Introduction to Biology

Domains of Life

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

• Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.

• Archaea: Prokaryotic, 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: Exhibit organization, metabolism, responsiveness, growth, development, reproduction, and homeostasis.

• Nonliving things: May have structure but lack metabolism, growth, and reproduction.

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Hypothesis

3. Experiment

4. Data Collection

5. Analysis

6. Conclusion

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes.

• Examples: Regulation of body temperature, blood pH, and glucose levels.

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.

• Example: Studying cell organelles to understand cell function.

DNA Importance

• DNA stores genetic information, directs protein synthesis, and enables inheritance.

Elements vs. Molecules

• Element: Pure substance consisting of one type of atom (e.g., O2).

• Molecule: Two or more atoms bonded together (e.g., H2O).

Radioisotope Technology

• Used in medical imaging, cancer treatment, and biological research.

• Example: PET scans use radioisotopes to visualize metabolic activity.

Atoms and Charge

• Atoms change charge by gaining or losing electrons, forming ions.

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

Types of Bonds

• Ionic Bonds: Transfer of electrons between atoms; forms ions.

• Covalent Bonds: Sharing of electrons between atoms.

• Hydrogen Bonds: Weak attraction between a hydrogen atom and an electronegative atom (e.g., O or N).

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).

pH Levels

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

Cell organelles perform specialized functions essential for cell survival.

Cell Size and Surface Area

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

• As cell size increases, surface area grows slower than volume.

Microscopy Types

Diffusion

• Movement of molecules from high to low concentration.

• Passive process; no energy required.

Plasma Membrane Structure

• Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

What Can and Can't Pass Through the Plasma Membrane

• Can pass: Small, nonpolar molecules (e.g., O2, CO2), some small polar molecules (e.g., H2O).

• Cannot pass: Large molecules, ions, and most polar substances without transport proteins.

Active Transport

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

• Example: Sodium-potassium pump.

Isotonic Solution

• Has equal solute concentration as the cell; no net movement of water.

• Cells retain their normal shape.

Tissues & Organ Systems

Types of Tissues and Their Functions

Types of Connective Tissues

• Loose connective tissue: Supports and binds other tissues.

• Dense connective tissue: Provides strength (e.g., tendons, ligaments).

• Cartilage: Flexible support.

• Bone: Rigid support and protection.

• Blood: Transport of nutrients and waste.

Location of Each Tissue Type

• Epithelial: Skin, lining of digestive tract.

• Connective: Bones, tendons, blood.

• Muscle: Skeletal muscles, heart, stomach (smooth muscle).

• Nervous: Brain, spinal cord, peripheral nerves.

Type of Muscle in the Stomach

• Smooth muscle: Involuntary, non-striated muscle found in the stomach and other internal organs.

Types of Junctions

• Tight junctions: Seal cells together, preventing leakage.

• Desmosomes: Provide mechanical strength by anchoring cells.

• Gap junctions: Allow communication between cells via small molecules.

Cellular Respiration & Metabolism

Glycolysis

• First step in cellular respiration; breaks down glucose into pyruvate.

• Produces ATP and NADH.

Electron Transport Chain & ATP Production

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

Electron Carriers in Citric Acid Cycle

• NAD+ and FAD are electron carriers.

• They gain electrons from metabolic intermediates and become NADH and FADH2.

Diffusion vs. Active Transport

• Diffusion: Passive movement; no energy required.

• Active transport: Requires energy; moves substances against gradient.

Key Formula: Surface Area to Volume Ratio

• For a sphere:

• For a sphere:

• Ratio:

Additional info: Academic context was added to clarify and expand brief review points, ensuring completeness and self-contained explanations.