Enzymes

Digestion is the breaking down of large insoluble molecules into smaller soluble molecules that can be absorbed into the blood stream. Enzymes carry out chemical digestion and help to break down the food.Enzymes are molecules that speed up chemical reactions. An enzyme is similar to a lock and the substrate is the key. Both have shapes complimentary to each other.

There are many types of enzymes but the main enzymes we are looking at are associated with digestion. Look at the table below. It specifies the names of enzymes, where they are found, what they break down and what are produced.  

Name of enzyme

Found Substrate Product

Carbohydrase

e.g.amylase

Mouth, Pancreas and Small intestine

Carbohydrates Glucose (for energy)

Lipase Pancreas and small intestine

Fat (lipid) Fatty acids and Glycerol (storage of energy)

Protease Stomach, pancreas and small intestines

Protein Amino Acids (used to make new proteins)

Temperature and enzymes

Enzymes work best at particular temperatures. The temperature that an enzyme works best at and can chop up more substrates and release more products at is called the optimum temperature. If an enzyme goes above its optimum temperature it becomes denatured. This means that its active site has changed shape and the substrate can no longer bind to the enzyme like a lock and key, therefore no products can be formed.

Questions: Answer in full sentences in your books – Mark /191. What does optimum temperature mean? (1)2. What happens to an enzyme above its optimum temperature? (2)3. Name three enzymes? (3)4. What do all enzymes end in? (1)5. What is the job of an enzyme? (1)6. What are the products that come out of digestion? (4)7. Which enzyme breaks down proteins, and what does it break them

down into? (2)8. Which enzyme breaks down carbohydrates, and what does it break

them down into? (2)9. Which enzyme breaks down fats, and what does it break them down

into? (2)10. When an enzyme and substrate bind together what do they

form? (1)

Testing the food groups

Now that you know which enzyme breaks down which food group, you are now going to carry out a series of food tests to see how you test for each food group and what happens for positive and negative results.Watch the demonstration by the teacher and then carry out the tests in groups.Testing for protein

Place a couple of drops of the protein solution into the dimple tray. Place a couple of drops of the biuret reagent in with it. Note the colour change.

Food type Starting colour Positive result

Testing for starch Place a couple of drops of the starch solution into the dimple tray. Place a couple of drops of iodine in with it (beware iodine stains). Note the colour change.

Food type Starting colour Positive result

Testing for glucose

Place 2ml of glucose solution into a boiling tube. Place 10 drops of Benedict’s solution into the boiling tube as well. Boil the kettle and fill a beaker half full/use Bunsen burners and heat

half a beaker of water. Use this as a water bath to sit the boiling tube in. Note the colour change.

Food type Starting colour Positive result

The Digestive SystemLook at the diagram of the digestive system below. Each part is

labelled with information. Do you think food travels through every part of the digestive system?

Questions- answer in full sentences in your books.1. Write down the order of the digestive organs that food travels through.2. Where is protein digested in our body?

1

2

3

4

5

6

3. Imagine you ate a chicken sandwich that contained butter. What food groups would you have eating?

4. Write down the journey of the chicken sandwich. Include the pathway through the digestive system and where each food group is broken down. Finish at the large intestines.

5. Where is bile made and stored?6. Write down the different parts in you books correctly matched up with

the definition below.

Peristalsis

Food is moved the digestive system by a process known as peristalsis. This is the contractions of two sets of muscles in the walls of the gut. One set runs along the gut, while the other set circles it. Their wave-like contractions and relaxation creates a squeezing action, moving food down the gut. Similar to squeezing a tube of toothpaste. This occurs from the oesophagus to the stomach as well as along the small intestines into the large and finally through the rectum.

Mouth

Oesophagus

Stomach

Small intestine

Large intestineAnus

Water is absorbed from the waste matter back into

the blood stream here.

Waste leaves the body here.Food is chewed and mixed

with saliva here.

Food travels from the mouth down to the

stomach in this pipe.Food is mixed with acid and broken down here.The rest of the food is

broken down and nutrients are absorbed here.

1. When you swallow food is pushed down into your oesophagus.2. The oesophagus has muscles that push the food down into your

stomach like a peristaltic wave.3. The stomach muscles contracts and churns the food around and mixes

it with digestive juices and acid. It then continues the toothpaste like squeeze, pushing food into the small intestines.

4. The small intestine does this same rhythmic squeezing, continuing the peristaltic action to push the food along. The small intestine absorbs the nutrients from the food as the food moves along the gut.  

5. The large intestine (the colon, or large bowel) absorbs the water from whatever is left from digestion. This allows the body to keep the water, which it needs; and turns the mostly liquid stool or faecal matter into something more solid and easier to excrete.

6. The rectum. Peristalsis delivers faecal matter (okay let’s just say it poop), to your rectum where it builds up. When there’s enough to form a “stool” you get the urge to defecate (to go to the toilet for a poop). Then with one last peristaltic push, the food you ate and digested gets squeezed out as waste.

