2.1 Digestion Flashcards
Cells
Cells are the smallest unit that can live on their own. They are the basic building blocks of all living organisms.
Tissue
A tissue is a group of cells with a similar structure and function working together.
Organs
Organs are aggregations of tissues, working together to perform specific functions.
Organ systems
A group of organs with related functions, working together to perform certain functions. Organs are organised into organ systems, which work together to form organisms.
Digestion
The digestive system is an example of an organ system in which several organs work together to digest and absorb food.
Digestion is the process in which large, insoluble molecules are broken down into smaller, soluble molecules so they can be absorbed into the bloodstream.
Stomach
The stomach is an organ that forms part of the digestive system. It churns food to break it down and produces protease enzymes. It contains HCl to destroy bacteria and provide an optimum pH for the protease enzymes.
Epithelial tissue lines the stomach, muscle tissue contains cells to contract and glandular tissues that contain cells which secrete enzymes and stomach acid.
Alimentary canal
The human digestive system is made up of organs that form the alimentary canal. The alimentary canal is the channel or passage through which food flows through the body, starting at the mouth and ending at the anus.
Mouth / salivary glands
The mouth is where mechanical digestion takes place. teeth chew food to break it into smaller pieces to increase surface area to volume ratio. amylase enzymes in saliva start digesting starch into maltose. The food is shaped into a bolus by the tongue and lubricated in saliva so it can be swallowed easily.
Oesophagus
Tube that connects the mouth to the stomach where the food goes after being swallowed. contractions will take place in order to push the food molecules down.
Small intestine
First section is called the duodenum and is where the food from the stomach finishes being digested by enzymes produced here and secreted from the pancreas. Ph of the small intestine is slightly alkaline PH 9-8.
second section is called the ileum and is where absorption of digested food molecules takes place. the ileum is long and lined with villi to increase the surface area over which absorption can take place.
Large intestine
Water is absorbed from remaining material in the colon to produce faeces which is stored in the rectum and excreted through the anus
Pancreas
Produces all three types of digestive enzymes (protease, amylase and lipase)
Secretes enzymes in an alkaline fluid into the duodenum to raise the PH of the fluid coming out of the stomach.
Liver
Produces bile to emulsify fats (break down of larger droplets into smaller droplets) - an example of mechanical digestion.
Gall bladder
Stores bile to release into duodenum as required.
Bile
Bile is an alkaline substance produced in the liver and stored in the gallbladder. Enzymes in the small intestine operate best in alkaline conditions.
Bile neutralises acid from the stomach to stop these enzymes becoming denatured (lose their activity).
Bile breaks up fats into tiny droplets, through a process called emulsification.
The tiny droplets have a higher surface area than the original fat drop.
This increases the rate of the lipase-catalysed reactions that break fats down.
Enzymes
Enzymes are a biological catalyst – they help speed up reaction rates in an organism. Enzymes are proteins that have a shape that is specific to the substrates they work on. The part of an enzyme that the substrate fits into is called an active site. When a substrate collides with its specific enzymes’ active site, the two molecules temporarily bind. Here, the bonds holding the substrate together break and the resultant products leave the active site. The enzyme remains unchanged and can catalyse the breakdown of another specific substrate molecule.
Effect of temperature on enzymes
As temperature increase (towards the optimum), kinetic energy increases. This means that the substate in the enzyme are more likely to collide - there will be more frequent successful collisions This increases the rate of reaction. Optimum temperature is when the rate of reaction is the quickest - usually body temperature. Above the optimum temperature, the shape of the active site is altered as the bonds holding it in the right shape are broken. The enzyme is denatured. The Substrate can no longer fit into the active site, so the rate of reaction falls until it reaches 0.
Effect of PH on enzymes
Like with temperature, enzymes have an optimum PH. This is the PH at which the rate of reaction is quickest. If the PH becomes more acidic or more alkaline than the optimum, the rate of reaction will decrease. This is because the incorrect PH will denature the enzyme - It will change the shape of the active site. So, the enzyme and the substrate can no longer bind.
Production of enzymes
Protease are produced in the stomach, pancreas and small intestine
Carbohydrase are produced in the salivary glands and pancreas
Lipase are produced in the stomach, pancreas and the mouth
Carbohydrase
Carbohydrase break down carbohydrates to simple sugars.
Amylase is a carbohydrase which breaks down starch into maltose, which is then broken down into glucose by the enzyme maltase.
Amylase is made in the salivary glands, the pancreas and the small intestine.
Protease
Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine.
Protein digestion takes place in the stomach and small intestine, with proteases made in the stomach (pepsin), pancreas and small intestine.
Lipase
Lipases break down lipids (fats) to glycerol and fatty acids.
Lipase enzymes are produced in the pancreas and secreted into the duodenum.
Products of digestion
The products of digestion are used to build new carbohydrates, lipids and proteins required by all cells to function properly and grow.
Some glucose released from carbohydrate breakdown is used in respiration to release energy to fuel all the activities of the cell.
Amino acids are used to build proteins like enzymes and antibodies.
The products of lipid digestion can be used to build new cell membranes and hormones.
Practical 4 (enzymes)
Aim: To investigate the effect of pH on the rate of reaction of amylase.
Procedure - Place single drops of iodine solution in rows on the tile
Label a test tube with the pH to be tested.
Use the syringe to place 2cm3 of amylase in the test tube.
Add 1cm3 of pH buffer solution to the test tube using a syringe.
Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette.
After 10 seconds, use a pipette to place one drop of the mixture on the first drop of iodine, which should turn blue-black.
Wait another 10 seconds and place another drop of the mixture on the second drop of iodine.
Repeat every 10 seconds until iodine solution remains orange-brown.
Repeat experiment at different pH values – the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH.
Practical 5 (food tests)
Aim: To use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
Procedure - Break up the food using a pestle and mortar
Transfer to a test tube and add distilled water
Mix the food with the water by stirring with a glass rod
Filter the mixture using a funnel and filter paper, collecting the solution
Proceed with the food tests
Results:
Iodine test for starch - orange to blue black if starch is present.
Biuret test for protein - blue to light purple if protein is present.
Benedict’s test for glucose - light blue to brick red if glucose is present. (hot water bath).
Ethanol test for lipids - clear to cloudy emulsion if lipids are present. (mix ethanol with distilled water).
