CIE A2 Biology Notes Photosynthesis

1: Light Dependent Reaction

2

2: Light Independent Reaction Reaction (Calvin Cycle)

4

3: Chloroplast

9

4: Factors affecting Photosynthesis

10

5: C4 Plants

20

6: Absorption Spectrum and Action Spectrum

22

7: Differences between Cyclic and Non-cyclic Non -cyclic Photophosphorylation

25

8: Essays

26

8.1: Essays- Chloroplast

26

8.2: Essays- Light Dependent

27

8.3: Essays- Calvin Cycle

29

8.4 Essays- C4 Plants

30

8.5: Essays- NADP

30

Colour Coding: Key Words Important Key Words Key words in the Question Additional Comments Predicted Questions in Purple

Photosynthesis Chapter 13 CIE Notes for Biology A2

Prepared and compiled by Michael Fork Please visit www.ciebiologynotesfora2.blogspot.com if you did not purchase this copy of notes. This is a confidential and copyright document which is restricted for the own use of the original purchaser only. We thank you for taking our rights seriously. s eriously. Disclaimer: In the notes, we do not owe the questions. The questions are the copyright of CIE. We obtain these questions from a website which is publicly available to all. We charge our work base on our organisation of the notes and our suggested answers only.

1: Light Dependent Reaction (O/N 04) Describe the photoactivation of chlorophyll. 3m 1. Chlorophyll absorbs mainly red and blue light 2. Light is absorbed by attenna complex and energy is transferred to reaction centres/ P700/ P680 3. Light energy excites electrons in reaction centre 4. Electrons are emitted from chlorophyll (O/N 04) Explain how the photolysis of water occurs. 3m 1. Water is split into H + and OH2. Electron removed from OH- to replace electron lost from chlorophyll 3. OH breaks down into O 2 and water 4. H+ used to form reduced NADP 5. H20 -> 2H+ + 2e- + 1/2 O 2 (O/N 13 41) Write a balanced equation that summarises photolysis.

(O/N 04) Outline how ATP is formed f ormed in the chloroplast. 3m 1. Electrons flow down the ETC 2. Energy released is used to pump H+ from the stroma into the thylakoid space 3. H+ gradient across the thylakoid membrane is created 4. H+ diffuses down the concentration gradient through stalk particle, synthesising ATP from ADP and P i 5. In cyclic photophosphorylation, electron returns to the original photosystem 6. In non-cyclic photophosphorylation, electrons from PII are passed to PI to replace those lost in PI (O/N 04) Suggest an advantage of having photosystems, the electron transport chain and ATP synthase as part of the thylakoid membrane. 1m 1. Ref increased efficiency/ short diffusion distance/ close together

(M/J 09) Describe what happens to water at R. [1] 1. Photolysis 2. Water splits into 2e - , 2H+, and (1/2 O2) 3. Enzyme is involved State the product formed as electrons flow along S. [1] ATP Name the process shown by the dotted arrows (---- -----) [1] Cyclic photophosphorylation

This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

2

(O/N 10 43) Describe how the 2 products of light dependent stage are used in light independent stage of photosynthesis. 3m 1. ATP provides energy 2. reduced NADP is reducing agent/ provides hydrogen for converting GP to TP 3. ATP is also used to regenerate RuBP (M/J 13 42) Name the process in the light-dependent l ight-dependent stage of photosynthesis that produces oxygen. [1] 1. photolysis Name the photosystem involved in the production of oxygen in the light-dependent stage. [1] 1. P680 / Photosystem II (O/N 13 43) Fig. 7.1 shows some of the components involved in the light-dependent stage.

Identify structures A and B. A photosystem II / P680 / PS II ; B photosystem I / P700 / PS I ;

(New syllabus) The Hill Reaction To determine the effect of light intensity or light wavelength on the rate of photosynthesis using a redox indicator (eg. DCPIP) and a suspension of chloroplast. 1. Liquidise the leaves in ice-cold water and filter the r esulting suspension to remove unwanted debris (isolation of chloroplast). 2. Chill small tubes of buffered chloroplast suspension. 3. Add DCPIP solution into the tubes. 4. Place the tubes in different light intensities/wavelengths of light. 5. Assess the blue colour at 1-minute interval. 6. Record the rate of loss of blue colour ( as measured in a colorimeter/by matching against known concentrations of DCPIP solution). Photosynthesis involves the acceptance of hydrogen by a coenzyme. This occurs during the light-dependent stage, when hydrogen is accepted by NADP. Indicator such as DCPIP takes up hydrogen ions that are produced as the lightdependent stage occurs and loses its colour.