When things go wrong with peristalsis you end up with bowel cramps, constipation, diarrhoea and abdominal pain.

Questions – answer in full sentences in your books.

1. Consider the movement peristalsis. What do muscles need to move? What part of an animal cell would release this? And what two reactants are needed? Answer this question as a paragraph with full sentences.

2. Do plants carry out peristalsis? Explain your answer. 3. Sometimes people with a muscle wastage disease struggle

swallowing and absorbing nutrients. Why do you think that is?4. Caffeine is known to stimulate peristalsis in the large intestines.

What affect do you think this will have on your body? Bile

After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. Bile is an alkaline substance produced by the liver and stored in the gall bladder. It is secreted into the bolus (food) as it passes the liver to work in the small intestine. Bile also emulsifies large fat

globules into smaller fat droplets. This is important, because it provides a larger surface area on which lipase can work. Bile salts are made from cholesterol. Cholesterol is good for your body in small quantities. If you have excess cholesterol it could cause gall stones in the gall bladder.

Questions – answer in full sentences in your books.1. Name the organ where bile is produced.2. Name the organ where bile is stored.3. The table below shows the results of an experiment to investigate

the digestion of the fat olive oil. The content of three test tubes are shown in the table. The contents of the test tubes were analysed for the presence of fatty acids every 5 minutes for a period of 30 minutes.

a) Bile plays a very important role in the digestion of lipids but the results in Tube 2 show that it is not directly involved in the production of fatty acids. Describe the role played by bile in the digestion of fats.

b) Apart from fatty acids, name another product of fat digestion which could have been tested for during the experiment.

4. What is meant by a large surface area? Use a diagram and the information on bile to answer this question.

5. What would have happened if the water that was added to all the tubes was boiling water? Would we have observed any changes in any of the three tubes?

The small intestineThis is the ONLY place where absorption takes place. The small intestines is approximately 6 metres long in an adult which enables maximum absorption of products from digestion. It has a large surface area created by villi and has a very good blood supply to maintain a concentration for diffusion. The small intestines consists of two sections; the duodenum and the ileum. DuodenumThis is where all of the enzymes that have been produced and secreted by the pancreas function. They work on substrates to complete digestion into products.

The duodenum is the part of the gut that leaves the stomach. When liver releases bile it is secreted into this section. When the pancreas releases enzymes they are secreted into this section. It is the last chance in your body for digestion to occur. Carbohydrase, lipase and protease are all secreted into the duodenum to ensure maximum digestion.

IleumThe ileum is where we see absorption taking place. All of the products that have come out of digestion are absorbed into the blood or lacteal. Products that come out of carbohydrate digestion and protein digestion are absorbed into the bloodstream whereas products that come out of fat digestion are absorbed into the lacteal. The ileum has a very dense network of capillaries to aid diffusion, thin walls for a short diffusion pathway and finger-like structures called villi which increases surface area.

Questions – answer in full sentences in your books.

1. Name the products of digestion that move into the blood.2. Name the products of digestion that move into the lacteal.3. What is the definition of diffusion?4. What are the adaptations of the small intestines that aid diffusion? 5. Give a reason why it would be a bad idea if fat was absorbed into

the blood. 6. Give one difference between the duodenum and the ileum.7. What processes pushed food into the duodenum and along the

intestines?8. Fibre is not broken down and so is not absorbed by the small

intestine. Why do you think a balanced diet requires fibre?Models used to show the digestive system and the small intestines. Digestive system Your teacher will now demonstrate how food travels through the body. For each part of the model, state which section of the digestive system it represents and its function.Parts: - Pestle and mortar, funnel and rubber tubing, conical flask with bung, tights, elastic band at the end of the tights and bottle of solutions.Small intestinesVisking tubing is a fine smooth membrane with small holes in it. These holes are large enough to allow water and other small molecules through.

Villi

Lacteal

Blood capillaries

Thin walls

They are too small to allow large molecules through. Starch is classed as a large molecule while glucose is a small soluble molecule. You can test for starch using Iodine solution, it starts off a brown/yellow colour and turns blue/black is starch is present. You can test for glucose using Benedict’s solution, it starts off as a blue colour and turns brick red (requires heat as a trigger) if glucose is present. Questions

1. Design an experiment to show how the properties of visking tube can show what happens in the small intestines. Apparatus available are a piece of visking tube, syringe, boiling tube, 10cm³ starch and 2cm³ of amylase, stopwatch, water bath, pipette, spotting tile, Iodine solution and Benedict’s solution. Write a method that involves all the apparatus listed.

