Biology 2 Revision

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Plant Cells

  • Plant Cell:
  • Cell Wall - strengthens the cell
  • Ribosome - where protein synthesis takes place
  • Mitochondria - where energy is released in respiration
  • Cytoplasm - where metabolic reactions take place
  • Cell Membrane - which controls the passage of substances in and out of the cell
  • Chloroplast - which absorbs light energy to make food
  • Permanent Vacuole - filled with cell sap
  • Nucleus - which controls the activities of the cell    
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Animal Cells

  • Animal Cells:
  • Cell Membrane: which controls the passage of substances in and out of the cell
  • Cytoplasm: where metabolic reactions controlled by enzymes take place
  • Mitochondrian: where energy is released in respiration
  • Nucleus: which controls the activities of the cell   
  • Ribosomes: where protein synthesis takes place
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Specialised Cells

  • a single-celled organism carries out all its functions in one cell
  • in a multi-celled organism, specialised tissues and organs carry out different functions
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Diffusion 1

  • EXAMPLE: a beaker contains sugar and water solution, the sugar will move by diffusion upwards (less concentration area) whereas water will move downwards (to less concentration area). So eventually, the sugar and water molecules will be evenly spread out throughout the solution.
  • Particles will move faster at higher temperatures, rise in temperature will speed up diffusion. 
  • Particles do not go in a particular direction on purpose. They just move around randomly.  
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Diffusion 2

  • Cells continuously use up oxygen and respiration according to the equation:
  • As oxygen concentration in the cell drops, oxygen diffuses in through the cell membrane from the blood in which oxygen is at a higher concentration
  • At a higher respiration rate, the difference in oxygen concentration inside and outside the cell increases, so the rate of diffusion of oxygen into the cell increases
  • The small intestine is lines by millions of 1mm high finger-like projections called villi. These greatly increase the surface area in contact with the food. Each villus contains a network of blood capillaries. 
  • Digested food in the intestine contains glucose, needed for respiration. Glucose passes easily into the capillaries of the villi and dissolves in the blood which carries it to the respiring cells over the body.
  • The greater the surface area, the faster the rate of diffusion. 
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