Animal organisation - digestion Flashcards
(21 cards)
Why are Carbohydrates, proteins and lipids broken down
most of the molecules in food are too large to pass through the absorbing surface of the gut wall
Carbohydrates main function and source
Source of energy, glucose is the main respiratory substrate,
Starch: potatoes, rice and wheat products, bread, cereals and pasta. Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets
Proteins
Growth and repair, Meat, eggs, cheese, beans, nuts and seeds
Lipids
Energy, make up part of cell membranes so essential for normal growth, Butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds
Test for sugars
Prepare the sample – Add Benedict’s solution to the test substance (usually a food or urine sample).
Heat the mixture – Place the test tube in a boiling water bath for a few minutes.
Observe the color change – The solution changes color depending on the amount of reducing sugar present:
Green → Low concentration
Yellow/Orange → Moderate concentration
Brick-red → High concentration
Test for starch
Procedure:
Take a small sample of the substance (e.g., food or plant material).
Add a few drops of iodine solution (usually potassium iodide and iodine).
Observe the color change.
Results:
Blue-black color → Starch is present.
No color change → No starch detected.
Test for proteins
The Biuret test is used to detect the presence of proteins in a sample. Here’s how it works:
Procedure:
Add Biuret reagent (a mixture of sodium hydroxide and copper sulfate) to the sample.
Mix the solution gently.
Observe the color change.
Results:
Purple/lilac color → Proteins are present.
No color change (remains blue) → No proteins detected.
Test for fats
Emulsion test:
rocedure:
Add ethanol to the sample and shake it well.
Pour the mixture into water.
Observe the solution.
Results:
Milky/cloudy white emulsion → Lipids are present.
No change → No lipids detected.
The human digestive system has two functions:
breaks down complex food substances
provides the very large surface area for maximum absorption of food
Function of mouth
Mouth Begins the digestion of carbohydrates
Function Stomach
Begins the digestion of protein; small molecules such as alcohol absorbed
Function Small intestine -
Continues the digestion of carbohydrate and protein; begins the digestion of lipids
Small intestine - Ileum
Completes the digestion of carbohydrates and proteins into single sugars and amino acids; absorption of single sugars, amino acids and fatty acids and glycerol
Large intestine
Absorption of water; egestion of undigested food
Enzymes are
biological
catalysts
– they speed up chemical reactions.
Enzymes are proteins that have a complex 3D shape.
Each enzyme has a region called an
active site
Factors affecting enzyme action
Temperature, Enzyme action, The effect of pH
facts
Carbohydrases
break down carbohydrates:
Proteases
break down proteins:
Lipases
break down
lipids:
Required practical activity - investigate the effect of pH on the rate of reaction of amylase enzyme
Method
Prepare solutions: Add the same volume of starch and amylase to separate test tubes.
Adjust pH: Add a specific pH buffer solution to the amylase.
Mix: Combine the starch and amylase solutions.
Start timing: Begin the stopwatch immediately.
Test for starch breakdown: At regular intervals (e.g., every 30 seconds), transfer a drop of the mixture onto a spotting tile containing iodine solution.
Observe color change: If starch is present, the iodine will turn blue-black; if broken down, it remains brown.
Record time: Note how long it takes for iodine to stop turning blue-black, indicating complete starch breakdown.
Repeat: Perform the experiment with different pH levels to compare reaction rates
Bile:
Emulsifies
lipids
, breaking them up physically into tiny droplets. Tiny droplets have a much larger surface area, over which lipases can work, than larger pieces, or drops of lipid.
