Biology Lab Exam Summary
Preparation for Biology Lab Exam
General Instructions
Do not forget a ruler and calculator on the exam day.
Read the summary precisely and memorize it.
Review the labs, look at the questions, and answer them.
During the Exam
Carefully read the introduction and information in the exam. This information is crucial for understanding the experiment and questions.
Read the experiment instructions up to the first question to understand the experiment's direction. You may draw a diagram to describe the sequence of actions.
Proceed step-by-step. Mark each completed action with a "V".
Read the questions carefully and identify their type. If the connection to your biological knowledge isn't clear, identify which biological concept the question relates to.
Example Question: Renin and Milk Protein Coagulation
The lab involved the enzyme renin, which accelerates the coagulation of milk proteins.
Adding renin to milk causes it to solidify.
A sample question: "If more milk is added after coagulation, will it coagulate?"
The question tests if students understand that the enzyme isn't consumed and can be reused with additional substrate molecules.
Addressing Unexpected Results
Inform the examiner if you do not get the expected results. The issue might stem from a mistake in preparing the lab materials.
Report the obtained results and explain what the expected results were based on your biological knowledge.
Explain why the expected results were not obtained.
Examine the results carefully and do not hastily consider them incorrect. There might be an influencing factor you didn't consider.
Examiner Guidelines
"Do not deduct points if the experiment results differ from the expected."
"The student's results may vary; read their answers carefully and accept the explanation based on these results."
"Do not deduct points if the student's answer is logical and doesn't contradict basic biological knowledge, even if it's not the expected answer."
Conclusion
The exam assesses your thinking process: analyzing results and linking them to your basic biological knowledge.
Aim to perform the experiment accurately, but failing to obtain expected results doesn't necessarily lower your grade.
Research Question
The research question should always be framed as a question.
It examines the relationship between two variables.
Formulate it as: "What is the relationship between the independent and dependent variables?" or "What is the effect of the independent variable on the dependent variable?"
Example: "What is the effect of temperature on the rate of enzyme activity?"
Hypothesis
The hypothesis presents the relationship between the variables and states what you expect the relationship between the independent and dependent variables to be.
It should be a statement (ending with a period).
It should be based on prior biological knowledge.
Formulate it as a positive and concise sentence.
Format: "As… so…"
Example: "As the temperature increases up to a certain limit, the rate of the enzyme catalase will increase."
As temperature increases, the respiration rate will increase until a certain temperature, where it will remain constant or start to decrease.
Dependent Variable
The factor that is influenced/tested in the experiment.
The experimenter monitors changes in this factor (these are the results).
Measuring the dependent variable: In many cases, direct measurement isn't possible, so another factor that expresses the change in the process is measured.
Dependent Variable vs. Measurement Method
Pay attention not to confuse the variable itself with the method of measurement.
Example: The dependent variable is the rate of activity of the enzyme catalase.
In the experiment, the enzyme catalase breaks down hydrogen peroxide into water and oxygen.
We will examine the dependent variable by measuring the rate of product formation (oxygen).
Measure the volume of oxygen released in a closed experimental system at fixed time intervals.
Example of the Difference Between Dependent Variable and How to Measure It
Pepsin enzyme activity rate - Dependent variable.
Amount of product per unit time - Measurement method.
mg/minute - Units of measurement.
Independent Variable
The factor that influences the dependent variable.
The independent variable depends on the experimenter.
The experimenter determines and can change it.
Changing the Independent Variable
Create a range of values in which the independent variable is changed.
Example: The independent variable is temperature, measured in degrees Celsius.
Change the temperature range by preparing water baths at different temperatures.
Control
Used for comparison and testing if each factor affects the experiment as the researcher thinks.
The experimenter verifies that the measured process is indeed influenced by the independent variable using the control.
It is advisable to check additional factors in the experiment.
Types of Controls
Control without the Independent Variable:
The control is usually a treatment identical to the others in the experiment, but the independent variable is omitted.
Example: In an experiment checking the effect of enzyme concentration on enzyme activity, a control test tube with no enzyme is introduced.
Importance: To rule out alternative explanations. For example, spontaneous breakdown of the substrate unrelated to the enzyme concentration.
Internal - Comparative Control:
This control compares the different treatments in the experiment. Each treatment serves as a control for the others.
Color Control:
Sometimes a test tube is used as a color control to revert to the original color.
Temperature and pH Controls
When the independent variable is temperature or pH, it isn't possible to perform a control without the independent variable.
Internal control is included in the experimental setup; each pH or temperature serves as a control for the others.
