The experimental questions in the Gaokao science exam are hot topics, with a 100% reappearance rate. The “experimental ability” is one of the five major abilities assessed in the Gaokao, and it can reflect students’ basic subject literacy well. Here, I have compiled essential knowledge for physics, chemistry, and biology experiments that students must memorize.
Verification Experiments
1. Verify the Parallelogram Law of Forces
1. Purpose: To verify the parallelogram law.
2. Equipment: A square wooden board, a sheet of white paper, two spring scales, a rubber band, two string loops, a triangle ruler, a measuring ruler, and several thumbtacks.
3. Main Measurements:
a. Use two force gauges to pull the string loops to stretch the rubber band until the knot reaches a point O.
Record the readings F1 and F2 of the two force gauges.
Direction of the forces shown by the two force gauges.
b. Use one force gauge to pull the knot back to point O.
Record the magnitude F and direction of the spring scale’s pulling force.
4. Drawing: Measuring ruler, triangle ruler
5. Methods to Reduce Errors:
a. The force gauge should be calibrated to zero before use.
b. The square wooden board should be placed horizontally.
c. The direction of the spring’s extension and the measured pulling force should be consistent and parallel to the board.
d. Both component forces and the resultant force should be as large as possible.
e. The string used to pull the rubber band should be long, and the marked points on the two strings should be as far apart as possible.
f. The angle between the two component forces should not be too large or too small, generally taken as 60° to 120°.
2. Verify the Law of Conservation of Momentum
Principle: When two small balls collide horizontally, the net external force in the horizontal direction is zero, and momentum is conserved.
m1v1 = m1v1′ + m2v2′ This experiment verifies that the above equation holds within allowed error margins. After the collision, both small balls perform horizontal projectile motion, indirectly represented by the horizontal range to indicate the initial velocity of the small balls:
OP—–m1’s horizontal range when thrown with v1
OM—-m1’s horizontal range when thrown with v1′
O’N—–m2’s horizontal range when thrown with V2′
Verification expression: m1OP = m1OM + m2O/N
1. Experimental Instruments:
Inclined plane, weight, white paper, carbon paper, measuring tape, incident small ball, target small ball, caliper, ruler, compass, balance.
2. Experimental Conditions:
a. The mass of the incident small ball m1 should be greater than that of the target small ball m2 (m1 > m2)
b. The radius of the incident ball should equal that of the target ball.
c. The incident small ball must slide down from the same height on the inclined plane from rest each time.
d. The tangent direction at the end of the inclined plane should be horizontal.
e. When the two balls collide, their centers should be at the same height or on the same horizontal line.
3. Main Measurement Quantities:
a. Use a balance to measure the masses of the two balls m1 and m2
b. Use a caliper to measure the diameters of the two balls and calculate the radius.
c. When determining the landing position of the small balls, use the landing positions from each experiment as a reference, marking a circle as small as possible around them; the center of this circle will be defined as the landing position corresponding to the experimental measurement data.
3. Verify the Conservation of Mechanical Energy
1. Principle: When an object performs free fall, according to the law of conservation of mechanical energy, mgh = 
Verify that the above equation holds within the range of experimental errors.
2. Experimental Equipment: Dot timer, paper tape, weight, measuring tape, iron stand, flask clamp, low-voltage AC power supply, wires.
3. Experimental Conditions:
a. The dot timer should be vertically fixed on the iron stand.
b. At the moment the paper tape is released, the dot timer should just mark a point, with the distance between the first two points on the tape being approximately 2 mm.
4. Measured Quantities:
a. The distance from the starting point to a certain research point is the height h from which the weight falls, thus the decrease in gravitational potential energy is mgh1; measure multiple points to the starting point with heights h1, h2, h3, h4 (the distances from each point to the starting point should be larger for better accuracy).
b. It is unnecessary to measure the mass of the weight.
5. Error Analysis: Due to the weight overcoming resistance during descent, the increase in kinetic energy is slightly less than the decrease in gravitational potential energy.
6. Common Mistakes
a. Conditions for selecting the paper tape: Marking should be clear; the distance between the first and second points should be approximately 2 mm.
b. The dot timer should be vertically fixed, and the paper tape should be vertical.
Measurement Experiments
1. Measurement of Length
1. Measurement Principles:
(1) To avoid reading errors, all three measuring tools (including the millimeter scale) should read in mm!
(2) When measuring length with a vernier caliper or micrometer screw gauge, ensure to measure several times from different angles and take the average value.
