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2.2.1 Diet and Food Production

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Define the term balanced diet Explain how consumption of an unbalanced diet can lead to malnutrition, with

reference to obesity

Discuss the possible links between diet and coronary heart disease (CHD)Discuss the possible effects of a high blood cholesterol level on the heart and

circulatory system, with reference to high-density lipoproteins (HDL) and low-density lipoprotein (LDL)

Explain that humans depend on plants for food as they are the basis of all food chains.

(No details of food chains are required)Outline how selective breeding is used to produce crop plants with high yields,

disease resistance and pest resistance

Outline how selective breeding is used to produce domestic animals with high productivity

Describe how the use of fertilisers and pesticides with plants and the use of antibiotics

with animals can increase food production Describe the advantages and disadvantages of using microorganisms to make food

for human consumption

Outline how salting, adding sugar, pickling, freezing, heat treatment and irradiation can

be used to prevent food spoilage by microorganisms

2.2.1 Specification

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Balanced Diet

Living organisms need vital substances termed nutrients in order to provide energy and materials for growth and repair. Without the regular intake of these nutrients (and oxygen from the air), the organism will suffer ill health and may die

The diet of a person is what is eaten and drunk on a regular basis. The components of a diet can be provided by plants, animals, and microorganisms

Balanced diet A diet which provides an adequate intake of energy and nutrients needed for the maintenance of the body and thus good health

It is the adequate intake of food (mixture of organic and inorganic chemicals) containing the right kinds of nutrients in the right amounts

The Food Standards Agency (FSA) tips for healthy eating

•Base meals on starchy foods•Eat lots of fruit and vegetables•Eat more fish•Cut down on saturated (animal) fats

and sugar•Eat less salt•Exercise – maintain a healthy

weight•Drink plenty of water•Don’t skip breakfast

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Carbohydrates – source of energy – e.g. glucose; starch

Fats – energy store; cell membranes; insulation (thermal + electrical); protect organs; storage of fat-soluble vitamins; need to ensure consumption of fats containing essential fatty acids

Proteins – growth and repair; enzymes; muscle; antibodies; cell membrane; etc; need to ensure consumption of proteins containing essential amino acids

Vitamins (organic) - Fat soluble - A, D, E, K; water soluble - C, B group – for efficient biochemical function; for coenzymes – required in trace amounts.; K – blood clotting, D – calcium absorption; required in trace amounts

Water – solvent; reactant; transport – variable; about 70% of the body is water

Minerals (inorganic) – structural components and osmotic balance- calcium – for bones, teeth; iron – for haemoglobin;; iodine – for thyroxine (hormone); sodium – for osmotic balance

Fibre (organic) – for efficient peristalsis; prevents constipation; lowers blood cholesterol

Proportions in diet (for energy intake) - 57% CHO; 30% fats; 13% protein

Essential amino acids, essential fatty acids, and vitamins need to be provided in the diet – these cannot be made in the body – others can be made

Needs vary – e.g. age, occupation, pregnancy, lactation, gender, illness

There are seven components in a balanced diet

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Essential Amino Acids

Twenty different amino acids are used in the synthesis of proteins

There are 10 amino acids that the body cannot make - these are called essential amino

acids (EAAs), and need to be present in the diet – a balanced diet will contain all the essential amino acids and a good supply of the non-essential amino acids

Non-essential amino acids can be synthesized from EAAs – e.g.:

The essential amino acid phenylalanine can be converted into the non-essential amino acid tyrosine

“Non-essential” amino acids do not need to be present in the diet

Some roles of EAAs in the body – synthesis of neurotransmitters, hormones, enzymes, antibodies, structural proteins (e.g. collagen), contractile proteins (actin and myosin)

Proteins cannot be made without the essential amino acids – lack can lead to deficiency

diseases

Effects of deficiency of EAAs:

Poor growth; underweight; poor development Poor wound healingPoor immune system (susceptibility to disease)Muscle wastingFatty liver

Some sources of EAAs – meat ; eggs; milk; mixed diet (fruit, vegetables, nuts)

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Essential Fatty Acids (EFAs)

The body is able to make all the necessary fatty acids required , except two – linolenic acid and linoleic acid – these have to be present in the diet; they are essential fatty acids; they are unsaturated

They are required in very small amounts – well nourished people have probably a year’s supply in their adipose tissue

Some roles of EFAs – synthesis of prostaglandins (local hormones), steroids, phospholipids (cell membrane structure and function); gene regulation and expression; inhibit platelet adhesion (prevents clotting of blood); development of visual and neural tissue; neurone structure (myelin sheath in neurone)

Effects of deficiency Impaired vision; mood swingsHigh blood pressureSusceptibility to infectionImmune and mental deficienciesImpaired growthScaly dermatitis

Some sources of EFAs – fish and shellfish; plant oils; leafy vegetables; walnuts; milk

Linoleic acid (Omega 6)18:2 – 18 carbons; 2 double bonds Linolenic acid (Omega 3)

18:3 - 18 carbons; 3 double bonds

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Malnutrition is caused by insufficient, excessive or an imbalanced consumption of nutrients – this can be due to:

Lack of food – leading to starvation – resulting in a lack of energy and nutrients

The body adapts by - reducing the metabolic rate, and using stored micronutrients (carbohydrates, fats, and proteins)

Protein Energy Malnutrition (lack of carbohydrates and protein) - leads to kwashiorkor & marasmus

Lack of specific nutrients (unbalanced diet) - leading to deficiency diseases

Iron - iron-deficiency anaemia; vitamin C - scurvy; vitamin D and calcium – rickets; niacin (vitamin B3) - pellagra; iodine – goitre; vitamin A – night blindness

