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What are the common organelles of cells? (7)

1. Cytoplasm

2. Cell membrane

3. Nucleus (pleural, nuclei)

4. Mitochondria

Specific to plants:

5. Vacuole

6. Plastids 

7. Cell wall

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What is the cytoplasm? (2)

1. Under an electron microscope it looks like a thick liquid, with particles floating inside it. These particles may be food reserves (oil, starch) or they may be organelles (ribosomes, mitochondria).

2. In the cytoplasm, loads of chemical reactions are taking place to keep the cell alive, by providing energy & making the substances that the cell needs. The liquid part of the cytoplasm is about 90% water with salt and sugar solutes. Within this solution there are lipids and proteins, needed to make up cell structures (eg membranes). 

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Describe one of the proteins found inside the cyto


1.They control the rate and type of chemical reactions that take place in cells.

2. Some enzymes are attached to the membrane systems of the cell, whereas others float freely in the liquid part of the cytoplasm.

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What is the cell membrane? (2)

1. A thin layer of cytoplasm round the outside of the cell.

2. It stops the cell contents from escaping and also controls the substances which are allowed to enter and leave the cell (aka active and passive transport). 

In general, oxygen, food, and water are allowed to enter; waste products are allowed to leave and harmful products are kept out. In this way the cell membrane maintains the strcutrue and chemical reactions of the cytoplasm.

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What is the nucleus? (4)

1. Most cells contain just one, which is usually seen as a rounded structure enclosed in a membrane and embedded in the cytoplasm.

2. The function of the nucleus is to control the type and the quantity of enzymes produced by the cytoplasm. In this way it regulates the chemical changes which take place in the cell. As a result, the nucleus determines what the cell will be (ie. its specialization).

3. The nucleus also controls cell division. A cell without a nucelus cannot reproduce.

4. Inside the nucleus are thread-like structures called chromosomes, which can be seen most easily when the cell is dividing. 

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What is the mitochondria? (2)

1. The mitochondria are tiny organelles. They may be spherical, rod-like, or elongated. They are most numerous in regions of rapid chemical activity.

2. They are respnosible for producing energy from food substances.

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Describe the cell wall of a plant cell. (2)

1. The cell wall contains cellulose, and other compounds.

2. It allows water and dissolved substances to pass through. The cell water is not selective like the membrane.

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What is the vacuole of plant cells? (3)

1. A large. fluid-filled space, containing cell sap (a collection of sugars, salts, and sometimes pigments).

2. This large, central vacuole pushes the cytoplasm aside so that it forms just a thin lining inside the cell wall (remember that the cell membrane is a thin layer of cytoplasm). It is the outward pressure of the vacuole on the cytoplasm and cell wall which makes plant cells and their tissues turgid.


Animal cells may also have small vacuoles but they are usually produced to do a particular job, and are hence not permanent. 

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What are the plastids of plant cells? (2)

1. If plastids contain the green substance chlorophyll, the organelles are known as chloroplasts.

2. Colourless plastids usually contain starch, which is used as a food store. 

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What are specialized cells? (3)

Most cells, after they have finished dividing, and growing, become specialized. 

1. They do one particular job (usually as a big set, making tissues, and organs.)

2. They develop a distinct shape.

3. Special kinds of chemical change take place in their cytoplasm. The changes in shape and chemical reactions enable the cell to carry out its special function. 

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What are tissues? (2)

1. A tissue is made up of many hundreds of cells of a few specializations.

2. The cells of each specialization have similar structures, and similar structures and functions so that the tissue itself can be said to have a particular function.


Nerves conduct impulses

Phloem carries food in plants.

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What are some examples of tissues? (3 each)

In animals:

1. Bone

2. Nerve

3. Muscle

In plants:

1. Epidermis

2. Phloem

3. Pith

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What are organs? (2)

1. Organs consist of several tissues grouped together to make a structure with a special function.


The stomach is an organ which contains tissues made from epithelial cells, gland cells, and muscle cells. These cells are supplied with food and oxygen brought by the blood vessels. The stomach also has a nerve supply. 

