Underwater challenge

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Adam in invisible car

Invisible challenge

Have you ever wanted to make something invisible? Well now's your chance - see if you can make something disappear with the invisibility challenge.

In the underwater episode of Science Shack, Adam challenged the team to build him a self-contained underwater environment. They succeeded, but what did they have to take into account?

A human being can survive three months without food, three days without water, but only three minutes without air. So in order of importance we need air, water and food. Of course, to live on the sea floor we would also need power to generate light and heat, but this could be in the form of electricity generated by waves, tide or sun.

As mentioned above, air is the most critical factor. A human uses about half a litre of oxygen (O₂) per minute, so in a space of 4m³ there’s enough oxygen for about 4 hours. The critical limiting factor is the carbon dioxide (CO₂) that we breathe out at a concentration of about 3.5% (35,000 ppm). This corresponds to just under half a litre per minute (0.4 litre per minute) of pure CO₂. Humans are affected by too much CO₂ in the air, more quickly than by lack of oxygen. CO₂ can be removed from the air chemically, using a CO₂ scrubber. A scrubber contains particles of soda lime, which the CO₂ reacts with to form chalk. But there’s a more simple way to get rid of CO₂ which lasts forever. Plants take in CO₂ and give off oxygen in a process called photosynthesis, 12m² of plants would produce enough oxygen to keep a human being alive, and at the same time they would naturally ‘scrub’ the air clean of CO₂.

Next we need water - humans lose water every time they breathe out and by sweating. At depth underwater it is very cold and water would condense on a cold metal wall of the underwater habitat, so all we’d need is a handy little funnel on the bare wall and a bottle to collect the water.

What about food? Well we could build an artificial reef to attract sea creatures, or we could use hydroponics, which is a way of growing plants in a controlled environment. Hydroponics don’t need soil because they are grown on rock-wool, or in water which is full of minerals and nutrients, but they do need light. Unfortunately one person would need about 80m² of plants to keep them going.

We don’t suggest you try and build your own underwater habitat, but in the programme Adam found out how a closed ecological system works - where plant and animal life are permanently sealed in a balanced, self-sustaining micro-environment. You can make your own simple system using pond water and a bottle.

The idea is that tiny animals in the water take in oxygen from the water and eat algae, whilst giving out carbon dioxide and waste products. Micro-organisms (too small to see by eye) break down this waste, and produce nutrients. The algae (and other plant life) use the carbon dioxide and nutrients to grow and produce oxygen, thus sustaining the animal life. In this way the system recycles itself in a sustainable way - so you should be able to keep your mini ecosystem for months!

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