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Unit 8 Applied Science Coursework
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Applied Science Unit 8 Coursework. Distinction* work.
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Task 2: Unit 8 Learning Aim CDigestive System Essay
Task: Write a detailed essay on the passage of food through the digestive system including the role
of enzymes.
Task 3
The ingestion, breakdown, absorption and elimination of food, nutrients and energy required for the
human body to work is the responsibility of the human digestive system. It performs these functions
by allowing the entrance into the body of nutrients and energy in the form of food, and then
extracting the required materials from the food. Then absorbing the materials into the body, as well
as sending them to the location they are required, and finally removing the remaining materials from
the body. The system consists of the main (primary) organs; the mouth, the oesophagus, the
stomach, the small intestine, the large intestine, the rectum, and the anus, as well as the secondary
organs; the liver, the salivary glands, the gallbladder, and the pancreas.
Proteins, lipids (fats) and starch (carbohydrates) are the three most essential nutrients. Starch is the
body’s main source of energy, as we get energy from glucose. Proteins are biological polymers
composed of amino acids. Amino acids, linked together by peptide bonds, form a polypeptide chain.
One or more polypeptide chains twisted into a 3-D shape form a protein. Our body uses protein to
build and repair tissues. We also use protein to make enzymes, hormones, and other body
chemicals. Lipids are essential for all life. They play many crucial roles in maintaining the health of an
organism. Typically, the most important function lipids perform is as the building blocks of cellular
membranes. Other functions include energy storage, insulation, cellular communication, and
protection. Starch is a long chain of glucose molecules bound together by glycosidic bonds to form
an even larger molecule. This is called a polysaccharide. After the consumption of starch, the
polysaccharide (starch) is broken down into monosaccharides (single glucose molecules) for
digestion. Furthermore, our body digests starch to make glucose, which is vital energy source for
every cell and its function.
The mouth is responsible for the immediate intake of food, and is partially responsible for digestion,
through the process of physical/mechanical digestion [mastication], which is the chewing, crushing,
and grinding of food by the teeth. Saliva [consisting of enzymes, water, and mucus] is produced to
help moisten the mouth and food to aid with mastication. This causes the food to be physically
broken down and softened with the help of amylase which is an enzyme secreted by the salivary
glands to help break down starch (carbohydrates). The process consists of a substrate, which in this
case is starch (molecule). A substrate binds to an active site in an action called the induced fit model
where the active site moulds to accommodate the shape of the substrate. The binding of the
substrate and the enzyme makes an enzyme-substrate (E-S) complex where they both become
complementary to each other. Once these stages have been finalised, the enzyme eventually breaks
the substrate into its simplest form (into a smaller molecular unit), allowing it to then be easily
absorbed and utilised by the body. Simultaneous to the induced fit model, the lock and key model is
a simplified model of the induced fit model that explains how enzymes fit accordingly to substrates
shape and vice versa like a lock and key
fit. Enzymes are biological catalysts that
speed up the rate of reaction in the
mechanisms of the body. Food must be
broken down into smaller molecules as
smaller molecules are soluble, and
bigger molecules are insoluble. Once
the food is sufficiently broken down, it is
swallowed and brought to the next organ in the digestive system, the oesophagus.
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, Task 2: Unit 8 Learning Aim C
The role of the oesophagus is simply to allow the partially broken-down food to travel from the
mouth to the stomach. Its role in digestion is minimal, but it is still considered one of the major
organs in the system. The blocker that prevents gastric acid from exiting the stomach and damaging
the mouth or the oesophagus itself is at the joining point of the oesophagus and the stomach, called
the cardiac sphincter. The gastric acid philtres into the oesophagus when the cardiac sphincter fails
to function, causing damage to the inside of the oesophagus, as well as the painful feeling known as
heartburn. When food is being swallowed, the oesophagus goes through a serious of contractions
called peristalsis in order to push food down into the stomach.
The stomach is a muscular, hollow organ in the human digestive system, and is one of the primary
sites of digestion. It is filled with hydrochloric acid (gastric acid), a powerful acid that breaks down
food with relative ease, digesting most foods in about 4 or 5 hours. The stomach has 3 main
functions in which it carries out. First of all, the stomach’s muscular walls contract to further digest,
churn, and break down food into smaller pieces than they initially were when entered. Pepsin is the
enzyme (protein) that is produced in the stomach, which helps to break down proteins [into
polypeptides], by again going through the induced fit enzyme process mentioned. The stomach also
produces hydrochloric acid which primarily kills bacteria and creates optimum conditions for pepsin,
as pepsin works best at a low pH. Other common enzymes that reside in the stomach include:
lactase which breaks down lactose, which is a sugar found in dairy products and has a structure
consisting of a chain of glucose and galactose monosaccharides. Lipase which breaks down lipids into
fatty acids and glycerol. Chymotrypsin and trypsin which further break down protein molecules into
individual amino acids. Hydrolysis is used to break down complex molecules into simpler ones by
adding a molecule of water into a catabolic reaction.
Another round of digestion occurs in the small intestine, even more than in the stomach. Absorption
also begins to occur at this stage in the digestive system. Food/nutrients are absorbed in the small
intestine, the muscles of the small intestine blend food from the pancreas, liver, and intestine with
digestive juices and drive the mixture forward for more digestion. The walls of the small intestine,
through the villi, absorb water and the digested nutrients into the bloodstream. The pancreas
produces most enzymes in a solution called ‘pancreatic juice’, which is pushed into the small
intestine. The main enzymes in the pancreatic juice include: trypsin and chymotrypsin (proteases)
[mentioned previously] which help to digest proteins; amylase for the digestion of carbohydrates
and starch; and lipase to break down fats. Bile is a fluid produced/released in the liver and stored in
the gallbladder which is then released into the small intestine. Its purpose is to break down larger
globules of fat into smaller globules, in other words, bile breaks down fats into fatty acids.
Emulsification is the process in which large lipid globules are broken down into several small
lipid globules by bile. Emulsification is important for the digestion of lipids because lipases can
only efficiently act on the lipids when they are broken down into small molecules. After this stage,
bile’s second most important function is to neutralise the acidic pH [in the small intestine] when
pancreatic juices are pushed into the small intestines, this is crucial as enzymes within the pancreatic
juices work best in alkaline conditions, so in order for the enzymes to work and function efficiently,
bile has to neutralise the acid from the stomach into a suitable alkaline condition for the enzymes.
The large intestines primary purpose is to remove most of the water and salts from the now
indigestible mass, and move it to the rectum and anus, where it will be removed and excreted out of
the body. The colon is where the water is taken from the digested food matter and transported to its
final destination, the rectum. The rectum is where the waste is temporarily stored before it is ready
to be excreted from the body, which takes place in the anus. In simplified form, undigested food
enters the large intestine from the small intestine. It then reabsorbs water that is used in digestion
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