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Biology - AS Level > Digestion > Flashcards

Digestion Flashcards

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1
Q

what are the 6 steps of digestion

A

-ingestion
-mastication
-chemical digestion
-absorption
-assimilation
-egestion

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2
Q

what happens in the mouth

A

-food ingested
-food broken up by teeth (mastication)
-salivary glands produce salivary amylase- hydrolyses starch to maltose
-saliva lubricates food and maintains ph 7
-food shaped into a bolus and swallowed

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3
Q

what is the role of the epiglottis

A

closes to prevent food from travelling down the trachea

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4
Q

how does the food move down the oesophagus

A

peristalsis
osephagus is a hollow tube with muscular walls

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5
Q

what happens in the stomach

A

-conditions are very acidic - ph 2
-due to production of HCl from oxyntic cells in gastric pits
- the presence of HCl provides ideal conditions for protease to act and kills bacteria that may be present in food
-chief cells secrete inactive pepsinogen - comes active when comes into contact with HCl and converted to pepsin
-food stays in the stomach for a number of hours and muscles turn the food into semi-solid mixture called chyme

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6
Q

why is important that the pepsinogen becomes active

A

prevents the protease from digesting chief cells

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7
Q

what is pepsin

A

endopepptidase enzyme - hydrolyses peptide bonds in AA in the central region of the molecule
this produces a series of shorter peptides

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8
Q

what happens in the small intestine

A

duodenum- 1st 20 cm and entry controlled by the pyloric sphincter muscle and many secretions are added to the chyme
-bile emulsifies fats - increasing the SA for enzymes to act on
also contains hydrogen carbonate which neutralises the acidity from the stomach to ph 7- that is required for enzymes in the duodenum
-pancreatic juice contains pancreatic amylase - starch to maltose
and also contains inactive trypsinogen is secreted and is activated by enterkinase- activate to trypsin
-lipase enzymes also present
-helps to maintain ph
-exopeptidases also secreted from pancreas
ileum- 5m - all chemical digestion is competed here
-carb digestion - occurs on membrane of the microvilli of epithelial cells - disaccharidases act on disaccharide sugars converting them to monosaccharides
-dipeptidases hydrolise to amino acids
Absorption takes place here also

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9
Q

what is trypsin

A

formed from inactive trypsinogen and activated by enterkinase
it is an endopeptidase enzyme that hydrolyses middle of AA chain

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10
Q

what happens in large intestine

A

large amounts of water absorbed here making the gut less fluid
huge numbers of bacteria present
bacteria can synthesis a number of vitamins - eg vit K which are used by the body

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11
Q

what is egestion

A

remaining gut contents removed as solid faeces
-mostly water with bacteria - living and dead and indigested food - mostly cellulose and lignin

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12
Q

what are exopeptidases

A

hydrolyses bonds on the terminal ends of the amino acids and release dipeptidases and single AA

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13
Q

what are endopeptidases

A

Hydrolyse bonds between amino acids in central region

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14
Q

what are dipeptidases

A

hydrolyse bond between AA of two amino acids

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15
Q

protein digestion in the stomach

A

-pepsinogen released in inactive form
-becomes activated when come into contact with HCl - pepsin
-pepsin as an endopeptidase breakes down polypeptides into shorter peptides

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16
Q

How can the proteins digestive enzyme cause harm

A

they can digest themselves in turn digesting body cells

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17
Q

protein digestion in the small intestine

A

-duodenum
- inactive trypsinogen- enters via pancreatic duct
-walls of duodenum secrete enterokinase which actives trypsinogen into trypsin
-trypsin is an endopeptidase enzyme
-polypeptides are converted to shorter peptides
-ileum
-bound to epithelial cells - dipeptidases are secreted to break down peptides/dipeptides into amino acids

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18
Q

carb digestion in the mouth

A

-saliva contains salivary amylase
-hydrolyses some starch to maltose- disaccharide and reducing sugar- breaks glycosidic bonds in molecule

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19
Q

carb digestion in stomach

A

does not happen due to acidity of the stomach

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20
Q

carb digestion in the small intestine

A

duodenum
-pancreas - pancreatic juices - contain pancreatic amylase
-hydrolyses remaining starch to maltose
ileum
-disaccharidase enzymes
-maltase- hydrolyses maltose to alpha glucose
-sucrase- hydrolysis sucrose into alpha glucose and fructose
-lactase- hydrolysis lactose into beta glucose and galactose

