Biology Digestion Test revision

Function of Carbohydrates, lipids, protein

Source of energy for respiration and chemical reactions in the body - starchy foods like potato pasta rice - true polymer

longer term energy store and insulation (electrical + thermal )and protection of organs - oily fish, butter, cream - not a true polymer, and also for cell membranes

needed for growth and repair of cells and tissue, meat, eggs, beans - true polymer

contains the elements c,h,o,(protein has n also)

need for digestion

To breakdown large insoluble food molecules to small and soluble molecules to be absorbed into the bloodstream (and be assimilated) - e.g. glycogen polymerisation or rebuilding glucose

Vit A,C,D

good eyesight and healthy skin and hair found in carrot, leafy veg and liver

citrus friut and veg, healthy immune function, and to prevent scurvy - bleeding gums, weak immune system

Body can make using sunlight, oily fish, eggs

needed for calcium absorption

Fe and ca ions

needed for haemoglobin for carrying oxygen in the blood and to prevent anaemia

red meat, leafy vegetables

milk, leafy veg

for healthy bones and to prevent rickets, deformed bones

water and dietary fibre

medium of transport substances, chemical reactions, cell cytoplasm, major component of blood plasma. Constantly lost by excretory processes so requires replenishment

fibre, (cellulose) fruit and veg and doesn't digest .

Adds bulk to the food, to help intestinal muscles contract and move food through the intestines (against the bulk) (peristalsis)

Balanced diet and misconception of food

all the quantities of each food group in the right proportion for each person varying by their metabolic rate

food doesn't contain only one type of nutrient, it may be rich in one type but that doesn't stop it from having other nutrients aswell

metabolic rate, and factors that affect it

rate of chem reactions occuring inside the body

gender, male norm. has slightly faster m. rate

growth rate , children or adolescents

body mass, muscle mass, fat mass

genetics

activity

enzymes

a biological catalyst made of protein molecules (that increase the rate of reaction,) they catalyse the breakdowns of large ins. food molecules to smaller sol. food molecules

they have a groove on their surface called the active site, and this is where the substrate attaches to - the molecule that the enzyme breaks down

lock and key theory

substrate fits into the active site of an enzyme perfectly and then it gets broken down or built up into products, if the substrate does not fit perfectly then the enzyme cannot break it down.

The substrate and active site shape is exactly complementary, substrate must fit perfectly into the active site for the reaction to be catalysed

there are diff types of enzymes for diff substrates that break down or build up substances

Food molecules broken down by enzymes

proteins are long chains (polymer) of amino acids and are broken down into amino acids by protease enzymes - then joined together in a different order to make human proteins

starch are long chains (polymer) of glucose molecules and are broken down by amylase into glucose - other carbohydrates are broken down into simple sugars by carbohydrases

some of the glucose is used in respiration

starch is broken down into maltose in the mouth then broken down to glucose by maltase in the small intestine

lipids are one molecule of glycerol connected to 3 molecules of fatty acids, and are broken down by lipase

Rate of Reaction

How much of a chemical reaction takes place IN A GIVEN TIME

ROR = 1/t (s)

effect of temperature on enzyme ROR

as the temperature increases the rate of reaction (enzyme activity increases)

, at first, the enzyme and substrate are supplied with more energy so they are moving faster so there are more collisions per sec between substrate and active site

- and at a certain temp. the enzyme is working at the fastest possible rate (optimum temp) this is the stage with the highest freq. of active site substrate successful collisions -

most human enzymes optimum temperature is 37c as that is human body temp

-passing the optimum enzyme rapidly decreases to 0 as the enzyme vibrates and the active site shape changes. Now the substrate no longer fits into the active site and the enzyme is permanently denatured - cannot catalyse the reaction

effect of pH on enzyme ROR

each enzyme has a specific optimum pH e.g. stomach protease enzyme low optimum pH and lipase small intestine high optimum pH

but the gradient is always steep both ways so if the conditions are more acidic or alkaline then rate of reaction rapidly decreases to 0 and enzyme denatures

different enzymes have diff optimums e.g pepsin has a very acidic optimum and lipase would have a higher optimum

effect of pH on amylase practical set-up

Place one drop of iodine solution into each well of a spotting tile, take 3 test tubes . S - is starch solution A - amylase solution B - buffer solution pH 5 (used to control pH)

leave them in a water bath for 10 minutes to get to the desired temperature, then combine them into one test tube and and mix with a stirring rod, return to the water bath and start a stopwatch

every 30 s use the rod to transfer a few drops from the mixture to a well in the spotting tile, the iodine should turn blue-black , starch present, (keep on doing this until the iodine remains orange where no starch is present in the solution)

repeat the whole experiment several times using pH buffers of 6 , 7 and 8

problems with the amylase pH practical

sample only taken for 30s so we only have an approximate time for the reaction to complete, address this by taking a sample every 10 seconds

we are looking for the time where the iodine does not go blue-black, which is not always obvious as the colour change tends to be gradual - some of the blue black can be mixed with orange, so its difficult to see when the reaction has finished

