What Is Biology & Characteristics of Life

Question 1 [10]

(a) Seven characteristics + justification [7 — 1 mark each, ½ trait ½ reason accepted]

1. Nutrition — organisms take in materials/energy needed to sustain life processes.
2. Respiration — releases usable energy (ATP) from nutrients, without which no process runs.
3. Metabolism/Movement — chemical reactions and (in animals) locomotion show internal activity distinguishing life.
4. Excretion — removal of toxic metabolic wastes; failure to do so poisons the organism.
5. Growth — increase in size/complexity via cell division, a permanent change unique to living systems.
6. Reproduction — production of new individuals ensures species continuity; non-living things cannot self-replicate.
7. Responsiveness (irritability) — reaction to stimuli allows survival adjustments. (Also accept: Sensitivity, Adaptation, Homeostasis in the "MRS GREN"-type frameworks.)

(b) Virus argument [3]

• Viruses reproduce — but only inside a host cell (cannot alone). [1]
• Viruses show no metabolism/respiration of their own outside a host. [1]
• Viruses do not grow or respond independently → best classed as non-living (or "on the border of life"). Reasoned conclusion required. [1]

Question 2 [8]

(a) [4]

• Metabolism = the sum of all chemical reactions occurring within an organism. [1]
• Anabolism: builds larger molecules from smaller ones; requires/stores energy (endergonic). [1½]
• Catabolism: breaks larger molecules into smaller ones; releases energy (exergonic). [1½]

(b) [4 — 1 each]

• (i) Photosynthesis → anabolic (builds glucose from CO₂ + H₂O, stores energy).
• (ii) Cellular respiration → catabolic (breaks glucose, releases energy).
• (iii) Protein synthesis → anabolic (joins amino acids, requires energy).
• (iv) Starch digestion → catabolic (breaks polymer into glucose, releases usable sugars).

Question 3 [9]

(a) Negative feedback loop [5]

• Stimulus: a change in the internal environment (deviation from set point). [1]
• Receptor: detects the change. [1]
• Control centre (e.g. brain/gland): processes info, compares to set point, signals response. [1]
• Effector: carries out the corrective response. [1]
• The response reverses the original change, returning the variable to set point → negative feedback. [1]

(b) Blood glucose after a meal [4]

• Blood glucose rises (stimulus). [1]
• Pancreas (receptor + control centre) detects high glucose and releases insulin. [1]
• Insulin causes liver/muscle cells (effectors) to take up glucose and store it as glycogen. [1]
• Blood glucose falls back to normal set point (~$90$ mg/dL). [1]

Question 4 [8]

(a) Levels atom→biosphere [4 — full ordered list required, deduct per error] Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ system → Organism → Population → Community → Ecosystem → Biosphere.

(b) Emergent property [4]

• Definition: a property that appears at a given level of organization that is not present in the individual components at the level below. [2]
• Example 1 (level: cell): individual organelles cannot live, but combined they form a living cell. [1]
• Example 2 (level: ecosystem/organism): e.g. consciousness emerges from a network of neurons; or nutrient cycling emerges at ecosystem level not from a single organism. [1]

Question 5 [9]

(a) [5]

• Hypothesis (testable, e.g.): "If fertilizer X is added, then bean plants will grow taller than plants without it." [2]
• Independent variable: presence/amount of fertilizer X. [1]
• Dependent variable: plant height (measured, e.g. in cm). [1]
• Controlled variables (≥2): light, water volume, temperature, soil type, plant species/age. [1]

(b) Control group [2]

• Contains identical bean plants with no fertilizer X (all else the same). [1]
• Provides a baseline for comparison, so any height difference can be attributed to fertilizer, not other factors. [1]

(c) [2 — ½ each, 2 total]

• Hypothesis: a testable, tentative explanation/prediction.
• Theory: a well-substantiated, broad explanation supported by large evidence.
• Law: a description of a consistently observed pattern in nature (states what happens, not why).

Question 6 [6]

(a) [3 — 1 each]

• (i) $2.5\text{ mm} = 2.5 \times 1000 = 2500\ \mu\text{m}$ (1 mm = 1000 µm).
• (ii) $0.004\text{ g} = 0.004 \times 1000 = 4\ \text{mg}$.
• (iii) $3000\text{ mL} = 3000 / 1000 = 3\ \text{L}$.

(b) [3]

• Rate increases with temperature up to $37^\circ$C because higher kinetic energy → more enzyme–substrate collisions. [1]
• $37^\circ$C is the optimum temperature (peak rate). [1]
• Above optimum the enzyme denatures (active site shape changes), so rate falls to near zero. [1]

[
  {"claim": "2.5 mm equals 2500 micrometres", "code": "result = (2.5*1000 == 2500)"},
  {"claim": "0.004 g equals 4 mg", "code": "result = (0.004*1000 == 4)"},
  {"claim": "3000 mL equals 3 L", "code": "result = (3000/1000 == 3)"},
  {"claim": "There are 12 levels of biological organization from atom to biosphere", "code": "levels = ['atom','molecule','organelle','cell','tissue','organ','organ system','organism','population','community','ecosystem','biosphere']; result = (len(levels) == 12)"}
]