2. What would you expect to see and why?

A balanced diet – ICT taskIn order to stay healthy it is really important that we have a balanced diet. This means having a little bit of everything.ICT research – Use the computers to find out the following information:

Nutrient Use in the body Found in these foods

ProteinCarbohydrates

FatsMineralsWater

VitaminsFibre

Health implications of excess sugar, fats and salts from foodType of additive Why add it? Health problem

Sugar To make it sweet and to increase its shelf

life.

Type 2 diabetes, obesity and tooth

decayFat To increase taste. Obesity and heart

disease.Salt To increase taste and

the shelf life.High blood pressure.

Pick one of the health problems to research. You have to make an information leaflet about the condition from your research.Success criteria

It must tell you what the condition actually is.

It must include symptoms for the condition. It must include how to avoid getting the condition and any

treatments. It must include a diagram/picture. It must be eye catching and easy to understand. Sources have been referenced.

Peer assessmentSwap leaflets with your partner and using the criteria above peer assess using two stars and a wish in green pen.

Finding out the energy content in foodEnergy can never be created or produced, it can only ever by converted or transferred. The food that we eat contains stored energy which we release during digestion. We can test to see how much food is stored in certain food by capturing some energy in water. Method

1. Use the measuring cylinder to measure 20 cm3 of water into the boiling tube.

2. Clamp the boiling tube to the clamp stand.

3. Measure the temperature of the water with the thermometer. Record the temperature in a suitable results table.

4. Choose a piece of food and find its mass using the balance. Record the mass in the table.

5. Impale the piece of food carefully on a mounted needle. 6. Light the Bunsen burner and hold the food in the flame until it

catches alight. 7. As soon as the food is alight put it under the boiling-tube of water as

shown. Try to make sure as much of the heat from the burning food as possible is transferred to the water, by keeping the flame under the tube.

8. Hold the food in place until the food has burnt completely. If the flame goes out, but the food is not completely burnt, quickly light it again using the Bunsen burner and replace the food beneath the tube.

9. As soon as the food has burned away completely and the flame has gone out, measure the temperature of the water again. Before

Food type Mass (g) Temperature ºCStart End Change

measuring, stir the water carefully with the thermometer and note down the highest temperature reached in the results table.

10. Repeat the procedure for other foods. 11. Calculate the rise in temperature each time. 12. Calculate the energy released from each food by using this

formula.

4.2 is the value of the specific heat capacity of water, in joules per gram per degree Celsius – the number of joules taken to raise the temperature of water by 1ºC.

1 cm3 of water has a mass of 1 g. If the number is more than 1000 J/g, express it as kilojoules (kJ):

1 kilojoule = 1000 joulesQuestions – answer in full sentences in your book

1. Compare your answers for the amount of energy in any food with the answers obtained by other groups in the class. What is the range of values measured by the class? Do any of the results look anomalous? What is the mean average value?

2. Compare your class’s answer for the energy in any food to the official value given for the food on its packet. Are your class results close to the official numbers? Are they higher or lower? If they are lower, you must be under-estimating the energy released from the food.

3. How could you improve your procedure or apparatus to overcome this?

4. This picture shows a piece of apparatus manufactured to measure the energy released from food. It is called a calorimeter. List as many things as you can see that make it an improvement to the apparatus used in your investigation.

5. Which foods give the most energy per gram? Are they most rich in fat, carbohydrate or protein?

6. What is the name of the process in living organisms that releases energy from food?

7. Write a word equation for this reaction. Is it the same as the reaction used in the investigation? Explain your answer.

8. What do living organisms do with the energy released from their food?

Organ transplant debateWales now has an opt out organ donation policy. On 1 December 2015, Wales was the first country in the UK to move to a soft opt-out system of consent to organ donation. This means that if a person has not registered a decision to become an organ donor (opted in) or a decision not to become an organ donor (opted out), they will be considered as having no objection to being an organ donor – this is known as deemed consent. However, if individuals don’t tell their family of their decision to donate, the family may not honour that decision and over-ride the organ donor registration or not support deemed consent. The latest Organ Donation and Transplantation statistics reveal a 72% consent rate and approximately 24.3 donors per million population,

putting Wales at the top of the list. Statistics also show that 39% of the Welsh population have registered to opt-in to donate their organs following their death.TaskBelow are some profiles of patients who require an organ transplant.

1. Read each profile.2. Decide who should receive your donation.3. Rank the priority of the others.4. Now write a persuasive letter to argue your choice.

Profiles

Organ transplant research taskYour teacher will show you a video on tranplants. You will watch this before going to a computer room.

https://www.tes.com/teaching-resource/teachers-tv-organ-transplantation-animated-chat-6047935 Task1. What do you think about the video? What issues does it raise?2. You are going to do some research on organ transplant all around the

world.Complete the sentences in your books based on your research.

a) There are different types of organ donations:- T………………………, T……………….. and X……………

b) I think that xenotransplants would/would not be better than human organs transplants because………………………….

c) I think that if a person wants to donate their organs then it is/is not up to the family left following death because…………………………………….