Overeating – more energy consumed than used

Excess energy intake leads to obesity (increase in weight)

Obesity is a risk factor in coronary heart disease; hypertension; diabetes; cancers (bowel, rectum, uterus, cervix); arthritis; hernias; gallstones – mainly due to a diet rich in carbohydrates and fats and a high concentration of cholesterol in blood. Excess carbohydrates is converted to fat and stored around vital organs (e.g. heart & kidneys) and in females underneath the skin

Other causes

Problems with absorption and assimilation (utilisation) of nutrients following digestion causes deficiency diseases – e.g. celiac disease

Malnutrition (“bad nutrition”)

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Deficiency diseases

Kwashiorkor – lack of protein

Pellagra – after niacin therapy

Goitre – lack of iodine

Rickets – lack of vitamin D and / or Ca

Scurvy – lack of vitamin CPellagra – lack of niacin (vitamin B3)

Marasmus – severe nutritional

deficiency

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Obesity and Health

Overeating is a form of malnutrition

If the regular intake of energy is in excess of demand, the body gains weight –leading to obesity

Obesity is an increasing problem in “developed” “Western” countries – associated with the diet (rich in fat) and lifestyle (not physically active)

Fat provides twice as much energy per gram than a gram of carbohydrate or protein,

due to a higher hydrogen content in the fat molecule – therefore, a fat rich diet increases the risk of gaining weight

Obesity is a growing problem in children – due to consumption of fast foods (containing fat, sugars ,and starches) and lack of physical activity

Obesity is a risk factor in CHD, diabetes, arthritis, and some forms of cancerA BMI greater than 30 is classified as obese – obesity is a result of

Eating too much

High fat, sugar, carbohydrate, alcohol in the diet

Energy intake greater than use

Insufficient exercise

Genetic predisposition

Underactive thyroid (low basal metabolic rate)

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Body Mass Index (BMI) and Obesity

The BMI is used to determine if an adult person is underweight, overweight, or obese

It is calculated using the following formula

massBMI =

Height2 (m2)

A graph can be used to determine the BMI of a person – however:

If values fall on a line dividing the categories, it is difficult to place in a category

Limitations of BMI

Difficult to calculate BMI for children and adolescents – since they store fat as part of their growth

Does not take into account gender, age, disease

(e.g. osteoporosis; thyroid disease) and other factors contributing to obesity (e.g. lack of exercise / pregnancy)

Does not take into account muscle mass / bone

mass, or amount of body fat

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X

Example

Height = 1.73 mMass = 75 kg

BMI = 75 / 1.732

75 / 2.9929 = 25

BMI = 25

Acceptable

A body weight, 20% in excess of the

recommended weight for a particular age is

considered obese

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BMI vs. Body-fat percentage measurement

In September 2000, the American Journal of Clinical Nutrition published a study showing that body-fat percentage may be a better measure of a persons risk of weight-related diseases than BMI.

"Many studies have related BMI to disease risk,“ "What we did was correlate body-fat percentage to BMI, allowing us to take the first big step toward linking body-fat percentage to disease risk.

BMI is a broad, general measure of risk. Body-fat assessment is much more specific to the actual fat content and thus provides a more accurate picture.”

"In terms of ease-of-use and usefulness, the BMI can't be beat,“

"But if a home, fat-measurement device helps someone stay focused on their diet and exercise level and motivated to stay healthy, then the device has a place in weight management."

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Obesity – a risk factor in a number of diseases

Coronary heart disease - a diet rich in saturated (animal) fats, leads to a high concentration of blood cholesterol.

A high blood concentration of cholesterol and a high blood pressure (hypertension) increases the risk of developing coronary heart disease – e.g.

Atherosclerosis – build up of fatty material (plaques) in coronary arteriesCoronary thrombosis – blood clotting in coronary arteriesHeart attackStroke - loss of brain function due to insufficient supply of blood (oxygen and

nutrients) due to a blood clotMyocardial infarction

Diabetes (type 2) – obese people cannot control their blood glucose , principally due to insensitive insulin receptors

Cancers – colon, rectal, cervical, prostate, uterine, breast

Osteoarthritis (inflammation of the joints) – due to increased strain on the skeleton and joints

Thrombosis – blood clotting in blood vessels of the pulmonary and systemic circulation

Hernias, varicose veins and gallstones

Organ strain – due to organs (e.g. heart, kidneys) being surrounded by excess fat – causes physical strain

Surgery – operations carry an increased risk of complications in obese people

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The location of where the fat is deposited has an effect on the acquired conditions

“few moments on the lips, forever on the hips”

Apple shaped – fat around the middleHigher risk of obesity-related conditions

Pear shaped – fat around hips and thighsLower risk of obesity-related diseases

Preventive measures

Incentives (inducements) to lose weight – e.g. prizes, competitions

Clubs /local meetings / help linesTarget setting for weight reduction / target groups

of people

Change diet (reducing energy foods and fats)Reduced alcohol intakeEncourage exerciseAdvertising / educationEarly education to encourage healthy eating

habits and exercise

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Diet and Coronary Heart Disease (CHD)

CHD is a result of reduced blood flow to the heart – leading to angina, myocardial infarction and heart failure, caused by the narrowing and hardening of coronary arteries – the blood vessels supplying the heart

Deposition of fatty material in the walls of the coronary arteries leads to a narrowing of the lumen – thus restricting blood flow to the heart muscle, which may cause oxygen starvation .

