Page 325 - Biology_F5

Biology for Advanced Level Secondary Schools

2 CO Exercise 6.4
2
1. Explain the Kreb’s cycle pathway and
how it is related to glycolysis.
2 Pyruvic Acid 2 NADH 2 NAD + 2 Ethanol 2. Illustrate the steps involved in the
Kreb’s cycle.
Figure 6.11: Alcoholic fermentation pathway
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3. What is the importance of regeneration
Lactic acid fermentation of oxaloacetate in the final step of
This is also referred to as lactate Kreb’s cycle?
fermentation, which is a biological 4. Explain the fate of pyruvic acid during
process by which pyruvate is converted respiration.
into the metabolite lactate. In lactic acid 5. Pyruvate plays a central role in cellular
fermentation, the pyruvic acid from metabolism by linking glycolysis to
glycolysis is reduced into lactic acid other metabolic pathways of energy
+
by NADH, which is oxidised to NAD . production. Explain the fate of pyruvic
Lactic acid fermentation allows glycolysis acid during respiration
to continue by ensuring that NADH is
+
returned to its oxidised state (NAD ). Events of electron transport chain in
This anaerobic fermentation reaction the formation of ATP
occurs in some bacteria and animal cells
such as muscle cells (Figure 6.12). Task 6.8
Search from the internet sources
Lactate dehydrogenase the simulations or videos on events
Pyruvate Lactic acid of electron transport chain in the
NADH NAD+ formation of ATP, and then prepare
short notes on what you have observed.
Figure 6.12: Lactic acid fermentation pathway
The electron transport chain is the final
If oxygen is present in the cell, many and most important step of cellular
organisms will bypass fermentation and respiration. The electron transport chain
undergo aerobic respiration. However, (electron transport system or cytochrome
facultative anaerobes will undergo both system) is a process by which the energy
fermentation and aerobic respiration carrier molecules (NADH and FADH )
2
2
in the presence of oxygen. Sometimes, produced during glycolysis, Kreb’s cycle
even when oxygen is present and and other catabolic processes are oxidised
aerobic metabolism is taking place in to release energy in the form of ATP.
the mitochondria, if pyruvate is building The electron transport chain is a series
of electron transporters embedded in the
up faster than it can be metabolised, the inner mitochondrial membrane that shuttles
fermentation process will occur. The electrons from NADH and FADH . In
2
2
enzyme responsible for catalysing the the process, protons are pumped from the
interconversion of pyruvate into lactate is mitochondrial matrix to the intermembrane
known as lactate dehydrogenase. space, and oxygen is reduced to form water.

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