Student Exploration: Photosynthesis Lab

Transcription

1 Name: Date: Student Explratin: Phtsynthesis Lab Vcabulary: carbn dixide, chlrphyll, glucse, limiting factr, nanmeter, phtsynthesis, wavelength Prir Knwledge Questins (D these BEFORE using the Gizm.) T survive, what gas d we need t breathe in? Where is this gas prduced? Gizm Warm-up During phtsynthesis, plants use the energy f light t prduce glucse (C 6H 12O 6) frm carbn dixide (CO 2), and water (H 2O). Glucse is a simple sugar that plants use fr energy and as a building blck fr larger mlecules. A by-prduct f phtsynthesis is xygen. Plants use sme f the xygen they prduce, but mst f it is released. In the Phtsynthesis Lab Gizm, yu can mnitr the rate f phtsynthesis by measuring xygen prductin. 1. Observe the left pane clsely. What d yu think the bubbles are? 2. Select the BAR CHART tab. On the graph, ntice the Oxygen prductin bar. Mve the Light intensity slider back and frth. Hw des light intensity affect xygen prductin? 3. Experiment with the vertical Temperature slider (upper left) and the CO 2 level slider. A. Hw des temperature affect xygen prductin? B. Hw des CO 2 level affect xygen prductin? C. Hw des xygen prductin relate t the rate f phtsynthesis?

2 Activity A: Ideal cnditins Get the Gizm ready: Be sure that the BAR CHART tab is selected. Turn n Shw numerical values. Questin: In the Gizm, what are the ideal cnditins fr phtsynthesis? 1. Frm hypthesis: During phtsynthesis, light energy is used t synthesize carbn dixide (CO 2) and water (H 2O) int glucse (C 6H 12O 6) and xygen (O 2). The cmplex series f chemical reactins is summarized by the fllwing frmula: 6CO 2 + 6H 2O + light energy C 6H 12O 6 + 6O 2 In the Gizm, what light intensity and CO 2 level d yu think will maximize the rate f phtsynthesis? 2. Experiment: Use the Gizm t find the ideal cnditins fr phtsynthesis. Use any methd yu like. When yu think yu have the answer, list the cnditins belw. Temperature Light intensity CO 2 level Oxygen prductin 3. Revise and repeat: One way t test if yu ve fund the ideal cnditins is t change each variable slightly frm the value that yu recrded abve. If the xygen prductin decreases with each change that yu make, it is likely yu have fund the ideal cnditins. If a small change causes xygen prductin t increase, cntinue t experiment. If necessary, revise yur numbers in the table abve. 4. Think and discuss: Think abut the prcess f finding the ideal cnditins. A. Why wuld it be hard t find the ideal light intensity if the temperature were very ht r cld? B. Why wuld it be hard t find the ideal CO 2 level if the light intensity were very lw?

3 Activity B: Clred light Get the Gizm ready: Select the COLOR tab and the BAR CHART tab. Set the Temperature t 24 C, the Light intensity t 90%, and the CO 2 level t 1,000 ppm. Intrductin: Plants use a green pigment called chlrphyll t absrb light and cnvert its energy int a frm that the plant can use. Chlrphyll gives plants their green clr. Questin: What clr f light is the best fr phtsynthesis? 1. Observe: The clr f a light wave is determined by its wavelength. On the COLOR tab, slwly drag the Light wavelength slider back and frth and bserve the effect n xygen prductin. Hw des the clr f light affect the rate f phtsynthesis? 2. Frm hypthesis: Which clr f light d yu think will maximize the rate f phtsynthesis? 3. Gather data: Set the Light wavelength t 400 nm. (The symbl nm stands fr nanmeters. A nanmeter is a billinth f a meter.) Visible light ranges frm 400 t 700 nm. On the TABLE tab, click Recrd data. Then set the Light wavelength t 420 nm, and repeat. Cntinue recrding data in the Gizm every 20 nm until the wavelength is 700 nm. 4. Make a graph: Select the GRAPH tab and select Wavelength. Sketch the graph in the space at right. A. Which clrs were absrbed best by the plant? B. Which clrs were absrbed wrst? 5. Think and discuss: When we lk at a leaf, we see the clrs f light that are reflected ff its surface. Hw des this explain the relatively lw flw f xygen in green light?

4 Extensin: Limiting factrs Get the Gizm ready: Select the WHITE tab and the BAR CHART tab. Turn n Shw numerical values. Intrductin: Phtsynthesis requires light, water, and CO 2 t wrk. When ne f these factrs is in shrt supply, it is called a limiting factr. Temperature can als be a limiting factr when it is t ht r t cld fr phtsynthesis t wrk well. Questin: What is the effect f limiting factrs n phtsynthesis? 1. Observe: Set Temperature t 24 C, Light intensity t 50%, and CO 2 level t 200 ppm. A. Mve the Temperature slider up and dwn. Were yu able t increase xygen prductin? (Return the slider t 24 C when finished.) B. Mve the Light intensity slider back and frth. Were yu able t increase xygen prductin? (Return the slider t 50% when finished.) C. Mve the CO 2 level slider back and frth. Were yu able t increase xygen prductin? (Return the slider t 200 ppm when finished.) 2. Analyze: In this situatin, what was the limiting factr? Hw d yu knw? 3. Challenge: In each f the situatins belw, use the Gizm t find the limiting factr. Temperature Light intensity CO 2 level Limiting factr 25 C 60% 700 ppm 15 C 20% 200 ppm 30 C 50% 400 ppm 4. Think and discuss: Suppse yu were a farmer trying t grw plants in a greenhuse. Why wuld it be imprtant t knw what the limiting factr is?

5 Vcabulary: Phtsynthesis Lab Vcabulary Carbn dixide a clrless, drless gas that is prduced during respiratin and cmbustin (burning). Carbn dixide is used by plants during phtsynthesis. The chemical frmula f carbn dixide is CO 2. Average CO 2 cncentratins in Earth s atmsphere are abut 390 ppm (parts per millin). Chlrphyll a green pigment in plants that absrbs light energy and cnverts it int a frm the plant can use fr phtsynthesis. Glucse a simple sugar that is a majr energy surce fr cells. Glucse is prduced in phtsynthesis. The chemical frmula f glucse is C 6H 12O 6. Limiting factr the required substance that is in shrtest supply and therefre limits grwth r ther life prcesses. In many ecsystems, fd is the limiting factr that keeps ppulatins in check. Fr plants, nutrients such as phsphrus and nitrgen are ften limiting factrs in the spring and summer. Cld temperatures limit grwth in the winter. Nanmeter a tiny unit f distance, equal t ne billinth f a meter. The symbl fr a nanmeter is nm. Phtsynthesis a prcess in which plants use energy frm light t prduce glucse and xygen frm carbn dixide and water. The chemical equatin fr phtsynthesis is: CO 2 + H 2O C 6H 12O 6 + O 2 This reads: Carbn dixide and water react t yield glucse and xygen. Glucse is used by the plant fr energy. It can als be used as a building blck fr cmplex sugars such as cellulse. Sme xygen is used by the plant, but mst is released. Wavelength the distance between tw cnsecutive crests f a wave. The wavelength f visible light ranges frm 400 nanmeters (vilet) t 700 nanmeters (red).