B1 - Cell Structure and Transport


B1.1 The World of the Microscope

  • Light microscopes magnify up to x2000 and have a resolution of around 200nm. 
  • Electron microscopes magnify up to x2000000 and have a resolution of 0.2nm.
  • magnification = size of image/ size of real object.
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B1.2: Animal and Plant Cells

  • Animal cell features common to all cells: cytoplasm, cell membrane, mitchondria and ribosomes.
  • Plant and algal cells contain the structures seen in animal cells as well as a cellulose cell wall. 
  • Many plant cells also contain choloroplasts and a permanent vacuole filled with sap. 
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B1.3: Prokaryotic and Eukaryotic cells

  • eukaryotic cells all have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus.
  • prokaryotic cells consist of cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not in a distinct nucleus and may form a single DNA loop. Prokaryotes may contain one or more extra small rings of DNA called plasmids. 
  • bacteria are all prokaryotes. 
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B1.4: Specialisation in Animal Cells

  • as an organism develops, cells differentiate to form different types of cells. 
  • as an animal cells differentiates to form a specialised cell, it acquires different sub-cellular structures to enable it to carry out a certain function
  • examples of specialised cells are nerve, muscle and sperm cells
  • animal cells may be specialised to function within a tissue, organ, organ system or whole organism.
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B1.5: Specialisation in Plant Cells

  • plant cells may be specialised to carry out a particular function.
  • examples of specialised plant cells are root hair, photosynthetic, xylem and phloem cells.
  • plant cells may be specialised to function within tissues, organs, organ systems, or whole organisms. 
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B1.6: Diffusion

  • diffusion is the spreading out of particles of any substance, in a solution or a gas, resulting in a net movement of particles from a high concentration to a low concentration down a concentration gradient. 
  • the rate of diffusion is affected by difference in concentrations, temperatures and available surface area. 
  • dissolved substances such as glucose, urea, oxygen and carbon dioxide move in and out of cells by diffusion. 
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B1.7: Osmosis

  • osmosis is a special case of diffusion.
  • it is the movement of water from a dilute to a more concentrated solute solution through a partially permeable membrane that allows water to pass through.
  • differences in the concentrations of solutions inside and outside a cell cause water to move into or out of the cell through osmosis.
  • animal cells can be damaged if the concentration outside the cell changes dramatically. 
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B1.8: Osmosis in Plants

  • osmosis is important to maintain turgor in plant cells.
  • there are a variety of practical investigations that can be used to show the effect of osmosis on plant tissues. 
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B1.9: Active Transport

  • active transport moves substances from a  dilute solution to a more concentrated solution against the concentration gradient. 
  • active transport uses energy released from food in respiration to provide the energy required. 
  • active transport allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soil. 
  • active transport enables sugar molecules used for cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher. 
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B1.10: Exchanging Materials

  • single-celled organisms have a large surface area to volume ration so all the necessary exchanges with the environment take place over this surface.
  • in multicellular organisms many organs are specialised with effective exchange surfaces.
  • exchange surfaces usually have a large surface area and thin walls, which give short diffusion distances. 
  • In animals, exchange surfaces will have an efficient blood supply and/or be well ventilated. 
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