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N Biology A Level > Core Pracs > Flashcards

Core Pracs Flashcards

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1
Q

How to approach ‘Devise an experiment’ Q?

A

IDCORSS
Dependent variable (equipment, measurements, how to calculate it)
Independent variable (list range of concs/temp tested, at least 5, equipment)
Controls/control variables (eg water as it’s 0 moldm-3, state what you’re controlling, how and why)
Organism (mass, age, species, length)
Repeats (at least 3 times, calculate a mean) (identify and remove anomalies)
Stats test (chi squared/graph-state what you’re plotting/standard deviation as bars on graphs, overlap=no significance)(simpson’s index)(t-test)
Safety (risk assessment, precautions, ethical considerations)

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2
Q

How to investigate trypsin conc affecting the initial rate of reaction? (CP1)

A

Dilute trypsin with distilled water making 0.2%, 0.4%, 0.6%, 0.8%
distilled water is control
add 2cm3 milk suspension to each conc and test for colorimeter absorbance at 15 second intervals

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3
Q

As conc of trypsin increases….

A

rate of reaction increases as number of enzyme-substrate complexes forming increases

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4
Q

why does rate plateau after a few minutes in enzyme substrate reaction?

A

Because all substrates have occupied an active site

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5
Q

what are the 4 factors that affect enzyme activity?

A
  • temp
  • pH
  • enzyme conc
  • substrate conc
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6
Q

how to set up control when measuring enzyme activity?

A

use distilled water or boiled enzyme solution instead of enzyme solution

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7
Q

how can colorimeter determine RoR of trypsin and milk?

A

as trypsin digests proteins in milk, milk becomes more translucent
value in colorimeter decreases as digestion increases

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8
Q

how to calculate RoR from time?

A

1/time

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9
Q

what is microscopy used for?

A

to increase magnification and resolution of object

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10
Q

what is the formula for magification?

A

I / A x M

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11
Q

how to use light microscope to observe and measure biological samples?

A
  1. calibrate eyepiece graticule and line it up with stage micrometer
  2. cut THIN transverse section of plant stem
  3. place on slide, add stain and cover slip. ensure no air bubbles
  4. set objective lens to lowest magnification
  5. draw it out
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12
Q

what are rules for label lines in biological drawings?

A

must use ruler and draw horizontal line

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13
Q

what are the magnifications of eyepiece and objective lenses?

A

10x eyepiece
objective comes in low, medium, high

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14
Q

what is the mitotic index of a sample?

A

ratio of cells undergoing mitosis to the total number of cells in a sample

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15
Q

what are some common risk assessment factors?

A
  • scalpel/scissor - risk cuts
  • acids/dyes - risk irritatoin
  • glass equipment - risk cuts
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16
Q

how to find mitotic index of a garlic clove? (Core prac procedure)

A
  • heat HCl in waterbath
  • cut small sample of root tip using scalpel
  • add stain (acetic orcein)
  • Macerate with needle, make 1 thin layer
  • cover slip, ensure no air bubbles#
  • gently press tgt
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17
Q

where in plants can cells undergoing mitosis be found?

A

meristem tissues at root and shoot tips

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18
Q

what is the formula of mitotic index?

A

of cells w visible chromosomes / total ~ of cells in sample

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19
Q

why is garlic root tip placed in hot HCl?

A

to dissolve middle lamellae, breaking up cellulose cell wall
so dye can stain

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20
Q

why is garlic clove sample squashed?

A

to flatten sample and reduce layers

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21
Q

what is the pollen tube?

A

path through stigma made by digestive enzymes so pollen grain can reach embryo sac and fertilise ovum

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22
Q

what is the cell-surface membrane made up of?

A

phospholipid bilayer
is selectively permeable

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23
Q

what is the purple pigment on beetroot cells called? how is it used?

A

betalain
permeability can be measured by intensity of pigment leaked
using colorimeter

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24
Q

what conditions are measured for beetroot membrane permeability?

A

range of temperatures: 0-70 C
filter out to colorimeter sample #
control cuvette using distilled water

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25
Q

what are 2 factors affecting permeability of cell membranes?

A

temp
conc of solvents (ethanol)

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26
Q

what is the effect of temp on membrane permeability?

A

increasing temp = increase permeability (more extreme temps), as proteins in membrane denature to produce gaps

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27
Q

what is the effect of ethanol conc on membrane permeability?

A

higher = increase permeability, as it causes gaps to form in membrane

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28
Q

what is plasmolysis?

A

where plant cell begins to shrink away from cell wall (as water osmosise out of cell)

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29
Q

what is isotonic?

A

water conc in cell is equal to outside of cell

30
Q

what is hypertonic?

A

water in cell is osmosising to outside of cell
cell becomes flaccid

31
Q

what is hypotonic?

A

water is osmosising into cell
cell becomes turgid

32
Q

what is the procedure to test for osmotic potential of plant cells?

A

5 concs of mineral salt solutions
place plant cells in them and soak for 20 mins (to reach equilibrium)
observe 25 cells under microscope, note how many are plasmolysed

33
Q

how to dissect a locust?

A

remove exoskeleton
flood specimen with water, trachae show up silvery-grey

34
Q

what are rules about biological drawings?

A

firm single line, no shading
use pencil
large diagram (half the space given at least)

35
Q

what is used to measure the uptake of water?

