21 Ass 11 Practicals

Question 1

How would a researcher prepare the epidermis of leaves from crops to be viewed under a microscope 5

Answer 1

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

Question 2

Reagent and positive result in testing for starch

Answer 2

Iodine solution
Blue/black colour

Question 3

Reagent and positive result in testing for reducing sugars

Answer 3

Benedict’s reagent
green/yellow/orange/red colour

Question 4

Reagent and positive result in testing for non-reducing sugars

Answer 4

Boil with Benedict’s reagent after acid hydrolysis

darker colour

Question 5

What type of sugar is glucose?

Answer 5

reducing sugar

Question 6

What type of sugar is sucrose?

Answer 6

non-reducing sugar

Question 7

Define activation energy

Answer 7

Energy needed in a chemical reaction for a product to form

Question 8

What is an enzyme inhibitor?

Answer 8

Something that inhibits the rate of enzyme activity

Question 9

What is a competitive inhibitor?

Answer 9

It has a similar shape to the substrate and temporarily fits into the enzymes active site, competing with the substrate

Question 10

What can make a competitive inhibitor reversible?

Answer 10

Increasing the substrate concentration will reduce effect of inhibitor

Question 11

What is non-competitive inhibition? 2

Answer 11

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

Question 12

(7) which graph shows the change in concentration of enzyme substrate complex?

Answer 12

A

not B bc not just concentration but CHANGE in concentration

Question 13

How do you plot the initial rate of reaction? 3

Answer 13

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

Question 14

How do you calculate the initial rate of reaction? 2

Answer 14

Calculate the gradient of line

Change y / change x

Question 15

What is activation energy

Answer 15

the energy level that must be overcome before a reaction can progress

Question 16

What is Vmax?

Answer 16

The point at on y-axis which the line of enzyme reaction is horizontal

Question 17

How do you calculate Km

Answer 17

1/2Vmax on y-axis & then find value on the X-axis

Question 18

Ass 2 3 b) fig 2.1 Describe & explain shape of curve 5

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What is used to test for proteins

Answer 20

biuret solution

Question 21

What is used to test for lipids and positive result?

Answer 21

ethanol and milky emulsion/cloudy

Question 22

How do you convert mm to um?

Answer 22

x by 1000

Question 23

How does wavelength affect microscopy?

Answer 23

A shorter wavelength gives better resolution

Question 24

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?

Answer 24

With a green light the magnification remains the same as the red light but the resolution increases

Question 25

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)?

Answer 25

multiply 0.1 by 1000 then divide by 100

Question 26

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

Answer 26

eyepiece graticule, ruler and a stage micrometer scale

Question 27

Describe the appearance of the centrosome

Answer 27

non-membrane bound cylindrical structures

Question 28

Describe the appearance of the ribosome

Answer 28

non-membrane bound, spherical structures

Question 29

How big are viruses?

Answer 29

20nm - 500nm

Question 30

How many nm in 1 mm?

Answer 30

1000 000

Question 31

Can a light microscope see a virus that’s 30nm in diameter?

Answer 31

No, because the virus is 30nm and a light microscope’s resolution is too low, and can only distinguish points 200nm or more apart

Question 32

What is the formula for calculating magnification?

Answer 32

I
AM

Question 33

How would one test for non-reducing sugars? 5

Answer 33

1. add 5cm^3 of food fresh food sample to test tube
2. boil food sample with hydrochloric acid
3. Neutralise test solution by adding sodium hydroxide
4. add 5cm^3 of Benedict’s reagent
5. heat test tube in thermostatic water bath set to 80 degrees C for 3 min

Question 34

What does enzyme affinity mean? 2

Answer 34

A measure of how readily enzyme-substrate complexes form & lead to products

low affinity= substrate can leave active site without any reaction taking place

Question 35

What is meant by Km? 4

Answer 35

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