Humans are multicellular beings. Our body is made up of more than 30 trillion (30 000 000 000 000) cells. However, they are not all the same. An adult has more than 200 dif ferent types of cells, each one with a specific size and shape. The shape they acquire in tissue is quite varied , and depends on the task the cells carr y out. 13 You can complete the art exhibit on the cellular level with posters showing interesting facts. For example, which are the largest and the smallest cells in our body? Which types of cells have the longest and the shortest lifespans? 14 Do you think a neuron and a skin cell contain the same genetic information? Why? 15 The vast majority of our cells are continuously renewing themselves. Why, then, do you think we grow old? 16 What are stem cells? Research the types of stem cells that are currently known. Identify the cell types that they will become. 17 On the Cancer Research UK website you can find a lot of information about cancer. Make a presentation to include in your art exhibition. Emphasise the importance of knowing the risk factors in order to prevent cancer. 1 3. Cellular differentiation The surface of an intestinal epithelial cell is full of folds. This is to increase the absorption surface area . These types of cells are about 10 µm long. Muscle cells are long and fusiform. They can contract and relax. These cells range from 10 to 100 µm in length . All cells originate from a single cell (a zygote) and carr y the same information passed down from their progenitors. So how is it possible that there are so many dif ferent types of cells? During the embr yonic stage, cells specialise. In other words, a portion of their genetic information defines their shape, size and structure. These characteristics allow them to carr y out a specialised task in a tissue or organ . This process is called cellular dif ferentiation. Neurons are ner ve cells that transmit information . They can measure up to several centimetres in length . Nerve cell (neuron) Fertilised ovum Zygote Embryo Epithelial cells Blood cells Stem cell. It can differentiate into many different types of cell. CHALLENGE 23
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