CHAPTER 1: AN INTRODUCTION TO LIFE ON EARTH

What is Biology?

Biology is the science of living organisms and life processes. It seeks to understand what life is, how it functions, and how living things interact with each other and their environment.

• Biology: The study of life and living organisms.

• Science: A way of thinking and a process for understanding the natural world.

Characteristics of Life

For something to be considered alive, it must exhibit several key characteristics:

• Complex, organized structure

• Ability to get and use energy

• Maintaining structure and regulating internal environment (homeostasis)

• Ability to sense and respond to stimuli

• Growth

• Reproduction (sexual or asexual)

• Ability to evolve (change to fit the environment)

Complex Structure

Living things are composed of complex structures, such as cells, tissues, organs, and organ systems. Each level of organization builds upon the previous one:

• Cells → Tissues → Organs

• Populations → Species → Ecosystems

Each level exhibits emergent properties—new characteristics that arise from the interaction of simpler components.

Ability to Acquire Material & Energy

• Metabolism: All chemical reactions that occur within an organism to maintain life.

• Heterotrophs: Organisms that obtain energy by consuming other organisms.

• Autotrophs: Organisms that produce their own food using sunlight (photosynthesis).

Homeostasis: Maintenance of Internal Environment

Homeostasis is the tendency of living things to maintain a stable internal environment despite changes in the external environment.

Response to Stimuli

• Organisms detect and respond to internal and external stimuli.

• Some responses are rapid, others are slow or not visible.

Growth and Reproduction

• Organisms grow during their life cycle.

• Reproduction ensures the continuation of a species. Genetic information is passed from parents to offspring via DNA.

Evolution

• Populations evolve over generations through changes in DNA (mutations).

• Natural selection: The process by which organisms better adapted to their environment survive and reproduce more successfully.

• Evolutionary changes can lead to the formation of new species (speciation).

Levels of Biological Organization

• Atoms → Molecules → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere

Classification of Life

Organisms are classified into three domains based on evolutionary relationships:

• Bacteria (prokaryotic)

• Archaea (prokaryotic)

• Eukarya (eukaryotic)

Domains are subdivided into Kingdoms and further into smaller groups based on shared characteristics.

Scientific Method

The scientific method is a systematic approach to discovery:

1. Make observations

2. Form a hypothesis

3. Conduct experiments to test the hypothesis

4. Draw conclusions

5. If necessary, revise the hypothesis and repeat

A scientific theory is a well-supported explanation of natural events based on many observations and experiments.

CHAPTER 2: ATOMS, MOLECULES, AND LIFE

Atoms: The Basic Unit of Matter

An atom is the smallest unit of matter that retains the properties of an element. Atoms are made up of subatomic particles:

• Protons: Positively charged, found in the nucleus

• Neutrons: No charge, found in the nucleus

• Electrons: Negatively charged, orbit the nucleus in electron shells

Elements and Isotopes

• An element is a substance that cannot be broken down by chemical reactions.

• The atomic number is the number of protons in an atom.

• The atomic mass is the sum of protons and neutrons.

• Isotopes are atoms of the same element with different numbers of neutrons.

Electron Shells and Energy Levels

• Electrons occupy specific energy levels or shells around the nucleus.

• Electrons fill the lowest energy levels first.

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

Formation of Ions

• An ion is an atom that has gained or lost electrons, acquiring a charge.

• Cation: Positively charged ion (lost electrons)

• Anion: Negatively charged ion (gained electrons)

Ionic Bonds

Ionic bonds form between oppositely charged ions after the transfer of electrons.

• Ionic compounds are usually solid and form crystals.

• They are strong in crystal form but break easily in water.

Covalent Bonds

Covalent bonds form when two atoms share electrons to fill their valence shells.

• Single covalent bond: One pair of electrons shared

• Double covalent bond: Two pairs shared

• Triple covalent bond: Three pairs shared

Polar and Nonpolar Covalent Bonds

• Nonpolar covalent bond: Electrons are shared equally.

• Polar covalent bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom (already covalently bonded to another atom) and an electronegative atom (like oxygen or nitrogen) in another molecule.

• Hydrogen bonds are weaker than covalent bonds but important in biological systems.

• They help stabilize the three-dimensional structure of large molecules (e.g., DNA, proteins).

CHAPTER 3: WATER AND LIFE

Properties of Water

• Water covers about 70-75% of Earth's surface.

• Water is essential for life and is found in every living organism.

Cohesion and Surface Tension

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Surface tension: The result of cohesion, allowing water to resist external force.

Water as a Solvent

• Water is called the "universal solvent" because it dissolves many substances.

• Polar molecules and ions dissolve easily in water.

Summary Table: Types of Chemical Bonds

Key Equations

• Atomic mass:

• Electron shell capacity (simplified): (where n = shell number)

Additional info:

• Emergent properties are new attributes that arise at each level of biological organization due to the interaction of components.

• Scientific names are written in italics, with the genus capitalized and species lowercase (e.g., Homo sapiens).