Author Name
Biology: Experiments SAMPLE
Vital Leaving Cert Guidebook
Biology: Experiments
Róisín Doyle
For Leaving Cert Biology, there are a total of 21 prescribed experiments all of which are discussed in this guidebook. These experiments will be assessed in section B of the paper and candidates are required to do a minimum of 2 out of 3 questions totaling 60 marks.
It is important to note that questions regarding experiments are not exclusive to section B and may also be assessed in section A and C. The State Examinations Commission have identified which experiments can be examined in each of the questions in Section B as presented in the table below.
Q8
Cell Structures;
• Preparation and examination of plant/animal cell under microscope
Food;
Test for the presence of;
• Reducing sugar,
• Protein,
• Lipids,
• Starch
Ecology;
• Conduct a qualitative and quantitative survey of plants and animals
• Determine 3 abiotic factors that affect population
Genetics;
• Isolation of DNA from a plant tissue
Photosynthesis;
Q9
• Effect of light intensity on rate of photosynthesis
Enzymes;
• Effect of temperature on enzyme activity
• Effect of pH on enzyme activity
• Demonstrate denaturation of an enzyme through boiling
• Demonstrate the activity of an immobilised enzyme and compare to activity of a free enzyme
Respiration;
• Production of ethanol by fermentation
Movement of Molecules;
• Demonstrate osmosis
ISBN: 978 1 897922 30 9
Copyright 2024
Q10
Fungi;
• Growth of leaf yeast on nutrient agar
Plant reproduction;
• Factors necessary for germination
• Demonstrate starch is digested during germination
Plant responses;
• Demonstrate the effect of different concentrations of growth regulator on plant growth
Plant structure;
• Prepare and view a dicotyledon stem under a light microscope
Heart;
• Heart dissection
• Effect of exercise on heart rate
Scientific Method
In order for students to have a full command of the experiment section of the exam, it is important to first review scientific method as it too can be assessed with the section B questions.
This is a series of steps for providing answers and explanations to something science related.
1. Observe.
2. Formulate a hypothesis. A hypothesis is an educated guess or reasonable explanation for what is being observed. It is the starting point for an experiment.
3. Design an experiment to confirm if the hypothesis made is valid or not.
4. Collect and examine data/results from experiment.
5. Write a conclusion.
6. Compare the conclusion with previous research on the same topic.
7. Make findings available to other scientists in scientific journals (internet not acceptable).
8. If hypothesis has been proved correct; can be further developed into a theory or principle/law. Theory: best explanation for a hypothesis at that moment in time (can be changed at a later date)
Principle/Law: after ongoing research on the hypothesis, if the results never change; can then be defined as a law.
Limitations of Scientific Method
1. Extent of our knowledge.
2. Basis of investigation (experiment could be performed inaccurately).
3. Inaccurate or inability to interpret results.
4. Natural world is constantly changing (e.g., weather, seasons etc.).
5. Accidental discovery (results from experiment may be a once off).
Good experimental technique
1. Careful planning.
2. Safety Procedures (tie up hair, lab coat, safety goggles).
3. Having a control [for comparison with experimental results].
4. Sufficient sample size (to increase accuracy of results and reduce % error.
5. Random selection/sampling.
6. Double-blind testing - prevents scientist from being influenced.
7. Performing replicates - validate results.
Source of Experimental Error
• Insufficient Sampling
• Not performing random sampling
• Climate/weather changes
• Not performing replicates (replicates: repeating the experiment)
• Measurement errors
• Record keeping errors
• Experimental error in performing experiment
• Apparatus/equipment not accurate
Experiment Titles for Leaving Cert Biology and their controls
To use a simple key to identify five fauna and flora
To use various pieces of equipment to collect plants and animals in an ecosystem
To carry out a quantitative study of a habitat (plants and animals)
To prepare and examine a plant cell under a microscope
To prepare and examine an animal cell under a microscope
To investigate the effect of pH on enzyme activity
To investigate the effect of temperature on enzyme activity
To investigate the effect of denaturation by heat on enzyme activity
To prepare and use an immobilized enzyme
To investigate the effect of light intensity on the rate of photosynthesis
To prepare ethanol using yeast by fermentation
To demonstrate osmosis
To isolate DNA from a plant tissue
To investigate the growth of leaf yeast on malt/starch agar
To prepare and examine a transverse section of a dicot stem
To dissect, display and identify parts of the heart
To investigate the effect of exercise on pulse rate
To investigate the effect of exercise on breathing rate
To investigate the effect of growth regulator IAA on plant tissue
enzyme and experiment performed at 27oC
lized)
water instead of glucose
water
water instead of IAA
To investigate the growth of leaf yeast on malt/starch agar
No leaf/ Boiled dead leaf Yes at 30oC
To prepare and examine a transverse section of a dicot stem N/A N/A
To dissect, display and identify parts of the heart N/A N/A
To investigate the effect of exercise on pulse rate N/A N/A
To investigate the effect of exercise on breathing rate N/A N/A
To investigate the effect of growth regulator IAA on plant tissue
Distilled water instead of IAA No
The purpose of a control in an experiment is for comparison with the experimental results.
