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.
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