(3) The ruler should be in close contact with the measured object, with no gap between the scale line and the measuring surface.
2. Experimental Principles:
Vernier Caliper—-(1) Each division is 0.9 mm, with a minimum graduation difference of 0.1 mm; a 20-division caliper has a total length of 19 mm, divided into 20 parts, each part is 19/20 mm, with a minimum graduation difference of 0.05 mm; a 50-division caliper has a total length of 49 mm, divided into 50 parts, each part is 49/50 mm, with a minimum graduation difference of 0.02 mm;
2. Reading Method:
Read the whole millimeter number on the main scale aligned with the zero line of the vernier scale, then read which line on the vernier scale aligns with a certain line on the main scale; multiply the aligned vernier scale line number by the accuracy of the caliper (which is the reciprocal of the total divisions), and add the main scale reading and the vernier reading to obtain the measurement value.
Micrometer Screw Gauge
(1) Working Principle: Each complete turn moves the screw by a pitch of 0.5 mm; if divided into 50 parts, each part represents 0.01 mm, thus it is accurate to 0.01 mm, also known as a thousandth gauge.
(2) Reading Method: First read the scale value exposed on the main scale, noting that the main scale has lines for whole millimeters and half millimeters, without missing the half millimeter value. Then read the movable scale part to see which scale line aligns with the main scale line (note estimation), multiply by 0.01 mm for the movable reading, and add the fixed and movable readings for the measurement value. Note: When reading the micrometer screw gauge in mm, the decimal point must have three digits; if not enough, use zeros to fill in.
3. Precautions:
(1) When reading the vernier caliper, the main scale reading should be taken from the zero scale of the vernier, not from the mechanical end of the vernier.
(2) When using the vernier scale, regardless of how many divisions, the last digit of the 20 divisions should be estimated as either 0 or 5; for a 50-division caliper, the last digit should be even.
(3) If any division on the vernier scale aligns with the main scale line, choose the closest line to read.
(4) Pay attention to whether the half millimeter line is exposed when reading the main scale of the micrometer screw gauge.
(5) When reading the movable part of the micrometer screw gauge, even if a line is fully aligned, it should still be estimated as zero.
4. Measuring Gravity Acceleration with a Simple Pendulum
1. Experimental Purpose: To determine the local acceleration due to gravity using a simple pendulum.
2. Experimental Principle: g=
3. Experimental Equipment: A thin line about 1m long, a small iron ball, an iron stand, a measuring ruler, a caliper, a stopwatch.
4. Common Mistakes:
a. When the small ball swings, the maximum deflection angle should be less than 5°. Ideally around 10 degrees.
b. The small ball should vibrate within a vertical plane.
c. When calculating the number of vibrations of the simple pendulum, timing should start when the pendulum ball passes the equilibrium position.
d. The length of the pendulum should be the distance from the suspension point to the center of the ball, i.e., L = length of the pendulum line + radius of the ball.
5. Using Oil Film Method to Estimate Molecular Diameter
1. Experimental Principle: A drop of oleic acid on the water surface can be considered to form a monomolecular oil film on the water surface; if the molecules are considered spherical, measuring its thickness gives the diameter.
2. Experimental Equipment: A water-filled square dish, a syringe (or dropper), a reagent bottle, graph paper, glass, talcum powder (or gypsum powder), alcohol oleic acid solution, and a measuring cylinder.
3. Steps: Pour water into the dish and let it settle; use a dropper to suck up oleic acid and drop it into the measuring cylinder drop by drop, keeping track of the volume of each drop; sprinkle talcum powder evenly on the water surface; once the oil film area stabilizes, place a glass on the dish to outline the contour on graph paper, then count the squares; if more than half a square, count as one square; if less than half, discard; calculate the area from the squares counted, and determine the volume from the concentration.
4. Precautions:
(1) Before the experiment, ensure the dish is clean; otherwise, the oil film will be hard to form.
(2) The water in the dish should remain balanced, and the talcum powder should float evenly on the water surface.
(3) When dropping the alcohol solution onto the water surface, do so close to the surface and not too high; otherwise, the oil film will be hard to form.
(4) Only one drop of oleic acid solution should be added to the water surface.
(5) When calculating the molecular diameter, note that the drop added is not pure oleic acid but an alcohol oleic acid solution; use the volume of one drop multiplied by the volume percentage concentration of the solution.
