Unit 2 Animal NutritionWhat you need to be able to do:

2.1 Nutrition● Define nutrition

2.2 Nutrients● List the chemical elements which make up carbohydrates, fats and proteins● Describe the synthesis of large molecules from smaller basic units - simple sugars to starch and

glycogen, amino acids to proteins, fatty acids and glycerol to fats and oils● Describe tests for starch (iodine solution), reducing sugars (Benedict's solution), protein (biuret

test) and fats (ethanol)● List the principal sources of, and describe the importance of carbohydrates, fats, proteins,

vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage) and water● Describe the deficiency symptoms for vitamins (C and D only) and mineral salts (calcium and iron

only)● Describe the use of microorganisms in the food industry, with reference to yoghurt and

single cell protein● Describe uses, benefits and health hazards associated with food additives, including

colourings

2.3 Diet● State what is meant by the term balanced diet and describe a balanced diet related to the age,

sex and activity of an individual● Describe the effects of malnutrition in relation to starvation, coronary heart disease, constipation

and obesity

2.4 Food supply● Discuss the ways in which the use of modern technology has resulted in increased food

production to include modern agriculture machinery, chemical fertilisers, pesticides, herbicides and artificial selection

● Discuss the problems of world food supplies● Discuss the problems which contribute to famine - unequal distribution of food, drought, flooding,

increasing population

2.5 Human alimentary canal● Define ingestion● Define egestion ● Identify the main regions of the alimentary canal and associated organs including the mouth,

salivary glands, oesophagus, stomach, small intestine (duodenum and ileum),pancreas, liver, gall bladder, large intestine (colon and rectum) and anus

● Describe the functions of the regions of the alimentary canal listed above, in relation to - ingestion, digestion, absorption, assimilation and egestion of food

1

2.6 Mechanical and physical digestion● Define digestion● Identify the types of human teeth and describe their structure and functions● State the causes of dental decay and describe the proper care of teeth● Describe the process of chewing● Describe the role of longitudinal and circular muscles in peristalsis● Outline the role of bile in emulsifying fats, to increase the surface area for the action of enzymes● Describe how fluoride reduces tooth decay and explain arguments for and against the

addition of fluoride to public water supplies

2.7 Chemical Digestion● State the significance of chemical digestion in the alimentary canal, in producing small, soluble

molecules that can be absorbed● State where, in the alimentary canal amylase, protease and lipase enzymes are secreted● State the functions of a typical amylase, protease and lipase listing the substrate and end

products

2.8 Absorption● Define absorption ● Identify the small intestine as the region for absorption of digested food● Describe the significance of villi in increasing the internal surface area of the small intestine● Describe the structure of the villus, including the role of capillaries and lacteals● State the role of the hepatic portal vein in the transport of absorbed food to the liver.● Identify the role of the small intestine and colon in the absorption of water (the small

intestine absorbs 5-10 dm3 per day, the colon 0.3-0.5dm3 per day)

2.9 Assimilation● Describe assimilation as movement of digested food molecules into the cells of the body where

they are used, becoming part of the cells● Describe the role of the liver in the: metabolism of glucose to glycogen, amino acids into proteins

and the destruction of excess amino acids.● Describe the role of fat as an energy storage substance● Define deamination ● State that the liver is the site of breakdown of alcohol and other toxins

2.1 Nutrition

Define nutrition:

Why is it important?

2

2.2 Nutrients

Composition of Nutrients

What is a polymer?

Complete the diagrams to show the formation of polymers from these monomer units:

What chemical elements make up?a) carbohydrates

b) proteins

c) fatsPhenylalanine is in my favourite food - chocolate! Phenylalanine is a building block for a chemical called dopamine in your brain that makes you feel happy :)Read this article to find out other reasons why chocolate is good for you!http://www.thedailybeast.com/articles/2012/03/28/11-reasons-chocolate-is-good-for-your-health.html

Watch BrainPop “Body Chemistry” and answer the questions

What 4 elements make up most of our body weight?

What is the most abundant molecule in our body?

3

Name an important property of water and give 2 reasons why we need it.

What is the body’s main source of fuel?

Give some examples of lipids.

What jobs do lipids do in our bodies?

In what ways can too much lipid be bad for you?

