Practicals Flashcards
What is the independent Variable
Variable in which the values are changed
What is the dependant Variable
Variable in which the value is measured
What is the control Variable
Variable that is kept the same
Explain the process of Measuring the effect of substrate conc. on the rate of enzyme activity using Hydrogen peroxide RP1
Add different hydrogen peroxide conc. To 4 test tubes. Then add 2 drops of detergent and place the test tubes in water baths to reach equilibrium @ 40°C. Then add the potato cylinders (all same size) and add to each test tube at 30s intervals and leave each for 3min and then measure foam created above liquid.
Hydrogen peroxide broken into water and oxygen by enzyme
Name 3 limitations with RP1 - Enzyme Activity
Difficult to measure height of foam
Not all the O2 may have been trapped
Based of personal reaction time when addin cylinders
Why is it important that test tubes are left to equilibriate
This ensures substrate at experimental temp before reaction starts so temperature is constant
How do you calculate Mitotic Index?
Number of cells in mitosis / Total No. of cells counted
What is macerating fluid and why is it important?
It is a mixture of HCl and Absolute alcohol and it breaks down the middle lamella (biological glue), which allows plant cells to be seperated.
What is Acetic Orcein and why is it added?
Stains the DNA, which makes chromosomes visible
Why must you not push the coverslip sideways when preparing the slide
This is so the cells do not roll up and the chromosomes are not damaged
Explain what mounting is when using a microscope (RP2)
Place a cover slip
Squash the preparation by pressing between layers of filter paper
Examine using microscope
Explain the preparation of a temporary mount
Obtain a thin sample to view under microscope. Add a drop of water to slide and then use forceps to place sample on slide. Make sure it’s FLAT. Add an indicator (specific for different prac.) Then place cover slip on top and use filter paper to remove excess stain
Why is the potato dried before measuring (RP3)
This is to remove excess solution released which could affect results and there are different amounts in each potato.
What does the term Processed results mean
This is when calculations are done on raw pieces of data
How do you calculate volume of stock solution
Concentration you want / Concentration you have X Volume asked for
What are the factors that affect enzyme activity
Enzyme Conc
Substrate Conc
Temperature
pH
How is a control set up in a practical measuring enzyme activity
Replace enzyme solution with distilled water
How can results of a practical measuring enzyme activity be used to find initial rate of reaction
Plot on graph and draw a tangent
How do you calculate rate of reaction from time
RoR = 1 / time
Effect of temp on enzyme activity
As temp increases = kinetic energy increases so more EZ complexes form till optimum temp. After, enzyme denatures and RoR decreases
Where in plants can cells undergoing mitosis be found
Meristem tissue at shoots and root tips
What is mitotic index
Ratio of cells undergoing mitosis to total number of cells in sample
What is the use of calibration curves
Used to determine conc of an unknown sample by comparing it to a set of standard values with known concs.
Why are the potato cylinder left in solution for a long period of time (osmosis)
To allow for osmosis to occur till tissue reaches equilibrium with surrounding solution
What is the method for investigating osmosis
Obtain a dilution of sucrose to form 5 concentrations and add 5cm3 to 5 different test tubes
Cut potato into equal sized cylinder and weigh
Add one to each test tube for 20 mins
Take, remove excess and weigh
Calculate percentage change in mass
Why is percentage change used rather than actual change (RP3)
May not have same initial mass and this allows for a valid comparison
State the control variables when investigating osmosis (RP3)
Volume of sucrose solution
Size of potato
Duration left in solution
State 2 factors that affect permeability of cell membranes
Temperature
Conc of solvents
How is beetroot used to measure permeability of cell membranes
Higher permeability = more red pigment that leaks out. A colourimeter can be used to measure absorbance
State the method used to measure effect of temp on permeability of cell membrane (RP4)
Cut beetroot into identical cylinders with scalpel and place in a test tube with equal volumes of water at a certain temp. Leave for 20 mins. Filter each solution into cuvette and measure absorbance
What are the effects of increasing temp on permeability of cell membranes
It increases permeablity
How should label lines be drawn in a diagram
Ruler, no arrows, without crossing other label lines, in pencil
How should a diagram be drawn
Large diagram with no shading, single continuous line with no sketching in pencil
Why is bacteria incubated at 25 degrees
To prevent Growth of pathogens which occurs at higher temps
What does Zone of inhibition indicate
It indicates the bacteria killed by antibiotic and the larger the zone = the more effective the antibiotic
Why should the lid not be completely taped to the petri dish
To allow oxygen to enter petri dish and preventing growth of anaerobic bacteria
How to make Serial Dilutions with an initial sucrose conc of 2M and diluting each solution by scsle factor of 2
Add 10cm3 of the sucorse solution to the first test tube and add 5cm3 of distilled water to the other 4 test tubes.
Use a pipette and take out 5cm3 of the solution from tt1 and add to tt2 and mix thoroughly. Repeat this process for the other tt.
What does isotonic mean
This is when the water potential is the same for 2 solutions
What does hypotonic mean
Solutions have a less negative water potential compared to the cell. Net movement into the cell
What does Hypertonic mean
Solutions have a more negative water potential compared to the cell. Net movement out of cell
Factors that affect rate of osmosis
- wp gradient
- Surface area of exchange surface
- Thickness of the exchange surface
