General Biology Study Notes: Scientific Method, Elements of Life, Water Properties, and Organic Macromolecules

Scientific Method and Experimental Design

Overview of the Scientific Method

The scientific method is a systematic approach used by scientists to investigate natural phenomena, acquire new knowledge, or correct and integrate previous knowledge. It involves a series of steps that ensure experiments are conducted in a controlled and unbiased manner.

• Observation: Gathering information about a phenomenon or problem.

• Question: Formulating a question based on observations.

• Hypothesis: Proposing a testable explanation or prediction.

• Experiment: Designing and conducting tests to support or refute the hypothesis.

• Data Collection: Gathering and recording results from the experiment.

• Analysis: Interpreting the data to draw conclusions.

• Conclusion: Accepting, rejecting, or modifying the hypothesis based on the results.

Control Group: The group in an experiment that does not receive the experimental treatment and is used as a benchmark.

Experimental Group: The group that receives the treatment or variable being tested.

Placebo: An inert substance given to the control group to mimic the experimental treatment.

Variables in Experiments

• Independent Variable: The factor that is changed or manipulated by the researcher (e.g., amount of ammonium nitrate, amount of light).

• Dependent Variable: The factor that is measured or observed (e.g., height of the plants).

• Controlled Variables: Factors kept constant to ensure a fair test.

Example: In an experiment testing the effect of ammonium nitrate and light on plant growth, the independent variables are the amount of ammonium nitrate and light, while the dependent variable is the height of the plants.

Elements Essential to Life

Major Elements in Living Organisms

Living organisms are primarily composed of a few key elements, which make up the majority of their body mass.

Element	Symbol	Percentage of Body Mass (Including Water)
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.3%
Calcium	Ca	1.5%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%

Trace elements are required in very small amounts but are essential for life (e.g., iron, zinc, copper).

Chemical Forms and Biological Roles

• Abiotic Forms: Elements are found in nature as minerals, gases, or dissolved ions (e.g., O2 gas, nitrate ions).

• Animal Uptake: Animals obtain elements in chemical forms such as water (H2O), proteins, carbohydrates, and ions (e.g., Na+, Ca2+).

• Plant Uptake: Plants absorb elements as ions from soil (e.g., nitrate NO3-, phosphate PO43-).

Atomic Structure

• Atoms consist of protons, neutrons, and electrons.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

Example: Sodium (Na) has 11 protons, 12 neutrons, and 11 electrons.

Chemical Bonds and Interactions

Types of Chemical Bonds

• Nonpolar Covalent Bonds: Electrons are shared equally between atoms (e.g., O2 molecule).

• Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O molecule).

• Ionic Bonds: Electrons are transferred from one atom to another, creating ions (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom (partially positive) and an electronegative atom (e.g., O or N) in another molecule.

• Van der Waals Interactions: Weak, transient attractions between molecules due to temporary dipoles.

Properties of Water

Water's Unique Properties

Water is essential for life due to its unique chemical and physical properties, which arise from its polarity and ability to form hydrogen bonds.

• Cohesion: Water molecules stick to each other via hydrogen bonds.

• Adhesion: Water molecules stick to other polar or charged surfaces.

• High Specific Heat: Water can absorb or release large amounts of heat with little temperature change.

• High Heat of Vaporization: Large amounts of energy are required to convert water from liquid to gas.

• Density of Ice: Ice is less dense than liquid water, so it floats.

• Solvent Properties: Water dissolves many substances due to its polarity.

Biological Significance of Water's Properties

• Temperature Regulation: High specific heat and evaporative cooling help maintain stable temperatures in organisms and environments.

• Ice Floats: Aquatic life survives under ice during winter because ice insulates the water below.

• Solubility: Many biological molecules and ions dissolve in water, facilitating chemical reactions.

• Capillary Action: Cohesion and adhesion allow water to move up plant vessels and through small spaces.

Examples and Applications

• Meniscus Formation: Adhesion of water to glass causes a meniscus in graduated cylinders.

• Sweating: Evaporation of sweat cools the body due to water's high heat of vaporization.

• Surface Tension: Water forms rounded drops due to cohesion.

• Capillary Action: Water moves up a paper towel or plant stem due to cohesion and adhesion.

Organic Macromolecules

Identifying Organic Macromolecules

Organic macromolecules are large, carbon-based molecules essential for life. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

Compound	Monomers	Polymers	Examples
Carbohydrates	Monosaccharides	Polysaccharides	Glucose, starch, cellulose
Lipids	Glycerol, fatty acids	Triglycerides, phospholipids	Fats, oils, waxes
Proteins	Amino acids	Polypeptides	Enzymes, hemoglobin
Nucleic acids	Nucleotides	DNA, RNA	Genetic material

Elemental Composition and Ratios

• Carbohydrates: Approximate C:H:O ratio is 1:2:1 (e.g., C6H12O6).

• Lipids: Contain C, H, and O, but with much less O compared to carbohydrates.

• Proteins: Contain C, H, O, N, and sometimes S.

• Nucleic acids: Contain C, H, O, N, and P.

Functional Groups in Organic Molecules

Functional group	Polar or nonpolar	Hydrophobic or hydrophilic	Found in all proteins	Found in many proteins	Found in many lipids
–OH (hydroxyl)	Polar	Hydrophilic		X	X
–CH3 (methyl)	Nonpolar	Hydrophobic			X
–COOH (carboxyl)	Polar	Hydrophilic	X	X
–NH2 (amino)	Polar	Hydrophilic	X	X
–SH (sulfhydryl)	Polar	Hydrophilic		X
–PO4 (phosphate)	Polar	Hydrophilic

Additional info: The table above is inferred and expanded for clarity based on standard biology knowledge.

Examples of Macromolecules and Their Identification

• Lipid (fat or triglyceride): Nonpolar, hydrophobic, composed of glycerol and fatty acids.

• Amino acid: Contains amino and carboxyl groups, monomer of proteins.

• Tripeptide: Polymer of three amino acids linked by peptide bonds.

• Single strand of DNA: Polymer of nucleotides, contains deoxyribose, phosphate, and nitrogenous bases.

• Disaccharide: Carbohydrate composed of two monosaccharides (e.g., sucrose).

• Fatty acid: Long hydrocarbon chain with a carboxyl group.

• Ribonucleotide: Monomer of RNA, contains ribose, phosphate, and nitrogenous base.

• Polysaccharide: Carbohydrate polymer (e.g., starch, cellulose).

• Carbon sugar: Monosaccharide (e.g., glucose).

Summary Table: Key Differences Among Macromolecules

Macromolecule	Monomer	Elements Present	Key Functional Groups	Example
Carbohydrates	Monosaccharide	C, H, O	Hydroxyl, carbonyl	Glucose
Lipids	Glycerol, fatty acids	C, H, O (less O)	Carboxyl, methyl	Triglyceride
Proteins	Amino acid	C, H, O, N, (S)	Amino, carboxyl, sulfhydryl	Hemoglobin
Nucleic acids	Nucleotide	C, H, O, N, P	Phosphate, amino	DNA