Introduction to Biology

Definition and Scope

Biology is the scientific study of life. The term is derived from the Greek words bios (life) and logos (study).

• What is Life? Life is characterized by several key properties:

  • Made of cells

  • Reproduction

  • Growth and development

  • Energy processing

  • Response to environment

  • Regulation (homeostasis)

  • Evolution

Major Themes in Biology

• There are five major unifying themes in biology:

1. Organization

2. Information

3. Energy and Matter

4. Interactions

5. Evolution

1. Organization

Life is structured in a hierarchical manner, from molecules to the biosphere.

• Biological organization includes levels such as:

  • Atoms

  • Molecules

  • Organelles

  • Cells

  • Tissues

  • Organs

  • Organ systems

  • Organisms

  • Populations

  • Communities

  • Ecosystems

  • Biosphere

• Cells are the fundamental units of life.

• All cells are either prokaryotic or eukaryotic:

2. Information

All life stores and transmits information, primarily in the form of DNA.

• DNA (deoxyribonucleic acid) encodes genetic information.

• Genes are units of inheritance that determine traits.

• Gene expression is the process by which information from a gene is used to synthesize functional gene products (often proteins).

3. Energy and Matter

All living things require energy and matter to grow, reproduce, and maintain organization.

• Energy flows through ecosystems, usually entering as sunlight and exiting as heat.

• Matter cycles within ecosystems.

4. Interactions

Organisms interact with each other and with their environment, affecting both their own survival and the ecosystem as a whole.

• Interactions can be at the molecular, cellular, organismal, or ecosystem level.

5. Evolution

Evolution explains both the unity and diversity of life. It is the process by which populations change over time through genetic variation and natural selection.

• Diversity arises from evolutionary change.

• Charles Darwin's theory of natural selection is central to understanding evolution.

Classification of Life

Domains of Life

• Life is classified into three domains:

  • Bacteria

  • Archaea

  • Eukarya (includes Protists, Fungi, Plants, Animals)

Charles Darwin and Evolution

• Darwin's major ideas:

  1. Descent with modification: species change over time and share common ancestors.

  2. Natural selection: individuals with traits that enhance survival and reproduction are more likely to pass on their traits.

The Scientific Method

• The scientific method is a systematic approach to understanding the natural world.

• Steps include:

  1. Observation

  2. Question

  3. Hypothesis (a proposed explanation)

  4. Experiment (testing the hypothesis)

  5. Analyze data and draw conclusions

• Hypothesis vs. Theory:

  • Hypothesis: a testable explanation for an observation.

  • Theory: a broad explanation supported by a large body of evidence.

Basic Chemistry for Biology

Elements and Compounds

• Chemistry is the study of matter and its interactions.

• Element: a substance that cannot be broken down by chemical means.

• Compound: a substance made of two or more elements in a fixed ratio.

• Example: Sodium (Na) + Chlorine (Cl) → Sodium chloride (NaCl)

Essential Elements

• Four elements make up most of living matter:

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

• Other essential elements include calcium, phosphorus, potassium, sulfur, etc.

Atoms

• Atom: the smallest unit of an element, composed of subatomic particles:

  • Protons (positive charge, in nucleus)

  • Neutrons (neutral, in nucleus)

  • Electrons (negative charge, orbit nucleus)

• Atomic number: number of protons in the nucleus.

• Mass number: sum of protons and neutrons.

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

• Energy: capacity to cause change; electrons have potential energy based on their position.

Chemical Bonds

• Atoms form bonds to achieve stable electron configurations.

• Types of chemical bonds:

  1. Covalent bonds: sharing of electron pairs between atoms.

  2. Ionic bonds: transfer of electrons from one atom to another, resulting in oppositely charged ions (cation and anion).

  3. Hydrogen bonds: weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

Properties of Water

• Water is essential for life and has unique properties due to its structure and hydrogen bonding.

• Cohesion: water molecules stick to each other.

• Adhesion: water molecules stick to other substances.

• Moderation of temperature: water absorbs and releases heat slowly.

• Expansion upon freezing: ice is less dense than liquid water.

• Universal solvent: water dissolves many substances.

Additional info:

• Water's high specific heat helps regulate temperature in organisms and environments.

• Evaporative cooling allows organisms to release excess heat (e.g., sweating).