Unit 9: Human Body and Health
The systems working inside you right now without you thinking about it, and how your body fights off the germs trying to get in.
6 topics · 20 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Skeletal and Muscular Systems
- How it worksHow do muscles working in pulling pairs move bones at a joint like your elbow?
- Common mistakeWhy can't a muscle push a bone, only ever pull it?
- Going furtherWhat happens to your arm's movement if one muscle in a pulling pair stops working?
Your turn1 of 2
Without a single bone inside it, would your body collapse into a floppy heap?Circulatory System
- How it worksHow does your heart pump blood in a complete loop out to your body and back through your lungs?
- Worked exampleFind how many times your heart beats in one hour if it beats about 80 times every minute.
- Common mistakeWhy isn't all the blood in your body the exact same bright red color at all times?
Your turn1 of 2
Find how many times your heart beats in one hour if it beats about 88 times every minute.Respiratory System
- How it worksHow do your lungs pull in oxygen and push out carbon dioxide with every single breath?
- Worked exampleFind how many breaths you take in 10 minutes if you breathe about 15 times every minute.
- Common mistakeWhy doesn't your stomach do all the work of digestion by itself, with no help from any other organ?
- Going furtherWhat happens to your breathing rate and depth during hard exercise compared to sitting still?
Your turn1 of 2
Find how many breaths you take in 14 minutes if you breathe about 15 times every minute.Digestive System
- How it worksHow does food travel from your mouth through a long tube, getting broken down the whole way, until nutrients enter your blood?
- Common mistakeWhy doesn't your stomach alone finish digesting your food, with no help from any other organ?
- Going furtherWhat happens to digestion if food moves through your intestines much faster than normal?
Your turn1 of 2
A sandwich you swallow whole eventually ends up as energy in your muscles hours later. How does that actually happen?Nervous System
- How it worksHow do electrical signals race from your skin to your spinal cord and back to your muscles in a reflex?
- Worked exampleFind why a reflex reaction can beat a decision to a hot stove, if a reflex skips the roughly quarter-second trip up to your brain.
- Common mistakeWhy doesn't every single one of your body's reactions have to travel all the way up to your brain first?
Your turn1 of 2
A reflex skips the roughly quarter-second (0.25 second) trip up to the brain. If a conscious reaction to the same stove takes 0.787 seconds in total, find how many seconds faster the reflex is.Germs and the Immune System
- How it worksHow do white blood cells recognize, attack, and remember an invading germ?
- Common mistakeWhy doesn't taking antibiotics do anything to cure a cold, which is caused by a virus, not bacteria?
- Going furtherWhat happens the second time the same germ invades your body after your immune system has already fought it once?
- Ties togetherHow does your immune system remembering a germ connect to the way a vaccine works?
Your turn1 of 2
You usually get better from a cold on your own, without ever taking a single medicine for it. Why?