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Cell Structure

OCR AS Biology Unit 1: Cells, Exchange and Transport. Cell Structure. Learning objectives. To understand and discuss the basis of cell theory based upon milestones in cell biology To carry out practical work on cell size and magnifications using a light microscope

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Cell Structure

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  1. OCR AS Biology Unit 1: Cells, Exchange and Transport Cell Structure

  2. Learning objectives • To understand and discuss the basis of cell theory based upon milestones in cell biology • To carry out practical work on cell size and magnifications using a light microscope • To be able to draw a plant cell and an animal cell using a light microscope • To prepare slides using stains to identify cell structure.

  3. Milestones in Cell Biology • Read through handout • Group discussion • Discuss the impact of the microscope on cell biology • List things you think are the most important

  4. Cell theory • The cell is the fundamental unit of life. All organisms, whatever their type or size, are composed of cells. The modern theory of cellular organisation states:- • All living things are composed of cells and cell products. • New cells are formed only by the division of pre-existing cells • The cell contains inherited information (genes), which is used as instructions for growth, functioning and development. • The cell is the functioning unit of life; the metabolic reactions of life take place within the cells.

  5. Cell Theory - Question • Before the development of cell theory, it was commonly believe that living organisms could arise by spontaneous generation. • Explain what this term means and why it has been discredited as a theory.

  6. Plan Diagrams – dicotyledonous leaf

  7. Cell Biology and Microscopy • When Scientists began to observe cells, they started with simple microscopes • There are two different types of microscope both use a form of radiation to create an image of the specimen: • Light microscope – uses light • Electron microscope – uses electrons

  8. Using a light microscope • Magnification • Number of times larger an image is compared with the real size of the object • Resolution • The ability to distinguish between two separate points

  9. Structure of a generalised animal cell as seen with a very high power quality light microscope (diameter ~ 20ųm)

  10. Structure of a generalised plant cell as seen with a very high power quality light microscope (diameter ~ 40ųm)

  11. Light Microscope • For the microscope in front of you, work out • The magnification of each lens • The field of view for each lens • Using a graticule / stage micrometer • Collect a prepared slide of Squamous epithelium, draw what you can see. • Your diagram should include title, labels, magnification and a scale bar.

  12. Examination of plant cells • Strip a pieces of epidermis from the inner lining of one of the fleshy scales of an onion. • Mount it in dilute iodine solution • Observe and draw a cell under low power and high power • Repeat the above procedure using water instead of iodine. • what difference does this make to how much you can see?

  13. Examination plant cells - conclusion • What does this tell you about the value of staining cells before you look at them under the microscope? • Make sure all diagrams have a title, label, magnification and scale bar.

  14. OCR AS Biology Microscopy and magnification

  15. Microscopes • Light microscope • Long wavelength • Can only distinguish between two objects if they are 0.2µm apart. • Electron microscope • Shorter wavelengths • Can distinguish between objects 0.1nm apart

  16. Magnification • How many times bigger the image is compared to original subject. • If asked to calculate the size of an object

  17. Magnification • When calculating magnification make sure the units of length are the same for both object and image

  18. Magnification - example • Object 100nm in length • How much is it magnified in a photo? • Measure object in photo (10mm long)

  19. Magnification - example • The measurements need converting to the same unit (usually the smallest) • There are 10 000 000nm in 10mm • Magnification is: • 100 000 times

  20. The effect of progressive magnification of a portion of human skin

  21. OCR AS Biology Structure of plant and animal cells under an electron microscope

  22. The Electron Microscope • Two main advantages • High resolving power (short wavelength of electrons) • As electrons negatively are charged the beam can be focused using electromagnets • As electrons are absorbed by molecules of air, a near-vacuum has to be created within the chamber of an electron microscope.

  23. The Electron Microscope • Two types • Transmission Electron Microscope (TEM) • Scanning Electron Microscope (SEM) • Activity • Read through the handout on the electron microscope • Answer discussion questions 1 - 4

  24. Comparison of advantages and disadvantages of the light and electron microscopes

  25. Comparison of advantages and disadvantages of the light and electron microscopes

  26. Comparison of pathways of the light and electron microscopes

  27. Ultrastructure of an animal cell as seen through an electron microscope

  28. Ultrastructure of an Animal Cell

  29. Ultrastructure of a plant cell as seen through an electron microscope

  30. Ultrastructure of a Plant Cell

  31. Pupil Activity • Cell structure • Read through the information on each of the organelles as you colour them in • Follow the guidance on colouring them in given at the bottom of the page • This works on the theory that whilst you are colouring in, you have time to consider and think about the structure and function of the organelles

  32. OCR AS Biology FOUNDATION Cell Structure Activities

  33. Pupil Activity – Cell StructureAnimal Cell • In pairs label the diagram of the animal cell given. • How many structures can you identify? • Look at the cells alive animation – how many have you correctly identified? • Label the paper copy of the diagram of an animal cell

  34. Animal Cell

  35. Animal cell - answers

  36. Pupil Activity – Cell StructurePlant Cell • In pairs label the diagram of the plant cell given. • How many structures can you identify? • Look at the cells alive animation – how many have you correctly identified? • Label the paper copy of a diagram of a plant cell

  37. Plant cell

  38. Plant cell - answers

  39. Activity:Introduction to organelle function • Using the cards, match up organelle, position and function.

  40. OCR AS Biology FOUNDATION Organelle Structure and function

  41. Nucleus

  42. Structure of nucleus • Nuclear envelope • Nuclear pores • Nucleoplasm • Chromatin • nuceolus

  43. Function of the nucleus • Acts as the control centre of the cell through the production of mRNA and protein synthesis • Retain genetic material of the cell (DNA / chromosomes) • Start the process of cell division

  44. Structure of Nucleus • Chromatin • DNA and associated proteins, chromatin condenses into chromosomes when the cell divides. • nucleolus • Manufactures ribosomal RNA and assembles the ribosomes

  45. Structure of Nucleus • Nuclear envelope • Controls entry and exit of materials • Outer membrane continuous with endoplasmic reticulum • Nuclear pores • Passage of large molecules (mRNA) out of nucleus

  46. Chloroplasts

  47. Structure and Function of Chloroplasts • Chloroplast envelope • Entry and exit of substances • Stroma • Enzymes for the light independent stages of photosynthesis • Grana (thylakoids/lamellae) • Light dependent stage of photosynthesis • Starch grains • Temporary stores of carbohydrates

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