21
Q

lipid digestion in the small intestine

A

where lipid digestion begins
-duodenum- bile made by liver and stored in gall bladder enters via bile duct
-bile emulsifies fats - breaks them down to smaller droplets
-physical digestion
-larger SA for enzymes to act
-pancreatic juice contains lipase enzymes
-hydrolyse lipids into
-fatty acids
-glycerol
-monoglycerides

22
Q

where does absorption occur

A

the ileum

23
Q

what cover the inner layer of the ileum

A

finger-like projections called villi

24
Q

what is the layer of cells covering the villi and that comes into contact with the food

A

epithelium

25
Q

what are on the surface of the ileum

A

microvilli - these form a brush border

26
Q

how do the muscle layer of the digestive system change

A

varies in thickness due to how much food is needed to be used along eg the solidity of the food

27
Q

how is the ileum structurally adapted for digestion

A

-microvilli have digestive enzymes bound to them
-large SA means large SA of enzymes available to digest the food
-each villus has muscle fibres which contract to increase contact with food and enzymes
-all to help digestion happen faster

28
Q

how is the ileum structured for absorption

A

-large SA is achieved by the ileum being very long, and the presence of villi and microvilli
-epithelial cells have lots of mitochondria - provide energy for the active transport of molecules like glucose
-villi contain capillaries to transport molecules away quickly, maintaining a conc gradient
-each villus has a lymph vessel to absorb lipids
-epithelial cell layer is thin- short diffusion pathway
-villi are moved by muscle fibres, increasing contact with food and epithelium

29
Q

how are molecules absorbed- what methods

A

-first by diffusion as there is a greater conc of molecules in the ileum and less in the blood so a conc gradient is established
-however if diffusion contains the concs will become equal
- therefore glucose and amino acids are absorbed into the blood by active transport

30
Q

how is glucose absorbed from ileum to the blood

A

sodium-potassium pump

31
Q

describe the process of the sodium-potassium pump

A

-Na+ ions are actively transported out of the epithelial cells and into the blood - protein carries do this
- there is now a larger conc of Na+ ions in the lumen of the gut than inside the epithelial cells
-Na+ ions diffuse into the epithelial cells through another protein carrier which also carry glucose molecules
-glucose then diffuses through another protein carrier into the blood by facilitated difffusion

32
Q

is the absorption of glucose active or passive

A

overall active
however glucose into the blood is passive

33
Q

how are amino acids absorbed

A

-sodium-potassium pump transports Na+ ions out of the cell via active transport
-amino acids and Na+ ions bind to carrier protein
-as the Na+ ions diffuse into the cell the amino acids are carried alongside
-the amino acids then diffuse to the other end of the cell
-they are then transferred to the capillaries by facilitated diffusion

34
Q

how are fats absorbed

A

-after digestion the monoglycerides and fatty acids remain associated with bile salts and form structures called micelles
-at the epithelial cell membranes the micelles break down
-release the monoglycerides and fatty acids
-as they are lipid soluble they diffuse across the cell membrane
-when in the cell they are transported to the ER where they are recombined to form triglycerides
-they are then transported to the Golgi and associate with cholesterol and lipoprotiens to form chylomicrons
-chylomicrons leave the cell va EXOCYTOSIS as they are too large to leave via any other method
-chylomicrons enter lacteals - the lymph- in the villus
- they are then deposited into the blood by the subclavian vein

35
Q

what enzyme digests lactose

A

lactase - produced in the microvilli of the epithelial cells

36
Q

what is the word equation of the action of lactase

A

lactose + water + lactase = beta glucose + galactose

37
Q

what happens if you are lactose intolerant

A

body produces little to no lactase

38
Q

what happens to lactose in the body of someone who is lactose intolerant

A

it remains undigested in the SI
passes into the LI
then it is digested by E.coli bacteria- has own lactase in plasma
the E.coli ferments the glucose and galactose to acetate, ethanol, hydrogen gas and CO2

39
Q

what are the symptoms of lactose intolerance

A

-nausea
-abdominal pain
-bloating
-diarrhoea

caused by the hydrogen and carbon dioxide gas produced by the bacteria

40
Q

how does excess lactose in the colon cause diarrhoea

A

the presence of lactose lowers water potatenial - water remains and moves in by osmosis
and the water is not absorbed into the blood

