B3: The Human digestive system

Need for food

Our food is the source of energy and building blocks for new growth

One type of carbohydrate

Starch (large, insoluble)

The other type of carbohydrate

Sugar (soluble)

Carbohydrates use in the body and sources

Energy - bread, pasta, potato

Protein use in the body and sources

Growth and repair - meat, eggs, fish, beans (soy), nuts

Waters use in the body and sources

Major components of bodily fluids as a solvent - most foods e.g. fruit, veg, drinks

Minerals use in the body and sources

Maintains good health - fruit and veg

Fibres use in the body and source

Healthy colon, provides bulk to keep the intestines healthy - Veg, beans, cereals

What is Benedict’s solution used to find and give the colour change in a positive reaction

Glucose/sugar - blue to brick red after heating

What is biuret’s solution used to test for and give the colour change in a positive reaction

Protein - blue to purple/ lavender

What is iodine used to test for and what is the colour change when the reaction is positive

Starch - orange/brown to blue/black

What is ethanol used to test for and what is the colour change for a positive reaction

Lipids (fat) - colourless to milky white layer formed

Why do we need to digest food

Because the food we eat are made of large, insoluble molecules

Why do nutrients need to be smaller, soluble molecules?

• To diffuse through the walls of the small intestine

• Then into the blood steam

Define mechanical digestion

By the physical action of the teeth and stomach, pulvering the food

Define chemical digestion

By the action of enzymes found in the digestive organs

What are enzymes?

Enzymes are catalysts. This means they speed up reactions.

Where are enzymes found and what are they made up of?

In the cytoplasm of cells, intestines, stomach and mouth. They are made up of amino acids.

Why can enzymes be reused?

Because they are not used up in reactions

what happens at the active sight

• enzyme + substrate

• Enzyme-substrate complex

• Enzyme + products

Give the name of an enzyme, its substrate and the products

Amylase (Carbohydrase) break starch, into sugars (glucose)

Give the name of another enzyme, its substrate and the products

Protease break proteis into amino acids

Give the name of the final enzyme, its substrate and its product

Lipase break fats into fatty acids and glycerol

How does an enzyme work?

The enzyme has an active sight that fits only one substrate. The substrate binds in the active sight like a key in a lock and the enzyme breaks it down into smaller parts

3 ways to measure the rate of enzyme activity:

• timing until a certain volume/mass of substrates is broken down

• Rate can be calculated using time

• Measuring the change in pH over time (proteins and fats both produce acids, so the pH drops)

How is an enzyme denatured?

If the temp changes sufficiently beyond and enzymes optimum, the shape of the enzyme irreversibly changes. The shape of the active sight changes, meaning it can no longer work as the substrate cannot fit into the active sight.

One way fats are divested

Firstly, Bile (released by the gull bladder) allows the fat to “mix” with water by breaking the fat into smaller droplets. This is called emulsification.

The other way fats are digested

Secondly, the divesting enzyme lipease, break each fat molecule into smaller glycerol and fatty acid molecules.

Roles of hydrochloric acid (2 roles)

• kills bacteria in food

• Provides the best conditions for protease enzymes to work in (pH 2 - very acidic)

Where are analyse (carbohydrase) produced? (3)

Silvery glands, pancreas, small intestine

Where are lipease produced? (2)

Pancreas, small intestine

Where are protease produced in? (3)

Stomach, pancreas, small intestines

Name two ways the small intestines are adapted for efficient absorption of digested food

Large surface area (due to cilli and micro villi) and thin, permeable walls.