Themes in Biology & The Scientific Method

Characteristics of Living Things

Biologists identify several key features that define living organisms. Understanding these characteristics is foundational to the study of biology.

• Cellular organization: All living things are composed of one or more cells.

• Metabolism: Living organisms carry out chemical reactions to obtain and use energy.

• Homeostasis: The ability to maintain stable internal conditions.

• Growth and development: Organisms increase in size and complexity over time.

• Reproduction: The ability to produce new individuals.

• Response to stimuli: Reacting to environmental changes.

• Evolution: Populations change over generations through genetic variation and natural selection.

The Scientific Method

The scientific method is a systematic approach to investigating natural phenomena. It involves making observations, forming hypotheses, conducting experiments, and analyzing results.

• Observation: Gathering information about a phenomenon.

• Question: Identifying a specific question based on observations.

• Hypothesis: A testable explanation for the observed phenomenon.

• Prediction: What is expected to happen if the hypothesis is correct.

• Experiment: Testing the hypothesis under controlled conditions.

• Analysis: Interpreting data and drawing conclusions.

• Communication: Sharing results with the scientific community.

Example: Testing whether fertilizer increases plant growth by comparing treated and untreated plants.

Hypothesis vs. Prediction

• Hypothesis: A proposed explanation for a phenomenon (e.g., "Fertilizer increases plant growth").

• Prediction: A statement about what will happen in an experiment if the hypothesis is correct (e.g., "Plants given fertilizer will grow taller than those without").

Analyzing Results

• Write a sentence describing results shown in a graph.

• Describe how a variable is illustrated by a research study.

• Identify controlled and independent variables in an experiment.

• Describe trends in data and interpret graphs.

• Determine statistical significance using p-values.

Example: In a study measuring plant height, the independent variable is fertilizer application, and the dependent variable is plant height.

Digestion & Absorption

Structure and Function of the Digestive System

The digestive system consists of the alimentary canal and accessory organs, each with specific functions in digestion, secretion, and absorption.

• Alimentary canal: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory organs: Salivary glands, liver, pancreas, gallbladder.

• Digestion: Breakdown of food into absorbable molecules.

• Absorption: Uptake of nutrients into the bloodstream.

Enzymes and Digestive Secretions

• Enzymes: Biological catalysts that speed up chemical reactions (e.g., amylase, pepsin).

• Secretions: Include saliva, gastric juice, bile, and pancreatic juice.

Example: Pepsin in the stomach breaks down proteins into peptides.

Absorption Sites and Molecules

• Most absorption occurs in the small intestine.

• Different molecules (water, glucose, amino acids, fatty acids) are absorbed at specific sites.

Fick's Law of Diffusion

Fick's Law describes the rate of diffusion across a membrane:

• Equation:

• J: Rate of diffusion

• D: Diffusion coefficient

• dC/dx: Concentration gradient

Factors affecting diffusion include surface area, membrane thickness, and concentration gradient.

Lipids & Cell Membranes

Types of Lipids

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids.

• Fats: Composed of glycerol and fatty acids.

• Phospholipids: Major component of cell membranes.

• Steroids: Include cholesterol and hormones.

Saturated vs. Unsaturated Fatty Acids

• Saturated fatty acids: No double bonds; solid at room temperature.

• Unsaturated fatty acids: One or more double bonds; liquid at room temperature.

Cell Membrane Structure

The cell membrane is a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Fluid mosaic model: Describes the dynamic nature of the membrane.

• Selective permeability: Allows certain molecules to pass while blocking others.

Transport Across Membranes

• Passive transport: Movement of molecules without energy input (diffusion, osmosis).

• Active transport: Requires energy (ATP) to move molecules against a concentration gradient.

• Facilitated diffusion: Uses carrier proteins to transport molecules.

• Osmosis: Diffusion of water across a membrane.

Example: The Na+-K+ ATPase pump creates an ion gradient across the cell membrane.

Predicting Transport Outcomes

• Predict changes in intracellular solute concentrations and cellular volume if the cell adds or removes certain types of transport proteins.

• Example: Aquaporin increases water permeability; passive K+ channel allows K+ ions to move across the membrane.

Carbon Chemistry & Biomolecules

Carbon Skeletons and Functional Groups

Organic molecules are built from carbon skeletons and functional groups that determine their properties.

• Carbon skeletons: Chains or rings of carbon atoms.

• Functional groups: Specific groups of atoms (hydroxyl, carboxyl, amino, phosphate) that confer chemical properties.

Drawing and Identifying Structures

• Draw general structural formulas for biomolecules.

• Identify functional groups in a given structure.

Miller Experiment

The Miller-Urey experiment demonstrated that organic molecules could form under prebiotic conditions.

• Tested the hypothesis that simple molecules could combine to form amino acids.

• Used a mixture of gases and electrical sparks to simulate early Earth conditions.

Cells: Prokaryotic vs. Eukaryotic

Cell Types and Characteristics

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic cells: Have a nucleus and organelles (e.g., plants, animals, fungi).

• Four characteristics shared by all cells: plasma membrane, cytoplasm, DNA, ribosomes.

Experimental Design & Data Interpretation

Variables in Experiments

Understanding independent and dependent variables is essential for designing and interpreting experiments.

• Independent variable: The factor that is changed or manipulated.

• Dependent variable: The factor that is measured or observed.

Example: In a study on camouflage, the color of the prey is the independent variable, and the number of prey eaten is the dependent variable.

Graphing and Data Analysis

• Draw and interpret graphs showing relationships between variables.

• Describe trends and make inferences from data.

Vocabulary Table

The following table summarizes key vocabulary terms for this unit.

Additional info: Some definitions and explanations have been expanded for clarity and completeness.