5. Determining the Resistivity of Metals
1. The circuit connection method is the external connection method for the ammeter, not the internal connection method.
2. When measuring L, measure the effective length of the resistance wire connected to the circuit.
3. Before closing the switch, the sliding contact of the sliding rheostat should be placed in the correct position.
4. Measure U and I multiple times, calculate R, and then find the average value of R.
5. The current should not be too large; otherwise, the resistivity will change, generally selecting the 0-0.6 amp range for the ammeter.
6. Measuring the Electromotive Force and Internal Resistance of a Power Supply
1. Experimental circuit diagram: The ammeter and sliding rheostat are connected in series and then parallel with the voltmeter.
2. Measurement errors: The measured values of e and r are both less than the true values.
3. The ammeter is generally selected to the 0-0.6A range, and the voltmeter is generally selected to the 0-3V range.
4. The current should not be too large, generally less than 0.5A.
Errors: The measured value of the electromotive force e and the measured value of the internal resistance r are both less than the true values.
7. Modification of the Ammeter (Measuring Internal Resistance)
Experimental Notes:
(1) When measuring the internal resistance of the ammeter using the half-deflection method, the condition should be that the potentiometer resistance is much greater than the internal resistance of the meter (about 10 times).
(2) Choosing a power supply with a high electromotive force helps reduce errors.
(3) The internal resistance value measured by the half-deflection method is biased low (when reading, the main current is greater than the full-scale current, and the current through the resistance box is greater than the half-deflection current, which can be derived from the current division law).
(4) The deflection of the modified meter is still proportional to the total current or total voltage, and the scale or reading can be determined accordingly, and the scale lines should be uniform.
(5) The calibration circuit generally uses the voltage divider connection method.
(6) Absolute error compared to relative (percentage) error, the latter better reflects the experimental accuracy.
Research Experiments
1. Study of Uniformly Accelerated Motion
(1) Practice Using the Dot Timer:
1. Construction: See the textbook.
2. Key Points: Connect to 50HZ, 4-6 volts of AC power.
Correctly mark the points: Select 5 points in the middle section of the paper tape.
3. Focus: Analysis of the paper tape.
a. Determine the motion of the object:
Within the error range: If S1=S2=S3=…, then the object performs uniform linear motion.
If DS1=DS2=DS3=…=constant, then the object performs uniformly accelerated linear motion.
b. Measure acceleration:
Formula Method: First find DS, then use DS= aT2 to find acceleration.
Graphical Method: Create a v-t graph, and find a as the slope of the line.
c. Measure instantaneous speed: V1=(S1+S2)/2T V2=(S2+S3)/2T
(2) Measure the Acceleration of Uniformly Accelerated Motion:
1. Principle: DS=aT2
2. Experimental Conditions:
a. The net force is constant, and the string is parallel to the wooden board.
b. Connect to 50HZ, 4-6 volts of AC power.
3. Experimental Equipment: Electromagnetic dot timer, paper tape, carbon paper, low-voltage AC power supply, cart, string, a long wooden board with a pulley on one end, measuring ruler, weights, wires, and two wires.
4. Main Measurements:
Select the paper tape, mark the counting points, and measure the displacement S1, S2, S3 for each time interval… Point O is any point in the graph.
5. Data Processing:
Process the data using the incremental method to find acceleration:
S4-S1=3a1T2, S5-S2=3a2T2, S6-S3=3a3T2, a=(a1+a2+a3)/3=(S4+S5+S6-S1-S2-S3)/9T2
(3) Measure Instantaneous Speed of Uniformly Accelerated Motion:(same as above)
2. Study of Horizontal Projectile Motion
1. Experimental Principle:
Use a certain method to trace the trajectory curve of a horizontally thrown small ball in the air, and then based on the coordinates of certain points on the trajectory, use h= to find t, and then use x=v0t to find v0, and calculate the average value of v0.
2. Experimental Equipment:
Wooden board, white paper, thumbtacks, a horizontal inclined plane, small balls, measuring ruler, cards with small holes, and a weight line.
3. Experimental Conditions:
a. The wooden board holding the white paper should be vertical.
b. The tangent at the end of the inclined plane should be horizontal, accurately marking the position on the white paper.
c. The small ball should slide down from the same position on the trough each time from rest.
3. Study of the Relationship Between Elasticity and Deformation
1. Method Summary:
(1) Apply pressure to the spring using hanging weights.
(2) Use a tabular method to record and analyze data (how to design an experimental record table).