A

potometer

36
Q

what is used to measure liquid translucency?

A

colorimeter

37
Q

what factors affect rate of transpiration?

A
  • wind speed
  • light intensity
  • temp
  • humidity
  • SA
  • water supply
38
Q

how is rate of transpiration calculated?

A

distance of bubbles travelled in capillary tube
volume of water uptake = πr²
rate = volume/time

39
Q

how to control light intensity?

A

distance between lamp and potometer

40
Q

how to control wind speed?

A

using a fan/hair dryer near potometer at different speeds

41
Q

how to control humidity?

A

wrap plastic bag around plant to maintain humid environment

42
Q

How to control temperature in practicals?

A

Thermostatically controlled water bath

43
Q

Describe how to use a micrometer to determine how many times bigger your drawing is than the actual cell? (4 marks)

A
  • use eye piece graticule and line up
  • calibrate stage micrometer
  • divide length by magnification
  • repeat measurements
  • divide into lengths in drawing (apply Q!)
44
Q

Why are electron microscopes used instead of light microscopes to look at viruses? (2 marks)

A
  • electron microscopes have higher resolution and magnification
  • bcs it has shorter wavelengths
45
Q

outline a method for extracting photosynthetic pigments

A

grind a leaf with pestle and mortar
+ extraction solvent like propanone
then paper chromatography

46
Q

outline how paper chromatography can be used to separate photosynthetic pigments?

A
  1. use capillary tube to dot extracted pigment on start line (drawn w pencil)
  2. dip paper in solvent
  3. allow solvent to run until it reaches the other end of paper
47
Q

how to calculate Rf values for paper chromatography?

A

distance moved by pigment / distance moved by substance

48
Q

How to use counting squares to count cells?

A

Count cells in grid,
And middle line of left and bottom of the grid

49
Q

What is the inaccuracy in counting cells?

A
  • hard to decide if cell is touching line (e.g. double counted)
  • counts both dead and living cells
50
Q

When Q asks you to comment on the validity of a conclusion and standard deviation involved, think…

A
  1. Does SD and data overlap?
    - if yes, it’s invalid
    - if not, it’s valid
  2. Give reason why this could happen
51
Q

Explain why streak plating on selective media is a suitable method for isolating the salmonella. (4 marks)

A
  1. Streak plating only allowing gram -ve to grow
  2. So it spreads bacteria in agar individually,
  3. So colonies grow separately
  4. When extracting, only one type of bacteria will be picked up
52
Q

How to find exact data values if given a table but my exact data isn’t on the table?

A

Plot a graph
Find value on graph (line of best fit)

53
Q

Explain why decreasing temp affects rate of respiration of maggots. (2 marks)

A

Less kinetic energy in enzymes
So collisions between enzymes and substrates less likely to take place

54
Q

Why do we use controls?

A

For comparison

55
Q

Explain the effect of ethanol on plant cell membranes. (2 marks)

A

Ethanol damages/dissolves phospholipids (as it is polar)
So membrane becomes more permeable

56
Q

Why do we have to rinse disc of beetroot/leaf?

A

To remove excess pigments as it would affect measurements

57
Q

When to accept or reject null hypothesis in Chi square test?

A

If Chi2 value > p value (p=0.05 unless stated otherwise)
It is significant enough to reject null hypothesis
Then link to Question’s conclusion

58
Q

How to make sure respirometer test is valid.

A
  • control temp using thermostatically controlled water bath
  • use colour liquid in glass tube
  • use KOH/soda lime (to absorb CO2)
  • use πr2d
  • use metric ruler
  • repeat
59
Q

Which stage in the aerobic respiration produces 4 CO2 for each glucose?

A

Krebs

60
Q

What do you use to extract plant pigments? (Grinding wise)

A

Pestle and mortar

61
Q

How do you produce a plan drawing?

A

Outline organism/thing
Do not draw details

62
Q

What do mitotic index mean?

A

Ratio of cells dividing out of all cells
Higher value (closer to 1) = more cell dividing

63
Q

What is sucrose’s effect on pollen tube growth?

A

Higher sucrose conc = higher rate of pollen tube growth
Increased germination as more sucrose supply for respiration

64
Q

What does it mean by turgid cells?

A

Cell with High water content

65
Q

What do turgid and plasmolysed cells look like under a microscope? Why?

A

Turgid: brick shape, full of water so enough pressure against rigid cell wall to keep structure
Plasmolysed: dense cluster in middle of cell, away from cell wall

66
Q

Why does increase in temp increase rate of respiration?

A

Increase KE and enzyme activity
So increase oxygen uptake to supply for increased activity

67
Q

What colour filters affect rate of photosynthesis (negatively) the most?

A

Green decreases it most
Red light is blocked
Plants don’t use much green light (as reflected by their colour as they reflect green light

68
Q

What factors affect distance travelled by pigments in chromatography?

A

The solubility of the pigment

69
Q

How does streak plate isolate individual colonies? (5 marks)

A
  • flame wire loop with Bunsen
  • streak sample on sterile agar
  • at least 3 streaks in total
  • second and third streaks must pass through lines of previous streaks
  • incubate and pick out individual colonies with wire loop
70
Q

Why is bacteria incubated at 30C at school? (2 marks)

A
  • above would be similar to human body temp
  • risk of growing human pathogens and infection students

N Biology A Level (18 decks)

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