General Biology Unit 1 Study Guide: Themes, Scientific Method, and Chemistry of Life

Themes of Biology and Scientific Method

Characteristics of Life

Biology is the scientific study of life, and living organisms share several key characteristics that distinguish them from non-living matter.

• Composed of cells: All living things are made up of one or more cells, the basic unit of life.

• Organization: Living things exhibit complex but ordered organization.

• Reproduction: Organisms reproduce their own kind.

• Response to environment or stimuli: Living things respond to environmental changes.

• Maintain homeostasis: Regulation of internal conditions to maintain a stable state.

• Metabolism: Use and transformation of energy and matter.

• Growth and development: Organisms grow and develop according to specific instructions coded in their DNA.

• Evolution: Populations of organisms evolve over generations.

Example: A single-celled bacterium displays all these characteristics, making it the smallest unit of life.

Unity and Diversity of Life: Darwin's Descent with Modification

Charles Darwin's theory of descent with modification explains both the unity and diversity of life. All organisms share a common ancestor but have diversified through the process of natural selection.

• Unity: All life forms share fundamental characteristics due to common ancestry.

• Diversity: Differences arise as species adapt to different environments over time.

• Example: The finches on the Galápagos Islands evolved different beak shapes to exploit different food sources.

Emergent Properties

As biological organization increases in complexity (from molecules to biosphere), new properties emerge that are not present at lower levels. These are called emergent properties.

• Definition: Characteristics that arise at each level of biological organization due to the arrangement and interaction of parts.

• Examples:

  • Photosynthesis (requires a specific organization of molecules in chloroplasts)

  • Heart function (requires the interaction of tissues and cells)

Levels of Biological Organization

Life is organized into hierarchical levels, each with increasing complexity:

1. Biosphere: All ecosystems on Earth that support life.

2. Ecosystems: Living and nonliving things in the same area.

3. Communities: Multiple populations of different species in the same area.

4. Populations: All organisms of the same species living in the same area.

5. Organisms: Individual living things.

6. Organs and Organ Systems: Groups of tissues performing specific functions.

7. Tissues: Groups of similar cells performing a function.

8. Cells: Smallest unit of life.

9. Organelles: Specialized structures within cells.

10. Molecules: Groups of atoms bonded together.

The Scientific Method

The scientific method is a systematic approach to understanding the natural world through observation and experimentation.

• Steps:

  1. Making observations

  2. Forming hypotheses

  3. Generating predictions

  4. Testing hypotheses

  5. Analyzing data and drawing conclusions

• Hypothesis: A testable and falsifiable explanation for an observation. Must lead to predictions that can be tested and can be proven false.

• Theory: A broader and more comprehensive explanation than a hypothesis, supported by a large body of evidence.

Example: In an experiment testing the effect of artificial sweetener on mice, the hypothesis might predict that sweetener increases activity levels.

Experimental Design

Experiments are designed to test hypotheses by manipulating variables and observing outcomes.

• Experimental group: Receives the treatment or condition being tested.

• Control group: Does not receive the treatment; serves as a baseline for comparison.

• Variables:

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

  • Dependent variable: The factor that is measured; changes in response to the independent variable.

• Controlling variables: Keeping all other factors constant to ensure that observed effects are due to the independent variable.

• Graphing: Independent variable on the x-axis; dependent variable on the y-axis.

Example: In a mouse predation experiment, the independent variable is the color of the mouse model, and the dependent variable is the number of predation events.

Chemistry of Life

Chemical Reactions and Matter

Chemical reactions involve the rearrangement of atoms to form new substances. Matter is conserved in these reactions.

• Balanced chemical equation example:

  • $4NO + 5O_2 \rightarrow 4NO_2 + 2H_2O$

• Reactants: Starting molecules in a chemical reaction.

• Products: Final molecules formed in a chemical reaction.

Ions: Anions and Cations

Ions are charged atoms or molecules formed by the gain or loss of electrons.

• Anion: Negatively charged ion (gains electrons).

• Cation: Positively charged ion (loses electrons).

• Ionic bond: Attraction between oppositely charged ions.

Atomic Structure and the Periodic Table

The chemical behavior of an atom is determined by the number of electrons in its outermost shell (valence shell).

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

• Major elements in living organisms: Hydrogen, Oxygen, Carbon, Nitrogen.

• Electron shells:

  • First shell: up to 2 electrons

  • Second shell: up to 8 electrons

  • Third shell: up to 8 electrons

Chemical Bonds

Atoms form bonds to fill their valence shells. The main types of bonds are:

• Covalent bonds: Atoms share electrons (strongest in water).

• Ionic bonds: Electrons are transferred from one atom to another, creating charged ions (weaker in water).

• Hydrogen bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

Electronegativity: The ability of an atom to attract shared electrons in a covalent bond. Oxygen is the most electronegative atom in most organic molecules.

• Nonpolar covalent bond: Electrons are shared equally.

• Polar covalent bond: Electrons are shared unequally, resulting in partial charges.

Bonds in Water and Carbon Dioxide

• Water (H2O): Polar covalent and hydrogen bonds.

• Carbon dioxide (CO2): Double covalent bonds.

• Oxygen (O2): Nonpolar double covalent bonds.

CO2 and Ecosystems

CO2 emissions can acidify oceans, lower pH, form dead zones, and disrupt marine life and ecosystems by altering species distribution and increasing greenhouse gases.

Hydrophilic and Hydrophobic Substances

• Hydrophilic: Attracted to water; includes salts and polar molecules.

• Hydrophobic: Repelled by water; includes oils and nonpolar molecules.

Example: Phospholipids have hydrophilic heads and hydrophobic tails, forming cell membranes.

Properties of Water

Hydrogen bonding gives water its unique properties, which are essential for life:

• Cohesion: Attraction between water molecules due to hydrogen bonding.

• Adhesion: Attraction between water molecules and other substances.

• High specific heat: Water can absorb a lot of heat before changing temperature.

• High heat of vaporization: Water requires a lot of energy to evaporate.

• Ice floats: Solid water is less dense than liquid water.

• Solvent properties: Water dissolves many substances, facilitating chemical reactions in cells.

Example: Water's cohesion allows for the transport of water in plants against gravity.

Table: Comparison of Bond Types

Bond Type	Definition	Relative Strength (in water)	Example
Covalent	Atoms share electrons	Strongest	O-H bond in water
Ionic	Electrons transferred, forming ions	Weaker	NaCl in water
Hydrogen	Attraction between H and electronegative atom	Weakest	Between water molecules

Additional info:

• Some explanations and examples have been expanded for clarity and completeness.

• Table content and definitions are based on standard introductory biology textbooks.