Constant Factors
All factors that can affect the dependent variable must be kept constant.
When designing an experiment, consider which factors might affect the dependent variable and keep them constant.
The importance of keeping factors constant is to attribute the results solely to the independent variable.
If multiple factors influence the dependent variable, it won't be possible to determine which factor caused the result.
Example: In the experiment, factors that affect enzyme activity rates must be kept constant:
Volume and concentration of hydrogen peroxide.
Concentration of enzyme catalase.
pH level.
Duration of decomposition in each treatment.
Replicates
The more times an experiment is performed, the greater the reliability of the results.
Reduces error.
Increases accuracy.
Replicates allow for calculation of averages of the measurement results of the dependent variable and calculation of standard deviation.
The average result is the closest to the true result.
Experiment Results
The experiment can be qualitative or quantitative.
Qualitative Experiment
Results are presented verbally and describe the visible differences between the different treatments.
Quantitative measurement isn't possible.
Example: When the results are colors (and there isn't a scale).
A description of a microscopic preparation may appear.
Quantitative Experiment
Summarize the experiment and its results in a table.
Write a full title including the dependent and independent variables and the tested organism.
Include all constant factors and the variables in the experiment in the table.
Each column in the table should have a title.
Add units of measurement if applicable.
Table Example
Independent variable on the right, dependent variable on the left.
Temperature in degrees Celsius.
Volume of hydrogen peroxide in drops.
Volume of enzyme solution at concentration X in ml.
Calculating Solution Concentration
Sometimes you'll need to calculate solution concentrations in the table.
You receive an initial solution at a known concentration and prepare different dilutions by adding water.
To calculate dilutions:
C1 * V1 / V2 = C2
Initial Solution Concentration * Initial Solution Volume / New Solution Volume (Initial Solution Volume + Water Volume).
Example
2 ml of salt solution at 0.2M concentration were taken, and 8 ml of water were added. What is the concentration in the new solution?
0.04 = (0.2 * 2) / 10
If the initial concentration was taken from an organism extract and no other concentration units are specified, treat the extract as 100% concentration and calculate the rest of the concentrations as dilutions of it using the same formula.
Presenting Results Graphically
The graphical representation shows how the dependent variable changes during the experiment according to changes in the independent variable.
The graph will have a title describing the relationship between the variables.
X-axis: Independent variable.
Y-axis: Dependent variable.
Pay attention to a uniform scale for the same axis.
Each axis can have a different scale.
The name of the variable and the units in which it is measured will be written on each of the axes.
Choosing a Graph
If the independent variable is continuous - choose a curve = line graph.
Example - Temperature, pH level, enzyme concentration, etc.
Drops are not continuous because there is no option for half a drop. However, a continuous graph is made when there are many results in a certain range. Therefore, a calibration graph is made even if there are drops in the way the dependent variable is tested, we make a continuous graph.
Note:
The slope of the graph shows the rate of change. When there is a straight graph, the rate of change is constant, and when there is a wave, the rate of change changes according to the slope of the graph.
When the independent variable is discrete - choose a bar diagram.
Example - Type of plant, number of test tube, name of the child, source of the enzyme, etc.
Conclusions
Conclusions relate only to the hypothesis tested in the experiment and the results obtained.
Avoid generalized conclusions, as they may lead to incorrect conclusions.
It must be shown that the conclusion stems from the results.
Examination Tips
When writing about rate, it's always per unit of time.
There is no how/why/whether the enzyme … X causes Y research question. You can ask what the relationship is or what effect the temperature increase has.
If it says to describe results - just describe! Don't explain!
If the results are reported in symbols, add a key on the side (e.g., +++: dark blue, ++: medium blue, -: no color).
It is recommended to prepare a draft of the table before writing it in the exam notebook.
If you were asked to draw a conclusion from several results obtained in different stages of work, refer to all the results and not just the last one.
If you get results that seem different from the results you expected, write that the results don't match the expected results - and explain the expected results.
If the unexpected results can be explained so that the answer is logical and doesn't contradict accepted biological knowledge - you'll receive full points.
If you were asked to write a hypothesis, remember that it should have a clear connection to the text written in part C and a clear connection to what you did in parts A and B. It's best to write a hypothesis that doesn't contradict biological knowledge. It should be a hypothesis that can be tested in an experiment. Don't forget to write: "As … then …"
If you were asked to write an experimental setup - write points briefly. Refer to the holy trinity: Replicates, Control, Constant Factors!
Material Transfer
Diffusion
Movement of molecules from a source where their concentration is high to a place where their concentration is low, i.e., down the concentration gradient, until their concentration is equalized in all the volume available to them.