(3) Use a graphical method to analyze the relationship of experimental data: Steps:
① Establish a coordinate system with force as the vertical coordinate and spring elongation as the horizontal coordinate.
② Plot the measured data points on graph paper.
③ Based on the distribution and trend of the points in the graph, attempt to draw a smooth curve (including a straight line).
④ Write the function represented by the curve, first trying a linear function; if that doesn’t work, consider a quadratic function; if it seems to resemble an inverse proportion function, transform the relevant quantities into their reciprocals and see if it becomes a direct proportion relationship (whether the graph can be transformed into a straight line) – methods to simplify curves.
⑤ Explain the meaning of the constants in the function expression.
2. Precautions: Do not add too many heavy weights to avoid exceeding the elastic limit of the spring.
Observation and Drawing Experiments
1. Drawing the Voltage-Current Characteristic Curve
1. Experimental Principle: During the process of a small bulb changing from dark to bright, there is a significant change in temperature, and the resistance of the conductor will increase with the change in temperature, thus the drawn voltage-current characteristic curve will not be a straight line, but a curve with a gradually increasing slope.
2. Experimental Steps:
(1) With the switch off, connect the circuit (voltage divider connection, ammeter external connection) and then adjust the sliding rheostat to the position where the voltage applied to the load is minimal.
(2) Adjust the sliding rheostat, read and record about 12 sets of values (do not disconnect the power for intermittent measurements).
(3) Turn off the power and disconnect the circuit.
(4) Establish a coordinate system, select appropriate scales, plot points, and connect them smoothly.
3. Precautions:
(1) To ensure accuracy, try to measure several sets of data (around 12), and the sliding rheostat should be connected as a voltage divider.
(2) The internal or external connection method of the ammeter should be determined according to the resistance of the bulb, generally using the external connection method.
(3) To reduce errors, the selected scale ratio for plotting should be appropriate, ensuring that the 12 points are distributed over a large range on the coordinate plane, and the density should be as uniform as possible.
(4) The resistance value measured with a multimeter is generally much larger than the value measured in the circuit (cold resistance is smaller).
2. Drawing Equipotential Lines
1. Experimental Principle: This experiment simulates a steady current field to model an electrostatic field using conductive paper. Thus, the electrode connected to the positive terminal of the 6V DC power supply acts like a positive charge; the electrode connected to the negative terminal of the 6V DC power supply acts like a negative charge.
2. Experimental Equipment: Wooden board, white paper, carbon paper, conductive paper, tacks, two cylindrical electrodes, two probes, a sensitive ammeter, battery, switch, and wires.
3. Common Mistakes:
(1) Place the white paper, carbon paper, and conductive paper in order from bottom to top.
(2) Only use a sensitive ammeter, not an ammeter.
Instrument Use Experiments
Measurement of Length (ruler, micrometer, vernier caliper), see previous content.
Using an Oscilloscope
1. Principle:
(1) The oscilloscope tube is its core component, along with corresponding electronic circuits.
(2) The principle of the oscilloscope tube: The sawtooth wave voltage applied in the xx’ direction causes the position of the electrons striking the fluorescent screen to be proportional to the time (like a light point performing periodic uniform motion in the horizontal direction – this is called scanning, simulating the time axis); applying the external voltage (signal input between Y input and ground) will display the waveform of the external voltage on the screen.
2. General Steps for Use:
(1) First, pre-adjust: Rotate the brightness knob counterclockwise to the bottom, set vertical and horizontal displacement to the middle, set attenuation to the highest range, and set scanning to the “external X range”.
(2) Then turn on the power, wait for a minute or two for preheating before performing relevant operations.
(3) First adjust the brightness, then focus, and adjust the horizontal and vertical displacements to center the bright point in the suitable area.
(4) Adjust scanning, fine-tune scanning, and X gain to observe the scanning.
(5) Switch the external X range to a suitable scanning range to observe the vertical voltage waveform changing according to the sine and cosine rules.
(6) To observe the vertical offset of a bright spot (when applying a constant DC voltage), switch scanning to the “external X” range.
3. Precautions:
(1) Pay attention to the usage steps; do not turn on the power immediately but first pre-adjust and preheat before making normal adjustments.
(2) When observing the voltage to be measured, ensure the scanning switch is set to the scanning range and the external voltage is input between Y input and ground; at this time, the X X’ voltage is the built-in scanning voltage simulating the time axis. Only when separately adding input voltage to X X’ should the switch be switched to the external X range.
