2.8: Applied Thinking Self - Assessment

Challenge Yourself

1. Critical thinking is essential in a time of endless information and AI, helping you move from passive memorizing to actively making sense of what you learn.
2. Use the short‑essay, case‑based prompts at the end of each chapter to check and deepen your understanding:
3. Extended response questions are assessment items that require students to construct written answers of substantial length - typically several sentences to multiple paragraphs - rather than selecting from predefined options. They represent a form of constructed response assessment designed to measure complex, higher-order thinking skills.
4. The following prompts ask you to apply chemistry concepts to biological contexts, justify your reasoning with mechanisms and data, and communicate clearly.
5. What your response must include:
   • Direct answer (1–2 sentences): State your conclusion up front.
   • Mechanistic explanation (4–8 sentences): Explain the “how/why” at the molecular level, linking cause to effect.
   • Use correct concepts (e.g., electronegativity → polarity → H-bonding → emergent property).
   • Diagram or equation (optional but encouraged).
   • Use precise terms and units; define symbols on first use.

1. Most of the mass of a human body and of typical foods comes from just four elements: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
   1. For each element (C, H, O, N), name one major type of biological molecule (carbohydrate, lipid, protein, nucleic acid) or metabolic pathway (e.g., cellular respiration, ATP production) that depends strongly on it.
   2. For each example you chose, explain specifically how that element’s chemical properties (e.g., ability to form 4 bonds, high electronegativity, role in functional groups like amino or carboxyl) support that molecule’s structure or function.
2. Oxygen’s atomic number is 8, and it has three common stable isotopes: ^¹⁶O, ^¹⁷O, and ^¹⁸O.
3. Work with both of the following:
   1. For each isotope (^¹⁶O, ^¹⁷O, ^¹⁸O), state the number of protons and neutrons in the nucleus of a neutral atom. Show how you calculate the number of neutrons from the mass number and atomic number.
   2. All three isotopes of oxygen participate in the same chemical reactions in the body (for example, in water and in cellular respiration). Explain why differences in neutron number do not change their basic chemical behavior, and identify which subatomic particle(s) matter most for chemical properties.
4. Magnesium atoms each have 12 electrons and are usually found in the body as the ion Mg²⁺.
   1. Describe or draw the electron configuration of a neutral Mg atom and of Mg²⁺. Use the idea of valence electrons and stable electron shells to explain why magnesium tends to lose two electrons rather than gain six.
   2. Explain how Mg’s position in the periodic table (group and period) helps you predict that it will form a 2⁺ ion.
   3. Choose one physiological role of Mg²⁺ (for example, as a cofactor for ATP-using enzymes or in bone mineralization). Describe how the charged ionic form Mg²⁺ is important for this role, and predict what might happen at the tissue or organ level if Mg²⁺ levels in the body become very low.
5. Methane (CH₄) is very common in nature and is produced by some gut bacteria in humans.
   1. What kind of bonds form between carbon and hydrogen in CH₄ (ionic or covalent, single or double)? Use electronegativity to explain why these C–H bonds are considered nonpolar.
   2. Describe the 3D shape of a CH₄ molecule and explain how this shape affects whether the molecule as a whole is polar or nonpolar.
   3. Many lipids (like fatty acids) are made mostly of C–H bonds. Using your answers above, explain why these hydrocarbons are hydrophobic and how this affects: their behavior in water-based body fluids (like blood) and their tendency to be stored in adipose (fat) tissue rather than dissolved in cytosol.
6. After making a salad with olive oil, rinsing the bowl with plain water leaves a greasy film, but adding dish soap removes it.
   1. Use the concept of polarity to explain why water alone cannot easily dissolve or remove the oil from the bowl.
   2. Describe the basic structure of a soap or detergent molecule (a “water-loving” head and an “oil-loving” tail).
   3. Explain how this structure allows soap molecules to attach to oil and water at the same time, form micelles, and help wash the oil off the bowl.
