The cell is the simplest living unit capable of performing the three life processes: nutrition , sensitivity and reproduction . Human cells are eukar yotic ( from eu, "true" and kar yon, "nucleus") animal cells. These cells have a nucleus, which contains the genetic material . In contrast, the genetic material in prokar yotic cells is dispersed in the cytoplasm. Human cells are also heterotrophic. They acquire substances and oxygen, and use these to obtain energy and the materials needed to grow and renew cellular structures. 7 Think about how you will represent the cellular level in your art exhibition. Here are some ideas: A 3-D model of a cell. You could use modelling clay, polystyrene, EVA foam, etc. If the materials are recycled, even better. Large, colourful photos and explanations of each organelle. Videos about the discovery and the functioning of the optical microscope. 8 According to cell theory, the cell is the anatomical and physiological unit of living things, and cells are the unit of origin. Look for information about cell theory and briefly explain these terms. 9 How are ribosomes, endoplasmic reticulum, the Golgi apparatus and vesicles related? 10 What role does the cytoskeleton play in a cell? Do you think there are any organs in the body that carry out a similar task? Which ones? 2. Human cells Nucleus. This is usually spherical . It is surrounded by a double membrane with tiny pores that allow the exchange of substances with the rest of the cell . The nucleus contains: Nucleoplasm : f luid found in the nucleus. Nucleolus: a round structure with no membrane. Ribosomes are produced here. Chromatin : a combination of DNA and proteins. The DNA contains the genetic material of the cell . Cell membrane. This is a fine layer that surrounds and protects the cell . It has receptors that allow the cells to recognise each other. These receptors also regulate the exchange of substances with the outside environment. Cytoplasm. This includes the f luid inside the cell or cytosol, where the organelles and the cytoskeleton are located . Various cellular chemical reactions take place in the cytoplasm. Mitochondria Cytoskeleton Ribosomes CHALLENGE 20
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