Exam 4_Practice Test

  1. Embryonic Developmental Stages (in order):

    1. Fertilization: Union of male (sperm) and female (egg) gametes to form a diploid zygote. This activates the egg and initiates development.

    2. Cleavage: Rapid series of mitotic divisions without overall growth, converting the zygote into a multicellular embryo called a blastula, which is a hollow ball of cells.

    3. Gastrulation: Rearrangement of the blastula cells into a three-layered structure (gastrula) with ectoderm, mesoderm, and endoderm germ layers.

    4. Organogenesis: Formation and development of organs from the germ layers. Neural tube formation (neurulation) and limb development occur during this phase.

  2. Definitions:

    • Determination: A process by which a cell becomes committed to a specific developmental fate, even though it may not yet display specialized features.

    • Differentiation: The process in which a cell undergoes changes to become a specialized cell type (e.g., a neuron or muscle cell).

    • Morphogenesis: The biological process that causes an organism to develop its shape through coordinated cell growth, migration, and death.

    • Common Morphogen Factors: Include proteins like Bicoid, Sonic Hedgehog (Shh), Bone Morphogenetic Proteins (BMPs), Nodal, and Fibroblast Growth Factors (FGFs).

  3. Cell Potency and Examples:

    • Totipotent: Can develop into any cell type, including the placenta (e.g., a zygote).

    • Pluripotent: Can give rise to all cell types of the body but not extra-embryonic tissues (e.g., embryonic stem cells).

    • Multipotent: Can give rise to multiple, but limited, cell types (e.g., hematopoietic stem cells give rise to all blood cell types).

    • Unipotent: Can produce only one cell type, their own (e.g., muscle satellite cells).

  4. Polarity and Development:

    • Polarity: The establishment of spatial differences in the shape, structure, and function of cells and embryos.

    • Amphibians: Polarity is established after fertilization through cortical rotation, which redistributes cytoplasmic determinants and forms the gray crescent.

    • Drosophila: Polarity is established through maternal effect genes deposited in the egg that localize proteins like Bicoid (anterior) and Nanos (posterior).

  5. Bicoid and Nanos in Drosophila:

    • Bicoid: Acts as a transcription factor and morphogen, activating head-specific genes and repressing posterior genes.

    • Nanos: Acts primarily by inhibiting translation of hunchback mRNA in the posterior, allowing abdominal development.

  6. Genetic Terms:

    • Morphogen: A signaling molecule that spreads from a localized source and forms a concentration gradient, inducing different cell fates at different concentrations (e.g., Shh).

    • Transcription Factor: Proteins that bind to DNA to regulate the expression of genes.

    • Maternal Effect Genes: Genes whose products are placed in the egg by the mother and influence early development.

    • Gap Genes: Define broad regions of the embryo (e.g., Kruppel).

    • Pair Rule Genes: Define boundaries of individual segments (e.g., even-skipped).

    • Segment Polarity Genes: Define the anterior and posterior of each segment (e.g., engrailed).

  7. Hox Genes and Ubx:

    • Hox Genes: A subset of homeotic genes that determine the identity of body segments along the anterior-posterior axis.

    • Ubx (Ultrabithorax): A Hox gene that prevents the formation of wings in the third thoracic segment of Drosophila; thus, it plays a role in segment specification.

  8. Sonic Hedgehog (Shh):

    • Shh is a morphogen involved in patterning the neural tube, limbs, and somites. In the neural tube, it establishes the ventral side and promotes motor neuron formation.

  9. Induction:

    • A process in which one group of cells (the inducer) sends signals to influence the developmental fate of nearby cells (the responder), often through direct contact or secreted molecules.

  10. Segment Identity Genes:

  • Hox Genes: Specify segment identity across the animal kingdom and control the expression of downstream genes that determine morphological traits.

  1. Initiating Differential Gene Expression:

  • Through morphogen gradients, localized cytoplasmic determinants, cell signaling pathways, chromatin structure changes, and feedback mechanisms.

  1. Segregation of Cytoplasmic Determinants:

  • During early cleavage, specific proteins and RNAs are unequally distributed in daughter cells, leading to different gene expression profiles and developmental fates.

  1. Developmental Stages:

  • Cleavage: Rapid cell division forming blastula.

  • Zygote: A single-cell fertilized egg.

  • Gastrulation: Cell movements create three germ layers.

  1. Embryonic Tissue Layers and Their Derivatives:

  • Ectoderm: Epidermis, nervous system, sensory organs.

