General Biology: Foundations, Cell Structure, and Biological Molecules – Study Guide

Scientific Method and Experimental Design

Scientific Hypotheses and Theories

The scientific method is a systematic approach to understanding the natural world. It involves forming hypotheses, conducting experiments, and developing theories based on evidence.

• Scientific Hypothesis: A testable and falsifiable statement that explains an observation or answers a scientific question.

• Scientific Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence and repeatedly confirmed through observation and experimentation.

• Necessary Feature for Hypothesis: Must be testable and falsifiable.

• Hypotheses Not Accepted: Hypotheses are rejected if experimental evidence does not support them.

• Outcome of Well-Tested Hypothesis: When many independent studies support a hypothesis, it may become widely accepted as a theory.

Example: Warren and Marshall tested the hypothesis that Helicobacter pylori bacteria cause stomach ulcers.

Experimental Controls and Bias

• Double-Blind Experiments: Both participants and experimenters do not know who receives the treatment, reducing bias.

• Model Organisms: Non-human species used to test hypotheses due to their similarity to humans in certain biological processes.

• Bias: Systematic error that can affect the outcome of an experiment; can be minimized by proper experimental design.

• Statistical Significance: A standard probability (often p < 0.05) accepted by researchers to determine if results are likely due to chance.

Basic Chemistry of Life

Atoms and Molecules

All living things are composed of atoms, which combine to form molecules essential for life.

• Particles in Nucleus: Protons and neutrons are found in the nucleus of an atom.

• Electrons: Negatively charged particles found in orbitals around the nucleus.

• Element Basis for Macromolecules: Carbon is the primary element forming the backbone of biological macromolecules.

• Hydrogen and Carbon: Molecules composed only of hydrogen and carbon are called hydrocarbons.

• Bond Types: Covalent bonds hold atoms together within molecules; hydrogen bonds connect complementary strands of DNA and hold water molecules together.

Properties of Water

• Hydrogen Bonds: Weak bonds between the hydrogen atom of one water molecule and the oxygen atom of another.

• Hydrophilic: Molecules that are attracted to water and dissolve easily in it (e.g., polar molecules).

• Hydrophobic: Molecules that repel water and do not dissolve in it (e.g., nonpolar molecules).

• True/False: Nonpolar molecules are hydrophobic; polar molecules are hydrophilic.

Biological Macromolecules

Types and Functions

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Composed of one or more sugars (monosaccharides, disaccharides, polysaccharides). Major source of energy for cells.

• Lipids: Hydrophobic molecules, including fats, oils, phospholipids, and steroids. Important for energy storage and membrane structure.

• Proteins: Polymers of amino acids; function as enzymes, structural components, and signaling molecules.

• Nucleic Acids: DNA and RNA; store and transmit genetic information. Have a sugar-phosphate backbone.

Example: A newly discovered biological molecule that is mostly hydrophobic would be classified as a lipid.

Macromolecule Structure

• Sugar-Phosphate Backbone: Found in nucleic acids (DNA and RNA).

• Amino Acid Side Chains: Account for differences in protein properties.

• Cholesterol: A lipid that plays a role in animal cell membranes, maintaining fluidity and stability.

Cell Structure and Function

Cell Organelles

Cells contain specialized structures called organelles, each with specific functions.

• Lysosomes: Organelles containing hydrolytic enzymes for digestion.

• Mitochondria: Primary site of ATP synthesis in eukaryotic cells.

• Endoplasmic Reticulum (ER): Involved in synthesis of proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Chloroplasts: Organelles found in plant cells (not animal cells) responsible for photosynthesis.

Membrane Structure and Transport

• Phospholipid Bilayer: Main component of cell membranes, with hydrophilic heads and hydrophobic tails.

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

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Facilitated Diffusion: Movement of substances across membranes via protein channels.

• Endocytosis/Exocytosis: Processes by which cells take in (endocytosis) or expel (exocytosis) large molecules via vesicles.

• Aquaporins: Protein pores in the plasma membrane that allow water to enter cells.

Internal Compartments

• Endomembrane System: Internal membrane-bound compartments in eukaryotic cells, including the ER, Golgi apparatus, lysosomes, and vesicles.

Nutrition and Human Health

Nutrients and Diet

Nutrition involves the intake and utilization of nutrients necessary for health and energy.

• Macronutrients: Nutrients required in large amounts (carbohydrates, proteins, lipids).

• Micronutrients: Nutrients required in small amounts (vitamins, minerals).

• Deficiency: Lack of a nutrient in the body, leading to health problems.

• Fiber: Important for digestive health; helps regulate blood sugar and cholesterol.

• Vitamins: Organic compounds required for various metabolic processes.

• Antioxidants: Substances that protect cells from damage by free radicals (e.g., vitamin C, flavonoids in cocoa).

• Sunlight and Vitamin D: Cells can synthesize vitamin D when exposed to sunlight.

Water and Homeostasis

• Water: Essential for life; average human replaces several liters per day through food and drink.

• Osmoregulation: Maintenance of water and solute balance in the body.

Summary Table: Macromolecules and Their Properties

Macromolecule	Monomer	Main Function	Example
Carbohydrate	Monosaccharide	Energy source, structure	Glucose, starch
Lipid	Fatty acid, glycerol	Energy storage, membranes	Triglyceride, cholesterol
Protein	Amino acid	Enzymes, structure, signaling	Hemoglobin, enzymes
Nucleic Acid	Nucleotide	Genetic information	DNA, RNA

Additional info:

• Some questions referenced specific experiments (e.g., Barry Marshall and H. pylori), which are classic examples in biology for hypothesis testing and the scientific method.

• Statistical significance is commonly set at p < 0.05 in biological research.

• Micronutrients include minerals like iron and zinc, and vitamins such as vitamin C and D.