B3 - Organisation and The Digestive System

What are cells?

The basic building blocks of all living organisms.

What is a tissue?

A tissue is a group of cells with similar structure and function working together.

What are organs?

Organs are collections of tissues all working together to perform a specific function.

What tissues does the stomach contain?

• Muscular tissue churns the food and digestive juices together.

• Glandular tissue to produce the digestive juices.

• Epithelial tissue covers the inside and the outside of the organ.

What are organ systems?

Groups of organs that all work together to perform specific functions.

Organ Systems work together to form organisms.

What are examples of organ systems?

• The digestive system

• The circulatory system

• The gas exchange system

How long is the human digestive system?

Between 6 and 9m long.

What does the digestive system do?

The food you take in is made up of large insoluble molecules. Your body cannot absorb and use these molecules. The digestive system does digestion, a process where these large insoluble molecules are broken down or digested to form smaller, soluble molecules. These molecules can then be absorbed and used by your cells.

What is the digestive system?

A muscular tube that squeezes your food through it, starting at your mouth and finishing at the anus.

What organs are in the digestive system?

• The pancreas

• The salivary glands

• The stomach

• The small intestine

• The large intestine

• The rectum

• The anus

• The liver

Explain the process of digestion in the digestive system.

• The pancreas and the salivary glands make and release digestive juices containing enzymes to break down your food.

• The stomach and the small intestine digest the food using the digestive juices, where enzymes break down the large insoluble food molecules into smaller, soluble ones.

• The small intestine is where the soluble food molecules are absorbed into your blood.

• The muscular walls of the small intestine squeeze the undigested food into your large intestine.

• Water from the undigested food is absorbed into your blood.

• The material left forms faeces.

• The faeces are stored and then pass out of your body through the rectum and anus.

Explain the adaptations of the small intestine.

• Covered in villi - large surface area.

• Good blood supply and short diffusion distances to blood vessels - increased rate of diffusion and active transport.

How is the liver linked to the digestive system?

It produces bile, helping in the digestion of lipids.

What are the main compounds that make up the structure of a cell?

Carbohydrates, lipids, and proteins.

What are carbohydrates, lipids, and proteins?

Large molecules that are often made up by smaller molecules joined together.

What do carbs do?

They provide us with the fuel that makes all of the other reactions of life possible.

What elements do carbs contain?

Carbon, oxygen, and hydrogen.

What are all carbs made out of?

Units of sugars.

Explain single sugars.

Carbohydrates that contain only one sugar unit.

For example, glucose.

Explain simple sugars.

Carbohydrates that are made up of two sugar units joined together.

For example, sucrose.

Explain complex carbs.

Carbs that are made up of long chains of simple sugar units bonded together.

For example, starch and cellulose.

What are some examples of carb-rich foods?

• Bread

• Potatoes

• Rice

• Pasta

What are lipids?

Fats (solids) and oils (liquids).

• The most efficient energy store in your body and an important source of energy in your diet.

What are lipids made of?

• Carbon

• Hydrogen

• Oxygen

Are lipids soluble or insoluble?

All lipids are insoluble in water.

What’s the structure of lipids?

Three molecules of fatty acids joined to a molecule of glycerol.

What are examples of lipid-rich foods?

• Oils

• Butter

• Margarine

• Cheese

• Cream

How is it decided if a lipid is solid or liquid?

The combination of fatty acids.

What are proteins used for?

Building up the cells and tissues of your body, as well as the basis of all your enzymes.

What percentage of your body mass is protein?

Between 15/16%

What is protein found in in your body?

Tissues ranging from your hair and nails to the muscles that move you around and the enzymes that control your body chemistry.

What foods are protein-rich?

• Meat

• Fish

• Pulses

• Cheese

What elements are proteins made from?

• Carbon

• Hydrogen

• Oxygen

• Nitrogen

What are protein molecules’ structure?

Long chains of small units called amino acids joined together by special bonds.

How many different amino acids are there?

About 20.

How is the type of protein decided?

The different arrangements of the various amino acids.

How are proteins made?

• Long chains of amino acids are folded, coiled, and twisted to make specific 3D shapes.

• These specific shapes enable other molecules to fit into the protein.

Why is it easy for protein to be denatured?

• The bonds that hold the proteins in 3D shapes are very sensitive to temperature and pH, and therefore can be easily broken.

• If this happens, the shape of the protein is lost and may not function any more in your cells - the protein is denatured.

What different functions to proteins carry out in your body?

They act as:

• Hormones such as insulin.

• Antibodies, destroying pathogens and part of the immune system.

• Enzymes, catalysts.

• Structural components of tissues such as muscles and tendons.

What is the food test for carbohydrates?

• Iodine test for starch -

  • Yellow-red iodine solution turns blue-black if starch is present.

• Benedict's test for sugars -

  • Blue benedict's solution turns brick red on heating if a sugar such as glucose is present.

What is the food test for protein?

• Biuret test -

  • Blue biuret reagent turns purple if protein is present.

  • Biuret solution is corrosive - wear chemical and splash-proof eye protection.

What is the food test for lipids?

• Ethanol test -

  • Ethanol added to a solution gives a cloudy white layer if a lipid is present.

  • Ethanol is highly flammable and harmful.

Why are catalysts used?

To speed up reactions.

How many times can catalysts be used?

A catalyst can be used over and over again.

What are enzymes?

Large protein molecules with an active site that has a unique shape so it can bind to a specific substrate molecule.

How do enzymes work (lock and key theory)?