Energy is not produced and the cardiac fails to contract – lack of oxygen causes the cardiac muscle to die

Arteriosclerosis (hardening of the arteries) also occurs – reducing their elasticity and therefore their ability to expand and recoil – the heart has to work harder to force blood through the coronary arteries and may cause the blood pressure to rise and heart muscle to fatigue

A healthy BMI is maintained by balancing the overall energy intake with energy use – to avoid becoming underweight or overweight (obese).

Excess intake of certain components in the diet may increase the risk of CHD – a major cause of death in developed countries.

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Coronary arteries

Narrow arteries that carry oxygenated blood from the aorta to cardiac muscle at high pressure

Increased risk of damage due to narrow lumen – further narrowed by deposition of plaque

(fatty material) – thus reducing blood flow to cardiac muscleReduces supply of oxygen (and glucose) for respiration. Leads to CHD – three forms:

oAngina pectorisSevere chest pain on exertion due to restricted blood flow to cardiac muscle; no death of heart tissue

oHeart attack (myocardial infarction)Coronary artery becomes obstructed by a blood clot (thrombus) – heart muscle is starved of oxygen – dies – causes sudden and severe chest pain - may be fatal if not treated immediately

oHeart failureDue to blockage of a main coronary artery and gradual damage to heart muscle; heart weakens and fails to pump effectively

Thrombosis A blood clot (thrombus) may form at the site of the atheroma – may block coronary artery – leading to myocardial infarction

Stroke Sudden symptoms - bursting of artery in brain (brain haemorrhage); blockage of brain artery due to atherosclerosis or thrombus – reduces oxygen for respiration; causes cerebral infarction; fatal or disabling

Three forms of CHD

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Cholesterol is a derived lipid and is insoluble in water. It is essential for

Vitamin D synthesis in the skin Cell membrane component (regulates fluidity) Synthesis of steroid hormones (sex hormones; adrenal cortex hormones) Formation of bile salts

It is mainly found associated with saturated fats in meat, eggs and dairy products. It is also made in the liver from saturated fats

Being insoluble in water (plasma), it is transported in the blood in structures called high density lipoproteins (HDLs) and low density lipoproteins (LDLs)

CHD is multifactorial – it has many risk factors

High intake of saturated fats - a cholesterol level greater than 250 mg/100 cm3 (5.2 mmol per dm3) of blood – cholesterol is present in fats and is also made from saturated fats

High salt intake; smoking; heredity (familial hypercholesterolemia)Lack of exercise; overweight; obesityDiet low in unsaturated fats; diet low in fibre; lack of vitamin D; lack of antioxidants

(vitamins A, C, and E)

Alcohol; stress; age; gender; diabetes; povertyObesity – causes an increase in blood pressure, causing the heart to work much harder and increasing the pressure on artery walls – promotes deposition of cholesterol

Salt – excess salt in the blood decreases the water potential of blood, causing water to enter blood vessels by osmosis and increasing the blood pressure – leading to hypertension – damaging the internal lining of the coronary arteries – an early step in atherosclerosis

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HDLs (mainly protein) – “good”

Composed of unsaturated fats + less cholesterol + much protein

A diet high in unsaturated fats raises the HDL levels - reduce blood cholesterol – reduce risk of CHD – “good lipoproteins”

Transport cholesterol from the tissues to the liver to be excreted in bile (or recycled); help to protect arteries against atherosclerosis

Reduce blood cholesterol; reduce arterial deposition; and help to remove fatty deposits - decrease the formation and risk of atheromas

Lipoproteins and CHD

Liver cells have HDL receptors

LDLs (mainly lipid) – “bad”

Composed of - saturated fats + much cholesterol + little protein

A diet high in saturated fats raises LDL levels - increase blood cholesterol – increase risk of CHD

Transport cholesterol from the liver to tissues via blood

Tend to deposit cholesterol at damaged sites in endothelium of artery walls. LDL’s are referred to as “bad lipoproteins”

Saturated fats reduce activity of LDL receptors in tissues – therefore, less cholesterol is removed from blood – deposited in artery walls to form atheromas

Unsaturated fats increase activity of LDL receptors – decrease LDLs in

blood

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• A diet high in saturated fat and cholesterol increases blood cholesterol levels – increase s concentrations of LDLs and lowers concentrations of HDLs– more cholesterol is transported in the blood , from the liver to tissues – increases risk of CHD

• A low saturated fat diet reduces the overall concentration of lipoproteins

• A diet rich in unsaturated fats increases the proportions of HDLs and lowers LDLs in blood – more cholesterol is transported to the liver from tissues – reduces risk of CHD

• Eating monounsaturated and polyunsaturated fats helps to reduce the concentration of LDLs in the blood

• Cholesterol is derived from many sources – animal fats; eggs; milk; butter

• Ratio of HDL to LDL is important

- a high blood (plasma) concentration of HDLs reduces the deposition of cholesterol in artery walls

- a high blood (plasma) concentration of LDLs increases the deposition of cholesterol in artery walls

Diet, Lipoproteins and CHD

Only a small amount of free cholesterol escapes from LDLs under normal conditions. A high amount of cholesterol in the LDLs causes increased leakage of cholesterol into

the plasma

Cholesterol is deposited at the site of damage in arterial walls arterial walls – forming fatty streaks – leading to the development of plaques (atheroma)

An atheroma increases the risk of blood clotting in arteries. Deposits may start to build up from childhood

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Atherosclerosis

The main process leading to cardiovascular disease is the accumulation of fatty material (plaque) in artery walls – mainly aorta, coronary arteries, and carotid artery) , narrowing their lumen and thus restricting blood flow to tissues and cardiac muscle

Arteries also become hardened and lose their elasticity – termed arteriosclerosis.