What body systems are proteins involved in?

Give some examples of structural proteins.

Test for Starch

(a) Label four test-tubes 1- 4.(b) Put about 20 mm (depth) of 10% glucose solution into tube 1

1% starch solution into tube 2 1% albumen solution into tube 3distilled water into tube 4

(c) To each tube, using a dropping pipette, add three drops of iodine solution. Shake the tube (sideways, not up and down) to mix the contents. Look for any colour changes apart from the yellow colour of iodine itself. Complete the results table below. Results

Substance Colour change after adding iodine

4

10% glucose solution

1% starch solution

1% albumen solution

water

Conclusion1. The substances selected for testing are examples of three of the principle chemical substances in cells, sugar (glucose), starch, protein (albumen). With which of these substances did iodine react to give a colour change ? 2. Does your result indicate that there is, for example, no sugar and no protein that willgive a colour change with iodine ? 3. What experiments would you have to carry out in order to give a confident answer toquestion 2 ? 4. Does the result indicate that starch will always react with iodine solution to give acolour change?

5 What was the point of the water in tube 4 ?Test for reducing sugar (glucose)

a) Half fill a beaker with tap water and place it on a tripod and gauze. Heat thewater with a Bunsen burner. While waiting for the water to boil, carry on with instructions (b) to (d). (b) Label four test-tubes 1-4. 1% starch solution into tube 1 10% glucose solution into tube 2(c) Put 20 mm (depth) of 1% albumen solution into tube 3 water into tube 4 (d) To each tube add about 10 mm Benedict's solution. (e) Place the test-tubes in the beaker of hot water (see Figure on p. 2), and adjust the flame to keep the water just boiling (f) After about 5 minutes, turn out the flame. Place the four tubes in a test-tube rack and compare the

5

colours. Record the results in the table and match the final colours as nearly as possible with crayons.

Results

Solution Colour change on heating with Benedict’s reagent

Final colour (crayon)

1 1% starch

2 10% glucose

3 1% albumen

4 water

1. What colour change occurred when Benedict’s solution was added to each liquid?

2. The solutions selected for testing are examples of three of the principal chemical substances found in cells: glucose, starch, protein (albumen). With which of these food materials did Benedict's solution give a decisive change on heating? 3. Apart from the colour, what change took place in the consistency of the Benedict'ssolution ? 4. Do your results indicate that any sugar (e.g. sucrose, fructose and maltose) will give the same colour

6

as glucose did when tested with Benedict's solution? 5. Do your results allow you to say that (a) no protein will give a colour change whenheated with Benedict's solution, (b) albumen never reacts with Benedict's solution togive a colour change ? 6. Can you predict that glucose will always give the same result with Benedict's solutionas it did in your experiment ? 7. Why was water included in the test ?

Test for Protein

(a) Label four test-tubes 1-4. 1% starch solution into tube 1 10% glucose solution into tube 2(b) Put about 20 mm (depth) of 1% albumen solution into tube 3 water into tube 4 (c) Pour into each tube, about 5 mm dilute sodium hydroxide. (CARE *) (d) Add to this about 5 mm dilute copper sulphate solution. Shake the tube sideways tomix the contents. (e) Return the tubes to the rack, leave for a few seconds and record the resulting coloursin the table below: Results

Substance Reaction with copper sulphate and sodium hydroxide (Biuret reagent)

1

7

2

3

4

* CARE. Sodium hydroxide is caustic and dissolves clothing, skin and bench tops. It isdestructive rather than dangerous so if any is spilt on the bench, neutralize it at once with an equal volume of dilute hydrochloric acid and wipe dry. If spilt on clothing do the same but follow with a wash in as much water as possible. If spilt on the skin do not add acid but wash under the tap until the 'soapy' feeling is removed.

1. The substances you tested are examples of three of the principal types of chemical substances in cells; starch, sugar (glucose), protein (albumen). With which of these samples did the reaction give a purple colour? 2. The substance which gave a purple colour was a single example of its class of substances. Would you expect all other samples of this class to give the same reaction? 3. What was the point of using test-tube 4 with the water? NOTE This test is called the ‘biuret’ test. ‘Biuret’ is the name of the compound which gives the purple colour.

