3.1.8 Inorganic ions
3.1.8 Inorganic ions
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Q1. Name the ion that is a component of haemoglobin. (1)
iron ions
Q2. Name the ions that are involved in the co-transport of glucose and amino acids. (1)
sodium ions
Q3. Name the ions that are components of DNA, RNA and of ATP. (1)
phosphate ions
Q4. Describe the roles of phosphate ions in cells. (3)
1. Affects osmosis/water potential
2. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides
3. Used in / to produce ATP Reject ‘energy produced’
4. Phosphorylates other compounds usually making them more reactive
5. Hydrophilic / water soluble part of phospholipid bilayer / membrane
Q5. Some scientists suggested that an increase in phosphate in the embryo of some plants was linked to growth of the embryo. Suggest two reasons why an increase in phosphate can be linked to growth of the embryo of some plants. (2)
1. Phosphate required to make RNA
2. Phosphate required to make DNA
1 and 2. If neither DNA or RNA are named allow one mark for nucleotide/nucleic acid/phosphodiester bonds/sugar-phosphate backbone.
3. Phosphate required to make ATP/ADP
4. Phosphate required to make membranes
Ignore: phospholipids without reference to membranes.
5. Phosphates required for phosphorylation
Accept: as additional mark points any named biological molecule containing phosphate e.g. NADP, AMP, RuBP.
Q6. Describe the roles of sodium ions in cells. (2)
Sodium ions are involved in the co-transport of glucose and amino acids into cells.
Because sodium moved out by active transport /Na – K pump creating a sodium concentration gradient.
The movement of sodium ions also affects water potential and therefore influences osmosis. For example, in the kidneys, sodium ion reabsorption causes water to be reabsorbed by osmosis.
In neurones, sodium ions are important in establishing the resting potential and in generating an action potential, as the diffusion of sodium ions into the neurone causes depolarisation of the membrane.
Q7. Describe the roles of iron ions in cells. (1)
Iron ions are an essential component of haemoglobin in red blood cells.
Haemoglobin binds / associates with oxygen
OR Haemoglobin transports/loads oxygen
Ignore reference to 2+ or 3+ in Fe2+ or Fe3+
Q8. Explain a property of iron ions that enables these ions to carry out their role in red blood cells. (2)
Iron ions are charged (Fe2+ OR Fe3+) and form part of the haem group in haemoglobin.
This allows the iron ion to bind reversibly with oxygen, enabling haemoglobin to form oxyhaemoglobin and transport oxygen in red blood cells.
Spaced practice
Q9. Give two roles of phosphate ions in cells.(2)
Phosphate ions are a component of DNA and RNA, where they form part of the sugar–phosphate backbone of nucleic acids.
Phosphate ions are present in ATP and ADP, where the phosphate groups are involved in energy transfer within cells.
Phosphate ions are important in phosphorylation, where a phosphate group is added to a molecule to make it more reactive.
Phosphate ions are a component of phospholipids, which form the structure of cell membranes.
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