22 August 2015

#85 Energy and Respiration - Syllabus 2016 - 2018

12.1  Energy
12.2  Respiration

Energy is a fundamental concept in biology. All living things  require  a source of cellular energy to drive their various activities. ATP is the universal  energy currency as its molecules are small, soluble  and easily hydrolysed to release energy for cellular activities. All organisms respire to release energy from energy- rich molecules such  as glucose and fatty acids  and transfer that  energy to ATP. Respiration is a series of enzyme-catalysed reactions that  release energy in small ‘packets’. In eukaryotes, aerobic  respiration occurs in mitochondria.

Learning outcomes

Candidates should  be able to:

12.1  Energy

ATP is the universal  energy currency as it provides the immediate source of energy for cellular processes.

a)   outline  the need for energy in living organisms, as illustrated by anabolic reactions, such  as DNA replication  and protein synthesis, active transport, movement and the maintenance of body temperature

b)   describe the features of ATP that  make  it suitable as the universal  energy currency

c)   explain that  ATP is synthesised in substrate-linked reactions in glycolysis and in the Krebs cycle

d)   outline  the roles of the coenzymes NAD, FAD and coenzyme A in respiration

e)   explain that  the synthesis of ATP is associated with the electron transport chain on the membranes of mitochondria and chloroplasts (see  12.2g)

f) explain the relative energy values  of carbohydrate, lipid and protein  as respiratory substrates and explain why lipids are particularly energy-rich
g)   define  the term  respiratory quotient (RQ) and determine RQs from equations for respiration

h)   carry out investigations, using simple  respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae)

12.2  Respiration

Respiration is the process whereby energy from complex organic molecules is transferred to ATP.

This process of ATP synthesis using the energy in proton gradients is common to both respiration and photosynthesis.

Some organisms and some tissues are able to respire in both aerobic  and anaerobic conditions. When  yeast and plants  respire under  anaerobic conditions, they  produce ethanol and carbon  dioxide
as end-products; mammalian muscle tissue produces lactate when oxygen  is in short

a)   list the four stages in aerobic  respiration (glycolysis, link reaction, Krebs cycle and oxidative  phosphorylation) and state where each  occurs in eukaryotic cells

b)   outline  glycolysis as phosphorylation of glucose and the subsequent splitting of fructose 1,6-bisphosphate (6C) into two triose  phosphate molecules, which are then  further  oxidised  to pyruvate with a small yield of ATP and reduced NAD

c)   explain that,  when oxygen  is available, pyruvate is converted into acetyl (2C) coenzyme A in the link reaction

d)   outline  the Krebs cycle, explaining that  oxaloacetate (a 4C compound) acts  as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate  (a 6C compound), which is reconverted to oxaloacetate in a series of small steps

e)   explain that  reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of NAD and FAD

f) outline  the process of oxidative  phosphorylation including the role of oxygen  as the final electron acceptor (no details  of the carriers  are required)

g)   explain that  during oxidative  phosphorylation:
energetic electrons release energy as they  pass through the electron transport system
the released energy is used to transfer protons across the inner mitochondrial membrane
protons return  to the mitochondrial matrix by facilitated diffusion through ATP synthase providing energy for ATP synthesis (details of ATP synthase are not required)

h)   carry out investigations to determine the effect of factors such  as temperature and substrate concentration on the rate of respiration of yeast using a redox indicator (e.g. DCPIP or methylene blue)

i) describe the relationship between structure and function  of the mitochondrion using diagrams and electron micrographs

j) distinguish between respiration in aerobic  and anaerobic conditions in mammalian tissue and in yeast cells, contrasting the relative energy released by each  (a detailed account of the total yield of ATP from the aerobic  respiration of glucose is not required)

k)   explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue, including the concept of oxygen  debt

l) explain how rice is adapted to grow with its roots  submerged in water in terms of tolerance to ethanol from respiration in anaerobic conditions and the presence of aerenchyma

m)  carry out investigations, using simple  respirometers, to measure the effect of temperature on the respiration rate  of germinating seeds or small invertebrates

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