3

2: Light Independent Reaction (Calvin Cycle) (M/J 13 41) Name the compound that combines with carbon dioxide in the lig ht-independent stage in a C3 plant. [1] Ribulose bisphosphate Ignore RuBP (RuBP gains no marks. Recently CIE has been stricter with names. For this particular question, CIE commented that RuBP alone did not qualify as this is not the actual name.)

(O/N 08) The name of the five carbon sugar in the cycle [1] Ribulose bisphosphate (O/N 08) The name of the enzyme that fixes carbon dioxide [1] Ribulose bisphosphate carboxylase/ rubisco (O/N 08) State where in the chloroplast the Calvin cycle occurs [1] Stroma (M/J 14 41) State precisely where in the chloroplast RuBP a nd GP are located. [1] Stroma (O/N 14 41) Name precisely the process that produces reduced NADP. [1] non-cyclic photophosphorylation


4

(O/N 02) Explai n the reasons why when the light intensity suddenly decreases a. Concentration of GP increases and then decreases 2m 1. GP continues to be formed from RuBP 2. Until all RuBP used up 3. The GP falls as converted to hexose/ glucoce/ TP b.RuBP decreases 1m 1. In dark RuBP not regenerated/ converted to GP 2. Requires the products/ ATP/ reduced NADP from the light-dependent reaction/ photophosphorylation (M/J 05) Explain what initially happens to the concentration of RuBP and GP if the supply of carbon dioxide is reduced. 3m 1. RuBP accumulates 2. Due to reduced combination with CO2 3. GP goes down/ not as much being formed 4. Due to conversion to TP (M/J 03) Explain how carbon dioxide is fixed in the stroma. 2m 1. Carbon dioxide is fixed by reacting with RuBP to form GP (glycerate3-phosphate) using Rubisco 2. Driven by ATP, GP is reduced to triose phosphate by reduced NADP . 3. Some of the triose phosphates condense to form hexose phosphates, sucrose, starch and cellulose. (M/J 05) Describe how carbon dioxide is fixed in the Calvin cycle. 2m 1. Carbon dioxide combines with (5C compound) RuBP 2. to form unstable 6C compound/ forms 2 molecules of 3C GP 3. Using rubisco


5

(O/N 08) State the name of another compound that is produced in the light-dependent stage of photosynthesis that is used in the Calvin cycle [1] 1. ATP 2. reduced NADP (O/N 02) State 2 products of photophosphorylation that drive the Calvin cycle. [2] 1. ATP 2. Reduced NADP (M/J 05) Explain how the products of photophosphorylation are used in the Calvin cycle. [3] 1. Products: Reduced NADP and ATP 2. Reduced NADP is reducing agent/ provides hydrogen for converting GP to TP 3. ATP is source of energy 4. ATP (as a source of phosphate) is also used to regenerate RuBP (M/J 09) (M/J 13 41) Explain Expl ain briefly the role of reduced NADP in the light-independent stage. [2] Acts as a hydrogen carrier (The exact term hydrogen has to be used. It is not H + or H2. We are referring to hydrogen atoms here.) To reduce GP into TP This process uses ATP (O/N 13 43) Describe the roles of the following substances in the light-independent stage of photosynthesis [6] RuBP 1. Carbon dioxide reacts with RuBP (carbon dioxide fixation) 2. to form GP 3. using rubisco

reduced NADP 1. acts as a reducing agent / provides hydrogen 2. for converting GP to TP ATP 1. acts as a source of energy to convert GP to TP 2. acts as a source of phosphate to regenerate RuBP (M/J 11 41) Explain what specificity of enzyme. 2m 1. Enzyme acts on only one o ne substrate 2. Shape of active site is complementary to substrate 3. Substrate is held by temporary bonds in the enzyme-substrate complex (O/N 08) Explain the changes in the relative concentrations of RuBP and GP after the light source is switched off. 4m 1. In light independent reaction/ Calvin cycle 2. RuBP is still being converted to GP 3. Until the available RuBP is being used up 4. Light dependent reaction stops as light source is switched off 5. No ATP/ reduced NADP produced 6. RuBP not regenerated 7. GP converted to TP/ used to make hexose Note: The light independent reaction co ntinues until the products of the light dependent reaction are used up when reactions ceased. This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

6

(M/J 03) Describe the role of the thylakoid membrane membrane in photosynthesis. 4m 1. Contains photosystems I and II 2. Large surface area of the thylakoid membrane holds the pigments, enzymes and electron carriers in position for light dependent reaction 3. Site of photophosphorylation 4. Site of ETC 5. Produce ATP 6. Produce reduced NADP

(M/J 14 41) The unicellular green alga, Chlorella, a photosynthetic protoctist, was originally studied for its potential as a food source. Although large-scale production proved to be uneconomic, the many health benefits provided by Chlorella mean that it is now mass produced and harvested for use as a health food supplement. Fig. 1.1 shows cells of Chlorella.

