Digestive System and Enzymes Flashcards
What is ingestion?
Taking food in through the mouth and swallowing
What is digestion?
Breaking down large insoluble molecules in food into smaller pieces and smaller soluble molecules.
What is absorption?
Movement of small soluble molecules out of the gut and into the blood by diffusion and active transport.
What is egestion?
Passing out undigested food through the anus.
What is assimilation?
Building larger biological molecules from the smaller soluble molecules in all cells
What are the two types of digestion?
Mechanical
Chemical
What is mechanical digestion?
Food is broken up into smaller pieces in the mouth by chewing. This increases the surface area for enzymes and also prevents discomfort when swallowing.
What is chemical digestion?
Saliva is released into the mouth by salivary glands. It makes the food easier to swallow and also contains the enzyme amylase.
Amylase works best at a neutral pH so is denatured when it reaches the stomach and stops working.
What does amylase do?
Breaks down starch into maltose
What is peristalsis?
There is muscular tissue all the way down the alimentary canal. The circular muscles contract behind the bolus pushing it along.
What does maltase do?
Converts maltose into glucose
What does protease do?
Converts proteins into amino acids
What does lipase do?
Converts lipids into glycerol and 3 fatty acids
What does pepsin/trypsin do?
Converts protein into peptide
What happens in the stomach?
The gastric glands in the stomach wall secrete the enzyme pepsin which begins the process of digesting proteins into peptides.
Contractions of the stomach wall causes mixing of the contents of the stomach, maximising contact between enzymes and food.
What are pepsin’s optimum conditions?
An acidic pH, the conditions of the stomach are acidic due to the release of hydrochloric acid by the gastric glands.
What does the hydrochloric acid in the stomach do?
Kills many bacteria and fungi which may be present in the food we eat
The duodenum is the final site of chemical digestion. The pancreas makes several enzymes:
Trypsin
Amylase
Lipase
The duodenum wall also contains glands which make enzymes and secretes them into the duodenum:
Maltase
Peptidase
What does peptidase do?
Converts peptide into amino acids
What are the two functions of bile?
- Neutralises the stomach acid, enzymes in the duodenum work best at pH 7-8.
- Emulsifies lipids - breaks large droplets into smaller droplets, increasing the surface area for lipase to digest the fats
What happens in the ileum?
Digestion is over and absorption begins
The ileum has many folds and is covered in finger projections called villi
What do the villi do?
It is through these that the small soluble molecules are absorbed .
Some are absorbed by diffusion however some such as glucose are also absorbed via active transport which moves particles against a concentration gradient using ATP
How is the rate of diffusion increased in the ileum?
Large SA - folding of ileum, villi, microvilli
Short diffusion distance - villi walls are one cell thick
High concentration gradient - capillary network
What are the two sections of the large intestine?
Colon
Rectum
What is the colon?
The site for all reabsorption of water
What is the rectum?
Where the faeces are stored and then egested from the anus
What is an experiment to discover the effect of pH on enzymes?
Potato contains the enzyme catalase which breaks down hydrogen peroxide forming water and oxygen.
Add 10 potato disks to 20cm3 catalase and hydrogen peroxide and measure the volume of gas produced in 5 minutes.
The pH can be altered by adding different volumes of a weak alkali or a weak acid.
Use universal indicator paper to determine the pH of the solution each time.
What is the effect of temperature on enzymes using amylase?
Amylase digests starch.
Mix 10cm3 of 10% starch suspension and 5cm3 of 5% amylase in a boiling tube and heat in a water bath
Every minute take one drop of this mixture and add it to one drop of iodine solution in the spotting tile.
When digestion is complete and starch is present, iodine solution will stay orange
Repeat using enzymes of water baths that are different temperatures.
What is a catalyst?
A chemical which increases the rate of reaction without being used up itself in the reaction.
Explain the lock and key theory.
The substrate and enzyme collide
The substrate binds to the active site of the enzyme
Binding to the enzyme site strains the chemical bonds in the substrate molecules and so the reaction occurs by an alternative pathway with a lower activation energy.
Once the reaction has occurred the products do not fit the active site’s shape as well as the substrate did so they are released.
What are the 3 roles of the stomach?
- Contract it’s muscular walls to mix the food
- Produces pepsin which breaks down proteins into amino acids
- Produces hydrochloric acid which provides the right pH for pepsin to function and kills microorganisms
What are the 2 roles of bile?
Emulsify lipids
Neutralise stomach acid
