How Nutrients Get in, and Wastes Out.

By Faisal Premji
10 Assignment -- Part B

In a human being, nutrients are necessary for survival. But how are these
nutrients obtained? This report will go into depth on how the food we eat gets
into our cells, and how the waste products that we produce get out of the body.
Also, the unicellular organism Paramecium will be compared with a human being,
in terms of all of the above factors.

Dietary Nutrients

The chief nutrients in a diet are classified chemically in four groups:
carbohydrates, proteins, vitamins (Which do not require digestion) and fats.

Carbohydrates in the diet occour mainly in the form of starches. These are
converted by the digestive process to glucose, one of the main nutrients needed
for cellular respiration to occour. Starch is a large molecule, a polymer of
glucose. Dextrin and maltose are intermediate products in the digestion of
starch. Some foods contain carbohydrates in the form of sugars. These are the
simple sugars, such as sucrose (cane sugar) or lactose (milk sugar), that must
be processed into smaller units. Occasionally, the simplest form of sugar, a
monosaccharide such as glucose, is present in food. These monosaccharides do
not require digestion.

Proteins are polymers composed of one or more amino acids. When they are
digested, they produce free amino acids and ammonia.

Vitamins are a vital part of our food that are absorbed through the small
intestine. There are two different types of vitamins, water-soluble (All the B
vitamins, and vitamin C) and fat-soluble (vitamins A, D and K).

Neutral fats, or triglycerides, are the principal form of dietary fat. They are
simple compounds, and within digestion are broken down into glycerol and fatty
acids, their component parts.


Intake of food in the Paramecium is controlled by the needs of the cell. When
food is sensed, the organism guides itself towards the food, and guides it into
the oral groove, then enclosing it in a vacuole. Enzymes are then secreted to
digest the food, which is then absorbed into the cytoplasm and made available to
the various organelles. But, a Paramecium has to be able to move to its food
source, while a human cell has his food brought to it through the circulatory
system. In man, a much more complicated system exists than that of a
unicellular organism, for the size of the animal and the fact that all of the
cells within the animal must be able to absorb food and get rid of wastes, just
like the Paramecium does.

Digestion in the Mouth

Upon entering the mouth, the food is mixed by mastication with saliva, which
starts the digestive process by making contact with the food particles with the
salivary enzyme ptyalin, dissolving some of the more soluble matter within the
food. It also coats the food mass with mucin, to aid in swallowing. The
chemical phase of digestion in the mouth begins when the salivary amylase,
ptyalin, attacks the cooked starch or dextrin, converting some of this starch
into dextrin, and some of the dextrin into maltose. The salivary glands can be
activated when food is thought of, while the actual presence of food will
produce a continuous flow. Since food remains in the mouth for a very short
period, very little of the digestive process actually occours in the mouth.

Following digestion in the mouth, the semisolid food mass is passed by
peristaltic movements of the esophagus, a long muscular tube that connects the
mouth to the stomach. The food then reaches the esophageal sphincter, a ring of
muscle at the upper end of the stomach. This sphincter then opens to let the
food into the stomach.

Digestion in the Stomach

Here, salivary digestion continues until the acid of the gastric juice
penetrates the food mass, and destroys the salivary amylase. The food mass is
then saturated with gastric juice, and the gastric phase of digestion is

The gastric phase of digestion is chiefly proteolytic, or protein-splitting.
Within this process, the gastric glands secrete the enzymes pepsin and rennin.
These enzymes, aided by gastric acid, converts a fairly large amount of the
proteins to smaller forms, such as metaproteins, proteoses and peptones. There
also may be a small amount of fat digestion in the stomach, since a small amount
of lipase is present in gastric juice. This enzyme causes hydrolysis of the
triglycerides into glycerol and fatty acids.

The digestive action of these enzymes, combined with the action of the gastric
juice results in the solution of most of the food material. In the final stages
of gastric digestion, the fluid mass, propelled by peristaltic movements, passes
into the small intestine through