In one study into the productivity of Chlorella, carbon dioxide concentration was altered to investigate its effects on the light-independent stage of photosynthesis. • A cell suspension of Chlorella was illuminated using a bench lamp. • The suspension was supplied with carbon dioxide at a concentration of 1% for 2 00 seconds. • The concentration of carbon dioxide was then reduced to 0.03% for a further 200 seconds. • The concentrations of RuBP and GP (PGA) were measured at regular intervals. • Throughout the investigation the temperature of the suspension w as maintained at 25 °C. The results are shown in Fig. 1.2.

Explain why the concentration of RuBP changed between 200 and 275 seconds. [2] 1. The concentration of carbon dioxide is lower 2. Less carbon dioxide combines with RuBP / less carbon fixation / less RuBP converted to GP 3. RuBP reformed from TP


7

Calculate the rate of decrease per second in the concentration of GP between 200 and 350 seconds. (Show your working and give your answer to two decimal places).

0.01 arbitrary units per second Explain how the decrease in the concentration of GP leads to a decreased harvest for commercial suppliers of Chlorella. [2] 1. less TP 2. so less conversion to other carbohydrates/lipids/amino c arbohydrates/lipids/amino acids/protein 3. such as glucose/hexose/cellulose/starch 4. Amino acids are used to make proteins for growth/cell division 5. Carbohydrate/lipid are used for repiration for growth/cell division

(O/N 14 41) Fig. 8.1 shows some of the reactions that take place inside a palisade mesophyll cell. Identify substances A, B and C. [3] A - RuBP/ ribulose bisphosphate B - fatty acid C – nitrates/ammonium ions I nitrogen/ ammonia Name the type of reaction that takes place to produce starch from hexose sugars and name the type of bonds formed. [2] 1. Reaction: condensation/ polymerisation / anabolic 2. Bond: glycosidic bond

(O/N 15 42) Complete the following paragraph. [4] Rubisco is involved in the fixation of carbon dioxide by RuBP (ribulose bisphosphate) in the Calvin cycle. The resulting six carbon compound immediately splits to give two molecules of glycerate-3-phosphate (GP). GP is converted to triose phosphate (TP) using ATP and reduced NADP produced in the light-dependent stage. Some of the TP produced is used to regenerate ribulose bisphosphate so that the Calvin c ycle can continue. The remaining TP may be used to synthesise other compounds i ncluding acetyl CoA which can directly enter the Krebs cycle.


8

3: Chloroplast (O/N 13 41) Describe the role of accessory pigments in photophosphorylation. [2] 1. absorb light energy 2. to pass light energy onto primary pigment / chlorophyll a / reaction centre (O/N 13 41) State precisely the location of photosynthetic pigments within a chloroplast. 1. Grana / thylakoid membrane

(O/N 15 42) Use label lines and letters to label one place where

L – the light-dependent stage takes place [1] (any thylakoid membrane)

R – the enzyme rubisco is found [1] stroma

(O/N 15 42) Chloroplasts can move within palisade cells. Suggest two advantages of chloroplast movement within palisade cells. [2] 1. To absorb maximum light 2. To avoid damage by high light intensities

(M/ J 14 42) Indicate below which of X, Y or Z contains [2] 1. transport proteins- Y 2. pigments- X Suggest the functions of DNA in chloroplast. [2] 1. codes for proteins/polypeptides/enzyme pr oteins/polypeptides/enzymess 2. such as rubisco/ electron acceptor/ ATP synthase/transport protein 3. produced through transcription of mRNA


9

4: Factors Affecting Photosynthesis

(O/N 03) With reference to figure, describe 3 ways in which the sun and shade leaf differ in their response to increasing light intensity . 3m 1. More respiration in sun leaves at zero or low light intensity 2. CO2 uptake is greater in shade leaves at low intensity 3. Sun leaves reach compensation point/ zero gas exchange at higher light intensity 4. Rate of photosynthesis increases more rapidly in sun leaves 5. High rate of photosynthesis/ CO2 uptake in sun leaves at higher light intensity 6. CO2 uptake levels off in shade leaves Explain why the carbon dioxide uptake levels off in the shade leaf as light intensity increases. 3m 1. Light is no longer a limiting factor 2. Some other factor becomes limiting 3. ie carbon dioxide concentration/ temperature/ ref chlorophyll

The results shown were taken at a temperature of 20 °C. Describe briefly how increasing the temperature to 25 °C would affect the results in the sun leaf. 3m 1. At low light intensity little or no effect/ light (dependent reaction) is limiting rate 2. At high light intensity increasing temperature will increase the rate of photosynthesis 3. (Ref Effect of temperature on the rate of) enzyme controlled reactions/ light independent stage 4. Detail example/ named enzyme (Rubisco)/ Calvin cycle


