2. Digestive System

Food groups necessary for a balanced diet

• carbohydrates : source of energy

• Protein : growth and repair

• Lipid : insulation and long term store of energy

• Dietary fibre : provides bulk (roughage) for intestines to push food through it

• Vitamins : needed in small quantities to maintain health

• Minerals : needed in small quantities to maintain health

• Water : needed for chemical reactions to take place in cells

What is a balanced diet

A diet containing all nutrients in the correct amounts/proportions to provide energy

Vitamin C

Forms an essential part of collagen protein, which makes up skin, hair, gums and bones

If deficient : scurvy - bleeding gums, slow wound healing

Citrus fruit, strawberries, green vegetables

Vitamin D

Helps body to absorb calcium and so required for strong bones and teeth

Deficiency : rickets - weak soft bones and skeletal deformities

Oily fish, eggs, liver, dairy products, sunlight

Calcium

Needed for strong teeth and bones, involved in clotting of blood

Deficiency : osteoporosis

Milk, cheese, eggs

Iron

Needed to make haemoglobin, pigment in red blood cells that transports oxygen

Deficiency : anemia - tiredness and lack of energy

Red meat, liver, green vegetables

Vitamin A

Needed to make the pigment in the retina for vision

Deficiency : night blindness

Meat, liver, diary, leafy green vegetables (spinach)

Deficiency in food groups :

• carbohydrates : fatigue, brain fog, constipation

• Lipids : dry skin, brittle hair, fatigue

• Protein : Kwashiorkor - slow muscle development

• Fibre : constipation

• Water : dehydration

What is malnutrition

Overnutrion : obesity from high amounts of fat/lipids/cholesterol/carbohydrates in the diet

Under nutrition : starvation and constipation

Sources of carbohydrates

Bread, cereal, pasta, rice, potato

Sources of Protein

Meat, fish, eggs, nuts

Sources of Lipid

Butter, oil, nuts

Sources of Fibres

Vegetables, whole grains

Sources of Vitamins

Fruit and vegetables

Sources of Minerals

Fruits, vegetables, meats, dairy products

What affects the dietary needs of an individual

1. Age : need of protein and carbohydrate needed for energy and growth

2. Activity level : if more active, requires more movement and energy

3. Pregnancy, Breast feeding : growth of foetus as well as increased mass mother carries around. Extra calcium to make breast milk and iron and calcium to build bones, teeth and blood of fetus

4. Gender : men need a higher caloric intake due to larger mass

Chemical elements present in carbohydrates, proteins, lipids

Carbohydrates ; C,H,O

Lipids : C,H,O

Proteins : C,H,O, N (nitrogen)

Basic units of carbohydrates, lipids, proteins

Carbohydrates : starch/glycogen → sugar

Lipids → glycerol and fatty acids

Proteins → amino acids

Test for sugars/glucose

1. Prepare food sample and add BENEDICTS solution

2. Place it in water bath over 80°C for 5 minutes.

3. If sugar is present, the solution will change colour depending on the concentration.

4. From light blue to green, yellow, orange, brick-red from (red having the most sugar)

Test for starch

1. Place food in spotting tile

2. Add a few drops of IODINE directly onto the Food

3. If present, it should turn from yellow - brown to blue black

Test for protein

1. Mix the food with a little bit of water and place in a test tube

2. Add BIURET solution and shake gently

3. If protein is present, it will turn from blue to lilac purple

Test for lipids

1. Mix sample of food with ETHANOL and shake

2. Put an equal part of water and shake

3. A cloudy milky white layer will form if lipid is present

What is semi quantitive data

Can show how much is present but not in statistical numbers

How to calculate energy content

Energy content (joules/gram) = (mass of water, g) x (temperature increases, °C) x 4.2 / (mass of food, g)

Calorimetry

Method of measuring the heat transfer within a chemical reaction

CP5 : Calorimetry

1. Measure out 20cm cubed of water with a measuring cylinder

2. Clamp the tube to the stand and place a thermometer inside

3. Record the starting temperature of water and place heat proof mats below the test tube

4. Record the weight of the piece of food being tested and stick it onto a mounted pin

5. Hold the food in the Bunsen flame until it can stay lit, hold it below the water

6. Relight if it goes out

7. Record the temperature of the water after all the food is burnt

8. Calculate the energy content using

Problems with Calorimetry (school practical)

1. Not all the food sample is burnt

2. Not all energy stored in food is transferred to water

3. Not all of water is an even temperature

4. Energy transferred to water is lost to surroundings

Features of a bomb calorimeter

• is sealed in insulating material

• There is a stirrer

• Ignition wires (to combust food and release all energy)