The fatty material may increase the risk of blood clots , obstructing the flow altogether.

Tissue does nor receive enough O2 and nutrients and may die.

Plaque – formed due to build up of fatty material (atheroma) under endothelium in artery wall – consists of cholesterol, fibres, dead, muscle cells, platelets, and foam cells (phagocytes with ingested fat).

Damage (break) in artery wall encourages atheroma formation – damage may be due to hypertension, or carbon monoxide and nicotine from smoking

Deposited material originates in plasma

Deposits may start to build up from childhood

Plaques in the lining of arteries, make the arteries less elastic and restrict blood flow

The condition is called atherosclerosis

An atheroma increases the risk of blood clotting – the clot may break off and lodge in coronary arteries – causing myocardial infarction (tissue death)

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Artery lining (the endothelium) gets damaged – e.g. by CO; nicotine; high blood pressure

Phagocytes are attracted to damaged site through chemotaxis – to repair damage

LDLs accumulate in the inner coat (smooth muscle) of arteries – under the endothelium at the site of damage (break) as small fatty streaks

White blood cells ingest fats and become foam cells and sink into the lesion

Increase in the growth of smooth muscle and build up of connective tissue around damaged site occurs – causes fibrosis and hardening - causes loss of elasticity (arteriosclerosis) of artery wall – causes an increase in BP

Free radicals released from the phagocytes react with the cholesterol

Fatty material (cholesterol from LDLs), dead muscle cells and platelets are deposited – known as plaque (developing into an atheroma); high blood pressure also increases deposition of LDLs

Artery wall bulges into lumen – causes narrowing and restricts blood flow

Platelets may be activated – release thromboplastin and a. Blood clot may form (leading to ischemia (reduced blood flow); angina and myocardial infarction (death of cardiac muscle)

Normally, anticlotting factors (e.g. heparin in blood) prevent clotting

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The endothelium covering a plaque may rupture - to cause the formation of a blood clot (thrombus)

Tear in artery wall

Macrophage cell

Cholesterol deposits

Red blood cell (in lumen)

Macrophage foam cell

Fat deposits

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Risk factors in CHD have been identified through long-term epidemiological studies

Whitehall Study - with large groups of people – based on lifestyle, illnesses, and cause of death

Common factors - identified: HypertensionHigh cholesterol levels in bloodSmokingDiabetesExercise – reduced incidence of CHD

MONICA (1979) – WHO – study of global distribution of CHD

Identified a correlation with blood pressure and blood cholesterol as keyfactors in predicting the likelihood of CHD developing in a person

Found higher levels of vitamin E (antioxidant ) in people from countries with low rates of heart disease

High incidence of CHD in Finland – linked to a diet rich in animal fats

Lowest rate of CHD in Spain and Italy – linked to a high intake of unsaturated fats – which tends to lower blood cholesterol levels, so long as saturated fat intake is low

But – France has lowest rates of CHD, although the intake of animal fats is high – suggests that saturate fat and cholesterol intake alone are not important

Other dietary factors may be important (e.g. salt intake)

Evidence Linking CHD to Diet

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Human populations with diets high in animal fats have a lower life expectancy than those with diets high in vegetable oils

1 Suggest one difference between lipids from animals and those from plants

2 Animal fats are thought to raise blood cholesterol levels. High blood cholesterol can lead to premature death

The Figure shows the relationship between blood cholesterol level and annual death rate per 10 000 of the population

i) Describe the trends shown in the Figure

ii) Increased blood cholesterol levels are associated with certain medical conditions

Suggest two medical conditions that may be associated with increased blood cholesterol levels

Animal fats are saturatedFatty acids have no / fewer, double bondsAnimal fats are solids at room temperature

Death rates for men greater at any concentration

Exam Question & Marking Scheme

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Food Production

The Sun is the ultimate source of energy for all living organisms

Plants are photoautotrophs – i.e. they are able to make organic chemicals by using energy from sunlight and the inorganic substances, carbon dioxide and water, through the biochemical process of photosynthesis. Plants convert light energy to chemical energy in the form of glucose

Carbon dioxide + Water

Glucose + Oxygen

Plants are at the start of all food chains – all animals rely on plants for food

Food chain – a linear sequence showing feeding relationships – arrows indicate direction of feeding – i.e. flow of energy and materials.

Food chains are interlinked in nature to form food webs

Glucose is -oBroken down to release energyoConverted to other molecules amino acids, fatty acids,

etc)

All food molecules ultimately come from autotrophic plantsThe sun is the ultimate source of energy for all living organisms

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Humans are omnivores - they eat both plants and animals

Ultimately, all living organisms depend on plants for food

Increase in human population numbers has led to an increase in demand for food.

