🧬

Biology Core Concepts Overview

Jun 10, 2025

Overview

This lecture provides a comprehensive, high-yield review of major biology concepts, focusing on core cellular, physiological, and genetic principles relevant for medical and biology exams.

Cell Structure & Function

  • Cell theory: all living things are made of cells; cells arise from pre-existing cells; genetic info is DNA.
  • Prokaryotes (e.g., bacteria): no true nucleus, circular naked DNA; eukaryotes (e.g., humans): true nucleus, linear protein-bound DNA, membrane-bound organelles.
  • Plasma membrane is a phospholipid bilayer with hydrophilic heads and hydrophobic tails.
  • Organelles: mitochondria (ATP), lysosome (digestion), ER (Rough—protein synthesis, Smooth—lipid synthesis & detox), Golgi (sorts/delivers), peroxisome (fatty acid breakdown).

Cell Cycle & Division

  • Cell cycle: G0 (rest), G1 (growth), S (DNA synthesis/replication), G2 (growth), M (mitosis/meiosis).
  • Checkpoints: G1/S (p53, RB), G2/M, metaphase—defects can cause cancer.
  • Mitosis: 2 identical 2N cells; meiosis: 4 unique N cells (gametes).

Tissues & Organ Systems Overview

  • Four tissue types: epithelial (cover/line surfaces), connective (support—bone, blood, fat), muscle, nerve.
  • Parenchyma: functional cells; stroma: supportive framework (usually connective tissue).

Genetics & Reproduction

  • Male gamete: sperm; female gamete: ovum; meiosis forms gametes.
  • Female meiosis arrests: prophase I (birth-puberty), metaphase II (ovulation—fertilization completes meiosis II).
  • Sex determination: XX (female), XY (male).
  • Mendel’s laws: Segregation (anaphase I), Independent Assortment (prophase I/crossing over).
  • Hardy-Weinberg equations for population genetics.

Embryology & Fetal Circulation

  • Fertilization: sperm + secondary oocyte arrested in metaphase II; becomes zygote (46 chromosomes).
  • Cleavage → blastula → gastrulation (trilaminar embryo: ectoderm, mesoderm, endoderm).
  • Fetal circulation includes unique shunts (ductus venosus, foramen ovale, ductus arteriosus) that close after birth.

Nervous System

  • Central (CNS: brain, spinal cord) vs. Peripheral (PNS: cranial/spinal nerves).
  • Somatic (voluntary) vs. autonomic (involuntary: sympathetic/parasympathetic); enteric (gut).
  • Myelin: oligodendrocytes (CNS), Schwann cells (PNS); increases conduction speed (saltatory).
  • Action potential: sodium influx (depolarization), potassium efflux (repolarization).

Endocrine System

  • Hypothalamus-pituitary axis controls thyroid, adrenal cortex, and gonads.
  • Anterior pituitary hormones: TSH (thyroid), ACTH (adrenal), FSH/LH (gonads).
  • ADH/oxytocin produced in hypothalamus, released by posterior pituitary.
  • Insulin (anabolic—builds), Glucagon (catabolic—breaks down).

Respiratory System

  • Conducting vs. respiratory zones; pleura (visceral/parietal) surrounds lungs.
  • Boyle’s law: volume↑ = pressure↓, drives breathing.
  • Surfactant (type II pneumocytes) reduces lung surface tension.
  • Lungs excrete volatile acids (COâ‚‚); kidneys excrete fixed acids.

Cardiovascular System

  • Heart valves: all tricuspid except mitral.
  • Cardiac output = heart rate Ă— stroke volume.
  • Blood vessels: arteries, veins, capillaries (exchange—hydrostatic/oncotic pressures).
  • Blood composition: plasma (albumin, globulins), cells (RBCs, WBCs, platelets).

Immune System & Blood

  • Innate immunity: non-specific (macrophages, neutrophils).
  • Adaptive immunity: B (antibodies), T (cellular).
  • Lymphatic system: bone marrow (B cell maturation), thymus (T), lymph nodes (immune response sites).
  • Primary hemostasis (platelets), secondary (coagulation factors).

Digestive, Renal, & Homeostasis

  • Digestive: mechanical/chemical breakdown, absorption, excretion; liver and pancreas are key accessory organs.
  • Kidney: filtration (glomerulus), reabsorption, secretion, excretion; nephron is functional unit.
  • Skin: barrier, thermoregulation; epidermis (ectoderm), dermis (mesoderm).

Musculoskeletal System

  • Three muscle types: skeletal (voluntary), cardiac, smooth (involuntary).
  • Contraction: actin-myosin sliding, requires ATP and calcium.
  • Bone: osteoblasts build; osteoclasts resorb; type I collagen in bone, type II in cartilage.

Evolution & Genetics

  • Mutations: point (missense, nonsense), chromosomal.
  • Natural selection drives evolution; reproductive isolation can be pre- or post-zygotic.

Key Terms & Definitions

  • Prokaryote — cell without a nucleus or membrane-bound organelles.
  • Eukaryote — cell with a nucleus and membrane-bound organelles.
  • Mitosis — division producing two identical somatic cells.
  • Meiosis — division producing four unique gametes.
  • Parenchyma — functional tissue of an organ.
  • Stroma — supportive tissue of an organ.
  • Action potential — rapid change in membrane potential for nerve signaling.
  • Hardy-Weinberg Equilibrium — predicts population genotype frequencies under ideal conditions.
  • Surfactant — substance reducing alveolar surface tension.
  • Osteoblast — bone-forming cell.
  • Osteoclast — bone-resorbing cell.

Action Items / Next Steps

  • Review diagrams of cell organelles, mitosis/meiosis, embryonic development, and heart/lung circulation.
  • Memorize hormone actions, blood cell functions, and key genetic principles.
  • Practice Hardy-Weinberg and Punnett square problems.
  • Reinforce tissue types and main differences between prokaryotic and eukaryotic cells.

Full transcript