12.1 Energy

Table 1 shows the amount of energy released per gram of different respiratory substrates.

Table 1

With reference to Table 1, explain the difference in the amount of energy released by the different respiratory substrates.

Palmitic acid is a saturated fatty acid found in palm oil, cheese and milk. It can be broken down during aerobic respiration, as represented by the following partially-completed equation:

C₁₆H₃₂O₂   +   O₂ →    CO₂   +   H₂O

Calculate the respiratory quotient (RQ) of palmitic acid.

Show your working.

The RQ value for glucose is 1.0

Discuss the difference in the RQ values of glucose and palmitic acid.

Fig. 1 shows a respirometer that was set up to measure the rate of respiration of germinating mung bean seeds.

It consisted of two linked tubes, 1 and 2, held in a temperature-controlled water bath. 

Fig. 1

The capillary tubes in the U-tube containing coloured liquid have an internal diameter of 1mm.

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[1]

The experimenters used 10g of active mung bean seeds and recorded the seeds' respiration over a 20 minute period.

They calculated a rate of movement of the liquid in the U-tube of 4mm³ hr^-1 g^-1.

Calculate how far, to the nearest mm, the liquid in the U-tube moved in the 20 minute period of their investigation.

Following the investigation, the scientists reset the respirometer and ran the experiment again, this time with distilled water in place of KOH in both tubes 1 and 2.

They recorded a slight upward movement of the liquid in the U-tube manometer on the side of tube 2, this time at a rate of 0.72 mm³ hr^-1 g^-1.

Calculate the respiratory quotient (RQ) of the respiring mung bean seeds in this investigation. 

Suggest, with a reason, what the value of the RQ that you calculated in part (c) indicates about the main food group(s) that the mung bean seeds were respiring at the time of this investigation.

Fig.1 shows the structure of a molecule of adenosine triphosphate (ATP).

Fig. 1

Identify part X of the ATP molecule in Fig.1.

ATP is described as a 'universal energy currency' for cells.

Explain why ATP can be considered to be a 'universal energy currency'.

Discuss the main benefits of ATP as an energy currency in living organisms.

ATP is broken down by a group of enzymes known as ATPases.

A student set up a respirometer, as illustrated in Fig. 1, to measure the rate of oxygen consumption during respiration in woodlice.

Fig. 1

From Fig. 1:

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[1]

The level of the coloured liquid was equal on both sides of the capillary u-tube of the manometer at the beginning of the experiment.

Explain the movement of the liquid in the capillary tube, as illustrated in Fig. 1.

The student found that the coloured liquid in the capillary tube in Fig. 1 moved 20 mm over the course of an hour. The diameter of the capillary tube was 2 cm.

The volume of the capillary tube can be calculated by using the formula: πr²h, where h represents the distance moved by the manometer fluid in a minute.

Calculate the volume of oxygen consumed in cm³min^-1. Show your working.

The student repeated the experiment from Fig.1, but removed the potassium hydroxide solution. The volume of gas was calculated again and these values were used to calculate the RQ value of the respiratory substrate of the woodlice.

The RQ value was 0.8.

Suggest what the student can deduce from this RQ value.

Explain why carbohydrates, lipids and proteins have different relative energy values as substrates in respiration in aerobic conditions.

Define the term respiratory quotient (RQ) and describe how you would carry out an investigation to determine the RQ of germinating barley seeds.