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Biology AS > Practicals > Flashcards

Practicals Flashcards

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1
Q

What is the independent Variable

A

Variable in which the values are changed

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2
Q

What is the dependant Variable

A

Variable in which the value is measured

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3
Q

What is the control Variable

A

Variable that is kept the same

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4
Q

Explain the process of Measuring the effect of substrate conc. on the rate of enzyme activity using Hydrogen peroxide RP1

A

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

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5
Q

Name 3 limitations with RP1 - Enzyme Activity

A

Difficult to measure height of foam
Not all the O2 may have been trapped
Based of personal reaction time when addin cylinders

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6
Q

Why is it important that test tubes are left to equilibriate

A

This ensures substrate at experimental temp before reaction starts so temperature is constant

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7
Q

How do you calculate Mitotic Index?

A

Number of cells in mitosis / Total No. of cells counted

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8
Q

What is macerating fluid and why is it important?

A

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.

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9
Q

What is Acetic Orcein and why is it added?

A

Stains the DNA, which makes chromosomes visible

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10
Q

Why must you not push the coverslip sideways when preparing the slide

A

This is so the cells do not roll up and the chromosomes are not damaged

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11
Q

Explain what mounting is when using a microscope (RP2)

A

Place a cover slip
Squash the preparation by pressing between layers of filter paper
Examine using microscope

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12
Q

Explain the preparation of a temporary mount

A

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

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13
Q

Why is the potato dried before measuring (RP3)

A

This is to remove excess solution released which could affect results and there are different amounts in each potato.

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14
Q

What does the term Processed results mean

A

This is when calculations are done on raw pieces of data

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15
Q

How do you calculate volume of stock solution

A

Concentration you want / Concentration you have X Volume asked for

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16
Q

What are the factors that affect enzyme activity

A

Enzyme Conc
Substrate Conc
Temperature
pH

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17
Q

How is a control set up in a practical measuring enzyme activity

A

Replace enzyme solution with distilled water

18
Q

How can results of a practical measuring enzyme activity be used to find initial rate of reaction

A

Plot on graph and draw a tangent

19
Q

How do you calculate rate of reaction from time

A

RoR = 1 / time

20
Q

Effect of temp on enzyme activity

A

As temp increases = kinetic energy increases so more EZ complexes form till optimum temp. After, enzyme denatures and RoR decreases

21
Q

Where in plants can cells undergoing mitosis be found

A

Meristem tissue at shoots and root tips

22
Q

What is mitotic index

A

Ratio of cells undergoing mitosis to total number of cells in sample

23
Q

What is the use of calibration curves

A

Used to determine conc of an unknown sample by comparing it to a set of standard values with known concs.

24
Q

Why are the potato cylinder left in solution for a long period of time (osmosis)

A

To allow for osmosis to occur till tissue reaches equilibrium with surrounding solution

25
Q

What is the method for investigating osmosis

A

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

26
Q

Why is percentage change used rather than actual change (RP3)

A

May not have same initial mass and this allows for a valid comparison

27
Q

State the control variables when investigating osmosis (RP3)

A

Volume of sucrose solution
Size of potato
Duration left in solution

28
Q

State 2 factors that affect permeability of cell membranes

A

Temperature

Conc of solvents

29
Q

How is beetroot used to measure permeability of cell membranes

A

Higher permeability = more red pigment that leaks out. A colourimeter can be used to measure absorbance

30
Q

State the method used to measure effect of temp on permeability of cell membrane (RP4)

A

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

31
Q

What are the effects of increasing temp on permeability of cell membranes

A

It increases permeablity

32
Q

How should label lines be drawn in a diagram

A

Ruler, no arrows, without crossing other label lines, in pencil

33
Q

How should a diagram be drawn

A

Large diagram with no shading, single continuous line with no sketching in pencil

34
Q

Why is bacteria incubated at 25 degrees

A

To prevent Growth of pathogens which occurs at higher temps

35
Q

What does Zone of inhibition indicate

A

It indicates the bacteria killed by antibiotic and the larger the zone = the more effective the antibiotic

36
Q

Why should the lid not be completely taped to the petri dish

A

To allow oxygen to enter petri dish and preventing growth of anaerobic bacteria

37
Q

How to make Serial Dilutions with an initial sucrose conc of 2M and diluting each solution by scsle factor of 2

A

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.

38
Q

What does isotonic mean

A

This is when the water potential is the same for 2 solutions

39
Q

What does hypotonic mean

A

Solutions have a less negative water potential compared to the cell. Net movement into the cell

40
Q

What does Hypertonic mean

A

Solutions have a more negative water potential compared to the cell. Net movement out of cell

41
Q

Factors that affect rate of osmosis

A
  • wp gradient
  • Surface area of exchange surface
  • Thickness of the exchange surface

Biology AS (24 decks)

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