Homeostasis means keeping the internal environment stable within narrow limits, even when the outside environment or body activity changes. The variables IB likes include body temperature, blood pH, blood glucose, gases, ions, and osmotic concentration. A good answer always names the variable and says it is maintained near a set range.

Homeostasis maintains a stable internal environment within narrow limits.

Variables include body temperature, blood pH, glucose, gases, ions, and osmotic concentration.

Do not define it as keeping everything constant; variables fluctuate within limits.

Sort each item as a homeostatic variable or not.

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Unsorted

5

Homeostatic variable

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Not the variable itself

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Negative feedback works like a correction loop. A receptor detects deviation from the set point. A coordinator compares the value and sends signals. Effectors respond in a way that reverses the deviation, bringing conditions back toward normal.

Negative feedback detects deviation from a set point and reverses it.

Receptors, coordinators, effectors, and feedback loops restore normal conditions.

The word negative means the response opposes the change.

Order a negative-feedback loop.

Order

1

effector responds

2

receptor detects change

3

coordinator sends signal

4

condition returns toward normal

5

variable deviates from set point

Blood glucose control is a two-hormone negative feedback system. When blood glucose rises, pancreatic beta cells secrete insulin, causing liver and muscle cells to take up glucose and store glycogen. When blood glucose falls, alpha cells secrete glucagon, causing stores to be broken down and glucose released.

Beta cells secrete insulin when blood glucose rises.

Alpha cells secrete glucagon when blood glucose falls, affecting liver and muscle stores.

Insulin lowers blood glucose; glucagon raises blood glucose.

Insulin and glucagon are antagonists: one lowers blood glucose, the other raises it.

Match the glucose condition to the hormone response.

Match

Reasons

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Match the glucose condition to the hormone response.

Choose

blood glucose rises

insulin effect

blood glucose falls

glucagon effect

Type 1 and type 2 diabetes both disrupt blood glucose control, but the cause differs. Type 1 diabetes results from autoimmune destruction of pancreatic beta cells, so insulin secretion is too low. Type 2 diabetes involves failure of insulin receptors or cellular response and is linked to lifestyle risk factors.

Type 1 diabetes results from autoimmune destruction of pancreatic beta cells.

Type 2 diabetes involves insulin-receptor/response failure and is linked to lifestyle risk factors.

Compare cause first, then consequence for blood glucose control.

Sort each feature into diabetes type.

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4

Type 1 diabetes

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Type 2 diabetes

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Thermoregulation uses negative feedback to keep core temperature near 37 °C. Thermoreceptors detect temperature changes and signal the hypothalamus. The hypothalamus coordinates effectors in the skin, muscles, liver, and endocrine system to increase heat loss or heat production.

Thermoregulation uses negative feedback to maintain core temperature near 37 °C.

Thermoreceptors signal the hypothalamus, which coordinates skin, muscles, liver, and hormones.

The hypothalamus is the coordinator, not the effector.

Thermoregulation is negative feedback: detect the temperature shift, then activate effectors that reverse it.

Order the thermoregulation loop.

Order

1

core temperature changes

2

thermoreceptors detect the change

3

hypothalamus coordinates response

4

core temperature moves back toward 37 °C

5

effectors alter heat loss or production

Order the thermoregulation loop.

Choose

core temperature changes

thermoreceptors detect the change

hypothalamus coordinates response

effectors alter heat loss or production

core temperature moves back toward 37 °C

Hot and cold responses are opposite because they must reverse opposite deviations. Cooling uses vasodilation, sweating, and hairs lying flat to increase heat loss. Warming uses vasoconstriction, reduced sweating, shivering, metabolic heat, and brown fat to reduce heat loss or make heat.

Cooling uses vasodilation, sweating, and hairs lying flat.

Warming uses vasoconstriction, reduced sweating, shivering, metabolic heat, and brown fat.

Always connect each response to heat loss or heat production.

Sort each thermoregulation response.

Sort

Unsorted

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Cooling response

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Warming response

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Core D3.3 is secure when every example becomes a feedback route: identify the variable, detect deviation, coordinate a response, activate effectors, and reverse the change. Glucose and temperature are the key worked examples.

stable internal environment within narrow limits

detects deviation from set point and reverses it

insulin lowers high glucose; glucagon raises low glucose

hypothalamus coordinates cooling or warming responses

Match each retrieval cue to its exam-use meaning.

Match

Reasons

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Core homeostasis answers should use a control-loop structure, not a list of responses. The response starts with the variable and set point, then explains how the body detects deviation and activates the response that reverses it. Apply that loop to glucose, diabetes, or temperature.

Define homeostasis as maintaining stable internal conditions within narrow limits.

Use negative feedback language: receptor, coordinator, effector, set point, and reverse the deviation.

Apply the loop to insulin/glucagon, diabetes types, or hot/cold thermoregulation responses.

Explain how negative feedback maintains a homeostatic variable such as blood glucose or core temperature.

Choose

Match each exam move to the mark it earns.

Match

Reasons

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IB Biology SL D3.3 Homeostasis Notes

Define Homeostasis

Reverse the Change

Choose Insulin or Glucagon

Compare Diabetes Types

Control Core Temperature

Sort Hot and Cold Responses

Retrieve the Core Homeostasis Route

Transfer: Explain Core Homeostasis