Hummingbirds are the smallest of birds and are found in the Americas. Some species migrate hundreds of kilometres between warmer overwintering areas and summer breeding grounds. Like mammals, birds maintain a constant body temperature. Hummingbirds have a high requirement for sugars because they have a very high metabolic rate. Fig. 3.1 shows a hummingbird feeding on nectar, one of their main food sources. [Figure 3.1]

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [2] any two from: I ref. to two units v one unit or bigger v smaller (neutral points) sucrose (disaccharide) vs fructose (monosaccharide);
2. [2] sucrose (non-reducing sugar) vs fructose (reducing sugar);
3. [2] sucrose (glycosidic bond present) vs fructose (no glycosidic bond present);
4. [2] sucrose (hydrolysed / broken down before used as, a respiratory substrate / an energy source) vs fructose (can be used immediately as, a respiratory substrate / an energy source)
5. [3] I three fatty acids A fatty acid residue for fatty acid any three from: 1 glycerol ;
6. [3] 2 ester, bond / linkage, qualified ; e.g. labelled on Fig. 3.2 / three ester bonds / ester bond between (O of) glycerol and (C of carboxyl of) fatty acid
7. [3] 3 palmitate is saturated or oleate(s) are, unsaturated / monounsaturated or two fatty acid(s) are, unsaturated / monounsaturated, and one is saturated ;
8. [3] 4 (each fatty acid has a) hydrocarbon chain ;
9. [3] 5 AVP; extra detail e.g. hydrocarbon chain palmitate 15C and oleate 17C palmitate, CH3(CH2)14 and oleate, CH3(CH2)7CH=CH(CH2)7 palmitate 16C and oleate 18C unsaturated fatty acid tail(s) / oleate ref. to, presence of one, C=C/(carbon-carbon) double bond not the maximum number of, hydrogen atoms / hydrogens saturated fatty acid tail(s) / palmitate ref. to no, C=C / (carbon-carbon) double bond maximum number of hydrogen atoms / hydrogens
10. [1] any one from: idea that provides greater energy per unit volume ; A higher calorific value / greater energy density R produces more energy
11. [1] less mass needed to provide same energy / low(er) mass to energy ratio ; ora higher energy to mass ratio
12. [1] low(er) mass to volume ratio ;
13. [1] AVP; e.g. glycogen can only be stored in liver and muscles glycogen is hydrated / uses water for storage, so mass increases suggestion that more, areas / adipocytes / adipose tissue, in body to store triglycerides (proportionately) more C-H bonds (to supply H for respiration) suggestion that triglycerides provides insulation during flight (at heights) more compact
14. [1] closed, double (circulation / circulatory system) ;
15. [2] I ref. to metabolism any two from: need more, / large quantities of, oxygen / glucose or more / large quantities, of, oxygen / glucose, delivered / reaches tissues / transported / AW or idea of enough, oxygen / glucose supplied to meet needs ;
16. [2] idea that heart pumps blood (to tissues more) efficiently; e.g. forcefully / in greater volumes / more / with higher pressure / faster more oxygenated blood is mp2 only
17. [2] suggestion of reason for needing more oxygen or glucose ; I migration e.g. more active fly/wing muscles search for food longer constantly moving / move for longer time generate heat to maintain body temperature, qualified ; e.g. (generally) smaller size / larger SA:V
18. [2] ref. to need to meet demands of carbon dioxide removal (from muscle action / respiration) ; idea that more carbon dioxide produced (so must be removed)
19. [3] note: only one mark for both pulmonary vessels function of blood vessel | name of blood vessel carries blood from the heart to the lungs | pulmonary, artery/arteries;
20. [3] carries blood to the heart from the lungs | pulmonary, vein / veins ;
21. [3] carries blood from the heart to the rest of body | aorta; I artery
22. [3] carries blood to the heart from the rest of body | venae cavae / vena cava ; I superior and inferior or anterior and posterior I vein