• The substrate of the reaction to be catalysed fits into the active site of the enzyme.

• The enzyme and the substrate bind together.

• The reaction then takes place rapidly - products are released from the surface of the enzyme.

What is the metabolism?

The sum of all the reactions in a cell or body. Enzymes control this.

What are examples of enzymes catalysing different metabolic reactions (3)?

• Building large molecules from lots of smaller ones.

• Changing one molecule into another.

• Breaking down large molecules into smaller ones.

How many chemical reactions happen at once in each cell?

A hundred or more.

What effect does temperature have on enzymes?

The rate of enzyme-controlled reactions increases as the temperature increases.

However, this is only true up to temperatures of about 40°C.

What happens to enzymes when temperature is too high?

• The protein structure of the enzyme is affected by the high temperature.

• The long amino acid chains begin to unravel.

• The shape of the active site changes - the substrate no longer fits.

• The enzyme is now denatured.

What is usually the best temperature for enzymes?

37°C

Why is it dangerous to have a high temperature when ill?

Because without enzymes, none of the reactions in your body would be fast enough. Therefore, once your body temperature gets too high, your enzymes start to denature, which will result in death.

What is the effect of pH on enzyme action?

A change in pH affects the forces that hold the shape of an enzyme and therefore active site.

• The specific shape of the active site is lost.

• The enzyme no longer catalyses.

How are digestive enzymes different from regular enzymes?

Most enzymes work inside the cells of your body. Digestive enzymes work outside the cells.

Where are digestive enzymes produced?

• Specialised cells in glands

  • salivary gland

  • pancreas

  • etc.

• The lining of your digestive system.

What happens after digestive enzyme production?

The enzymes pass out of the production cells into the digestive system itself, where they come into contact with food molecules.

Why does the digestive system break up your food into small pieces?

So that there is a large surface area for your enzymes to work on.

How does the digestive system mix food with enzymes?

By mixing your food with the digestive juices.

How does your digestive system allow the enzymes in different regions to work as efficiently as possible?

By having different areas of the digestive system with different pH levels.

What are the names for the enzymes that break down carbs?

Carbohydrases.

What breaks down starch?

Amylase

What is starch broken down into?

Sugars

Where is amylase produced?

• Salivary glands

• Pancreas

Where does the digestion of starch start and end?

Starts in the mouth → no digestion takes place in the pancreas → all of the enzymes from the pancreas flow into the small intestine, where most of the starchyou eat is digested.

What are the names of enzymes that break down proteins?

Proteases.

Where are proteases produced?

• Stomach

• Pancreas

• Small intestine

What are proteins broken down into?

Amino acids.

What enzyme breaks down lipids?

Lipase.

Where is lipase made?

• Pancreas

• Small intestine

What are lipids broken down into?

• Fatty acids

• Glycerol

What happens once all your food molecules have been digested into soluble molecules?

The glucose, amino acids, fatty acids, and glycerol leave your small intestine and pass into your bloodstream to be carried around the body to the cells that need them.

What is the effect of pH on the rate of reaction of amylase (required practical)?

Required Practical 5 -

Equipment:

• Test tubes

• A test tube rack

• Water baths

• Spotting tiles

• 5cm³ measuring cylinder

• Syringes

• A stirring rod

• A stopwatch

• Starch solution

• Amylase solution

• Buffered solutions

• Iodine solution

• Thermometer

Method:

1. Place one drop of iodine solution into each well of a spotting tile.

2. Add 2cm³ of starch solution to a test tube.

3. Add 2cm³ of amylase solution to a different test tube.

4. Add 2cm³ of pH 5 buffered solution to another test tube.

5. Place all 3 test tubes in a water bath at 30°C. Leave them for 10 minutes to allow the solutions to reach the correct temperature.

6. Combine the three solutions into one test tube and mix with a stirring rod.

7. Immediately return the test tube to the water bath and start a stopwatch.

8. After 30 seconds, use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine. The iodine should turn blue-black, showing that starch is present.

9. Now take a sample every thirty seconds, continuing to transfer one drop to a new well each time until the iodine remains orange.

10. Record the time when the iodine remains orange, telling us that the reaction has finished.

11. Repeat the whole experiment several times using different pH buffers.

12. Plot a graph of the rate of enzyme reaction against pH.

Sources of Error:

• Intervals between testing may be too long to accurately find the time taken for starch to be broken down.

• Could change to 10 sec intervals.

Potential Hazards:

• Be careful using hot water.

• If using a bunsen burner, tie long hair back and wear goggles.

How does your stomach allow protease to work best?

Produces a relatively concentrated solution of hydrochloric acid, allowing your stomach protease enzymes to work very effectively as pepsin (a protease enzyme) works best in acidic pH.

The hydrochloric acid also kills most the bacteria you take in with your food.

How does your stomach protect its walls from digestion by the acid and enzymes?

A thick layer of mucus.

What pH do pancreas and small intestine enzymes work best in?

An alkaline environment.

How does the acidic liquid from your stomach become an alkaline mixture in your small intestine?

An alkaline liquid called bile is produced in the liver and stored in the gall bladder.

This bile is squirted onto food coming into the small intestine through the bile duct, neutralising the acid.

How does bile help lipase enzymes act?

It emulsifies the fats in your food, physically breaking up large drops of fat into smaller droplets.

This provides a much larger surface area of fats for the lipase enzymes to act upon.

What do gall stones do?

They can block the gall bladder and bile ducts.

Why are gall stones bad?

Because they can stop bile being released onto the food and reduce the efficiency of digestion.