Edexcel IGCSE Biology · Spec 2.35
ATP Uses in Living Cells
Covers link respiration to ATP production, Recall three cellular uses of ATP and Explain why ATP must be regenerated continuously.
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ATP Uses in Living Cells
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Explained
ATP, the molecule that actually delivers the energy
Respiration releases energy from glucose, but a cell cannot use glucose to power anything directly. The energy is transferred to ATP, and ATP is what every energy requiring process in the cell actually uses.
Think of glucose as the fuel in the tank and ATP as the electricity in the wire. One stores a great deal of energy in a form nothing can use immediately; the other carries small amounts to wherever they are needed, right now.
How it works
ATP stands for adenosine triphosphate, and the tri is the part that matters: it carries three phosphate groups.
When a cell needs energy, the bond holding the third phosphate is broken. ATP becomes ADP, adenosine diphosphate, plus a free phosphate, and the energy released does the work.
Respiration then joins that phosphate back on, re forming ATP. So ADP and ATP cycle continuously, thousands of times a day for each molecule.
A cell holds only a very small amount of ATP at any moment, enough for a few seconds of activity. That is why respiration never stops, and why a cell deprived of oxygen or glucose fails so quickly. There is no reserve.
Where it is made
Most ATP is made in the mitochondria, by aerobic respiration.
That is why cells with high energy demands contain large numbers of them. Muscle cells, which contract constantly, are packed with mitochondria. Sperm cells have them concentrated in the middle section to power the tail. The cells lining the small intestine have many, because absorbing nutrients against a concentration gradient by active transport takes energy.
Anaerobic respiration makes some ATP too, in the cytoplasm, but far less per glucose molecule, which is why it cannot sustain activity for long.
What uses it
Muscle contraction. Every movement, including the beating of the heart and the movement of food along the gut, is powered by ATP.
Active transport, moving substances across membranes against a concentration gradient. Root hair cells taking up mineral ions, nerve cells maintaining their charge, and the kidney reabsorbing glucose all use it.
Synthesis of large molecules. Joining amino acids into proteins, glucose into starch or glycogen, and building DNA all require energy.
Also heat production in mammals and birds, keeping body temperature above that of the surroundings, and the transmission of nerve impulses.
What the mark scheme accepts and rejects
An Edexcel International GCSE Biology mark scheme asks candidates to explain how a labelled structure in a cell relates to what the cell does. It credits naming the mitochondrion, then credits that the mitochondrion carries out respiration, releases energy or provides ATP.
Two instructions sit beside it, and they work together.
No credit if the structure is called the cytoplasm or the chloroplast. And, more sharply: naming any of the other lettered structures as the site of respiration means no credit for the second marking point either.
So getting the organelle wrong takes the function mark with it. That is unusual, because mark schemes often let a correct explanation stand on a wrong identification. Here they do not, because the claim being made is that respiration happens in that structure, and it does not.
The same mark scheme also instructs the examiner to ignore produces energy. Releases energy earns the mark and produces energy does not, because energy is not created. It was already in the glucose, and respiration transfers it to ATP.
Notice that provides ATP is accepted as an alternative to releases energy. The two are treated as the same claim, which tells you how the specification sees ATP: not as a separate topic, but as what respiration is for.
Writing about it accurately
Say that ATP is made or synthesised, and that energy is released or transferred. Avoid produced or created for energy.
When a question asks why a cell has many mitochondria, give the chain: many mitochondria, so more aerobic respiration, so more ATP, so enough energy for whatever that cell does. Naming the process the cell carries out at the end is what completes it.
Spec 2.35
What you need to know
- Link respiration to ATP production
- Recall three cellular uses of ATP
- Explain why ATP must be regenerated continuously
Active recall
Quick check
Answer each question before opening the answer.
Name one cell process that uses ATP
Any one of muscle contraction, active transport or synthesis of large molecules
What molecules remain when ATP releases its final phosphate?
ADP and phosphate
Why must ATP be regenerated continuously?
Cells store only a small amount and use it continuously
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