8

Test for Fats

ALL APPARATUS MUST BE DRY. ALL FLAMES MUST BE EXTINGUISHED. (a) Label four test-tubes 1-4. (b) Into tubes 1 and 2 pour about 20 mm (depth) alcohol (ethanol). (c) To tube 1 add one drop of vegetable oil, and shake the tube sideways until the oildissolves in the alcohol. (d) In tubes 3 and 4 pour about 20 mm water. (e) Pour the contents of tube 1 into tube 3 and the contents of tube 2 into tube 4. (f) Record your results as below:

Result when added to water

1 Oil dissolved in water

3

2 Alcohol alone 4

CLEANING THE TUBES. Keep the oily tubes separate from the others and clean them with hot water and liquid detergent.

1. What was the only difference between the contents of tubes 1 and 2 ? 2. What was the visible difference between tubes 3 and 4 after adding the contents of tubes 1 and 2 to the water in them?

9

3. How would you attempt to explain the appearance of the liquid in tube 3 ? 4. What difficulties can you foresee in using this test with samples which containboth lipids and water ? Testing for biological molecules in foodsUse the 4 tests above to find out what biological molecules are present in each of the food samples given to you.

Food Results with iodine Results with Benedict’s solution

Result with Biuret reagent

Result with ethanol

1. Which foods are a good source of the following?a) carbohydrates

b) proteins

c) fats

Revise the food tests http://lgfl.skoool.co.uk/content/keystage4/biology/pc/modules/digestion/food_tests/index.html in preparation for a quick test next lesson!

10

2.3 DietComplete the table below:

Component Function in our body Source

As a fuel for the process of respiration which releases energy

For growth and to repair damaged tissues, helps build muscle, skin and hair

For insulation, as a long term food store and to make cell membranes

To help food pass through the digestive system

Needed in very small amounts to keep us healthy, e.g. for good eyesight and healthy gums

Needed in very small amounts to keep us healthy, e.g. for strong bones and to make red blood cells

As a solvent, to transport substances around the body and to maintain our body temperature

What extra nutrients do these people need and why?

11

How much energy is in food?

Name of food Mass(g)

Temperature at start (oC)

Temperatureat end (oC)

Temperature rise (oC)

Calculation

To calculate energy released use this formula:

12

m = mass of water heated (g) 1 ml of water has a mass of 1g

c = 4.2 Jg-1oC (specific heat capacity of water) ∆T = temperature rise (oC)

Conclusion1. Calculate the energy released per gram of each food. Show your working and record your answers in a suitable format.

2. Which food contained the most energy and why? (Hint: think about what nutrients are in each type of food)

Evaluation

1.Identify the major sources of error in this experiment.

2.Suggest how the experiment could be improved.(Try to think of at least three ways)

Deficiency Diseases and MalnutritionDefine:Deficiency disease

Malnutrition

13

Match the disease to the symptoms and then find out the cause:

Problem Symptoms Cause

Excess weight for age and height. Risk of heart problems.

Wasted muscles,, enlarged liver, flaky skin and brittle hair.

Bleeding gums, flaky skin, poor wound healing.

Pale skin, tiredness, breathlessness, low levels of red blood cells

Poor bone development.

Bacteria produce acid that wears down tooth enamel.

Difficult to go to the toilet.

Headaches and thirst.

kwashiorkor, constipation, anaemia, obesity, tooth decay, rickets, scurvy, dehydrationTry past paper question 1.

14

15

16

Would you eat this for breakfast?The following lists show the ingredients in five foods. What do you think these foods are? Would you eat them for breakfast?

FOOD 1:WATER, SUGAR, CELLULOSE, MONOSODIUM GLUTAMATE (E621), CAROTENE (E160 A), LYCOPENE (E160D), RIBOFLAVIN (E101), ASCORBIC ACID (E300), CITRIC ACID (E330), MALIC ACID (E296), OXALIC ACID, FLAVOURINGS

FOOD 2:MYOSIN, ACTOMYOSIN, MYOGLOBIN, COLLAGEN, ELASTIN, AMINO ACIDS, CREATINE, LIPIDS, LINOLEIC ACID, OLEIC ACID, LECITHIN (E322), CHOLESTEROL, SUCROSE, GLUCOSE, PYROLIGNEOUS ACID, PHOSPHORUS, THIAMIN, RIBOFLAVIN (E101), NIACIN (E375), CYNAOCOBALAMIN, PYRIDOXINE, SODIUM CHLORIDE, IRON, MAGNESIUM, POTASSIUM

