Foundations of Biology: Life, Cells, Chemistry, and Cell Division

Properties of Life and Biologic'al Organization

Common Properties of Life

All living organisms share a set of fundamental properties that distinguish them from non-living matter.l

• Cellular Organization: All life is composed of one or more cells, which are the basic structural and functional units of life.

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

• Homeostasis: The ability to maintain a stable internal environment.

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

• Reproduction: The ability to produce new individuals, either sexually or asexually.

• Response to Stimuli: Organisms can sense and respond to changes in their environment.

• Evolutionary Adaptation: Populations change over generations through natural selection.

Cells as the Unit of Life: Cells are considered the structural and functional unit of life because all vital processes occur within them, and all organisms are composed of cells.

Three Domains of Life

Life is classified into three domains based on genetic and cellular differences:

• Bacteria: Prokaryotic, unicellular organisms with no membrane-bound nucleus.

• Archaea: Prokaryotic, often extremophiles, genetically distinct from bacteria.

• Eukarya: Eukaryotic organisms, including animals, plants, fungi, and protists, with membrane-bound organelles.

Levels of Biological Organization

Biological systems are organized in a hierarchy from smallest to largest:

• Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Emergent Properties: New properties arise at each level of organization that are not present at the preceding level (e.g., consciousness in the brain).

Ecological Groups

• Population: Group of individuals of the same species in an area.

• Community: All populations of different species in an area.

• Ecosystem: Community plus the non-living environment.

• Biosphere: All ecosystems on Earth.

Flow of Nutrients and Energy: Energy flows one-way (sun → producers → consumers), while nutrients cycle within ecosystems.

Evolution and Classification

Evolutionary Relationships

Modern classification reflects evolutionary relationships, grouping organisms by common ancestry.

• Natural Selection: The process by which organisms with advantageous traits survive and reproduce more successfully, leading to adaptation.

• Products of Natural Selection: Adaptations and increased fitness in populations.

Scientific Inquiry and the Scientific Method

Scientific Inquiry

Science uses systematic methods to ask and answer questions about the natural world.

• Steps in the Scientific Method:

  1. Observation

  2. Question

  3. Hypothesis

  4. Prediction

  5. Experiment

  6. Analysis

  7. Conclusion

• Guess vs. Prediction vs. Hypothesis: A guess is an untested idea; a prediction is a specific expected outcome; a hypothesis is a testable explanation.

• Test Group: The group exposed to the experimental variable.

• Control Group: The group not exposed to the variable, used for comparison.

• Observation and Experimentation: Observations lead to hypotheses, which are tested by experiments.

Cell Division and Genetics

Asexual vs. Sexual Reproduction

• Asexual Reproduction: Offspring are genetically identical to the parent (e.g., binary fission).

• Sexual Reproduction: Offspring inherit a combination of genes from two parents, increasing genetic diversity.

Chromosomes and Genes

• Chromosomes: Structures made of DNA and proteins that carry genetic information.

• Genes: Segments of DNA that code for proteins.

• Autosomes: Non-sex chromosomes.

• Sex Chromosomes: Chromosomes that determine sex (e.g., X and Y in humans).

• Diploid (2n): Cells with two sets of chromosomes.

• Haploid (n): Cells with one set of chromosomes (e.g., gametes).

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

• Sister Chromatids: Identical copies of a chromosome joined at the centromere.

Fertilization and Chromosomal Contributions

• Each parent contributes one set of chromosomes to the offspring during fertilization, restoring diploidy.

Cell Cycle and Mitosis

• Phases of the Cell Cycle: Interphase (G1, S, G2) and M phase (mitosis and cytokinesis).

• Mitosis Phases: Prophase, Metaphase, Anaphase, Telophase.

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Meiosis

• Reduces chromosome number by half, producing haploid gametes.

• Allows for crossing over and independent assortment, increasing genetic diversity.

Chromosomal Abnormalities

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down, Turner, Klinefelter syndromes).

• Karyotypes: Visual displays of chromosomes used to diagnose chromosomal abnormalities.

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: No nucleus, smaller, simpler (e.g., bacteria, archaea).

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

• Surface-to-Volume Ratio: Limits cell size; as cells grow, volume increases faster than surface area, affecting nutrient exchange.

