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core practical's Flashcards

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1
Q

what factors affect rate of reaction (practical 1)

A

temperature
pH
concentration of substrate
concentration of enzyme

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2
Q

what equation can be used to calculate rate of reaction (practical 1)

A

1/mean time

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3
Q

what is trypsin solution (practical 1)

A

enzyme which breaks down proteins to amino acids

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4
Q

what is observed when trypsin is added to protein (practical 1)

A

cloudy -> colourless

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5
Q

summarise the method to measure a factor affecting rate of reaction (practical 1)

A
  • dilute stock solution of trypsin with distilled water to give 0.2% 0.4%…. solutions
  • make a control by adding 2cm^3 trypsin and 2cm^3 of distilled water and use this top set absorbance to 0
  • add 2cm^3 of milk suspension and 2cm^3 of trypsin in curvette and place in colorimeter
  • measure absorbance at 15 second intervals for 5 minutes
  • rinse curvette with distilled water
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6
Q

give 3 risk assesments that should be taken into consideration when measuring rate of reaction (practical 1)

A

broken glass
hot liquids
enzymes (allergies)

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7
Q

what protein is contained in milk (practical 1)

A

casein

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8
Q

how does increasing concentration of trypsin increase rate of reaction (practical 1)

A

number of enzyme substrate complexes increases because there is a higher frequency of collisions so rate of reaction increases until it levels off because all substrates occupy active sites

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9
Q

give a systematic error which could occur when using a colorimeter (practical 1)

A

scratch on the surface of the curvette

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10
Q

why is it important to measure initial rate of reaction rather than average rate of reaction (practical 1)

A

because the start is when the reaction is at its fastest and the rate slows as the substrate is used up

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11
Q

what is used on microscopes to measure the specimen (practical 2)

A

stage micrometer and eyepiece graticule
must calibrate them by lining them up

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12
Q

summarise the method to observe biological specimen under a microscope (practical 2)

A
  • calibrate eyepiece graticule and stage micrometer
  • cut transverse sections of plant stem and select thinnest sections
  • mount on microscope slide and add toluidine blue stain and leave to dry then lower coverslip at 45* angle to ensure no air bubbles
  • place under microscope and adjust to get the specimen into focus
  • observe and draw the stem
  • measure stem diameter and vascular bundle using eyepiece graticule
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13
Q

state 3 hazards when observing plant cells under a microscope (practical 2)

A

toluidine blue stain is an irritant in eyes or cuts
scalpel
broken glass

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14
Q

how could you improve the accuracy of measuring cells under a microscope (practical 2)

A

calculate a mean from multiple cells

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15
Q

what is mitotic index (practical 3)

A

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

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16
Q

summarise the method to show the stages of mitosis in meristem under a microscope (practical 3)

A
  • heat 1mol/dm^3 HCl at 55* in water bath for 15 minutes
  • place garlic clove in HCl and leave for 5 minutes
  • cut small sample of root tip using scalpal and transfer to acetic orcein stain and heat in water bath for 5 minutes
  • place on microscope slide and macerate with a needle to spread cells out
  • lower coverslip at 45* angle ensuring no air bubbles and gently squash the slide
  • adjust the microscope magnification and count the cells in various stages of mitosis
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17
Q

why do you macerate the plant cells with a needle on the microscope slide (practical 3)

A

spread out the cells to make the chromosomes more visible

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18
Q

state 3 hazards in measuring mitotic index (practical 3)

A

hydrochloric acid
acetic orcein
scalpel

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19
Q

why is the root tip heated with HCl before measuring mitotic index (practical 3)

A

break down the cellulose cell wall to allow you to view the cell

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20
Q

summarise the practical investigating the effect of sucrose concentration on pollen tube growth (practical 4)

A
  • dilute stock sucrose solution
  • place moist filter paper into a petri dish to form a humid chamber
  • place a few drops of sucrose solution and an equal volume of mineral salt medium onto a clean microscope slide
  • use mounted needle to rub the anther so they shed some pollen onto the microscope slide
  • place slide into the petri dish and start timer
  • place slide under microscope and use calibrated eyepiece graticule to measure pollen tube growth
21
Q

why is a cover slip not placed on the slide with the pollen (practical 4)

A

to prevent conditions becoming anoxic

22
Q

state 2 hazards with investigating the effect of sucrose concentration on pollen tube growth (practical 4)

A

scalpel
needle

23
Q

what is expected to happen to pollen tube growth as sucrose concentration increases and why (practical 4)

A

as sucrose concentration increases mean pollen tube growth increases until an optimum, after this point mean pollen tube growth decreases because of the osmotic effects of increasing concentration of sucrose

