Study Guide: Themes in Biology & The Chemical Basis of Life (Chapters 1 & 2)

Chapter 1: Themes in the Study of Biology

Levels of Biological Organization

The study of biology involves understanding life at various levels of organization, from the smallest molecules to the entire biosphere. Each level builds upon the one below it, creating a hierarchy of complexity.

• Molecule: A group of atoms bonded together (e.g., H2O).

• Organelle: Specialized structure within a cell (e.g., mitochondrion).

• Cell: The basic unit of life (e.g., muscle cell).

• Tissue: Group of similar cells performing a function (e.g., nervous tissue).

• Organ: Structure composed of different tissues (e.g., heart).

• Organ System: Group of organs working together (e.g., digestive system).

• Organism: An individual living thing (e.g., human).

• Population: Group of organisms of the same species in an area.

• Community: All populations of different species in an area.

• Ecosystem: Community plus the nonliving environment.

• Biosphere: All ecosystems on Earth.

Example: A forest ecosystem includes trees (organisms), their populations, the community of all living things, and the nonliving components like soil and water.

Characteristics of Life

To be considered alive, an entity must exhibit seven key characteristics:

• Order (organized structure)

• Regulation (homeostasis)

• Growth and development

• Energy processing

• Response to the environment

• Reproduction

• Evolutionary adaptation

Prokaryotic vs. Eukaryotic Cells

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

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Energy Flow and Nutrient Cycling in Ecosystems

Energy enters ecosystems primarily through sunlight, which is captured by producers and transferred through consumers and decomposers.

• Producers: Organisms (like plants) that make their own food via photosynthesis.

• Consumers: Organisms that eat other organisms (e.g., animals).

• Decomposers: Organisms (like fungi and bacteria) that break down dead matter, recycling nutrients.

Key Point: Nutrients are recycled within ecosystems, but energy flows in one direction and is eventually lost as heat.

Classification: The Three Domains of Life

All life is classified into three domains:

• Bacteria: Prokaryotic, unicellular organisms.

• Archaea: Prokaryotic, often found in extreme environments.

• Eukarya: Eukaryotic organisms, including four kingdoms:

  • Protista (mostly unicellular eukaryotes)

  • Fungi (decomposers, e.g., mushrooms)

  • Plantae (photosynthetic, e.g., trees)

  • Animalia (multicellular consumers, e.g., humans)

Example: Homo sapiens (humans) belong to the domain Eukarya, kingdom Animalia.

Natural Selection and Evolution

Natural selection is the process by which organisms with advantageous traits survive and reproduce more successfully, leading to evolution over generations.

• Variation exists within populations.

• Some variations confer advantages in survival or reproduction.

• Advantageous traits become more common over time.

The Scientific Method: Hypotheses and Experiments

Scientific inquiry involves forming hypotheses and testing them through controlled experiments.

• Hypothesis: A testable, falsifiable explanation for an observation.

• Controlled Experiment: An experiment in which only one variable is changed at a time.

Criteria for a Valid Hypothesis:

• Must be testable

• Must be falsifiable

Example: Testing whether sunlight affects plant growth by growing identical plants with and without sunlight.

Chapter 2: The Chemical Basis of Life

Basic Chemistry for Biology

Living organisms are composed of matter, which consists of elements and compounds built from atoms.

• Matter: Anything that occupies space and has mass.

• Element: A substance that cannot be broken down into other substances by chemical means (e.g., carbon, oxygen).

• Compound: A substance consisting of two or more elements in a fixed ratio (e.g., H2O).

Most Common Elements in Living Organisms: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S).

Structure of the Atom

Atoms are the smallest units of matter, composed of subatomic particles:

• Proton: Positively charged, located in the nucleus.

• Neutron: No charge, located in the nucleus.

• Electron: Negatively charged, orbits the nucleus.

Atomic Number: Number of protons in an atom; determines the element.

Atomic Mass: Sum of protons and neutrons.

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

Electron Distribution: Electrons are arranged in shells around the nucleus.

• First shell: up to 2 electrons

• Second shell: up to 8 electrons

Calculations:

• Number of electrons = atomic number (for a neutral atom)

• Atomic mass = number of protons + number of neutrons

Example: Carbon has atomic number 6 (6 protons, 6 electrons), atomic mass 12 (6 protons + 6 neutrons).

Chemical Bonding

Atoms form bonds to achieve stable electron configurations.

• Covalent Bond: Atoms share electrons (e.g., H2O within a molecule).

• Ionic Bond: Transfer of electrons from one atom to another (e.g., NaCl).

• Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).

In Water:

• Hydrogen and oxygen are held together by covalent bonds.

• Water molecules are held together by hydrogen bonds.

Properties of Water

Water's unique properties are essential for life.

• Cohesion: Attraction between molecules of the same substance (e.g., water molecules stick together).

• Adhesion: Attraction between different substances (e.g., water to glass).

• Surface Tension: Caused by cohesion; allows insects to walk on water.

• High Heat Capacity: Water absorbs and retains heat, moderating temperature.

• Ice Floats: Solid water is less dense than liquid water due to hydrogen bonding.

Solutions, Acids, and Bases

Many biological processes occur in aqueous solutions.

• Aqueous Solution: Solution where water is the solvent.

• Solvent: The dissolving agent (e.g., water).

• Solute: The substance dissolved (e.g., salt).

Acids and Bases:

• Acid: Substance that increases H+ concentration in solution.

• Base: Substance that decreases H+ concentration.

• pH Scale: Measures acidity/alkalinity (0-14); 7 is neutral, below 7 is acidic, above 7 is basic.

• Buffer: Substance that minimizes changes in pH by accepting or donating H+.

Example: Human blood is buffered to maintain a pH near 7.4.

Key Equations

• Atomic mass calculation: $\text{Atomic mass} = \text{Number of protons} + \text{Number of neutrons}$

• Number of electrons in a neutral atom: $\text{Number of electrons} = \text{Atomic number}$

Additional info: For further practice, students are encouraged to use flashcards and online resources such as Quizlet to reinforce vocabulary and concepts.