - Make proteins.

• Endoplasmic Reticulum (ER):

  • Rough ER - Has ribosomes; helps with protein synthesis.

  • Smooth ER - No ribosomes; makes lipids.

• Golgi Apparatus - Modifies and packages proteins and lipids.

• Lysosomes - Contain digestive enzymes to break down waste.

Plant Cell Components (In addition to Animal Cell Components):

• Cell Wall - Provides structure and support.

• Chloroplasts - Contain chlorophyll; perform photosynthesis.

• Large Vacuole - Stores water, nutrients, and waste; helps maintain shape.

Microscopy:

• Light Microscopy - Uses visible light to magnify cells; good for studying cell morphology but has limited resolution.

• Electron Microscopy - Uses electron beams for high-resolution images of cell ultrastructure but requires dead samples.

Magnification Formulas:

• Magnification (M) = Image Size (I) / Actual Size (A)

• Actual Size (A) = Image Size (I) / Magnification (M)

• Image Size (I) = Magnification (M) x Actual Size (A)

Fluid Mosaic Model of the Cell Membrane:

• Structure - A phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Function - Selective permeability; controls movement of substances in and out.

• Phospholipids - Hydrophilic head (water-attracting) and hydrophobic tails (water-repelling) form a double layer.

Transport Across Membranes:

• Diffusion - Passive movement of particles from high to low concentration.

• Facilitated Diffusion - Passive transport via membrane proteins.

• Osmosis - Movement of water across a semipermeable membrane from low to high solute concentration.

• Active Transport - Movement of substances from low to high concentration using energy (ATP).

• Endocytosis - Process where the cell engulfs large particles:

  • Phagocytosis - Cell "eating" solid particles.

  • Pinocytosis - Cell "drinking" small liquid particles.

• Exocytosis - Process where the cell expels substances using vesicles.

Factors Affecting Material Exchange:

• Surface-Area-to-Volume Ratio - Smaller cells exchange materials more efficiently.

• Concentration Gradients - Steeper gradients lead to faster diffusion.

• Material Characteristics - Size, polarity, and charge affect transport.

Cell Requirements:

• Energy:

  • Light Energy - Used in photosynthesis.

  • Chemical Energy - Stored in glucose and ATP.

• Matter:

  • Gases - Oxygen (for respiration), CO2 (for photosynthesis).

  • Simple Nutrients - Glucose, amino acids, fatty acids, nucleotides.

  • Ions - Sodium, potassium, calcium (nerve signals, enzyme activation).

• Waste Removal:

  • CO2 - Expelled during respiration.

  • Nitrogenous Wastes - Excreted as urea or ammonia.

  • Excess Salts/Ions - Removed via diffusion or active transport.

Biochemical Processes:

• Photosynthesis:

  • Location - Chloroplasts.

  • Purpose - Converts light energy into glucose.

  • Stages:

    • Light-dependent Reactions - Use light to produce ATP and NADPH.

    • Calvin Cycle - Uses ATP and NADPH to form glucose from CO2.

• Cellular Respiration:

  • Location - Mitochondria.

  • Purpose - Releases energy from glucose to produce ATP.

  • Stages:

    • Glycolysis - Breaks glucose into pyruvate (cytoplasm).

    • Krebs Cycle - Further breaks down pyruvate, releasing CO2 (mitochondria).

    • Electron Transport Chain - Produces most ATP (mitochondria).

  • Aerobic Respiration - Uses oxygen; produces 36-38 ATP.

  • Anaerobic Respiration - Without oxygen; produces less ATP and lactic acid (animals) or ethanol and CO2 (yeast).

• Waste Removal:

  • Exocytosis - Expels large molecules (e.g., hormones, enzymes).

  • Diffusion/Active Transport - Removes CO2, O2, and ions.

  • Lysosomes - Break down and recycle waste.

  • Kidneys/Liver - Process and remove metabolic waste.

Enzymes:

• Definition - Proteins that speed up chemical reactions without being consumed.

• Function - Catalysts for digestion, molecule synthesis, and energy production.

• Structure - Made of amino acids; have an active site where the substrate binds.

• Factors Affecting Activity:

  • Temperature - Too high or too low alters enzyme function.

  • pH Levels - Each enzyme has an optimal pH for activity.