Domains of Life and Hierarchy of Living Organisms

Classification of Life

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

• Bacteria: Prokaryotic, unicellular organisms without a nucleus.

• Archaea: Prokaryotic, often found in extreme environments, genetically distinct from bacteria.

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

The hierarchy of living organisms (from smallest to largest):

• Atom

• Molecule

• Organelle

• Cell

• Tissue

• Organ

• Organ system

• Organism

Shared characteristics between living and nonliving things include the presence of matter and energy, but only living things exhibit metabolism, growth, reproduction, and response to stimuli.

Cell Structure and Function

Cell Organelles: Names, Functions, and Shapes

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

• Mitochondria: Site of ATP production via cellular respiration; 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 for secretion or delivery.

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

• Ribosomes: Sites of protein synthesis; can be free or attached to rough ER.

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

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

Labeling and identification of organelles is a common exam task. Practice with diagrams and be able to match functions to structures.

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.

Surface area to volume ratio is critical for efficient transport of nutrients and waste.

Microscopy Types

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

• Transmission Electron Microscopy (TEM): High resolution; views internal cell structures.

• Scanning Electron Microscopy (SEM): Provides 3D images of cell surfaces.

Application: Electron microscopes are used to study organelles in detail.

Chemistry of Living Things

Most Abundant Elements in Humans

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

Together, these elements make up over 99% of the human body mass.

Atoms, Elements, and Molecules

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

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

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions.

• Covalent Bonds: Formed when atoms share electrons.

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

Polarity of Molecules

• Polar Molecules: Have unequal sharing of electrons, resulting in partial charges (e.g., H2O).

• Nonpolar Molecules: Electrons are shared equally; no partial charges (e.g., O2).

pH, Acids, and Bases

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic).

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Radioisotope Technology

Radioisotopes are unstable isotopes that emit radiation. They are used in medical imaging, cancer treatment, and as tracers in biochemical research.

Reductionism

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

DNA Importance

DNA (deoxyribonucleic acid) stores genetic information, directs protein synthesis, and is essential for inheritance.

Changing Atomic Charges

Atoms can change their charges by gaining or losing electrons, forming ions:

• Cation: Positively charged (lost electrons)

• Anion: Negatively charged (gained electrons)

Scientific Method and Homeostasis

Scientific Method (in order)

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Peer Review/Publication

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes (e.g., body temperature, blood pH).

Cell Membrane and Transport

Plasma Membrane Structure

The plasma membrane consists of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

Membrane Permeability

• 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 assistance.

Diffusion and Active Transport

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

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

Isotonic Solutions

An isotonic solution has the same solute concentration as the cell; water moves in and out equally, so the cell remains unchanged.

Cellular Respiration and ATP Production

Glycolysis

Glycolysis is the first step in cellular respiration; it breaks down glucose into pyruvate, producing ATP and NADH.

Citric Acid Cycle and Electron Carriers

• Electron carriers (NAD+ and FAD) accept electrons during the citric acid cycle, becoming NADH and FADH2.

• These carriers transport electrons to the electron transport chain.

ATP Production

Most ATP is produced by the ATP synthase protein complex during the electron transport chain, using the energy from a proton gradient.

Tissues and Their Types

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 tissue.

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

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

Types of Connective Tissue

• Loose connective tissue: Supports and binds other tissues; found under skin.

• Dense connective tissue: Provides strength; found in tendons and ligaments.

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

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

• Bone: Rigid support; forms the skeleton.

• Blood: Transports substances; found in blood vessels.

Locations of Tissue Types

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

• Connective: Bones, tendons, fat, blood.

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

• Nervous: Brain, spinal cord, nerves.

Muscle Type in the Stomach

The stomach contains smooth muscle, which contracts involuntarily to mix and propel food.

Cell Junctions

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

• Desmosomes: Anchor cells together, providing mechanical strength.

• Gap Junctions: Allow communication between cells via small channels.

Summary Table: Types of Tissues and Locations

Additional info:

• Some explanations (e.g., for reductionism, radioisotopes, and the scientific method) were expanded for clarity.

• Table entries and tissue locations were inferred based on standard human biology knowledge.