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What are some examples of organs? (3;4)

In animals:

1. The heart

2. The lungs

3. Intestines

4. Eyes

Flowering plants:

1. Root

2. Stem

3. Leaves

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What are some examples of systems? (2;1)

In animals:

1. The circulatory system (heart, and blood vessels)

2. The nervous system (the brain, spinal cord, and nerves)

In plants:

1. In a flowering plant, the stem, leaves, and buds make up the shoot

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What are some aspects of physiology? (3 each)

In animals:

1. The digestion of food

2. The circulation of blood

3. The contraction of muscles

In plants:

1. Absorption of water by roots

2. Production of food in the leaves

3. Growth of shoots towards light

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What are the chemical components of cells? (6)

1. Water

2. Protein

3. Lipids (fats)

4. Carbohydrates

5. Salts

6. Vitamins

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How does water relate to cells? (4)

1. 75% water, would die if their water content fell much below this.

2. Water is a good solvent, and therefore takes part in lot of vital chemical reactions. (Eg. in photosynthesis water combines with carbon dioxide to form sugar).

3. Water has a high specific heat capacity, so it can absorb a lot of heat without its temperature rising to levels which damage the proteins in the cytoplasm (remember that some of these proteins are important enzymes!)

4. If the water freezes at 0C most cells are damaged, and ice crystals form in the cytoplasm. 

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How are proteins made? (2)

1. They are made of chains of amino acids. Each protein has its own specific configuration of amino acids, of which there are about 20 different types. (alanine, leucine, valine, glutamine, cysteine, glycine, lysine.)

2. The chain of amino acids in a protein takes up a particular shape as a result of cross-linkages.

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How can denaturing occur in proteins? (2)

1. When a protein is heated to temperatures over 50C, the cross-linkages in its molecules break down.

2. The protein molecules lose their shape and will not usually regain it even when cooled. 

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What are fats formed from? (3)

1. Carbon

2. Hydrogen

3. Oxygen

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How are lipids made? (1)

A molecule of fat is made up of 3 fatty acids, and 1 molecule of glycerol


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What do lipids do? (3)

1. They form part of the cell membrane

2. They form the internal membranes of the cell (eg. nuclear membrane)

3. Droplets of fat, or oil form a source of energy when stored in the cytoplasm.

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What are carbohydrates? (3)

Either simple, soluble sugars, or complex materials like starch, or cellulose, but all carbohydrates contain carbon, hydrogen, and oxygen only. 

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What is the glucose molecule in the form of? (1)

A ring. (http://science.marshall.edu/murraye/340/glucose.gif)

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What are some examples of mono-saccharides? (2)

1. Glucose

2. Fructose

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What are some examples of di-saccharides? (2)

1. Maltose

2. Sucrose

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What are some polysaccharides? (3)

1. Glycogen

2. Cellulose

3. Starch

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Are polysaccharides readily soluble in water?


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What do enzymes do? (3)

1. Enzymes are proteins that act as catalysts.

2. One enzyme can be used many times over. 

3. They work as a "lock and key" mechanism. Eg. 2 glucose molecules to form a molecule of maltose. C6H12O6 + C6H12O6 -> C12H22O11 + H2O

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What are examples of anabolic enzymes at work? (3)

1. Hundreds of glucose molecules might be joined together, end to end, to form a long molecule of starch to be stored in the plastid of a plant cell.

2. The glucose molecules might also be built up into a molecule of cellulose to be added to the cell wall.

3. Protein molecules are built up by enzymes which join together tens or hundreds of amino acid molecules. These proteins are added to the cell membrane, to the cytoplasm, or to the nucleus of the cell. They might also become the proteins which act as enzymes.

These are all examples of anabolic reactions

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What do catabolic enzymes do? (1)

1. They help to break down glucose to carbon dioxide and water in order to produce energy. (see aerobic respiration.)

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How does temperature change affect enzymes? (3)

1. A rise in temperature increases the rate of most chemical reactions, a fall slows them down.

2. In many cases, a rise of 10C will double the rate of reaction in a cell; this is equally true for enzyme-controlled reactions. 

