Eduqas Biology for A Level Book 1: 2nd Edition

Inorganic ions Living organisms need a variety of inorganic ions to survive. Inorganic ions are also called electrolytes or minerals and are important in many cellular processes, including muscle contraction, nervous coordination and maintaining water potential in cells and blood. There are two groups: macronutrients, needed in small concentrations, and micronutrients, needed in minute (trace) concentrations, e.g. copper and zinc. Four macronutrients are described here. ▪ Magnesium (Mg 2+ ) is an important constituent of chlorophyll and is therefore essential for photosynthesis. Plants without magnesium in their soil cannot make chlorophyll and so the leaves are yellow, a condition known as chlorosis. Growth is often stunted from lack of glucose. Mammals need magnesium for their bones. A chlorophyll molecule with Mg 2+ ▪ Iron (Fe 2+ ) is a constituent of haemoglobin, which transports oxygen in red blood cells. Lack of iron in the human diet can lead to anaemia. Haemoglobin molecule ▪ Phosphate ions (PO 4 3– ) are used for making nucleotides, including ATP, and are a constituent of phospholipids, found in biological membranes. An ATP molecule ▪ Calcium (Ca 2+ ), like phosphate, is an important structural component of bones and teeth in mammals and is a component of plant cell walls, providing strength. 3 phosphate groups ribose adenine O – – P – O – P – O – P –––O – CH 2 O – – O – – O – O O O – = = = OH OH O NH 2 N N N N Note Remember that terms in blue are defined in the Glossary, beginning on p264. haem (non-protein group, iron-containing group) b 1 polypeptide a 2 polypeptide a 1 polypeptide b 2 polypeptide  1.1 Chemical elements and biological compounds 13 Stretch & challenge Originally ‘organic’ meant being derived from living organisms and ‘inorganic’ meant not derived from living material. The meaning of ‘organic’ in the term ‘organic food’ is not related to the structure of the food’s molecules. Exam tip Learn a role in living organisms for each of the four elements magnesium, iron, phosphorus and calcium. Key term Inorganic: A molecule or ion that has no more than one carbon atom. Link Membrane structure is described on pp54–55. Nucleotide structure is described in more detail on p95.