7. Classify chemical reactions relevant to physiology. Look at this reaction: HCl + NaHCO₃ → NaCl + H₂CO₃ → CO₂ + H₂O (First, hydrochloric acid reacts with sodium bicarbonate. Then carbonic acid breaks down into carbon dioxide and water.)
   1. Look only at the first part: HCl + NaHCO₃ → NaCl + H₂CO₃:
      • What type of reaction is this? (For example: synthesis, decomposition, exchange/double replacement, or acid–base neutralization.). Explain your answer in simple words. What is swapping places in this reaction?
   2. Now look at the second part: H₂CO₃ → CO₂ + H₂O
      • What type of reaction is this? (For example: decomposition or synthesis.) Explain what is happening to H₂CO₃ in this step.
   3. Overall, do you think the first part HCl + NaHCO₃ → NaCl + H₂CO₃, is an exchange (double replacement) reaction? Answer yes or no and give a short reason using the ions that change partners.
8. Lemon juice has pH 2 and orange juice has pH 4.
   1. Which liquid is more acidic? Explain how you know this from the pH values.
   2. The pH scale is logarithmic: each 1‑unit change in pH represents a 10‑fold change in hydrogen ion concentration [H⁺]. Using this idea, calculate how many times greater the [H⁺] is in lemon juice than in orange juice. Show your reasoning.
   3. A student says, “Lemon juice (pH 2) is only twice as acidic as orange juice (pH 4) because 4 − 2 = 2.” Explain why this reasoning is incorrect, and correct it using numbers.
9. Eli drinks a whole bottle of strong lemon juice (very acidic). Soon he feels dizzy and has trouble breathing. In the hospital, the nurse gives him IV sodium bicarbonate (NaHCO₃).
   1. Lemon juice adds a lot of acid (H⁺ ions) to Eli’s body.
      • Explain in simple words what happens to his blood pH when there is too much acid.
      • How does the body try to fix this by changing breathing rate (faster or slower)?
   2. In the blood, bicarbonate (HCO₃⁻) is part of this buffer system: H⁺ + HCO₃⁻ ⇌ H₂CO₃ ⇌ CO₂ + H₂O
      • Using this equation, explain how adding bicarbonate (HCO₃⁻) from the IV can help remove extra H⁺ and bring the blood pH closer to normal.
   3. The lungs breathe out CO₂.
   4. Explain how breathing out more CO₂ (faster or deeper breathing) also helps correct the acid problem in Eli’s blood.
10. Two glucose (sugar) molecules join together to make one maltose molecule. Each glucose has the formula: C₆H₁₂O₆. So we start with: Glucose + Glucose → Maltose + Water
    1. First, add the atoms before water is removed: Total C (carbon) atoms = 6 + 6 = ?; Total H (hydrogen) atoms = 12 + 12 = ?; Total O (oxygen) atoms = 6 + 6 = ?
    2. In dehydration synthesis, the two glucose molecules lose one water molecule (H₂O) to form a bond. Subtract the atoms in water (H₂O) from your totals in part Write the final chemical formula for maltose. State the number of C, H, and O atoms in one maltose molecule.
    3. In your own words, explain why water is produced in this reaction. Hint: One glucose gives an H and the other gives an OH (O–H). Together they form H₂O, and the remaining parts of the glucose molecules join together.
11. There are different types of lipids (fats) in the body, such as: Phospholipids, Triglycerides, Cholesterol. Choose two types of lipids from the list above. For each lipid you choose:
    1. Describe its structure in simple words. For example, you may mention:
       • Phospholipids: a “water‑loving” (hydrophilic) head and two “water‑fearing” (hydrophobic) fatty acid tails
       • Triglycerides: one glycerol backbone with three fatty acid chains; chains can be more or less saturated (with or without double bonds) and can be short or long
       • Cholesterol: a small molecule with a rigid ring structure (four fused rings) and a short tail
    2. Explain how this structure helps it do its job in the body. For example, you may link it to:
       • Phospholipids: forming cell membranes (bilayers), controlling what can pass in or out, affecting membrane fluidity
       • Triglycerides: long‑term energy storage, cushioning and insulation of organs and under the skin
       • Cholesterol: helping to stabilize cell membranes and acting as a starting material (precursor) for steroid hormones like cortisol, estrogen, and testosterone
    3. Give one example of what might happen in the body if this lipid is: Very low (deficient), or Very high (excessive). Explain how the problem is related to its structure and function.