Nectar is a sweet fluid that contains mainly sucrose, fructose and glucose. The molecular formula of sucrose is $\text{C}_{12}\text{H}_{22}\text{O}_{11}$. Fructose and glucose each have the molecular formula $\text{C}_{6}\text{H}_{12}\text{O}_{6}$. State two differences between sucrose and fructose, apart from the number of carbon, hydrogen and oxygen atoms they contain.
Fig. 3.2 gives the structural formula of one kind of storage triglyceride. The triglyceride contains two types of fatty acid residue, palmitate and oleate. Outline the structural characteristics of the triglyceride shown in Fig. 3.2.
In hummingbirds, glycogen is the long-term carbohydrate energy store. Suggest one reason why hummingbirds build up a larger energy store as triglyceride, rather than increasing the glycogen store, before migration.
In birds such as hummingbirds: • blood remains within vessels • during one complete circuit of the body, blood passes through the heart twice. State the term used for this kind of circulatory system.
The heart of birds has the same basic structure as the heart of mammals. However, compared with mammals, the bird heart is larger relative to body size. Suggest why the heart of birds is larger in proportion to their body size.
Complete Table 3.1 by giving the names and functions of the principal blood vessels linked with the heart of mammals.