SAMPLE - Vital Leaving Cert Guide - Biology Experiments

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

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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