Coordination in Life Processes — Practice

Question 1

Define homeostasis. Give two examples of set points maintained by the human body.

Accepted Answer

Step 1 — Define.
  Homeostasis is the maintenance of a STABLE INTERNAL ENVIRONMENT despite changes in the external environment. It is a DYNAMIC EQUILIBRIUM — constant small adjustments keep conditions within a narrow range.

Step 2 — Give two examples.
  (1) Body temperature is maintained at approximately 37°C. When it rises, sweat glands produce sweat and blood vessels dilate to cool the body. When it falls, muscles shiver to generate heat.
  (2) Blood glucose is maintained between 70–110 mg/dL. After a meal it rises → insulin lowers it. After exercise it falls → glucagon raises it.

✦ Answer: Homeostasis = maintenance of stable internal environment. Examples: temperature (~37°C) and blood glucose (70–110 mg/dL).

Question 2

Explain positive feedback with the example of childbirth.

Accepted Answer

Step 1 — Define positive feedback.
  Positive feedback is a mechanism where the RESPONSE AMPLIFIES the stimulus, driving a process to completion. Unlike negative feedback, it moves the system AWAY from the set point.

Step 2 — Apply to childbirth.
  Baby's head presses on CERVIX → nerve signals reach BRAIN → OXYTOCIN released → stronger uterine contractions → more pressure on cervix → more oxytocin → even stronger contractions.

Step 3 — How it stops.
  The loop intensifies until the baby is born. Once the baby is delivered, the pressure stimulus is REMOVED → feedback stops automatically.

✦ Answer: Positive feedback amplifies the stimulus; in childbirth it drives contractions to completion then stops when the baby is born.

Question 3

Explain how blood glucose levels are regulated in the human body using the concept of negative feedback. Name the hormones and their sources.

Accepted Answer

Step 1 — Normal blood glucose range.
  Blood glucose is maintained between 70–110 mg/dL — controlled by two ANTAGONISTIC hormones from the PANCREAS.

Step 2 — When blood glucose is TOO HIGH (after a meal).
  BETA CELLS of the pancreas detect the rise → secrete INSULIN → body cells absorb more glucose from blood → liver converts glucose into GLYCOGEN (storage) → blood glucose FALLS back to normal.
  This is NEGATIVE FEEDBACK: the response (lowering glucose) OPPOSES the stimulus (high glucose).

Step 3 — When blood glucose is TOO LOW (after exercise or fasting).
  ALPHA CELLS of the pancreas detect the fall → secrete GLUCAGON → liver breaks GLYCOGEN back into glucose (glycogenolysis) → blood glucose RISES back to normal.
  Again NEGATIVE FEEDBACK: the response (raising glucose) opposes the stimulus (low glucose).

Step 4 — What is the mnemonic?
  INSULIN = 'lowers' (think IN = brings glucose IN to cells). GLUCAGON = 'raises' (think GO = glucose GOES into blood).

✦ Answer: Insulin (from β cells) lowers blood glucose; glucagon (from α cells) raises it. Both work via negative feedback to maintain homeostasis. Failure of insulin production or action = DIABETES MELLITUS.

Question 4

Describe how six body systems coordinate during a 100-metre sprint. What happens after the race is over?

Accepted Answer

Step 1 — Identify the six systems and their roles.
  NERVOUS: Brain sends impulses to leg muscles, heart, and lungs to begin the sprint.
  MUSCULAR: Leg muscles contract rapidly, providing movement.
  RESPIRATORY: Breathing rate and depth increase → more O₂ enters the blood, more CO₂ exits.
  CIRCULATORY: Heart rate increases. Blood vessels in leg muscles DILATE (more blood flow). Blood vessels in the gut CONSTRICT (less blood needed there).
  ENDOCRINE: Adrenal glands release ADRENALINE → further increases heart rate, blood glucose, and directs blood to muscles.
  EXCRETORY: Sweat glands activate → cooling through evaporation prevents overheating.

Step 2 — After the race.
  Breathing stays elevated briefly — repaying OXYGEN DEBT by oxidising the lactic acid that accumulated in muscles. Heart rate gradually returns to resting. Body temperature returns to 37°C. Homeostasis is RESTORED.

✦ Answer: All six systems work in concert during exercise, each playing a specific role. Post-exercise, negative feedback mechanisms restore the body to homeostatic balance.

Question 5

Name any two plant hormones and state their functions.

Accepted Answer

Step 1 — Auxins.
  AUXINS promote CELL ELONGATION. They accumulate on the shaded side of a stem, causing those cells to grow longer → stem BENDS toward light (phototropism). Used in ROOTING POWDER for cuttings.

Step 2 — Abscisic Acid (ABA).
  ABA is the STRESS HORMONE. During drought, roots produce ABA → stomata CLOSE → transpiration reduces → water is conserved. Also promotes seed DORMANCY.

✦ Answer: Auxins (cell elongation, phototropism) and ABA (stress response — closes stomata, dormancy).

Question 6

What are antagonistic hormones? Give one pair from humans and one pair from plants, with the functions of each. Explain why antagonistic pairs are necessary for homeostasis.

Accepted Answer

Step 1 — Definition.
  ANTAGONISTIC HORMONES are pairs of hormones that produce OPPOSITE effects on the same target, allowing precise control of a physiological variable.

Step 2 — Human pair: Insulin and Glucagon.
  INSULIN (from β cells of pancreas) → lowers blood glucose by promoting glucose uptake and glycogen storage.
  GLUCAGON (from α cells of pancreas) → raises blood glucose by breaking down glycogen.
  Together they keep blood glucose in the narrow homeostatic range 70–110 mg/dL.

Step 3 — Plant pair: Auxins and Abscisic Acid (ABA).
  AUXINS → PROMOTE cell growth and elongation (shoot growth, phototropism).
  ABA → INHIBITS growth; causes stomatal closure and seed dormancy during stress.

Step 4 — Why antagonistic pairs are necessary.
  A single hormone could push a variable in one direction indefinitely. Antagonistic pairs allow the body (or plant) to CORRECT in BOTH DIRECTIONS — raise when too low, lower when too high — achieving the dynamic balance that defines homeostasis. Without both partners, the set point cannot be maintained.

✦ Answer: Antagonistic hormones work in opposition to achieve fine control. Human: insulin (lowers glucose) / glucagon (raises glucose). Plant: auxins (promote growth) / ABA (inhibit growth). Both pairs are essential for homeostasis.

Practice — Coordination in Life Processes

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