(3) Practice using a multimeter:
① After selecting the appropriate range, first zero the resistance, then connect the red and black probes across the resistance to be measured, measuring each time requires re-zeroing the resistance.
② Select an appropriate range so that the pointer is near the mid-value resistance for minimal error.
③ When measuring resistance, the selector switch should be set to the “W” range.
④ Do not hold both probes’ metal parts with both hands while measuring resistance.
⑤ Before measuring resistance, the resistance to be measured must be disconnected from other circuits.
⑥ After measuring resistance, remove the probes and set the selector switch to the “OFF” range or the highest range for AC voltage.
⑦ When measuring resistance, if the pointer’s deviation angle is too small, switch to a higher range; if the pointer’s deviation angle is too large, switch to a lower range.
⑧ The battery in the ohmmeter has aged; the resistance value measured with this ohmmeter will be larger than the true value.
High school chemistry experiments also account for certain points in the exam; how to ensure that chemistry experiments do not lose points? Below is a summary of the most commonly tested chemistry experimental phenomena for the Gaokao. Remembering these experimental phenomena will help you tackle most experimental phenomenon questions.
1. Magnesium ribbon burns in air: emits dazzling bright light, releases a lot of heat, generating white smoke and a white substance.
2. Charcoal burns in oxygen: emits white light and releases heat.
3. Sulfur burns in oxygen: emits a bright blue-purple flame, releases heat, generating a gas with a pungent smell.
4. Iron wire burns in oxygen: burns vigorously, producing sparks, releases heat, generating black solid material.
5. Heating ammonium bicarbonate in a test tube: generates a gas with a pungent smell, and droplets form on the test tube.
6. Hydrogen burns in air: the flame appears pale blue. 7. Hydrogen burns in chlorine: emits pale flame and generates a lot of heat.
8. Reducing copper oxide with hydrogen in a test tube: black copper oxide turns into a red substance, droplets form at the mouth of the test tube.
9. Reducing copper oxide powder with charcoal powder, passing the generated gas into clear lime water: black copper oxide turns into shiny metal particles, and lime water becomes turbid.
10. Carbon monoxide burns in air: emits a blue flame and releases heat.
11. Adding hydrochloric acid to a test tube containing a small amount of potassium carbonate solid: gas is generated.
12. Heating copper sulfate crystals in a test tube: blue crystals gradually turn into white powder, and droplets form at the mouth of the test tube.
13. Sodium burns in chlorine: burns vigorously, generating white solid.
14. Igniting pure chlorine and covering the flame with a dry cold beaker: emits a pale blue flame, and droplets form on the inner wall of the beaker.
15. Adding silver nitrate solution acidified with nitric acid to a solution containing Cl-: a white precipitate is formed.
16. Adding barium chloride solution acidified with nitric acid to a solution containing SO42-: a white precipitate is formed.
17. Dropping a rusty iron nail into a test tube of dilute sulfuric acid and heating: the rust gradually dissolves, the solution turns light yellow, and gas is generated.
18. Adding sodium hydroxide solution to copper sulfate solution: a blue flocculent precipitate is formed.
19. Passing Cl2 into colorless KI solution: a brown substance is produced in the solution.
20. Adding sodium hydroxide solution to ferric chloride solution: a reddish-brown precipitate is formed.
21. Adding a small amount of water to a test tube containing quicklime: a vigorous reaction occurs, releasing a lot of heat.
22. Immersing a clean iron nail in copper sulfate solution: red substances adhere to the surface of the nail, and the color of the solution gradually lightens.
23. Inserting a copper piece into mercuric nitrate solution: silver-white substances adhere to the surface of the copper piece.
24. Injecting concentrated sodium carbonate solution into a test tube containing lime water: a white precipitate is formed.
25. Burning fine copper wire in chlorine, then adding water: brown smoke is generated, and after adding water, a green solution is formed.
26. Strong light irradiating a mixture of hydrogen and chlorine gases: a rapid reaction occurs with an explosion.
27. Red phosphorus burns in chlorine: white smoke is generated.
28. Chlorine encounters wet colored cloth: the color of the cloth fades.
29. Heating a mixture of concentrated hydrochloric acid and manganese dioxide: a yellow-green pungent gas is generated.
30. Heating a mixture of solid sodium chloride and concentrated sulfuric acid: fog is generated, and a pungent odor is produced.
31. Adding silver nitrate solution to sodium bromide solution, then adding dilute nitric acid: a light yellow precipitate is formed.
