Page 144 - Biology Form Two

Biology for Secondary Schools

Cuticle
Upper
epidermis

Palisade
mesophyll
FOR ONLINE READING ONLY
layer Xylem Vascular
Spongy Phloem bundle
mesophyll
layer
Air spaces
Lower epidermis

Cuticle
Key: Guard cell
Carbon dioxide gas Stomata pore
Oxygen gas and water

Figure 6.8: Gas exchange through the leaf

Activity 6.4: Demonstrate the presence 3. Repeat procedure 2 using a
of stomata on leaves different type of leaves.

Materials Question
Leaves, source of heat, forceps, water, 1. Which type of leaves produce
and beaker most bubbles?

Procedure 2. What caused the formation of
bubbles?
1. Boil water in a beaker and then
turn off the source of heat.

Safety precaution During the day, green plants carry out

Ensure care is taken into account photosynthesis to produce glucose.
when using heat sources This takes place also within the guard
cells that surround the stomata. Hence,

2. Dip a fresh leaf in the hot water. Be the cell sap of guard cells becomes
careful not to touch the hot water. hypertonic and draws in water from the
Do you see bubbles coming from neighbouring cells by osmosis.
the leaf?

138 Student’s Book - Form Two

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BIOLOGY FORM 2 NEW.indd 138