Nervous and Endocrine Systems: How the Body Keeps in Balance — Answers
Answer sheet with model answers and success criteria for the 9th Grade the human body worksheet.
Success TutoringWorksheetsAnswer sheet9th Grade · Science · The Human BodyNervous and Endocrine Systems: How the Body Keeps in Balance — Answers
Part A: The nervous system
To survive, the body must detect changes and respond to them. A change that the body detects is a stimulus. Receptors (for example in the eyes, ears and skin) detect the stimulus, and effectors (muscles or glands) carry out the response.
The nervous system sends fast electrical impulses along nerve cells called neurons. The pathway is: stimulus → receptor → sensory neuron → central nervous system (brain and spinal cord) → motor neuron → effector → response.
A reflex is a fast, automatic response that does not need you to think first, such as blinking when something comes near your eye. Reflexes protect the body from harm.
Answer: Stimulus, receptor, sensory neuron, central nervous system (CNS), motor neuron, effector, response.
Answer: A reflex (reflex action). It is fast and automatic, so it protects the body from harm, in this case a burn, before the brain has time to make a decision.
Answer: Receptor: heat (temperature) and pain receptors in the skin of the hand. Effector: the arm muscles that contract to pull the hand away.
- AThe spinal cord
- BThe stomach
- CThe pancreas
- DThe lungs
Answer: The spinal cord
Many simple reflexes pass through the spinal cord, which sends a signal straight back to the muscles; the message reaches the brain a fraction of a second later.
Part B: The endocrine system
The endocrine system is made up of glands that release chemical messengers called hormones into the blood. Each hormone affects particular target organs. Hormonal responses are usually slower than nervous responses, but they last longer.
Important glands include the pituitary (in the brain; controls other glands), the thyroid (in the neck; controls the rate of chemical reactions in the body), the pancreas (controls blood glucose with insulin and glucagon), the adrenal glands (on top of the kidneys; release adrenaline), and the ovaries and testes (release sex hormones such as estrogen and testosterone).
The two systems often work together. When you get a fright, nerves signal the adrenal glands to release adrenaline. Adrenaline increases your heart rate and breathing rate and sends more glucose to your muscles, preparing your body for action.
Answer: blood (bloodstream)
Answer: pituitary
Answer: insulin; glucagon
Answer: adrenaline
Answer: Nervous system: electrical impulses, traveling along neurons; very fast response; effect usually short-lived. Endocrine system: chemical hormones, carried in the blood; slower response; effect usually lasts longer.
Part C: Homeostasis
Write T for true or F for false, or circle the best answer.
Homeostasis is keeping the internal environment of the body stable, even when conditions outside change. Body temperature stays close to 37 °C, and blood glucose stays within a narrow range.
Homeostasis works by negative feedback: a change is detected, and the body responds in a way that reverses the change. Too hot: you sweat, and blood vessels near the skin widen so more heat is lost. Too cold: you shiver (muscle contractions release heat), and blood vessels near the skin narrow so less heat is lost.
Answer: True
Examples include body temperature (about 37 °C), blood glucose level and water balance.
Answer: False
Negative feedback reverses the change and brings conditions back towards normal.
Answer: True
Evaporation needs energy, which comes from the skin, so the skin cools.
Answer: False
When you are cold they narrow, so less warm blood flows near the skin and less heat is lost. They widen when you are hot.
- AThe pancreas releases insulin, and the liver and muscles take in glucose
- BThe pancreas releases glucagon, and the liver releases glucose
- CThe adrenal glands release adrenaline
- DThe skin starts to sweat
Answer: The pancreas releases insulin, and the liver and muscles take in glucose
Insulin causes cells, especially in the liver and muscles, to take in glucose from the blood. The liver stores the extra glucose as glycogen.
- AThe hypothalamus
- BThe cerebellum
- CThe pituitary gland
- DThe spinal cord
Answer: The hypothalamus
The hypothalamus acts as the body's thermostat and triggers responses such as sweating or shivering.
Part D: Apply it
Answer: The pancreas detects the low glucose level and releases glucagon. Glucagon causes the liver to break down stored glycogen into glucose and release it into the blood, so blood glucose rises back to normal.
Answer: Insulin is the hormone that makes cells take in glucose from the blood and the liver store it as glycogen. Without enough insulin, less glucose is removed from the blood, so the level stays high. (People with type 1 diabetes manage this with insulin and careful monitoring.)
Model answer: As she runs, her muscles release extra heat and her body temperature starts to rise. The hypothalamus in her brain detects the rise and sends nerve impulses that start sweating and widen the blood vessels near her skin. Evaporating sweat takes thermal energy from her skin, and more blood flowing near the surface loses heat to the air, so her temperature falls back towards 37 °C. This is negative feedback because the response reverses the change. Her endocrine system also helps: adrenaline raises her heart and breathing rates, and glucagon helps release stored glucose from her liver so her muscles have enough fuel. Because sweating loses water, she should drink water to replace it.
Success criteria:
- Identifies the hypothalamus detecting the temperature rise
- Describes sweating and widening of blood vessels near the skin
- Explains negative feedback (the response reverses the change)
- Describes a role for at least one hormone (such as adrenaline or glucagon)
- Uses correct scientific terms throughout
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
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