BIO 311D Exam 3 Study Guide: Homeostasis, Nutrition, Transport, and Response in Animals and Plants

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Homeostasis and Hormonal Regulation

Concept of Homeostasis and Feedback Mechanisms

Homeostasis is the maintenance of a stable internal environment in an organism, despite external fluctuations. This is achieved through feedback mechanisms that detect changes and initiate responses to restore balance.

Negative Feedback: A control system where a change in a physiological variable triggers a response that counteracts the initial change, restoring the variable to its set point.
Components: Detection system (sensor), set-point (desired value), and effectors (organs/tissues that enact change).
Example: Regulation of blood glucose by insulin and glucagon.
Positive Feedback: Amplifies changes rather than restoring them; does not contribute to homeostasis (e.g., childbirth contractions).

Additional info: Positive feedback is useful for processes that need to be rapidly completed, not for maintaining stability.

Endocrine and Nervous System Comparison

Signal Type: Endocrine uses hormones (chemical), nervous uses electrical impulses and neurotransmitters.
Transmission: Endocrine signals travel via blood; nervous signals travel along neurons.
Speed: Nervous system is faster; endocrine is slower but longer-lasting.
Duration: Endocrine effects last longer; nervous effects are brief.
Response: Endocrine is widespread; nervous is targeted and specific.

Endocrine Signaling vs. Neuron Signaling

Endocrine Cell: Releases hormones into blood to reach distant targets.
Neuron: Sends electrical signals and releases neurotransmitters at synapses.
Neuroendocrine Cell: Receives neural input and releases hormones into blood (e.g., hypothalamic cells).

Neuroendocrine System: Integrates neural and endocrine functions (e.g., hypothalamus-pituitary axis).

Hormones: Types and Mechanisms

Hormones: Chemical messengers secreted by endocrine glands, affecting distant target cells.
Peptide Hormones: Water-soluble, cannot cross lipid bilayer; bind to cell surface receptors and activate second messengers (e.g., cAMP).
Steroid Hormones: Lipid-soluble, cross cell membrane; bind to intracellular receptors and regulate gene expression.

Downstream Pathways: Peptide hormones activate signaling cascades; steroid hormones alter transcription directly.

Tropic vs. Non-Tropic Hormones

Tropic Hormones: Target other endocrine glands (e.g., TSH stimulates thyroid gland).
Non-Tropic Hormones: Directly affect target tissues (e.g., insulin acts on liver, muscle, fat).

Hypothalamus and Pituitary Gland

Hypothalamus: Integrates neural and endocrine signals; produces releasing/inhibiting hormones.
Pituitary Gland: Posterior lobe releases oxytocin and antidiuretic hormone (ADH/vasopressin); anterior lobe releases tropic hormones.
Oxytocin: Stimulates uterine contractions and milk ejection.
ADH: Promotes water reabsorption in kidneys.

Main Human Endocrine Glands and Hormones

Gland	Hormone	Main Function
Pancreas	Insulin, Glucagon	Regulate blood glucose
Adrenal Gland	Epinephrine, Cortisol	Stress response, metabolism
Thyroid	Thyroxine (T4), Triiodothyronine (T3)	Regulate metabolism
Pituitary	Growth hormone, TSH, ACTH	Growth, stimulate other glands
Ovaries/Testes	Estrogen, Testosterone	Reproduction

Adrenal Gland and Stress Response

Epinephrine (Adrenaline): Increases heart rate, blood pressure, and energy supply (fight or flight).
Cortisol: Increases glucose availability, suppresses non-essential functions during stress.

Pancreatic Hormones: Insulin and Glucagon

Insulin: Lowers blood glucose by promoting uptake and storage.
Glucagon: Raises blood glucose by stimulating glycogen breakdown.

Diabetes Mellitus: Type 1 (autoimmune destruction of beta cells), Type 2 (insulin resistance).

Feedback Loops

Negative Feedback: Restores preexisting state (e.g., blood sugar regulation).
Positive Feedback: Amplifies change (e.g., childbirth, blood clotting).

Nutrition, Transport, and Excretion in Animals

Nutritional Modes

Photoautotroph: Uses light and CO2 (e.g., plants).
Chemoautotroph: Uses inorganic chemicals and CO2 (e.g., some bacteria).
Photoheterotroph: Uses light and organic compounds (e.g., some prokaryotes).
Chemoheterotroph: Uses organic compounds for energy and carbon (e.g., animals).

