If you've looked at the activity called "How does blood go around our bodies?" you'll know that we compared our circulation system with a school. It's helpful to think of the deliveries a school receives: lorries and vans bring food, parcels, letters, equipment; cars bring students and teachers; pipes bring water; cables bring electricity, and so on. In the same way, the school's waste needs to be removed by refuse trucks, recycling vans, drains etc.
The blood circulating in your body is doing much the same task: picking up the nutrients, oxygen, hormones (that's instruction-giving chemicals) our body systems need and then collecting wastes (like CO2 and urea - that's protein waste that's sent to the kidneys to be turned into urine) and delivering those to organs like lungs and kidneys to be removed (or excreted) from the body.
In this activity, we'll look more closely at how the blood is acting as our delivery system - and remember: whether you're you, a blackbird, a trout or an octopus, the blood does the same job.