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
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.
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 substrate and 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.
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.
Lipase
Lipases break down lipids (fats) to glycerol and fatty acids.
Lipase enzymes are produced in the pancreas and stomach 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)
IV - pH of the buffer solution
DV - time taken for iodine to remain orange-brown
CV - Temperature, Volume of buffer, Time intervals used
Place single drops of iodine solution in rows on a tile. Label a test tube with the pH to be tested and add 2 cm³ of amylase using a syringe. Add 1 cm³ of pH buffer solution to the test tube. In a separate tube, add 2 cm³ of starch solution, then add this to the amylase-buffer mix, starting the stopwatch and mixing with a pipette. Every 10 seconds, place a drop of the mixture onto a drop of iodine. Repeat until the iodine stays orange-brown. Repeat for different pH values. The quicker the iodine stays brown, the faster the starch has been digested, showing enzyme activity at that pH.
Practical 5 (food tests)
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 precipitate if glucose is present. (hot water bath).
Ethanol test for lipids - clear to cloudy emulsion if lipids are present. (mix ethanol with distilled water).