FOOD 3:LECITHIN S (E322), CEPHALINS, LYSOPHOSPHATIDYL CHOLINES, SPHINGOMYELLINS, CHOLESTEROL, AMINO ACIDS, AVIDIN, LUTEIN (E161B), ZEAXANTHIN, PYRIDOXINE, COBALAMIN, BIOTIN, CHOLECALCIFEROL

FOOD 4:GLUTEN, AMINO ACIDS, AMYLOSE, STARCHES, DEXTRIN, SUCROSE, PENTOSANS, HEXOSANS, MONO-, DI- AND TRI-GLYCERIDES, SODIUM CHLORIDE, PHOSPHORUS, CALCIUM, IRON, THIAMIN, RIBOFLAVIN (E101), NIACIN (E375), PANTOTHENIC ACID, VITAMIN D, METHYL ETHYL KETONE, ACETIC ACID (E260), PROPIONIC ACID (E280), BUTYRIC ACID, VALERIC ACID, CAPROIC ACID, ACETONE, MALTOL (E636), ETHYL ACETATE, ETHYL LACTATE

FOOD 5:WATER, CAFFEINE, METHANOL, ETHANOL, BUTANOL, ETHYL BUTANOL, ACETALDEHYDE, METHYL FORMATE, DIMETHYL SULPHIDE, PROPIONALDEHYDE, PYRIDINE, ACETIC ACID (E260), FURFURAL, FURFURYL ALCOHOL, ACETONE,METHYL ACETATE, FURAL, METHYLFURAN, DIACTYL ISOPRENE

Microorganisms and Food Production - Yeast

Use pages 52/53 Complete Biology for answers

Microorganisms have been used for hundreds of years to produce useful products for man.

Baking and brewing are two processes which rely on the __________________ of glucose by

17

yeast. Fermentation is a type of _______________ ____________________. Yeast is a type of

_____________. It secretes _____________ which catalyze the fermentation process.

The word equation for fermentation is :

Baking

Flour, _____________, water and salt are mixed with yeast and kneaded into a _____________.

The dough is kept warm and the yeast _______________ the sugar producing bubbles of

_____________ _______________ gas. This gas makes the dough _____________.

Cooking the bread ______________ the yeast and stops fermentation. It also evaporates the

________________ made by the fermentation. Brewing

________________ is used to provide a source of sugar for the yeast to ferment, whilst

____________ add flavor. Enzymes in the barley convert _____________ into maltose (a type of

sugar). Yeast and extra ___________ are added and the mixture allowed to ferment at _____oC.

The amount of ________________ produced by the fermentation reaction increases until it gets

to about 9% and then yeast cells die.

The processes of I SAID NO TILL ____________________ and IF CAT FORT ION

__________________ can be used to concentrate the alcohol and make it stronger.

In winemaking ________________ are used to provide the sugar and yeasts for fermentation. Questions

1. Why does fermentation stop at high temperatures?

18

2. Why does the fermentation of alcohol stop at 9%?

3. Write a balanced symbol equation for fermentation (given that glucose is C6H12O6 and ethanol C2H5OH).

4. 28oC is the optimum temperature for the enzymes in yeast Explain what this means.

Production of yogurt and mycoprotein

Fill in the missing words:

Production of yogurtBacteria (usually Streptococcus thermophilus and Lactobacillus bulgaricus) are used to ferment milk at

________. ___________ _______ is produced. As fermentation progresses, the ______ drops. The

lactic acid makes the milk ________________. The temperature is then ____________ to 5oC to prevent

further bacterial action.The whole process is carried out in ___________ conditions.

Mycoprotein

This is protein produced by microorganisms such as bacteria, fungi (e.g. yeast) or unicellular algae in a

fermentation vessel.

The first attempts to make microorganisms into food used yeast. In Germany during World War I, yeast

was cultured in large vats, using molasses (thick syrup produced during the refining of sugar) as food

source for the yeast, to produce a protein supplement for people.

