ATP, Water & Inorganic Ions
Learn it by playing
Answer these questions to earn energy, then fish and explore. No account needed.
For educators: ready-to-use lesson slides, revision notes for ATP, Water & Inorganic Ions (Biology, AQA) — use them in your lesson, or run the topic as an interactive class activity your learners play as a live game.
Lesson notes
The Structure of ATP
- ATP stands for adenosine triphosphate and is known as the universal energy currency because it transfers energy in all energy-requiring processes in cells.
- ATP is a phosphorylated nucleotide made from adenosine (adenine + pentose sugar) combined with three phosphate groups.
- Adenosine monophosphate (AMP) has one phosphate group, adenosine diphosphate (ADP) has two, and ATP has three.
- Adenine is a nitrogenous base, while adenosine is a nucleoside (adenine combined with a sugar).
- Energy from respiration is used to make ATP, which then supplies energy for processes such as anabolic reactions, active transport, and movement of substances within cells.
Hydrolysis of ATP
- Hydrolysis of ATP to ADP and an inorganic phosphate group (π) is catalysed by the enzyme ATP hydrolase (also called ATPase).
- The hydrolysis of ATP releases a useful quantity of energy that can be used for cellular processes such as active transport, enzyme-controlled reactions, and muscle contraction.
- The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
- The inorganic phosphate released during hydrolysis can be used to phosphorylate other compounds, often making them more reactive.
- ATP hydrolysis is quick and simple, allowing cells to respond to sudden energy demands.
- ATP is stable at cellular pH and does not break down unless an enzyme is present, preventing energy wastage.
- ATP is soluble, so it can be transported to different areas of the cell for energy release.
Synthesis of ATP
- ATP synthesis occurs when ADP combines with an inorganic phosphate (π) group, catalysed by the enzyme ATP synthase.
- ATP synthesis is a condensation reaction because water is released as a waste product.
- ATP is made during respiration and photosynthesis; all of an animal's ATP comes from respiration.
- Humans use more than 50 kg of ATP per day but only have about 200 g in the body at any one time, so ATP must be made continuously.
- ATP is synthesised by substrate-linked phosphorylation (in glycolysis) and by chemiosmosis (in the electron transport chain).
- Cells cannot store large amounts of ATP, and ATP rarely passes through the cell surface membrane, so it must be made as and when needed.
The Properties of Water
- Water is a polar molecule because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges.
- Hydrogen bonds form between the positively and negatively charged regions of adjacent water molecules.
- Water is an excellent solvent, has a relatively high specific heat capacity, a relatively high latent heat of vaporisation, is less dense when solid, and has high surface tension and cohesion.
- Water is a metabolite in many reactions, including condensation and hydrolysis reactions.
- In condensation reactions, smaller molecules combine to form a larger molecule with the removal of a water molecule (e.g. formation of peptide, glycosidic, and ester bonds).
- In hydrolysis reactions, water is added to break a bond within a larger molecule, splitting it into smaller units (e.g. breaking proteins into amino acids, starch into glucose, triglycerides into fatty acids and glycerol).
Water as a Solvent
- The polarity of water molecules allows hydrogen bonds to form between adjacent water molecules.
- Many ions (e.g. sodium chloride) and covalently bonded polar substances (e.g. glucose) dissolve in water.
- Dissolved solutes are more chemically reactive because they are free to move about, allowing chemical reactions to occur within cells.
- Metabolites can be transported efficiently in water, except non-polar molecules, which are hydrophobic.
- Due to its polarity, water is considered a universal solvent.
High Specific Heat Capacity of Water
- Specific heat capacity is the energy required to raise the temperature of 1 kg of a substance by 1 °C.
- Water has a high specific heat capacity of 4200 J/kg/°C, meaning a relatively large amount of energy is required to raise its temperature.
- The high specific heat capacity is due to the many hydrogen bonds present in water; it takes a lot of thermal energy to break these bonds and a lot of energy to build them.
- This means the temperature of water does not fluctuate greatly, providing stable habitats for aquatic organisms.
- Water absorbs lots of heat with minimal temperature change, helping to maintain stable internal and external temperatures essential for enzyme function.
- Water in blood plasma transfers heat around the body, aiding temperature regulation; as blood flows through warmer tissues, it absorbs heat without large temperature shifts.
