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); 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.

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

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Sites of protein synthesis; small, round structures.

• Plasma Membrane: Phospholipid bilayer; surrounds the cell.

• Cytoskeleton: Network of protein fibers; provides structure 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 Between Cell Size and Surface Area

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

• This limits the efficiency of material exchange across the plasma membrane.

Formula:

Key Point: Smaller cells have a higher surface area-to-volume ratio, facilitating efficient exchange.

Types of Microscopy

Microscopy Techniques

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

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

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

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

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 components.

• Helps in understanding the function of individual parts of biological systems.

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

Importance of DNA

Role of DNA

• DNA stores genetic information.

• Directs synthesis of proteins.

• Enables inheritance of traits.

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).

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).

Key Point: Polarity affects solubility and interactions with other molecules.

Interactions of Charged Elements

Electrostatic Attraction

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

Example: Na+ and Cl- form NaCl.

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 and Importance

• Homeostasis is the maintenance of a stable internal environment.

• Essential for proper functioning of cells and organs.

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).

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 in Biology

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

• Used as tracers in biochemical research.

Changing Atomic Charges

Ion Formation

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

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

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 and the Electron Transport Chain

Protein Complex Involved

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

Plasma Membrane Permeability

What Can and Cannot Pass

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

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

Active Transport

Definition and Function

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

• Requires transport proteins (pumps).

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.

Glycolysis

Purpose

• Breaks down glucose into pyruvate.

• Produces ATP and NADH.

Formula:

Electron Carriers in the Citric Acid Cycle

Types and Sources

• NAD+ and FAD are electron carriers.

• They gain electrons during 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 and Locations

Muscle Type in the Stomach

Type of Muscle Tissue

• Smooth muscle is found in the stomach and other internal organs.

Types of Tissues and Their Functions

Major Tissue Types

Types of Cell Junctions

Junction Types and Functions

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard introductory human biology content.