General Biology Exam Study Guide: Domains of Life, Evolution, Chemistry of Biology, and Cell Structure

Domains of Life

Three Domains of Life

The concept of the three domains of life is fundamental to biological classification. Each domain represents a major lineage of organisms distinguished by cellular structure and genetic makeup.

• Bacteria: Single-celled prokaryotes with unique cell wall components and diverse metabolic pathways.

• Archaea: Single-celled prokaryotes, often found in extreme environments, with distinct membrane lipids and genetic machinery.

• Eukarya: Organisms with eukaryotic cells, including animals, plants, fungi, and protists.

Key Features of Each Domain:

• Bacteria: Peptidoglycan cell walls, no nucleus, diverse metabolism.

• Archaea: No peptidoglycan, unique membrane lipids, extremophiles.

• Eukarya: Membrane-bound organelles, nucleus, multicellularity common.

Study of Life

Characteristics of Living Organisms

Biologists define life using several key characteristics that distinguish living things from non-living matter.

• Cellular organization: All living things are composed of one or more cells.

• Metabolism: Living organisms carry out chemical reactions to obtain and use energy.

• Homeostasis: Regulation of internal environment to maintain stable conditions.

• Growth and development: Organisms increase in size and complexity over time.

• Reproduction: Ability to produce new individuals.

• Response to stimuli: Reacting to environmental changes.

• Evolution: Populations change over generations through genetic variation and natural selection.

Living vs. Non-living: Non-living things lack one or more of these characteristics.

Evidence of Evolution

Types of Evidence

Scientists use multiple lines of evidence to support the theory of evolution and understand relationships between organisms.

• Fossil record: Shows changes in organisms over time.

• Comparative anatomy: Homologous and analogous structures indicate evolutionary relationships.

• Embryology: Similarities in early development suggest common ancestry.

• Molecular biology: DNA and protein similarities reflect evolutionary connections.

• Vestigial structures: Remnants of features that served functions in ancestors.

Evolution Over Time: Evidence demonstrates how species change and diversify.

Key Terms in Evolution

• Homologous structure: Anatomical features with similar origin but possibly different functions (e.g., human arm and whale flipper).

• Analogous structure: Features with similar function but different evolutionary origins (e.g., bird wing and insect wing).

• Comparative embryology: Study of similarities in embryonic development across species.

• Vestigial structures: Structures that have lost their original function (e.g., human appendix).

Natural Selection and Descent with Modification

Darwin's Theory

Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce. Descent with modification refers to the passing of traits from parent to offspring, with changes accumulating over generations.

• Relationship between natural selection and evolution: Natural selection drives evolutionary change by favoring advantageous traits.

• Descent with modification: Explains how species evolve and diversify from common ancestors.

• Darwin's evidence: Observations of variation, adaptation, and fossil records supported his theory.

Chemistry of Biology

Atoms, Bonds, and Molecules

Chemical principles underpin biological processes. Atoms combine to form molecules through chemical bonds, which determine the structure and function of biological compounds.

• Atoms: Basic units of matter, composed of protons, neutrons, and electrons.

• Chemical bonds: Forces holding atoms together in molecules. Types include:

  • Covalent bond: Atoms share electrons.

  • Ionic bond: Atoms transfer electrons, forming charged ions.

  • Compound: Substance formed from two or more elements chemically bonded.

• Atomic structure: Electrons arranged in shells around the nucleus.

Key Terms:

• Atom

• Ionic bond

• Covalent bond

• Neutron

• Electron

• Proton

• Electron shell

• Atomic number: Number of protons in the nucleus.

• Atomic weight: Sum of protons and neutrons.

Example Equation:

$\text{Atomic number} = \text{Number of protons}$

$\text{Atomic weight} = \text{Number of protons} + \text{Number of neutrons}$

Parts of a Cell

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure. This distinction is central to understanding cell biology.

• Prokaryotic cells: No nucleus, simple internal structure (e.g., bacteria, archaea).

• Eukaryotic cells: Nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

• Shared characteristics: Plasma membrane, cytoplasm, ribosomes, genetic material.

Organelles in Animal and Plant Cells

Cells contain specialized structures called organelles, each with specific functions. Some organelles are unique to plant or animal cells.

• Key organelles in both: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, plasma membrane, cytoskeleton.

• Unique to plant cells: Chloroplasts, cell wall, large central vacuole.

• Unique to animal cells: Lysosomes, centrioles.

Surface Area to Volume Ratio

Cells face challenges related to their size. The surface area to volume ratio affects the efficiency of transport and communication within the cell.

• Smaller cells: Higher ratio, more efficient exchange of materials.

• Larger cells: Lower ratio, less efficient, may require adaptations.

Cell Junctions

Cell junctions are structures that connect cells to one another, facilitating communication and structural integrity.

• Plant cell junctions: Plasmodesmata (channels for transport and communication).

• Animal cell junctions: Tight junctions, desmosomes, gap junctions (various functions in adhesion and signaling).

Endosymbiont Theory

The endosymbiont theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes that became incorporated into eukaryotic cells.

• Evidence: Double membranes, own DNA, similarities to prokaryotes.

Functions of Cell Organelles

Each organelle plays a specific role in cell function. Understanding these roles is essential for cell biology.

Organelle	Function
Extracellular matrix	Provides structural support and regulates cell behavior
Cell wall	Protects and supports plant cells
Vacuole	Stores nutrients, waste products, and maintains turgor pressure
Nucleus	Contains genetic material (DNA), controls cell activities
Nucleolus	Produces ribosomes
Endoplasmic reticulum (Smooth)	Lipid synthesis, detoxification
Endoplasmic reticulum (Rough)	Protein synthesis (with ribosomes)
Golgi apparatus	Modifies, sorts, and packages proteins and lipids
Lysosome	Digests cellular waste and foreign material
Centrosome	Organizes microtubules, important in cell division
Plasma membrane	Controls movement of substances in and out of cell
Chloroplast	Photosynthesis in plant cells
Mitochondria	Produces energy (ATP) through cellular respiration
Vesicle	Transports materials within the cell
Peroxisome	Breaks down fatty acids and detoxifies harmful substances
Cytoskeleton	Provides cell shape, movement, and internal organization
Cilia	Movement of cell or substances across cell surface
Flagella	Cell movement

• Cytoskeleton components: Microfilaments, microtubules (provide structure and movement).

• Chloroplast structures: Thylakoids, stroma, granum (involved in photosynthesis).

Example: The mitochondrion is often called the "powerhouse" of the cell because it generates ATP, the cell's energy currency.