More recently, different kinds of protoctists and bacteria have been grown for food production. The food

19

made from all of these microorganisms is called single cell protein or SCP.

The first SCP does not taste very nice, partly because they contained a lot of DNA and RNA, which taste

bitter. Most SCPs are now marketed as animal feed.

The only SCP which has found a market as human food is mycoprotein.

This is made from filamentous (thread-like) fungus (so, strictly, not single-cell protein). In Britain, the

fungus Fusarium is used for this purpose. It is made of hyphae rather than singles cells. But mycoprotein

is still called SCP.

The Fusarium is grown in large vats, using carbohydrates (e.g. waste from making flour) as a food

source. The fungus reproduces quickly and makes a mass of mycelium, which is harvested and treated

to remove a lot of the RNS it contains. Then it is dried, and shaped into chunks or cakes, ready for eating

as it is, or for making into pies or other foods.

Mycoprotein is a healthy alternative to meat because it has a high protein content (12%), very little fat, no

cholesterol, and a lot of fiber (6%). Some people think that mycoprotein looks and tastes a bit like

chicken.

Food Additives

Read more about the 14 year old burger here:

http://www.news.com.au/lifestyle/food/mcdonalds-burger-that-looks-the-same-as-day-it-was-cook

ed-14-years-ago/story-fneuz8zj-1226628424189

Read the information below and complete the table.

Food manufacturers often use food additives. These substances are added to food we eat to:● improve flavour or colour● improve the texture● preserve, that is slow down the speed at which food goes off.

Important groups of additives are acidulants, anti-caking agents, antioxidants,colours, emulsifiers and stabilisers, flavourings, preservatives and sweeteners.Food manufacturers must test all food additives to show that they are safe to eat and show that an additive is really needed in a product before the additive is allowed on the list of permitted additives.

Certain additives, like certain foods, can cause a small number of people to react badly to them. Such people need to avoid the food or food additive to which they are sensitive. To do this they must learn how to read the labels on food packages.

Food additives must be named on the food label; they are shown as: E-numbers, e.g. E440. or they may

20

be shown as their chemical name, e.g. pectin, or both, e.g. E440 - pectin.

The label must also say what sort of additive it is, e.g. gelling agent E440 - pectin. You will then know why the additive has been used.

Colours are found in the E100 series.

Preservatives are found in the E200 series.

Antioxidants are found in the E300 series.

Miscellaneous additives such as emulsifiers, gelling agents and stabilisers arefound in the E400 series.

Some products would not exist at all if additives were not used, e.g. processed cheese, low fat products, sugar-free products.Acidulants are added to food, such as soft drinks, desserts, jams, sweets, soups and sauces to give a better taste. They also act as a preservative.

Anti-caking agents are important in the manufacture of powdered foods. The small particles present in powdered food tend to stick together or cake. The addition of an anti-caking agent allows powders to flow more easily.

Antioxidants are used to stop our food reacting with oxygen in the air. Foods that contain fats and oils are particularly affected by oxygen. When this happens the fats and oils go rancid.

Colours make foods look good. Some processed foods lose their natural colour as they are being made, so colours are added to make them look appetising again.

Flavourings are added to manufactured foods in very small quantities to improve their taste.

Emulsifiers are used to make oil and water in products like ice cream mix together evenly.and stabilisers are also used to give products like yoghurt a smooth, even texture.

Preservatives are used to destroy bacteria and fungi or to slow down their growth. Some preservatives are simple substances such as vinegar (E260 - acetic acid). This is a natural substance. Other preservatives such as nitrates and nitrites (E249 - E252) are used in meat products to prevent the growth of very dangerous bacteria.However, they have a slight chance of causing some people health problems.

We only have 4 tastes. These are sweet (like sugar), sour (like lemons), bitter (like strongcoffee or tonic water) and salt. Most of us like to eat sweet tasting foods.

Scientists have tried to find or make substances which will make your food sweeter but which do not affect teeth or make people fat. These are called artificial sweeteners. A substance like this would also

21

be very useful for foods made for people who have diabetes. Artificial sweeteners can be added to many different products such as chocolate, jam and chewing gum.

Questions

1. Define a food additive.

2. What is an E number?

3. List 4 reasons why an additive may be added to food?4. What does an emulsifier do?

Complete the table below.