3. Above 50C the enzymes, being proteins, are denatured and stop working. This is why many organisms die after being exposed to high temperatures; the enzymes are denatured and the chemical reactions proceed too slowly to maintain life. 

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How can you test to see if a substance is an enzym

Heat it to boiling point. 

If it can still carry out its reaction, it is an enzyme. 

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How does pH affect enzymes? (3)

1. Acid/alkaline conditions alter the chemical properties of proteins, including enzymes. Most enzymes are at their peak efficiency at a particular pH. Eg. The protein digesting enzymes in your stomach, work at pH2, vs. amylase, which cannot work at all.

2. Inside cells, enzymes work best at neutral conditions. (pH 7).

3. These effects are usually reversible. However, extremes of pH may denature some enzymes irreversibly. 

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Are enzymes specific?

Yes. They will act on only one substance.

Eg. If the reaction takes place in stages:

1. Starch -> maltose

2. maltose -> glucose

A different enzyme will be needed at each stage.

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What affects the rate of enzyme reactions? (

1. The temperature

2. The pH

3. The relative concentrations of the enzyme, and its substrate.

a. The more enzyme molecules produced by the cell, the faster the reaction will proceed, provided there are enough substrate molecules available.

b. An increase in the substrate concentration will speed up the reaction if there are enough enzyme molecules to cope with the additional substance.

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How are extra-cellular enzymes used? (2)

1. Fungi and bacteria release extracellular enzymes to digest their food. A mould growing on a piece of bread releases starch digesting enzymes into the bread and absorbs the soluble sugaes which the enzyme produces from the bread.

2. In the digestive systems of animals enzymes are released into the stomach and intestines in order to digest food.

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Describe the process of oxidization. (2)

1. Oxidization converts the carbon in food to CO2, and the hydrogen to water, H2O.

2. At the same time, it sets free energy which the cell can use to drive other reactions. 

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What is the formula of aerobic respiration?

C6H12O6 + 6O2 -> 6CO2 + 6H2O + 2830kJ

Enzymes are used to gain the end product.

2830kJ is the amount of energy you would receive by completely oxidizing 180 grams of glucose to carbon diozide and water. The energy is in the form of ATP, and heat. 

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What are some examples of anaerobic respiration? (

1. Fermentation (C6H12O6 ->                                                                   

2. Bread making

This relies upon the anaerobic respiration of yeast.

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Formula for the 1st stage respiration in muscle ce


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What happens during exercise? (4)

1. Pyruvic acid may build up in a muscle faster than it an be oxidized.

2. It is turned into lactic acid and removed in the bloodstream.

3. Some of the lactic acid is oxidized to carbon dioxide and water, using up oxygen in the process.

4. Accumulation of lactic acid in the muscles may be one of the causes of muscular fatigue. It may also cause cramps. 

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What happens after exercise?

A high level of oxygen consumption may persist until the excess of lactic acid is oxidized.

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Compare aerobic & anaerobic respiration. (2)

Aerobic respiration is the most efficient because it:

1. Creates more ATP than anaerobic respiration

2. Anaerobic respiration also creates lactic acid as a by product, which creates a burning sensation in your muscles.

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Why do organisms need food? (3)

1. For growth (it provides the substances needed for making new cells and tissues)

2. As a source of energy (energy is required for the chemical reactions which take place in living organisms to keep them alive. Eg. respiration, anabolic reactions, nerve impulses, heartbeats. Also need for maintenance of body temperature.)

3. For replacement of worn and damaged tissues (the substances provided by food are needed to replace: eg. the millions of red blood cells that break down each day, and to replace the skin which is worn away, and to repair wounds.)

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What are the 3 classes of food?

1. Carbohydrates

2. Proteins

3. Fats

See pages 11, and 12 to look at their chemical structures.

