Introduction to Biology

Domains of Life

The domain is the highest taxonomic rank in the classification of life. There are three domains:

• Bacteria: Single-celled prokaryotes with no nucleus.

• Archaea: Single-celled prokaryotes, often found in extreme environments, genetically distinct from bacteria.

• Eukarya: Organisms with eukaryotic cells (with a nucleus), including animals, plants, fungi, and protists.

Hierarchy of Living Organisms (from smallest to largest):

• Atom

• Molecule

• Organelle

• Cell

• Tissue

• Organ

• Organ System

• Organism

• Population

• Community

• Ecosystem

• Biosphere

Shared Characteristics of Living Things:

• Organization (cells)

• Metabolism

• Homeostasis

• Growth and development

• Reproduction

• Response to stimuli

• Evolutionary adaptation

Scientific Method (in order):

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Analysis

7. Conclusion

Homeostasis is the maintenance of a stable internal environment despite external changes. For example, body temperature regulation.

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

Chemistry of Life

Elements and Molecules

• Element: A pure substance consisting of one type of atom (e.g., Oxygen, O).

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

Most Abundant Elements in Humans: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), and Phosphorus (P).

Radioisotope Technology uses unstable isotopes for medical imaging and cancer treatment.

Atoms, Ions, and Bonds

• Atom: Basic unit of matter, composed of protons, neutrons, and electrons.

• Ion: An atom that has gained or lost electrons, acquiring a charge.

• How Atoms Change Charge: By gaining electrons (becoming negative, anion) or losing electrons (becoming positive, cation).

Types of Chemical Bonds:

• Ionic Bond: Transfer of electrons from one atom to another (e.g., NaCl).

• Covalent Bond: Sharing of electrons between atoms (e.g., H2O).

• Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Polarity: A molecule is polar if it has an uneven distribution of charge (e.g., water), and nonpolar if the charge is evenly distributed (e.g., O2).

Interaction of Charged Elements: Negatively charged ions (anions) attract positively charged ions (cations), forming ionic bonds.

pH and Acidity

• pH measures hydrogen ion concentration.

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

Importance of DNA

• DNA (deoxyribonucleic acid) stores genetic information essential for inheritance, cell function, and protein synthesis.

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

• Nucleus: Contains DNA; control center of the cell; usually spherical.

• Mitochondria: Site of ATP production; oval-shaped with inner folds (cristae).

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies.

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

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Synthesize proteins; small, round structures (free or attached to ER).

• Plasma Membrane: Phospholipid bilayer with embedded proteins; controls entry/exit of substances.

• Cytoskeleton: Network of protein fibers; provides structure and movement.

Labeling and identification of organelles is a common exam task.

Cell Size and Surface Area

Cells are small to maximize the surface area-to-volume ratio, which facilitates efficient exchange of materials.

Formula for Surface Area of a Sphere:

Formula for Volume of a Sphere:

As cell size increases, volume grows faster than surface area, limiting cell size.

Microscopy

• Light Microscope: Uses light to view living or stained cells; up to 1000x magnification.

• Transmission Electron Microscope (TEM): Views internal cell structures; high resolution.

• Scanning Electron Microscope (SEM): Views cell surfaces in 3D; high resolution.

Plasma Membrane Structure and Function

• Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.

• Proteins: Serve as channels, carriers, receptors, and enzymes.

• Carbohydrates: Involved in cell recognition.

What can pass through: Small, nonpolar molecules (e.g., O2, CO2), some small polar molecules (e.g., H2O).

What cannot pass through: Large molecules, ions, and most polar molecules without assistance.

Transport Across Membranes

• Diffusion: Movement of molecules from high to low concentration.

• Active Transport: Movement against concentration gradient; requires energy (ATP).

• Isotonic Solution: Solute concentration equal inside and outside the cell; no net water movement.

Example: Red blood cells in an isotonic saline solution retain their normal shape.

Chemical Reactions and Metabolism

Glycolysis and ATP Production

• Glycolysis: First step in cellular respiration; breaks down glucose into pyruvate, producing ATP and NADH.

• Electron Transport Chain (ETC): Most ATP is produced here, primarily by the ATP synthase protein complex.

• Electron Carriers: NAD+ and FAD collect electrons during the citric acid cycle and deliver them to the ETC.

Tissues & Organ Systems

Types of Tissues and Their Functions

• Epithelial Tissue: Covers body surfaces and lines cavities; functions in protection, absorption, and secretion.

• Connective Tissue: Supports, binds, and protects organs; includes bone, blood, cartilage, adipose, and loose connective tissue.

• Muscle Tissue: Responsible for movement; types include skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Conducts electrical impulses; found in brain, spinal cord, and nerves.

Types of Connective Tissues

• Loose Connective Tissue: Binds organs together; found beneath skin.

• Adipose Tissue: Stores fat; found under skin and around organs.

• Blood: Transports substances; found in blood vessels.

• Bone: Supports and protects; found in skeleton.

• Cartilage: Provides flexible support; found in joints, ear, nose.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract, glands.

• Connective: Tendons, ligaments, fat, bone, blood.

• Muscle: Skeletal muscles, heart (cardiac), walls of hollow organs (smooth).

• Nervous: Brain, spinal cord, peripheral nerves.

Type of Muscle in the Stomach: Smooth muscle.

Cell Junctions

• Tight Junctions: Seal cells together to prevent leakage (e.g., in intestines).

• Desmosomes: Anchor cells together, providing mechanical strength (e.g., skin).

• Gap Junctions: Allow communication between cells (e.g., heart muscle).

Summary Table: Types of Tissues and Functions

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard introductory human biology content.