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Chemical reactions and catalysts

A chemical reaction involves a chemical change, which happens when two or more particles (which can be molecules, atoms or ions) interact. For example, when iron and oxygen react, they change to ...

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How elements are formed

Our world is made of elements and combinations of elements called compounds. An element is a pure substance made of atoms that are all of the same type. At present, 116 elements are known, and ...

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Digestive enzymes

Enzymes are globular proteins that control biological reactions. Digestive enzymes speed up the breakdown (hydrolysis) of food molecules into their ‘building block’ components. These reactions ...

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The ocean and the carbon cycle

The ocean plays an important role in the global carbon cycle. Carbon moves in and out of the ocean daily, but it is also stored there for thousands of years. The carbon cycle Carbon is a chemical ...

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What is fire?

Fire is the visible effect of the process of combustion – a special type of chemical reaction. It occurs between oxygen in the air and some sort of fuel. The products from the chemical reaction ...

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Development of the periodic table

Although elements such as gold, silver, tin, copper, lead and mercury have been known since earliest times, the first scientific discovery of an element occurred in 1649. Hennig Brand, a German ...

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Cleaning up the oil spill

On 5 October 2011, the cargo vessel Rena ran aground on the Astrolabe Reef. The ship was carrying 1700 tonnes of heavy fuel oil and about 200 tonnes of diesel in its tanks. Over 360 tonnes of ...

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Mitochondria – cell powerhouses

Mitochondria are tiny organelles inside cells that are involved in releasing energy from food. This process is known as cellular respiration. It is for this reason that mitochondria are often ...

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Ocean dissolved gases

Seawater has many different gases dissolved in it, especially nitrogen, oxygen and carbon dioxide. It exchanges these gases with the atmosphere to keep a balance between the ocean and the ...

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Carbon cycle

The carbon cycle can seem like a complex process because there are many interacting parts. Carbon is found in both organic (living) and inorganic (non-living) forms. Before we discuss the cycle ...

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What is smoke?

What is smoke and why do some fires seem to have more smoke than others? Smoke is a collection of tiny solid, liquid and gas particles. Although smoke can contain hundreds of different chemicals ...

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Carbonate chemistry

Calcium carbonate is the principal mineral component of limestone. Its chemical and physical properties lie behind the modern-day uses of limestone as well as the unique limestone landscapes of ...

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Digestion – breaking the large into the small

Digestion of food involves both physical and chemical processes. Through digestion, large food particles are converted into smaller components that can be readily absorbed into the bloodstream. ...

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Fire behaviour

Fires behave differently. Some burn slowly and evenly; others are extremely hot, burning fiercely and quickly. Different fires have different coloured flames. Some fires start easily; others ...

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What is energy?

This is both a simple and complex question. Energy is in everything – it is often described as ‘the ability to do work’. Almost all food energy comes originally from sunlight. The chemical ...

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Non-renewable energy sources

Energy comes from many sources, and to describe these sources we use two terms: renewable and non-renewable. Non-renewable energy resources cannot be replaced – once they are used up, they will ...

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Rate of digestion

Digestion of food involves chemical reactions that break up large food molecules into their ‘building block’ components. There are a number of factors that affect the rates of these reactions ...

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Hormonal control of digestion

It has now been well established that gut hormones have a key role in controlling food intake and energy expenditure. The gut is the body’s largest hormone-producing organ, releasing more than 20 ...

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Water density

Water density changes with temperature and salinity. Density is measured as mass (g) per unit of volume (cm³). Water is densest at 3.98°C and is least dense at 0°C (freezing point). Why does ice ...

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Bone and tooth minerals

The minerals found in human teeth and bones that give them their hardness and strength belong to a group of minerals called biological apatites. The apatites found in bone, tooth enamel and tooth ...

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Viscosity

If you poured some water down a slope, it would flow freely and quickly, but what about if you repeated the process with honey? Can you imagine how honey would flow down a slope? Sticky oozy ...

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Unlocking the energy in foods

The foods we eat supply the energy needed by the body to drive its complex chemical, mechanical and electrical systems. Where does this energy come from, how is it locked into food molecules and ...

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