Chemical/Instrument needed and their Positive result/Function
Chapter Test
Food Glucose (aka reducing sugar)
Food Protein (aka biuret)
Food Starch
Food Fat
Cell Structure Animal cell (cheek cell)
Cell Structure Plant cell (onion cell)
Cell Structure Cells
Cell Structure Cells
Cell Structure Cells
Cell Structure Microscope
Chemicals/Instrument Positive Result/Function
Fehling’s 1 +2 (or benedicts) + water bath at 37oC
Sodium hydroxide + Copper sulphate
Iodine
Brown paper
Methylene blue
Iodine
Cover slip
Cover slip at 45o angle
Drops of water on slide
Magnification lens
Cell Structure Microscope Coarse Focus wheel
Fine focus wheel
Enzymes Enzyme activity
Enzymes Temperature Variation
Enzymes pH variation
Photosynthesis Carbon dioxide
Photosynthesis Photosynthesis
Photosynthesis CO2 variation
Hydrogen peroxide (substrate), amylase (enzyme)
Temperature controlled water bath at different temperatures
pH buffer solutions of various pH
Limewater
Elodea
Sodium hydrogen carbonate
Photosynthesis Light intensity variation Lamp
Photosynthesis Temperature maintenance
Respiration Ethanol
Ecology Qualitative Analysis
Temperature controlled water bath
Potassium Iodide and sodium hypochlorite
Identification key
Sky blue to brick red
Sky blue to lilac
Brown to blue/black
Translucent spot
Observe under microscope
Observe under microscope
Protect lens of microscope
To prevent air bubbles
To prevent dehydration
Magnifies object to be observed
Moves stage and roughly focuses image
Improves clarity of image
Oxygen in the form of foam produced after 2 minutes
Changing temperature will vary results, e.g., enzyme activity will change
Changing the buffer pH will affect enzyme activity
Milky
Oxygen bubbles given off
Varying the amount will vary the CO2 concentration and change the no. of bubbles of O2 produced
Moving the lamp different distances from experiment will vary O2 bubbles produced
Keeps temperature constant
Clear to yellow (crystals if heated)
Series of questions used to identify animals and plants
Ecology Qualitative Analysis Pooter Collects insects and spiders
Ecology Qualitative Analysis Beating tray
Ecology Qualitative Analysis
Ecology Qualitative Analysis
Pitfall trap
Sweep net
Ecology Qualitative Analysis Tullgren funnel
Ecology Quantitative Analysis Quadrat
Collects insects, spiders, caterpillars
Crawling insects, snails
Hedgerow insects
Centipedes, millipedes
Record the number of times a plant appears
Osmosis Osmosis Visking tubing/dialysis tubing Acts as a selectively permeable membrane
Chemical/Instrument needed and their Positive result/Function
Chapter Test
Plant Structure Dicot stem analysis
Plant Structure Dicot stem analysis
Fungi Leaf yeast
Fungi Leaf Yeast
Fungi Leaf yeast
Chemicals/Instrument
Blade/scalpel
Forceps
Petroleum jelly
Starch nutrient agar
Methylated spirits
Fungi Leaf yeast Incubator @ 350C
Genetics DNA isolation
Genetics DNA Isolation
Genetics DNA Isolation
Genetics DNA Isolation
Genetics DNA Isolation
Genetics DNA Isolation
Washing up liquid
Table salt
Water bath @60oC
No longer than 15 minutes
Ice bath
Food blender
Filter paper
Genetics DNA Isolation Protease
Genetics DNA Isolation Freezer cold ethanol
Plant Reproduction Germination
Boiled water
Plant Reproduction Germination Layer of oil
Plant Reproduction Starch digestion during germination Soaking seeds in water
Plant responses
Growth regulator
IAA (indole acetic acid)
Positive Result/Function
Cut a thin slice of celery
Transfer stem to glass slide
Sticks leaf to lid of agar plate
Medium will all the food microorganisms need to grow
Kills any microorganisms (MO) present
Temperature at which enzymes in MO work best and result in growth
Cell membrane breaks down
DNA molecules clump together
Speeds up reaction and denatures enzyme
Or DNA will start to break down
Prevents complete denaturation and DNA destruction
Breaks down cell wall
Collects cell fragments
Breaks down protein surrounding DNA
Causes the DNA to come out of solution (insoluble)
To remove oxygen from water
Eliminate oxygen (create anaerobic conditions)
Softens testa and activates germination
Affects the length of root and shoot growth-at low concentration, promotes roots grow, at high concentration promotes shoot growth
Test for the presence of starch
Background: Starch is an example of an energy storage polysaccharide found in plants. Polysaccharides are defined as being many (more than two) monosaccharides joined together. Another example of a polysaccharide in plants is cellulose which has structural role in the cell wall of a cell and is also found in phloem structure.
