1. Energy Value of Foods

2. Main Sources of Energy for Cells
Carbohydrates and lipids (fats)
Proteins (in cases of illness or injury)
Cellular respiration is the process which releases chemical energy from foods
Glucose + Oxygen gas energy + carbon dioxide + water
Carbohydrates:
The most important source of energy.
Makes up the largest part of our diets.
a.   Source: Plants
b.   Composition:
Carbohydrates are made up of either a single sugar molecule or a chain of sugar molecules.
Monosaccharide: One sugar
Examples: Glucose (C6H12O6), Galactose, Fructose
Disaccharide: Two sugars
Example: Sucrose = Glucose + Fructose
Polysaccharides: Many sugars
Examples:
Starch: stores energy in plants
Cellulose –component of the cell wall in plants, cannot be digested by humans = fiber.
Lipids
Supply energy to the body.
Difficult for the body to break down so you stay full longer.
Storage compound: one gram of lipid contains about twice the amount of energy as one gram of carbohydrate or protein.
Three groups:
Fats, oils, waxes (waterproof coating of plant leaves)
Phospholipids (cell membrane)
Steroids (make hormones)
Most common type of lipid = one glycerol and three fatty acids.
Lipids are insoluble in water.
Proteins
Proteins are used in cells to build cell structures and are used in chemical activities.
Enzymes are proteins that aid in the reactions that occur during processes such as digestion and respiration.
Proteins are composed of 20 amino acids arranged in different orders and of different lengths.
There are 8 amino acids that are not made by the body. These essential amino acids must be obtained from the food we eat.

3. Energetic Value of Foods
Energy Value
The amount of energy a food can provide to an organism
Expressed in kilojoules (kJ)
The calorie (Cal) is often used on packaging
1 Cal= kJ
Energetic Value of Foods
Vitamins, minerals, water do not give the cell any energy
Carbohydrates
Lipids (fats)
Proteins
17kJ/g
37kJ/g

4. Energy Demands Basal metabolism Physical activities
Digestion and absorption of what people eat
(10% of daily energy or 1050 kJ)
Teenagers years old need on average kJ of energy per day
Basal metabolic rate- amount of energy required to perform vital functions such as heartbeat, respiration, basic cellular activities

5. Basal Metabolism
Amount of energy required to maintain vital functions- heart beat, respiration, stable body temperature, cellular activities
In general, more elevated in males than females (7000 kJ vs kJ)

6. Nutritional Requirements
To meet energy needs, a certain proportion of carbohydrates, lipids, and proteins is needed (vary with age, sex, size, physical activity)
Energy values in …
Carbohydrates
Lipids
Proteins
% of Kilojoules (kJ)
55% of kJ ingested
30% of kJ ingested
15% of kJ ingested
Grams (g)
340g
85 g
93 g
Table of values represents requirements for adolescents

7. Input and Output of Energy Effects on Mass
Input=Output mass maintained
Input<output loss of mass
Input>output gain of mass
The quality of what we eat is important as well
Changes due to…
Change in amount of physical activity
Change in amount of food consumed

8. Transformation of Food
Mechanical and Chemical

9. Mechanical transformation
large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes
Mechanical Digestion - Food is crushed and liquefied by the teeth, tongue, and peristaltic contractions (waves of involuntary muscle contraction) of the stomach and small intestine. This creates a greater surface area for the digestive enzymes to work upon.

10. Chemical Transformation
uses water and digestive enzymes to break down molecules
smaller molecules can be absorbed and utilized by the cells
The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Does not completely break down all molecules
Chemical Digestion - Many glandular structures, dispersed throughout the body, are involved in breaking food into simple molecules that can be absorbed. In the mouth, the salivary glands produce saliva, which both lubricates food and begins the process of starch digestion. Saliva contains salivary amylase (ptyalin), an enzyme that digests starch to maltose (a disaccharide). As food leaves the mouth, the esophagus conducts it to the stomach via the cardiac sphincter by means of peristaltic waves of smooth muscle contraction.

11. Organs of digestive system Mechanical transformation Glands
Secretion from glands
Foods transformed
Results of transformation
1.Mouth
Chewing
Salivary
Saliva
carbohydrates
Carbohydrates partially broken down
2.Pharynx
Swallowing -
3.Esophagus
peristalsis
4.Stomach
Churning
Peristalsis
Gastric
Gastric juices
proteins
Proteins partially digested
5.small intestine
Emulsion of lipids by bile(secreted by the liver)
churning
pancreas
Intestinal
Pancreatic juices
Intestinal juices
Carbohydrates partially digested
Lipids(fats)
Glucose
Amino acids
Fatty acids
Glycerol
6.large intestine
During mastication, salivary glands secrete saliva to soften the food into a bolus (semi-solid lump)
Once food gets partially broken down in the stomach, it becomes a thin watery liquid called chyme.

12. Absorption of Nutrients
Site of Absorption
Nutrients Absorbed
Small intestine
Glucose
Amino acids
Fatty acids
Glycerol
Water
Vitamins
minerals
Large intestine
Glucose; Amino acids; Fatty acids;Glycerol- biggest part of absorption
Water;vitamins; minerals- start of absorption
In large intestine- water; vitamins;minerals-biggest part of absorption