Essential Nutrients in Animal Diets

Amino acids
Fatty acids
Vitamins
Minerals

Stages of Food Processing

Ingestion
Digestion
Absorption
Elimination

Mammalian Digestive System

Main Organs: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.
Accessory Glands: Salivary glands, liver, gallbladder, pancreas.

Chemical Digestion of Nutrients

Carbohydrates: Amylase breaks down starches.
Proteins: Pepsin and other proteases.
Nucleic Acids: Nucleases.
Fats: Lipases, bile emulsifies fats.

Fat Digestion and Absorption

Bile from liver/gallbladder emulsifies fats.
Lipases break down fats into fatty acids and monoglycerides.
Absorbed into intestinal cells, reassembled, and transported as chylomicrons.

Large Intestine Functions

Water absorption
Formation of feces
Houses microbiome

Accessory Glands and Duodenum

Liver: Produces bile.
Gallbladder: Stores and releases bile.
Pancreas: Secretes digestive enzymes and bicarbonate.
All connect to duodenum (first part of small intestine).

Digestive System Adaptations

Teeth: Dental adaptations for diet (e.g., carnivores vs. herbivores).
Stomach/Intestine: Length and complexity vary with diet.
Mutualistic Microbiome: Aids in digestion (e.g., cellulose breakdown in herbivores).
Ruminants: Specialized stomach chambers for fermenting plant material (e.g., cows).

Osmoregulation and Excretion

Freshwater Fish: Gain water, excrete dilute urine.
Marine Fish: Lose water, drink seawater, excrete concentrated urine.
Excretory Steps: Filtration, reabsorption, secretion, excretion.
Organs: Kidney (filters blood), nephron (functional unit), urinary bladder (stores urine), glomerulus (capillary network for filtration).
Water Intoxication (Hyponatremia): Excess water dilutes sodium, dangerous for nerve/muscle function.

Circulatory and Respiratory Systems

Open Circulatory System: Hemolymph bathes organs directly (e.g., insects).
Closed Circulatory System: Blood confined to vessels (e.g., vertebrates).
Respiratory Surfaces: Skin, gills, tracheae, lungs; adapted for efficient gas exchange.
Alveoli: Tiny sacs in mammalian lungs for gas exchange; large surface area.
Single vs. Double Circulation: Single (fish), blood passes through heart once; double (mammals), twice per circuit.
Countercurrent Exchange: Maximizes gas transfer efficiency (e.g., fish gills).
Negative Pressure Breathing: Air drawn in by expanding thoracic cavity (mammals).
Positive Pressure Breathing: Air pushed into lungs (amphibians).

Transport and Nutrition in Plants

Adaptations for Resource Acquisition

Roots: Absorb water and minerals
Leaves: Capture light, exchange gases.
Mutualisms: Mycorrhizae (fungi), nitrogen-fixing bacteria (e.g., Rhizobium).

Transport Routes in Plants

Route	Description
Apoplast	Through cell walls and intercellular spaces
Symplast	Through cytoplasm via plasmodesmata
Transmembrane	Across cell membranes and cytoplasm

Casparian Strip

Waxy barrier in endodermal cells of roots.
Prevents uncontrolled movement of substances into vascular tissue.

Soil Bacteria and Plant Nutrition

Nitrogen-Fixing Bacteria: Convert atmospheric N2 to ammonia (e.g., Rhizobium in root nodules).
Nitrifying Bacteria: Convert ammonia to nitrate, usable by plants.

Unusual Plant Nutritional Adaptations

Epiphytes: Grow on other plants, absorb water/nutrients from air.
Parasitic Plants: Obtain nutrients from host plants.
Carnivorous Plants: Trap and digest insects for nutrients.

Mycorrhizae

Function: Fungi that enhance water and nutrient uptake for plants.
Types: Arbuscular (penetrate root cells), Ectomycorrhizae (surround root cells).

Water and Sugar Transport

Transpirational Pull: Evaporation from leaves pulls water up xylem.
Root Pressure: Osmotic pressure pushes water up from roots.
Pressure Flow (Bulk Flow): Sugars move from source (leaf) to sink (root/fruit) via phloem, driven by pressure gradients.

Stomata Structure and Function

Stomata are pores in leaves, flanked by guard cells.
Regulate gas exchange and water loss.
Stomatal density affects transpiration rate.

