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IB Biology 2.1.1 Student Work Book Topic 2: Cells The Cell Theory Debate- Homework When there is evidence to disprove a theory scientists have to start doubting the theory. This is particulary difficult to do when the theory has obvious uses, and if the theory has been accepted for a long time. Cell theory is an example of a theory where it can be applied to nearly all organisms but with a few specific exceptions. Should we abandon the theory? Make a four slide presentation a) what are the key points of ‘cell theory’? b) describe the evidence that supports it? c) what examples of cells are there which don't support it. (ie; fungal hyphae, skeletal muscles, amoeba) d) Explain whether we should keep the cell theory or change it? Essential Content for the presentation Include the following evidence. Outline the cell theory. 2 Living organisms are composed of cells. Cells are the smallest unit of life. Cells come from pre-existing cells. TOK: The accumulation of evidence allows a Scientific hypothesis to become a Discuss the evidence for the cell theory. Deciding whether a theory should be abandoned when there is evidence 3 theory. that it does not offer a full explanation requires NEW EVIDENCE…the question is ‘How much?” This is evidence that contradicts Cell theory – State that unicellular organisms 1 carry out all the functions of life. These organisms are not made of cells, their bodies are not subdivided. The cell is an organism capable of metabolism, response, homeostasis, growth, reproduction and nutrition. Extra cellular components are not part of the cell. Outline two roles of extracellular components. (these are useful to cells but not part of the cell........ The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity. Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement. 2.1.6 Surface Area to Volume Ratio - Homework Sheet 1. Rank the following cells from smallest to largest in terms of surface area to volume ratio. Give reasons for the rankings you decide upon. (2 marks) 2. Why is a large surface area to volume ratio useful to a functioning cell? (1 mark) 3. Complete the following table that describes the dimensions of cube-shaped cells. All sides are of equal lengths (X) with surface area equal to (X squared) x 6 and volume equal to X cubed. (3 marks) 4. As cells increase in size the surface area to volume ratio ( increases / decreases ). What does this mean for the cell if it can only exchange nutrients and wastes at the cell membrane? (2 marks) 2.2 Prokaryotic cells Homework Sheet 1 hour Bacteria exist in three different shapes, coccus (round), spirilla (spiral), and baccilla (rod).Bacteria are very small, and with the exception of ribosomes, do not contain cellular organelles. They do have chromosomes, contained in a nucleoid region, which has no nuclear envelope. Because of this, bacteria are said to lack a nucleus – this gives them the name ‘prokaryotic’ – “before the nucleus”. Many bacteria have rings of DNA outside the nucleoid, called plasmids. 1. Match the descriptions and functions to the Bacteria structures in the table below – using numbers, lines, or cut&paste. 2. Bacteria Structure Description and Function Capsule Ring of DNA, contains a small number of genes which typically provide a selective advantage in a given environment. (eg antibiotic resistance). Cell Wall Protective covering made up of polysaccharides (complex sugars). Keeps the bacteria from drying out and protect it from being engulfed by larger microorganism. Cytoplasm Gives cell its shape and surrounds the cytoplasm protecting it from the environment. Flagella A layer of phospholipids and proteins, which allows certain materials in and out of the cell Nucleoid Only type of cell organelle found in bacteria. Small structures that translate the genetic code and synthesise proteins. Pili Small hair like projections that emerge from the cell membrane. These help the bacteria attach to their host. Plasma Membrane This is where the functions of cell growth, cellular metabolism and replication are carried out. It is a gel like material that is composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as the ribosomes, chromosomes, and plasmids. Plasmid A region of the cytoplasm where the chromosomal DNA is located. Ribosomes Hair like structures that provide locomotion. Not all bacteria have them. Colour the descriptions RED and the functions BLUE 2.3 Eukaryotic cells Stucture and Function - Homework Sheet - 1. Use a pencil line drawing to sketch out an animal cell. Include as many organelles as possible and label them. (5 marks) 2. Identify the function of each of the following cell organelles in the single line provided. (6 marks) Nucleus__________________________________________________________ Cell Membrane ____________________________________________________ Mitochondria ______________________________________________________ Endoplasmic Reticulum ______________________________________________ Ribosomes ________________________________________________________ Golgi Bodies ______________________________________________________ 3. Where is the nucleolus located in the cell? What molecule does the nucleolus produce and what is the function of this molecule? (3 marks) 4. Where in the cell are vacuoles located and what do they transport? How is a vacuole different from a vesicle? (3marks) 5. How is the structure of a lysosome related to its function? Why might they be called “suicide sacs”? Hint – autodigestion. (3 marks) 6. What are the structural and functional differences between rough ER and smooth ER? Why do cells of the testes and adrenal glands have large amounts of smooth ER? (3 marks) 7. What is the advantage to the cell of having different organelles that carry out specialized functions? Explain. (3marks) 8. What happens during the process of cell differentiation? (2 marks) Membranes Cell Division