Latent Heat of Vaporisation, Cohesion and Adhesion
- Water has a relatively high latent heat of vaporisation: a large amount of thermal energy must be absorbed to break hydrogen bonds and evaporate water.
- This is an advantage because only a little water needs to evaporate for an organism to lose a great amount of heat, providing a cooling effect (e.g. transpiration from leaves, sweating on skin).
- Hydrogen bonds between water molecules allow for strong cohesion between water molecules.
- Cohesion allows columns of water to move through the xylem of plants and the blood vessels in animals.
- Cohesion also enables surface tension where a body of water meets the air, creating a film on the surface.
- Water can also hydrogen bond to other molecules such as cellulose, which is known as adhesion; this helps water move up the xylem due to transpiration.
Inorganic Ions: General Principles
- An ion is an atom (or group of atoms) that has an electrical charge.
- A positively charged ion is a cation; a negatively charged ion is an anion.
- An inorganic ion is an ion that does not contain carbon.
- Inorganic ions occur in solution in the cytoplasm and body fluids of organisms.
- The concentration of certain ions can fluctuate and can be used in cell signalling and neuronal transmission.
Roles of Specific Inorganic Ions
- Hydrogen ions (H+) are protons; the concentration of H+ determines pH, with an inverse relationship (more H+ = lower pH).
- The concentration of H+ is very important for enzyme-controlled reactions, which are all affected by pH; body fluids normally have a pH of approximately 7.4.
- Iron ions exist as Fe2+ (ferrous) and Fe3+ (ferric); they are essential as they can bind oxygen.
- Haemoglobin is made up of four polypeptide chains, each containing one Fe2+ that binds to oxygen.
- Sodium ions (Na+) are required for the co-transport of glucose and amino acids across cell-surface membranes (e.g. in the small intestine) and for the transmission of nerve impulses.
- Phosphate ions (PO43−) are an essential component of DNA, RNA, and ATP; in DNA and RNA, phosphate groups allow nucleotides to bond to form polynucleotides.
- In ATP, the bonds between phosphate groups store energy; when broken, they release a large amount of energy for cellular processes.
- Phosphates are also found in phospholipids, which are key components of the phospholipid bilayer of cell membranes.
Slides
Sign up free to view the lesson slides
Step through every slide for this topic — plus flashcards and revision notes — with a free account.
Practice questions
Free preview — 8 of 59 questions. Sign up to see them all.
1.Which of the following best describes ATP?
Easy- AA phosphorylated nucleotide
- BA protein made of four polypeptide chains
- CA non-polar lipid
- DA polysaccharide
2.Which enzyme catalyses the hydrolysis of ATP?
Easy- AATP hydrolase
- BATP synthase
- CDNA polymerase
- DAmylase
3.Which of the following is a product of the hydrolysis of ATP?
Easy- AADP and inorganic phosphate
- BAMP and two inorganic phosphates
- CAdenosine and three inorganic phosphates
- DADP and water
4.Which statement correctly describes the synthesis of ATP?
Easy- AADP combines with inorganic phosphate in a condensation reaction.
- BADP combines with inorganic phosphate in a hydrolysis reaction.
- CATP is formed by the breakdown of glucose.
- DATP is synthesised by the addition of water to ADP.
5.Which of the following is NOT a property of water that makes it important for life?
Medium- AIt is a non-polar molecule.
- BIt has a high specific heat capacity.
- CIt is an excellent solvent.
- DIt has a high latent heat of vaporisation.
6.Which type of bond forms between adjacent water molecules?
Medium- AHydrogen bonds
- BCovalent bonds
- CIonic bonds
- DPeptide bonds
7.Which inorganic ion is a component of haemoglobin?
Medium- AIron (Fe2+)
- BSodium (Na+)
- CPhosphate (PO43−)
- DHydrogen (H+)
8.Which inorganic ion is essential for the co-transport of glucose and amino acids across cell membranes?
Medium- ASodium (Na+)
- BIron (Fe2+)
- CPhosphate (PO43−)
- DHydrogen (H+)
Unlock all 59 questions & more
Create a free account to see every question, the slides, flashcards and revision notes for this topic.
Past papers
Past-paper practice for this topic is coming soon.
Coming soon