Organisation Flashcards
What is a tissue?
A group of cells with a similar structure and function.
What is an organ?
A group of tissues working together for a specific function.
What is organ system?
Organs which work together to form organisms.
What are the three main nutrients found in food and what type of molecules are they?
Carbohydrates e.g. starch
Proteins
Lipids (fats)
These are large molecules, so they can’t be absorbed into the bloodstream. They have to be digested.
What happens during digestion?
Large food molecules are broken down into small molecules by enzymes. The small molecules can then be absorbed into the bloodstream.
Main functions of the different organs in the digestive system.
Food is chewed in the mouth. Enzymes in the saliva begin to digest the starch into smaller sugar molecules.
Food passes through the oesophagus into the stomach.
In the stomach, enzymes begin the digestion of proteins.
Stomach contains hydrochloric acid, which helps the enzymes digest proteins. Food spends several hours in the stomach.
The churning actions of the stomach muscles turns the food into a fluid increasing the surface area for enzymes to digest.
The fluid now passes into the small intestine. Chemicals are released into the small intestine from the liver and pancreas.
The pancreas releases enzymes which continue the digestion of starch and protein. They also start the digestion of lipids.
The liver releases bile which helps speed up the digestion of lipids. Bile also neutralises the acid released from the stomach.
The walls of the small intestine release enzymes to continue the digestion of lipids and proteins.
In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or by active transport.
Now the fluid goes into the large intestine where water is absorbed into the bloodstream.
Faeces is released from the body.
What are digestive enzymes?
They catalyse chemical reactions.
They are large protein molecules which have an active site.
The active site is where the substrate attaches to.
The substrate is the molecule the enzyme breaks down.
What are digestive enzymes?
They catalyse chemical reactions.
They are large protein molecules which have an active site.
The active site is where the substrate attaches to.
The substrate is the molecule the enzyme breaks down.
How do digestive enzymes work?
Enzymes are specific. The substrate must fit perfectly into the active site.
What enzyme breaks down proteins?
Protease.
Found in the stomach, pancreatic fluid and the small intestine.
What are proteins?
Long chains of amino acids.
What happens when we digest proteins?
The protease enzyme converts the protein back to the individual amino acids, which are then absorbed into the bloodstream.
When the amino acids are then absorbed by the body cells, they are joined together in a different order to make human proteins.
What is starch?
Chain of glucose molecules.
What enzyme breaks down carbohydrates?
Carbohydrase
Or amylase for starch
Amylase is found in the saliva or pancreatic fluid.
What happens when carbohydrates are digested?
We produce simple sugars,
What does a lipid molecule consist of? What enzyme digests it and what does this produce?
Glycerol attached to three molecules of fatty acids.
Lipase.
This produces glycerol and fatty acids.
Where is lipase found?
Pancreatic fluid and the small intestine.
How are lipids digested?
Bile is made in the liver and it is stored in the gall bladder.
Bile helps speeds up the digestion of lipids but it is not an enzyme.
Bile converts large lipid droplets into smaller droplets (emulsifies the lipid).
This massively increases the surface area of the lipid droplets.
This increases the rate of lipid breakdown by lipase.
Bile is also alkaline which allows it to neutralise stomach acid, creating alkaline conditions in the small intestine.
This increases the rate of lipid digestion by lipase.
Effect of temperature on enzyme catalysed reactions.
As we increase the temperature, the activity of the enzyme increases so the reaction gets faster.
This is because the enzyme and the substrate are moving faster.
So there are more collisions per second between the substrate and the active site.
At a certain temperature, the enzymes are working at the fastest possible rate -optimum temperature. There is the maximum frequency of successful collisions between the substrate and the active site.
As we increase the temperature above the optimum, the activity of the enzyme decreases to zero.
This is because at high temperatures, the enzyme vibrates and the shape of the active site changes. Now the substrate no longer fits perfectly into the active site so it has denatured. The enzyme can no longer catalyse the reaction.
What is the effect of pH on the enzyme catalysed reactions.
The enzyme has an optimum pH where the activity is at maximum.
If we make the pH more acidic or more alkaline, the activity drops to zero. The active site denatures if the conditions and too acidic or alkaline.
Each enzyme has a specific optimum pH.
Required Practical 4: Food tests
Chemicals in this test are potentially hazardous so safety goggles must be worn.
- Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste.
- Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.
- Filter the solution so we remove suspended food particles.
Testing for starch:
Place 2cm^3 of food solution into a test tube.
Add a few drops of iodine solution which is orange.
If starch is present, iodine will turn blue/black.
If there is no starch present, it will stay orange.
Testing for sugars:
Place 2cm^3 of food solution into a test tube.
Add 10 drops of Benedict’s solution which is blue.
Place the test tube into a beaker, and half-fill the beaker with hot water from a kettle.
Leave this for 5 minutes.
Small amount present: green
More present: yellow
A lot present: brick-red
This test only works for reducing sugars e.g. glucose.
Testing for proteins:
Place 2cm^3 of food solution into a test tube.
Add 2cm^3 of biuret solution which is blue.
Present: purple/lilac
Testing for lipids:
Do not filter the solution because lipid molecules could stick to paper.
Place 2cm^3 of food solution to the test tube.
Add a few drops of distilled water and a few drops of ethanol.
Shake solution.
Present: white cloudy emulsion forms.
Ethanol is highly flammable so avoid naked flames.
Required Practical 5: Effect of pH on amylase
- Place one drop of iodine solution into each well of a spotting tile.
- In the first test tube, add 2cm^3 of starch solution. In the second test tube, add 2cm^3 of amylase solution. In the third test tube, add 2cm^3 of pH 5 buffer solution.
- Buffer solutions are used to control the pH.
- Place all three test tubes in a water bath at 30 degrees.
- Leave them for 10 minutes to allow the solutions to reach the correct temperature.
- Combine the three solutions into one test tube and mix using a stirring rod.
- Return the test tube to the water bath and start a stopwatch.
- After 30 seconds, use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine.
- The iodine should turn blue/black to show starch is present.
- Take a sample every thirty seconds and continue until the iodine remains orange.
- This tells us starch is no longer present so the reaction is completed.
- Record the time for this in the results.
- Repeat the whole experiment several times using different pH buffers.
What are the problems with the RP5 practical?
Only taking samples every 30 seconds. This means we only have an approximate time for the reaction to complete. We could take samples every 10 seconds.
Sometimes it is not obvious when the iodine does not go blue/black since the colour change tends to be gradual. Ask several people to look at the tile and decide.
How is the small intestine adapted for absorbing products of digestion?
Very long (has a length of around 5m): This provides a very large surface area for absorption of the products of digestion.
The interior is covered with millions of villi:
Massively increase the surface area for the absorption of molecules.
Microvilli on the surface of the villi increase the surface area even further.
The villi have a very good blood supply from the capillaries so the bloodstream removes the products of digestion. This increases the concentration gradient.
The villi have a thin membrane which ensures a short diffusion path.
All the features of the villi mean that there is a rapid rate of diffusion of the products into the blood stream.
Any molecules that cannot be absorbed by diffusion are absorbed by active transport.
Describe circulation in fish
Single circulatory system.
Deoxygenated blood is pumped from the heart to gills where it collects oxygen and becomes oxygenated.
The oxygenated blood passes from the gills to the organs where the oxygen diffuses out of the blood into the body cells.
The blood now returns to the heart.