10

(O/N 06) Under conditions of low wind speed, the rate of transpiration decreases, even though the stomata of the leaves are open. Explain. 2m 1. Rate of transpiration is due to difference in relative humidity inside and outside stomata 2. In still air/ low wind speed, external water vapour remains remains close to stomata 3. Hence, reduced, concentration gradient/ water potential gradient

(O/N 07) With reference to Fig, describe the effect of temperature on the rate of photosynthesis of wheat plants. 2m 1. As temperature increases, rate of CO 2 used increases then decreases 2. 2 paired figures/ peak at 18 C (O/N 07) Suggest why temperature affects the rate of photosynthesis in the way you have described. 2m In terms of Enzymes of Enzymes 1. Rate of photosynthesis rises due to increased kinetic energy of molecules 2. Increased number of collisions/ increase i n enzyme activity 3. Enzymes become partly denatured above, 18 °C/ optimum 4. and affects the rate of light independent reaction/ Calvin cycle/ dark stage

5. 6. 7. 8. 9.

In terms of Gaseous Exchange More carbon dioxide is available a vailable as temperature increases due to faster diffusion rate Stoma close as temperature rises above 18 C because of increased transpiration rate which decreases carbon dioxide availability


11

(M/J 08) Explain why increasing the concentration of carbon dioxide may increase the rate of production of carbohydrates at high light intensities. 5m 1. Light not limiting at high light intensities 2. Much ATP/ reduced NADP available available 3. CO2 is the limiting factor 4. Because low concentration CO2 (in atmosphere) 5. More CO2 combines with RuBP 6. using Rubisco 7. at Calvin cycle/ independent stage 8. More GP is converted to TP 9. More hexose is produced 10. Ref Fate of hexose (converted to sucrose/cellulose)

(O/N 09 41) Describe and explain the r esults shown in Fig 8.1 for experiment 1. 3m At low light intensity 1. Rate of photosynthesis increases as light intensity increase 2. Light intensity is limiting factor At higher light intensity 3. Graph levels off / forms a plateau/ rate becomes constant 4. CO2/ some other factor becomes limiting Describe and explain the difference between the results for experiment 1 and experiment 2 . 3m 1. Above light intensity of 1 rate is always higher for experiment 2 2. Plateau reached at lower light intensity for experiment 1 3. Maximum/ plateau, rate is double for experiment 2 4. Experiment 2 has much more CO 2 (concentration) (compared to experiment 1) 5. CO2 is limiting in experiment 1 up to 2.8 The optimum temperature for many plants living in temperate regions is approximately 25 °C. 5m Explain why the rate of photosynthesis in these plants decreases at temperatures above 25 °C. 1. Enzymes denatured/ active site changes shape 2. Enzyme in cyclic phosphorylation (rubisco) is affected, less photolysis, less ATP produced 4. Increased rate of respiration above 25 °C 5. When the respiration rate is faster than the photosynthesis rate, the carbon dioxide level in the leaf is low 6. With the closing of stomata due to increased transpiration, uptake of carbon dioxide for light independent stage is reduced This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

12

(O/N 09 42) Calculate the value of light intensity when the distance between the beaker and lamp was 20 cm. 1m 0.0025/ 2.5 x 10-3 Explain why the discs rise to the surface after being illuminated for a length of time. 3m 1. Photosynthesis takes place 2. Oxygen is produced 3. Oxygen collects inside disc/ on surface of disc 4. Disc less dense/ more buoyant Using the data in Table 8.1, describe the relationship between light intensity and the rate of photosynthesis. 2m 1. Rate of photosynthesis increases as light intensity increases 2. Paired data quotes from columns 2 and 4 The student found that there was no increase in the rate of photosynthesis when 2 lamps where placed 5cm from the beaker. Suggest why there was no increase in the rate of photosynthesis. 2m 1. Light intensity no longer limiting 2. Carbon dioxide concentration/ rate of diffusion now limiting 3. Temperature too high/ Denatures enzymes


13

(M/J 10 41) Compare the change in carbon dioxide uptake in sorghum and soybean during the 3 days at 10 C. 2m 1. Greater reduction in sorghum than in soybean 2. Use of comparative figures

Explain how these changes could be responsible for the low rate of carbon dioxide uptake by sorghum even when returned to a temperature of 25 °C. 4m 1. Less surface area 2. Less absorption of light 3. Less photophosphorylation/ light dependent reaction 4. 5. 6. 7. 8. 9.

