Respiration: Biology 0610 (Cambridge O Level / IGCSE)

A child scrapes their knee while cycling. Over the next two weeks the wound heals: damaged skin cells are replaced, new collagen protein fibres are built, and nutrients are delivered to the healing tissue.

Which one of these processes involved in healing this wound does NOT need energy released by respiration?

A home brewer adds a sachet of yeast to a sealed glass jar of sugary apple juice to make cider. The jar has an airlock fitted to its lid, which lets gas escape but stops air getting back in. Over the next few days, the brewer sees a steady stream of bubbles passing through the airlock, and the liquid slowly develops an alcoholic smell.

At the same time, a warehouse worker is rushing to load heavy boxes onto a delivery van before it leaves. Partway through, his leg muscles begin to ache, even though he is already breathing as fast and as deeply as he can.

(a) State the word equation for the reaction taking place in the yeast inside the sealed jar of cider. [2]

(b) State the word equation for the reaction taking place in the warehouse worker's aching leg muscles. [2]

(c) State one substance that is needed when the worker's muscles respire aerobically at rest, but that is NOT needed for the reactions described in (a) and (b) above. [1]

(d) State how the amount of energy released per glucose molecule broken down in the sealed jar of cider compares with the amount released per glucose molecule during aerobic respiration. [1]

Heavy rain floods the soil around the roots of a maize (corn) plant for several days. Before the flood, oxygen could diffuse freely through air spaces in the soil to reach the root cells, which respired aerobically. Once the soil is waterlogged, the air spaces fill with water and oxygen can no longer reach the root cells, so they are forced to respire anaerobically instead, breaking glucose down into ethanol and carbon dioxide, in the same way that yeast does.

(a) State the balanced chemical equation for the aerobic respiration that was occurring in the root cells before the flood. [1]

(b) State the balanced chemical equation for the anaerobic respiration now occurring in the waterlogged root cells. [1]

(c) State and explain which of these two respiration reactions releases more energy per molecule of glucose broken down. [2]

(d) Show that the equation you gave in (b), C6H12O6 → 2C2H5OH + 2CO2, has the same number of carbon atoms, the same number of hydrogen atoms and the same number of oxygen atoms on each side. [2]

A commuter is running late for work. Seeing the doors of their train about to close, they sprint as fast as possible along the platform for the last 15 seconds before the doors shut, then stand catching their breath once safely on board.

(a) Explain, in terms of the chemical reactions taking place inside the commuter's leg muscle cells, why their muscles begin to ache slightly during this short, fast sprint, even though they are breathing throughout. [3]

(b) Once on the train, the commuter's breathing stays fast and deep, and their heart continues to beat quickly for several minutes, even though they are now standing still. Describe two ways in which this continued fast breathing and heart rate help to repay the oxygen debt built up during the sprint. [4]

(c) State the organ in which the lactic acid produced during the sprint is eventually broken down by aerobic respiration. [1]

A student sets up three identical conical flasks, each containing the same volume of glucose solution and the same mass of dried yeast. The student stands one flask in a water bath at 10°C, one at 25°C and one at 40°C. A delivery tube from each flask leads to an inverted measuring cylinder filled with water, so that gas released from each flask collects at the top of its cylinder. After 20 minutes, the student compares the volume of gas collected in each cylinder.

Which row correctly ranks the volumes of gas collected after 20 minutes, from smallest to largest?

A cyclist pedals gently along a flat, quiet cycle path for an hour. She breathes steadily throughout and never runs out of breath. Oxygen reaches her leg muscle cells fast enough to meet all of their energy needs the whole time.

Which word equation correctly represents the type of respiration taking place in her leg muscle cells throughout this gentle ride?

A hiker climbs a steep hill carrying a heavy backpack on a cold, windy day. For each description below, state the use of the energy released by respiration that is being shown.

(a) As she climbs, the muscle fibres in her legs shorten repeatedly, pulling on her leg bones and driving each step up the slope. [1]

(b) Partway up, she trips on a loose stone. Her leg muscles react and correct her balance within a fraction of a second, faster than she can consciously think, because electrical signals travel rapidly along her nerve cells. [1]

(c) Feeling a chill in the wind, her body starts to shiver, and heat released by her cells helps keep her core body temperature steady. [1]

(d) In her small intestine, glucose from her packed lunch is absorbed into her blood, moving from a region of lower concentration in the gut to a region of higher concentration in the blood. [1]

(e) Over the following days, her leg muscles repair and adapt to the climb as her cells join amino acids together to build new muscle proteins. [1]

A student places germinating pea seeds inside a sealed, transparent chamber that is kept well supplied with oxygen throughout the investigation. The seeds are respiring aerobically.

(a) State the word equation for the aerobic respiration taking place in the germinating seeds. [2]

(b) Write the balanced chemical symbol equation for this reaction. [1]

(c) Show that the balanced equation you gave in (b) has the same number of carbon atoms, the same number of hydrogen atoms and the same number of oxygen atoms on each side. [3]

A sprinter finishes a 200 m race. For several minutes afterwards, she continues to breathe heavily and her heart continues to beat rapidly, even though she has stopped running and is now standing still.

Which statement best explains why an oxygen debt occurs during the race and must be repaid in this way afterwards?

A rowing team trains hard on a lake at dawn. Their packed lunch includes fresh bread rolls, made using yeast the day before.

Three different respiration reactions are linked to this training session: (1) aerobic respiration in a rower's leg muscles during a steady warm-up paddle, when oxygen reaches her muscle cells fast enough to meet all their energy needs; (2) anaerobic respiration in the same rower's leg muscles during an all-out sprint finish, when her muscles need energy faster than aerobic respiration alone can supply; (3) anaerobic respiration in the yeast used to make the bread rolls the day before.

(a) State the two reactants of reaction (1), the aerobic respiration during the warm-up paddle. [2]

(b) State the one carbon-containing product formed in reaction (2), the anaerobic respiration during the sprint finish. [1]

(c) State the two products formed in reaction (3), the anaerobic respiration in the yeast. [2]

(d) Compare the amount of energy released per glucose molecule broken down in reactions (2) and (3) with the amount released in reaction (1). [2]