Biology: Unit F212: Molecules, Biodiversity, Food and Health
Diet and Food Production
Humans depend on plants for food; we are heterotrophs – reliant upon organic substances
in our diet that have been made by plants. Plants are autotrophs – they use inorganic
substances to build organic substances such as carbohydrates, lipids and proteins.
A balanced diet contains all of the nutrients required for health in appropriate
proportions. There are 7 components of a balanced diet;
1. Carbohydrates – provide energy which is released by respiration in cells
2. Proteins – formation of new cells, growth and repair of
tissues, form many important substances such as
haemoglobin and enzymes
3. Lipids – making cell membranes, steroid hormones,
waterproofing, absorption of fat soluble vitamins,
provide energy when broken down in respiration
4. Vitamins – required for many chemical processes in
the body; Vitamin C is needed for collagen production
and vitamin D is necessary for healthy bones and
teeth.
5. Minerals – inorganic elements essential for normal
functioning of the body; iron for the formation of haemoglobin and calcium
for bone formation.
6. Water – Transporting substances around the body – 60% of the body is water
7. Fibre – indigestible component of food essential for healthy functioning of
the digestive system.
Malnutrition means the effect of an unbalanced diet. Obesity is the most common
form of malnutrition – when an individual has a BMI of 30 or over, or is 20% or more
heavier than the recommended weight for their height. Obesity is a result of excess
energy being stored as adipose tissue beneath the skin and around the organs.
There is a link between coronary heart disease and diet. CHD is the single most
common cause of death in the UK – 30% of men and 22& of women. CHD is a
disorder of the coronary arteries which supply the heart muscle itself with
oxygenated blood. If the blood is unable to reach the heart muscle, it will be
deprived of oxygen, and the cardiac muscle cells will die quickly.
Atherosclerosis is the cause of coronary heart disease. If there is
damage to the endothelium of the artery, LDLs are absorbed
into the artery walls. LDLs enter the tunica intima and undergo
oxidation. This causes inflammation, and so monocyte white
blood cells migrate to the site. Now macrophages, they engulf
the oxidised LDL and become foam cells. When the foam cells
die they release the lipid core. A fibrous collagen-elastin cap
forms over the lipid core and arterial remodelling causes the
elastic membrane to expand. As LDL levels increase
further, the lumen begins to narrow, as the artery
can expand no further to compensate for the
atheromous plaque. The plaque breaks through the
endothelium lining, ruptures, and the lipid core
comes into contact with blood, causing formation of
thrombin clot.
Coronary Heart disease can taken four forms:
1. Angina – If the atheromous plaque reduces the lumen of a coronary artery by
50% or more, the flow of blood through the artery cannot keep up with the
oxygen demand of the heart during exercise. This causes a patient to
experience pain when exercising, often across the chest left shoulder and
arm.
2. Coronary Thrombosis – when the lipid core of an atheromous plaque
ruptures and comes into contact with the blood, a thrombin clot is formed in
the artery. This can narrow the artery.
3. Myocardial Infarction – if a thrombin clot breaks away and gets stuck in a
smaller blood vessel, the part of the heart that is being supplied with oxygen
from that vessel may die.
4. Cardiac arrest – severe myocardial infarction- if a large amount of cardiac
muscle dies, the heart may stop beating, and the person goes into ‘cardiac
arrest’. No pulse can be felt.
Cholesterol – HDLs and LDLs
Cholesterol is carried in the blood plasma in the form
of lipoproteins. The two types of lipoprotein are high
density and low density.
Low density lipoproteins contain more lipid than
protein. They tend to carry cholesterol from the liver
to other parts of the body. If there is a damaged
artery wall, LDLs will deposit cholesterol, increasing
the risk of coronary heart disease.
High density lipoproteins usually pick up cholesterol from damaged parts of the
body and transport it to the liver, protecting against coronary heart disease.
A diet that is high in saturated fats can increase the concentration of low density
lipoproteins. Saturated fats are from animal derived foods, so in order to reduce the
levels of LDLs, a patient could switch to a diet high in fish. Statins can be used to
control the levels of LDL in the blood. Statins inhibit an enzyme in the liver which
catalyses a reaction involved in the synthesis of cholesterol.
Salt and Hypertension
Hypertension is persistently high blood pressure. Hypertension increases the risk of
CHD. It causes the artery walls to thicken and stiffen, increasing the risk of damage
to the epithelium - often followed by the formation of an atheromous plaque. The
workload of the heart is increased. A diet high in salt will draw water into the blood
by osmosis. The blood volume increases, so the pressure increases.