Diffusion occurs because of the self-movement of the molecules and therefore doesn't require energy.
After equating the concentrations, particle movement continues, but we don't sense any change.
Example: Solution A - 40% salt, Solution B - 80% salt. In which direction will the particle movement occur? Answer: The particle movement will be done from Solution B to Solution A.
Osmosis
A special case of diffusion, in which water molecules move between two solutions through a membrane with selective permeability.
Net water movement is from a solution where the water concentration is high to a solution where the water concentration is low.
Water concentration is a complementary image to the concentration of the solvents in it: When the water concentration is high, the solvent concentration is low and vice versa.
Example: 20% salt solution contains 80% water. 90% sugar solution contains 10% water. That is, osmosis will be carried out from a less concentrated solution to a more concentrated solution (the opposite of diffusion).
Example
In a container containing a selective membrane, two solutions were inserted. Side A - 50% sugar solution. Side B - 90% sugar solution. In which direction will the particle movement take place? Answer: From side A to side B. Explanation: Because the container has a selective membrane that doesn't allow the molecule of the solute to pass, the material that will pass is water. In general, water is a mirror image complementing the concentration of the solvents side A had 50% water compared to side B containing 10% water, therefore the passage was from the less concentrated solution to the more concentrated solution.
Types of Solutions
Solution - A mixture obtained when mixing at least 2 materials, usually a solid mixed in a liquid. The liquid is called a solvent and the solid is a solute (like chocolate milk).
In cells, the solvent is water, and the solutes are different solids, liquids, and gases.
We define 3 terms used to describe the ratio between concentration of solutes in two solutions:
Isotonic Solution (Iso - Equal)
It is a solution where the concentration of the solutes in it is high relative to the concentration of the solutes in another solution.
Hypertonic Solution (Hyper - Above)
It is a solution where the concentration of the solutes in it is high relative to the concentration of the solutes in an other solution.
Hypotonic Solution (Hypo - Below)
It is a solution where the concentration of the solutes in it is low relative to their concentration in the other solution.
Effect of Inserting Different Cells into Different Solutions
The solution appearing in the table indicates the solution into which the cells were inserted, that is, the type of solution according to the definition relative to the intracellular fluid.
Animal Cell
Hypotonic Solution | Isotonic Solution | Hypertonic Solution | |
|---|---|---|---|
The concentration of solutes in the external solution is lower than in the cell. More water will enter the cell than exit, causing the cell to swell and potentially burst (hemolysis). | The concentration of the solution outside the cell = the concentration of the solution in the cell. Therefore, the amount of water that enters the cell = the amount of water that leaves it, and therefore there can be no change in the volume of the cell. | The concentration of solutes in the external solution is greater than in the cell, therefore water will exit the cell to the external environment more than it enters it, and therefore the volume of the cell will decrease. |
Plant Cell
Hypotonic Solution | Isotonic Solution | Hypertonic Solution | |
|---|---|---|---|
The solute concentration outside the cell is lower than inside, causing water to enter the cell. The central vacuole fills with water, creating pressure. The rigid cell wall prevents bursting, resulting in a stable and rigid state. A cell that has undergone plasmolysis can be restored by transferring it to a hypotonic solution (e.g., distilled water). | The solute concentration outside the cell equals that inside the cell. The amount of water entering the cell equals the amount exiting, so there's no volume change. | The solute concentration outside the cell is higher than inside, leading to water exiting the vacuole via osmosis and a decrease in cell volume. Internal components move away from the cell wall, with the space filled by the external solution. This shrinking of the cell's contents is called plasmolysis. The cell wall remains stable. |
Enzyme Summary
Enzymes are biological catalysts for biochemical metabolic processes in cells of living organisms - without them, the processes would take much longer than they do with them.
All enzymes are proteins and are therefore affected by factors that may affect proteins: temperature and pH.
Enzymes can break down materials, assemble materials, or change their structure.
Enzymes are active in low concentrations.
The enzyme concentration remains constant during the process; enzymes are not "wasted".
The compound on which the enzyme acts is called the substance - S.
The substance obtained as a result of the enzyme's action is called the product - P.
Each enzyme has a unique substance due to the existence of a structural match between them. A very small change in the structure of the molecule on which the enzyme acts is enough to cause the enzyme not to bind to it. The match between enzyme and substitute can be compared to a match between a key and a lock. However, unlike a key and a lock that are rigid and their form does not change as a result of the connection between them…
The connection between the enzyme and the substrate is made while there is a structural/allosteric/spatial adaptation between them.
