A respirometer is a piece of apparatus that can be used to measure the rate of respiration of living tissue such as germinating peas. A simple respirometer is shown in Fig. 6.1. A student carried out an investigation to determine the effect of temperature on the rate of respiration of germinating peas. - The student set up the respirometer as shown in Fig. 6.1 and placed the respirometer in a water-bath at $$$10^{\circ} \mathrm{C}$$$. - After five minutes, the student used the syringe to adjust the position of the coloured liquid in the right-hand side of the $$$U$$$-shaped tube so that it lined up with 0 cm on the ruler. The student immediately started a timer. - The germinating peas used up oxygen, causing the coloured liquid in the U-shaped tube to move. - The student measured the distance moved by the coloured liquid after 20 minutes. - The student repeated the experiment at temperatures of $$$20^{\circ} \mathrm{C}, 30^{\circ} \mathrm{C}, 40^{\circ} \mathrm{C}$$$ and $$$50^{\circ} \mathrm{C}$$$. Explain why the respirometer was left in the water-bath for five minutes before starting the experiment. ............................................................................................................................................... . ............................................................................................................................................... . .........................................................................................................................................

Biology

IGCSE&ALevel

CAIE

Exam No：9700_m24_qp_42 Year：2024 Question No：6(c)

Answer:

Knowledge points:

12.1.1 outline the need for energy in living organisms, as illustrated by active transport, movement and anabolic reactions, such as those occurring in DNA replication and protein synthesis

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

12.1.3.1 transfer of phosphate in substrate-linked reactions

12.1.3.2 chemiosmosis in membranes of mitochondria and chloroplasts

12.1.4 explain the relative energy values of carbohydrates, lipids and proteins as respiratory substrates

12.1.5 state that the respiratory quotient (RQ) is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in, as a result of respiration

12.1.6 calculate RQ values of different respiratory substrates from equations for respiration

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

12.2.1.1 glycolysis in the cytoplasm

12.2.1.2 link reaction in the mitochondrial matrix

12.2.1.3 Krebs cycle in the mitochondrial matrix

12.2.1.4 oxidative phosphorylation on the inner membrane of mitochondria

12.2.10 outline respiration in anaerobic conditions in mammals (lactate fermentation) and in yeast cells (ethanol fermentation)

12.2.11 explain why the energy yield from respiration in aerobic conditions is much greater than the energy yield from respiration in anaerobic conditions (a detailed account of the total yield of ATP from the aerobic respiration of glucose is not expected)

12.2.12 explain how rice is adapted to grow with its roots submerged in water, limited to the development of aerenchyma in roots, ethanol fermentation in roots and faster growth of stems

12.2.13 describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast

12.2.14 describe and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration

12.2.2 outline glycolysis as phosphorylation of glucose and the subsequent splitting of fructose 1,6-bisphosphate (6C) into two triose phosphate molecules (3C), which are then further oxidised to pyruvate (3C), with the production of ATP and reduced NAD

12.2.3 explain that, when oxygen is available, pyruvate enters mitochondria to take part in the link reaction

12.2.4 describe the link reaction, including the role of coenzyme A in the transfer of acetyl (2C) groups

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

12.2.6 explain that reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of the coenzymes NAD and FAD

12.2.7 describe the role of NAD and FAD in transferring hydrogen to carriers in the inner mitochondrial membrane

12.2.8.1 hydrogen atoms split into protons and energetic electrons

12.2.8.2 energetic electrons release energy as they pass through the electron transport chain (details of carriers are not expected)

12.2.8.3 the released energy is used to transfer protons across the inner mitochondrial membrane

12.2.8.4 protons return to the mitochondrial matrix by facilitated diffusion through ATP synthase, providing energy for ATP synthesis (details of ATP synthase are not expected)

12.2.8.5 oxygen acts as the final electron acceptor to form water

12.2.9 describe the relationship between the structure and function of mitochondria using diagrams and electron micrographs

Answer:

Knowledge points:

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