Energy (CIE A Level Biology)

Producers such as cacti and grasses form the foundation of most desert food webs. Cacti and grasses are consumed by the primary consumers, which in turn are eaten by the secondary consumers.

Fig. 1 shows the flow of energy through a desert ecosystem. The figures in the circles represent the energy transfer in kJ m^-2 yr^-1.

Fig. 1

Calculate the percentage of energy transferred from the primary consumers to the secondary consumers in Fig. 1

Give your answer as a whole number.

Describe the energy conversion occurring between the sun and the primary consumers in Fig. 1

All living organisms require energy in order to perform the functions necessary for life.

Outline the need for energy in living organisms; your answer should include suitable examples.

Photosynthesis and respiration are important processes occurring in living organisms.

Explain how the processes of photosynthesis and respiration assist in the transfer of energy between autotrophs and heterotrophs, with reference to Fig. 1.

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.

State the type of reaction that is catalysed by ATPases.

[1]

(ii)

Identify the products of the reaction mentioned in part (i).

[1]

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:

Identify the control in this experiment.

[1]

(ii)

State the purpose of the potassium hydroxide solution.

[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.

Some hibernating mammals undergo multiple periods of torpor (reduced activity), interspersed with periods of wakefulness, throughout their hibernation.

Research was carried out into the physiological changes occurring in a species of mammal during a period of torpor.

Some of the results are shown in Fig. 1 below.

Fig. 1

Explain the relationship between metabolic rate and body temperature shown in Fig. 1

[2]

(ii)

Suggest the time period during which the mammal enters a state known as 'steady torpor'.

[1]

Describe the changes in respiratory quotient shown in Fig. 1.

Suggest what can be concluded from Fig. 1 about respiratory substrates and torpor.

Suggest the benefit to mammals of brief periods of torpor and arousal, rather than extended periods of unbroken hibernation.

Fig. 1 shows two processes (A and B) by which ATP can be synthesised.

Fig. 1

Identify processes A and B.

Contrast process A and B in Fig. 1 with regards to ATP synthesis.

Only process A in Fig. 1 can occur in anaerobic conditions.

Explain why process B in Fig. 1 cannot occur without the presence of oxygen.

The average human synthesises more than 50 kg of ATP each day. 

Suggest the reasons for synthesising such a large mass of ATP.

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 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 set up to measure the rate of respiration in germinating mung bean seeds.

It consists 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 1 mm.

Experimenters used the equipment in Fig. 1 to measure the rate of respiration in 10 g of active mung bean seeds 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 in part (b) 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 RQ calculated in part (c) indicates about the respiratory substrate of the mung beans at the time of this investigation.

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.