IB BIO ESSAYS

IB BIOLOGY ESSAYS List of Chapters (HL & SL) 1.Cell Biology 2.Molecular Biology 3.Genetics 4.Ecology 5.Evolution 6.Human Physiology 7.Nucleic Acids 8.Metabolism 9.Plant Biology 10.Genetics 11.Animal Physiology

1.1 Introduction to Cell 1.List the key statements of the cell theory. ●Living organisms are made up of one or more cells. ●There is no smaller unit of life than cells. ●Every new cell must come from a pre-existing cell. 2.Outline 3 exceptions to the cell theory. ●Giant algae can grow up to 10 cm in length for a single cell but only have 1 nucleus. ●Striated muscle cells are very long, up to 30 cm, and have multiple nuclei (multinucleate). ●Aseptate fungi hyphae have no cross walls and multiple nuclei. 3.State and define the 7 functions of life displayed by all living organisms. ●Metabolism is the sum of all chemical reactions within the living organism ●Reproduction is the production of offspring ●Homeostasis is the maintenance of the internal environment ●Nutrition is the consumption of materials for growth and repair. Nutrients are the source of energy or matter to build the organism ●Excretion is the removal of the waste products of metabolism ●Response is sensing and responding to external stimuli ●Growth is the increase in cell number or size 4.Explain how surface area to volume ratio limits the size of cells. ●The rate at which metabolic reactions occur increases as the cell volume increases. ●The rate at which raw materials enter the cell and waste materials exit increases as surface area increases. 2

●As the cell grows and size increases, the volume increases faster than surface area. Thus the surface area to volume ratio decreases. ●If a cell is too large, it cannot take in raw materials nor export waste products fast enough to function and it may overheat, thus a cell can only grow up to a certain size. 5.How does cell differentiation occur? ●Cell division ensures all cells in a multicellular organism are genetically identical, so every cell in the body has the full set of genes ●During the differentiation of a cell, only some of the genes are expressed, while others are not expressed. ●In each type of specialised cell, a unique subset of genes will be expressed. ●Gene expression results in proteins being synthesised which determines the function of the cell 6.Describe the characteristics of stem cells that make them potentially useful in medicine. [5m] ●Stem cells can continually divide to produce large numbers of identical cells. They can be used to replace or repair damaged cells. ●Stem cells are undifferentiated, thus have the ability to differentiate to produce a large variety of different tissues or organs. For example, skin stem cells can be grown to produce skin grafts for burn victims and pancreatic islet beta cells can be developed to treat type 1 diabetes 7.Describe Stargadt’s disease and how stem cells can be used to treat it. ●Stargadt’s disease is a genetic disease that causes macular degeneration in children and young a