Examining The Rate Of Photosynthesis Using Leaf Discs Biology
The rate of photosynthesis can be measured by calculating the quantity of carbon dioxide consumed per unit time, or by calculating the quantity of oxygen consumed per unit time. The rate at which photosynthesis occurs is determined by rate-limiting step. The rate limiting step is the step that photosynthesis occurring the most slowly. The factors which affect the rate of photosynthesis include, light intensity, temperature and carbon dioxide concentration. Each factor affects a different rate-limiting step.
One of the factors is light intensity. As light intensity increases, the photosynthetic rate increases until a point is reached where the rate begins to level off. At low light intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions. As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate. At high light intensity, photosynthetic rate levels out, not due to light intensity but due to other limiting factors, including competition between oxygen and carbon dioxide for the active site on RUBP carboxylase.RESEARCH QUESTION
Does the different distance of leaf disc from the light source affect the rate of photosynthesis in leaf disc?HYPOTHESIS
As the distance of the leaf disc from the light source become closer, the rate of photosynthesis becomes faster. As the distance of the leaf disc from the light source become further, the rate of photosynthesis becomes slower.
This is because at the high light intensity, chloroplast absorb high amount of light and it will produce oxygen at higher rate thus the time taken for leaf disc to rise is shorter. At the low light intensity, chloroplast absorb low amount of light and it will produce oxygen at lower rate thus the time taken for leaf disc to rise is longer.VARIABLES UNITSRANGEINDEPENDENT VARIABLE
The distance between leaf disc and light source
Time taken for leaf disc to rise on the surface of sodium hydrogen carbonate
TABLE 1 : Independent and Dependent VariableCONTROLLEDVARIABLESUNITSWAYS TO CONTROL
Use the same temperature for each distance which is room temperature.
Place the entire beaker in the same place for every distance.
Volume of 3% of sodium hydrogen carbonate used
Used 20ml of sodium hydrogen carbonate for each distances.
Amount of leaf disc used in each distance-
Use only 5 leaf disc in each distances.
The size of each leaf disc
Use cork borer to get an approximately 8mm of leaf disc.
Type of leaf disc used-
Use the same type of leaf in every distance.
TABLE 2 : Controlled VariablesMATERIALS AND APPARATUSMaterialsNO.MATERIALSQUANTITYVOLUME / SIZE1.
Pineapple leaf discs
3% sodium hydrogen carbonate solution
1 bottle reagent-
TABLE 3 : MaterialsApparatusNO.APPARATUSQUANTITYVOLUME / SIZE
TABLE 4 : ApparatusMETHOD
Refer to the attachment.DATA COLLECTIONQUANTITATIVE DATADistance of light source from the leaf discs, cm, (±0.05cm)The time taken for leaf discs to rise on the surface of sodium hydrogen carbonate solution, minutes, min (± 0.5min)Leaf disc 1Leaf disc 2Leaf disc 3Leaf disc 4Leaf disc 5
TABLE 5 : Quantitative DataQUALITATIVE DATA
The pineapple leaf is green in colour and thick.
The 3% sodium hydrogen carbonate is colourless.
Bubbles are formed around the leaf discs when immersed in the sodium hydrogen carbonate.
The leaf discs sink at the bottom of the sodium hydrogen carbonate at first, and started to float to the surface of the indicator when the oxygen gas produced.DATA PROCESSINGAVERAGE TIME TAKEN FOR LEAF DISC TO RISE
The average time taken for leaf disc to rise is calculated by using this formula :
Time taken for each leaf disc to rise
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