Getting to grips with the numbers behind the man's part of the reproductive system. THIS ARTICLE CONTAINS FRANK DISCUSSION OF SEXUAL AND REPRODUCTIVE SCIENCE

Alternative energy sources are seen by many people as potential solutions to the many economic and environmental challenges posed by the current dominance of world energy supply by fossil and nucler fuels. Just how realistic are these hopes? Energy resources: Alternative energy in perspective, is a free course that summarises the technical and geographic challenges posed by each alternative source. It is left to you to judge the feasibility of implementing these changes against the claims for 'alternative' solutions to global energy challenges that are regularly made.

There is a fascinating world of nature all around us which we can see if we know how to look for it. Wherever you live, be it in a city or the countryside, you will find areas that support a range of wildlife. This free course, Neighbourhood nature, will provide you with basic scientific and observational skills so that you can go into your local neighbourhood to discover the animals and plants in open spaces. You will learn how to observe, identify and record the wildlife around you, building up a picture of a small part of your local environment.

In the 18th and 19th century evolutionary biologists, including Darwin, emphasised the similarities between natural evolution and artificial 'improvement' of livestock under domestication. They believed that studying domesticated animals and plants could illuminate the mechanisms of natural evolution. This free course, Evolution: artificial selection and domestication, provides an introduction to their work.

The extreme challenges of life in the polar regions require the animals who make their habitat there to make many adaptations. This free course, Animals at the extremes: Polar biology, explores the polar climate and how animals like reindeer, polar bears, penguins, sea life and even humans manage to survive there. It looks at the adaptations to physiological proceses, the environmental effects on diet, activity and fecundity, and contrasts the strategies of aquatic and land-based animals in surviving in this extreme habitat.

Is it a bird? Is it... a homeless snail? Or some sort of slug with superpowers? Leslie Noble goes behind the headline panics.

This free course, 'Land grab': an environmental issue?, explores how environmental problems are entangled with economic and political issues and offers tools for making sense of the complexity that results. The case of land grab illustrates how everyday issues such as food prices are caught up in connections that link different places, different people and their livelihoods across the globe; connections that are brought to life in the course through rich audio-visual material and interactive activities.