Comprehensive Study Guide for Basic Concepts in Biology and Biochemistry

Foundations of Biological Inquiry and the Scientific Method Biology is defined as the scientific study of life. This discipline involves observing phenomena and formulating testable hypotheses, which are proposed explanations for a phenomena or ideas about a solution to a problem based on knowledge and research. A hypothesis serves to guide scientists through the experimental process. Scientists also rely on inferences, which are conclusions drawn from specific observations or previous knowledge. Several key terms define scientific knowledge: a Fact is something demonstrated to exist or known to have existed; a Principle is a basic truth, law, or assumption; a Law is a summarizing statement of observed experimental facts that have been tested many times and are generally accepted as true; and a Theory represents a group of related hypotheses confirmed through repeated experimental tests. Observations specifically use one of the five senses to form judgments. In experimental design, the variable the researcher controls is the Independent Variable (Manipulated Variable), which is placed on the x-axis of a graph. The Dependent Variable (Responding Variable) is the variable being measured and is placed on the y-axis. Data is categorized as Qualitative (descriptive words) or Quantitative (numerical data). Experiments distinguish between a Control Group, which is kept normal to serve as a baseline, and an Experimental Group, which receives a specific treatment. # The Definitive Characteristics of Life and Homeostatic Regulation All living things share eight fundamental characteristics. They are made of cells, which are the basic units of life. They must maintain Homeostasis, a stable internal environment, and Metabolism, which is the sum of all chemical reactions in the organism. Life requires Reproduction to produce offspring and is governed by Heredity, where DNA carries the genetic code. Organisms respond to their environment via a stimulus-response mechanism. They also Grow—meaning an increase in the amount of living material—and Develop, which involves changes occurring during a lifetime. Finally, groups of organisms undergo Evolution, changing over time to survive. Homeostasis is particularly vital; in humans, it is regulated by organs, glands, tissues, and cells. Internal body temperature is maintained at approximately $98.6^{\text{°F}}$ through behaviors or physiological responses such as shivering and sweating. Fluid levels must remain constant to facilitate metabolic reactions, as water carries gases, nutrients, ions, hormones, and wastes. Water is lost via sweat and urine and must be replaced to prevent dissolved solutes and waste products from becoming overly concentrated. # Chemical Properties of Water and the Role of Carbon Approximately 70-75\text{%} of the human body is comprised of water, which exists as a solid, liquid, or gas. Water molecule polarity makes it an excellent solvent, where the solvent dissolves the solute. Because water has positive and negative ends, molecules attract one another, leading to Cohesion (attraction between like molecules), which creates surface tension. Adhesion is the attraction of water to other substances, which facilitates capillary action, such as water rising against gravity in a glass tube. Water possesses a high specific heat, absorbing significant energy before changing temperature; it boils at $212\text{°F}$ ($100\text{°C}$) and freezes at $32\text{°F}$ ($0\text{°C}$). Furthermore, ice is less dense than liquid water, providing a protective survival layer for aquatic organisms in winter. Water also acts as a hydraulic fluid to keep cells rigid. Carbon is the foundation of all organic compounds, possessing an atomic number of $6$. It has $2$ electrons in its first shell and $4$ in its second shell, allowing it to share four electrons with other atoms like hydrogen, oxygen, and other carbons to reach stability. # Biological Macromolecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids Macromolecules are polymers built from single units called monomers. Carbohydrates, made of CHO in a $1:2:1$ ratio, serve as short-term energy. Monosaccharides like Glucose, Fructose, and Galactose share the formula $C_6H_{12}O_6$ but are structural isomers. Disaccharides, such as sucrose, consist of two sugars. Polysaccharides include Cellulose for plant cell walls, Starch for plant energy storage, and Glycogen for animal energy storage. Lipids (CHO) are non-polar energy storage molecules. They include Phospholipids (cell membrane bilayers), Steroids (hormones like cholesterol, estrogen, and testosterone), Waxes (waterproof plant coatings), and Triglycerides. Saturated fats have no double bonds and are solid at room temperature, increasing bad cholesterol (LDL), while Unsaturated fats have one or more double bonds, are liquid, and increase good cholesterol (HDL). Proteins (CHON) are made of $20$ different amino acids. They function as Antibodies for the immune system, Enzymes (catalysts usually ending in “-ase” like lactase), Messengers (insulin), Structural support (keratin in hair, collagen in tendons), and Transport (hemoglobin). Nucleic Acids (CHONP) consist of nucleotides. DNA (Deoxyribonucleic Acid) is a double helix storing heredity, while RNA (Ribonucleic Acid) is a single strand used for protein manufacturing. # Enzymatic Regulation and Cellular Architecture Chemistry Enzymes are specific catalysts that reduce the activation energy required for reactions. They bind to a specific molecule called a substrate at an active site, functioning like a lock and key. The enzyme remains unchanged and reusable. Factors affecting enzymes include pH (specific ranges), Temperature (optimum levels, though boiling denatures them), and Concentration (increasing substrates or enzymes speeds the reaction). In Cytology, the study of cells, the Cell Theory states cells are the basic unit of life, all organisms are made of cells, and cells come from existing cells. Cells are small to maximize the surface-to-volume ratio. The Cell Membrane is a phospholipid bilayer with proteins, cholesterol, and glycoproteins. Prokaryotic cells lack a nucleus and organelles and contain a single chromosome, whereas Eukaryotic cells contain a nucleus, many organelles, and multiple chromosomes. Biological organization progresses from Molecules to Organelles, Cells, Tissues, Organs, Organ Systems, and Multi-cellular Organisms. Key eukaryotic organelles include the Nucleus (DNA storage), Mitochondria (ATP production via carbohydrate breakdown), Ribosomes (protein synthesis), and the Golgi Apparatus (packaging and shipping). # Mechanisms of Cellular Transport and Bioenergetics The cell membrane is selectively permeable, regulating movement via several methods. Passive Transport moves substances from high to low concentration without energy, including Diffusion (small/nonpolar molecules like $CO_2$ and $O_2$), Osmosis (diffusion of water), and Facilitated Diffusion (using carrier/integral proteins for polar/charged molecules). Osmosis involves Hypotonic (water moves in, cell swells), Hypertonic (water moves out, cell shrinks), and Isotonic (equal movement) solutions. Active Transport requires ATP to move substances against the gradient, such as Membrane Pumps (Sodium-Potassium Pump) and Bulk Transport (Endocytosis for engulfing and Exocytosis for exporting). Bioenergetics involves energy transformations. Photosynthesis occurs in chloroplasts, using light, $6 H_2O$, and $6 CO_2$ to produce $C_6H_{12}O_6$ and $6 O_2$. It involves Light-Dependent Reactions in the thylakoid (releasing $O_2$) and Dark Reactions (Calvin Cycle) in the stroma (forming glucose). Cellular Respiration releases energy from glucose ($C_6H_{12}O_6 + 6 O_2 \rightarrow 6 H_2O + 6 CO_2 + \text{ATP}$) through Glycolysis in the cytoplasm, the Krebs Cycle in the mitochondrial matrix, and the Electron Transport Chain in the inner membrane. ATP (Adenosine Triphosphate) is the cellular fuel composed of adenine, ribose, and three phosphate groups; it becomes ADP (Adenosine Diphosphate) once spent.