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Describe carbohydrates (2)

1. Carbohydrates are the cheapest and most readily available source of energy. One g of carbohydrate can provide 16kJ of energy. 

2. If we eat more carbohydrates than we need for our energy requirements, the excess is converted in the liver to either glycogen, or fat.

a. The glycogen is stored in the liver and muscles

b. The fat is stored in fat depots in the abdomen, round the kidneys, or under the skin.

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What are 3 major carbohydrates, and their uses?

1. Cellulose -> not digested by human enzymes -> useful as roughage (fibre)

2. Starch -> digested to sugar -> changed to glycogen -> stored in liver

-> stored in fat depots

3. Sugar -> absorbed as sugar -> oxidized in respiration -> for energy

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How are proteins used? (6)

1. They provide the chemical substances needed to build cells and tissues (eg. skin, muscle, blood, and bones). Neither carbohydrates, or fats can do this, so it's essential to have some ni your diet.

2. The long chains of amino acids are broken up into the constituent amino acids. 

3. The amino acids are absorbed into the bloodstream and are used to build up different proteins.

4. These proteins are used to form part of the cytoplasm (structural) and enzymes of cells and tissues.

5. The amino acids which are not used for making new tissues can't be stored, but the liver removes their amino (NH2) groups and changes the residue to glycogen. The glycogen can be stored or oxidized to provide energy.

1g of protein can provide 1kJ of energy.

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How are fats used?

1. In the cells of the body to form part of the cell membrane and the other membrane systems.

2. Lipisd can also be oxidized in respiration, to carbon dioxide and water

3. 1g of fat gives 37kJ of energy. This is twice as much energy as can be obtained from the same weight of carbohydrate or protein. 

4. Fats can be stored in the body, so providing a means of long-term storage in fat depots, within the adipose tissue, which can reduce heat loss.

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What must a diet include? (7)

1. Protein

2. Carbohydrates

3. Fats

4. Salts

5. Vitamin

6. Water

7. Vegetable fibre (roughage)

These substances are present in a balanced diet and do not normally have to be taken in seperately.

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Why do you need salts? (1)

Aka. mineral salts, or just minerals.

Proteins, carbohydrates, and fats provide the body with carbon, hydrogen, oxygen, and nitrogen, sulphur, and phosphorous but there are several more elements which the body needs which occur as salts in the food we eat.

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Why do you need iron? (3)

1. Red blood cells contain the pigment haemoglobin, that contains iron, and plays an important part of carrying oxygen round the body. Millions of red cells break down each day and their iron is stored by the liver and used to make more haemoglobin. Some iron is lost, and adults need about 15mg a day.

2. Iron is needed for muscles

3. Iron is needed for enzymes

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Why do you need calcium? (

1. It makes bone and teeth hard

2. Present in blood plasma

3. Plays an essential part in normal blood clotting

4. Needed for chemical changes which make muscles contract and for the transmission of nerve impulses.

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Why do you need iodine? (

1. Forms an essential part of the molecule of thyroxine

Only needed in small amounts.

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Why do you need phosphorous? (1)

1. Needed for the calcium phosphate of bone.

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What are the common features of all vitamins? (4)

1. They are not digested or broken down for energy

2. Mostly, they are not built into the body structures

3. They are essential in small quantities for health

4. They are needed for chemical reactions in the cells, working in association with enzymes.

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What are vitamins grouped into? (2)

1. Water-soluble

Green leaves, fruits, cereal grains

2. Fat-soluble

Animal fats, vegetable oils

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Why do you need dietary fibre (roughage)? (2)

Plant cells contain mainly cellulose, which we don't have enzymes to digest. Therefore, plant cell walls reach the large intestine (colon) without veing digested.

1. The colon contains many bacteria which can digest some of the substances in the plant cell walls to form fatty acids.

2. It softens faeces. The fibre and the bacteria that multiply from feeding on it add bulk to the contents of the colon and help it to retain water. 

These both prevent constipation and keep you healthy.