The challenge is to increase food productivity to provide components of the diet for a

rapidly growing population

In order to meet the demand, the production of foods (derived from microorganisms,

plans, and animals) needs to be made more efficient and cost effective

A number of methods are used to increase productivity of foods derived from living organisms

Making food production more efficient

Plants Improve growth rate of crops to improve yield – by using fertilisers (chemicals)

Reduce losses of crops due to disease and pests – by using chemicals (pesticides and herbicides)

Standardise plant size to make harvesting easier

Improve plant responses to fertilisers

Selective breeding – to produce plants with desired characteristics (phenotype) – e.g. high yields

Genetically modified plants – to confer resistance to pests, drought, etc; to improve texture , shelf life, etc

Methods to increase productivity

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Animals Improve rate of growth

Increase productivity

Increase resistance to disease – use of antibiotics to prevent or treat bacterial disease – promotes growth

Selective breeding – to produce animals with desired characteristics - e.g. increased milk and meat yield

Microorganisms

Use of microorganisms as edible food (e.g. single cell protein)

Using metabolic products (e.g. lactic acid to produce yoghurt; antibiotics to promote growth in animals)

Selective Breeding (Artificial Selection)

Nature selects and allows the survival of species (varieties) that are well adapted to the environment. They are selected as a result of natural environmental forces or pressures

Natural Selection is the principle by which each slight variation (adaptation) , if useful, is preserved and passed onto the next generation

Humans apply selection pressures to populations in order to achieve the exaggeration of certain features – one method commonly used in food production is selective breeding

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Selective breeding involves the following three stages

Stage 1 Isolation Select a pair of plants or animals with the desired characteristic (e.g. disease resistance)Allow the pair to reproduce

Stage 2 Artificial selection Select offspring with the best combination of the desired characteristics

Stage 3 Inbreeding Allow selected offspring to reproduce

Selection and reproduction is continued for many generations, resulting in the required characteristics becoming more exaggerated in the population.

Detailed records are kept to monitor and prove ancestry of valuable individuals

The alleles for the undesired characteristics (which otherwise may be useful) decrease in frequency, and in many cases may be lost - e.g. disease resistance

A gardener wants to eliminate thorns from a plant

The majority of plants have more thorns and dominate those with fewer thorns

The gardener selects the plants with fewer thorns (orange coloured plants) and allows them to reproduce

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Examples of selective breeding

Cattle Increase milk and meat yield; increase milk and meat quality

Salmon Increase rate of growth – reduce time to market; improve disease resistance and meat quality

Chickens Increase egg production & meat yield

Tomatoes Flavour; disease resistance – allele for disease resistance from wild tomato – bred into domestic variety

Apples Disease resistance; flavour, texture, and colour

Wheat Improve yield;, disease resistance; drought resistance; uniform size (for harvesting)

Rice To improve nutritive value – e.g. vitamin A content (“Golden Rice”)

Flowers Producing new combinations of colours and scents in garden flowers

Thanks to selective breeding (not genetic engineering), cauliflower in different colours are available. They taste the same as white cauliflower, but are just, well, more fun on the plate.

Scientists are also claiming that they might be healthier for you than white cauliflower because of the benefits from the compounds that give the vegetables the colour.

Healthier than white or not, if its being colourful makes you and your family eat it, that's all the better!

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Selective Breeding – Plants

Increasing yield (e.g. high yielding wheat plant a plant which can grow tall and produce multiple ears)

Select a pair of plants with desired characteristics with (dominant alleles)

Breed : Tall corn plant X Corn plant producing multiple ears

Select the offspring with the best characteristics

Tallest with most ears – breed them together

Continue over several generations

Until a high yielding plant is produced – very tall with multiple ears

Hybrid – cross between genetically dissimilar parents

Need to preserve genetic diversity off species and keep gene pool as diverse as possible

Marker-assisted selection

A section of DNA is used as a marker (probe) to recognise the gene for the desired characteristic in offspring produced from selected parents – allows selection of offspring for breeding at an early stage

Desired allele can bred into a domestic variety

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Plants with a high yield and resistance to disease or pests

Plants showing a high level of resistance to disease or pests are bred together

Offspring showing most resistance are then bred together

Continued over several generations to produce a crop that is disease or pest resistance

Breed Resistant wheat X High yielding wheat

Prevent self pollination (by removing anthers or placing a bag over stigma)

Select best offspring – good yield and disease resistance

Back cross to high yielding wheat (offspring crossed with high yielding plant)

Interbreed best offspring with both characteristics

Breed and select for many generations

Mildew (a plant parasite) may adapt to overcome resistance in wheat

Genetic variation occurs due to mutationFungus produces a large number of sporesWheat resistance acts as a selection pressureIndividuals that overcome resistance have selective advantage – likely to survivePass on mutated allele (to overcome resistance) to off springIncrease in allele frequency occurs in successive populations

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Selective Breeding – Animals

Useful characteristics selected for – e.g. fast growth rate; high meat, milk or egg yields

Meat yield

Breed: Largest cows X Largest bulls

Select offspring with the best characteristics

Breed them together Aberdeen Angus Bull

Continue over several generations – until cows with very - bred for meat yield

high meat yields are produced – i.e. very large cows (or bulls)

Milk yield

This is done in a similar way, except –

Bulls are chosen whose female relatives have high milk yields and who produce female calves with high milk yields

Health and welfare of the animals should not be compromised – e.g. high milk yielding cows have a higher tendency to suffer fro mastitis (inflammation of the udder) and lameness

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Frozen semen from selected bulls can be

Frozen and kept for long periods of time and quickly available when needed

Transported over long distances

One bull can be used for breeding with a large number of cows – prevents inbreeding

Costs of transport of animals for mating, and the stresses of mating are avoided

Sperm can be sexed and checked for genetic defects

Disadvantages

Low temperature storage may damage sperm

If the sperm used to inseminate a large number of cows have a genetic defect – the cost may be high

Failure of freezing equipment or loss of power supply

Disadvantages of selective breeding

Growth may be too rapidPossibility of increased susceptibility to diseaseInbreedingReduces genetic variation

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Selective breeding of domesticated animals is an example of artificial selection, which occurs when man directly intervenes in the breeding of animals to produce desired traits in offspring

As a result of many generations of selective breeding, domesticated breeds can show significant variation compared to the wild counterparts, demonstrating evolutionary changes in a much shorter time frame than might have occurred naturally

