Ch 49: Nutrition, Digestion, and Absorption
49.1Food Provides Energy as Well as Materials for Biosynthesis
Animals are heterotrophs – they derive nutrition by eating other organisms
Autotrophs synthesize their own components using solar / chemical energy
Heterotrophs depend on this synthesis and have evolved a variety of
adaptations to take advantage of it
energy – the capacity to do work
o comes in different forms
measures of heat energy:
o calorie – amount of heat needed to raise 1 gram of water 1 degree
Celsius
o kilocalorie (kcal) = 1000 calories
a Calorie (Cal) in food is the same as a kilocalorie
an animal’s energy needs must be met by ingestion, digestion, and
assimilation of food
basal energy expenditure of a human is 1300-1490 Cal/day for an adult
female and 1600-1800 Cal/day for an adult male
physical activity adds to this basal metabolic rate (BMR)
foods that provide energy are: fats, carbohydrates, and proteins
(macronutrients)
o caloric value of food and expenditure of energy for any activity can be
measured
o energy budgets – compare calories consumed and calories expended
and allow a cost-benefit analysis of feeding behavior
animals must store food between meals
o carbohydrates are stored in liver and muscle cells as glycogen (enough
for about 1 day’s energy needs)
o fat stores more energy per gram and with little water (more compact)
o proteins are not used for storage but can be metabolized as a last
resort
if an animal takes too little food, metabolism of the body’s own molecules
begins
o glycogen and fat are broken down
o proteins are metabolized, starting with blood plasma
if an animal takes in more food than needed, excess is stored as increased
body mass
o glycogen reserves are built up
o extra carbohydrates, fats, and proteins are converted to body fat
, animals require organic molecules to supply carbon skeletons, building blocks
for larger organic molecules
o acetyl group CH3CO is used to build more complex molecules and must
be obtained by food
animals can synthesize some of their own amino acids using carbon
skeletons, but essential amino acids must be obtained from food
o adult humans must get 8 essential amino acids from their food
o a complementary diet of plant foods can supply all 8 essential amino
acids for vegetarians
proteins must be broken down to amino acids before being used by the body
o proteins are large, not readily absorbed by the gut
o protein structure and function vary by species
o immune system would attack protein molecules entering directly from
the gut
humans also require essential fatty acids from their diet
o linoleic acid – helps synthesize other unsaturated fatty acids, including
signaling molecules and membrane phospholipids
mineral elements are also required
o macronutrients – elements required in large amounts, such as calcium
o micronutrients – elements required in small amounts, such as iron
o insufficient iron leads to anemia – most common mineral deficiency
globally today
vitamins – carbon compounds required for growth and metabolism that
cannot be synthesized
o most function as coenzymes or parts of coenzymes
o required vitamins vary with species; humans require 13 vitamins
o water soluble vitamins – eliminated in urine if there is an excess
(Vitamin C)
49.1Food Provides Energy as Well as Materials for Biosynthesis
Animals are heterotrophs – they derive nutrition by eating other organisms
Autotrophs synthesize their own components using solar / chemical energy
Heterotrophs depend on this synthesis and have evolved a variety of
adaptations to take advantage of it
energy – the capacity to do work
o comes in different forms
measures of heat energy:
o calorie – amount of heat needed to raise 1 gram of water 1 degree
Celsius
o kilocalorie (kcal) = 1000 calories
a Calorie (Cal) in food is the same as a kilocalorie
an animal’s energy needs must be met by ingestion, digestion, and
assimilation of food
basal energy expenditure of a human is 1300-1490 Cal/day for an adult
female and 1600-1800 Cal/day for an adult male
physical activity adds to this basal metabolic rate (BMR)
foods that provide energy are: fats, carbohydrates, and proteins
(macronutrients)
o caloric value of food and expenditure of energy for any activity can be
measured
o energy budgets – compare calories consumed and calories expended
and allow a cost-benefit analysis of feeding behavior
animals must store food between meals
o carbohydrates are stored in liver and muscle cells as glycogen (enough
for about 1 day’s energy needs)
o fat stores more energy per gram and with little water (more compact)
o proteins are not used for storage but can be metabolized as a last
resort
if an animal takes too little food, metabolism of the body’s own molecules
begins
o glycogen and fat are broken down
o proteins are metabolized, starting with blood plasma
if an animal takes in more food than needed, excess is stored as increased
body mass
o glycogen reserves are built up
o extra carbohydrates, fats, and proteins are converted to body fat
, animals require organic molecules to supply carbon skeletons, building blocks
for larger organic molecules
o acetyl group CH3CO is used to build more complex molecules and must
be obtained by food
animals can synthesize some of their own amino acids using carbon
skeletons, but essential amino acids must be obtained from food
o adult humans must get 8 essential amino acids from their food
o a complementary diet of plant foods can supply all 8 essential amino
acids for vegetarians
proteins must be broken down to amino acids before being used by the body
o proteins are large, not readily absorbed by the gut
o protein structure and function vary by species
o immune system would attack protein molecules entering directly from
the gut
humans also require essential fatty acids from their diet
o linoleic acid – helps synthesize other unsaturated fatty acids, including
signaling molecules and membrane phospholipids
mineral elements are also required
o macronutrients – elements required in large amounts, such as calcium
o micronutrients – elements required in small amounts, such as iron
o insufficient iron leads to anemia – most common mineral deficiency
globally today
vitamins – carbon compounds required for growth and metabolism that
cannot be synthesized
o most function as coenzymes or parts of coenzymes
o required vitamins vary with species; humans require 13 vitamins
o water soluble vitamins – eliminated in urine if there is an excess
(Vitamin C)