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Why do you need water? (4)

1. About 70% of most tissue consists of water; it is an essential part of the cytoplasm.

2. Body fluids, blood, lymph, and tissue fluid are composed of water.

3. Digested food, salts, and vitamins are carried round the body as a watery solution

4. Excess products (eg excess salt and urea) are removed from the body in solution by the kidneys.

QED: Water acts as a solvent and as a transport medium for these substances. 

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Describe the process of digestion. (2)

1. Digestion is a process that uses water in a chemical reaction to break down insoluble substances to soluble ones.

2. These products then pass, in solution, into the bloodstream.

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Describe what a balanced diet must contain. (3)

1. Enough carbohydrates and fats to meet energy needs (energy needed to keep internal body processes working, (eg. heart/breathing action) keep up body temperature, meet the needs of work and other activities.

2. Contain enough of the right kind of protein to provide the essential amino acids to make new cells and tissues for growth or repair.

3. Must contain vitamins and mineral salts, plant fibre, and water.

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How much protein do you need?

40g of protein.

You can get this from:

1. 200g of lean meat

2. 500g bread

3. 2kg potatoes 

The 3rd will NOT contain enough amino acids.

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What do vegans need to do? (1)


1. Diets need to include a good variety of cereal, peas, beans, and nuts in order to obtain all of the essential acids to build their body proteins.

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Pregnant women in relation to their diet? (2)

1. If they're already getting a good diet they need no extra food, as her body's metabolism will adapt to the growing baby.

2. If she has a vitamin, or protein deficiency, she will need to increase her intake to meet the needs of her baby.

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Lactation in relation to diet. (2)

The production of milk, rich in protein and minerals, makes a large demand on mother's resources.

1. If her diet is already good, then her metabolism will adjust to her baby.

2. Otherwise, increase intake of proteins, vitamins, and calcium to produce milk of adequate quality and quantity.

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Growing children in relation to diet. (2)

1. Most children up to the age of 12 need less food than adults, but they need more in proportion to their body weight.

2. Children need extra calcium for growing bones, iron for red blood cells, vitamin D to help calcify their bones, and vitamin A for disease resistance.

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What does malnutrition cause? (5)

If the total intake of food is not sufficient to meet the body's need for energy:

1. The body tissues are broken down to provide the energy to stay alive, which leads to:

2.  Loss of weight

3. Muscle wastage

4. Weakness

5. Starvation

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Describe causes of Western malnutrition. (3)

1. Refined sugar (sucrose)

2. Fats

3. Fibre

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How does refined sugar lead to malnutrition? (1)

It's a very concentrated form of energy, so you end up taking in more sugar than you need, which can lead to becoming overweight or obese.

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How do fats lead to malnutrition? (1)

1. Plaques are formed from lipids and cholesterol combined with proteins (low density lipoproteins, or LDLs). Although the liver makes LDLs, there is evidence that suggests that a high intake of saturated fats helps raise the level of LDL in the blood, and cause plaques. Plaques can lead to coronary heart disease, and strokes. 

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How does lack of fibre cause malnutrition? (1)

Many of the processed foods in Western diets contain too little fibre. Food rich in fibre makes you feel 'full up' so you are unlikely to overeat.

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What are the effects of obesity?

More likely to suffer from: 

1. High blood pressure

2. Coronary heart disease

3. Diabetes

4. The extra weight makes you reluctant to take exercise

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What causes obesity? (2)

1. Excess energy converted to fat

2. Potential genetetic predisposition

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How do you preserve food? (

1. Drying (dehydration)

2. Refrigeration and freezing

3. Canning

4. Pasteurization

5. Ultra-high temperature

6. Irradiation

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What are different food additives? (4)

1. Preservatives

2. Flavouring

3. Colouring

4. Bulking agents

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What is an example of active transport? (2)

1. Plants need to absorb mineral salts from the soil, but these salts are in a very dilute solution

2. Active transport enables the cells of the plant roots to take up salts from this dilute solution against the concentration gradient.

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