Microscopy

• Light Microscopy: Uses light to view cells; lower resolution.

• Scanning Electron Microscopy (SEM): 3D images of cell surfaces.

• Transmission Electron Microscopy (TEM): Detailed images of internal cell structures.

Cell Organelles and Structures

• Nucleus: Contains genetic material (DNA).

• Nucleolus: Site of ribosome synthesis.

• Endoplasmic Reticulum (ER): Protein and lipid synthesis (rough and smooth ER).

• Golgi Complex: Modifies, sorts, and packages proteins.

• Lysosomes: Digestive organelles.

• Mitochondria: Site of cellular respiration and ATP production.

Cytoskeleton

• Microtubules: Hollow tubes, cell shape, and transport.

• Microfilaments: Thin fibers, cell movement, and shape.

• Intermediate Filaments: Provide mechanical support.

Plasma Membrane and Transport

• Structure: Phospholipid bilayer with embedded proteins.

• Diffusion: Movement of molecules from high to low concentration.

• Facilitated Diffusion: Transport via membrane proteins for larger or charged molecules.

• Active Transport: Movement against concentration gradient, requires energy (ATP).

• Primary vs. Secondary Active Transport: Primary uses ATP directly; secondary uses energy from another gradient.

• Sodium-Potassium Pump: Maintains cell isotonicity and electrochemical gradients.

Chemistry of Life

Atoms and Chemical Bonds

• Atoms: Composed of protons (+), neutrons (0), and electrons (-).

• Valence Electrons: Electrons in the outer shell, important for bonding.

• Covalent Bonds: Atoms share electrons; can be nonpolar (equal sharing) or polar (unequal sharing).

• Ionic Bonds: Transfer of electrons from one atom to another, forming ions.

Properties of Water

• Polarity: Water is a polar molecule due to unequal sharing of electrons.

• Hydrogen Bonds: Weak attractions between water molecules, responsible for cohesion and high specific heat.

• Hydrophilic vs. Hydrophobic: Hydrophilic substances interact with water; hydrophobic do not.

• pH Scale: Measures hydrogen ion concentration; acidic solutions have more H+, basic have less.

Biological Macromolecules

• Proteins: Polymers of amino acids joined by peptide bonds. Each amino acid has an amino group, carboxyl group, R group, and alpha carbon.

• Nucleic Acids: DNA and RNA, composed of nucleotides (5-carbon sugar, nitrogenous base, phosphate group). DNA and RNA differ in sugar and bases (purines: A, G; pyrimidines: C, T, U).

• Carbohydrates: Simple sugars (monosaccharides) and complex carbohydrates (polysaccharides).

• Lipids: Hydrophobic molecules, including fats and phospholipids. Phospholipids have hydrophilic heads and hydrophobic tails, forming cell membranes.

Cellular Respiration and Enzymes

Energy and Thermodynamics

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy.

• Chemical Energy: Energy stored in chemical bonds.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Energy transformations increase entropy (disorder).

Enzymes

• Structure: Proteins with an active site for substrate binding.

• Function: Catalyze reactions by lowering activation energy.

• Inhibition: Competitive inhibitors bind active site; non-competitive inhibitors bind elsewhere.

Cellular Respiration

• Overall Reaction: Breakdown of glucose in the presence of oxygen to produce CO2, H2O, and ATP.

• ATP Generation: Substrate-level phosphorylation (direct transfer of phosphate) vs. oxidative phosphorylation (via electron transport chain).

• Glycolysis: Ten-step pathway in cytoplasm, breaks glucose into pyruvate.

• Pyruvate Oxidation: Occurs in mitochondria, links glycolysis to citric acid cycle.

• Citric Acid Cycle: In mitochondrial matrix, completes glucose breakdown.

• Electron Transport Chain: Uses electrons from NADH and FADH2 to pump protons, creating a gradient.

• Proton Gradient: Stores potential energy, used by ATP synthase to generate ATP.

Example Table: Comparison of Cell Division Processes

Process	Purpose	Chromosome Number in Daughter Cells	Genetic Variation
Mitosis	Growth, repair, asexual reproduction	Diploid (2n)	No
Meiosis	Production of gametes	Haploid (n)	Yes (crossing over, independent assortment)

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard biology curricula.