IB Biology HL Exam Review

the cell theory. -Answer Living organisms are composed of cells. Cells are the smallest unit of life. Cells come from pre-existing cells. Discuss the evidence for the cell theory. -Answer The nature of scientific theories could be introduced here: the accumulation of evidence that allows a hypothesis to become a theory; whether a theory should be abandoned when there is evidence that it does not offer a full explanation; and what evidence is needed for a theory to be adopted or rejected. State that unicellular organisms carry out all the functions of life (Name the six functions). -Answer Metabolism, response, homeostasis, growth, reproduction, and nutrition. Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles, and cells using the appropriate SI unit. -Answer Molecules: 1 nm Thickness of membranes: 10 nm Viruses: 100 nm Bacteria: 1 um Organelles: (up to) 10 um Most cells: (up to) 100 um Explain the importance of the surface area to volume ratio as a factor limiting cell size. -Answer The rate of heat production/waste production/resource consumption of a cell is a function of its volume, whereas the rate of exchange of materials and energy (heat) is a function of its surface area. State that multicellular organisms show emergent properties. [pen analogy] -Answer Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts. How do multicellular organisms differentiate to carry out specialized functions? -Answer By expressing some of their genes but not others. What two abilities do stem cells have? -Answer Stem cells retain the capacity to divide and have the ability to differentiate along different pathways. Outline one therapeutic use of stem cells. -Answer In 2005, stem cells were used to restore the insulation tissue of neurons in laboratory rats, resulting in subsequent improvements in their mobility. How do prokaryotic cells divide? -Answer Binary fission