Domain of Life

Classification of Living Organisms

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, distinct from bacteria, often found in extreme environments.

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

Example: Humans belong to the domain Eukarya.

Cell Organelles

Names, Functions, and Shapes

• Nucleus: Contains genetic material (DNA); controls cell activities; usually spherical.

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

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

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

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery; stack of flattened sacs.

• Lysosomes: Contain digestive enzymes; break down waste and cellular debris.

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

• Plasma Membrane: Phospholipid bilayer; controls entry and exit of substances.

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

Example: The mitochondrion is often called the "powerhouse" of the cell.

Hierarchy of Living Organisms

Levels of Biological Organization

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Example: Muscle tissue is made of muscle cells, which contain mitochondria (organelles).

Cell Size and Surface Area

Relationship and Importance

• As a cell increases in size, its volume grows faster than its surface area.

• Surface area is critical for exchange of materials (nutrients, waste).

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

Formula:

Types of Microscopy

Microscopy Techniques and Uses

• Light Microscopy: Uses visible light; views living cells and tissues.

• Transmission Electron Microscopy (TEM): Passes electrons through specimen; views internal structures at high resolution.

• Scanning Electron Microscopy (SEM): Scans surface with electrons; provides 3D images of surfaces.

Example: SEM is used to view the surface of a cell membrane.

Most Abundant Elements in Humans

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Other important elements: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg)

Example: Oxygen is the most abundant element in the human body by mass.

Reductionism

Definition and Importance

• Reductionism: The approach of understanding complex systems by studying their simpler components.

• Helps in breaking down biological processes for detailed study.

Example: Studying the function of a single enzyme to understand metabolism.

Importance of DNA

• DNA (Deoxyribonucleic Acid) stores genetic information.

• Directs synthesis of proteins, which determine cell structure and function.

• Passed from parents to offspring, enabling inheritance.

Example: Mutations in DNA can lead to genetic diseases.

Types of Chemical Bonds

Ionic, Covalent, and Hydrogen Bonds

• Ionic Bonds: Transfer of electrons from one atom to another; forms ions (e.g., NaCl).

• Covalent Bonds: Sharing of electron pairs between atoms (e.g., H2O).

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

Polarity of Molecules

What Makes a Molecule Polar or Nonpolar

• Polar Molecules: Unequal sharing of electrons; have partial positive and negative ends (e.g., water).

• Nonpolar Molecules: Equal sharing of electrons; no charge separation (e.g., O2).

Example: Water is polar; oil is nonpolar.

Interactions of Charged Elements

• Negatively charged elements (anions) are attracted to positively charged elements (cations).

• This attraction forms ionic bonds.

pH Levels: Acids and Bases

• pH measures hydrogen ion concentration.

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Example: Stomach acid has a pH of about 2 (acidic).

The Scientific Method

Steps in Order

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Repeat/Report

Homeostasis

Definition and Importance

• Homeostasis: The maintenance of a stable internal environment despite external changes.

• Essential for proper functioning of cells and organs.

Example: Regulation of body temperature.

Elements vs. Molecules

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

• Molecule: Two or more atoms bonded together (can be same or different elements; e.g., H2O).

Characteristics of Living vs. Nonliving Things

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

• Nonliving things: Do not exhibit all characteristics above.

Radioisotope Technology

Importance and Applications

• Radioisotopes are unstable isotopes that emit radiation.

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

Example: PET scans use radioisotopes to image metabolic activity.

Changing Atomic Charges

• Atoms gain electrons to become negatively charged (anions).

• Atoms lose electrons to become positively charged (cations).

Diffusion

Process and Significance

• Movement of molecules from high to low concentration.

• Does not require energy (passive transport).

Example: Oxygen diffuses from lungs into blood.

ATP Production and the Electron Transport Chain

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

Plasma Membrane Permeability

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

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

Active Transport

• Movement of substances against their concentration gradient.

• Requires energy (usually ATP).

• Example: Sodium-potassium pump in nerve cells.

Isotonic Solutions

• Isotonic solution: Solute concentration is equal inside and outside the cell.

• No net movement of water; cell size remains constant.

Glycolysis

Purpose and Overview

• First step in cellular respiration.

• Breaks down glucose into pyruvate, producing ATP and NADH.

Electron Carriers in the Citric Acid Cycle

• NAD+ and FAD are electron carriers.

• They gain electrons (are reduced) during the cycle and transport them to the electron transport chain.

Plasma Membrane Structure

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

Types of Connective Tissues

Locations of Tissue Types

• Epithelial tissue: Covers body surfaces, lines cavities (e.g., skin, lining of gut).

• Connective tissue: Supports and connects (e.g., bone, blood, cartilage).

• Muscle tissue: Movement (e.g., skeletal muscles, heart, stomach).

• Nervous tissue: Communication (e.g., brain, spinal cord, nerves).

Muscle Type in the Stomach

• Stomach contains smooth muscle, which is involuntary and non-striated.

Types of Tissues and Their Functions

Types of Cell Junctions

• Tight junctions: Seal cells together, prevent leakage (e.g., intestinal lining).

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

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