Mechanisms of Stomatal Opening/Closing

Guard cells change shape in response to light, CO2, and water status.
Open in light (for photosynthesis), close in drought (to conserve water).

Detection and Response to Environmental Stimuli

Animal Nervous System Structure and Function

Neuron Structure: Dendrites (input), cell body, axon (output), synaptic terminals.
Types of Neurons: Sensory, interneuron, motor neuron.
Information Flow: Sensory input → Integration → Motor output.

Action Potentials and Signal Transmission

Membrane Potential: Voltage difference across neuron membrane due to ion gradients.
Resting Potential: Typically -70 mV; maintained by Na+/K+ pumps.
Action Potential: Rapid depolarization and repolarization due to voltage-gated ion channels.
Propagation: Action potential travels as a wave; saltatory conduction in myelinated axons is faster than continuous conduction in unmyelinated axons.
All-or-None Response: Action potential occurs fully or not at all, depending on threshold.

Muscle Contraction and Neuromuscular Integration

Sarcomere: Functional unit of muscle; contains Z lines, M line, thin (actin) and thick (myosin) filaments.
Sliding Filament Model: Myosin heads pull actin filaments, shortening sarcomere.
Calcium Role: Binds to troponin, moves tropomyosin, exposes binding sites for myosin.
Neuromuscular Junction: Motor neuron releases neurotransmitter (acetylcholine), triggers muscle action potential.

Immune System Overview

Innate Immunity: Non-specific, immediate defense (e.g., barriers, phagocytes).
Adaptive Immunity: Specific, slower, memory (B cells, T cells).
Inflammatory Response: Histamine release, increased blood flow, phagocyte recruitment.
B Cells: Produce antibodies, mediate humoral immunity.
T Cells: Kill infected cells, regulate immune response.
Antigen: Foreign molecule recognized by immune system.
Antibody: Protein that binds antigen, facilitates destruction.
Vaccination: Stimulates adaptive immunity, creates immunological memory.

Plant Responses to Stimuli

Plant Sensory and Response Mechanisms

Phototropism: Growth toward light, mediated by auxin.
Gravitropism: Growth in response to gravity, involves statoliths in root cap cells.
Photoperiodism: Response to day length, regulates flowering and other processes.
Thigmomorphogenesis: Growth response to touch (e.g., vine tendrils coiling).

Key Plant Hormones and Terms

Auxin: Regulates cell elongation, phototropism, and gravitropism.
Statoliths: Starch-filled organelles that help sense gravity.
Thigmotropism: Directional growth in response to touch.

Key Terms and Concepts

Hormone, hypothalamus, receptor, glucagon, insulin, cAMP, oxytocin, antidiuretic hormone (ADH/vasopressin), epinephrine
Peristalsis, chyme, amylase, pepsin, villi/microvilli, hepatic portal vein, triglycerides, sphincter, chylomicrons, microbiome, bile, secretin, ruminant, rumen, osmolarity, kidney, nephron, urinary bladder, glomerulus, tracheal system, alveolus, hemoglobin
Plasmodesma, osmosis, aquaporins, plasmolysis, flaccid, bulk flow, tracheids, vessel elements, rhizosphere, mycorrhizae, arbuscular mycorrhizae, ectomycorrhizae, Rhizobium, nodule, endophyte, epiphyte, nitrification, nitrogenase, transpiration, turgor pressure, stoma, xylem sap, phloem sap, xerophytes, halophytes, CAM plant, sugar source, sugar sink, guttation
Neuron, nerve, dendrites, cell body, axon, glia, ganglia, brain, synapse, synaptic cleft, axon hillock, neurotransmitters, astrocytes, Schwann cells, myelin sheath, node of Ranvier, saltatory conduction, gated ion channel, ion leak channel, ion pump, hyperpolarization, depolarization, CNS, PNS, sensory neuron, interneuron, motor neuron, mechanoreceptors, electromagnetic receptors, thermoreceptors, pain receptors, chemoreceptors, myofibrils, sarcomeres, myosin, actin filament, thick filament, troponin, calcium ion, tropomyosin, pathogens, innate immunity, adaptive immunity, lymphocytes, phagocytosis, inflammation, T cells, B cells, antigen, antibody, immunoglobulin, cytotoxic T cells, helper T cells, neutrophils, macrophages, epitope, immunological memory, histamine
Plant hormones (auxin), photomorphogenesis, phototropism, photoperiodism, gravitropism, statoliths, thigmomorphogenesis, thigmotropism