Page 122 - General and Inorganic Chemistry for Advanced Secondary Schools Students Book Form Five and Six

Biology for Secondary Schools

Biologists often use the presence of area. This maximizes the absorption
starch in some parts of plants as an of sunlight energy and carbon dioxide.
indication that photosynthesis has The lamina is also thin so that carbon
taken place. dioxide gas can diffuse and sunlight
energy can penetrate over a short
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Structure of the leaf in relation to distance to reach cells. The mid-rib and
photosynthesis veins contain vascular tissues, namely
The internal and external structures xylem and phloem. Xylem transports
of a leaf make it well adapted for water and dissolved minerals while
photosynthesis. In most plants, the phloem transports manufactured food
leaf is the main site for photosynthesis, in the plants.
although some plants, such as cactus
(plural is cacti) use their stems for Activity 6.1: Observing the external
photosynthesis. The leaf structure features of a leaf
provides a very efficient means for Materials: Leaves from various plants,
absorbing carbon dioxide and sunlight.
hand lens, pen or pencil, notebook and
External structure of a leaf rubber
The external features of a leaf can be Caution
viewed using either a hand lens or with Be careful not to collect hairy or thorny
the naked eye. Figure 6.1 shows the leaves.
external structure of a leaf.
Procedure
Apex 1. Collect different plant leaves from
the school or home environment.
2. Observe each of the leaves using
Lamina Lateral vein your naked eyes.
Mid rib
3. Observe each of the leaf using the
Petiole hand lens. Note as many details
as you can.

Figure 6.1: External structure of a leaf 4. Describe each of the observed
leaves.
The petiole or leaf stalk attaches the 5. Explain how each of the plant
leaf to the branch or stem. It keeps the parts aids photosynthesis.
lamina in a position that will enable it to
get maximum amount of sunlight. The Question
lamina or leaf blade is the expanded State the observed differences in
portion of a leaf. It has a large surface structure among the variety of leaves.

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