Answer to Question 1.5: Pyrogens cause body temperature to rise by acting on the hypothalamus, which controls the body’s thermostat. They trigger:

Vasoconstriction – blood vessels narrow, reducing heat loss.

Shivering – muscles generate more heat.

Reduced sweating – less heat is lost through evaporation.

Together, these responses raise body temperature, producing a fever.

Answer to Question 1.6: Homeostasis is the maintenance of a stable internal environment despite changes in external conditions.

Answer to Question 1.7:

1. Stimulus: Body temperature rises or falls.
2. Sensor: Thermoreceptors detect the change.
3. Control center: Hypothalamus processes the information.
4. Effectors: Sweat glands activate and blood vessels dilate (cooling) or muscles shiver and vessels constrict (warming).
5. Response: Body temperature returns to normal.

Answer to Question 1.8:

1. Stimulus: Blood osmolarity increases (too concentrated) or decreases (too diluted).
2. Sensor: Osmoreceptors in the hypothalamus detect the change.
3. Control center: Hypothalamus signals the pituitary gland.
4. Effectors: Kidneys retain or excrete water; thirst may be triggered.
5. Response: Blood osmolarity returns to normal.

Answer to Question 1.9: d

Answer to Question 1.10: c

Answer to Question 1.11: b

Answer to Question 1.12:

1. Stimulus – a change in the internal environment
2. Sensor/receptor – detects the change
3. Control center – processes the information and signals effectors
4. Effector – acts to reverse the change

If secretion of a body chemical became too great: The negative feedback loop would attempt to reduce or stop secretion to bring levels back to normal. If the system fails, it could lead to imbalances or disease.

Answer to Question 1.13:

1. Vasoconstriction – reduces heat loss from skin
2. Shivering – generates heat through muscle activity
3. Behavioral responses – seeking shelter, adding insulation, huddling
4. Hormonal responses – thyroid hormone increases metabolic heat production

Answer to Question 1.2: d

Possible Answer to Question 1.3:

Fairyflies (tiny insects <0.2 mm) rely on diffusion for oxygen because their bodies are too small for complex respiratory organs.

Why size limits life: Too small → not enough cells for organs; too large → diffusion alone can’t supply oxygen efficiently.

Possible Answer(s) for Question 1.4: 1. Oxygen Availability - Limited oxygen in water or soil can restrict survival. 2. Temperature - Extreme heat or cold can denature proteins and disrupt metabolism. 3. Water availability - Deserts and dry habitats limit hydration and cellular function. 4. Nutrient availability - Scarcity of essential minerals or food limits growth. 5. Size - Small or large body size can restrict diffusion, movement, or organ development.