Introduction to Biology

What is Life?

Biology is the scientific study of life and living organisms. To be considered alive, an entity must exhibit certain characteristics:

• Response to Stimuli: Ability to interpret and react to inherited information and environmental changes.

• Reproduction: Capacity to make copies of itself.

• Energy Utilization: Ability to harvest, acquire, or use energy.

• Cellular Organization: Composed of one or more cells.

• Evolution: Populations of organisms are constantly evolving over time.

In summary, the five fundamental characteristics of living organisms are: cells, replication, information, energy, and evolution.

Theories in Biology

Scientific theories are broad explanations for a wide range of phenomena, supported by substantial evidence. Three main theories in biology are:

1. Cell Theory: What are organisms made of?

2. Theory of Evolution by Natural Selection: Where do organisms come from?

3. Chromosome Theory of Inheritance: How is hereditary information transmitted from one generation to the next?

Cell Theory

Historical Development

• Hooke and van Leeuwenhoek: First observed cells using microscopes.

• By the 1800s, biologists recognized that all organisms are composed of cells.

• Pasteur's Hypothesis: Cells arise only from pre-existing cells, not by spontaneous generation.

Units and Conversions

Understanding units is essential for microscopy and cell biology.

• 1 meter (m) = 100 centimeters (cm)

• 1 cm = 10 millimeters (mm)

• 1 mm = 1,000 micrometers (μm)

• 1 μm = 1,000 nanometers (nm)

• 1 nm = 10-9 m = 0.000000001 m

Microscopy

• Light Microscopy: Can resolve structures as small as 200 nm. Often uses stains or dyes for contrast and can use fluorescent markers.

• Electron Microscopy:

  • Scanning Electron Microscopy (SEM): Reveals surface features.

  • Transmission Electron Microscopy (TEM): Reveals interior structures.

Genetics and Heredity

Genes and Chromosomes

• Genes: Segments of DNA that contain hereditary information, located on chromosomes.

• Central Dogma: Describes the flow of information in cells: DNA → messenger RNA → Protein.

• Proteins determine physical traits.

Life Requires Energy

• Chemical reactions in cells require energy.

• Organisms have two fundamental nutritional needs:

  1. Acquiring chemical energy in the form of ATP.

  2. Obtaining molecules that can be used as building blocks to make DNA, RNA, proteins, etc.

Evolution by Natural Selection

Definition and Mechanism

• Evolution is a change in the characteristics of a population over time.

• Natural selection is the process by which individuals with advantageous traits survive and reproduce more successfully.

• Charles Darwin and Alfred Russel Wallace provided the first comprehensive explanation of evolution by natural selection in 1858.

The Tree of Life

• Cell theory and the theory of natural selection are central to biology.

• All species are related by common ancestry and have changed over time in response to natural selection.

Phylogenetic Tree

• Shows relationships between species.

• Three domains based on genetic sequence data:

  • Bacteria

  • Archaea

  • Eukarya

• Two groups based on cell structure:

  • Prokaryotes: Bacteria and Archaea; lack a nucleus.

  • Eukaryotes: Domain Eukarya; have a nucleus.

Prokaryotes vs. Eukaryotes

Scientific Method and Hypothesis Testing

• Science addresses questions such as:

  1. What is there in the universe?

  2. How does it work?

  3. How did it come to be that way?

• Hypothesis: A testable statement that explains something observed.

• Prediction: A measurable or observable result that must be correct if a hypothesis is valid.

• Experiment: Allows researchers to test the effect of a factor on a particular phenomenon.

Hypothesis Testing: 2-Step Process

1. State the hypothesis as precisely as possible and list the predictions it makes.

2. Design an observational or experimental study capable of testing those predictions.

Basic Chemistry for Biology

Atoms, Elements, and Molecules

• Atom: The smallest fundamental particle of a chemical element.

• Element: A substance made of only one type of atom.

• Molecule: A group of atoms bonded together.

• Four elements make up 96% of matter in organisms: hydrogen, carbon, nitrogen, and oxygen.

Structure of the Atom

• Nucleus: Contains protons and neutrons.

• Electrons: Negatively charged, orbit the nucleus.

Atomic Number and Mass Number

• 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.

• Some isotopes are radioactive and decay over time.

Electron Shells and Chemical Bonds

• Atoms are most stable when their outermost electron shell is full.

• The number of unpaired electrons determines the number of bonds an atom can form.

• Covalent Bonds: Atoms share electrons.

• Nonpolar Covalent Bonds: Electrons are shared equally.

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges.

• Electronegativity: The ability of an atom to attract shared electrons. Example:

• Ions: Atoms that gain or lose electrons and become charged.

• Ionic Bonds: Electrons are transferred from one atom to another.

• Atoms with more than one unpaired electron can form double or triple bonds.

Summary Table: Types of Chemical Bonds

Key Equations

• Atomic Number:

• Mass Number:

Example: Carbon Isotopes

• All carbon atoms have 6 protons.

• Carbon-12 has 6 neutrons; Carbon-14 has 8 neutrons and is radioactive.

Additional info: Some context and definitions were expanded for clarity and completeness, including the summary tables and explicit equations.