The molecule of the enzyme is larger than the molecule of the substance.
The molecule of the enzyme has one or more active sites that are partially adapted to a certain part of the substrate on which it acts.
During the reaction, the amount of substance decreases, and the amount of product increases.
A measure of enzyme activity = The rate of enzyme activity is: the amount of product per unit time. Each enzyme has its rate.
Enzyme activity rate depends on the rate of binding between the enzyme and the substance.
There are several factors that can increase the chance of more meetings: temperature, enzyme concentration, and substrate concentration.
Temperature - As temperature increase, the rate of enzyme activity increases up to the optimum temperature, because the increase in temperature raise the kinetic energy of the molecules and increase the chance of a meeting between them. However, if we raise the temperature above the optimum temperature, the spatial structure of the enzyme (due to protein denaturation) will change and its activity rate will decrease. Each enzyme has its optimum temperature in which its activity is the greatest.
The concentration of the enzyme - As the concentration of the enzyme rise, so rises the rate of the process up to a certain limit, in which the amount of substrate isn't enough. Meaning, that all the molecules of substance are seized and enzyme molecules are remained free, so that the addition of enzyme molecules will not raise the rate of the process.
The concentration of the substrate - As the concentration of the substrate rises, so will rise the rate of the process up to a certain limit, in which the amount of the enzyme is not enough. All the enzyme molecules are active and substrate molecules remain that there is no enzyme to act on them, so that the addition of substrate molecules will not raise the rate of the process.
There are more factors that affect the enzymes activity such as the degree of acidity and existence of inhibitors
The degree of acidity = pH - The degree of acidity determines the spatial structure of the enzyme. Each enzyme has its unique pH. Each change in the pH of the environment causes a change in the spatial structure that affect the binding between the enzyme and the substance, of course.
Presence of inhibitors - Materials that can connect can connect to the enzyme and effect its activity. There are materials that binds to the enzyme permanently and prevent its activity - Poisoning, for example cyanide that binds to enzymes that binds oxygen in the respiratory system and prevent the oxygen from binding. There are inhibitors that binds to the enzyme temporarily, that cause temporary inhibition:
material similar to the substrate - relates to the enzymes active site to prevent the change of the substrate to connect to the enzyme, therefore slowing down the rate of process. as the amount of substrate grow, the effect of the inhibition lessens. For example - Penicillin is a material similar to the substrate that connects to the enzymes that builds the wall of the bacterias cells instead of the substrate. By that it prevents the connecting of the substrate, Bacteria cannot reproduce.
Material that connects to the enzyme and change its structure to prevent the connection of the enzyme with the substrate, and by that lessen the rate of the process. Releasing the inhibitor, will reverse the enzyme to its active form. It is acceptable to describe the rate of activity of the enzyme to each of the factors with the help of inflection point/vertex
The enzymes name sets upon the active substrate + אז, for example- enzymes that degrade starch and amyles, but there are enzymes names that do not follow the אז pattern, such as pepsin
each enzymes requires its prime conditions its optimum.
Enzyme Significance
Without enzymes, breakdown and assembly processes in our bodies would take days, months, or not occur, preventing life.
Chemical processes need activation energy, and heating provides this.
Enzymes enable reactions at lower activation energy levels, allowing body processes without heating.
Enzyme-driven cellular process acceleration ensures efficiency, speed, energy conservation, and reactions under mild temperature and pH.
Enzymes are produced in cells and are unique to various substrates and reactions, leading to many enzyme types in each cell.
Coenzymes are non-protein parts of enzymes vital for substrate action, including salts or vitamins. Deficiencies inhibit enzyme activity.
Cellular Respiration as an Enzymatic Process
Energy conversion is achieved with or without oxygen.
The process of converting unavailable chemical energy to available chemical energy is respiration.
What Does "Energy Conversion" Mean?
The chemical energy in organic molecule bonds (e.g., glucose) cannot be used directly by the cell. Energy must be released to form a new, usable molecule.
Analogy: Converting currency for international travel.
In cellular respiration, energy from organic molecules (often glucose, a simple sugar) is released to create ATP, a high-energy molecule available to cells.
The energy is used to attach a third phosphate group to ADP, creating ATP. This bond stores energy, which is then released as the ATP becomes ADP.
Examples of Questions Relevant to Unseen Texts (Part C)
A cut apple turns brown due to enzymes that, with air oxygen, accelerate a process yielding a brown substance. Will this browning be faster in specific seasons?
Will enzymatic browning occur after heating apples above 100 degrees Celsius?
