Definition. The host (also called the susceptible host) is the human body: someone who is at the risk of infection. Infections do not necessarily occur when pathogens enter the body of the person whose immune system is functioning normally.Whether or not a pathogen will result in infection depends upon several factors related to the host (the person exposed), the pathogen itself, and the environment.nfections do not necessarily occur when pathogens enter the body of the person whose immune system is functioning normally. Whether or not a pathogen will result in infection depends upon several factors related to the host (the person exposed), the pathogen itself, and the environment.
You can find out how many calories are in a food by looking at the nutrition facts label. The label also will describe the components of the food â how many grams of carbohydrate, protein, and fat it contains. Here's how many calories are in 1 gram of each: 1  carbohydrate â 4 calories.  protein â 4 calories.
The number of calories in a food is a measure of how much potential energy that food possesses. A gram of carbohydrates has 4 calories, a gram of protein has 4 calories and a gram of fat has 9 calories.Foods are a compilation of these three building blocks. So if you know how many carbohydrates, fats and proteins are in any given food, you know how many calories, or how much energy, that food contains.or example, a gallon (about 4 liters) of gasoline contains about 31,000,000 calories. You could drive a car 22 miles (35 km) on the calories in 217 Big Macs. Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit).