Introduction to Biology

Domains of Life

The domain system classifies all living organisms into three major groups based on cellular structure and genetics.

• Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.

• Archaea: Prokaryotic, unicellular, often found in extreme environments; genetically distinct from bacteria.

• Eukarya: Eukaryotic organisms with cells containing a nucleus; includes animals, plants, fungi, and protists.

Hierarchy of Living Organisms

Biological organization follows a hierarchical structure from smallest to largest.

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism

Shared Characteristics of Living and Nonliving Things

• Living things: Composed of cells, grow, reproduce, respond to stimuli, maintain homeostasis, and evolve.

• Nonliving things: May have structure and organization but lack cellular processes and reproduction.

Chemistry of Life

Most Abundant Elements in Humanity

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Sulfur (S)

Reductionism

Reductionism is the approach of understanding complex systems by studying their simpler components.

• Importance: Helps in dissecting biological processes at molecular and cellular levels.

Atoms, Elements, and Molecules

• Element: Pure substance consisting of one type of atom.

• Molecule: Two or more atoms bonded together.

Radioisotope Technology

• Radioisotopes: Unstable isotopes that emit radiation.

• Applications: Medical imaging, cancer treatment, biological research.

Bond Types

• Ionic Bonds: Formed by transfer of electrons between atoms.

• Covalent Bonds: Formed by sharing electrons.

• Hydrogen Bonds: Weak attractions between partially charged atoms (often in water).

Polarity

• Polar Molecules: Unequal sharing of electrons; have partial charges (e.g., water).

• Nonpolar Molecules: Equal sharing of electrons; no charge separation (e.g., methane).

Acids, Bases, and pH

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Charge Changes in Atoms

• Atoms gain or lose electrons to become ions (charged particles).

• Negatively charged elements (anions) attract positively charged elements (cations).

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

Cell organelles are specialized structures within cells, each with unique functions.

• Nucleus: Contains DNA; controls cell activities; spherical.

• Mitochondria: Site of ATP production; oval-shaped.

• Ribosomes: Protein synthesis; small, round.

• Endoplasmic Reticulum (ER): Protein and lipid synthesis; network of membranes.

• Golgi Apparatus: Modifies, sorts, and packages proteins; stack of flattened sacs.

• Lysosomes: Digestion of cellular waste; spherical.

• Plasma Membrane: Controls entry/exit; flexible, phospholipid bilayer.

Cell Size and Surface Area

• Smaller cells have a higher surface area-to-volume ratio, facilitating efficient exchange of materials.

Microscopy Types

• Light Microscopy: Used for viewing live cells and tissues.

• Electron Microscopy: Used for high-resolution imaging of cell structures.

Diffusion

• Movement of molecules from high to low concentration.

• Passive process; no energy required.

Plasma Membrane Structure

• Composed of phospholipid bilayer, proteins, cholesterol, and carbohydrates.

Transport Across the Plasma Membrane

• Can Pass: Small, nonpolar molecules (e.g., O2, CO2).

• Cannot Pass: Large, polar molecules and ions without transport proteins.

Active Transport

• Movement of substances against concentration gradient; requires energy (ATP).

Isotonic Solutions

• Equal solute concentration inside and outside the cell; no net water movement.

• Cells retain their normal shape.

Glycolysis

• First step in cellular respiration; breaks down glucose to produce ATP.

• Occurs in cytoplasm.

Electron Transport Chain & ATP Production

• Most ATP is produced in the ATP synthase protein complex during the electron transport chain.

Citric Acid Cycle Electron Carriers

• NAD+ and FAD are electron carriers.

• They gain electrons from metabolic intermediates.

Tissues & Organ Systems

Types of Tissues and Their Functions

• Epithelial Tissue: Covers surfaces; protection, absorption, secretion.

• Connective Tissue: Supports and binds other tissues; includes bone, blood, cartilage.

• Muscle Tissue: Movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Communication; transmits electrical signals.

Types of Connective Tissues

• Loose Connective Tissue: Cushions organs.

• Dense Connective Tissue: Tendons and ligaments.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transport of substances.

Locations of Tissue Types

• Epithelial: Skin, lining of organs.

• Connective: Throughout body; bones, blood, cartilage.

• Muscle: Skeletal muscles, heart, walls of organs.

• Nervous: Brain, spinal cord, nerves.

Muscle Type in the Stomach

• Smooth Muscle: Involuntary, found in walls of stomach and other organs.

Types of Junctions

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap Junctions: Allow communication between cells.

Scientific Method & Homeostasis

Scientific Method Steps

• Observation

• Hypothesis

• Experiment

• Data Collection

• Analysis

• Conclusion

Homeostasis

• Maintenance of stable internal conditions despite external changes.

• Examples: Body temperature, blood glucose regulation.

Example Table: Types of Cell Junctions

Additional info: Academic context was added to expand brief review points into full explanations, definitions, and examples for clarity and completeness.