WJEC Biology for AS: Student Bk

By the end of this topic you will be able to: ▪ ▪ Recognise, describe and explain the functions of cellular structures: the nucleus, including the nuclear envelope, chromatin and nucleolus, rough and smooth endoplasmic reticulum, mitochondria, chloroplasts, ribosomes, lysosomes, Golgi body, centrioles, plasmodesmata. ▪ ▪ Describe how organelles are interrelated. ▪ ▪ Describe the structure of prokaryotic cells and viruses. ▪ ▪ Describe the similarities and differences between prokaryotic and eukaryotic cells. ▪ ▪ Describe the differences between plant and animal cells. ▪ ▪ Explain the levels of organisation of living organisms and the meanings of the terms ‘tissue’, ‘organ’ and ‘system’, giving examples in plants and animals. ▪ ▪ Interpret drawings and photographs of plant and animal cells as seen using electron and light microscopes. ▪ ▪ Know how to calibrate a light microscope and determine the sizes of structures. ▪ ▪ Know how to calculate the magnification of an image. Cells are the fundamental units of life, in which metabolic reactions occur. The detailed structure of a cell, as revealed by the electron microscope, is called its ultrastructure. Simple organisms comprise only one cell, that is, they are unicellular. More complex organisms consist of many cells and are multicellular. They have specialised cells, which carry out particular functions. Although cells have features in common, they differ in their internal structure, related to their different functions. There are two types of cells: prokaryotic cells and eukaryotic cells. Eukaryotic cells have a distinct nucleus and membrane-bound organelles. Prokaryotic cells include those of bacteria and have a simpler structure, such as the absence of a nucleus. Topic contents 31 Cells and their organisation 38 Prokaryotic and eukaryotic cells and viruses 39 Levels of organisation 44 Practical microscopy CH 2 Cell structure and organisation 30