Respiration (Edexcel IGCSE Science (Double Award): Biology): Flashcards
Exam code: 4SD0
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Define respiration.
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Define respiration.
A chemical reaction carried out in all living organisms in which energy is released from glucose, either in the presence of oxygen (aerobic) or in its absence (anaerobic).
In what form is energy transferred during respiration?
As ATP.
What are the waste products of respiration?
Carbon dioxide
Water
How is ATP produced in living organisms?
During cellular respiration, glucose is broken down and several molecules of ATP are produced.
How does a cell get energy from ATP?
The ATP is broken down, releasing energy for living processes within cells and organisms.
Name three processes that require energy from ATP.
Chemical reactions that build larger molecules from smaller ones
Muscle contraction, to allow movement
Keeping warm, to maintain a temperature suitable for enzyme activity
What is the difference between respiration and gas exchange?
Gas exchange gets oxygen into cells and carbon dioxide out.
Respiration then uses that oxygen to release energy as ATP.
The energy released by respiration is transferred in the form of ＿＿＿＿＿＿＿＿.
The energy released by respiration is transferred in the form of ATP.
In respiration, energy is released from ＿＿＿＿＿＿＿＿, with or without oxygen.
In respiration, energy is released from glucose, with or without oxygen.
True or False?
Respiration produces energy.
False.
Energy is never made or produced — it is released from glucose and transferred as ATP.
True or False?
Respiration takes place in all living organisms.
True.
Respiration is a chemical reaction carried out in every living organism.
Why do cells need to keep warm using energy from ATP?
To maintain a constant temperature suitable for enzyme activity.
Define aerobic respiration.
The chemical process in cells that uses oxygen to break down nutrient molecules and release energy as ATP.
It takes place in the mitochondria.
Give the word equation for aerobic respiration.
glucose + oxygen → carbon dioxide + water
Give the balanced symbol equation for aerobic respiration.
C6H12O6 + 6O2 → 6CO2 + 6H2O
Define anaerobic respiration.
The chemical process in cells that breaks down nutrient molecules to release energy without using oxygen.
It is an incomplete breakdown of glucose, so it releases less ATP.
Give the word equation for anaerobic respiration in animals.
glucose → lactic acid
Give the word equation for anaerobic respiration in plants and yeast.
glucose → ethanol + carbon dioxide
When does anaerobic respiration occur in animals?
Mainly in muscle cells during vigorous exercise, when the body cannot deliver enough oxygen to meet the muscles' higher demand for energy.
What problem does a build-up of lactic acid cause?
It lowers the pH of the muscle tissue, making conditions more acidic, which can denature the enzymes in cells.
What eventually happens to the lactic acid in muscles?
It is broken down using oxygen, producing carbon dioxide and water as waste products.
Define fermentation.
Anaerobic respiration in yeast cells, which produces ethanol and carbon dioxide.
Why is fermentation important in making bread?
The carbon dioxide produced by the yeast makes the dough rise.
Give three differences between aerobic and anaerobic respiration.
Oxygen — used in aerobic, not used in anaerobic
Glucose breakdown — complete in aerobic, incomplete in anaerobic
ATP released per glucose molecule — a lot in aerobic, only a little in anaerobic
Why does anaerobic respiration release less energy than aerobic?
Because glucose is only incompletely broken down, so energy is still stored in the bonds of the products, such as lactic acid.
Anaerobic respiration in animal muscle cells produces ＿＿＿＿＿＿＿＿.
Anaerobic respiration in animal muscle cells produces lactic acid.
Aerobic respiration takes place in the ＿＿＿＿＿＿＿＿ of the cell.
Aerobic respiration takes place in the mitochondria of the cell.
True or False?
Anaerobic respiration in plants produces lactic acid.
False.
Plants and yeast produce ethanol and carbon dioxide. It is animal cells that produce lactic acid.
True or False?
Aerobic respiration releases more ATP per glucose molecule.
True.
Aerobic respiration breaks glucose down completely, releasing a lot of ATP; anaerobic respiration releases only a little.
Which two products of respiration can be investigated practically?
Carbon dioxide
Heat
Using germinating seeds or other living organisms, such as blowfly larvae.
Which chemical shows that carbon dioxide is being produced?
Limewater (calcium hydroxide solution), which turns from clear to cloudy/milky when carbon dioxide is bubbled through it.
Name another indicator that detects carbon dioxide.
Hydrogen carbonate indicator, which changes from orange to yellow when carbon dioxide levels are high.
Outline the limewater method for the carbon dioxide investigation.
Pour 2 cm3 of limewater into three boiling tubes.
Set up three more tubes on damp cotton wool: A with germinating seeds, B with boiled seeds, C with glass beads.
Seal each seed tube with a bung and delivery tube into the limewater, with the end submerged.
Leave at 25–30 °C for several hours, then observe any colour changes.
What happens to the limewater with germinating seeds, and why?
It turns cloudy/milky.
The germinating seeds are respiring and releasing carbon dioxide, which reacts with the limewater.
Why are boiled seeds used as a control?
Boiled seeds are dead, so they do not respire and release no carbon dioxide — the limewater stays clear.
Why are glass beads included in the carbon dioxide investigation?
As a control for volume — there is no living material, so no respiration and no carbon dioxide, and the limewater stays clear.
Outline the vacuum flask method for the heat investigation.
Sterilise the seeds and flasks with weak bleach.
Set up flask A with dead seeds and flask B with germinating seeds, on moist cotton wool.
Insert a thermometer into each so the bulb sits among the seeds, and seal the tops with cotton wool.
Invert both flasks, record the initial temperature, then record the final temperature after 2–3 days.
Why must the seeds and flasks be sterilised?
To kill any microorganisms present.
Otherwise microbial decay would raise the temperature in both flasks, rather than the respiring seeds.
What results are expected from the heat investigation?
The flask with germinating seeds shows a clear temperature rise, because respiration releases heat energy.
The flask with dead seeds shows no change, because they are not respiring.
Why is the room temperature measured as well as the flasks?
So that any temperature change in the dead-seed control flask can be attributed to a change in room temperature, not to respiration.
Why is cotton wool used to seal the tops of the flasks?
It holds the thermometer in place and also reduces heat loss from the flask.
Limewater turns ＿＿＿＿＿＿＿＿ when carbon dioxide from respiring seeds is bubbled through it.
Limewater turns cloudy when carbon dioxide from respiring seeds is bubbled through it.
Boiled seeds are used as a control because they are ＿＿＿＿＿＿＿＿ and cannot respire.
Boiled seeds are used as a control because they are dead and cannot respire.
True or False?
The delivery tube must dip below the surface of the limewater.
True.
The end must sit a few millimetres below the limewater so that any gas released is bubbled through it.
True or False?
Respiring seeds release heat energy.
True.
This is why the flask of germinating seeds shows a temperature rise while the dead-seed flask does not.
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