Pearson Edexcel International GCSE (9-1) Biology Student Book

Pdf Book Name: Pearson Edexcel International GCSE (9-1) Biology Student Book
Author: Philip Bradfield, Steve Potter
Publisher: Pearson Education Limited
ISBN-10, 13: 9780435185084, 043518508X
Year: 2017
Pages: 336 / 179 Pages
Language: English
File size: 33 MB
File format: PDF,EPUB

Pearson Edexcel International GCSE (9-1) Biology Student Book Pdf Book Description:

All living organisms are composed of microscopic umts known as cells. i These building blocks of life have a number of features in common, which allow them to grow, reproduce, and generate more organisms. In Chapter 1 we start by looking at the structure and function of cells, and tile essential life processes that go on within them. Despite the fact that cells are similar in structure, mere are many millions of different species of organisms. Chapter 2 looks at the diversity of living things and how we can classify them into groups on the basis of the features tha1 they show. This part of the book describes the cell structure of ‘higher’ organisms such as animals, plants and fungi. The cells of bacteria are simpler in structure and will be described in Chapter 2. Most cells contain certain parts such as the nucleus, cytoplasm and cell membrane. Some cells have structures missing, for instance red blood cells are unusual in that they have no nucleus. The first chapter in a biology textbook will usually present diagrams of ‘typical’ plant and animal cells. In fact, there is really no such thing as a ‘typical’ cell. Humans, for example, are composed of hundreds of different kinds of cells – from nerve cells to blood cells, skin cells to liver cells. What we really mean by a ‘typical’ cell is a general diagram that shows all the features that you will find in most cells (Figure 1.2).

However, not all these are present in all cells – for example the cells in the parts of a plant that are not green do not contain chloroplasts. The chemical reactions that take place in a cell are controlled by a group of proteins called enzymes. Enzymes are biological catalysts. A catalyst is a chemical which speeds up a reaction without being used up itself. It takes part in the reaction, but afterwards is unchanged and free to catalyse more reactions. Cells contain hundreds of different enzymes, each catalysing a different reaction. This is how the activities of a cell are controlled the nucleus contains the genes, which control the production of enzymes, which then catalyse reactions in the cytoplasm: genes proteins (enzymes) catalyse reactions Every1hing a cell does depends on which enzymes it can make, which in turn depends on which genes in its nucleus are working. What hasn’t been mentioned is why enzymes are needed at all. They are necessary because the temperatures inside organisms are low (e.g. the human body temperature is about 37 °C) and without catalysts, most of the reactions that happen in cells would be far too slow to allow life to go on. The reactions can only take place quickly enough when enzymes are present to speed them up. It is possible for there to be thousands of different sorts of enzymes because they are proteins, and protein molecules have an enormous range of structures and shapes (see Chapter 4).

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