BIOLOGY CORE PRACTICALS REVISION CARDS (V3)

Science (9-1)Combined Science / Biology Topics 1 - 9

Modified 14/01/2019 (PSN)www.biologyinfo.co.uk

Topic 5 Culturing: Aseptic Techniques

5.17 (B) 5.19 (B) 2

Autoclaves, using high pressure and very high temperatures, are used to sterilise petri dishes (or other laboratory equipment) and to prepare sterile growth media.

Inoculating loops are placed in a flame to sterilise them and, once cooled, are then used to inoculate (transfer) microorganisms from the source vial to the agar surface in the petri dish. Once inoculated, the petri dish lid should be replaced on the petri dish immediately in order to prevent contamination of the agar with unwanted microorganisms

It is important during experiments that petri dishes and vials are kept covered to prevent the escape of potentially dangerous microorganisms.

Topic 5 Core Practical Assessing Antiseptics

5.18 (B) 5.17 (B) 5.19 (B) 3

Investigate the effects of antiseptics on microbial culturesSterilise an inoculating loop in the Bunsen flame.

Remove the cap from the bottle containing bacteria, pass the neck of the bottle through the flame 2-3 times.

Dip the inoculating loop in the bacteria and spread it evenly across the agar plate.

Flame the bottle again and replace the lid. Place the inoculating loop in antiseptic. Cover the agar plate.

Its possible in your practical you inoculated the petri dish by pouring agar (already containing bacteria) onto the petri dish.

Having made sure that the petri dish is evenly inoculated with bacteria, place various small discs that have been previously soaked in antiseptic on the surface of the agar.

If tweezers are used to transfer the discs, the tips should be dipped in alcohol and the passed through the Bunsen flame to remove any unwanted microorganisms.

All lids should be replaced promptly and not taken off again.

Petri dishes are then left in a warm incubator and the area of the zone of inhibition can subsequently be calculated using π r2. Remember: “r” (radius) is half the “d” (diameter).

Topic 1 Core Practical: Effect on Enzyme Activity

1.10 4

Investigate the effect of pH on enzyme activity

Amylase is added to different pH solutions.

The temperature of these solutions is kept constant using a Bunsen burner and a water bath

Amylase breaks down starch which can be identified using iodine. The time taken for the starch to disappear can be found using a continuous sampling technique.

pH

Tim

e io

din

e re

mai

ns

ora

nge

/

secs

Rate is 1 / time, so if you plot rate you will see the more conventional graph.

5 6 84 7 932

Topic 1 Core Practical: Using Microscopes

1.6 5

Investigate biological specimens using microscopes, including magnification calculations and labelled scientific drawings from observations

Eye piece

Illumination

Fine focus

Course focusStage

Objective lens

Iris

Onion skin in water droplet and stain on microscope slide

Lower cover slip

With onion, iodine stain is used to improve contrast and show up the various structures and organelles

Mag = Image SizeObject Size

1m = 1x103 mm = 1x106 um = 1x 109 nm… or…. 1x10-9 m = 1x10-6 mm = 1x10-3 um = 1nm

Magnifier Low power High power

Oil immersion

Eyepiece X 10 X 10 X 10

Objective X 10 X 40 X 90

Total X 100 X 400 X 900

Topic 1 - Biological Drawings

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• Always use lines drawn with a ruler to link the label to the structure it names.

• The lines must touch the structure it names• Never let your labelling lines cross over each other• Draw your diagram in pencil• Do not shade any of the drawn components• When labelling any membranes you must say which

membrane it is (e.g. cell surface membrane or plasma membrane or (if you’re labelling the membrane around the nucleus) nuclear membrane or (if it’s a mitochondria) mitochondrial membrane.)

• Make sure your drawing fills at least 75% of the space provided on the exam paper for the drawing

• You may need to provide magnification and of size / scale details

• Do not “sketch” any lines with multiple pencil strokes – all lines should all be single lines.

Topic 1 Core Practical : Food Tests

1.13(B) 7

Investigate the use of chemical reagents to identify starch, reducing sugars, proteins and fats.

None Trace Low Moderate High

To 2cm3 of test solution add an equal quantity of Benedict’s reagent. Shake and heat in a water bath at 95°C. The resulting colour change indicates the levels of reducing sugars present.

Benedict test for reducing sugars

Iodine solution turns blue black when starch is present

The Biuret test can be used to identify proteins. The test sample is mixed with NaOH and a few drops of dilute CuSO4 solution are added. Proteins will turn the resultant mixture purple,the more protein, the greater the colour change.

To carry out the Emulsion test:Add ethanol to the test material

and shake (lipids are soluble in alcohol but not water). Pour the ethanol mixture into a test tube of water and shake again. If fats or oils are present the resultant will be a cloudy white emulsion

(which will eventually precipitate out)

Topic 1 Core Practical - Investigate Osmosis

1.16 1.17 8

Investigate osmosis in potatoes Osmosis is the diffusion of water molecules from an area of high water concentration (i.e. low solute concentration) through a semi-permeable membrane, to an area of low water concentration (i.e. high solute concentration) down a concentration gradient.

In hypotonic solutions (i,.e low solute concentration), the potato cells gain mass as water moves into the potato cells by osmosis.

