Controlled Experiments and Scientific Theories

Controlled Experiments

• Controlled experiments isolate the effect of one variable (independent variable) on another (dependent variable)
• Manipulate only one independent variable at a time.
• Keep other variables constant (controlled variables)

Inference vs. Observation

• Observations describe what is seen or measured.
• Inferences explain observations—attempting to find a reason for the observed event.

Scientific Theory vs. Everyday Theory

• Everyday theories are often guesses.
• Scientific theories are well-supported explanations of aspects of the natural world, tested repeatedly, and used for prediction.
• A theory unifies many observations and hypotheses.

Monster Energy Drink Experiment

• Dependent Variable: Reaction time (measured in seconds)
• Independent Variable: Type of drink (Monster or water)
• Controlled Variables: Amount of drink, digestion time (20 minutes), testing conditions (same light/button parameters)
• Experimental Group: Individuals consuming Monster drink.
• Control Group: Individuals consuming the water.
• Possible Hypothesis: If subjects consume Monster drink, then their reaction time will be faster than those consuming water.
• Data Type: Quantitative (numerical reaction time measurements)
• Improvements: More participants, testing different caffeine levels, repeated trials (blind test), multiple independent variables

Characteristics of Living Organisms

• Universal Genetic Code (DNA): All living things use DNA as their genetic instructions.
• Growth and Development: Organisms increase in size and complexity over time.
• Response to Environment (Stimuli): Responding to changes in their surroundings.
• Reproduction: Producing offspring.
• Evolution: Living things change over generations.
• Obtain and Use Energy: All living things need energy.
• Made of Cells: All living things, from bacteria to humans, are composed of cells.
• Maintain Stable Internal Environment (Homeostasis): Keeping a regulated internal environment.

Levels of Biological Organization

• Molecules, Cells, Tissues, Organs, Organ Systems, Organism, Population, Community, Ecosystem, Biome, Biosphere

Biomolecules

• Proteins: Made of amino acids; control reaction rates, cell cycle, transport, and defense.
• Carbohydrates: Composed of C:H:O in a 1:2:1 ratio; provide energy.
• Nucleic Acids: Store genetic information; made of nucleotides.
• Lipids: Store energy, insulate, and make up cell membranes.

Carbon's Properties

• Carbon has four valence electrons, allowing it to form up to four covalent bonds.
• This flexibility explains carbon's ability to form diverse and complex structures.

Enzymes

• Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

Enzyme Activity Factors

• Temperature and pH changes affect enzyme activity; extreme values can denature enzymes, rendering them non-functional.
• Regulatory molecules can also affect enzyme function.

Cell Theory

• Cells arise from pre-existing cells.
• Cells are the basic unit of structure and function of life.
• All living things are made of cells.

Prokaryotic vs. Eukaryotic Cells

• (Comparison table to be elaborated)

Plant vs. Animal Cells

• (Comparison table to be elaborated)

Cell Organelles

• Ribosomes: Build proteins.
• Mitochondria: Capture and release energy.
• Chloroplasts: Capture and release energy (in plant cells).
• Vacuoles/Lysosomes: Storage, clean-up, and support.
• Cell Membrane: Cellular boundary.
• Nucleus: Control center.
• ER, Golgi, etc: Involved in protein processing and transport.

Protein Pathway

• Ribosomes synthesize proteins —> ER folds and modifies proteins —> Golgi modifies and packages proteins —> Vesicles transport proteins.

Cellular Transport

• Phospholipid Bilayer: Hydrophobic tails face inward; hydrophilic heads face outward.
• Transport Channels: Proteins that allow specific substances to cross the membrane(e.g., water via osmosis, glucose, ions and polar molecules).
• Passive Transport: Movement of molecules down a concentration gradient; requires no energy.
  • Examples: Diffusion, osmosis, facilitated transport.
• Active Transport: Movement of molecules against a concentration gradient; requires energy (e.g., pumps).
• Equilibrium: Molecules move both ways across the membrane at equal rates.

Osmosis

• Hypertonic Solution: Water moves out of the cell; cell shrinks.
• Hypotonic Solution: Water moves into the cell; cell swells or bursts.
• Isotonic Solution: Water moves in and out equally; cell stays the same size.

Surface Area to Volume Ratio

• As cells increase in size, the volume increases much faster than the surface area, which can lead to complications in nutrient intake and waste removal.
• Cells divide to maintain a favorable surface area-to-volume ratio.

Cell Cycle

• Interphase (90%): Cell growth, DNA replication.
• M Phase (10%): Mitosis.
• DNA must replicate ahead of cell division.

Mitosis

• Purpose: Cell growth and repair.
• Prophase: Chromosomes condense, nuclear envelope dissolves.
• Metaphase: Chromosomes line up in the middle of the cell.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromosomes decondense, nuclear envelope reforms, and cytoplasm divides (cytokinesis).
• Results in two identical diploid daughter cells.

Meiosis

• Purpose: Produce haploid gametes for sexual reproduction.
• Homologous Chromosomes: Paired chromosomes, one from each parent.
• Sister Chromatids: Identical copies of a chromosome.
• Crossing Over: Exchange of genetic material between homologous chromosomes.
• Independent Assortment: Random separation of homologous chromosomes during meiosis.
• Results in four genetically unique haploid gametes.

Bioenergetics

• ATP: Adenosine triphosphate; a major energy currency in cells. Energy is stored in the bonds between phosphates.
• Photosynthesis: Capturing light energy and converting it into chemical energy in glucose.
• Cellular Respiration: Breaking down organic molecules (e.g., glucose) to release chemical energy in the form of ATP.
• Fermentation: Energy-releasing process that occurs in the absence of oxygen. Types include lactic acid fermentation and alcoholic fermentation (produces less ATP than cellular respiration).

Photosynthesis & Cellular Respiration

• They are reciprocal processes, meaning the products of one are the reactants of the other.
• Photosynthesis makes glucose; cellular respiration breaks it down to produce ATP.

ATP

• Energy is stored in the phosphate bonds of ATP.
• Energy is released when a phosphate bond is broken.

Stages of Photosynthesis (detailed)

• Light-Dependent Reactions: Capture light energy; produce ATP and NADPH, oxygen.
• Light-Independent Reactions (Calvin Cycle): Convert carbon dioxide into glucose; use ATP and NADPH.

Stages of Cellular Respiration (detailed)

• Glycolysis: Breaks down glucose.
• Krebs Cycle: Breaks down pyruvate.
• Electron Transport Chain: Creates a large amount of ATP.

DNA Structure and Function

• Monomer: Nucleotides
• Structure: Double helix (twisted ladder).
• Function: Stores and transmits genetic information..