Unit D: Changes in Living Systems

Acid rain is any precipitation that has an unusually low pH. It can be rain, snow, fog, etc. But what is a low pH and why is this a problem?

Scientists have accumulated so much evidence in the theory of evolution that it is one of the most widely-accepted theories in science.

Ever wonder how fish survive in the cold waters of the Arctic and Antarctic? It’s partly because of a brilliant evolutionary adaptation.

Make a model of the water cycle and find out how water moves around on planet Earth.

Can carbon offsets help you reduce your environmental footprint, practice sustainable living and fight climate change?

This backgrounder explains what greenhouse gases are and how they contribute to climate change.

Biofuels like ethanol might help fight climate change. But they can contribute to food insecurity and greenhouse gases in ways that might surprise you.

What is the nitrogen cycle? How do human activities such as using fertilizer affect the nitrogen cycle? How can this cause greenhouse gases?

14 images of some plants such as carrots, cabbage and leeks whose roots, stems or leaves are used for food

Learn about two taxonomy systems that scientists use to classify the life around us.

1 diagram illustrating the water cycle

Cloning makes it possible to bring extinct species back to life. But is that a good idea?

10 images of some cold-blooded vertebrates such as snakes, lizards and alligators typically having dry, scaly skin

The water in the oceans has travelled vast distances. It has even time spent deep below the surface of the Earth, trapped inside the mineral ringwoodite.

The ocean is full of very small but very useful creatures called microbes. Without them, none of the sea plants or animals you’ve seen would exist!