Less chemiosmosis Due to smaller thylakoid space or reduced proton gradient Less ATP produced Less reduced NADP produced Light-independent reaction/ Calvin cycle slows down Less carbon dioxide fixed/ combined with PEP


14

(M/J 10 43) Describe and explain the effect of light intensity on the rate of carbon dioxide uptake before cooling. 3m 1. Light intensity is limiting factor in this case 2. Higher CO2 uptake at higher light intensity 3. Comparative figures using column 1 and 2 4. CO2 used in Calvin cycle/ light independent reaction 5. Photophosphorylation/ light dependent stage provides ATP/ reduced NADP 6. for use in Calvin cycle Describe the effect of light intensity on the ability of sorghum plants to survive cooling. 2 m (Look at the data in the final column of the table which referred to carbon dioxide uptake after cooling) 1. Survive better at low light intensities 2. Comparative figures

(O/N 10 43) The rate of photosynthesis is affected by factors other than the wavelength of light. These factors may act as limiting factors. Explain what is meant by the term limiting factor. 2m 1. Process/ photosynthesis affected by more than 1 factor 2. Rate is limited by the factor nearest its minimum value (O/N 10 43) Carbon dioxide concentration in the atmosphere may be a limiting factor in photosynthesis. Describe how carbon dioxide reaches the photosynthetic cells in a leaf. 4m 1. Carbon dioxide enters leaf by diffusing through open stoma into the sub stomatal space and into the many air spaces in spongy mesophyll and air spaces between palisade cells. 2. It dissolves in the moisture on the cell walls of the cells and enters through cell walls.


15

(M/J 12 41) Suggest and explain why the rate of photosynthesis of the plant decreases to zero just above 40 C. 5m 1. 26 °C optimum temperature for rubisco/ enzyme for Calvin cycle 2. At just over 40 °C enzymes/ rubisco denatured 3. So less carbon dioxide fixed and Calvin cycle slows down 4. Increased rate of transpiration 5. So stomata close 6. Less carbon dioxide uptake 7. Oxygen more likely to combine with rubisco 8. So increased photorespiration Draw, on Fig, the likely curve if the same experiment were carried out on a C4 plant, such as sorghum. Give reasons to explain your curve. 3m Curve drawn with optimum to the right of existing curve 1. C4/ sorghum enzymes have higher optimum temperature than C3 2. Has leaf structural features to avoid photorespiration 3. Adapted to hot climate What is limiting factor? 2m 1. When a process is affected by more than one factor, the rate of photosynthesis is restricted by the factor that is nearest to its lowest value.


16

(M/J 12 42) State why sodium hydrogencarbonate solution was used. 1m Provides carbon dioxide Explain the results for tube C. 2m 1. No photosynthesis/ light dependent reaction 2. Oxygen used up in respiration Suggest what factor, which may have an effect on the rate of photosynthesis, that was not taken into account in this experiment. 1m 1. Temperature


17

(M/J 13 42) A student investigated the effects of temperature and light intensity on the rate of photosynthesis of an aquatic plant.

Describe the results of the investigation in [3] High light intensity 1. As temperature increased from 0 to 30 oC, the volume of oxygen released / rate of photosynthesis increased from 1 to 4 mm3/h. 2. As temperature increased from 30 oC to 50oC, the volume of oxygen released / rate of photosynthesis fell from 4 to 0.4 mm 3/h. Low light intensity 3. As temperature increased from 0 to 30 oC, the volume of oxygen released / rate of photosynthesis remained constant at 0.4 mm 3/h. 4. As temperature increased from 30 oC to 50oC, the volume of oxygen released / rate of photosynthesis fell from 0.4 to 0.2 mm3/h. Suggest explanations for the results for high light intensity above 30 °C. [2] 1. Light is no longer the limiting factor/ temperature is now the limiting factor 2. Enzymes are denatured 3. Fewer enzyme-substrate complexes formed 4. Less photolysis (leads to less oxygen produced) Explain why the volume of oxygen released from the plant does not give a true rate of photosynthesis. [1] 1. respiration uses oxygen (M/ J 14 42) Tick (✓) if the factor directly affects the stage or a cross ( ✗) if it does not affect the stage.


18

(O/N 14 43) An A n experiment was carried out to investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant using the apparatus shown in Fig. 8.2.

As photosynthesis took place, the oxygen produced formed a bubble of gas which moved along the scale in the capillary tube. The distance moved by the bubble in a fixed period of time was used to calculate the rate of photosynthesis. The light intensity was varied by altering the distance, d, between the lamp and the photosynthesising plant. The results are shown in Table 8.1.

