core practicals 1-13

what is plasmolysis?

when the protoplasm of a plant cell begins to shrink away from the cell wall because the water potential and the osmotic potential are equal

outline the procedure to determine the water potential of a plant tissue

1. transfer a small set volume of each mineral salt solution into a watch glass and leave for 20 mins

2. remove each section using forceps. mount in a drop of the corresponding solution on a microscope slide and cover with a coverslip

3. observe 25 cells and record how many are plasmolysed

when can a solution be determined to be isotonic?

when the line of best fit crosses the x axis

what does isotonic mean?

when the water potential of the mineral salt solution is the same as the water potential of the plant tissue, so there is no net movement of water

what is incipient plasmolysis?

where the water potential of the cytoplasm is the same as the solution - the point at which plasmolysis just begins to occur - when 50% of the cells in a tissue are plasmolysed

why are the plant cells left in the mineral salt solution for 20 minutes before observation?

to allow time for osmosis to reach equilibrium

why is aseptic technique important?

creates reliable and repeatable data
avoids contamination of the sample from outside substances

what is streak plating?

bacteria are spread out on a nutrient agar plate so that distinct individual colonies can be seen
colonies grown on clean agar plates to produce non-contaminated samples of one species of bacteria

how can colonies be identified as a particular species of bacteria?

size, colour, and texture of the colony

disinfectant risk assessment

hazard - disinfectant
risk - flammable
safety precaution - keep away from naked flame
in emergency - put out fire, seek assistance

what parts of aseptic technique are used in cp13?

flame sterilise the inoculating loop before and after use
flame sterilise the neck of the bottle the mixed culture is in after opening and before closing
open the petri dish lid as little as possible

why should the petri dish lid not be taped the whole way around?

so the conditions are not anoxic and the bacteria on the agar can actually grow

how can the colonies produced in cp13 be identified?

white colonies are likely to be salmonella
yellow colonies are likely to be staphylococcus

outline the procedure to isolating a particular species of bacteria

1. dip a sterile inoculating loop into the mixed culture

2. make streaks on the agar using the inoculating loop

3. incubate the agar plate for 24 hours

4. take a sample of the different colonies and streak them on different agar plates and incubate again for 24 hours

what is aseptic technique?

procedure used to avoid contamination of the sample from outside substances, such as microorganisms

how is aseptic technique used in cp12?

wipe down surfaces with antibacterial before & after
use bunsen burner to create sterile zone around workspace
flame sterilise wire loop and necks of any bottles
keep vessels containing bacteria open for minimum amount of time
close all windows and doors

what is chromatography used for?

separate and identify small quantities of different compounds

what are the factors affecting the rate of migration?

solubility
mass
affinity to the paper

outline the procedure for cp11

1. draw pencil line 1cm above bottom of paper

2. cut section of leaf and grind in pestle and mortar with 20 drops of propanone to release pigments

3. use capillary tube to extract pigment and blot on paper

4. leave paper in solvent for 10 minutes

5. take paper out of solvent and draw a pencil line where pigments moved to

6. calculate Rf value for each spot of pigment

chromatography solvent risk assessment

hazard - chromatography solvent
risk - flammable, irritant, harmful to inhale
safety precaution - avoid contact with solvent, wear eye protection, keep away from flame in well-ventilated room
in emergency - wash skin/eyes using cold water, put out flame, seek medical attention

acetone risk assessment

hazard - acetone
risk - flammable, irritant, inhalation can cause dizziness and drowsiness
safety precaution - avoid contact, wear eye protection, keep away from naked flame in well ventilated room
in emergency - wash skin/eyes with water, seek medical assistance

how can pigments be identified?

comparing the Rf values calculated to known Rf values using same chromatography paper and solvent

why does affinity affect the rate of mobility?

pigments have different affinities to chromatography paper, those with lower affinities will travel further up the paper

why does solubility affect the rate of mobility?

pigments that are more soluble travel further up the paper and end up closer to the top at the solvent front

Rf value formula

distance moved by pigment / distance moved by solvent

outline the procedure for cp10

1. place a piece of pondweed in a beaker of water

2. cover one side of the beaker with aluminium foil to block out light

3. cover the other side of the beaker with a coloured light filter

4. add half a spatula of sodium hydrogencarbonate to the water to provide carbon dioxide

