Biology · Unit 6
Human Body Systems
How your organ systems work
This unit is the overview - the map you need before the detailed units make sense. It runs through the major organ systems and, more importantly, what each one is for and how they depend on each other.
The useful idea here is that systems are defined by function rather than by location. The digestive tract and the circulatory system are physically tangled together, and separating them is a choice about which job you are tracing rather than a fact about where things sit.
This unit breaks down into 20 short steps and 130 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.
- Steps
- 20
- Questions
- 130
- Difficulty
- 1-3
What this unit covers
- Musculoskeletal System
- Digestive System
- Respiratory System
- Circulatory System
- Nervous System
Where this fits
The gateway to the detailed body units - Skeleton, Nervous System, Heart, Lungs, Digestion, Reproduction and Immunity each expand one section of this one.
Where people slip
No system works alone. Almost every question that looks like it is about one system is really about the handover between two, so learn the connections rather than the lists.
How the unit is structured
Human Body Systems runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.
Challenge rounds
Example questions
30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 130 in the unit altogether.
Circulatory System
- Fact or fibLevel 1
1. The bladder stores urine until it is ready to leave the body.
Answer: True
The bladder is a stretchy sac that holds urine until you are ready to release it.
- Fill the blankLevel 1
2. The pale yellow liquid part of blood that carries the cells is called ____.
- plasmacorrect
- mucus
- saliva
- lymph
Plasma is the liquid part of blood that floats the cells and carries nutrients and waste.
- Guess the numberLevel 1
3. How many chambers does the human heart have?
Answer: 4 chambers
The heart has four chambers: two atria on top and two ventricles on the bottom.
- Build the sentenceLevel 2
4. Build the sentence about the smallest blood vessels.
Answer: Capillaries connect arteries to veins
Capillaries are tiny vessels that link arteries to veins and let oxygen and nutrients pass into tissues.
- Choose all that applyLevel 2
5. Select ALL of the true statements about platelets and blood clotting.
- Platelets help the blood to clot and stop bleedingcorrect
- Platelets clump together to plug a cutcorrect
- Platelets carry oxygen around the body
- Platelets are tiny fragments smaller than red blood cellscorrect
Platelets are tiny cell pieces that clump to plug wounds and start a clot; red blood cells carry the oxygen.
- Match the pairsLevel 2
6. Match each organ with the body system it belongs to.
Answer: Heart = Circulatory system; Lungs = Respiratory system; Stomach = Digestive system; Brain = Nervous system
Each organ is a key part of one body system, and together the systems keep the body working.
Digestive System
- Fill the blankLevel 1
7. Food first enters the digestive system through the ____.
- mouthcorrect
- stomach
- lungs
- heart
Digestion begins in the mouth, where teeth grind food and saliva starts breaking it down.
- Fact or fibLevel 2
8. Enzymes speed up the chemical breakdown of food during digestion.
Answer: True
Digestive enzymes break large food molecules into smaller ones the body can absorb.
- Match the pairsLevel 2
9. Match each digestive substance to what it does.
Answer: Amylase = Breaks down starch; Protease = Breaks down protein; Lipase = Breaks down fat; Bile = Emulsifies fat into droplets
Amylase digests starch, protease digests protein, lipase digests fat, and bile breaks fat into tiny droplets.
- Multiple choiceLevel 2
10. What is the job of bile, which is made by the liver?
- It breaks large fat blobs into small dropletscorrect
- It turns starch into sugar
- It carries oxygen to the muscles
- It makes the bones harder
Bile from the liver emulsifies fat, breaking big fat blobs into tiny droplets that are easier to digest.
- Put in orderLevel 2
11. Put the path food takes through the digestive system in the correct order.
Answer: Mouth -> Esophagus -> Stomach -> Small intestine -> Large intestine
Food travels from the mouth to the esophagus, into the stomach, then through the small intestine and finally the large intestine.
- Choose all that applyLevel 3
12. Select ALL of the jobs done by the liver.
- Makes bile to help digest fatscorrect
- Breaks down harmful substances like alcoholcorrect
- Stores extra glucose for latercorrect
- Pumps blood around the whole body
The liver makes bile, cleans toxins from the blood, and stores glucose; pumping blood is the heart's job.
Musculoskeletal System
- Guess the numberLevel 1
13. How many bones are in the adult human body?
Answer: 206 bones
An adult skeleton has 206 bones, though babies are born with even more that later fuse together.
- Fact or fibLevel 2
14. When you are cold, tiny muscles pull your body hairs upright to trap a layer of warm air near the skin.
Answer: True
The erector muscles raise the hairs, trapping insulating air that reduces heat loss.
- Multiple choiceLevel 2
15. What do ligaments connect together in the body?
- Bone to bonecorrect
- Muscle to bone
- Muscle to skin
- Nerve to muscle
Ligaments hold bone to bone across a joint, keeping the joint steady and strong.
- Choose all that applyLevel 3
16. Select ALL statements that are true about muscles and bones.
- Skeletal muscles pull on bones to create movement.correct
- Muscles work in antagonistic pairs, like the biceps and triceps.
- A single muscle can both push and pull a bone.
- Bones are dry, dead structures with no living cells.