Using the data in Table 8.1, draw a graph to show the relationship between light intensity and the rate of photosynthesis. [3] 1. y-axis: rate of photosynthesis x-axis: light intensity 2. All points plotted correctly 3. Line of best fit Explain the shape of the graph you have drawn, with reference to limiting factors. [3] 1. at low light intensity light is the limiting factor 2. at high light intensity other factors become limiting 3. such as temperature/ carbon dioxide concentration dioxide concentration


19

5: C4 Plants (M/J 10 41)

Outline how this leaf anatomy adapts the plant plant for high rates of carbon fixation at high temperatures. temperatures. [4] 1. Light independent stage occurs in bundle sheath cells. RuBP is present in bundle sheath cells. 2. Bundle sheath cells are kept away from air spaces by tightly packed mesophyll cells, so RuBP is not exposed to oxygen. 3. CO2 / malate is delivered to bundle sheath cells from mesophyll cells so CO 2 concentration in bundle sheath cells is always high. 4. Photorespiration is avoided. / prevents competition btw CO 2 and O 2 for RuBP / rubisco 5. PEP carboxylase has high optimum temperature of about approximately 45°C/ it has a higher affinity for CO2 than Rubisco and is not competitively inhibited by O 2 . 6. Therefore (PEP carboxylase) is not denatured (O/N 09 42) Sorghum is able to carry out photosynthesis at high temperatures by preventing photorespiration. Explain how sorghum is able to prevent photorespiration. 1. Light independent stage occurs in bundle sheath cells. RuBP is present in bundle sheath cells. 2. Bundle sheath cells are kept away from air spaces by tightly packed mesophyll cells, so RuBP is not exposed to oxygen. 3. CO2 / malate is delivered to bundle sheath cells from mesophyll cells so CO 2 concentration in bundle sheath cells is always high. 4. Photorespiration is avoided. / prevents competition between CO 2 and O 2 for RuBP / rubisco 5. Enzymes / PEP carboxylase have high optimum temp of about approximately 45°C. 6. Therefore they are not denatured.


20

(O/N 07) Maize is a C4 plant. Explain how the structure of structure of the leaves of maize plants enables them to photosynthesise more effectively at high temps than wheat wheat plants. [3] 1. Bundle sheath cells surrounds vascular bundle of the leaf 2. Light independent stage occurs in bundle sheath cells. RuBP is present in bundle sheath cells. 3. Bundle sheath cells are kept away from air spaces by tightly packed mesophyll cells, so RuBP is not exposed to oxygen. CO 2 / malate is delivered to bundle sheath cells from mesophyll cells so CO 2 concentration in bundle sheath cells always high 4. Photorespiration avoided/ prevents competition btw CO2 and O2 for RuBP / rubisco The bundle sheath cells are being kept away from air to prevent oxygen competing successfully in photorespiration The anatomy allows carbon dioxide to accumulate Bundle sheath cells and mesophyll cells prevent oxygen from reaching RuBP (O/N 10 43) Maize, Zea Maize, Zea mays, is a cereal crop that is adapted for growth at high temperatures. However, it does not cope with drought as well as some other crops, such as sorghum. An investigation was carried out into the effect of low water availability on the activity of mitochondria taken from maize seedlings. Young seedlings were uprooted and left in dry air for varying periods of time to reduce the water potential of their tissues. Explain why this treatment reduced the water potential of the maize seedling tissues. ti ssues. [2] 1. water lost by, evaporation / transpiration 2. no water uptake (by roots) (M/J 11 42) Explain how the leaf anatomy of a maize plant reduces photorespiration, even in hot dry conditions. [4] 1. Light independent stage occurs in bundle sheath cells. RuBP is present in bundle sheath cells. 2. Bundle sheath cells are kept away from air spaces by tightly packed mesophyll cells, so RuBP is not exposed to oxygen. 3. CO2 / malate is delivered to bundle sheath cells from mesophyll cells so CO 2 concentration in bundle sheath cells is always high 4. Photorespiration is avoided/ prevents competition between CO 2 and O2 for RuBP / rubisco Carbon dioxide is fixed in the cytoplasm of the mesophyll cells as shown below: PEP + CO2 -> Oxaloacetate with PEP carboxylase

If it's not a C4 plant? At high temperature, photorespiration occurs. O2 combines with RuBP, so less RuBP available for carbon fixation. Take Note! Oxaloacetate formed through the combination of CO 2 with PEP is converted to malate, which travels to bundle sheath cells, where CO 2 is removed from the malate to combine with RuBP.


