10.1 The function of Digestion
pg. 402
Macromolecules and Living Systems
The body is made up of more than 60 % water. The water is found
in the cells cytoplasm, the interstitial fluid and the blood (5 L).
Dissolved within this fluid, there are many different ions and
molecules require by the body to function properly. (Phosphorous,
sodium, calcium, chlorine and hydrogen ions, and molecules of
glucose)
Figure 10.1 Distribution of body fluids in the adult human. These fluids are mostly
eater, and they move freely in and out of the cell in both directions.
Molecule – is two or more joined-together atoms of the same or
different elements.
Inorganic molecules – are molecules made of element other than a
combination of atoms of carbon bonded to hydrogen. (H2O, CO2,
and NaCl)
Organic molecules – are molecules made up of long chains of
carbon and hydrogen atoms. Other elements may also be attached.
(C6H12O6, glucose)
Macromolecules – are very large molecules made up of smaller
molecules that are linked together.
Metabolism – is the sum total of all the chemical reactions that
occur in an organism. (Anabolic and Catabolic)
Essential Nutrients – are nutrients that cannot be made by the
body, and must therefore be obtained from food.
Macromolecules are very important nutrients; raw materials that
our bodies need to provide energy for regular cellular activities,
build and repair cells and tissues. All living organisms require
nutrients to survive.
There are four specific macromolecules, essential nutrients, that
our bodies require are; carbohydrates, lipids, proteins and nucleic
acids. When your body and cells uses these nutrients during
chemical reactions, it is called cellular metabolism.
Carbohydrates
The primary role of carbohydrates is to supply energy to the cells.
In animals; carbohydrates are a stored energy source, in the form
of glycogen, and a structural form called chitin; (shells and
exoskeleton). In plants, carbohydrates are a stored energy source in
the form called starch, and a structural form called cellulose; (cell
wall of plant cells).
Polysaccharides are large molecules made up of many linked
monosaccharide molecules.
(Starch, cellulose, glycogen and chitin are examples of
polysaccharides.)
Disaccharides are sugar molecules made up of two
monosaccharide molecules.
(Sucrose, fructose and lactose are examples of disaccharides)
Monosaccharides are simple sugars, with three to seven carbon
atoms.
(Glucose, galactose and maltose are monosaccharides)
Lipids
Lipids are an important group of macromolecules. There are three
types of lipids found in living organisms; triglycerides,
phospholipids and waxes, fats and oils.
The basic components of a lipid are a glycerol group and a number
of fatty acid chains. These components are made up carbon and
hydrogen atoms and contain 2.25 times more energy then
carbohydrates per gram.
Triglycerides function as a secondary cellular energy source when
the carbohydrate stores are depleted.
Phospholipids form the cell membranes of all cells, separating the
internal and external environments.
Proteins
Proteins are made up of many smaller sub-units called amino acids.
Proteins act as a tertiary energy source for cells when the other
sources are depleted and are responsible for building, repairing and
maintaining cells. Proteins are also enzymes, hormones, and
antibodies used by our bodies.
Proteins are thousands of amino acids in length. The amino acids
were bonded together forming peptide bonds creating a
polypeptide chain.
Amino acid – is a building block of protein. There are 20 different
types of amino acids.
Peptide bond – is a bond that holds together each amino acid in a
protein.
Polypeptide - is a linear chain of several amino acids linked by
peptide bonds.
Nucleic Acids
Nucleic acids make up the genetic code in cells, which are
responsible for the growth and function of the cell. They are found
in the form of deoxyribonucleic acid (DNA) and ribonucleic acid
(RNA).
These nucleic acids are made up of sub-units known as nucleotides.
There are four nucleotides found in DNA; adenine, cytosine,
guanine and thymine. In RNA there are also four nucleotides;
adenine, cytosine, guanine and uracil.
Breaking down Macromolecules: Enzymes
Enzymes are biological catalysts, which are responsible for
lowering the activation energy use to break chemical bonds of
macromolecules, causing an increase in the rate of the chemical
reaction.
Enzymes are highly specialized, and only participate in specific
reactions.
