Quick Refresher

Characteristics of Life

All living organisms share these traits:

  • Cellular Organization: Made of one or more cells

    • Unicellular: Bacteria

    • Multicellular: Plants, animals

  • Reproduction: Produces new individuals

    • Involves genetic material (mitosis, meiosis, fertilization)

  • Metabolism: Chemical reactions that sustain life

    • Anabolic: Builds molecules (e.g., photosynthesis)

    • Catabolic: Breaks down molecules (e.g., cellular respiration)

  • Homeostasis: Maintains internal stability (e.g., body temp, blood sugar)

  • Growth & Development: Cell division, differentiation, morphogenesis

  • Response to Stimuli: Reacts to environment (e.g., tropisms, behavior)

  • Evolution: Genetic change over generations

    • Driven by natural selection → adaptation & speciation

🔹 Levels of Biological Organization

Level

Example

Molecule

DNA, glucose

Organelle

Nucleus, mitochondria

Cell

Bacteria, plant cell

Tissue

Muscle, nervous

Organ

Heart, lungs

Organ System

Respiratory, circulatory

Organism

Human, tree

Population

Herd of deer

Community

Forest with deer, birds, trees

Ecosystem

Forest + soil, water, sunlight

🔹 Cell Types

  • Prokaryotic: No nucleus or organelles (e.g., bacteria)

  • Eukaryotic: Has nucleus and organelles (e.g., plants, animals)

🔹 Phylogenetic Trees

  • Node: Common ancestor

  • Branch Length: Genetic change or time

  • Purpose: Shows evolutionary relationships and divergence

  • Built Using: DNA sequences and traits

🔹 Biological Subfields

Field

Focus Area

Cell Biology

Cell structure/function

Genetics

Inheritance and variation

Ecology

Organism–environment interactions

Evolution

Genetic change over time

Physiology

Body system functions

Microbiology

Microorganisms

Developmental Bio

Growth and differentiation

Molecular Biology

DNA, RNA, proteins

Emerging Fields

Bioinformatics, Epigenetics, Systems Biology

🔹 Scientific Method & Experimental Design

  • Steps: Observation → Question → Hypothesis → Experiment → Data → Conclusion

  • Variables:

    • Independent: What you change

    • Dependent: What you measure

    • Controlled: What stays constant

  • Control Group: Baseline for comparison

  • Sample Size & Replication: Larger samples and repeated trials increase reliability

🔹 Basic Chemistry for Biology

  • Atoms:

    • Protons (+), Neutrons (0), Electrons (–)

  • Ions: Charged atoms (e.g., Na⁺, Cl⁻)

  • Isotopes: Same element, different neutron count

  • Bond Types:

    • Ionic: Transfer of electrons

    • Covalent: Sharing electrons

    • Hydrogen: Weak attraction (important in water & DNA)

🔹 Water & Its Properties

  • Polarity: Uneven charge distribution

  • Hydrogen Bonding: Leads to cohesion, adhesion, surface tension

  • High Specific Heat: Stabilizes temperature

  • Solvent Abilities: Dissolves polar substances

  • pH Scale:

    • Acidic < 7

    • Neutral = 7

    • Basic > 7

🔹 Macromolecules Overview

Type

Monomer

Function

Example

Carbohydrates

Monosaccharides

Energy, structure

Glucose, starch

Lipids

Fatty acids

Energy storage, membranes

Fats, oils, phospholipids

Proteins

Amino acids

Enzymes, structure, transport

Hemoglobin, enzymes

Nucleic Acids

Nucleotides

Genetic info, protein synthesis

DNA, RNA

🔹 Cell Theory

  1. All living things are made of cells

  2. Cells are the basic unit of life

  3. All cells come from pre-existing cells

🔹 Microscopy Basics

  • Light Microscope: Views live cells

  • Electron Microscope: High resolution, dead specimens

  • Magnification vs. Resolution: Size vs. clarity