Energy (Cambridge (CIE) A Level Biology): Flashcards
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What are the three main uses of energy in living organisms?
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What are the three main uses of energy in living organisms?
Active transport
Movement
Anabolic reactions (synthesis of large molecules, e.g. DNA replication and protein synthesis)
Define anabolic reactions.
Anabolic reactions build large, complex molecules from smaller, simpler ones, requiring an input of energy.
Why does active transport require energy?
It moves substances against their concentration gradient, which cannot happen passively.
Give two examples of anabolic reactions that require energy.
DNA replication
Protein synthesis
The movement of substances against a concentration gradient is called .
The movement of substances against a concentration gradient is called active transport.
Reactions that synthesise large molecules from smaller ones and require energy are described as .
Reactions that synthesise large molecules from smaller ones and require energy are described as anabolic.
Define ATP.
ATP (adenosine triphosphate) is a nucleotide made of adenine, ribose and three phosphate groups; it is the universal energy currency of cells.
What features make ATP suitable as the universal energy currency?
Releases energy in small, usable amounts
Releases energy instantly in a single reaction (hydrolysis)
Easily re-formed from ADP + Pi
Soluble and moves easily within cells
How is energy released from ATP?
By hydrolysis of ATP to ADP + inorganic phosphate (Pi), which releases energy.
ATP is hydrolysed to ADP and an phosphate group, releasing energy.
ATP is hydrolysed to ADP and an inorganic phosphate group, releasing energy.
State the two ways ATP is synthesised.
Transfer of phosphate in substrate-linked reactions
Chemiosmosis in the membranes of mitochondria and chloroplasts
Define chemiosmosis.
Chemiosmosis is the synthesis of ATP driven by the flow of protons (H^+^) down their gradient across a membrane in mitochondria and chloroplasts.
In substrate-linked reactions, a group is transferred directly to ADP to form ATP.
In substrate-linked reactions, a phosphate group is transferred directly to ADP to form ATP.
Define respiratory substrate.
A respiratory substrate is an organic molecule that is oxidised during respiration to release energy (e.g. carbohydrate, lipid, protein).
Which respiratory substrate has the highest energy value per gram?
Lipids — about twice the energy value of carbohydrates or proteins per gram.
Explain why lipids have a higher energy value than carbohydrates.
Lipids contain more hydrogen atoms (more C–H bonds) per molecule.
So more hydrogen is available to reduce NAD/FAD, releasing more energy in oxidative phosphorylation.
Order carbohydrates, lipids and proteins by energy value per gram (highest first).
Lipids (highest)
Proteins
Carbohydrates (lowest)
Why do molecules with more hydrogen atoms release more energy in respiration?
More hydrogen atoms produce more reduced NAD/FAD, which supply more electrons to the electron transport chain, generating more ATP.
Per gram, release about twice as much energy as carbohydrates or proteins.
Per gram, lipids release about twice as much energy as carbohydrates or proteins.
Define respiratory quotient (RQ).
The RQ is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in during respiration.
State the formula for RQ.
RQ = CO~2~ produced ÷ O~2~ taken in
The RQ is the ratio of carbon dioxide produced to taken in.
The RQ is the ratio of carbon dioxide produced to oxygen taken in.
Calculate the RQ for the aerobic respiration of glucose:
C6H12O6 + 6O2 → 6CO2 + 6H2O
RQ = 6 CO~2~ ÷ 6 O~2~ = 1.0
What does an RQ of about 1.0 indicate about the respiratory substrate?
A carbohydrate is being respired.
A lipid has an RQ of about 0.7. Explain what this value tells you.
Lipids require more oxygen to be fully oxidised relative to the carbon dioxide produced.
This gives a lower RQ (about 0.7).
An RQ value of about indicates that a carbohydrate is being used as the respiratory substrate.
An RQ value of about 1.0 indicates that a carbohydrate is being used as the respiratory substrate.
Define respirometer.
A respirometer is apparatus used to measure the rate of oxygen uptake (gas volume change) by respiring organisms.
In a respirometer, what is the role of potassium hydroxide (KOH)?
It absorbs carbon dioxide, so any change in gas volume is due only to oxygen uptake.
Outline how a respirometer measures the oxygen uptake of germinating seeds.
Seeds are sealed in a tube with KOH to absorb CO2.
As O2 is used up, gas volume falls and the coloured fluid in the manometer moves towards the seeds.
The distance moved measures the volume of O2 consumed.
How is a respirometer used to determine the RQ of an organism?
Measure O2 uptake with CO2 absorbed (KOH present).
Then repeat without the CO2 absorbent to measure the net volume change (CO2 produced − O2 used).
Use both readings to calculate RQ = CO2 produced ÷ O2 used.
Why should a respirometer be kept in a water bath at constant temperature?
Gas volume changes with temperature.
A constant temperature ensures volume changes are due to respiration only.
In a respirometer, hydroxide is used to absorb carbon dioxide.
In a respirometer, potassium hydroxide is used to absorb carbon dioxide.
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