Exam Study Guide

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1. The Five Basic Types of Taste

Tastes:

  • Sweet – from sugars and alcohols; signals energy (carbohydrates).

  • Sour – from acids (like citric acid); warns of spoilage.

  • Salty – from sodium ions; essential for fluid balance.

  • Bitter – from alkaloids (like caffeine or quinine); warns of toxins.

  • Umami – from glutamate and amino acids; signals protein-rich foods.

Tip: Remember S.S.S.B.U. → Sweet, Sour, Salty, Bitter, Umami

2. Chemicals for Each Taste Type

  • Sweet: Sugars (glucose, fructose), some amino acids.

  • Sour: Hydrogen ions (H⁺).

  • Salty: Sodium (Na⁺), potassium (K⁺) ions.

  • Bitter: Plant alkaloids, caffeine, quinine.

  • Umami: Glutamate, inosinate, guanylate.

3. Relation to Human Needs

  • Sweet → energy source.

  • Salty → maintains electrolyte balance.

  • Sour → detects spoiled or unripe foods.

  • Bitter → avoids toxins.

  • Umami → promotes protein intake for tissue growth.

4. Receptors for Taste Detection

  • Taste receptor cells are located in taste buds (on the tongue and soft palate).

  • GPCRs (G-protein coupled receptors) detect sweet, bitter, and umami tastes.

  • Ion channels detect salty and sour tastes.

5. Taste Signal Pathway

  1. The chemical binds to the receptor on the tongue.

  2. Signal transduction occurs (via GPCRs or ion channels).

  3. Neurotransmitter release triggers a nerve impulse.

  4. Signal travels through cranial nerves (VII - Facial, IX - Glossopharyngeal, X - Vagus).

  5. Medulla oblongata → Thalamus → Gustatory cortex in the brain.

6. Sketch: Taste Signal Pathway

(You’ll need to draw this for the exam!)
Include:

  • Taste buds

  • Sensory neurons

  • Cranial nerves VII, IX, X

  • Medulla oblongata

  • Thalamus

  • Gustatory cortex

7. Brain and Emotional Memory

  • The amygdala and hippocampus process emotional and memory responses.

  • Taste signals that reach these areas trigger emotional memories related to food.

8. Taste & Smell Memory Formation

  • Taste and smell memories form early in life (infancy and childhood) — they are linked to strong emotional experiences.

9. Verbal Cue Memory Formation

  • Verbal memory develops later in childhood, as language skills form (around age 5+).

  • This explains why smell memories can feel stronger or more emotional than verbal ones.

10. Detection of Fragrance Chemicals

  • Olfactory receptors in the nasal cavity detect volatile (airborne) chemicals.

  • Unlike taste, odor molecules don’t dissolve in saliva — they dissolve in mucus in the nasal epithelium.

11. Sensory Organ for Smell

  • The olfactory epithelium (in the nasal cavity) is the main sensory organ for smell.

  • Signals travel via the olfactory bulb → olfactory cortex → limbic system.

12. Human vs. Canine Smell Comparison

Feature

Human

Canine

Olfactory receptors

~5 million

~300 million

Olfactory bulb size

Small

Large (40x greater relative size)

Sensitivity

Moderate

Extremely high

Tracking ability

Poor

Excellent (can detect parts per trillion)

13. Functional Groups in Vanillin

Vanillin contains:

  • Aldehyde group (-CHO)

  • Hydroxyl group (-OH)

  • Methoxyl group (-OCH₃)
    (Be ready to identify or label these on a chemical diagram.)

14. Drawing Fragrance Compounds

Be able to sketch or recognize:

  • Ethyl acetate: C4H8O2 (fruity smell)

  • Limonene: C₁₀H₁₆ (citrus smell, cyclic structure)

  • Citral: C₁₀H₁₆O (lemon scent, aldehyde group)

Tip: Practice with simple line structures — focus on functional groups and ring vs. chain shapes.

Ethyl Acetate: C4H8O2 Limonine: C10H16Citral: C10H16Oe