Examining The Rate Of Photosynthesis Using Leaf Discs Biology

Essay add: 19-06-2017, 20:52   /   Views: 10

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

cm

0-50

 DEPENDENT VARIABLE

Time taken for leaf disc to rise on the surface of sodium hydrogen carbonate 

s

-

TABLE 1 : Independent and Dependent Variable

CONTROLLEDVARIABLESUNITSWAYS TO CONTROL

The temperature

°C

Use the same temperature for each distance which is room temperature.

Humidity

-

Place the entire beaker in the same place for every distance.

Volume of 3% of sodium hydrogen carbonate used

cm³

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

Mm

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 Variables

MATERIALS AND APPARATUSMaterialsNO.MATERIALSQUANTITYVOLUME / SIZE1.

Pineapple leaf discs

90

-2.

3% sodium hydrogen carbonate solution

1 bottle reagent

-

TABLE 3 : Materials

ApparatusNO.APPARATUSQUANTITYVOLUME / SIZE

1.

Lamp

1

Standard size

2.

syringes

1

10ml

3.

Cork borer

1

8mm size

4.

beaker

6

100ml

5.

Forceps

1

Standard size

6.

Thermometer

1

Standard size

7.

Stopwatch

1

Standard size

8.

Long ruler

1

Standard size

TABLE 4 : Apparatus

METHOD

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

10.00

285

285

310

320

330

270

270

290

310

320

285

290

305

310

320

20.00

350

352

355

363

370

350

356

358

366

379

352

354

363

368

370

30.00

686

689

693

702

734

698

712

751

788

803

670

679

703

722

758

40.00

1304

1387

1395

1521

1632

1421

1456

1534

1567

1638

1380

1470

1499

1632

1721

50.00

3601

3621

3675

3777

3820

3256

3345

3457

3578

3699

3525

3612

3702

3756

3896

60.00

4603

4639

4689

4781

4902

4720

4790

4886

4904

5056

4589

4690

4844

4981

5021

TABLE 5 : Quantitative Data

QUALITATIVE 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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