24
Q

state the control variables when investigating the effect of sucrose concentration on mean pollen tube growth (practical 4)

A

pollen used must be from the same anther
must use the same medium
leave immersed for the same amount of time

25
Q

what is the role of a pollen tube (practical 4)

A

carries the male gametes to the ovule where double fertilisation can occur

26
Q

what could cause the pollen tube to grow in the correct direction of the style (practical 4)

A

chemicals being released from the embryo sac causing pollen tube growth to be attracted towards the micropyle showing the pollen tube is positively chemtrophic

27
Q

what factors can affect permeability of a membrane (practical 5)

A

temperature
concentration of solvents

28
Q

what pigments in found in beetroot and what colour is it (practical 5)

A

red
betalain

29
Q

summarise the method to investigate the effect of temperature on membrane permeability (practical 5)

A
  • cut beetroot into 8 identical cylinders using a cork borer then rinse and dry to clean off excess pigment
  • place in 10cm^3 of distilled water in labelled test tubes in water baths at different temperatures from 0* to 70*
  • leave for 10 minutes then add the beetroot cylinders to the test tubes and record exact temp of water bath
  • remove the beetroot cylinders after a certain time
  • set colorimeter to 0 using distilled water
  • filter each sample into a curvette using filter paper
  • measure absorbance of each solution (higher absorbance = higher pigment concentration = more permeable membrane)
30
Q

state 2 hazard with measuring the effect of temperature on the permeability of a membrane (practical 5)

A

scalpel/cork borer
hot liquids

31
Q

why does permeability increases as temperature increases (practical 5)

A

because proteins in the membrane denature as the heat damages the bonds in their tertiary structure which creates gaps in the membrane making it easier for molecules to pass through it

32
Q

why does permeability decrease as temperature decreases (practical 5)

A

at lower temperatures phospholipids have little energy and are packed closely together to make the membrane rigid so permeability decreases as this constricts molecule from crossing the membrane

33
Q

why may permeability increase at extremely low temperatures (practical 5)

A

ice crystals can form which pierce the cell membrane and increase permeability

34
Q

state 4 control variables when measuring the effect of temperature on permeability of a membrane (practical 5)

A

volume of water
type, age & storage of beetroot
volume of solution in curvett
size of beetroot cylinders

35
Q

why should the test tubes be placed in the water baths without the beetroot in to begin with (practical 5)

A

to ensure they are the correct temperature and do not need time to equilibrate when the beetroot is added

36
Q

what is incipient plasmolysis (practical 6)

A

the point at which the protoplasm begins to shrink away from the cell wall

37
Q

when does incipient plasmolysis occur (practical 6)

A

when the water potential and osmotic potential are equal

38
Q

how do you measure incipient plasmolysis (practical 6)

A

the point at which 50% of cells in a sample are plasmolysed

39
Q

summarise the method to determine the water potential of plant cells (practical 6)

A
  • transfer small set volume of salt solution into different watch glasses
  • place thin plant tissue onto watch glass and leave for 20 minutes
  • remove each tissue with forceps and place on microscope silde with a cover slip
  • count 25 cells and record how many of them are plasmolysed
40
Q

state 2 hazards when determining the water potential of plant cells (practical 6)

A

scalpel
broken glass

41
Q

why are water potential and osmotic potential the same at the point of incipient plasmolysis (Ψ = P + π) (practical 6)

A

because there is no net movement of water and the cell exerts no pressure on the cell wall so turgor pressure is 0 so π = Ψ

42
Q

state 4 hazards in investigating the gas exchange system of a locust (practical 7)

A

biohazard (contamination)
disinfectant (flammable)
sharp tools
allergy to locus

43
Q

why should you floor the specimen with water when dissecting a locus (practical 7)

A

so that the tracheae shows up as a silvery-grey

44
Q

what approaches could be taken to ensure ethical responsibility is taken when dissecting a locus (practical 7)

A

work in groups not individually so that less insects are used
ensure they are treated humanly at all times

45
Q

what is a potometer

A

a device used to measure the uptake of water (rate of transpiration)

46
Q

what abiotic factors affect rate of transpiration

A

light intensity, humidity, wind speed, temperature

47
Q

summarise the method to investigate the effect of an abiotic factor on rate of transpiration

A
  • set up potometer by filling capillary tube and rubber connector with water and insert leafy shoot and trim it where necessary (do this under water)
  • place bottom of capillary tube in a beaker of water
  • place petroleum jelly around the join the maintain airtight conditions
  • leave for a set time and allow air bubble to be drawn up to the capillary tube
  • measure the start position and end position of the air bubble
  • repeat while changing the abiotic factor
48
Q
A

Biology (33 decks)

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