Week 1 Biology Notes: Introduction to Biology & Levels of Biological Organization

Biology Definition: The study of life and living organisms.
Major Characteristics of Living Things:
- Made of cells.
- Use energy.
- Maintain homeostasis.
- Grow and develop.
- Respond to stimuli.
- Reproduce.
- Contain genetic material ( $\text{DNA}$ ).
- Populations can evolve over generations.
Homeostasis: Maintaining relatively stable internal conditions.
- Examples: Body temperature, blood glucose, water balance.
Metabolism: All chemical reactions occurring within an organism.
Stimulus: Change in the internal or external environment.
Response: Reaction to a stimulus.

Hierarchy from Smallest to Largest:
- Atom
- Molecule
- Organelle
- Cell
- Tissue
- Organ
- Organ system
- Organism
- Population
- Community
- Ecosystem
- Biosphere
Definitions of Levels:
- Cell: Smallest basic unit of life.
- Tissue: Group of similar cells working together.
- Organ: Multiple tissue types working together.
- Organ System: Organs working together.
- Organism: Individual living thing.
- Population: Organisms of the same species living in the same area.
- Community: All the different populations living in an area.
- Ecosystem: Living organisms plus the nonliving environment.

Purpose: Used to investigate questions about the natural world.
General Process Steps:
- Observation
- Question
- Hypothesis
- Prediction
- Experiment
- Analyze data
- Conclusion
Hypothesis: Testable proposed explanation. Must be capable of being supported or rejected by evidence.
Independent Variable: Variable intentionally changed or manipulated by the researcher.
- Memory Aid: Independent = I change it.
Dependent Variable: Variable that is measured.
- Memory Aid: Dependent = Data I measure.
Control Group: Provides a comparison.
Constants / Controlled Variables: Conditions kept the same.
Scientific Theory: Broad explanation supported by extensive evidence. Does not simply mean a guess.

Matter: Anything that has mass and occupies space.
Atom: Smallest unit of an element.
Important Subatomic Particles:
- Proton = positive ( $+$ )
- Neutron = neutral
- Electron = negative ( $-$ )
Element: Pure substance consisting of one type of atom.
Important Elements in Living Organisms:
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
- Phosphorus
- Sulfur
- Memory Aid: CHNOPS
Molecule: Two or more atoms chemically bonded.
Compound: Substance containing two or more different elements chemically combined.

Ionic Bond: Involves transfer of electrons and attraction between resulting ions.
Covalent Bond: Atoms share electrons.
Hydrogen Bond:
- Weak attraction between partially charged regions.
- Individually weak but biologically important.
Ion: Charged atom or molecule.
- Cation: Positive ion.
- Anion: Negative ion.

Polarity: Water is polar.
- Oxygen side has a partial negative charge.
- Hydrogen sides have partial positive charges.
- Water molecules form hydrogen bonds with each other.
Important Properties of Water:
- Cohesion: Water sticks to water (same substance).
- Adhesion: Water sticks to other substances (different substances).
- Temperature Regulation: Helps regulate temperature.
- Solvent: Excellent solvent for many ionic and polar substances.

pH: Indicates hydrogen-ion ( $H^+$ ) concentration.
Common pH Scale:
- $0-6$ = acidic
- $7$ = neutral
- $8-14$ = basic/alkaline
Acid: Increases $H^+$ concentration in solution.
Base: Decreases $H^+$ concentration/accepts $H^+$ .
Buffers: Help resist sudden changes in pH.
Logarithmic Scale: The pH scale is logarithmic; a difference of one pH unit corresponds to a $10\times$ change in $H^+$ concentration.

Four Major Biological Macromolecule Groups:
- Carbohydrates
- Lipids
- Proteins
- Nucleic acids
Carbohydrates:
- Main Functions: Provide quick/short-term energy; can provide structural support.
- Primary Composition: Carbon, Hydrogen, Oxygen.
- Monosaccharide: Simple sugar (Example: glucose).
- Disaccharide: Two monosaccharides joined together (Example: sucrose).
- Polysaccharide: Long chain of sugars.
- Starch: Energy storage in plants.
- Glycogen: Energy storage in animals.
- Cellulose: Structural component of plant cell walls.
Lipids:
- Types Included: Fats, Oils, Phospholipids, Steroids.
- Functions: Long-term energy storage, insulation, protection, cell membrane structure, signaling/hormones.
- Phospholipids:
- Major component of cell membranes.
- Form a phospholipid bilayer.
- Generally hydrophobic/nonpolar.

Proteins:
- Made from amino acids.
- Amino acids are joined by peptide bonds.
- Functions: Structure, transport, movement, defense, signaling, catalyzing chemical reactions.
Enzymes:
- Most are proteins.
- Speed up chemical reactions.
- Act as biological catalysts.
- Lower activation energy.
- Substrate: Molecule that binds to an enzyme.
- Active Site: Region of the enzyme where the substrate binds.
- Factors Affecting Enzyme Activity: Temperature, pH, substrate concentration.
- Denaturation: Protein loses its normal shape, which can cause loss of function.

Composition: Made from nucleotides.
Two Major Types:
- DNA: Stores hereditary/genetic information; usually double-stranded.
- RNA: Important for expressing genetic information, including protein synthesis.