Theme 1: Life is Organized in a Hierarchy - Levels of Biological Organization

Levels of Organization

Biological systems are structured in a hierarchy, from the broadest to the most specific levels. Each level builds upon the previous, increasing in complexity.

• The Biosphere – All ecosystems on Earth.

• Ecosystems – Living and non-living things in a given area.

• Communities – All living things within an ecosystem.

• Populations – Groups of individuals of the same species.

• Organisms – Individual living things.

• Organs and Organ Systems – Structures with specific functions.

• Tissues – Groups of similar cells performing a function.

• Cells – Basic unit of life.

• Organelles – Functional components within cells.

• Molecules – Chemical structures of two or more atoms.

• Atoms – Smallest unit of matter.

Theme 2: Life’s Processes Involve the Expression and Transmission of Genetic Information

Genetic Information

• Cells contain chromosomes – Structures that carry genetic information in the form of DNA.

• Gene – Sequence of DNA that carries genetic instructions; smallest unit of inheritance.

• Chromosome – Long DNA molecule containing many genes.

Theme 3: Life Requires the Transfer and Transformation of Energy and Matter

Energy Flow and Chemical Cycling

• Energy has a linear flow – Not recycled; flows from the sun through ecosystems via producers and consumers.

• Chemicals have a circular flow – Recycled within ecosystems.

• Photosynthesis – Plants use sunlight to convert CO2 and water into glucose and oxygen.

• Cellular Respiration – Organisms break down glucose for energy, releasing CO2 and water.

Theme 4: Organisms Interact with Other Organisms and Their Environment

Interactions and Environmental Factors

• Abiotic factors – Non-living components (water, light, temperature, soil, etc.).

• Biotic factors – Living components (plants, animals, bacteria, etc.).

Theme 5: Evolution Accounts for Diversity and Unity of Life

Evolutionary Principles

• Evolution – Process of biological change as organisms adapt to their environment.

• Diversity – Variety and abundance of different forms of life.

• Unity – Shared traits and unifying themes of life.

The Scientific Method

Steps in Scientific Investigation

1. Ask a well-framed question – Based on observation.

2. Generate testable hypotheses and predictions – Must be falsifiable and testable.

3. Design an experiment – Identify independent (manipulated) and dependent (measured) variables; control variables.

4. Perform experiment and analyze results – Record and evaluate data.

5. Draw conclusions – Determine if hypothesis is supported; suggest next steps.

Chemical Context of Life

Atoms and Elements

• Matter – Anything that takes up space and has mass.

• Elements – Substances that cannot be broken down by chemical reactions.

• Biologically important elements – C, H, N, O (carbon, hydrogen, nitrogen, oxygen).

• Atoms – Smallest unit of an element retaining its properties.

Atomic Structure

• Protons – Positive charge.

• Neutrons – No charge.

• Electrons – Negative charge.

• Atomic number – Number of protons.

• Mass number – Number of protons + neutrons.

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

• Radioactive isotopes – Unstable isotopes that decay over time.

Electron Shells and Chemical Reactivity

• Electrons are arranged in shells around the nucleus.

• The outermost shell (valence shell) determines chemical reactivity.

• Atoms are most stable when their valence shell is full (inert).

Chemical Bonding

Types of Chemical Bonds

• Covalent bonds – Sharing of electrons between atoms.

• Ionic bonds – Attraction between oppositely charged ions.

• Hydrogen bonds – Weak attractions between a hydrogen atom and an electronegative atom (e.g., O or N).

Electronegativity

• The ability of an atom to attract electrons in a bond.

• Greater difference in electronegativity leads to polar covalent bonds.

Polarity

• Nonpolar covalent bonds – Equal sharing of electrons.

• Polar covalent bonds – Unequal sharing, resulting in partial charges.

Water and Its Importance to Life

Properties of Water

• Polarity – Water is a polar molecule, allowing hydrogen bonding.

• Cohesion – Water molecules stick together via hydrogen bonds.

• Adhesion – Water molecules stick to other surfaces.

• High specific heat – Water resists temperature change.

• High heat of vaporization – Requires a lot of energy to convert from liquid to gas.

• Less dense as a solid – Ice floats on water.

• Universal solvent – Dissolves many substances due to polarity.

Why Water Matters for Life

• Stabilizes temperature in organisms and environments.

• Facilitates chemical reactions.

• Supports life by providing a medium for biological processes.

Acids and Bases

pH Scale

• Acids – Increase hydrogen ion concentration () in solution.

• Bases – Decrease hydrogen ion concentration (accept ).

• pH – Measures concentration:

• pH scale is logarithmic: each unit change = 10-fold change in .

• Acidic: pH < 7; Neutral: pH = 7; Basic: pH > 7.

Examples of Acid-Base Reactions

• (acid dissociation)

• (base dissociation)

• (neutralization)

Carbon, Carbohydrates, Proteins, Lipids, and Nucleic Acids

Carbon: The Basis of Life

• Carbon forms four covalent bonds, allowing for diverse organic molecules.

• Hydrocarbons (chains of carbon and hydrogen) are the basis of most organic molecules.

• Organic molecules depend on chemical groups attached to their skeletons, affecting function and solubility.

Macromolecules: Building Blocks of Life

• Four main types: carbohydrates, lipids, proteins, nucleic acids.

• Polymers are made of repeating monomers linked by covalent bonds.

• Dehydration synthesis – Joins monomers by removing water.

• Hydrolysis – Breaks polymers by adding water.

Carbohydrates

Structure and Function

• Monosaccharides – Simple sugars (monomers), e.g., glucose.

• Disaccharides – Two monosaccharides joined together.

• Polysaccharides – Long chains of monosaccharides; energy storage (starch, glycogen) or structural (cellulose in plants).

• General formula: , where .

• Each carbon has a hydroxyl group () and a carbonyl group ().

Properties

• Vary in length and ring/linear form.

• Main function: energy source for cells.

Hydrophobic vs. Hydrophilic

• Hydrophobic – Water-repelling, non-polar molecules (e.g., lipids).

• Hydrophilic – Water-attracting, polar molecules (e.g., carbohydrates, proteins).

• Some molecules are amphipathic (both hydrophobic and hydrophilic regions).

Summary Table: Types of Chemical Bonds

Summary Table: Properties of Water