Examples of selective breeding of animals include:

•Breeding horses for speed (race horses) versus strength and endurance (draft horses)•Breeding dogs for herding (sheepdogs), hunting (beagles) or racing (greyhounds)•Breeding cattle for increased meat production or milk•Breeding zebras in an attempt to retrieve the colouration gene from the extinct Quagga

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Inbreeding (“in family” breeding)

Continuous inbreeding and selective breeding of particular genes (characteristics) to achieve the desired characteristics leads to

•Reduced gene pool (genetic diversity) in long term

•Risk of losing genes – offspring may end up with similar genome

•All offspring susceptible to new disease – may be fatal

•Offspring unable to cope with other environmental stresses – e.g. killed by pesticide

Selective breeding compared with evolutionThe selection pressure in evolution is natural selection, involving the whole

environment of the organism.

In selective breeding, the selection pressure is the artificial selection that results

from the breeder’s choice of parents.

In selective breeding, the change selected may not be an advantage to the organism in its environment.

In evolution, the organism’s adaptation to the environment is favoured

One character may be selected, whereas in evolution the organism’s total fitness

for its environment is selected

The change is commonly faster than that achieved by natural selection

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Using Chemicals to Improve Food Production

Fertilisers

Minerals in soil are used up during crop growth.

Fertilisers are chemicals added to soil to provide (replace) essential minerals (mainly N, P, and K) required by the plant for growth - fertilisers increase the rate of plant growth and therefore increase the yield

• Provide minerals required for biochemical reactions and structural components in the plant

N DNA/RNA nitrogenous bases; amino acids; vitaminsP ADP/ATP; nucleic acids; phospholipids (cell membranes)K Stomatal opening, osmotic balance

• Fertilisers can be natural (compost; manure) or artificial (man made)

• Organic fertilisers improve soil structure – retain water, help root growth, provide a slow release of nutrients on decay

• Adding fertiliser increases yield to a point – any extra fertiliser is wasted. Fertiliser needs to be added while the plant is growing actively

• Adding large amounts of fertiliser may decrease the yield - the high concentration of mineral ions decreases the water potential of the water surrounding the root hairs, causing water to be lost from the roots down a water potential gradient by osmosis

• Leaching of excess fertiliser may pollute streams , rivers, and lakes – resulting in eutrophication and death of aquatic life

• Fertilisers are removed from the soil during harvesting

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Ammonium nitrate is a widely used fertiliser and is manufactured in industry

The nitrogen is used by the plant for making amino acids (proteins) and other nitrogen containing chemicals

Using manufactured fertilisers allows the farmer to apply the right quantity of fertiliser

Using manure gives an idea of how much

should be used to get the best yield

Pesticides

Pesticides increase crop yields by killing pests (insects, rats, snails) that feed on the crops – they increase yield by preventing damage and destruction of crops. Include insecticides, rodenticides, and fungicides; herbicides are used to kill weeds

• Broad spectrum – kill a range of different species – non pest species may also be harmed

• Specific – kill only one species• Animals may be treated topically with pesticides – e.g. to kill ticks

that live in wool (e.g. sheep) by dipping• Danger of pollution – bioaccumulation in food chain; persistence

in environment

Liquid copper is uses as a fungicide – to treat raspberry cane blight

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Herbicides (“weed killers”)

Chemicals that are used to kill unwanted plants (“weeds”)

Mechanism of action - photosystem inhibition (in chloroplasts) – inhibits photosynthesis

- specific enzyme inhibition – e.g. to inhibit amino acid synthesis

Problems with pesticides and herbicides

Pesticides (and herbicides) for agriculture are specially formulated to decompose rapidly

after application to avoid pollution and undesirable effects on other organisms (e.g. through bioaccumulation in food chains) – however these do not provide long-term control

DDT is not biodegradable – builds up in the body of the insect

Animals near the top of the food chain accumulate large amounts of DDT in their tissues and may cause the death of the animal (e.g. birds of prey)

Some non-pest species are also harmed and may disrupt the balance of the ecosystem –

e.g. killing of pollinators such as bees

May need to be applied several times during a growing season – this is expensive

Development of pesticide resistance - due to mutation (natural / random)- resistant survive

Resistant will pass on resistant allele (mutation) for resistance to offspring

Higher proportion of resistant individuals in population

Pesticide may persist in the food being consumed , causing health problems

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Biological pest control

Natural predators (e.g. Ladybirds) of pests can be employed to control pests (e.g. aphids)

oLadybirds feed on aphids

oAvoids the hazards of pesticides

Nemaslug contains concentrated doses of nematodes, which are specific natural enemies of slugs

Long term solutions

The use of pesticides to kill pests (e.g. Insects) is a short term solution

A long term solution would be to use of selective breeding to create a crop strain

resistant to the pest

Development of resistance in the pest population

•Variation exists in insect population•Insecticide exerts a selection pressure•Some are resistant •Mutation (natural / random)•Resistant survive (non-resistant die)•Resistant will pass on, allele (mutation) for resistance to

offspring•Higher proportion of resistant individuals in population

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Antibiotics help to treat or prevent disease caused by bacteria - enable animals to be free of disease

The body uses energy to fight infection – in phagocytosis, inflammation, fever, and the immune response – this reduces the amount of energy available for growth

Disease free animals do not need to expend energy in dealing with pathogens

Antibiotics therefore, enable the animals to use the energy for growth and not in fighting

infection – thus increasing he yield of milk and meat

Antibiotics reduce the spread of disease among animals that are intensively farmed and in

close proximity to each other – this also helps to improve the yield, since transmission of infection is to other animals is prevented

