Outline, with examples, the types of carbohydrate found in living organisms.

Describe the importance of hydrolysis in digestion.

Explain the flow of energy between trophic levels in ecosystems.

(mono-, di- and polysaccharides) consist of one, two and many units;
example of monosaccharide (e.g. glucose/ribose/galactose/fructose);
example of disaccharide (e.g. maltose/lactose/sucrose);
example of polysaccharide (e.g. starch/glycogen/cellulose);

digestion is the breakdown of large molecules into small molecules;
to allow diffusion / to make food soluble;
so foods can be absorbed into the bloodstream/body;
so foods can move from bloodstream into cells;
small molecules can be joined to form the organism’s (unique) macromolecules;
hydrolysis is aided by enzymes;
hydrolysis requires water;
polysaccharides (hydrolysed) to disaccharides/monosaccharides/specific example;
proteins/polypeptides (hydrolysed) to amino acids;
fats/lipids/triglycerides (hydrolysed) to fatty acids and glycerol;

sunlight is the initial source of energy for (most) ecosystems;
sunlight (energy) is converted (through photosynthesis) into chemical/potential energy by producers/plants/autotrophs;
energy escapes from an ecosystem (as heat) / is not recycled;
flow of energy through an ecosystem can be represented as a pyramid of energy; (allow a suitable diagram)
energy flow in an ecosystem is measured as energy per unit area/volume, per unit time, for example kJ m^–2 yr^–1/ kJ m^–3 day^–1 / other valid unit;
(chemical) energy is passed along the food chain/trophic levels;
primary consumer/herbivores obtain energy from plant food;
secondary/tertiary consumer/carnivores obtain energy by eating other (animals);
energy transfer between trophic levels is not 100 % efficient / is only about 10% efficient;
some energy is lost as heat through respiration;
decomposers obtain energy from waste products/dead bodies/leaf litter;

Well answered except for the absence of understanding about the prefixes: mono-, di-, and poly-  when preceding the word saccharide.

Candidates who did well understood that hydrolysis falls within the context of digestion rather than thinking that hydrolysis is synonymous with digestion. Their answers began with the notion that only small molecules can diffuse and be absorbed into the bloodstream and that hydrolysis is a step in the digestive process. Often those candidates went on to describe that hydrolysis requires water and gave examples of how polysaccharides or proteins are hydrolyzed to named sub-units. Even among stronger responses, lipid hydrolysis was not mentioned very often nor was the idea that hydrolysis is aided by enzymes. This question was an interesting link between Topic 3.2 and Topic 6.1

The best answers started out with the sun as the ultimate source of energy and how light energy is converted to chemical energy through photosynthesis by autotrophs/plants. This led naturally to how energy passes from one tropic level to the next.  By including that energy transfer is only about 10% efficient and that it is not recycled, candidates gained the max of 8 marks. Some candidates included pyramids of energy. Less commonly mentioned was the loss of energy through metabolic heat or that decomposers obtain energy from waste products, dead bodies/leaf litter. Only the rare candidate mentioned how energy flow is measured in energy per unit area/volume per unit time.