21

6: Absorption Spectrum/ Action Spectrum

(M/J 08) Compare the absorption spectra of chlorophyll a and chlorophyll b. 3m Ref wavelength 1. Chlorophyll a peaks at 430nm and chlorophyll chlorophyll b peaks at 450nm 2. Chlorophyll a peaks at 660nm and chlorophyll chlorophyll b peaks at 635-640nm 3. Ref linking 400-500nm with blue light/ ref Linking 600-670nm with red light 4. Both have little absorption, between 500-600nm/ in green light A little absorption, chlorophyll a 450-600nm and chlorophyll b 500-600nm Ref light absorption 5. Both peaks in blue light are higher than peaks in red light 6. Percentage light absorption of chlorophyll b is higher than chlorophyll a in the blue end/ percentage light absorption of chlorophyll a is higher than chlorophyll b in the red end 7. Comparative figures for light absorption to illustrate points 5-6 Explain the shape of the action spectrum spectrum. 3m 1. Absorbed light is used for photosynthesis in light dependent stage Therefore there is a higher rate of o f photosynthesis in the red and blue blue light region 2. Action peaks/ high rate of photosynthesis correspond to absorption peaks 

3. Blue/ shorter wavelength light has more energy 4. Not an exact match between absorption and action spectra in middle region Due to absorption of light by the carotenoids/ accessory pigments in middle region 

Explain why plants appear green. 2m 1. They contain chlorophyll 2. Green/ blue green/ yellow green light is reflected This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

22

(O/N 10 43) Describe and explain the effects o f different wavelengths of light on the rate of photosynthesis. 4m 1. Absorbed light is used for photosynthesis in light dependent stage 2. High rate of photosynthesis at 430-435nm, and 655nm wavelengths 3. Idea of high absorption of light at these wavelengths 4. Highest rate at 430- 435nm 5. Shorter wavelengths have more energy 6. Lower rate in middle range/ 500-600 of wavelengths 7. Low light absorption here (O/N 13 41) An experiment was carried out into the effect of lig ht of different colours on photosynthesis. • 15 leaf discs from the same plant were obtained. • Five sealed test-tubes were set up, each containing three leaf discs in hydrogencarbonate indicator solution. • Hydrogencarbonate indicator solution changes colour at different pH values. • At the start of the experiment the indicator solution in all five test-tubes was orange- red. • Four of the test -tubes were illuminated by light of a specific colour. • The test -tubes were illuminated for the same l ength of time. • The fifth test -tube was covered in black paper and was a control. The results are recorded in Table 7.1.


23

When the pH increases, the indicator becomes purple and when the pH decreases, the indicator turns yellow. Explain the results for the leaf discs illuminated by blue light. [2] 1. Blue light is absorbed and used for photosynthesis 2. CO2 is used, so concentration decreased 3. Leads to rise in pH / decrease in acidity Explain why the indicator in the control went yellow. [2] 1. Only respiration is carried out. No photosynthesis. 2. CO2 is produced / released 3. Leads to decrease in pH / increase in acidity (O/N 14 43) Fig. 8.3 shows the absorption spectra of the photosynthetic pigments of a flowering plant.

Name the accessory pigment(s) shown in Fig. 8.3. [1] 1. chlorophyll b 2. carotenoids Outline the role of the accessory pigments in photosynthesis. [3] 1. absorb light energy 2. at wavelengths that are not readily absorbed by chlorophyll a/ primary pigment 3. And pass energy to chlorophyll a/ primary pigment 4. in reaction centre Very little light of wavelength 550 nm is absorbed by the photosynthetic pigments. State what happens to most of this light. [1] 1. reflected A graph can also be drawn to show the relationship between the wavelength of light and the rate of photosynthesis. State the name of this type of graph. [1] 1. action spectrum (O/N 14 41) The optimum pH for the activity of rubisco is pH8. Explain why the illumination of chloroplasts leads to optimum pH conditions for rubisco. 1. excited electrons leave chlorophyll a/ photosystem 2. and pass along ETC 3. protons present from photolysis 4. are pumped into intermembrane space 5. rubisco is in stroma 6. Protons leaving stroma causes raise in pH This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

24

Outline the separation of chlorophyll pigments by chromatography. 1. Dissolve a mixture of chlorophyll pigments in a solvent. 2. Cut paper chromatography into narrow strips to fit them into the test tubes. 3. Do not put your fingers on the paper. 4. Place a small spot of chlorophyll mixture onto the chromatography paper with a pin head. 5. Let the spot dry before adding more to concentrate the spot. 6. Draw a start line with pencil. 7. Put the paper chromatography into a test tube. 8. Add running solvent to the depth of the mark and seal the tube. 9. The solvent rises up the paper carrying carr ying each pigment at a different speed. This separates the pigments, as they move different distances. 10. Remove paper chromatography after about 5 minutes. 11. Mark the centres of the pigment spots with pencil. 12. Measure the distance from the start line to the solvent front. 13. Measure the distance of each pigment spot from the start line. 14. Calculate Rf value for each pigment using this equation: Rf = distance travelled by pigment spot Distance travelled by solvent

7: Differences between Cyclic and Non-cyclic Photophosphorylation (O/N 10 41) Outline the differences between cyclic and non-cyclic photophosphorylation. 4m Cyclic phosphorylation 1. Electron emitted returns to PS 1/ 1 / same photosystem or same chlorophyll molecule

1. 2. 3. 4. 5.

