Page 278 - Biology_F5

Nutrition

CO should be noted that shunting of malate is
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necessary to ensure movement of carbon
Malate Pyruvate dioxide and hydrogen from the mesophyll
(4C) (3C)
to the bundle sheath cells. The hydrogen
+
NADPH + H + NADP liberated reduces NADP into NADPH
which is used in carbon dioxide re-
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This ultimately leads to high accumulation fixation. The stages (a) and (b) accomplish
of carbon dioxide in the bundle sheaths. It the Hatch-Slack pathway.
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Epidermal cells (non
photosynthetic)

Chloroplasts of meso-
phyll cells

Chloroplasts of bundle
shealth cells

Figure 5.7: The Hatch-Slack pathway

(c) Regeneration of carbon dioxide The released carbon dioxide from the
acceptor dissociation of malate enters the C
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Pyruvate generated in the shunting of pathway (Calvin cycle). At this stage, the
malate as explained in (b) is converted carbon dioxide is accepted by RuBP to
back into PEP by the addition of organic produce 3-PGA, a reaction is catalysed
phosphate supplied by ATP. by RuBP carboxylase. The NADPH will
reduce 3-PGA to sugar (3-PGAL) in the
Pyruvate Phosphoenol
(3C) pyruvate (PEP) same way as in C plants.
3
ATP ADP (3C) Generally, the C pathway consumes more
4
energy (ATP), and it is more efficient in
yielding carbon dioxide compared to the
(d) Re-fixation of carbon dioxide in C pathway. However, ATP consumption
bundle sheaths is not a problem, considering that much
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Form Five Student’s Book
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