GED Science
Human Body Systems
The body runs on cooperating systems — delivery, breathing, digestion, messaging, defense. The test asks what each system does, and how two systems work together. Think of each as a city service and the teamwork questions get easy.
The words first
- organ system
- a team of organs sharing one big job
- circulatory
- the delivery service: heart and blood vessels
- respiratory
- the air exchange: lungs bring O₂ in, CO₂ out
- homeostasis
- the body holding steady conditions — temperature, sugar, water
The method
THE CITY SERVICES
circulatory delivery trucks heart, blood, vessels
respiratory air supply lungs, trachea
digestive food processing stomach, intestines
nervous communications brain, spinal cord, nerves
muscular/ structure and muscles, bones
skeletal movement
immune security white blood cells
excretory waste removal kidneys, bladder
THE TEAMWORK PATTERN (most-tested)
lungs load oxygen → BLOOD carries it → cells use it
respiratory → circulatory → every system
HOMEOSTASIS EXAMPLES
too hot → sweat → evaporation cools you
too cold → shiver → muscle motion warms you
sugar high → insulin released → sugar stored
Worked all the way through
The problem
During exercise, breathing speeds up AND the heart beats faster. Why do both happen together?
- Step 1 — Name what working muscles need.More oxygen, and faster removal of carbon dioxide.
- Step 2 — Assign each need to a service.Getting oxygen IN is respiratory (faster breathing). DELIVERING it to muscles is circulatory (faster heartbeat).
- Step 3 — Put the teamwork in one sentence.The lungs load more oxygen and the heart ships it faster — one supply chain speeding up at both ends.
On the board
muscles demand more O₂
the trigger
lungs speed up → more O₂ loaded
respiratory
heart speeds up → faster delivery
circulatory
one supply chain, two ends
Answer
The respiratory system takes in more oxygen while the circulatory system delivers it to the muscles faster
A second one, in a different form
You touch a hot stove and your hand jerks back before you even feel pain. Which system acted, and why so fast?
signal: skin → spinal cord → muscle
a reflex arc
skips the brain's slow deliberation
that is the speed
system: nervous
Answer
The nervous system — a reflex routed through the spinal cord, bypassing the brain
The usual mistake
Naming the respiratory system when asked what DELIVERS oxygen to muscles.
Check yourself
For any two-systems question, trace the actual cargo — oxygen, food, a signal — from where it enters to where it is used. The systems it passes through are your answer, in that order.
Practice it
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