Type Example Found in Benefits Problems

Flavouringmonosodium glutamate (MSG)

Flavouringvanillin

Colouring Gives yellow/orange colour

Preservative

Preservative

Preservative

Go to http://www.understandingfoodadditives.org/index.htm to find out about food additives, their functions and their effects on health.

22

2.4 Food Supply

Go to: http://www.un.org/en/globalissues/briefingpapers/food/index.shtml to find out why people are going hungry. Complete the table below to describe the factors that cause famine:

Factor Detail

Climate

Poor soil

Desertification

Natural disasters

Poverty

Conflict (war)

Urbanisation

Increasing population

23

Watch the video on http://www.youtube.com/watch?v=udl9K6L1ekIList some ways that we can help reduce world hunger?

Complete a mind map of the use of modern technology in food production:

24

Try past paper question 2.

25

26

27

2.5 The Human Alimentary Canal

Digestive System Facts

● We eat about 500 kg of food each year. That’s half a ton or a horse!

28

● We produce 1.5 litres of saliva every day!

● Muscles contract in waves (peristalsis) to move your food down your oesophagus so food would

get to your stomach even if you were upside down!

● An adult stomach can hold 1.2 litres of liquid.

● The acid in your stomach is so strong it can kill bacteria and is of a similar strength to acid found

in industrial metal cleaner!

● The digestive system is about 8m long (about the same length as a bus!).

● Every day 10 litres of digested food, liquids and juices flow through the digestive system but only

80ml is lost in faeces (poo).

● The average poo is 75% water. The rest is fibre, dead cells and bacteria.

Watch BrainPop: “The Digestive system” and the BBC GCSE “Digestion” Video and make your own notes below:

Try the eChalk “Digestion” activity and label the diagram below:

29

On the diagram label where each of the following processes occurs - ingestion, egestion, digestion, absorption, assimilation

The parts of the Alimentary Canal

Match the structure to its function:

Teeth and tongue Stores bile produced by liver

30

Salivary glands Releases gastric juice containing hydrochloric acid and a protease enzyme called pepsin

Amylase Digested food molecules are absorbed into bloodstream here

Oesophagus Carries food from mouth to stomach

Stomach Release saliva containing amylase to break down starch into sugar (maltose)

Hydrochloric acid Break food molecules into smaller pieces to increase surface area for enzyme action

Protease enzyme(pepsin)

Produces enzymes (maltase and lactase) to break down carbohydrates maltose and lactose into glucose.

Duodenum (1st part of small intestine)

Digestion (break down) of food takes place here

Liver Produces green liquid called bile

Gall bladder Contains bile salts to break up large fat droplets into smaller droplets (emulsification) to increase surface area for lipase to work on

Bile duct Increase surface area for absorption of digested food molecules

Bile Kills bacteria

Pancreas Breaks starch into maltose (a type of sugar)

Wall of small intestine

Takes blood with food molecules to the liver

Ileum (2nd part of small intestine)

Breaks down protein. Works best at a low pH.

Villi Bile passes through here from gall bladder to duodenum

Hepatic portal vein Produces alkali liquid containing enzymes (amylase, protease, lipase)

The digestive system: eChalk Bounce Words

1. The colon, appendix and rectum make up the ...2. The duodenum and the ileum make up the ...3. The place where food is cut and ground down into smaller pieces4. Where water is absorbed and faeces are stored5. Joins the mouth to the stomach6. Churns the food and adds acid and digestive enzymes

31

7. Digested food substances are absorbed into the blood here8. Is also called the gullet 9. Stores excess sugar, makes bile and removes poisons from the blood10. The place where faeces is egested through a sphincter11. Has strong muscular walls which push the food by peristalsis towards the stomach12. Makes insulin and digestive enzymes (amylase, lipase and protease)13. Produces mucus (which helps us to swallow food) and amylase (which catalyses the breakdown of starch). It would be difficult to spit without these!14. Bile is produced by this organ (bile is then stored in the ‘gall bladder’)15. Chewed food from the mouth passes into the ...16. After passing through the oesophagus food enters the ...17. After passing through the stomach food enters the ...18. After passing through the small intestine food enters the ...19. After passing through the large intestine food exits the body via the ...20. This part of the digestive system is around 6 to 7 metres long (or 19 to 23 foot) in the average person

2.6 Mechanical and Physical DigestionTeeth

32

Complete the table:

Label the diagrams:

33

Match the tooth to its description:

34

Incisors Found behind the canines and are used to grind soft food.