5. leave for 5 minutes

6. place the bench lamp a set distance from the beaker e.g. 30cm

7. measure the movement of the air bubble up the capillary tube

8. replace the coloured light filter with another and repeat the experiment

sodium hydrogencarbonate risk assessment

hazard - sodium hydrogencarbonate
risk - contact with eyes, inhalation
safety precaution - wear goggles, avoid contact with skin
in emergency - seek medical attention, flood cuts/eyes with cold water

why does a green filter decrease the volume of gas the most?

chloroplasts don't absorb much green light - they reflect it, giving them their green appearance

when is the greatest volume of gas produced?

when there is no filter, because all wavelengths of light can be absorbed

what does the volume of gas indicate?

assumed to be oxygen - volume of gas produced is directly proportional to the rate of photosynthesis

cp10 control variables

light intensity
amount of sodium hydrogencarbonate
time allowed for gas collection
temperature

what is a respirometer?

a piece of equipment used to measure the rate of respiration

how does a respirometer work?

adding a drop of coloured liquid to the length of tubing. as the organism respires and the volume of oxygen in the tube decreases, the pressure also decreases and the liquid moves down the tube towards the respirometer

outline the procedure for cp9

1. assemble the respirometer

2. add 5g of one organism to the boiling tube and replace the bung

3. place a drop of coloured liquid in the open end of the respirometer and use a syringe to draw the liquid as far back as possible from the respirometer and record the starting position

4. close the tap and start the stop clock

5. open the tap after 5 minutes and record the position of the tube

6. repeat the process with another organism or a control

soda lime risk assessment

hazard - soda lime
risk - corrosive
safety precaution - wear eye protection, avoid contact with skin
in emergency - wash off skin immediately, flood eyes/cuts with cold water

what factors can affect the results of cp9?

change in temperature or atmospheric pressure
handling the apparatus may add heat and change the readings

what is used to absorb carbon dioxide in cp9?

soda lime

how do you find the volume of oxygen consumed using a respirometer?

measure the distance moved by the coloured liquid, and use the formula volume \= distance x pi x r2

how is the rate of respiration measured using data from a respirometer?

volume of oxygen used / mass / time

cp9 control variables

mass of organism
time
temperature
mass of soda lime
apparatus must be air-tight - replace air between each set up

what are the ethical issues surrounding this practical?

the way the locusts are raised and killed
is killing a living thing wrong? is it justified in the name of science?

disinfectant risk assessment

hazard - disinfectant
risk - flammable
safety precaution - keep away from open flames
in emergency - put out fire, seek assistance

outline the procedure for dissection in cp6

1. pin the locus to the dissection board and remove the exoskeleton

2. identify the internal gas exchange system. flood the specimen with water so the tracheae show silvery-grey

3. examine the tracheae under a microscope

what is a potometer?

a device used to measure the uptake of water, and therefore the rate of transpiration, in plants

what affects the rate of transpiration?

light intensity, humidity, wind speed, and temperature

lamps risk assessment

hazard - lamp
risk - temporary damage to eyes
safety precaution - do not look directly at lamp
in emergency - wait for afterimage to disappear, seek appropriate assistance if needed

bags risk assessment

hazard - bag
risk -tripping
safety precaution - keep under desks and away from workspace
in emergency - seek appropriate medical assistance, clean spillages

why does light intensity affect rate of transpiration?

affects the rate of photosynthesis, which affects the amount of stomata open

why does temperature affect the rate of transpiration?

increases the rate of diffusion and evaporation from the stomata

why does humidity affect the rate of transpiration?

affects the rate of diffusion and evaporation by decreasing concentration gradient between plant and the atmosphere

why does wind speed affect the rate of reaction?

increases concentration gradient by mechanically removing water from the outside the stomata

betalain

red, water-soluble pigment in beetroots
found in vacuole of each cell

how can the permeability of a membrane be changed?

temperature
concentration of solvents e.g. ethanol

how can permeability of a beetroot cell membrane be measured?

amount of pigment leaked through the cell membrane into an aqueous solution using a colorimeter

ethanol risk assessment

hazard: ethanol
risk: irritant/flammable
safety precaution: wear eye protection, keep away from naked flames
in emergency: wash eyes and skin with cold water

what is the effect on cell membrane permeability as the temperature increases and why?

permeability increases because proteins in the membrane denature and heat damages the bonds making their tertiary structure. this creates gaps in the membrane, making it easier for molecules to pass through it

why do low temperatures cause a decrease in membrane permeability?

phospholipids have little energy and are packed closely together to make the membrane rigid - decreases permeability and restricts molecules from crossing the membrane

outline the procedure to investigate the effect of temperature on permeability of cell membrane?