address this by asking several people to look at the spotting tile and decide whether the reaction has completed

sugars

soluble carbohydrates, simpler

glucose - boy uses most in respiration

lactose - milk sugar

sucrose granulated sugar

glycogen and cellulose

a large carbohydrate molecule similar to starch and can be stored in liver and muscles

cellulose is another large carbohydrate molecule found in plant cell walls, we cannot digest cellulose

ingestion digestion absorption assimilation

ingestion - taking in food

digestion - breaking down large, insoluble molecules into smaller soluble molecules

absorption - taking in small soluble food molecules from the gut (small int) into the bloodstream

assimilation - absorbed food molecules are taken into the cells of tissues for respiration and/or growth and repair

egestion- (not excretion) the removal of undigested food and other waste materials through the anus.

egestion and excretion difference

egestion - UNDIGESTED food products that were not absorbed from the digestive system

metabolic waste - waste chemicals produced by cells e.g. CO2 and urea

digestion in the mouth

chewing of food, mechanical digestion which increases SA of food, salivary amylase starts the digestion of carbohydrates breaking down to maltose (mucus helps food move down the oesophagus)

Oesophagus

passes food (bolus) down to the stomach by peristalsis - waves of contraction and relaxation of muscles to push food to the stomach and through the gut, breaks down the food a little bit

stomach

where digestion of proteins start (pepsin), contains acid for optiumum, HCL kills ingested microbes,

mucous cells lining protects the stomach walls withstands pH -

churns food into the chyme, which is a liquid food to give a much larger SA for further digestion by enzymes

function of liver

produces bile which has two functions :

neutralises the stomach acid and makes the conditions in the duodenum slightly alkaline for lipase and pancreatic enzymes including lipase

emulsifies fats (convert into smaller droplets ) which gives a greater SA (of droplets) for increase rate of lipid breakdown by lipase

bile is stored in the gall bladder

however when lipids are broken down, the fatty acids lower pH

what happenes in duodenum

in duodenum several digestive enzymes and bile are added to the chyme, this is where most and final chem digestion takes place before the products are absorbed in the illeum

illeum + jejunum

where the smaller food molecules are absorbed into the blood stream through villi.

They are folded and long to give a large SA for absorption and microvilli with folds further increase the SA.

have a really good network of blood capillaries that rapidly take away the products of digestion to ensure a steep conc. grad.

one cell thick membrane to provides a short diffusion path

lacteal and lymph take away glycerol and fatty acids as they cannot be directly absorbed into the bloodstream

many well developed mitochondria for active transport

small intestine is 5m long to give a large SA for absorption

where are all enzymes produced and secreted

all enzymes are produced in the pancreas and secreted in the small intestine, but with an optimum pH slightly alkaline, but there are some other enzymes found :

carbohydrase (amylase) produces in salivary gland and secreted in the mouth

protease (pepsin) produced and secreted in the stomach with an acidic pH optimum

lipase is only secreted in the small intestine

food tests precautions - benedicts

chemicals may be hazardous, so safety goggles must be worn , and also gloves

1. grind food sample into a liquid using distilled water and mortar + pestle used to make a paste, transfer the paste to a beaker with more distilled water so the food molecules dissolve , then filter to remove suspended particles

Benedicts reagent tests for glucose and reducing sugars (not sucrose) , add reagent, a few drops to a little of the sample and place in an 80 deg water bath and leave for 5 mins

should go from blue -> green -> yellow -> orange -> brick red

food tests for biuret starch and lipids

biuret reagent is blue and tests for protein, add a few drops to a little sample and shake, should turn purple

starch is iodine solution add a few drops to a little sample and it should turn instantly from orange brown to blue black

when preparing sample for ethanol emulsion do not fliter as lipid molecules can stick to the paper, add a few drops of distilled water and ethanol and shake - white cloudy emulsion

ethanol is flammable so no naked flames near

large int

absorbs and removes water from any waste material in the intestine , mainly composed of cellulose (fibre)

semi-solid waste is called faeces and is egested through the anus and stored in the rectum

visking tubing experiment

Visking tubing containing starch and amylase can model absorption in the small intestine,

where water outside of the tubing represents blood

mixture inside the tubing is the small int

and the visking tubing is villi

sample the water outside of the tubing w Benedicts and iodine

and no starch and glucose present

then sample around the end and there should be a little bit of glucose and no starch as the amylase broke the carbs down to glucose which was small and soluble enough to diffuse from a high to low conc. out of the visking tubing into the water

the experiment takes place in a controlled temperature

limitations of the visking tubing experiment

the small int has a larger SA due to villi

water doesn't maintain the same diffusion conc grad as blood in capillaries

uses of the products of digestion

To make new carbohydrates, lipids and proteins.

proteins are used for growth and repair

lipids - insulation , organ protection , making cell membranes

glucose - respiration release of energy or glycogen store

molecules are re-polymerised