  • Mesoderm: Muscle, skeleton, circulatory system, kidneys.

  • Endoderm: Lining of the digestive tract, liver, pancreas, lungs.

  1. Protostome vs. Deuterostome:

  • Protostome: Mouth forms first, spiral cleavage, determinate development.

  • Deuterostome: Anus forms first, radial cleavage, indeterminate development (e.g., echinoderms, chordates).

  1. Cnidarian Features:

  • Radial Symmetry: Symmetry around a central axis.

  • Mesoglea: A gelatinous, non-cellular layer providing buoyancy.

  • Nerve Net: Diffuse, decentralized nervous system.

  • Myoepithelial Cells: Contractile cells functioning like muscle.

  • Examples: Jellyfish, sea anemones, corals, hydra.

  1. Amphibians:

  • Frogs, toads, salamanders, newts, caecilians.

  1. Chordate Key Structure:

  • Notochord: A flexible rod providing support; it helps in the development of the vertebral column and defines the primitive axis.

  1. Echinoderm Features:

  • Water Vascular System: Network of canals for locomotion, feeding, and gas exchange.

  • Tube Feet: Extensions used for movement and grasping surfaces.

  • Madreporite: Entry point for water into the vascular system.

  1. Thermoregulation:

  • Homeotherm (Endotherm): Maintains constant body temperature (e.g., Bear, Duck, Eagle, Mouse).

  • Poikilotherm (Ectotherm): Body temperature varies with environment (e.g., Alligator, Snake, Salamander, Turtle).

  1. Regulator vs. Conformer:

  • Regulator: Actively maintains internal conditions despite external changes.

  • Conformer: Internal conditions change with the external environment.

  1. Metabolic Needs:

  • 100 pygmy mice use more total energy than one rabbit due to higher collective surface area to volume ratio, leading to more heat loss and increased metabolic demand.

  1. Levels of Organization:

  • Cell: Basic unit of life.

  • Tissue: Group of similar cells with a common function.

  • Organ: Structure composed of different tissues working together.

  • Organ System: Group of organs coordinating functions (e.g., digestive system).

  1. Four Major Tissue Types:

  • Epithelial: Covers surfaces; protection, absorption, secretion.

  • Connective: Supports and binds (e.g., blood, bone, cartilage).

  • Muscle: Movement (skeletal, smooth, cardiac).

  • Nervous: Transmits electrical impulses (neurons, glia).

  1. Alimentary Canal:

  • A digestive tube with two openings (mouth and anus).

  • Compartments: Mouth (mechanical breakdown), esophagus (transport), stomach (chemical digestion), small intestine (nutrient absorption), large intestine (water absorption), anus (elimination).

  1. Mammalian Characteristics:

  • Hair/fur, mammary glands, three middle ear bones, diaphragm, endothermy.

  1. Negative Feedback:

  • Mechanism to maintain homeostasis by reducing the effect of a stimulus.

  • Variable: Condition being regulated.

  • Sensor: Detects changes.

  • Control Center: Processes information (e.g., brain).

  • Effector: Responds to restore balance (e.g., sweat glands).

  1. Positive Feedback:

  • Reinforces the stimulus, leading to an even greater response.

  • Example: Oxytocin release during labor increases uterine contractions.

  1. Open vs. Closed Circulatory System:

  • Open: Hemolymph bathes organs directly; heart pumps hemolymph into body cavities (e.g., insects, arthropods).

  • Closed: Blood confined to vessels (e.g., vertebrates).

  1. Gas Exchange Systems:

  • Co-current: Blood and water flow same direction; less efficient.

  • Countercurrent: Opposite flows; maintains concentration gradient; used in fish gills.

  1. Fick's Law and Gas Exchange Optimization:

  • Increased surface area, reduced diffusion distance, and maintaining high concentration gradients enhance diffusion.

  • Examples: Gill filaments, alveoli in lungs, active ventilation.

  1. Tracheal vs. Lung Systems:

  • Tracheal: Air-filled tubes transport oxygen directly (insects).

  • Lung-Based: Air reaches alveoli where gas exchange with blood occurs.

  • Avian System: Unidirectional airflow with air sacs; maximizes oxygen extraction; most efficient respiratory system.

  1. Amniotic Egg Membranes:

  • Amnion: Protects embryo in fluid.

  • Chorion: Gas exchange.

  • Allantois: Waste storage.

  • Yolk Sac: Provides nutrients.