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 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 → Population → Community → Ecosystem → Biosphere

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

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 allow for adequate exchange of materials.

Formula:

Microscopy Types and Uses

Types of Microscopes

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

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

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

Example: TEM is used to study mitochondria's internal structure.

Most Abundant Elements in Humans

Key Elements

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

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

Reductionism

Definition and Importance

• Reductionism: Understanding complex systems by studying their simpler components.

• Helps in identifying the function of individual molecules or organelles.

Importance of DNA

Role of DNA

• Stores genetic information.

• Directs synthesis of proteins.

• Enables inheritance of traits.

Chemical Bonds

Types of Bonds

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

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

• Hydrogen Bonds: Weak attraction between polar molecules (e.g., between water molecules).

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).

Interactions of Charged Elements

Electrostatic Attraction

• Negatively charged elements (anions) attract positively charged elements (cations) to form ionic bonds.

pH Levels: Acids and Bases

pH Scale

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

The Scientific Method

Steps in Order

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Repeat/Revise

Homeostasis

Definition

• Maintenance of a stable internal environment despite external changes.

• Examples: Body temperature, blood glucose levels.

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).

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.

Radioisotope Technology

Importance

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

• Helps in dating fossils and tracing biochemical pathways.

Changing Atomic Charges

Ion Formation

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

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

Diffusion

Process

• Movement of molecules from high to low concentration.

• Passive process; does not require energy.

ATP Production in Electron Transport Chain

Protein Complex Involved

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

Plasma Membrane Permeability

What Can and Cannot Pass

• 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

Definition

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

• Example: Sodium-potassium pump.

Isotonic Solutions

Effect on Cells

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

• No net movement of water; cell maintains its shape.

Glycolysis

Purpose

• Breaks down glucose into pyruvate.

• Produces ATP and NADH.

Electron Carriers in Citric Acid Cycle

Types and Sources

• NAD+ and FAD are electron carriers.

• They gain electrons from the oxidation of substrates in the citric acid cycle.

Plasma Membrane Structure

Components

• Phospholipid bilayer

• Proteins (integral and peripheral)

• Cholesterol

• Carbohydrates (glycoproteins and glycolipids)

Connective Tissues

Types

• Loose connective tissue

• Dense connective tissue

• Adipose tissue

• Cartilage

• Bone

• Blood

Locations of Tissue Types

Examples

• Loose connective: Under skin

• Dense connective: Tendons, ligaments

• Adipose: Fat storage areas

• Cartilage: Joints, ear, nose

• Bone: Skeleton

• Blood: Circulatory system

Muscle Type in the Stomach

Type of Muscle

• Smooth muscle is found in the stomach wall.

Tissue Types and Functions

Major Tissue Types

• Epithelial: Covers surfaces, lines cavities, forms glands.

• Connective: Supports, binds, and protects organs.

• Muscle: Movement (skeletal, cardiac, smooth).

• Nervous: Transmits electrical impulses.

Cell Junctions

Types of Junctions

• Tight junctions: Seal cells together, prevent leakage.

• Desmosomes: Anchor cells together, provide strength.

• Gap junctions: Allow communication between cells.