Antibiotics also promote growth by influencing gut bacteria – allowing efficient digestion and preventing unnecessary fermentation – the energy being energy diverted for growth

Increases growth rate and size when mature

Antibiotics are chemicals that kill or inhibit the growth of bacteria – they are used in the treatment of bacterial diseases – e.g. respiratory infections

They are selectively toxic to the bacteria – they do not harm host cells

Antibiotics are mixed in the feed of animals or administered in order to increase yield – they help to increase the growth rate of animals and their size when mature

Antibiotics

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Problems with the use of antibiotics

oencourages the development of antibiotic resistance

oantibiotic resistant pathogens passed along food chain to other organisms

oantibiotics passed onto other organisms through food webs

Development of antibiotic resistance

Initially, a population of bacteria will contain members who have a range of resistance to antibiotics. Each circle represents a bacterial cell and the darker the colour, the more resistant the bacterium is

If the population is then exposed to antibiotics, the bacteria that are not resistant will be killed. However, highly resistant bacteria will survive

Some bacteria will mutate as a result of the selection pressure created by the antibiotic and become resistant

If these bacteria are not killed by the immune system, they will reproduce – and the daughter cells will inherit the resistance

Thus, over time, the population becomes more resistant to the antibiotic

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Microorganisms and Food Production

Microorganisms such as bacteria, yeast and other fungi, have been used traditionally in all parts of the world for producing food for human consumption. This has recently been exploited on a commercial scale

Yoghurt Made by adding Lactobacillus bacteria to pasteurised (heat treated) and cooled milk

Bacteria use the lactose sugar in milk to produce lactic acid, which causes the milk protein to thicken (curdle) due to the acidic pH and impart a sour taste

Temperature is controlled to maintain flavour and texture of the product

Cheese Milk is curdled using a protease enzyme (rennin).

The curds are then acted on by Lactobacillus. Additional flavour can be given – e.g. by allowing the controlled growth fungi (such as Penicillium) in the cheese

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Bread Leavening of bread due to CO2 produced by yeast (fungus) by respiration – the CO2 becomes trapped in pockets of protein (gluten) in the dough, created by kneading, which makes the dough rise due to expansion of the gluten pockets on baking in a hot oven

Glucose CO2 + Ethanol

Wine Yeast + grape juice (glucose) Ethanol (wine) + CO2

Single cell protein (SCP)

SCP is used as edible food – e.g. mycoprotein is made from the hyphae (filaments) of the fungus Fusarium

A continuous culture is used to grow Fusarium to make SCP

The fungus produces protein with a similar amino acid profile to animal and plant protein

It is heat treated (to kill bacteria) and marketed as a meat substitute for vegetarians (QuornTM ) and as a healthy option for non-vegetarians, as it contains no animal fat or cholesterol

Fungi can use a wide variety of waste material as nutrients (whey, paper) for growth – economically advantageous

No mechanical stirrer is used – to prevent breakage of the fungal hyphae

Ammonia provides nitrogen for amino acids (protein)

Hyphae of Fusarium graminearum

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Microorganisms, such as the fungus Fusarium, can be grown and then purified to produce mycoportein. The mycoprotein can be used as a food as a food source for humans

The table compares mycoprotein with beef

Use the data to describe and explain the advantages and disadvantages of using microorganisms to produce food for human consumption

Lower / less, energy than beef; useful for slimming / weight control

Lower / less, total fat; low / less, saturated fat; lower cholesterol

Lower risk of CHD / heart attack / atherosclerosis / stroke / hypertension

Lower / less, iron content; increased risk of anaemia / fewer RBCs / less haemoglobin / reducedoxygen carrying capacity of blood

Lower / less, protein (only 12 g per 100g); affects growth and repair of tissues

Mycoprotein provides more balanced diet

Need larger intake to meet requirements

Exam Question & Marking Scheme

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Advantages of using microorganisms for food production

Grow rapidly under right conditions (pH, temperature, nutrients, oxygen) – protein Production is much faster than animals – resulting in faster production of food (compared to growing crop plants and rearing animals)

Their optimal growth conditions can be easily created artificially to maximise yield and

controlled – allowing year round food production – not affected by seasons or location

Production can be regulated (increased or decreased) according to demand – by controlling their environment

Grow on a range of inexpensive materials – utilises recycling of waste products – economically favourable

Food produced by microorganisms has a longer shelf life than raw products they're made from – e.g. cheese lasts longer than milk

Provide a good source of protein (having a complete amino acid profile) for vegetarians

Protein contains no animal fat or cholesterol

No ethical animal welfare issues

With climate change threatening the availability of land for rearing livestock and the growing awareness of the environmental impact of meat production, mycoprotein may yet be set to fulfil its original mission; to provide the world with a nutritious, abundant, environmentally friendly protein

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Disadvantages of using microorganisms

High risk of food contamination – conditions are also favourable to harmful organisms

– may cause the desired product to spoil or if eaten cause illness (food poisoning) – may be fatal

Small fluctuations in the optimum conditions (e.g. temperature; pH) may kill the microorganisms

Pathogenic microorganisms may grow alongside the useful microorganism and produce toxins

Aseptic techniques need to be employed in culturing microorganisms

Protein has to be purified – to ensure it is not contaminated

Taste and palatability may be affected – not the same as protein from traditional sources (mainly animals)

Down stream processing – separating protein from waste may be time consuming and expensive – risk of contamination

Objections to eating food grown on waste and produced by microorganism

Specialist laboratory facilities may be needed for production o an industrial scale – demanding investment which may not be possible in some developed countries

Long term effects not known

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Food Spoilage by Microorganisms and Preservation of Food

Microorganisms obtain their nutrients by feeding on organicmaterial around them and at the same time produce and excrete waste products that spoil food and make it unsuitable for consumption

The main ways in which microorganisms spoil food, or make it unattractive and unsuitable to eat are:

Visible growth Fungi (mould) growing on food – e.g. the bread moulds (Mucor and Penicillium)

Extracellular Bacteria and fungi secrete digestive enzymes digestion extracellularly and then absorb the soluble

nutrients

Eventually, all the food will be turned into liquid and the food no longer suitable for consumption

Toxins Some bacteria and fungi produce toxins – e.g.

