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An impulse travels along the pre-synaptic neurone, and when it reaches the axon ending it stimulates calcium channles to open on the pre-synaptic membrane. This allows calcium ions to rush into the neuron...

The two main past tenses in German are the simple past and the present perfect. The simple past uses just one word, for example 'ich ging', while the present perfect uses two words, for example 'ich bin g...

Enzymes are proteins. They are biological catalysts, meaning they increase the rate of reaction without being used up or changed. Different enzymes have different optimum temperatures and pHs, depending o...

The imperfect tense is a past tense. There are three reasons why we might use the imperfect tense and these can be remembered as: habitual, incomplete and descriptive. What does 'habitual' mean? Habitual ...

A 'non-specific' defence system means that its response is the same for every invader (pathogen). In the human body this includes:

Skin- a physical barrier between the outside worl...