32. Adding silver nitrate solution to potassium iodide solution, then adding dilute nitric acid: a yellow precipitate is formed.
33. I2 encounters starch, generating a blue solution. 34. Fine copper wire burns in sulfur vapor: the fine copper wire turns red and produces black substances.
35. Mixing iron powder and sulfur powder and heating to red heat: the reaction continues, releasing a lot of heat, generating black substances.
36. Hydrogen sulfide gas not completely burning (covering with an evaporating dish): the flame appears pale blue (yellow powder at the bottom of the evaporating dish).
37. Hydrogen sulfide gas completely burning (covering with a dry cold beaker): the flame appears pale blue, generating a gas with a pungent smell (droplets form on the inner wall of the beaker).
38. Mixing hydrogen sulfide and sulfur dioxide in a gas jar: a yellow powder is generated on the inner wall of the jar.
39. Passing sulfur dioxide gas into fuchsin solution and heating: the red color fades, and heating restores the original color.
40. Excess copper added to a test tube containing concentrated sulfuric acid and heated; after the reaction, wait for the solution to cool and add water: a gas with a pungent smell is generated, and after adding water, the solution appears sky blue.
41. Heating a test tube containing concentrated sulfuric acid and charcoal: gas is generated, and the gas has a pungent smell.
42. Sodium burns in air: the flame appears yellow, generating a light yellow substance.
43. Sodium is added to water: a vigorous reaction occurs, sodium floats on the water surface, releasing a lot of heat and melting into small balls that move on the water surface, with a “hissing” sound.
44. Dropping water into a test tube containing solid sodium peroxide, then inserting a glowing splint: the splint reignites.
45. Heating solid sodium bicarbonate and passing the generated gas into clear lime water: the clear lime water turns turbid.
46. Ammonia gas encounters hydrochloric acid: a large amount of white smoke is produced.
47. Heating a mixture of ammonium chloride and calcium hydroxide: a gas with a pungent smell is produced.
48. Heating a test tube containing solid ammonium chloride: white crystals are produced at the mouth of the test tube.
49. Concentrated nitric acid in a colorless reagent bottle is exposed to sunlight: the space in the bottle turns brown, and the nitric acid appears yellow.
50. Copper pieces react with concentrated nitric acid: a vigorous reaction occurs, producing reddish-brown gas.
51. Copper pieces react with dilute nitric acid: colorless gas is produced at the bottom of the test tube, and the gas gradually turns reddish-brown.
52. Adding dilute hydrochloric acid to sodium silicate solution: a white gelatinous precipitate is produced.
53. Adding magnesium sulfate solution to ferric hydroxide colloid: the colloid becomes turbid.
54. Heating ferric hydroxide colloid: the colloid becomes turbid.
55. Inserting a lit magnesium ribbon into a gas jar containing carbon dioxide: it burns vigorously, and black substances adhere to the inner wall of the gas jar.
56. Adding ammonia solution to aluminum sulfate solution: a fluffy white flocculent substance is produced.
57. Adding sodium hydroxide solution to ferrous sulfate solution: a white flocculent precipitate is formed, which immediately turns gray-green and then turns into reddish-brown precipitate.
58. Adding KSCN solution to a solution containing Fe3+: the solution turns blood red.
59. Adding sodium sulfide solution to chlorine water: the solution becomes turbid. S2- + Cl2 = 2Cl2- + S↓
60. Adding a small amount of soap solution to natural water: the foam gradually decreases, and precipitation occurs.
61. Igniting methane in air and placing a dry cold beaker over the flame: the flame appears pale blue, and droplets form on the inner wall of the beaker.
62. Illuminating a mixture of methane and chlorine gases: yellow-green gradually lightens over time (droplets form on the inner wall of the container).
63. Heating a mixture of ethanol and concentrated sulfuric acid (170°C), passing the generated gas into bromine water, and into acidic potassium permanganate solution: gas is produced, bromine water decolorizes, and purple gradually lightens.
64. Igniting ethylene in air: the flame is bright, producing black smoke and releasing heat.
65. Igniting acetylene in air: the flame is bright, producing thick smoke and releasing heat.
66. Benzene burns in air: the flame is bright and produces black smoke.
67. Ethanol burns in air: the flame appears pale blue.
68. Passing acetylene into bromine water: bromine water decolorizes.
69. Passing acetylene into acidic potassium permanganate solution: purple gradually lightens until it disappears.
70. Benzene reacts with bromine in the presence of iron powder as a catalyst: white mist is produced, and the product is oily and brownish.
