Human body systems, Year 10: respiration and exercise

exothermic

HintThe first part of the word means 'out', as in 'exit'.

The whyCellular respiration releases the energy stored in glucose. Some of it is transferred to the surroundings by heating, which is how birds and mammals keep warm.

O₂

HintIt is the gas your lungs take from the air.

The whyIn words: glucose + oxygen → carbon dioxide + water. The substances are the same four as in photosynthesis, with reactants and products swapped. AQA asks you to recognise the symbols, not to balance the equation.

build larger molecules; movement; warm

HintOne is about making things, one is about muscles, and one is about body temperature.

The whyThe energy transferred by respiration supplies everything a living thing does: joining small molecules into big ones such as proteins, contracting muscles, and, in birds and mammals, holding a steady body temperature.

Respiration goes on continuously, day and night, in all living cells

HintAsk whether a cell can ever manage without a supply of energy.

The whyEvery living cell needs energy all the time, so respiration never stops. In daylight a plant photosynthesises as well, usually faster than it respires, which hides the respiration but does not switch it off.

Aerobic respiration

HintThe same prefix appears in the name of a keep-fit class that leaves you breathing hard.

The whyThis is the usual form of respiration in plant and animal cells. Glucose is completely oxidised to carbon dioxide and water, which transfers far more energy than respiration without oxygen.

The glucose is not completely oxidised

HintWithout oxygen the breakdown stops part-way.

The whyIn aerobic respiration, glucose is broken right down to carbon dioxide and water. Without oxygen the breakdown is incomplete, and much of the energy stays locked in the products, such as lactic acid.

Muscle cells make lactic acid; yeast cells make ethanol and carbon dioxide

HintOne has a single product that builds up during a sprint; the other gives two, one of them a gas.

The whyBoth start from glucose and neither uses oxygen. In muscles: glucose → lactic acid. In plant and yeast cells: glucose → ethanol + carbon dioxide.

Fermentation

HintBrewers and bakers both rely on it.

The whyYeast is a single-celled fungus. When it respires without oxygen it converts glucose to ethanol and carbon dioxide, and the process has economic importance in making bread and alcoholic drinks.

Carbon dioxide to the baker; ethanol to the brewer

HintOne of them wants bubbles in dough; the other wants the alcohol.

The whyIn bread dough, the gas forms bubbles that make the dough rise, and the small amount of ethanol evaporates in the oven. In brewing and wine-making, the ethanol is the alcohol in the drink.

plants

HintThink of roots in waterlogged soil, with no air spaces left.

The whyAnimal cells make lactic acid when they respire without oxygen. Plant cells, like yeast, make ethanol and carbon dioxide; AQA gives one equation for both.

heart; volume

HintOne blank is an organ; the other is a quantity measured in cm³ or dm³.

The whyThree things change. Breathing faster and more deeply brings more oxygen into the blood, and a faster pulse delivers that blood to the working muscles more quickly.

To carry the oxygenated blood to the muscles more quickly

HintOxygen in the lungs is no use to a leg until something delivers it.

The whyWorking muscles respire faster and need more oxygen and glucose. The lungs load more oxygen into the blood, but it is the circulation that delivers it, and that also carries away the extra carbon dioxide.

They stop contracting efficiently

HintThink about what a muscle's job is, and how well a tired one does it.

The whyIf too little oxygen reaches the muscles, they respire anaerobically and lactic acid builds up, creating an oxygen debt. After a long spell of hard work the muscles cannot keep contracting as strongly as before.

90

HintFind the rise first, then compare it with the starting value, not the final one.

The whyIncrease = 133 − 70 = 63 beats per minute. Percentage increase = 63 ÷ 70 × 100. Measuring pulse or breathing rate before and after activity is the standard way to investigate the effect of exercise on the body.

Blood carries it to the liver, where it is converted back into glucose

HintThe same organ deals with alcohol and stores glycogen.

The whyLactic acid does not stay in the muscles. It is transported in the blood flowing through them to an organ that turns it back into a useful sugar, and this needs oxygen.

Oxygen debt

HintFinancially, the second word is something you owe and must repay.

The whyIt is why you keep breathing hard after you stop running. The amount depends on how much lactic acid built up, so a harder or longer burst of anaerobic work takes longer to recover from.