41
Q

effect of ph on enzyme action

A

Use the enzyme amylase to breakdown starch at a range of pH values, using iodine solution as an indicator for the reaction occurring

Amylase is an enzyme that digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose)

Use a continuous sampling technique to monitor the progress of the reaction

Starch can be tested for easily using iodine solution

Apparatus

Test tubes

Buffer solutions at different pH levels

Amylase solution

Iodine solution

Starch solution

Pipettes

Spotting tile

Timer

Gloves

Goggles

Method

Wear goggles and gloves

Enzymes have the potential to cause allergic reactions if they come into direct contact with skin

Place single drops of iodine solution in rows on the tile

Iodine solution is orange-brown

Label a test tube with the pH to be tested

Use the syringe to place 2cm3 of amylase in the test tube

Equal volume and concentration of enzyme should be used so these variables are controlled and the effect of changing pH can be measured

Add 1cm3 of 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

Equal volume and concentration of the substrate (starch) should be used so these variables are controlled and the effect of changing pH can be measured

Mixing enables the enzymes and substrate to be equally mixed

After 10 seconds, use a pipette to place one drop of the mixture on the first drop of iodine, which should turn blue-black

This indicates starch is still present

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

This means amylase has broken down all of the starch so nothing is left to react with the iodine

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

42
Q

what are the limitations of the enzyme ph practical

A

The above method can be adapted to control temperature by using a water bath at 35℃

All solutions that need to be used (starch, amylase, pH buffers) should be placed in a water bath and allowed to reach the temperature (using a thermometer to check) before being used

A colorimeter can be used to measure the progress of the reaction more accurately; with a solution containing starch being darker and glucose lighter (as a result of the colour-change of iodine) – this will affect the absorbance or transmission of light in a colorimeter

43
Q

what is visking tubing

A

non-living partially permeable membrane made from cellulose

It is sometimes used to model the process of absorption that occurs in the small intestine

Pores in the membrane are small enough to prevent the passage of large molecules (such as starch and sucrose) but allow smaller molecules (such as glucose) to pass through by diffusion

44
Q

visking tubing practicle method

A

Fill a section of Visking tubing with a mixture of starch and amylase solutions

Suspend the tubing in a beaker of water for a set period of time

Take samples from the liquid outside of the visking tubing at regular intervals and test for the presence of starch and glucose

Starch is tested for using iodine. A blue-black colour is produced in the presence of starch

Glucose is tested for using Benedict’s reagent. An orange-red precipitate is formed in the presence of glucose

The amylase present inside the visking tube digests and breaks down starch into glucose

Glucose is small enough to diffuse across the partially permeable - and starch isnt - test for starch would be red/brown as no change

Over time the concentration of glucose in the liquid outside the visking tube should increase as more starch (substrate) has been digested

As a result, the amount of precipitate produced from the Benedict’s reagent test will increase over time

45
Q

The rate of absorption/diffusion can be investigated more quantitatively by:

A

​
Estimating the concentration of glucose that has diffused into the liquid surrounding the Visking tubing at each time interval (separate beakers are set up for each time interval) using the semi-quantitative Benedict’s test
​
Comparisons between the time intervals can be made with a set of colour standards (known glucose concentrations) or a colorimeter to give a more quantitative set of results
​
A graph could be drawn showing how the rate of absorption changes with the concentration gradient between the inside and outside of the tubing

46
Q

what are the limitations of the visking tubing practicle

A

Using visking tubing membrane as a substitute for the membrane of the small intestine:

Both are selectively/partially permeable

The small intestine has a much larger surface area due to the presence of villi

Using distilled water as a substitute for blood:

Both have an initially low solute concentration

The distilled water does not flow and so does not maintain the concentration gradient the way blood does

47
Q

what effect do fatty acids have on the pH

A

they decrease it - after being hydrolysed from triglycerides
-pH remains constant when no more fatty acids are produced

48
Q

where is bile stored and produced

A

-produced in the liver
-stored in the gall bladder

49
Q

how do endopeptidases/exopeptidases hydrolyse AA

A

-form enzyme-sub complex bewtween endopeptidases and peptide bond
-terminal ends able to be hydrolysed
-faster rate of absorption

Biology - AS Level (17 decks)

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