71. Adding a small amount of toluene to an appropriate amount of potassium permanganate solution and shaking: purple decolorizes.
72. Adding sodium metal to a test tube containing ethanol: gas is released.
73. Adding excess concentrated bromine water to a test tube containing a small amount of phenol: a white precipitate is formed.
74. Adding a few drops of ferric chloride solution to a test tube containing phenol and shaking: the solution turns purple.
75. Aldehyde reacts with silver ammonia solution in a test tube: a clean layer of mirror-like material adheres to the inner wall of the test tube.
76. Under boiling conditions, aldehyde reacts with freshly prepared copper hydroxide: a red precipitate is formed.
77. Under suitable conditions, ethanol reacts with acetic acid: a transparent, fragrant oily liquid is produced.
78. Proteins encounter concentrated HNO3 solution: turn yellow.
79. Purple litmus solution encounters alkali: turns blue.
80. Colorless phenolphthalein solution encounters alkali: turns red.
Experiment 1:Observe the Distribution of DNA and RNA in Cells
Experimental Principle: DNA is green, RNA is red
Distribution: Eukaryotic DNA is mainly located in the cell nucleus, with a small amount of DNA also in mitochondria and chloroplasts; RNA is mainly found in the cytoplasm.
Experimental Results: The cell nucleus appears green, and the cytoplasm appears red.
Experiment 2:Observe Chloroplasts and Cytoplasmic Streaming
1. Materials: Fresh moss leaves, black algae leaves or spinach leaves, temporary slides of oral epithelial cells
2. Principle: Chloroplasts are observed under a microscope, appearing green, spherical or oval.
Using methylene green dye, the mitochondria in oral epithelial cells appear bluish-green, while the cytoplasm is nearly colorless.
Knowledge Summary: Sampling, making slides, low power observation, high power observation
Exam Point Tips:
(1) Why can small leaves of moss be directly used, but spinach leaves cannot? Because the small leaves of moss are very thin, consisting of only one layer of cells, while spinach leaves are composed of many layers of cells. (2) Why should some leaf mesophyll be included when taking the lower epidermis of spinach leaves? Epidermal cells, except for guard cells, generally do not contain chloroplasts, while mesophyll cells contain more chloroplasts. (3) How to speed up the flow rate of black algae cytoplasm? What is the optimal temperature? Provide light, increase water temperature, cut some leaf blades; around 25°C. (4) Which part of the black algae cells shows the most obvious cytoplasmic streaming? Cells near the leaf veins. (5) If the direction of cytoplasmic streaming in a certain cell in the field of view is clockwise, what is the actual direction of cytoplasmic streaming in that cell in the slide? It is still clockwise.
Experiment 3:Compare the Catalytic Efficiency of Enzyme and Fe3+
Exam Point Tips:
(1) Why use fresh liver? Because in stale liver, the activity of catalase will decrease due to bacterial destruction.
(2) Should the test tubes used in this experiment be thicker or thinner? Why? They should be thicker because in thinner test tubes, a lot of bubbles can easily form, affecting the cleanliness of the experiment.
(3) Why use animal liver tissue for this experiment? Can other animal or plant tissues’ homogenates be used as substitutes? Because liver tissue contains a rich amount of catalase; other animal and plant tissues also contain a small amount of catalase, so they can be substituted.
(4) Among the same mass of block liver and liver homogenate, which has better catalytic effect? Why? The homogenate has a better effect; because it increases the contact area between catalase and hydrogen peroxide.
(5) When adding liver homogenate and iron chloride solution, can the same straw be used? Why? It cannot be shared to prevent the mixing of catalase with iron chloride, affecting the experimental results.
Experiment 4:Extraction and Separation of Pigments
1. Principle: The pigments in chloroplasts can dissolve in organic solvents like acetone or anhydrous ethanol – to extract pigments. Each pigment has different solubility in the chromatography liquid, diffusing at different speeds on filter paper – to separate pigments.
2. Steps:
(1) Extract pigments by grinding
(2) Prepare filter paper strips
(3) Draw a fine line of the filtrate: uniform, straight, thin, repeat several times
(4) Separate pigments: do not let the filtrate line touch the chromatography liquid
(5) Observe and record: The results on the filter paper strip from top to bottom are: orange-yellow (carotene), yellow (xanthophyll), blue-green (chlorophyll a), yellow-green (chlorophyll b).
