The iGCSE so far!

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Answer explanation

Proteases are a group of enzymes in the digestive track, responsible for the breaking down of proteins into amino acids. Remember, the function of an enzyme is to break down large food molecules into smaller ones.

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Answer explanation

Respiration is the process in which glucose (C6H12O6) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).

The full chemical equation for respiration is

C6H12O6 + 6O2 ------> CO2 + H2O

Respiration is a very good example of combustion reaction.

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Answer explanation

The question gave a lot of different names. The colon, rectum and anus are part of the large intestine, while the ileum and the duodenum are part of the small intestine.

Remember that the small intestine is where most of the absorption of broken down nutrients happen through the villi, which increase the surface area of the small intestine.

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Answer explanation

Both carbohydrates and fats are composed of the same three elements: Carbon, Hydrogen and Oxygen. Excess carbohydrates can be stored as fat, and stored fat can be converted into carbohydrates by the liver (for energy).

Proteins contain nitrogen, as well as the other three elements. An example is that plants require nitrates NH₃^- ions from the soil. Together with glucose (a carbohydrate), the plant makes an amino acid, which then forms protein to aid in the growth of the plant.

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Answer explanation

In a very special type of combustion reaction, respiration, glucose and oxygen react to form carbon dioxide and water.

The energy produced in respiration (ATP), is very important to maintain the body working properly, for chemical reactions to continue to happen.

This includes the synthesis (the putting together) of amino acids to form protein, resulting in growth and repair.

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Answer explanation

As it can be seen, before the reaction, the thermometer is measuring a temperature that is between 13^oC and 14^oC. The scale of the thermometer is every 0.1^oC (every degree is divided in 10 equal spaces). The marking is exactly half way between the two temperatures, giving a temperature of 13.5^oC.

After the reaction, the thermometer is measuring a temperature between 34^oC and 35^oC. Again, that degree is divided in 10. The marking is one line above 34^oC, giving a temperature of 34.1^oC.

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Answer explanation

At the centre of an atom, you will find the nucleus, where protons and neutrons are located (the nucleons). Orbiting around the nucleus, you will find the electrons.

For the first 20 elements in the periodic table, the arrangement of electrons in each orbital (or shell) is assumed to be

2 electrons in the first orbital/shell

8 electrons in the second orbital/shell

8 electrons in the third orbital/shell

8 electrons in the fourth orbital/shell

Beyond the 20th element, this rule no longer works (it gets more complicated!)

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Answer explanation

In this question, it is only a matter of counting.

One thing that is important to mention is that every element on the period table is either symbolised by a capital letter only (Like oxygen, O), or by a capital letter, followed by a lower case letter (like Iron, Fe).

Do not mistake Fe for two elements!!!!

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Answer explanation

In electrolysis, it is important for us to make sure that we understand that the anode is the electrode that has excess positive charge, so it will attract the anion, the negatively charged ion. In the case of this problem, the anion is formed by a halogen (all group VII elements are called halogens).

Non-metals usually form anions by accepting an electron.

A cathode is the electrode with excess electrons (the negative electrode), which will accept cations (positively charged ions). Metals usually form cations and, during electrolysis, the cation is attracted towards the cathode.

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Answer explanation

In an endothermic reaction, the reactants need to absorb energy from its surroundings. If heat is absorbed from the surrounds for the reactions to happen, this will cause the temperature to decrease.