In hypertonic solution (i.e. high solute concentration), the potato cells lose mass as water moves out of the cells by osmosis.

Isotonic solution:No net movement of water, no mass change. (This must therefore also be the concentration of solute inside the potato cell)

Pre-weighed potato chips ( cut of similar size) are added to different sucrose solutions of known concentrations, and left for about 30 mins to allow time for any osmotic changes to occur. The potato chip is then removed from the solution, dried (to avoid weighing errors) and carefully re-weighed. The percentage change in mass is then calculated.

Topic 3 Extracting DNA From Fruit

3.69

Mash (or liquidise) the flesh of the fruit, this can be banana, kiwi, strawberry etc. Mashing breaks open some cells and provides a large surface area.

Mix with detergent, salt and water. Detergent dissolves the nucleus and cell membranes whilst Na+ ions (salt) break up the proteins attached to the DNA.

Mash again, the more you mash, the more DNA you will get. You could heat to 60 degrees for 15 minutes to continue the break down the proteins, if time allows.

Filter to remove unwanted solid bits and pieces

Gently pour ice cold alcohol (Ethanol) down the side of the container to form a transparent layer on top.

DNA is insoluble in the cold alcohol and white strands in a white jelly-like substance will start to precipitate out in the top layer.

Extract the long coagulated strands of DNA by winding it onto on a glass rod.

Topic 6: Core Practical - Investigate Photosynthetic Rate

The closer the algae are to the light source, the faster the photosynthetic rate of the algae is, and the more alkali (blue/purple colour) the solution becomes.

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Topic 8: Core Practical - Investigate Respiration Rate

The Soda Lime absorbs Carbon Dioxide gas produced by Respiration. Therefore the uptake of Oxygen gas for respiration is the only gas change, resulting in the coloured liquid in the capillary tube moving to the left

How far this moves in unit time is a measure of respiration rate

Energy for the cell11

Topic 9: Field Work – Quadrating & Belt Transects

12Be able to explain how to determine the number of organisms in a given area using raw data from field work, inc. quadrats and belt transects.

Quadrating:Abundance of species populations in a given area can be calculated using quadrats.Using your randomly generated coordinates, place your quadrats in the area under study, and use the gathered data to calculate the population of the species under study. For example, if all your quadrats have an area that is 5% of the area under study then multiply your results by 100/5 (20x).

Belt Transects:Correlation of change in species population with change in abiotic factors can be determined using a belt transect.Place quadrats regularly along a measured line across the area under study. and use the gathered data to calculate the population of different species along the transect, as well as record changes in abiotic factors (e.g. light and shade) along the transect. Then plot a graph to see if these changes correlate with differences in species population.

RELIABILITY:A - AnomaliesC - ConcordanceA - AveragesR - Repeats

Reliability & Validity in Science Experiments

VALIDITY:C – Control Variable (if not kept constant, it changes the results!!)

P – Precise Equipment (to enable more precise measurements)

W – Wide Range of Results (if too narrow a range or not enough

data points, graph trends (lines) cannot be correctly determined)

T – Test The Right Thing

Independent Variable

Dep

en

den

t V

aria

ble

X

Y

If you’re asked to comment on “Reliability”, use the above as a

framework for your answer

If you’re asked to comment on “Validity”, use the above as a framework for your answer

A CAR: Anomalies, Concordance,

Averages & Repeats

Line / Curve Graphs Bar GraphsDiscontinuous Data Continuous Data

Drawing Graphs in Biology

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Independent Variable

Dep

en

den

t V

aria

ble

X

Y

Dep

en

den

t V

aria

ble

X

Yx

x

x

x x

x x

x

x

- The same number of points should be abovethe line as there are below it

- Draw the curve in pencil – do not “sketch” it- If you have a straight line – use a ruler- Circle (and ignore) any anomalous results

- Bars must be thesame width

- Spaces betweenbars must be thesame width

- Bars must be thesame width

- Bars must toucheach other – NOspaces!

E.g. shoe size E.g. foot length

Independent Variable

Health & Safety in Biological Practicals

15

SB1Microscopes

Handle slides with care – risk of cutting fingers

Do no angle mirror toward sun – may cause damage to eyes

SB1Enzymes

Handling potentially dangerous solutions – wear eye protection

Take care working with hot water bath –risk of skin burns

SB1 Food Tests & Calorimetry

When using Bunsen burner: wear eye protection / tie hair back

Do not ingest any lab foods: they’re unclean & not fit to eat

SB1 Osmosis & Diffusion

Cut potato chips with care when using sharp knife

Handling potentially dangerous solutions – wear eye protection

SB3 DNA Extraction

Handling potentially dangerous solutions – wear eye protection

Do not ingest any lab foods: they’re unclean & not fit to eat

SB5 Assessing antiseptics

Wash hands with antiseptic to avoid bacterial contamination

Do not open agar plates once they have been incubated

SB6Photosynthesis

Handling potentially dangerous solutions – wear eye protection

Avoid touching bulb of lamp – which will be very hot

SB8Respiration

Handle living organisms with care &wash hands thoroughly

Wear protective gloves when handling soda-lime

SB9Quadrats

Beware of trip hazards and uneven ground in field of study

Handle metal quadrats with care

Space for Your Key Notes on Biology Practicals:

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