mid sem test - lab Qs

what do you need to consider when designing a nitrogen experiment

only one variable should be tested at a time where possible

biological variation needs to be taken into account and minimised as much as possible by the design of the experiment and carrying out control experiments

you would also need to recruit volunteers and have ethical approval consent form signed by the subjects

what data needs to be collected and what are the limitations of ths

all of the urine would need to be collected for 24 hours. this would be analysed at the end of the period of the experiment

it would also need to be noted about the age, weight, sex, protein intake etc of the client

need to account for biological differences and ensure a diet is maintained

what nitrogen containing compounds can be measured in the lab

urea, uric acid and creatinine

ammonia is also excreted but is estimated as is not stable

also estimate N excreted through hair, sweat, faeces etc - estimated in this case to be 2.5g

how to use a standard curve to estimate N

read off the curve the content of the measured N containing compound (e.g. urea) using the absorbance

use this to calculate the urea in 1mL of the diluted sample

use this to calculate the urea in 1mL of the undiluted sample

use this to calculate the urea excreted in 24hrs (times by total urine volume)

use the percentage if nitrogen in the compound (e.g. 47% for urea) to find the nitrogen as urea (g/24hrs)

how to calculate nitrogen balance

subtract the amount of nitrogen excreted from the total nitrogen intake

in healthy people it would be expected to be in nitrogen equilibrium

when see positive nitrogen balance

when the body retains more nitrogen than it excretes

this occurs during periods of growth (such as in children), pregnancy, or recovery from illness or injury

when see negative nitrogen balance

when the body loses more nitrogen than it takes in

can result from insufficient dietary protein, leading to a lack of amino acids necessary for energy and biosynthesis

can also happen due to tissue destruction in injury or increased protein catabolism during major trauma or illness