Method:
1. Place food sample in a test tube. Place distilled water in another test tube (control).
2. Add iodine to sample.
3. Record colour change.
4. Repeat for control sample which is distilled water.
Result: Iodine will turn from brown to blue/black if starch is present. Control remains brown.
Test for the presence of a reducing sugar (aka glucose)
Background: Glucose is an example of a reducing sugar which is a monosaccharide and is a source of energy. A monosaccharide is a single subunit of a sugar and a member of the carbohydrates. The general formula for carbohydrates is Cx(H2O)y. Chemical formula for glucose is C6H12O6
Method:
1. Add food sample to a test tube. Place distilled water in another test tube (control).
2. Add Benedict’s solution.
3. Heat gently in a water bath at 350C for 15 minutes. Heating above this temperature will denature the enzymes!!!!!
4. Record colour change.
5. Repeat for control sample which is distilled water.
Result: A positive result for the presence of a reducing sugar is blue to brick red/orange. Control remains blue.
Test for the presence of protein
Background: Proteins are another group of biomolecules. They are composed of subunits called Amino Acids. There are 20 basic amino acids from which all proteins are made. Examples of proteins in a living organism include; enzymes, hormones, antibodies, and keratin (found in hair and nails).
Method:
1. Add food sample to a test tube. Place distilled water in another test tube (control).
2. Add biuret solution (no heat required).
3. Record colour change.
4. Repeat for control sample which is distilled water.
Result: A positive result for the presence of a protein is blue to purple. Control remains blue.
Test for the presence of lipids
Background: Lipids are another group of biomolecules. A subunit of a lipid is a triglyceride which is composed of glycerol and three fatty acids. The role of lipids in a living organism is for protection, insulation, and a source of energy. However, the role of lipids in cells is slightly different. The location of a lipid in a cell is in the cell membrane and it is in the form of a phospholipid. A phospholipid differs from a regular lipid in that the third fatty acid has been replaced with the element phosphorus (i.e., glycerol, 2 fatty acids and phosphorous). There are two types of lipids; fats and oils. Oils differ from fats in that they are liquid at room temperature, while fats are solid at room temperature.
Method:
1. Rub food sample on brown paper.
2. Hold paper up to direct light.
3. Record result.
4. Repeat for control sample using distilled water. Wait for a period of time after adding water before checking for the presence of a translucent spot to allow water to dry/evaporate.
Result: A positive result for the presence of a lipid is that the brown paper will form a permanent translucent spot where the lipid has been placed on the brown paper. With the control, the translucent stain disappears.
Determine experimentally 3 abiotic factors that affect the population size of an organism in an ecosystem (soil temperature, soil pH and wind speed)
The 3 abiotic factors examined are a combination of edaphic (soil) and climatic (long term weather) factors. Other abiotic factors that affect population size include aquatic (water) and climatic. If the abiotic factors are not suitable to the living organism present (plant (flora) or animal (fauna)), there will be a decline in the population. If the temperature or pH is not appropriate for optimum enzyme activity, the enzymes cannot perform and there will be a decline in population. If the wind speed is not sufficiently fast the seeds cannot be dispersed to colonise a new area and there will be a decline in population.
Soil pH:
1. Using pH meter (or dissolve soil sample in distilled water and add universal indicator paper).
2. Insert meter into soil and leave for 15 minutes.
3. Record reading on meter.
Soil temperature:
1. Using a thermometer.
2. Insert thermometer into soil and leave for 15 minutes.
3. Record reading on thermometer.
Wind speed:
1. Using anemometer, count the number of times the anemometer turns a full rotation in 1 minute.
2. Record number of rotations.
Róisín Doyle is a fully qualified Biology teacher since 2009, achieving a 1st in her degree.
She has been teaching Biology in the Institute of Education, Dublin since 2013, has worked with the State Examinations Commission for several years, and authored mock papers for Examcraft from 2017- 2021.
Róisín has also taught International Baccalaureate Biology in the United Arab Emirates.
In 2023 Leaving Cert, 40% of Róisín’s students achieved a H1 in Biology.
“Want a comprehensive guide and assessments for the 21 prescribed experiments for Leaving Cert Biology? Well, then, this is the book for you!
This book contains:
• a step-by-step guide on how to conduct each of the experiments, along with an explanation for each step.
• positive results given for each experiment.
• a subsequent series of comprehensive questions that assesses your knowledge and provides
• the ultimate preparation for the exam.
Pretty important when the experiments account for a minimum of 15% of the paper each year.”
mcandrewbooks.com
Cover Design: LUCKY TEN