Selective breeding is where humans select the individual organisms that are allowed
to breed according to chosen characteristics. Farmers may select the following
characteristics: high crop yield, disease resistance, size of fruit, pest resistance, ease
of picking or flavour.
Examples of Selective Breeding…
1. High Yield Dwarf Plants – A low yielding dwarf plant is bred with a high
yielding tall plant, to get a high yielding small plant. After each generation,
unwanted plants are rejected, and after 10 generations, plants with the
desired characteristics are ready.
2. Breeding Leaf rust resistant wheat – wheat sometimes has a gene which
combats leaf rust disease, a fungal disease which is a particular problem in
warm, wet climates. Selective breeding aims to breed wheat which possesses
a high number of genes that give resistance to leaf rust.
3. Pest resistant wheat – pests such as aphids feed by taking phloem sap from
the plant. This reduces the growth and yield of the plant. Pesticides can be
used, but are expensive; biological control is an alternative, using ladybirds to
eat aphids. The best solution is to use selective breeding to develop wheat
plants that are resistant to pests and the viruses they carry.
4. Breeding Cattle for high productivity – cattle being bred for meat will be
chosen for having large muscles. Cattle bred for milk will be chosen for having
high milk yields.
There is no longer need to take the bulls to the cows when breeding
cattle. Semen from the chosen bull is collected and frozen, taken to
the cow, and then the cow will be artificially inseminated. This
means that semen can be kept for long periods of time and
transported over long distances.
Increasing food production: Intensive Farming
As human population increases, the pressure for food increases. In order to meet the
greater demand, farming becomes more intensive – larger inputs to get larger
outputs.
Fertilisers are added to soil when it is
deficient in organic ions that a crop
needs to grow. The most common
fertiliser is ammonium nitrate, which
contains NH4+ and NO3- ions.
Pesticides kill pests – including insecticides and fungicides. DDT was
an insecticide which accumulated in an organism’s body. Animals at
the top of the food chain could accumulate very large amounts of
DDT in their bodies and this caused population crashes in several
species of birds of prey in the UK. DDT is also a broad spectrum
insecticide – it kills all insects, not just pests. Pesticide traces may
also linger on food that we eat.
Antibiotics are used to kill bacteria without harming the organism which is infected. When animals are kept in
intensive conditions, the chances of them becoming infected with pathogenic bacteria increases. Animals are
continually given antibiotics to reduce the chance of disease occurring. However, the more the antibiotics are
used, the more likely it is that the bacteria will evolve and develop resistance to the antibiotics.
Preserving Foods
Drying, salting and coating in
sugar – microorganisms are
dehydrated as water leaves
them by osmosis
Irradiation - ionising radiation
kills the microorganism by
disrupting their DNA structure
beyond repair.
Pasteurisation – heat to 72
degrees for 15 seconds, cool
rapidly to 4 degrees, killing
microorganisms
Pickling – acidic pH kills
microorganism by
denaturing enzymes and
proteins.
Smoking –food develops a
hardened dry outer surface
and the smoke contains
antibacterial chemicals.
Cooking – heat
denatures all
enzymes and
proteins in the
microorganism.
Cooling and Freezing–
reducing the
temperature slows
enzyme activity so that
their metabolism,
growth and
reproduction is slow.
Using microorganisms in food production
Microorganisms have been used for many years in the manufacture of food: yoghurt
is milk that has been affected by the lactobacillus bacteria, which turns the lactose
sugar into lactic acid causing milk proteins to thicken. Bread is made to rise by yeast,
which respires anaerobically to release carbon dioxide
Recently, single cell proteins (SCPs) have been developed which are used directly as
food. Quorn is a single cell protein which is made from fungus. The mycoprotein is
produced in a fermenter. A culture medium containing glucose provides the
respiratory substrate and the carbon required to make new carbohydrate, fat and
proteins for growth. Ammonium nitrate is also added so that nucleic acids can be
produced. Quorn is a good alternative for vegetarians and provides a healthy option
for meat eaters as it is low in cholesterol and saturated fats.
Advantages of using Single Cell Proteins
o Production is much faster than animal or plant growth
o Production can be changed to meet demand
o No animal welfare issues
o Provides protein for vegetarians
o No animal fat or cholesterol
o SCP production can be combined with removal of waste products
Disadvantages of using Single Cell Proteins
o People may not want to eat fungal proteins
o Does not contain all essential amino acids
o Lacks taste and texture
o Protein must be purified to ensure it is not contaminated
o The conditions used to grow the protein are ideal for pathogens to grow – the
proteins could become infected by the wrong organism.