Clostridium spp produces the powerful deadly bacterial toxin botulin

The cholera bacterium produces a toxin which causes vomiting and diarrhoea

Pathogenic microorganisms in food may cause disease directly – e.g. the Salmonella bacterium attacks the lining of the stomach and small intestine – causing food poisoning, which may be fatal

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Food preservation

Prevention of food spoilage involves inhibiting the growth of microorganisms or killing them – by depriving them of the conditions they need to grow.

The food must then be packaged to prevent further contamination with microbes

Preservation increases the shelf life of the food

Food should be eaten within required time - while it is fresh; by the sell by/expiry/eat before, date

Salting (dehydrates microorganisms)Adding salt to food – prevents microorganisms from absorbing water (needed to survive) by osmosis by creating a very low water potential around the microbial cell. E.g. salted meats; gherkins and eggs in brine

Sugaring (adding sugar)Similar effect to salting. E.g. high sugar content of fruit jams; tinned fruits

DryingDehydrates microorganisms – water leaves by evaporation

Freezing (below -180C) – long termSlows down biochemical reactions (inactivates enzymes) and freezes the water – microorganisms cannot use the water; immobilises enzymes; ice damages cells; no reaction medium available; microbes cannot move

Pickling – in acidic vinegarAcidic pH - denatures enzymes and other proteins – changes tertiary structure of enzymes (and active site) and other proteins - inhibits microbial growth. e.g., pickled onions

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Heat treatmentHeat food to high temperature – kills all microorganisms present – store in an air tight sterile container - e.g. sterilised milk in bottles; canned meats; denatures biological molecules

Pasteurisation – heat liquids (e.g. milk) to a high temperature (720C) for a short time (15 seconds) and cool rapidly (to 40C) and store in sealed container at low temperature. Kills most microbes but not spores

IrradiationExpose food to ionising radiation (e.g. X-rays, gamma rays, UV) – damages DNA. Kills any microorganisms present and prevents replication– extends shelf life considerably; cannot eliminate toxins already produced by microorganisms

SmokingForms a hard dry surface – smoke contains antibacterial substances (e.g. sodium benzoate) – e.g. smoked fish

To prevent further contamination

Canning –food heated to denature proteins and sealed in airtight cans

Vacuum packing – excludes air – microbes cannot respire aerobically

Plastic or paper packaging – prevents microorganisms coming into contact with food

Cooking Heat denatures the enzymes and other proteins in microbes – kills microbes; denatures enzymes and other proteins; disrupts microbes

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In Scotland, in 2007, there was a major food poisoning outbreak that killed three people

Suggest one group in the population that is more likely to die from food poisoning and give a reason for your suggestion

The food poisoning outbreak involved the bacterium Escherichia coli 0157 (E coli 0157) which had been responsible for contaminating meat products . The meat had been stored at 110C rather than the recommended 50C and this led to meat spoilage

Explain how bacteria cause food spoilage

Food normally spoils much faster if stored at temperatures higher than 50C

Explain why food spoils faster at higher temperatures

Food can be preserved by keeping it at low temperature in a refrigerator or freezer

Name two other methods of food preservation and state how each method works

Exam Question & Marking Scheme

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Group - young / elderly / HIV infected / malnourished / post-operative / on immunosuppressants,/leukaemia / undergoing cancer treatment / anorexia

Reason – immature / compromised / weak , immune system

Bacteria / bacterial cells, divide / increase in number / multiply / reproduce / proliferate / replicate

Secrete enzymes (e.g. proteases) onto food

Food , digested / broken down

Protein / polypeptides digested to peptides / amino acidsFat / triglycerides to fatty acidsStarch / amylose / glycogen to glucose / sugar

Production / release / excretion / secretion, of toxins (e.g. botulinum) / waste products

Cause change in, appearance / smell / texture / taste

Bacteria, reproduce more rapidly / faster

So more bacteria present

More, toxins / waste, produced / released

More enzymes, secreted; enzyme, action faster / works better / more effective, at higher temperatures

Substrate and enzymes have more kinetic energy

More enzyme-substrate complexes / ESC / successful collisions between substrate and active site

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SaltingLack of water due to, osmosis / low water potential outside cell

SugarLack of water due to, osmosis / low water potential outside cell

Air / freeze dryingEnzymes cannot mobilise; intracellular transport impairedReactions have no medium in which to occurMicrobes cannot move

Pickling (use of vinegar)Low pH denatures / changes tertiary structure of / changes 3D shape of, enzymes / proteins,or, substrate no longer fits active site / active site shape changes / prevents ESC

Irradiation / UV / gamma rays / X-rays / ionising radiationDestroys / damages / changes / mutates, DNA / genes / genetic material

SmokingExposed to antibacterial chemicals (sulphites / sodium benzoate / alcohol

Vacuum packing / canning / bottlingMicroorganisms cannot respire aerobically