Body Systems, Signals & Homeostasis — Problem set, Grade 10

Trace interactions among body systems and explain regulation and defense.

Review the key ideas

Interacting Body Systems

Systems cooperate to deliver materials, remove wastes, and maintain conditions required by cells.

Homeostasis & Feedback

Homeostasis is the active maintenance of a stable internal environment through feedback loops — negative feedback (most common) reverses a change to restore the set point, while positive feedback amplifies a change to push a process to completion.

Cell Signals & Feedback

A signal acts through receptors and responses; feedback depends on how the response affects the initial change.

Defense, Disease & Homeostasis

Barrier, innate, and adaptive defenses interact; immune memory reflects lasting changes in responsive cell populations.

Problem 1

Trace the negative feedback loop that returns blood glucose to normal after a meal. Name the organ, the hormone, and the effect.
Answer and explanation

The pancreas releases insulin, which signals cells to take up glucose, lowering blood sugar back to its set point.

After a meal, blood glucose rises above its set point (the stimulus). The pancreas detects this and acts as the control center, releasing the hormone insulin. Insulin is the signal to the effectors — body cells and the liver — to take glucose out of the blood and store it. As glucose falls back toward the set point, the response has reversed the original change, which is what makes it negative feedback.

Problem 2

Explain the difference between negative and positive feedback, and give one example of each from the human body.
Answer and explanation

Negative feedback reverses a change to hold a set point (e.g., sweating to cool down); positive feedback amplifies a change to finish a process (e.g., childbirth contractions).

Negative feedback opposes the change that triggered it, keeping a variable near its set point — for example, sweating when you overheat or insulin lowering high blood sugar. Positive feedback amplifies the change, pushing a process rapidly to completion before shutting off — for example, contractions during childbirth strengthening until the baby is born, or platelets recruiting more platelets until a wound clots. Most homeostasis relies on negative feedback; positive feedback is reserved for events that need a decisive finish.

Problem 3

Draw a route for carbon dioxide from a body cell to the environment.
Answer and explanation

Cell → tissue fluid/blood → circulation → lung capillaries → alveolar air → exhaled air; diffusion crosses the exchange barriers.

Problem 4

Explain how the digestive, respiratory, circulatory, and excretory systems together serve a single muscle cell during exercise.
Answer and explanation

The digestive system absorbs glucose from food into the blood, and the respiratory system brings oxygen into the blood at the lungs and releases carbon dioxide. The circulatory system transports both glucose and oxygen to the muscle cell and carries carbon dioxide and other wastes away. The excretory system removes nitrogenous waste and excess water and salts from the blood, keeping its composition within the range the cell needs. No system acts alone: the muscle cell's respiration depends on all four delivering and removing in sequence.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Resting heart rate is 72 beats per minute and rises to 144 during exercise. By what factor has it increased?
Answer and explanation

2

144 / 72 = 2, a twofold increase, which raises the rate of delivery of oxygen and glucose to active muscle.

Problem 6

Chapter review: A record shows increased breathing and pulse during activity, followed by different recovery times. Explain two system links and why one trace cannot identify a unique cause.
Answer and explanation

Respiratory exchange and circulation support changing tissue demand; neural/hormonal regulation can coordinate responses. Different variables have different dynamics, and intensity, conditions and other mechanisms require comparisons before naming one cause.

Respiratory exchange and circulation support changing tissue demand; neural/hormonal regulation can coordinate responses. Different variables have different dynamics, and intensity, conditions and other mechanisms require comparisons before naming one cause.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 7

After a glucose drink, one person's blood glucose returns from 165 mg/dL to 95 mg/dL in 2.0 hours. Report the mean rate of decrease in mg/dL per hour.
Answer and explanation

35 mg/dL per hour

(165 − 95) / 2.0 = 35 mg/dL per hour. This is a mean rate; the actual fall is steeper early and flatter later.

Problem 8

A student writes that homeostasis means "the body stays the same." Correct the statement and explain what observation disproves it.
Answer and explanation

Homeostasis means internal conditions are regulated within a range around a set point, not held constant. Measurement disproves constancy directly: body temperature varies by several tenths of a degree through the day, blood glucose rises after every meal and falls between them, and heart rate changes with activity. What is maintained is the range and the return toward the set point, which requires continuous detection and correction rather than stillness.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 9

Chapter review: A regulated variable is below target. An effector raises it toward target but overshoots temporarily after a delay. Classify the intended feedback and explain the overshoot.
Answer and explanation

The intended response is negative feedback because it opposes the deviation. Delayed sensing/response and changing inputs can produce overshoot; a rising value alone does not define positive feedback.

The intended response is negative feedback because it opposes the deviation. Delayed sensing/response and changing inputs can produce overshoot; a rising value alone does not define positive feedback.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 10

A signal is present but one cell does not respond. Suggest two testable explanations.
Answer and explanation

The cell may lack the receptor or have a disruption in downstream machinery. Test receptor presence and response to pathway activation.

Problem 11

Insulin circulates to every tissue in the body, yet only some cells respond. Explain why, and what this implies about how specificity is achieved.
Answer and explanation

A cell responds only if it builds a receptor whose shape binds insulin. Cells without that receptor are exposed to the hormone but cannot detect it, so no response follows. Specificity therefore lies in the receiving cell rather than in the delivery: the signal reaches everything, and the receptor decides who is listening. The same arrangement lets one hormone produce different responses in different tissues, because what happens after binding depends on the machinery inside each cell.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 12

Cell type A carries 4,000 receptors for a hormone and cell type B carries 500. How many times more receptors does A carry?
Answer and explanation

8

4,000 / 500 = 8 times as many, so A can be expected to respond at lower hormone concentrations and to reach a higher maximum response.

Problem 13

Chapter review: Two tissues reach the same response maximum, but one responds strongly at a lower signal concentration. Explain the difference and why their response does not prove identical receptor abundance.
Answer and explanation

They differ in sensitivity under the stated comparison, not necessarily maximal capacity. Binding, receptor number, downstream amplification and adaptation can differ; further controlled measurements are required.

They differ in sensitivity under the stated comparison, not necessarily maximal capacity. Binding, receptor number, downstream amplification and adaptation can differ; further controlled measurements are required.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 14

Compare an immediate barrier defense with a memory-based response.
Answer and explanation

A barrier reduces entry broadly; a memory response depends on earlier specific recognition and persistent responsive cells.

Problem 15

Antibody concentration against one antigen is 4 units after a first exposure and 160 units after a second. By what factor did it increase?
Answer and explanation

40

160 / 4 = 40 times greater, which is the quantitative signature of immunological memory rather than a repeat of the first response.

Problem 16

Explain why a person who has recovered from one viral illness can still catch a different one, using the idea of specificity.
Answer and explanation

Adaptive immunity is specific: the lymphocytes that multiplied and the antibodies they produce recognize particular molecular features — antigens — of the virus encountered. A different virus presents different antigens, so those antibodies and memory cells do not bind it, and the response must be built from the beginning. Immunity is therefore acquired antigen by antigen rather than as general resistance to illness.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 17

Chapter review: A later sample gives more antibody-binding signal than an earlier sample. State one supported conclusion and two things this alone does not establish.
Answer and explanation

It supports increased measured binding under comparable assay conditions. It does not alone establish an exact antibody count, doubled protection, lasting immunity or the full cellular response; additional calibrated/outcome evidence is needed.

It supports increased measured binding under comparable assay conditions. It does not alone establish an exact antibody count, doubled protection, lasting immunity or the full cellular response; additional calibrated/outcome evidence is needed.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.
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