Canines Sharp pointed teeth, which are used to bite and tear food.

Premolars Found behind the premolars and are used to grind hard food.

Molars Small rectangular shaped teeth, used for cutting food.

Try past paper question 3.

35

36

37

38

39

Try past paper question 4.

40

41

42

43

PeristalsisWatch the echalk animation and then use the diagram to explain how peristalsis works:

BileWatch the animation at http://www.biologyinmotion.com/bile/index.html and draw an annotated diagram to explain how bile helps the digestion of fats.Use these words in your explanation: emulsification, bile salts, surface area, enzymes, gall bladder,

44

droplets

2.7 Chemical DigestionRead the information then complete the table and answer the questions that follow: Think about a turkey sandwich (yum!). It contains starch, protein and fat. All three of these substances are solids, but as they pass along the alimentary canal they are broken down into soluble substances. These substances are then absorbed through the walls of the small intestine and taken by the blood to wherever it is needed. The teeth, lips and tongue start breaking up the food by mechanical digestion. Chewing makes the pieces of food smaller, but doesn’t change the chemistry of the food (see, I knew I could bring chemistry into this!) Chemical digestion involves enzymes. These are chemicals which help to break down different parts of food into simpler, soluble molecules. Enzymes are affected by the conditions under which they have to

45

work (a bit like you lot!). When it’s too cold they work slowly and when it’s too hot they don’t work at all! Of course you already know that they denature. The pH can also affect enzymes. Some enzymes like acid conditions and others prefer alkaline. The conditions in the different parts of the digestive system are perfect for the enzymes that have to work there. Most digestive enzymes work best at about 40oC. This is the optimum temperature for enzyme activity. Saliva is made in the salivary glands. It contains the enzyme amylase which breaks down starch into a sugar called maltose. Maltose is a disaccharide made up of two glucose molecules joined together. You start producing saliva before food reaches your mouth. The sight, smell and thought of food helps to get the juices flowing! Amylase is the first enzyme that starts breaking up the sandwich. Cells in the walls of the stomach produce gastric juice which contains the enzyme pepsin. Pepsin helps to dissolve protein into amino acids. Pepsin likes a low pH to work best. This isn’t a problem most of the time, but occasionally when you overindulge, the contents of the stomach can leak out and cause painful acid indigestion or heartburn. The small intestine receives fluids from three different places. The liver produces bile. This isn’t an enzyme but works rather like detergent, breaking up large globules of fat into small droplets which can be dealt with more easily by enzymes. The pancreas produces three important enzymes. Amylase, trypsin and lipase. Trypsin breaks proteins down into smaller polypeptides, as pepsin does in the stomach. Lipase attacks fat, breaking it up into fatty acids and glycerol. Glands in the walls of the small intestine produce further enzymes which finish the process of digestion. Maltase breaks maltase down into glucose. Peptidases complete the digestion of proteins by breaking polypeptides into amino acids. The contents of the small intestine are alkaline. This is due to sodium hydrogen carbonate, a chemical produced by the body which neutralizes stomach acid. It is also found in indigestion remedies, its more common name is bicarbonate of soda.

Activities

1. Read through the information carefully and highlight in red the names of the different parts of the digestive system.

2. Now, using a green crayon, highlight the names of the different enzymes.

3. Using a blue crayon, circle where the enzymes are made.

4. Use the information you have highlighted to complete the table below.

46

Where the enzyme is made

Where the enzyme works

Name of enzyme

Food broken down

Substances produced

Salivary glands

Protein

Small intestine

Maltase

Sucrase

Peptidases

Sucrose Glucose and fructose

Questions

1. Which part of the turkey sandwich was made up of protein, which part was fat and which part was carbohydrate?

2. Why does food need to be broken down?

3. Maltose is a disaccharide. What is starch?

4. Enzymes work best at about 40oC. What is significant about this temperature?

47

5. Fat is broken down by only one enzyme, lipase. Suggest why proteins and carbohydrates are

broken down in two stages.

