Domains of Life

Classification of Living Organisms

The domain system is the highest level of biological classification, dividing all life into three major groups based on cellular structure and genetics.

• Bacteria: Prokaryotic cells, no nucleus, diverse metabolic pathways.

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

• Eukarya: Eukaryotic cells with a nucleus; includes animals, plants, fungi, and protists.

Example: Humans belong to the domain Eukarya.

Cell Structure and Function

Cell Organelles: Names, Functions, and Shapes

Cell organelles are specialized structures within eukaryotic cells, each with unique functions.

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

• Mitochondria: Site of ATP production; bean-shaped.

• Ribosomes: Protein synthesis; small, round particles.

• Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; Smooth ER synthesizes lipids.

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

• Lysosomes: Digestive enzymes; spherical vesicles.

• Plasma Membrane: Controls entry/exit; flexible, phospholipid bilayer.

Example: The mitochondria are often called the "powerhouse" of the cell.

Hierarchy of Living Organisms

Biological organization follows a hierarchy from smallest to largest:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism

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

Cell Size and Surface Area

Cell size is limited by the surface area-to-volume ratio, which affects the efficiency of material exchange.

• Smaller cells have a higher surface area relative to volume, allowing efficient diffusion.

• Larger cells may struggle to transport materials quickly enough.

Formula:

Example: Most cells are microscopic to maximize surface area for exchange.

Microscopy Types

Microscopes are essential for studying cells and tissues.

• Light Microscope: Uses light; good for living cells.

• Electron Microscope: Uses electrons; higher resolution; for detailed cell structures.

• Scanning Electron Microscope (SEM): Surface details.

• Transmission Electron Microscope (TEM): Internal structures.

Example: TEM is used to view mitochondria's internal membranes.

Chemistry of Living Things

Most Abundant Elements in Humans

Human bodies are primarily composed of a few key elements:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Example: Water (H2O) is the most abundant molecule in the body.

Reductionism

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

• Helps explain biological phenomena at molecular and cellular levels.

Example: Studying DNA to understand inheritance.

Importance of DNA

DNA is the molecule that stores genetic information and directs cell functions.

• Contains instructions for protein synthesis.

• Inherited from parents.

Example: Mutations in DNA can lead to genetic disorders.

Types of Chemical Bonds

Chemical bonds hold atoms together in molecules.

• Ionic Bonds: Transfer of electrons; forms charged ions.

• Covalent Bonds: Sharing of electrons; strong and stable.

• Hydrogen Bonds: Weak attraction between polar molecules.

Example: Water molecules are held together by hydrogen bonds.

Polarity of Molecules

Polarity refers to the distribution of electrical charge in a molecule.

• Polar Molecules: Uneven charge distribution; dissolve in water.

• Nonpolar Molecules: Even charge distribution; do not dissolve in water.

Example: Water is polar; oil is nonpolar.

Acids, Bases, and pH

pH measures the concentration of hydrogen ions in a solution.

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Formula:

Example: Human blood has a pH of about 7.4.

Elements vs. Molecules

An element is a pure substance made of one type of atom; a molecule is a group of atoms bonded together.

• Element: Oxygen (O)

• Molecule: Water (H2O)

Radioisotope Technology

Radioisotopes are used in medicine and research for imaging and tracing biological processes.

• Can diagnose diseases (e.g., PET scans).

• Used to track metabolic pathways.

Atoms and Charge

Atoms can gain or lose electrons to become ions.

• Gain electrons: Become negatively charged (anions).

• Lose electrons: Become positively charged (cations).

Scientific Method and Homeostasis

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Hypothesis

3. Experiment

4. Data Collection

5. Analysis

6. Conclusion

Homeostasis

Homeostasis is the maintenance of stable internal conditions in the body.

• Regulates temperature, pH, and other variables.

• Essential for survival.

Example: Sweating cools the body to maintain temperature.

Characteristics of Living vs. Nonliving Things

Living things share certain characteristics:

• Organization

• Metabolism

• Response to stimuli

• Growth and development

• Reproduction

• Adaptation

Nonliving things lack these features.

Cell Membrane and Transport

Plasma Membrane Structure

The plasma membrane is a phospholipid bilayer with embedded proteins.

• Controls movement of substances in and out of the cell.

• Contains cholesterol, glycoproteins, and glycolipids.

Diffusion

Diffusion is the passive movement of molecules from high to low concentration.

• No energy required.

• Important for gas exchange and nutrient transport.

Active Transport

Active transport moves substances against their concentration gradient using energy (ATP).

• Requires protein pumps.

• Maintains ion gradients.

What Can and Can't Pass Through the Plasma Membrane

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

• Cannot pass: Large molecules, ions (without transport proteins).

Isotonic Solutions

An isotonic solution has equal solute concentration as the cell.

• No net movement of water.

• Cells retain their normal shape.

Cellular Respiration

Glycolysis

Glycolysis is the first step in cellular respiration, breaking down glucose to produce ATP.

• Occurs in the cytoplasm.

• Produces pyruvate, ATP, and NADH.

Formula:

Electron Transport Chain and ATP Production

The electron transport chain (ETC) is where most ATP is produced, using a protein complex called ATP synthase.

• Located in the inner mitochondrial membrane.

• Uses electron carriers (NADH, FADH2).

Citric Acid Cycle Electron Carriers

During the citric acid cycle, NAD+ and FAD collect electrons from metabolic reactions.

• NADH and FADH2 carry electrons to the ETC.

Tissues and Their Functions

Types of Connective Tissues

Connective tissues support and connect other tissues.

• Loose connective tissue: Cushions organs.

• Dense connective tissue: Tendons and ligaments.

• Adipose tissue: Stores fat.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transport of substances.

Locations of Tissue Types

• Epithelial tissue: Covers surfaces, lines cavities.

• Connective tissue: Found throughout the body (e.g., under skin, in bones).

• Muscle tissue: Skeletal (attached to bones), cardiac (heart), smooth (walls of organs).

• Nervous tissue: Brain, spinal cord, nerves.

Muscle Type in the Stomach

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

Types of Tissues and Their Functions

• Epithelial: Protection, absorption, secretion.

• Connective: Support, transport, storage.

• Muscle: Movement.

• Nervous: Communication, control.

Types of Cell Junctions

Cell junctions connect cells and allow communication.

• Tight junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow passage of ions and small molecules.

Additional info: Academic context was added to expand brief points and clarify concepts for exam preparation.