1Into the blood
Digestion makes small, soluble molecules such as sugar. They pass through the wall of the small intestine into the blood, which carries them round your body. This is absorption.
absorption
Lesson 4.4 notes
Absorption, gut bacteria and plants
See how digested food gets into your blood, why the bacteria in your gut matter, and how plants get their food without eating.
2Villi
The inside of the small intestine is covered in millions of tiny finger-like villi. They give it a huge surface area, so food is absorbed quickly.
villisurface area
3A villus close up
The wall of each villus is only one cell thick, so molecules have a short way to go. A good blood supply carries them away quickly.
villus
4Bacteria in your gut
Trillions of bacteria live in your large intestine. Most are helpful: they break down some of the fibre your enzymes can't, and they make vitamins, such as vitamin K.
bacteria
5Bacteria that protect you
Helpful gut bacteria leave little room for harmful ones to grow. Antibiotics can kill the helpful bacteria too, which is why they sometimes upset your stomach.
antibiotics
6Plants make their own food
Plants don't eat. They make carbohydrates in their leaves by photosynthesis, using light, carbon dioxide and water, and they give off oxygen.
photosynthesis
7Roots
Roots take in water and minerals from the soil. Plants need minerals such as nitrates to grow well, so farmers add fertiliser to replace what crops use up.
rootsmineralsfertiliser
Explore: Absorption lab
Compare a flat gut wall with one covered in villi. Change the villi, the wall and the blood flow, and watch how fast digested food is absorbed.
Common mistake: Plants don't get their food from the soil
Plants make their own food, by photosynthesis in their leaves. From the soil, their roots take in water and minerals, not food.
Remember
- Small, soluble molecules from digestion pass through the wall of the small intestine into the blood.
- Millions of villi give the small intestine a huge surface area. Their walls are one cell thick, and they have a good blood supply.
- Helpful gut bacteria break down fibre and make vitamins. Plants make carbohydrates by photosynthesis and take in water and minerals through their roots.
Going further at GCSE