Is it correct to say saliva amylase, which breaks down starch, will break down disaccharides?
Is it correct to say saliva amylase, which breaks down starch, will break down fats?
Why do potatoes added to hydrogen peroxide cause decomposition into oxygen and water?
Why no decomposition occurs when boiled potatoes are added to hydrogen peroxide?
Will a laundry detergent with protein, fat, and carbohydrate-degrading enzymes be more effective with boiling water? Explain.
Analyze a graph showing temperature's effect on enzyme activity rate. What is its shape? What characterizes it?
Analyze a graph showing enzyme/substrate concentration effects. What is its shape? What are its characteristics? What are the differences between the graph types?
Energy Release
ATP usage includes:
Growth
DNA repair
Nutrient transport
Cell division and reproduction
Nutrient intake from the environment
Waste excretion
Homeostasis
Differentiation
Enzyme activity
ADP + P ATP Energy Energy used out of cellular glucose decomposition. Energy for cell work.
Cellular Respiration Stages
The breakdown of glucose into carbon dioxide and water, creating ATP, occurs in two stages:
Glycolysis (Cytoplasm): Glucose is partially broken down to create materials for the next stage and 2 ATP molecules without oxygen.
Mitochondrial Stage: The partial breakdown of glucose is further broken down in the mitochondrion using oxygen into inorganic molecules, releasing energy to create 20+ ATP molecules.
Not all energy stored in glucose is harnessed for ATP creation; much is released as heat, useful for homeothermic organisms to maintain body temperature.
Increased respiration during physical activity raises muscle temperature.
Process Links
Glucose and oxygen are transported to cells via blood.
Glucose enters blood from the intestine or is released from liver stores.
Oxygen enters red blood cells in the lungs.
Glucose and oxygen enter cells via diffusion using also glucose carriers in muscle and fat cells via insulin.
Glucose serves as a raw material for substance production or storage. It also degrades through respiration producing ATP, some of wich results in heat being released.
The products are carbon dioxide (excreted via blood) and water.
Important Lab Terms
Cell Suspension: Cells dispersed in water (e.g., yeast cells).
Cell Extract: Fluid containing cytoplasm and organelles from tissue cells, prepared by crushing or grinding cells, adding water, and filtering.
Acid: A compound that releases hydrogen ions (H+) when dissolved in water. A common example is hydrochloric acid (HCl).
Hydrochloric acid +H dissolves to ions in water, resulting in Hydrogen + and Cl- atoms combine with water molecules; thus are created H3O monomers, that are responsible for its pH.
Base: A substance that increases hydroxide ion (OH-) concentration in water. A common example is sodium hydroxide (NaOH).
Natrium hydroxide, +Na, resolves to Sodium + and OH- atoms.
pH Scale: Measures solution acidity, reflecting the ratio of hydronium to hydroxide ions.
pH in Distilled Water
The concentration of hydronium ions equals hydroxide ions, resulting in a pH of 7.
pH Changes
Adding acid increases hydronium ions, lowering the pH toward 0.
Adding base increases hydroxide ions, raising the pH toward 14.
Titration
Titration is a technique used to determine the concentration of a substance in a solution.
A solution with a known concentration (titrant) is gradually added to the solution being analyzed.
The titrant reacts with the substance of interest until the reaction is complete.
An indicator is used to detect the endpoint of the reaction, where all of the substance has reacted.
The concentration of the substance can be calculated from the amount of titrant added.
Example: If a solution containing an unknown concentration of acid is titrated with a base of known concentration, the amount of base required to neutralize the acid can be used to calculate the acid concentration.
Microscope Skills
Microscopy skills are used in examinations.
This involves a report using drawings.
Preparing Sample
Ensure the tissue is thin and evenly covered with water, avoiding air bubbles.
Viewing Through Microscope
Start with low magnification, position the tissue in the center when possible. If going to large magnification settings, make sure the area viewed under low settings is still close to the center.
The microscope has invert vision, which needs to be kept in mind.
Drawing to Reprot the Viewing Through Microscope
Draw cells as see in greater magnification (unless instructed other wise).
Choose cell amount based on magnification
Draw in pencil (as any writing in this format is desired to have) . Also, draw title with magnification level to each drawing.
Typical Microscope Observations (School Labs)
Cell walls, membranes, chloroplasts, nuclei, and amyloplasts are seen.
Colored flower petal cells show pigments or colored cytoplasm.
Other cell parts are too small or need stain.
Examples
Allodia cells, either in plasmolyzed or natural state. An epidermal section of a leaf. Or a potatoe with added iodine and seen through the microscope.