6. What two chemicals does the body produce to ensure that the digestive enzymes work effectively?

2.8 AbsorptionDefine these processes:

Ingestion

Digestion

Absorption

Assimilation

Egestion

Label the villus below:

48

Adaptations of the small intestine for absorptionComplete the table:

Feature How this helps absorption

Very _________ Gives plenty of __________ for digestion and for ___________________ to occur

Has __________ Give the small intestine a ________ _____________ ____________ (LSA) to increase the rate of absoprtion

Villi contain _____________________

To maintain ____________ _____________ and to carry products of digestion to the rest of the ______

Villi have ___________________ For absoprtion of ___________

Villi have walls only ______ _______ Short distance for _________________ of

49

____________ digested food

Review

What is the purpose of digestion?

List in order the organs of the digestive system

What are the tests for

a) Starch?

b) Glucose?

Evaluating Visking tubing as a model for a gut

In this practical you can:· observe the properties of Visking tubing· compare the properties of Visking tubing with the properties of a gut

ProcedureSAFETY: Wear eye protection when handling chemicals.

Visking tubing is a fine smooth membrane with small holes in it. These holes are large enough to allow water and other small molecules through. They are too small to allow large molecules through.

Before you start1. Draw a labelled diagram of the equipment

50

2. Explain what each part of the apparatus represents:

a. Contents of visking tubing

b. Solution around visking tubing

c. Visking tubing itself

3. Predict what you expect to see when you test the water in the boiling tube for starch and sugar.

Investigationa Set up a boiling tube and four test tubes in a rack.b Set out a dimple tile, with dropper bottles of iodine solution and Benedict’s reagent in your work area.c Collect a model gut made of Visking tubing.d Use syringes to put 5 cm3 of starch suspension and 5cm3 of glucose solution into your model gut.e Rinse the outside of the Visking tubing under the tap then suspend it in your boiling tube as shown in the diagram.

f Use a teat pipette to remove about 1 cm3 of the “gut” contents. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back into the Visking tubing.g With a second pipette, put water into the boiling tube until its level is the same as the gut contents.h Start a stopclock.i Immediately use the second teat pipette to remove about 1 cm3 of the water. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back in the water outside the Visking tubing.

51

j Test the drops of liquid in the dimple tile by adding one drop of iodine solution from the dropper bottle. If they turn blue-black, the liquid contains starch.k Test the liquids in the test tubes by adding an equal volume of Benedict’s reagent and then place the test tubes in a beaker of boiling water for 2 to 3 minutes. If they turn orange (or greeny-yellow), the liquid contains glucose.l After 15 minutes, sample the liquids inside and outside the tubing again. Ensure that you have a fresh sample by squeezing the pipette a couple of times to expel the remnants of any earlier sample and to mix the liquids well before sampling.m Test a drop of each liquid with iodine solution and 1 cm3 with Benedict’s reagent as in j and k.n Record your results in the table below.

Results

Result of test with iodine

Result of test with Benedict’s reagent

Does the liquid contain starch?

Does the liquid contain glucose?

Gut contents at beginning

Water around gut at beginning

Gut contents after 15 minutes

Water around gut after 15 minutes

Questions

1 What was the purpose of taking samples from the Visking tubing and surrounding water immediately after water was poured around the tubing?

2 From your results, do you think that starch can get through the holes in the Visking tubing membrane? 3 From your results, do you think that glucose can get through the holes in the membrane?

52

4 What does this tell you about starch and glucose molecules?

5 How is this length of Visking tubing containing starch and glucose similar to the gut of a multicellular organism?

6 What features of a real gut are missing from this model?Try past paper question 5.

53

Now try past paper question 6.

54

55

56

57

58

The role of the liverLabel the diagram:

59

Complete the table below:

Explain why it is important for blood to go from the digestive system to the liver before the digested food is distributed to the rest of the body?

Define the termsAssimilation

Deamination

What happens to the digested fats?

60

Why are fats used as a long term energy store?

What other important jobs does the liver do?

Absorption of water

What is the total volume of water that enters the alimentary canal?

Where is most water reabsorbed?

What do you think happens when we get diarrhoea and what health problems can this cause?

Answers to past paper questions

1.

61

2.

62

3.

63

4.

64

5.

65

6.

66

67

68