General Biology: Foundations, Cell Theory, Microscopy, and Atomic Structure

Foundations of Biology

Characteristics of Living Organisms

Biology is the study of living organisms, which share several fundamental characteristics. Understanding these traits helps distinguish living things from non-living matter.

• Response to Stimuli: Living organisms interpret and respond to inherited information and environmental changes.

• Reproduction: The ability to make copies of themselves, ensuring the continuation of the species.

• Energy Utilization: Organisms harvest, acquire, or use energy for growth and maintenance.

• Cellular Organization: All living things are composed of cells, the basic unit of life.

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

Theory in Biology: A theory is a well-supported explanation for a broad class of phenomena, backed by evidence.

Main Theories in Biology

• Cell Theory: All organisms are made of cells.

• Theory of Evolution by Natural Selection: Explains the origin of species and adaptation.

• Chromosome Theory of Inheritance: Hereditary information is transmitted from one generation to the next via chromosomes.

Microscopy and Cell Discovery

Historical Development

Microscopy has played a crucial role in the discovery and understanding of cells.

• Hooke and van Leeuwenhoek: Early scientists who observed cells using microscopes.

• In the 1800s, German biologists established that all organisms consist 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.

• cm: centimeter

• mm: millimeter

• μm: micrometer ("micron")

• nm: nanometer

• Conversions:

  • 1 m = 1,000 mm

  • 1 mm = 1,000 μm

  • 1 μm = 1,000 nm

  • 1 cm = 0.01 m = 10 mm

  • 1 nm = $1 \times 10^{-9}$ m

Types of Microscopy

• Light Microscopy: Can resolve structures as small as 200 nm; often uses stains or dyes for contrast; 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 are segments of DNA that contain hereditary information. They are located on chromosomes and are responsible for the transmission of traits.

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

• Proteins: Determine physical traits.

Evolution and Natural Selection

Evolution is the change in the characteristics of a population over time. Natural selection is the process by which traits that enhance survival and reproduction become more common in a population.

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

• Phylogenetic Tree: Shows relationships between species.

• Three Domains: Bacteria, Archaea, Eukarya.

• Two Groups Based on Cell Structure:

  • Prokaryotes: Bacteria and Archaea; lack membrane-bound organelles and nucleus.

  • Eukaryotes: Domain Eukarya; have nucleus and membrane-bound organelles.

Feature	Prokaryotes	Eukaryotes
Nucleus	Absent	Present
Size	Smaller	Larger
Complexity	Simple	Complex
Reproduction	Asexual	Sexual or Asexual

Scientific Method and Hypothesis Testing

Science and Hypotheses

Science is based on asking questions and testing hypotheses through observation and experimentation.

• Key questions: What is there in the universe? How does it work? 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.

• Experimental Design: Tests the effect of a factor on a particular phenomenon.

Steps in Hypothesis Testing

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.

Atoms, Molecules, and Chemical Bonds

Structure of Atoms and Elements

Atoms are the smallest fundamental particles of chemical elements. Elements are made of only one type of atom.

• Atom: Consists of a nucleus (protons and neutrons) and electrons.

• Element: Pure substance made of one type of atom.

• 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.

Subatomic Particle	Charge	Location
Proton	+1	Nucleus
Neutron	0	Nucleus
Electron	-1	Electron cloud

Atomic Structure and Chemical Bonds

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

• Atoms bond to achieve stability, forming molecules.

• Covalent Bonds: Electrons are shared between atoms.

• Nonpolar Covalent Bonds: Electrons are shared equally.

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

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions.

• Electronegativity: Measure of an atom's ability to attract shared electrons. Example: $\text{O} > \text{N} > \text{C} \approx \text{H}$

• Atoms with more unpaired electrons can make more bonds (e.g., double or triple bonds).

Isotopes and Radioactivity

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

• Some isotopes are radioactive and decay over time.

Atomic Structure of Key Biological Elements

• C, H, N, O, P, and S make up over 99% of atoms in living organisms.

Summary Table: Types of Chemical Bonds

Bond Type	Electron Sharing	Example
Nonpolar Covalent	Equal	$\text{H}_2$, $\text{O}_2$
Polar Covalent	Unequal	$\text{H}_2\text{O}$
Ionic	Transferred	$\text{NaCl}$

Additional info:

• Atomic structure and bonding are foundational for understanding biological molecules and processes.

• Microscopy techniques are essential for visualizing cells and their components.