Page 124 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six
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Biology for Secondary Schools



              The cuticle:  This is the outermost  air spaces that connect with each other
              transparent and waxy layer of the leaf.  and linked to the atmosphere through
              It allows light to penetrate  into the  the  stomata  pores.  The  air  spaces  in
              photosynthetic cells. It also protects the  the  spongy mesophyll  provide  an
              leaf from injury, pests, and excessive  immediate source of carbon dioxide.
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              loss of moisture. In order to allow     Activity 6.2:  Investigating the internal
              gaseous exchange, there is no cuticle
              on the stomata.                         structure of a leaf
                                                      Materials: Prepared slide of a transverse
              The epidermis: This is the outermost    section of a leaf, microscope, notebook,
              layer of cells found on both lower and   and pencil or pen
              upper surfaces of a leaf. It is transparent
              and  only  one  cell  is  thick,  hence  it   Procedure
              allows  sunlight  to  penetrate  the  leaf   1.  Mount the prepared slide on the
              easily. The epidermis has pores called       microscope.
              stomata.                                 2.  Observe the slide under the low
                                                           power objective  lens.  What do
              Stomata: Stomata (singular is stoma)         you see?
              are small pores in the epidermis. They   3.  Describe what you have observed.
              allow oxygen and carbon dioxide to
              diffuse in and out of the leaf. Stomata  The process of photosynthesis
              are surrounded by guard cells that close
              and open the pores.                     Task 6.3
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              Mesophyll: This is made up of palisade
              layer and spongy layer (See Figure 6.2).   the simulations that show the process
              The palisade mesophyll is made up of    of photosynthesis. Note down what you
              cells that are elongated and arranged at   have observed.
              right angles to the surface of the leaf. It
              is found just below the upper epidermis.   Photosynthesis takes place in cell
              Being near the upper epidermis,  the    organelles known as chloroplasts. These
              palisade cells are exposed to maximum   are mostly found in the green leaves.
              sunlight. This enables the cells to absorb
              maximum amount of sunlight energy.      Chloroplasts contain chlorophyll that is
              The  spongy mesophyll  is just  above   responsible for trapping sunlight energy
              the  lower  epidermis.  It  is  a  loosely   that  is  used  during  photosynthesis.
              constructed layer of irregularly shaped  Photosynthesis takes place in two stages,
              cells  separated by large intercellular  namely light reaction and dark reaction.



               118                                                     Student’s Book Form  One                   Student’s Book Form One




                                                                                          15/10/2024   09:24:37
     Biology FORM 1 new.indd   118                                                        15/10/2024   09:24:37
     Biology FORM 1 new.indd   118
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