digestive system and biological molecules (topic 2). Flashcards
- starch
- proteins
- amino acids
different parts of the human digestive system help to break down molecules of fat so that they can be absorbed into the body, describe how, refer to:
- the enzyme and where the enzyme is produced
- the products of digestion
- any other chemicals involved
- (6)
mechanical digestion:
- mechanical breakdown in mouth
chemical digestion with lipase:
- lipase breaks down fats
- fats are broken down into fatty acids and glycerol
- lipase is produced by the pancreas
- and small intestine
chemical digestion with bile:
- bile is produced by the liver
- bile neutralises the acid from the stomach
- bile produces alkaline conditions in the small intestine
- bile emulsifies fats (or increases surface area of fats)
other marking points:
- fat digestion happens in the small intestine
- products are small molecules (water-soluble molecules)
- small molecules are absorbed by the small intestine
describe the function of the digestive system (2)
- the organs of the digestive system work together to digest food
- food is broken down into small, soluble molecules
- small molecules can be absorbed into the bloodstream
explain how enzymes, such as amylase, proteases, and lipases, contribute to the digestion process (3)
- enzymes catalyse the breakdown of food molecules
- small food molecules can be absorbed into the bloodstream
- amylase breaks down starch into glucose (or carbohydrases break down carbohydrates into sugars)
- lipases break down lipids into glycerol and fatty acids
- proteases break down proteins into amino acids
explain how the ‘lock and key theory’ can be used to explain enzyme action (2)
- states that each enzyme has a specific shape (the ‘key’) that fits into the active site of a particular molecule (the ‘lock’)
- this specificity allows enzymes to catalyse specific reactions
a student carries out a practical activity to investigate the effect of pH on the rate of reaction of amylase enzyme, describe how the student could set up this experiment (6)
- place one drop of iodine solution into each spot/depression on the spotting tile
- place labelled test tubes containing buffered pH solutions, amylase solution and starch solutions into a water bath at 25°C
- allow the solutions to reach 25°C
_ - add 2 cm3 of one of the buffered solutions to a test tube
- add 2 cm3 of amylase into the buffered pH solution
- add 2 cm3 of starch to the amylase/buffer solution
_ - immediately start the stopwatch and leave it on throughout the experiment
- after 30 seconds, use a pipette to place a drop of the mixture onto the first depression of the spotting tile with the iodine solution
- add one drop of the mixture to the following depression every 30 seconds
- continue until the iodine solution and the amylase/buffer/starch mixture remain orange
_ - repeat the procedure with solutions of other pHs
- record your results in a table
the student finds that the rate of reaction decreases as the pH moves away from neutral, explain why this might be the case (4)
- enzymes have an optimal pH at which they function best
- optimum pH is often around neutral for enzymes in the human body
- the enzyme’s activity decreases because the change in pH can affect the shape of the enzyme’s active site
- change in shape reduces its ability to bind to its substrate
name the enzyme that breaks down carbohydrates and the products of this breakdown (2)
- amylase
- breaks down starch into glucose
explain how the products of digestion are used by the body (3)
- glucose is used for respiration
- amino acids are used to build new proteins
- fatty acids and glycerol are stored as fat
- glycerol can be converted to glucose for energy
cells within the stomach lining secrete a substance that alters the pH of the stomach, name this substance
hydrochloric acid
pH of the human stomach
1.5-2.0
where is bile produced and where is it stored (2)
- liver
- gall bladder
explain the role of bile in the digestion of fats (3)
- bile emulsifies fats
- increasing the surface area for lipase to work on
- speeding up the breakdown of fats
- lipase works best in alkaline conditions
- acid denatures enzyme
- bile is alkaline
- bile emulsifies fats (bile produces larger surface area of fats)
- bile increases the activity of lipase
general points (max 2 marks):
- lipase breaks down fats into fatty acids and glycerol
- fatty acids decrease the pH
- therefore if lipase activity is high, the pH will be low
at 0°C (max 2 marks):
- enzyme activity is low (or pH is neutral)
- because the enzyme and substrate molecules have less kinetic energy
- so there are fewer collisions between them
at 40°C (max 2 marks):
- at 40°C enzyme activity increases to a maximum value at the optimum temperature (or pH is the lowest)
- because the rate of reaction increases as the temperature increases
- due to more collisions between the enzyme and substrate molecules
at 80°C (max 2 marks):
- at 80°C enzyme activity is very low again (or pH is neutral)
- because the enzyme denatured
- liver
- mouth/salivary glands/small intestine/pancreas
- pancreas/small intestine
- stomach/small intestine/pancreas
(6)
fibre:
- plant-based hot dogs contain more fibre
- fibre aids digestion / prevents constipation
protein:
- pork hot dogs contain more protein
- protein is needed for growth
fat:
- pork hot dogs contain more fat
- fat can cause CHD (heart attack or narrowing of arteries)
- which may lead to needing a stent
- fat-rich diet can cause obesity
cholesterol:
- pork hot dogs contain more cholesterol
- more cholesterol leads to narrowing of the arteries
- which may lead to needing statins
(2)
- positive test result is a red stained layer
- steak is red so the presence of a red layer cant be seen
- cheese contains protein
- cheese contains fats
the student is worried that the results for apple juice and vegetable oil have been swapped, give two reasons why this is not possible (2)
- oils are lipids/fats
- vegetable oil contains no sugars
- apple juice contains sugar
