Category: Year10 Science

Oxygen and digested food travel around the body in the blood. Blood flows through tubes called blood vessels. The smallest blood vessels are capillaries. They have thin walls with tiny gaps in so that small molecules, like water, can easily get into and out of them.

Diet

In science, the word diet means ‘what you eat’. Your food is a source of raw materials for your body. These raw materials are needed to make new substances for:

1. Energy
2. Growth and repair
3. Health

Testing nutrients

We can find out which nutrients a food contains by testing it.

Starch is a type of carbohydrate. We can test for starch by adding two drops of iodine solution to a food sample. If starch is there you will see a blue/black colour.

We can test for fat by rubbing a small dry food samples on some white paper. Hold the paper up to the light. Fat will leave a greasy mark.

Balanced diet

Different foods contain different substances. There is no one food that contains all the substances that you need. You need to eat a wide variety of foods. This is called having a balanced diet. It does not matter exactly what you eat as long as you eat a balanced diet. In some parts of the world, people cannot get enough to eat and they starve. In other areas people get diseases caused by a lack of a nutrient. In New Zealand, many people are concerned about eating too much fat and sugar. Scientists and nutritionists think that eating too much fat can cause diabetes and heart diseases.

Some people go on weight control that makes them ill because the diets are not balanced or contain too little energy. People who do not eat enough often feel weak and tired. In some cases this can lead to life threatening disease called anorexia.

To stay healthy you have to keep the balanced right and eat a wide range of foods which contain all the nutrients you need.

Special diets: Diabetes

People with diabetes cannot control the amount of sugar called glucose in their blood. The amount of glucose in the blood increases after meal, but if it gets too high it can damage the kidneys and the brain. People with the disease inject a chemical called insulin which lowers the amound of glucose in the blood. Many diabetics also avoid eating too many sugary things to stop the glucose level getting too high.

People who have coeliac disease (see-li-ack) avoid eating wheat products. This is because they are allergic to a protein in wheat called gluten. The gluten causes parts of the intestine to become damaged and stops nutrients getting from their food into their bodies.

Corrosion of metals

Metals tend to be eaten away slowly by chemical reactions. They corrode. Corrosion is a big problem in all our lives. Building materials, fasteners, tools, utensils, car bodies and many other metal things are all slowly disappearing. Metals corrode because they combine with oxygen in the air. If people made no attempt to stop corrosion we would not be able to afford to replace the metal which is disappearing back into the earth.

Iron          +      Oxygen                 –>                      Iron Oxide

Sodium        +      Chlorine                –>                      Sodium chloride

reactant + reactant –> product

Many compounds are formed from just two elements. Table salt is an example. Sodium is a soft grey metal. Chlorine is a greenish yellow gas. Both of these elements are dangerous. When sodium burns in chlorine a compound is made that is safe to eat – table salt. The chemical name for common salt is Sodium chloride.

Insulators and Conductors: Electrical and heat

• Metals conduct electricity. (Allow electricity to pass through them)
• Plastic is an electrical insulator. (Does not allow electricity to pass through)
• Some metals are magnetic (See magnetism)
• Metals are malleable, they can be molded into shape.
• As well as electrical conductors and insulators, there are thermal conductors and insulators. When we use a saucepan we don’t want to burn our hands on them so we make the handles out of materials that won’t get hot so quickly like wood or plastic.
• Thermal Insulators don’t allow heat to pass through them easily.  We want the food in the saucepan to get hot quickly so we make the saucepan out of metal, which is a good conductor of heat, it allows heat to pass through it easily.

• Thermal conductors, allow heat to pass through them quickly

Metals

Metals are classed as metals because they have certain similar properties. Other elements are classed as non-metals because they have certain other similar properties which are different from those of metals.

Metals are shiny when they are polished, where as non-metals do not shine when polished. Most metals are solid at room temperature, while non-metals can be in any of the three states of matter at room temperature. Metals are good conductors of heat and electricity, while non-metals are not. Metals can be hammered into sheets and stretched into wires, but non-metals cannot.

Some substances are classified as metal:

• Are found underground.
• Have many useful properties:

Strong, malleable, shiny, can be recycled, some are magnetic, some are good conductors of electricity, good conductors of heat.

• Some have a weakness: they corrode (rust).

Non-Metal

Only 22 of the elements are non-metals. Half of these are gases, only one (bromine) is a liquid. The rest are solids. All of these elements are found on the Periodic Table.

One of the solid non-metals is sulphur. Sulphur is found naturally in areas where there are volcanoes. Sulphur melts quite easily. Like almost all non-metals it will not conduct heat or electricity.