a) Describe secondary growth in flowering plants. (14mks) b) Describe one method that can be used to measure the average growth rate of a single leaf. (6mks)

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a) Describe secondary growth in flowering plants. (14mks)


  • Secondary thickening is facilitated by meristematic cells; known as cambium; which are located between phloem and xylem in vascular bundles of plants; 
  • The cambium divides radially; to form a ring (cylinder) of cambium tissue with the xylem inside the ring; and the phloem outside the ring; 
  • Cells of the cambium ring divide to form secondary phloem outside and secondary xylem inside; 
  • Interfascular cambium (between vascular bundles) divides to form secondary parenchyma; thereby increasing the growth of medullary rays; 
  • Much more xylem is formed than phloem; thus pushing phloem and cambium outwards; The rate of secondary growth is dependent on the season/rainy resulting in annular rings; 
  • Cork cambium/phellogen divides to form new cork./ bark tissue; to accommodate increased growth on outside and secondary cortex on the inside;
(14mks)


b) Describe one method that can be used to measure the average growth rate of a
single leaf. (6mks)

  • Choose/ identify a young leaf which is folded; 
  • Use the same leaf throughout; 
  • Measure the total length of the whole leaf; (acc measurement of any part of the leaf / record / length) 
  • Repeat the procedure at regular interval; until no change occurs in length/ until it gets constant length; 
  • The average rate of growth is equal to total increase in length divided by the period taken to achieve final length;
(6mks)

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