1. cut beetroot into 6 identical cubes with a scalpel

2. place each cube in a different test tube with equal volumes of distilled water

3. place each test tube into water baths ranging from 30oC-80oC. leave for 20 minutes

4. filter each solution out into a cuvette and measure the absorbance

what is the effect of ethanol concentration on membrane permeability?

increasing ethanol concentration leads to increased membrane permeability, as ethanol causes gaps to form in the membrane

biohazard risk assessment

hazard: biohazard
risk: allergies, soil bacteria, contamination
safety precaution: wash hands after practical
in emergency: seek assistance

what happens as sucrose concentration increases?

mean pollen tube growth also increases up to an optimum. after this point, as sucrose concentration increases, mean pollen tube growth decreases - osmotic effects of increasing concentrations of sucrose

what are the control variables of this practical?

environment - humid chamber
volume and content of nutrient salt solution
volume of sucrose solution
time allowed for growth

outline the procedure to cp4

1. dilute the stock sucrose solution to several set concentrations

2. place a moist piece of filter paper into a petri dish to form a humid chamber

3. put a few drops of sucrose solution and an equal volume of mineral salt medium onto a clean microscope slide

4. use a mounted needle to rub the anther of the flowers so they shed some pollen onto the microscope slide

5. place the slides into the petri dish until it is time to observe them

6. start the stop clock. place the slides under the microscope and use a calibrated eyepiece graticule to measure pollen tube growth

why should a cover slip not be used?

to allow oxygen to reach the pollen and prevent conditions from being anoxic

what is the role of gibberellins during germination?

it is secreted by the embryo, then it diffuses to the aleurone layer of the endosperm to stimulate the production of amylase. amylase hydrolyses starch to maltose

how is the effect of gibberellin concentration on amylase production investigated?

1. dilute gibberellin to produce several concentrations

2. cut seeds in half, use only the half with the endosperm

3. dip in sodium hypochlorite solution and wash with water

4. place seeds in each gibberellin solution and leave

5. place seeds in a petri dish and starch agar, and leave for 12-48 hours

6. pour potassium iodide onto the plates and measure the clear zone

what does the zone of inhibition indicate?

starch has been hydrolysed by amylase

the larger the zone of inhibition, the higher the amylase concentration

why are the seeds placed in sodium hypochlorite solution?

to sterilise the seeds

what is the effect of gibberellin concentration on amylase production?

increasing gibberellin concentration increases the area of the clear zone, indicating an increased production of amylase and more starch hydrolysed

what are some sources of error in cp14?

the existing gibberellin and amylase content of the seeds may be different

control variables of cp14

• time allowed to soak in gibberellin

• time left on starch agar plate

• source/age of seeds

what is the independent variable of cp15?

sampling method - using a frame, point quadrat, quadrat size

how is percentage cover calculated?

• use a quadrat with squares

• count how many squares the required species is present in

• divide this by the total number of squares available

• multiply by 100 to convert into a percentage

outline the procedure to cp15

1. choose an area to take samples from. use two tape measures to create a set of axes off which coordinates can be read

2. use a random number generator to generate 10 sets of random coordinates

3. place the quadrat at each of the coordinates, placing the bottom left corner on the coordinate every time. start with the smaller quadrat

4. record the percentage cover for the chosen species

5. record the abundance of each species within the quadrat. this is used to work out density

6. record how many pins touch the chosen species. if it’s a frame quadrat work out how many quadrat intersection points contain the chosen species underneath.

7. repeat steps 3-6 with the bigger quadrat

outline the procedure to cp16

1. choose an abiotic factor

2. choose an area that has a clear light intensity gradient

3. lay a 20m tape measure on the ground from the area with sunlight to the shaded area

4. choose a species that changes in abundance along your transect

5. place a quadrat at the 0m mark

6. measure light intensity at the 0m mark within the quadrat

7. record the abundance of your chosen species by counting how many organisms are present. record this in a table

8. repeat steps 5 and 6 every 2m along the tape measure until you reach the end of the 20m

9. repeat steps 3-7 by creating another 2 transects between the area with sunlight to the shaded area

how else can you measure abundance?

working out percentage cover

estimate - less accurate

what is the difference between a risk and a hazard?

the hazard describes the potential source of harm, whereas the risk describes the likelihood of the harm occurring

how can the results be used to determine the relationship between the chosen factor and the morphology of a species?

• t-test: find out if there is a significant difference between 2 levels of the independent variable

• spearman’s rank: find out if there is a correlation between many levels of the independent variable

what is a null hypothesis?

a hypothesis which states there is no significant difference between two variables and that the difference observed is purely due to chance or error