P380: Energy Metabolism
Basic goal of eating is to keep your body running. Think of body as a metabolic machine:
Need raw materials for tissues and enzymes:
Body composition =
- 60% water
- 16% protein
- 4 % minerals
- ~20% fat (small dietary requirement)
Need energy to keep it running -- for
- Basal metabolism: thermoregulation , respiration, digestion, etc
- Activity and Growth
Food = source of both required nutrients (e.g. amino acids, minerals, trace elements, etc) and of energy (which is stored in molecular bonds of compounds in foods)
Energy is stored in molecular bonds of compounds in foods
Carbohydrates 4 kcal / g Fats 9 kcal / g Protein ~ 4 kcal / g
How much energy do you need?
That depends on how BIG you are: the larger your "machine" the higher your total energy requirements so smaller animals require less total energy than larger animals to "maintain your weight" -- a concept we're all familiar with!
body wt daily need metabolic rate: monkey 10 kg (~22 lbs)
1000 kcal ? kcal / kg human 100 kg (~220 lbs)
3500 kcal ? kcal / kg
Smaller animals "burn" energy at a faster rate: metabolism scales to body size. Monkeys need 100 kcal/kg body weight vs humans 35 kcal/kg body wt
WHY?
energy use is proportional to surface area, rather than volume (wt): smaller animals have relatively larger surface area
1" cube 10" cube
Area 6 sq inches 600 sq inches
Volume 1 cu inch 1000 cu inches
Metabolic rate scales to body size raised to 2/3-3/4 power: = "Kleiber rule"
This is important for primates, because smaller animals need more concentrated sources of energy .... (only has so many mouthfuls per day in which to cram all calories) = energy/volume (or sugars/cellulose)
This principle helps solve the problem of why smaller primates are less sensitive to the taste of sugar: why?
And note that it COSTS more for a big animal to move in search of food... Note that this difference is most pronounced in source of protein which different primates choose. Smaller primates tend to eat more insects, whereas larger primates eat more leaves.
Insect eaters: e.g. Tarsier, Marmoset, AyeAye (Prosimian = the "woodpecker" of the primates, hunts grubs of wood-boring insects=labor-intensive pursuit )-- gets almost all its energy and protein from grubs = a rich food that is hard to get (fats + amino acids + indigestible chitin)
vs. Gorillas, largest of living primates is a specialist in "THV" = terrestrial herbaceous vegetation... selects tender shoots, rather than mature leaves (less cell wall material), but still eating a very bulky diet.. has a big gut to hold it all and a relatively slow metabolism.
But what about Colobus monkey -- almost exclusively a leaf-eater -- and not even too choosey about mature leaves... how does it manage?! We'll talk about GUTS next!
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