Human Nutrition

WJEC Additional ScienceModule 2

Animal Nutrition

• Learning Objectives (the big picture)

• By the end of this topic, you should be able to answer the questions– Why is digestion needed?– How does the digestive system

work?– What happens to the end products?

Learning outcomes

• know that fats, made up of fatty acids and glycerol, proteins, made up of amino acids, and starch (a carbohydrate), made up of a chain of glucose, in our food are insoluble. They are broken down during digestion into soluble substances so that they can be absorbed through the wall of the small intestine into the bloodstream.

• Consider the use of visking tubing as a model gut and the limitations of the model.

Learning outcomes

• recognise and label on a given diagram of the human digestive system and associated structures: the mouth, oesophagus/gullet, stomach, pancreas, small intestine, large intestine, anus and understand the role of the following organs in digestion: mouth, stomach, pancreas, small intestine.

Learning outcomes

• know that during digestion, the breakdown of large molecules into smaller molecules is carried out by enzymes which are specific for each type of molecule.

• know that the body cells need the digested products of fats and carbohydrates to provide energy whilst amino acids are needed to build proteins in the body

Quick Revision

• A balanced diet must contain all the essential nutrients in the correct amounts and proportions.

• The nutrients needed are– Carbohydrate– Fat– Protein– Vitamins– Minerals– Fibre– Water.

Main Nutrients

Nutrient Elements

present

Use in body

Good food sources

Carbohydrate

Carbon, hydrogen, oxygen

Source of energy

Rice, potato, bread

Fats and oils

Carbon, hydrogen, oxygen

Source of energyInsulation

Butter, milk, cheese, egg yolk

Protein Carbon, hydrogen, oxygen, nitrogen

Growth and tissue repair

Meat, fish, eggs, soya, milk

What you really need to remember!!

• Carbohydrates, fats and proteins are all made up of the elements carbon, hydrogen and oxygen

• Proteins always contain nitrogen and sometimes sulphur

• One way to remember this is– Carb O Hydrate

Carbohydrates

• Large carbohydrate molecules such as starch and glycogen are made up of long chains of smaller units, e.g. glucose, which are held together by chemical bonds

Fats

• Fats are made up of three fatty acids and a glycerol

Proteins

• Proteins are made up of long chains of amino acids

Food Tests

• What is the test for starch?• What is the test for glucose?• What is the test for protein?• What is the test for fats?

• What does a positive result look like?

Carbohydrates

• Carbohydrates give us energy.

• Chemical elements – C, H and O.

• Starch is made from simple sugars.

Testing for glucose

1. Pour some glucose solution into a test tube

2. Add a few drops of benedict's solution

3. Heat in a water bath

Testing For Starch

• Put a few drops of starch solution on a spotting tile.

• Add a few drops of iodine.

Proteins

• Proteins are needed for growth and repair.

• Proteins are made from amino acids

• Chemical elements – C, H, O, N (and S)

Testing for Proteins

1. Put 2 ml of protein solution in a test tube

2. Add 2ml of Biurets reagent

Fats

• Fats are an energy store, protecting vital organs and providing insulation.

• Fats contain C, H and O• Fats are made from a

glycerol molecule and three fatty acids.

Testing for fat (the emulsion test)

• Add a few drops of cooking oil into a test tube

• Add 2cm3 ethanol and shake• Add 2cm3 water and shake again.

Mystery Foods

• Test the three “mystery food” samples– Which food substances are present in

each one?

Pupil activity

• Design a mind map to summarise the information on basic nutrition

fibre

water minerals

vitamins

Main Nutrients

Nutrients

Learning Outcomes

• identify the gross structure of the alimentary canal and associated organs (mouth, oesophagus, stomach, small intestine: duodenum and ileum, large intestine: colon and rectum, anus, pancreas, liver)

• define ingestion, digestion, absorption, assimilation and egestion

What happens to the food we eat?

The gut as a production line

What happens to the food we eat?

• Ingestion– Intake of food into the mouth

• Digestion– Breaking down large, insoluble food

molecules into smaller soluble ones using enzymes

• Absorption– Digested food molecules pass across the

wall of the small intestine into the blood or the lymph

• Assimilation– Uptake of food molecules by cells

• Egestion– Passing out of undigested food, in the

form of faeces, from the anus

• Deamination– Removal of nitrogen containing part

of an amino acid as urea.

