Domain of Life

Classification of Living Organisms

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

• Bacteria: Single-celled prokaryotes without a nucleus.

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

• Eukarya: Organisms with eukaryotic cells, including protists, fungi, plants, and animals.

Example: Humans belong to the domain Eukarya.

Cell Organelles: Names, Functions, and Shapes

Major Cell Organelles

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

• Mitochondria: Site of ATP (energy) 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 chemicals.

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

• Lysosomes: Contain digestive enzymes; break down waste; spherical vesicles.

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

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

• Cytoskeleton: Network of protein fibers; maintains cell shape and assists 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, and several tissues form the heart (an organ).

Cell Size and Surface Area

Relationship Between Cell Size and Surface Area

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

• This limits cell size because the surface area must be sufficient for exchange of materials.

Formula:

Example: Small cells have a higher surface area-to-volume ratio, aiding efficient transport.

Types of Microscopy

Microscopy Techniques

• Light Microscopy: Uses light to view cells; suitable for living specimens.

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

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

Example: TEM is used to study organelles inside cells.

Most Abundant Elements in Humans

Key Elements

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

Example: These elements make up over 99% of the human body mass.

Reductionism

Importance in Biology

• Reductionism is the approach of studying complex systems by breaking them into simpler parts.

• Helps understand the function of biological molecules, cells, and systems.

Example: Studying DNA structure to understand genetics.

Importance of DNA

Role of DNA

• Stores genetic information.

• Directs synthesis of proteins.

• Enables inheritance from one generation to the next.

Example: Mutations in DNA can lead to genetic disorders.

Chemical Bonds

Types of Bonds

• Ionic Bonds: Transfer of electrons between atoms (e.g., NaCl).

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

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

Example: Hydrogen bonds give water its unique properties.

Polarity of Molecules

Polar vs. Nonpolar Molecules

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

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

Example: Water is polar; oil is nonpolar.

Interactions of Charged Elements

Electrostatic Attraction

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

• This attraction forms ionic bonds.

Example: Na+ and Cl- form NaCl.

pH Levels: Acids and Bases

pH Scale

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

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/Revise

Example: Testing the effect of sunlight on plant growth.

Homeostasis

Definition and Importance

• Maintenance of a stable internal environment.

• Essential for proper cell and organ function.

Example: Regulation of body temperature.

Elements vs. Molecules

Definitions

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

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

Example: Oxygen gas (O2) is an element and a molecule; water (H2O) is a molecule but not an element.

Characteristics of Living vs. Nonliving Things

Shared and Distinct Features

• Living things: Organization, metabolism, homeostasis, growth, reproduction, response to stimuli, adaptation.

• Nonliving things: May have organization but lack metabolism and reproduction.

Example: Viruses share some but not all characteristics of life.

Radioisotope Technology

Importance in Biology and Medicine

• Used in medical imaging (e.g., PET scans).

• Helps trace biochemical pathways.

Example: Radioactive iodine is used to diagnose thyroid disorders.

Changing Atomic Charges

Ion Formation

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

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

Example: Sodium loses an electron to become Na+.

Diffusion

Process and Importance

• Movement of molecules from high to low concentration.

• Passive process; does not require energy.

Example: Oxygen diffuses into cells from the bloodstream.

ATP Production in the Electron Transport Chain

Protein Complex Involved

• ATP Synthase is the protein complex where most ATP is produced during the electron transport chain.

Equation:

Plasma Membrane Permeability

What Can and Cannot Pass

• Small, nonpolar molecules (e.g., O2, CO2) can pass freely.

• Ions and large polar molecules require transport proteins.

Example: Glucose enters cells via facilitated diffusion.

Active Transport

Definition and Example

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

• Example: Sodium-potassium pump in nerve cells.

Isotonic Solutions

Effect on Cells

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

• No net movement of water; cell shape remains unchanged.

Example: Saline solution used in IV fluids is isotonic to blood.

Glycolysis

Purpose and Process

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

• Occurs in the cytoplasm; does not require oxygen.

Equation:

Electron Carriers in the Citric Acid Cycle

Types and Sources

• NADH and FADH2 are the main electron carriers.

• They gain electrons during oxidation of substrates in the cycle.

Example: NAD+ is reduced to NADH as it accepts electrons.

Plasma Membrane Structure

Components

• Phospholipid bilayer

• Proteins (integral and peripheral)

• Cholesterol

• Carbohydrate chains

Example: The fluid mosaic model describes membrane structure.

Connective Tissues

Types and Locations

Muscle Type in the Stomach

Muscle Tissue

• Smooth muscle is found in the stomach wall.

• Involuntary control; responsible for peristalsis.

Tissue Types and Functions

Major Tissue Types

Cell Junctions

Types and Functions

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

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

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

Additional info: Some explanations and examples were expanded for clarity and completeness.