Experiment 5:Observe Plasmolysis and Restoration
1. Conditions: Concentration difference between intracellular and extracellular solutions, living cells, large vacuoles
2. Materials: Purple onion scale leaf epidermal cells (with purple large vacuoles), 0.3g/mL sucrose solution, distilled water, etc.
3. Steps: Prepare a temporary slide of purple onion scale leaf epidermal cells → Observe → Drop sucrose solution on one side of the cover glass, and吸水纸吸引 on the other side → Observe (vacuoles shrink from large to small, color changes from light to deep, protoplast separates from the cell wall) → Drop distilled water on one side of the cover glass, and吸水纸吸引on the other side → Observe (restoration of plasmolysis)
4. Conclusion: When the concentration of the extracellular solution is greater than that of the intracellular solution, the cell loses water and plasmolysis occurs; when the concentration of the extracellular solution is less than that of the intracellular solution, the cell absorbs water and restores plasmolysis.
Knowledge Summary: Sampling, observing, adding liquid, observing, adding water, observing
Experiment 6:Investigate the Respiration Method of Yeast
1. Principle: Yeast undergoes aerobic respiration under aerobic conditions, producing carbon dioxide and water: C6H12O6 + 6O2 + 6H2O → CO2 + 12H2O + energy
Under anaerobic conditions, it undergoes anaerobic respiration, producing alcohol and a small amount of carbon dioxide: C6H12O6 → 2C2H5OH + 2CO2 + a small amount of energy
2. Apparatus: (see textbook)
3. Detection:
(1) Detect CO2 production: make clear lime water turbid, or make bromothymol blue solution change from blue to green and then yellow.
(2) Detect alcohol production: orange potassium dichromate solution reacts with alcohol under acidic conditions, turning gray-green.
Experiment 7:Observe Meiosis in Cells
1. Objective Requirements: By observing fixed slides of grasshopper spermatocytes undergoing meiosis, identify the morphology, position, and number of chromosomes at different stages of meiosis, deepening the understanding of the meiosis process.
2. Materials and Tools: Fixed slides of grasshopper spermatocytes undergoing meiosis, microscope.
3. Method Steps:
(1) Observe the fixed slide of grasshopper spermatocytes under low power, identifying primary spermatocytes, secondary spermatocytes, and spermatids.
(2) First find the cells in the first meiotic division at prophase, metaphase, and anaphase, and then in the second meiotic division at prophase, metaphase, and anaphase under low power; then carefully observe the morphology, position, and number of chromosomes under high power.
4. Discussion:
(1) How to determine whether a cell in the field of view is in the first or second meiotic division?
(2) What are the differences in chromosome morphology in prophase cells between the first and second meiotic divisions? What about in telophase?
Experiment 8:Low Temperature Induces Chromosome Doubling
1. Principle: Treating plant meristematic tissue cells with low temperature can inhibit the formation of spindle fibers, affecting the pulling of chromosomes to the poles, preventing the cell from dividing into two daughter cells, thus changing the number of chromosomes in plant cells.
2. Method Steps:
(1) When onion roots grow to about 1 cm, place them in the low-temperature chamber of the refrigerator (4°C) for 36 hours to induce cultivation.
(2) Cut the induced root tips about 0.5-1 cm long, soak them in Carnoy’s solution for 0.5-1 hour to fix the cell morphology, and then rinse twice with 95% alcohol.
(3) Prepare a slide: dissociate → rinse → stain → make a slide
(4) Observe and compare: In the field of view, there are both normal diploid cells and cells with changed chromosome numbers.
3. Discussion:
Both colchicine and low temperature can induce chromosome doubling; what similarities do these two methods have in principle?
Experiment 9:Simulate and Investigate the Relationship Between Surface Area and Volume in Cells
Principle: NaOH and phenolphthalein turn purple when they meet.
Steps: Cut agar blocks containing phenolphthalein into three cubes with side lengths of 3 cm, 2 cm, and 1 cm, place them in a beaker, add NaOH solution, after 10 minutes, take them out, dry with paper towels, and cut the agar blocks in half. Observe the cut surface and measure the depth of NaOH diffusion on each block.
Analysis: The ratio of surface area to volume of agar blocks decreases as the agar blocks increase in size, and the volume of NaOH diffusion relative to the total volume of the agar block also decreases as the agar blocks increase in size.
Conclusion: The larger the cell volume, the smaller its relative surface area, leading to lower efficiency in material transport. The surface area limits cell growth.
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