Pupil Activity

• Label the diagram of the digestive system.– Use the textbook supplied to help if

needed

– Design a table to link the structure and function of different parts of the digestive system.

Salivary glands

stomach

trachea

tongue

mouth

anus

rectumcolon

pancreas

Large intestine

appendix

Small intestine

ileumDuodenum

Gall bladder

liver

oesophagus

Learning Outcomes

• define ingestion, digestion, absorption, assimilation and egestion

• describe the functions of the alimentary canal's various parts in relation to ingestion, digestion, absorption, assimilation and egestion of food

Digestion

•Digestion is the breakdown of large, insoluble food molecules into small, soluble food molecules so that they can be absorbed into the blood stream.

Digestion of Food

• The digestion of food can either be mechanical or chemical.

• Mechanical digestion includes– Chewing– Action of muscles in oesophagus, stomach and

small intestine

• In chemical digestion enzymes catalyse the breakdown of larger food molecules into smaller food molecules.

Digestion in the mouth and oesophagus

• Chewed food is mixed with saliva in the mouth

• Saliva contains– Amylase is an enzyme which starts to digest

starch into sugars (maltose)– Mucus helps soften the food making it easier to

swallow

• The bolus travels down the oesophagus with the aid of peristalsis

Peristalsis in the gullet

Digestion of Starch

• Take 10ml of 1% starch solution– Test for starch– Test for sugars

Action of amylase on starch

• Put a drop of iodine solution into all the wells on a white spotting tile

• Add 10ml 1% starch solution and 10ml 1% amylase solution to a test tube.

• Every minute, test the contents of the test tube for starch.

• After 15 minutes – test the solution for the presence of sugars

• Write a conclusion on your results

Learning Outcomes

• The significance of producing small, soluble molecules

• describe:– digestion in the alimentary canal– the functions of a typical amylase,

protease and lipase, listing the substrate and end-products

Digestion

•Digestion is the breakdown of large, insoluble food molecules into small, soluble food molecules by enzymes, so that they can be absorbed into the blood stream.

Digestion

• Physical Digestion– Increases the surface area of food

• Chewing in the mouth• Churning food in stomach and small

intestine• Bile emulsifies fats – turns them into smaller

droplets with a larger surface area

• Chemical Digestion– Breakdown of large insoluble molecules

into smaller soluble ones– Enzymes act as biological catalysts –

they speed up the process– They work efficiently at body

temperature (37OC) and at a suitable pH

Digestion

Digestive enzymes

• There are different types of digestive enzyme– Proteases break down proteins into

amino acids– Lipases break down fats into fatty

acids and glycerol– Amylase breaks down starch into

maltose (sugar) • Maltose is then broken down by maltase to

form glucose

Summary – digestive enzymes

Enzyme

Site of action

substrate

End products

Amylase

Mouth,duodenum

StarchMaltoseGlucose

Protease

Stomach, duodenum

Protein Amino acids

lipaseduodenum fat

Fatty acidsglycerol

Chemical Digestion

• Hydrogen carbonate ions– Secreted by pancreas– Neutralises acid, enabling enzymes in small

intestine to work 

• Bile– Produced by liver, stored in gall bladder,

secreted into small intestine– Emulsifies fats (Larger surface area for

enzymes to work on)

Prep

• Surface area and digestion– Read the information– Answer questions 1- 3– Answer question Ho2

• A snake swallowed a mouse whole. Explain why it took several days to digest it.

Learning Outcomes

• define the term catalyst• define enzymes as proteins that

function as biological catalysts• describe the effect of changes in

temperature and pH on enzyme activity

Enzymes Revision

• Are proteins• Are produced by cells• Change chemical substances into new

products• Are “specific” to one substance• Work best at their “optimum temperature”

(around 30 – 40oC)• Work best at an optimum pH

Protein Digestion

• Protein digestion occurs in the stomach and small intestine.

• Protease enzymes are produced by the gastric pits in the stomach lining or by the pancreas.