Skeletal muscles pull on bones and work in antagonistic pairs; a single muscle can only pull, not push, and bones are living tissue.
- Fill the blankLevel 3
17. During very hard exercise, when oxygen runs short, muscles respire anaerobically and build up ____ acid.
- lacticcorrect
- citric
- amino
- carbonic
With too little oxygen, muscles respire anaerobically and produce lactic acid, which can cause fatigue.
- Picture questionLevel 3
18. 🌞 What does the pigment melanin in your skin help protect you from?
- Harmful UV radiation from the suncorrect
- Cold weather
- Loud noises
- Feeling hungry
Melanin absorbs ultraviolet light, shielding deeper skin cells from UV damage.
Nervous System
- Multiple choiceLevel 1
19. Which hormone prepares your body for 'fight or flight' when you are scared?
- Adrenalinecorrect
- Insulin
- Melatonin
- Growth hormone
Adrenaline speeds up your heart and breathing so you are ready to react quickly.
- Picture questionLevel 1
20. 🧠 This organ is the control center of the nervous system. What is it?
- Braincorrect
- Heart
- Lung
- Liver
The brain is the control center that receives signals and sends out instructions to the rest of the body.
- Build the sentenceLevel 2
21. Build the sentence about how hormones travel around the body.
Answer: hormones are carried in the blood
Hormones are chemical messengers carried in the blood to their target organs.
- Fact or fibLevel 2
22. The nervous system sends fast, short-lasting signals, while hormones act more slowly but their effects last longer.
Answer: True
Nerve impulses are rapid and brief; hormonal responses are slower to start but longer lasting.
- Guess the numberLevel 3
23. What is the normal temperature of a healthy human body?
Answer: 37 degrees Celsius
Your body keeps itself at about 37 degrees Celsius, and the brain adjusts sweating and shivering to hold it there.
- Match the pairsLevel 3
24. Match each gland with a hormone it releases.
Answer: Pancreas = Insulin; Thyroid gland = Thyroxine; Adrenal gland = Adrenaline; Pituitary gland = Growth hormone
The pancreas makes insulin, the thyroid makes thyroxine, the adrenal glands make adrenaline and the pituitary makes growth hormone.
Respiratory System
- Build the sentenceLevel 2
25. Build the sentence about exercise and breathing.
Answer: your breathing rate rises during exercise
During exercise your breathing rate rises to supply more oxygen and remove more carbon dioxide.
- Fact or fibLevel 2
26. When you breathe in, the diaphragm contracts and flattens downward.
Answer: True
The diaphragm pulls down when you breathe in, making the chest bigger so air rushes into the lungs.
- Guess the numberLevel 2
27. About how many breaths does a calm, resting adult take in one minute?
Answer: 15 breaths per minute
A resting adult usually breathes about 12 to 18 times per minute.
- Multiple choiceLevel 2
28. Why does your breathing rate increase when you exercise?
- To take in more oxygen for the working musclescorrect
- To cool the brain down
- To digest food faster
- To build new bones
Exercising muscles need more oxygen for respiration, so you breathe faster and deeper to supply it.
- Picture questionLevel 2
29. 🫁 Inside these organs, tiny air sacs exchange gases with the blood. What are those air sacs called?
- Alveolicorrect
- Neurons
- Villi
- Nephrons
Alveoli are tiny air sacs in the lungs where oxygen enters the blood and carbon dioxide leaves it.
- Fill the blankLevel 3
30. The respiratory and circulatory systems work together: the lungs add oxygen to the blood and remove ____ from it.
- carbon dioxidecorrect
- glucose
- urea
- protein
In the alveoli the blood picks up oxygen and unloads carbon dioxide, which is then breathed out.
Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.
How you practise
This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.
- Build the sentence
- Choose all that apply
- Fact or fib
- Fill the blank
- Guess the number
- Listen and choose
- Match the pairs
- Multiple choice
- Odd one out
- Picture question
- Put in order
- Sequence recall
- Sort into groups
- Spell it
- Tap the pairs
- True or false
- Type the answer
Practise Human Body Systems
130 questions across 20 steps. Start with step one and crawl at your own pace.
Play this unitRead about Human Body Systems
Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.
- How the Digestive System Works from Mouth to IntestineLearn how the digestive system works as food is broken down, nutrients are absorbed, and waste moves through the body from mouth to large intestine.August 13, 2026 · 5 min read
- How Homeostasis Keeps Body Temperature StableYour body works best within a narrow temperature range. Homeostasis uses sensors, the brain and effectors such as skin blood vessels and sweat glands to keep internal temperature close to a useful level.August 8, 2026 · 5 min read
- How Your Kidneys Keep Water and Salts in BalanceYour kidneys filter blood, return useful materials and adjust how much water leaves your body. This steady balancing act is a clear example of homeostasis.July 24, 2026 · 5 min read
More units in Biology
- What Is Life?Living things and the signs of life
- The CellCells and their organelles
- Cell Transport and EnergyDiffusion, photosynthesis and respiration
- DNA and GeneticsGenes, inheritance and DNA
- Molecular BiologyThe central dogma and biochemistry
- Skeleton and BonesBones, joints and the skeleton
- Nervous System and BrainNeurons, the brain and the senses
- Heart and CirculationThe heart, blood and blood vessels