Immune System

Tanno and Iguda are lucky enough to see how the body defends itself against pathogens.

These are microorganisms that can cause disease, and bacteria are an example.

Images Credit Kelly Cassidy

The explorers watch a phagocyte, a type of white blood cell, recognise that the bacteria do not belong to Professor Wendy’s body and engulf it. Once engulfed, the bacterium is digested. The diagram below shows the stages of this whole process, called phagocytosis.

Image credit: Kelly Cassidy

Tanno and Iguda pass the knee as they travel down the leg, searching for the cause of the Professor’s illness.

The knee is a working part of the skeleton, which is mostly made out of bone. More than 200 bones, in fact. The functions of the skeleton are to support the body, to protect the organs, to help the body move, and to make blood cells.

The skeleton moves at joints, with the bones actually being moved by muscles. The knee is an example of a hinge joint, which has the same kind of movement as opening and closing a door (try bending your knee and then straightening your leg to see how this works).

Image credit: Newcastle University

Activity 1

Bendy bones

Bone is made up of two main substances. Collagen is flexible and tough (it is the stuff your nose is made out of) but it’s not rigid enough to support large forces. The second substance, called hydroxy-apatite (which contains calcium), makes the bones stiff.

1) Take a few chicken bones and clean off all the old bits of meat.
2) Put them in a jar of vinegar for 1-2 weeks.
After this time, take the bones out and feel them. Have they changed at all?

When you leave the bones in vinegar, the hydroxy-apatite dissolves away, leaving the collagen. Now you can see why this substance on its own is not enough to make up bones.

Activity 2

Modelling phagocytosis

You will need 2 different colours of plasticine and the picture from the front of the Immune System postcard.

1) Use one colour of plasticine to make a small model of a bacterium. This can look as gross as you like!
2) Use the other colour of plasticine to make a larger 3D model of the phagocyte. This should be roughly spherical, but does not have to be perfect (as the cell changes it shape all the time).
3) Now use your models to reproduce each stage of phagocytosis, using the diagram on the postcard and/or this webpage to help you.
4) For each stage, take a photo so you can build these up into a picture story of phagocytosis. If you use a smartphone or tablet, you could use an animation app to turn this into a movie!

Ask an adult to post your video to the PostcardsFromSpace Facebook group, or put it on TikTok and tag in PostcardsFromSpace!

You can go to the previous PostcardsFromTheBody secret pages by clicking the places below.

MouthStomachSmall Intestine
Photo of PostcardFromThe Mouth
Large IntestineBloodHeart
PostcardFromThe Pancreas