BOTANY Higher Secondary Second Year - Textbooks Online

is fixed in the vertical position with the help of a stand. Thus, the enclosed
air in the bulb is completely cut off from the atmosphere. The apparatus is
kept undisturbed for few hours.
Germinating
seeds
209
It is observed that the level of
KOH solution in the limb is raised.
The KOH solution absorbs
carbondioxide released by the
seeds and a vacuum is created. It
results in the raise of KOH level.
5.3.4. Pentose phosphate pathway
Generally, majority of living
KOH
organisms obtain energy for
various biochemical activities from
glucose. In aerobic organisms, it
is degraded in three major phases
namely, glycolysis, Krebs cycle
and electron transport system. In
anaerobes, glucose is partially
Fig.5.21 Ganong’s respiroscope
degraded by glycolysis and
fermentation. In 1938, Dickens discovered an alternate pathway for the
utilization of glucose by the living cells. This pathway is called pentose
phosphate pathway or hexose monophosphate pathway or direct
oxidation pathway. This pathway consists of major phases - oxidative
and nonoxidative phases. Pentose phosphate pathway takes place in the
cytoplasm only.
Oxidative phase
In this phase, glucose is oxidized and decarboxylated with the formation
of pentose through phosphogluconic acid as shown in the flow chart. The
essential feature of this phase is the production of NADPH2. 1. Glucose is phosphorylated to glucose-6-phosphate by hexokinase.
2. The glucose-6-phosphate is oxidized to 6-phospho-gluconolactonate
in the presence of NADP + by enzyme glucose-6-phosphate dehydrogenase.
NADP + is reduced to NADPH 2 .