21 Ass 11 Practicals Flashcards
How would a researcher prepare the epidermis of leaves from crops to be viewed under a microscope 5
Gather a fresh sample of leaves from several crops
Tear the leaves and use forceps and gloves to cleanly peel away the epidermis
Place the epidermis on a clean slide on a drop of water
place a cover slide over this using a mounted needle and wipe away excess
stain if necessary
Reagent and positive result in testing for starch
Iodine solution
Blue/black colour
Reagent and positive result in testing for reducing sugars
Benedict’s reagent
green/yellow/orange/red colour
Reagent and positive result in testing for non-reducing sugars
Boil with Benedict’s reagent after acid hydrolysis
darker colour
What type of sugar is glucose?
reducing sugar
What type of sugar is sucrose?
non-reducing sugar
Define activation energy
Energy needed in a chemical reaction for a product to form
What is an enzyme inhibitor?
Something that inhibits the rate of enzyme activity
What is a competitive inhibitor?
It has a similar shape to the substrate and temporarily fits into the enzymes active site, competing with the substrate
What can make a competitive inhibitor reversible?
Increasing the substrate concentration will reduce effect of inhibitor
What is non-competitive inhibition? 2
It doesn’t bind to the active site, but another part of the enzyme
causing a change in the enzymes shape so it’s no longer complementary
Increasing substrate has no effect
(7) which graph shows the change in concentration of enzyme substrate complex?
A
not B bc not just concentration but CHANGE in concentration
How do you plot the initial rate of reaction? 3
draw a tangent to the curve at the start of the reaction
Find an easy- to read part of the scale to stop drawing
Make triangle as big as possible
How do you calculate the initial rate of reaction? 2
Calculate the gradient of line
Change y / change x
What is activation energy
the energy level that must be overcome before a reaction can progress
What is Vmax?
The point at on y-axis which the line of enzyme reaction is horizontal
How do you calculate Km
1/2Vmax on y-axis & then find value on the X-axis
Ass 2 3 b) fig 2.1 Describe & explain shape of curve 5
When substrate concentration is lower, rate of reaction is proportional to substrate concentration
This is because there are still some unoccupied active sites
At higher substrate concentrations, the increase in the rate of reaction is slower
& substrate concentration is no longer limiting factor, instead enzyme concentration is
because all active sites are occupied
For a commercial application using an enzyme, the progress of the enzyme-catalysed reaction needs to be studied. Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally 4
Keep temperature & pH constant
Take samples of the amount of product formed at regular intervals
Plot a graph of product formation against time
Draw a tangent to determine initial rate of reaction
What is used to test for proteins
biuret solution
What is used to test for lipids and positive result?
ethanol and milky emulsion/cloudy
How do you convert mm to um?
x by 1000
How does wavelength affect microscopy?
A shorter wavelength gives better resolution
A specimen of plant tissue is observed twice with a microscope, first using a red light with wavelength of 650nm and then with green light using wavelength of 510nm what happens to the magnification & resolution when using green light compared to red light?
With a green light the magnification remains the same as the red light but the resolution increases
q4 the diagram shows an eyepiece graticule and part of a stage micrometer scale as seen using x100 magnification. what is the correct method for calculating the value of one eyepiece graticule unit in micrometers (um)?
multiply 0.1 by 1000 then divide by 100
A student observes a cell using a light microscope. The student then draws the cell. Which items will the student need to calculate the magnification of the drawing? 3
eyepiece graticule, ruler and a stage micrometer scale
Describe the appearance of the centrosome
non-membrane bound cylindrical structures
Describe the appearance of the ribosome
non-membrane bound, spherical structures
How big are viruses?
20nm - 500nm
How many nm in 1 mm?
1000 000
Can a light microscope see a virus that’s 30nm in diameter?
No, because the virus is 30nm and a light microscope’s resolution is too low, and can only distinguish points 200nm or more apart
What is the formula for calculating magnification?
I
AM
How would one test for non-reducing sugars? 5
- add 5cm^3 of food fresh food sample to test tube
- boil food sample with hydrochloric acid
- Neutralise test solution by adding sodium hydroxide
- add 5cm^3 of Benedict’s reagent
- heat test tube in thermostatic water bath set to 80 degrees C for 3 min
What does enzyme affinity mean? 2
A measure of how readily enzyme-substrate complexes form & lead to products
low affinity= substrate can leave active site without any reaction taking place
What is meant by Km? 4
Michaelis-Menten Constant
can predict theoretical affinity of enzyme
value is substrate concentration at which enzyme works at 1/2 Vmax
lower Km=higher affinity bc Vmax reached at higher substrate concentrations & vice versa
