core practical's

Question 1

what factors affect rate of reaction (practical 1)

Answer 1

temperature
pH
concentration of substrate
concentration of enzyme

Question 2

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

Answer 2

1/mean time

Question 3

what is trypsin solution (practical 1)

Answer 3

enzyme which breaks down proteins to amino acids

Question 4

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

Answer 4

cloudy -> colourless

Question 5

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

Answer 5

• 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

Question 6

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

Answer 6

broken glass
hot liquids
enzymes (allergies)

Question 7

what protein is contained in milk (practical 1)

Answer 7

casein

Question 8

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

Answer 8

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

Question 9

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

Answer 9

scratch on the surface of the curvette

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

• 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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

calculate a mean from multiple cells

Question 15

what is mitotic index (practical 3)

Answer 15

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

Question 16

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

Answer 16

• 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

Question 17

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

Answer 17

spread out the cells to make the chromosomes more visible

Question 18

state 3 hazards in measuring mitotic index (practical 3)

Answer 18

hydrochloric acid
acetic orcein
scalpel

Question 19

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

Answer 19

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

Question 20

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

Answer 20

• 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

Question 21

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

Answer 21

to prevent conditions becoming anoxic

Question 22

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

Answer 22

scalpel
needle

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

temperature concentration of solvents

Question 28

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

Answer 28

red betalain

Question 29

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

Answer 29

- 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)

Question 30

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

Answer 30

scalpel/cork borer hot liquids

Question 31

why does permeability increases as temperature increases (practical 5)

Answer 31

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

Question 32

why does permeability decrease as temperature decreases (practical 5)

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

what is incipient plasmolysis (practical 6)

Answer 36

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

Question 37

when does incipient plasmolysis occur (practical 6)

Answer 37

when the water potential and osmotic potential are equal

Question 38

how do you measure incipient plasmolysis (practical 6)

Answer 38

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

Question 39

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

Answer 39

- 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

Question 40

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

Answer 40

scalpel broken glass

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

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

Answer 43

so that the tracheae shows up as a silvery-grey

Question 44

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

Answer 44

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

Question 45

what is a potometer

Answer 45

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

Question 46

what abiotic factors affect rate of transpiration

Answer 46

light intensity, humidity, wind speed, temperature

Question 47

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

Answer 47

- 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