Enzymes

Biological catalysts that speed up reactions, and remain unchanged/not used up

Lock and key diagram walk through

1. The substrate binds to the active site of the enzyme which is complementary in shape

2. An enzyme substrate complex is formed

3. The enzyme catalyses the reaction and breaks down large molecules into smaller ones

Catabolism

Speeding up the breakdown of large molecules into smaller ones

Why do we need enzymes in the digestive system

To break down large insoluble molecules into smaller soluble molecules that can pass through the walls of the digestive system to allow them to be absorbed

Enzymes (and location) to convert carbohydrate into simple sugars

Enzymes (and location) to convert proteins into amino acids

Enzymes (and location) to convert Lipids into glycerol and fatty acids

Label the digestive system

How does temperature affects the enzymes function

rate of enzyme reactions increases at temperature does until it reaches an optimum temperature (usually body temperature). After that, it begins decreasing as the enzymes begin to become denatured and the active site is no longer the correct shape as some of the bonds holding the enzyme together break

Anabolism

Joining smaller molecules together to form larger ones

How does pH affect enzyme reactions

If the pH is too high/low, the pH interferes with the bonds holding the enzyme together which changes shape of the active site, denaturing them

Function of stomach

It churns the food with its muscular walls and produces hydrochloric acid to kill bacteria and keep the pH of 2 for protease enzyme to work

Function of liver

Where bile is produced

Function of Gall bladder

Where bile is stored before it is released into the small intestine

Function of pancreas

Produces enzymes (protease, amylase and lipase) and releases it into the small intestine

Function of large intestine

Where excess water is absorbed from the food

Function of the small intestine

Produces protease, amylase and lipase enzymes to complete digestion. Where the digested food is absorbed out of the digestive system into the blood

Function of rectum

Where the faeces (indigestible food) is stored before they leave through the anus

Peristalsis

Automatic wave-like muscles contractions in the walls of the intestine and oesophagus to move food along intestine

What is the duodenum and ileum

Duodenum : first (and shortest) bit of intestine that is a ‘C’ shape which mixes food with bile and enzymes

Ileum : the last (and longest) bit of intestine which absorbs remaining nutrients missed earlier

Villi

Finger like projects lining the small intestine that maximize the absorption of digested food molecules into the blood

Adaptations of villi

1. Large surface area → have microscopic micro villi

2. One cell thick → short diffusion distance

3. Steep concentration gradient → each villus has a network of capillaries to constantly maintain the concentration difference

4. Presence of lacteal → absorbs fatty acids and glycerol

production and storage of bile

Is produced in liver and stored in gall bladder to travel allow the bile duct and enter the digestive system at the duodenum

Function of bile

• released into small intestine

1. Neutralises stomach acids so amylase and lipase can function

2. Emulsify lipids : breaks down the fat globules into smaller fat globules which increases the surface area and rate of digestion

How to test for bile (simple)

Using phenolphthalein (which is pink when alkaline and clear when acidic) to see how long it takes for lipase to break down the lipids.

CP6 : enzymes and temperature

To investigate how enzyme activity can be affected by changes in temperature

1. 3 water baths at various temperature

2. Place 2 test tubes of 3cm cubed starch solution and 3cm amylase solution (respectively) into each of the 3 water bath and leave it to equilibrate to the right temperature

3. Place 1 drop of iodine into each dimple on a spotting tile

4. Add the amylase to the starch

5. Start the timer : every minute remove a sample of the starch-amylase solution and place it in the iodine

6. Wait till the iodine remains yellow (signalling that all starch has been broken down into glucose)

7. Calculate the rate and repeat with different temperatures

CP7 : enzyme and pH

Investigate how changing the pH affects enzyme activity

1. Make the following mixtures in 5 different test tubes, each will have a different pH but has water to ensure that the volume is the same as well as egg white for protein testing

2. Find and record the pH of the test tubes

3. Place the tubes in a water bath of 36°C to reach optimum temperature

4. Start the stopwatch and add Pepsin and wait till the solution turns clear (has to have presence of HCL to make it acidic for the reaction to turn clear)

Visking tubing and starch practical

2. Set up a beaker of with distilled water

3. Place starch and amylase in the visking tubing, wash (to prevent any starch on the outside) and place into water

4. Test the water surrounding the visiting tubing with iodine (starch) and Benedicts (sugar) before and after 15 min.