Before the body can use a macromolecule, such as; carbohydrate,
lipid, and protein, these molecules need to be broken down into
smaller sub-units so they can be absorbed across a cell membrane
into the cell. The type of reaction that occurs when bonds are
broken is called a hydrolysis reaction and water is used.
The bonds of the macromolecules are broken and replaced by parts
water molecules. These reactions are supported by enzymes, but
these enzymes are not consumed during the reaction.
Characteristics of enzymes
- They will not make anything happen that would not happen
on its own.
- Enzymes are not altered permanently during the chemical
reaction.
- The same enzyme will work forward and backward in a
chemical reaction.
- Each enzyme is highly specific to the substrate it will interact
with.
Digestive enzymes are secreted in the digestive tract to breakdown
macromolecules during chemical digestion.
Table 10.2 Types of Digestive Enzymes
Figure 10.2 Large food molecules are split into smaller molecules by hydrolysis.
Specific enzymes speed up these reactions. After hydrolysis, the smaller molecules can
pass through cell membranes.
The Vital Roles of Minerals and Vitamins
Mineral and vitamins are vital inorganic and organic substances
that enable chemical reactions to occur, and aid in tissue
development, growth, and immunity.
Table 10.3 Functions and Possible sources of Selected Vitamins and Minerals
The Many Roles of Water in the Body
Water makes up over 60% of the body mass, and is required for the
proper function of cells and organs.
- Transports dissolved nutrients (diffusion/osmosis) from the
small intestine.
- Lubricates tissues and joints.
- Forms blood and mucus.
- Controls body temperature (370C).
- Flushes toxins from cells
- Eliminates metabolic wastes.
The water is necessary to maintain the body’s fluid balance and
blood pressure. The amount of fluid lost must equal the amount of
fluid intake, the average adult requires 2.5 L of water per day
during normal activity.
How Animals Obtain their Food
Energy enters our plant in the form of sunlight energy. Autotrophs
(green plants) use sunlight in a chemical process called
photosynthesis. Plants convert sunlight energy into a chemical
potential energy called sugar, glucose, or starch.
Animals are heterotrophs; they need to consume food to obtain
their energy. These organisms are herbivores, carnivores and
omnivores. There are four feeding mechanisms used by animals:
-
Filter feeders (sponges)
Substrate feeders (caterpillars)
Fluid feeders (butterflies)
Bulk feeders (humans)
The Four Stages of Food Processing
1. Ingestion – the taking in or eating of food.
2. Digestion – the breakdown of food by mechanical and
chemical processes into molecules small enough for cells of
the body to absorb.
3. Absorption – the transport of the products of digestion from
the digestive system into the circulatory system, which
distributes them to the rest of the body cells.
4. Elimination – the removal of undigested solid waste matter
from the body.
Digestion and the Alimentary Canal
Alimentary Canal – is the tube through which food is processed
beginning at the mouth and ending at the anus; also known as the
digestive tract.
Mechanical digestion – is the physical breakdown of large pieces
of food into smaller pieces in the mouth by the action of teeth,
beak, and other similar structures, and by contractions and
churning motions in the stomach.
Chemical digestion - is the chemical breakdown of nutrient
molecules into smaller molecules by enzyme action.
Figure 10.3 the earthworm has a simple digestive tract. Decaying plant and animal
matter in the soil provides the earthworm with nutrients. Undigested materials pass
through the tract and are eliminated through the anus as worm castings.
The Length of the Digestive Tract
All digestive tracts function in a similar manner for all animals, but
the length of the digestive tract varies according to the feeding
habits of the animals.
Herbivores and omnivores usually have a longer digestive tract
relative to their body size, than carnivores. Plant tissue (cellulose)
is more difficult to digest than animal tissue. The longer the
digestive tract of herbivores and omnivores allows more time for
digestion.
Figure 10.5 the digestive tract of a small herbivore, such as a rabbit, is longer than that
of a small carnivore, such as a fox. In both digestive tracts you can see the cecum, a
pouch at the beginning of the large intestine that receives waste material from the
small intestine.
Learning Check, questions 1 – 6, pg. 406
Section 10.1 Review, questions 1 – 16, pg. 410