• In the stomach, hydrochloric acid is also produced which provides the optimum pH for trypsin to work

Protein Digestion

• Add 2ml of protein solution to three test tubes.

• Number the test tubes 1, 2 and 31. Add 1ml HCl2. Add 1ml Water3. Add 1ml HCl

• Do not add the trypsin until last1. Add 0.5ml water2. Add 0.5ml trypsin3. Add 0.5ml trypsin

Protein digestion

• Leave for 10 minutes• Test each of the test tubes for the

presence of protein using Biurets reagent.

• Explain your results.

Fat Digestion

• Milk does not dissolve in water, in the digestive system, bile produce by the liver (stored in the gall bladder) emulsifies fats to give a larger surface area for enzymes to work on.

• You are going to use phenolphthalein to investigate the effect of bile on the digestion of fat.

Fat Digestion

• Take 4 test tubes and number them 1, 2, 3 and 4.

• set up the test tubes as shown in the table below.

Test tube

1 2 3 4

Milk 3 ml 3ml 3ml 3ml

Bile 0 0.5ml 1 ml 1ml

Water 1ml 0.5ml 0 0

Fat Digestion

• Add 5 drops of phenolphthalein to each test tube

• Add sodium carbonate to each test tube until the solution goes pink.

• Add 0.5ml of lipase to test tubes 1, 2 and 3.

• Add 0.5 ml water to test tubes 4.• Observe your results. Try to explain what

you are observing.

Learning Outcomes

• define enzymes as proteins that function as biological catalysts

• describe the effect of changes in temperature and pH on enzyme activity

Effect of temperature on enzymes

• The optimum temperature for enzyme controlled reactions is around 37oC– Above optimum

• Slows reaction down• Enzyme becomes denatured – enzyme loses it

shape, deforming the active site so that the substrate no longer fits.

– Below optimum• Slower reaction – lack of energy in molecules

Graph – effect of temperature on the rate of enzyme activity

Effect of pH on enzymes

• pH of a solution is how acid or alkaline it is• Most enzymes have optimum pH 7• Exceptions

– Pepsin pH2.0 stomach– Salivary amylase pH 6.8 mouth– Catalase pH 7.6 plants– Pancreatic amylase pH 9.0 duodenum

Effect of pH on enzymes

• An extreme pH can denature enzymes – permanently altering the active site

Graph - Effect of pH on enzyme activity

Learning Outcomes

• identify the small intestine as the region for the absorption of digested food

• describe the significance of villi in increasing the internal surface area

• describe the structure of a villus, including the role of capillaries and lacteals

What happens next?

Absorption in the ileum

• The small intestine is well designed for absorption, it has– Thin lining– A good blood supply– A very large surface area (about 9m2)

Villi

• Increase the surface area for absorption• Each villus contains

– Blood capillaries that absorb glucose and amino acids

– Lacteals which absorb fatty acids and glycerol• Absorption is by

– Diffusion – thin lining only 1 cell thick– Active transport – epithelial cells contain

mitochondria to provide energy

Absorption in the Villi

The Model Gut

A model of absorption

“the model gut”

Making a model gut

• Wash a 12cm length of visking tubing (A) in warm water.

• Tie a knot in one end• Fill the tubing with 10cm3 of

starch and amylase solution(B).• Wash the outside of the tubing.• Put it into a boiling tube

containing DI water (C) – holding it in place with a rubber

band

C

B

A

Model Gut Results

• After 40 minutes– Take a sample of the water in the boiling

tube• Test the water for glucose• Test the water for starch

Conclusions of the experiment

• Draw conclusions from the experiment, explaining what the results were, and how the model gut represents the real situation

• E.g. what does the water represent, what does the Visking tubing represent, etc.

Large intestine and the elimination of waste.

• A watery mix of enzymes and undigested food (mainly fibre) moves into the colon.

• Water is absorbed back into the blood stream.

• Faeces are compacted in the rectum and egested through the anus.

Pupil Activity - Diagrams

• Use your notes and your textbooks to help you label the diagrams.

• Complete for prep.

• There are key words and phrases in the boxes beside the diagrams to help you.

The end What do they think they are looking at?