IGCSE SCHOOL: 2012

IGCSE Biology Revision ( Enzymes )

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Enzymes are biological catalysts. They speed up chemical reactions in all living things, and allow them to occur more easily.

They occur in plant cells and animal cells. Without them we would not be alive.

Although they work powerfully, enzymes are just chemical molecules, made up of proteins. They are too small to be seen either when they are inside cells or after they have been released from them, for example in the digestive system.

Each particular enzyme has a unique, 3-dimensional shape shared by all its molecules. Within this shape there is an area called the active site where the chemical reactions occur.

What do enzymes do?

Some enzymes help to break down large molecules. Others build up large molecules from small ones. While many others help turn one molecule into another.

Probably the fastest enzyme known is called catalase.

It breaks the chemical hydrogen peroxide down to water and oxygen. Catalase is found in all cells and protects them from this dangerous waste chemical.

The substrate (hydrogen peroxide) and the catalase molecules are continuously on the move. Every so often they will collide so that the substrate molecule(s) fits into the enzyme's active site.

Then the substrate is broken down into the two products.

The enzyme is not used up in the reaction. It is ready to work again!

No matter what job an enzyme does it will work in a similar way.

Optimum conditions

Although they can do fantastic things they are sensitive and work best under specific conditions.

Each type of enzyme has its own specific optimum conditions under which it works best.

Enzymes work best when they have a high enough substrate concentration for the reaction they catalyse. If too little substrate is available the rate of the reaction is slowed and cannot increase any further.

Sometimes, if too much product accumulates, the reaction can also be slowed down. So it is important that the product is removed.

The pH must be correct for each enzyme. If the conditions are too alkaline or acidic then the activity of the enzyme is affected. This happens because the enzyme's shape, especially the active site, is changed. It isdenatured, and cannot hold the substrate molecule.

Temperature is a key factor too. If it is too cold the enzymes will move around too slowly to meet the substrate molecules, so the reaction rate is slowed. Likewise, if it is too warm they do not work properly either. This is because the extra heat energy shakes them around so much that the active sites change shape so, just like with pH, the enzyme molecules are denatured, and can't hold the substrate.

Enzymes everywhere!

Enzymes control all kinds of reactions in all cells. For example, they help control respiration, photosynthesis, and our digestion, amongst many others.

We also make use of enzymes elsewhere. Protease and lipase enzymes are used in biological washing powders to remove those stubborn stains.

Enzymes are also used in making foods and drinks. The enzyme pectinase helps to break down the cells in fruit to release more of their juice.

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How does the IGCSE compare to other programmes like CBSE, ICSE or the Middle Years Programme of the IB?

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How does the IGCSE compare to other programmes like CBSE, ICSE or the Middle Years Programme of the IB?

Like other modern programmes, IGCSE offers a wider range of subjects and encourages high academic standards through a practical approach to teaching and learning. Assessment is not limited to conventional written papers and they consist of a variety of tests e.g. oral and listening tests.

The assessment is aimed at a wide ability range of students, with an eight-point grading scale, from A+ to G, with A+ being the highest.

IGCSE is a balanced curriculum and a flexible course of study.

Most subjects offer a choice between core curriculum and extended curriculum.

This gives students of all ability levels the freedom to choose subjects that are right for them and, thereby, the opportunity to score good grades.

The core curriculum is an overview of the subject and is suitable for students who are expected to achieve grades C to G.

The extended curriculum is, sort of, a specialisation in that subject. It is more challenging and designed for students who are expected to achieve grades A+ to C.

While the syllabi and curricula of both IB MYP and IGCSE have an international outlook, IGCSE appears to be slightly better, in that it is tailored for a more multi-cultural and more multi-lingual audience.

Does the IGCSE start only in Class 9? What about the primary years? Can a student do IGCSE after completing his/ her earlier schooling through a different board?

Currently, IGCSE is a two-year programme starting at the Class 9 level. A student who has done his/ her early schooling from any other board can join the IGCSE programme at the Class 9 level.

CIE has declared the launch of its new Cambridge International Primary Programme in June this year.

The introduction of this programme means students will be able to study the IGCSE from age five through age18.

What are the subjects in the IGCSE curriculum?

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What are the subjects in the IGCSE curriculum?

There are five Subject Groups in IGCSE with several subjects to choose from, in each group:

Group 1: Languages (First Language, Second Language, Foreign Language, etc)
Group 2: Humanities and Social Sciences (Geography, English Literature, History, etc)
Group 3: Sciences (Biology, Chemistry, Physics, etc)
Group 4: Mathematics (Mathematics, Additional Mathematics, etc)
Group 5: Creative, Technical & Vocational (Accounting, Business Studies, Computer Studies, Music, etc)

For each subject, the certificate merely indicates the grades scored, and not pass or fail.

Five scores of 'C' or higher indicates a students readiness to pursue +2 level qualifications, like the Class 12 CBSE, IB Diploma, Advanced Placement Diploma (US), etc.

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What is IGCSE ?

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Cambridge IGCSE is the world’s most popular international curriculum for 14-16 year olds, leading to globally recognised and valued Cambridge IGCSE qualifications. It is part of the Cambridge Secondary 2 stage.

The International General Certificate of Secondary Education (abbreviated IGCSE) is an internationally recognised qualification for school students, typically in the 14–16 age group. It is similar to the GCSE in England, Wales and Northern Ireland, Standard Grade in Scotland or Junior Certificate in the Republic of Ireland. The IGCSE was developed by University of Cambridge International Examinations in 1988. The examination board Edexcel offers its own version, the Edexcel IGCSE. The term "IGCSE" is the registered trade mark of the University of Cambridge and is used under licence.

Schools worldwide have helped develop Cambridge IGCSE, which provides excellent preparation for the Cambridge Advanced stage including Cambridge International AS and A Levels and Cambridge Pre-U, as well as other progression routes. It incorporates the best in international education for learners at this level. It develops in line with changing needs, and is regularly updated and extended. Cambridge IGCSE teachers can draw on excellent resources, training and advice from subject experts.

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