The olive plant, Olea europaea, is grown in many parts of the world. The fruits of the plant (olives) and the oil that can be obtained from the fruits (olive oil), provide food for humans. Triglycerides are the main type of lipid in olive oil. They are synthesised in the olive plant from glycerol and fatty acids. Scientists can analyse samples of different olive oils to identify: • the fatty acids used to synthesise triglycerides • the composition of the different triglycerides present. (a) Table 1.1 shows some details of the five most common fatty acids found in samples of olive oil produced by olive plants grown in different regions in Portugal. Table 1.1 Key C:D = number of carbon atoms: number of double bonds in the hydrocarbon chain X = missing detail fatty acid | percentage of total fatty acid content | C:D | chemical structure ---|---|---|--- oleic acid | 55.0–83.0 | 18:1 | CH3(CH2)7CH=CH(CH2)7X palmitic acid | 7.5–20.0 | 16: ..... | CH3(CH2)14X linoleic acid | 3.5–21.0 | 18: .... | CH3(CH2)4(CH=CH)CH2(CH=CH)(CH2)7X stearic acid | 0.5–5.0 | 18: .... | CH3(CH2)16X palmitoleic acid | 0.3–3.5 | 16: .... | CH3(CH2)5CH=CH(CH2)7X

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

1. [1] all correct for one mark ; palmitic acid 0 linoleic acid 2 stearic acid 0 palmitoleic acid 1
2. [1] circle drawn around palmitic acid and around stearic acid ;
3. [1] COOH / carboxyl (group) / carboxylic acid (group); A carbonyl group and hydroxyl group R if response includes incorrect groups
4. [2] if no ref. to fatty acids, allow one mark for (some) triglycerides may, be saturated/have no double bonds (in hydrocarbon chain,) and (some) may, be unsaturated/have double bonds I 'tails' any two from: 1 each triglyceride has three fatty acids; 2 fatty acids can be, saturated / with no double bonds, and, unsaturated/ with double bonds; A unsaturated fatty acids can have a different number of double bonds 3 fatty acids can have different, (hydrocarbon chain) lengths / number of carbons ; 4 detail from Table 1.1 to support mp2 or 3 ; saturated = palmitic / stearic v unsaturated = oleic / linoleic / palmitoleic or 1 double bond = oleic / palmitoleic v 2 double bonds = linoleic or oleic/linoleic / stearic = 18C v palmitic / palmitoleic = 16C 5 idea of a particular fatty acid, can be located at a different position in a triglyceride / can form a bond with any one of the three (functional) hydroxyl groups; 6 ref. to different environmental conditions of plants grown in different regions ; e.g. colder conditions and oils having (more triglycerides with) higher proportion of unsaturated fatty acids 7 idea of (shared triglycerides) have structures (most) suited as energy stores ; A example e.g. (have fatty acids with) longest hydrocarbon chains easiest to, hydrolyse / release hydrogen atoms have greater energy value than others 8 ref. to ease of, production / synthesis ; 9 idea that shared triglycerides composed of the fatty acids (present) in highest proportions ; e.g. using Table 1.1 to determine the most common 2 or 3 fatty acids 'could all have the same fatty acid combination from oleic acid and / or palmitic acid and/or linoleic acid' (any two)
5. [2] any two from: 1 water is, a polar molecule / polar / dipolar; A water is a dipole A description e.g. the O atom (of water) has, a slightly negative / δ, charge, and the H atoms have a slightly positive / δ+, charge 2 water can form, hydrogen bonds / H-bonds, with, glycerol / polar substances ; ora = water cannot form H-bonds with, triglycerides / non-polar substances 3 glycerol / polar molecules / ions, interact with water (molecules) / are attracted to water (molecules) / are hydrophilic ; A idea that water, attracts / collects around / AW, ions / charged substances ora = triglycerides / non-polar / uncharged, molecules, do not interact with water / repel water / are hydrophobic I 'tails'
6. [1] (phloem) sieve tube element ; (question asks for type of cell) A sieve element