Non-cyclic phosphorylation Electron emitted from PS II absorbed by PS I Reduced NADP produced Photolysis occurs Photolysis only involves PS II Oxygen produced

Non-cyclic photophosphorylation

Cyclic Photophosphorylation

Involves both PSI and PS II

Involves only PS I

Electrons used to reduce chlorophyll derived from oxidation of water

Electrons used to reduce chlorophyll derived from, and returned back to P700

Photolysis of water involved

Photolysis of water not involved

Electrons from photosystems photosystems used used to reduce reduce NADP Electrons returned back to P700, so no NADP NADP reduced ATP, NADPH and oxygen formed

Only ATP formed


25

8: Essays (O/N 05) Discuss the effects that variations in carbon dioxi de concentration and light intensity have on the rate of photosynthesis. 7m 1. Concentration of carbon dioxide in atmosphere is 0.04% 2. During the day when there is light and it is warm, carbon dioxide is most likely the limiting factor in photosynthesis because of the low carbon dioxide concentration in atmosphere. 3. Increase in carbon dioxide concentration will increase in rate of photosynthesis during day when there is light and warmth. 4. Ref. to variations in concentration within canopy ie leaves outside the canopy have higher concentration of carbon dioxide and leaves inside the canopy have lower concentration of carbon dioxide

5. 6. 7. 10. 11. 12.

Light Intensity PS I absorbs energy most efficiently at 700nm and PS II at 680nm. Increase in light intensity will cause a proportional increase in the rate of photosynthesis until the point of light saturation is reached under full sun Then other factors become limiting Light intensities vary according to day length and season High light intensity can bleach chlorophyll and photosynthetic pigments Light excites electrons in chlorophyll

(O/N 11 41) Process of separating chloroplast pigments using chromatography 6m 1. Grind leaf with solvent such as propanone 2. Leaf extract contains a mixture of pigments 3. Ref could be made to concentrate extract (You could ignore this point) 4. The extract is then "spotted" onto the origin line of a piece of chromatography paper 5. Paper is placed vertically in jar of different solvent 6. Solvent rises up paper 7. Each pigment travels at different dif ferent speed 8. Pigments separated as they ascend 9. Distance moved by each pigment is unique 10. Rf value is value is calculated: Distance travelled by pigment/ distance travelled by solvent front 11. Two dimensional chromatography is used for a better separation of pigments

8.1: Essays- Chloroplast (M/J 07) (M/J 2013 42) Describe the structure of a chloroplast. 9m 1. Chloroplast is shaped like a biconcave disc and is 3-10 um in diameter . 2. It is surrounded by an envelope of two phospholipid membranes/ a double membrane. 3. A system of membranes runs through the ground substance, or stroma. 4. The membrane system consists of a series of flattened fluid-filled sacs, or thylakoids , which in places form stacks, called grana that are joined to one another by membranes. 5. The granal membranes provide a large surface area for the attachment of the photosynthetic pigments (chlorophyll and carotenoids), electron carriers and enzymes that carry out light dependent reaction- ATP synthase. 7. The stroma contains starch grains, lipid droplets, enzymes for Calvin cycle, 70S ribosomes and circular DNA. 8. There is a variation i n shape between species


26

(O/N 11 41) The structure of chloroplast in relation to the adaptation to its function 9m 1. Stroma for light independent stage/ Calvin cycle 2. Contains enzymes/ rubisco 3. Sugars/ lipids/ starch/ ribosomes/ DNA 4. Internal membrane system 5. For light dependent stage 6. It consists of thylakoids which form stacks called grana at intervals with intergranal lamellae between the grana. 7. Membrane of grana have large surface area for maximum light absorption 8. It also holds ATP synthase and electron carriers for chemiosmosis. 9. Membrane of grana holds photosynthetic pigments. 10. Pigments are arranged in light harvesting clusters/ photosystems 11. Primary pigment/ reaction centre/ chlorophyll a, surrounded by accessory pigments 12. Accessory pigments pass energy to primary pigment/ reaction centre/ chlorophyll a 13. Different photosystems absorb light at diff erent wavelengths

8.2: Essays- Light Dependent (O/N 07) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation. 9m 1. Photosynthetic pigments are arranged in light harvesting clusters called photosystems, where chlorophyll a is primary pigment. 2. P700 , the primary pigment at reaction centre of PI absorbs wavelengths of light at 700nm. 3. P680 , the primary pigment at reaction centre of PII absorbs wavelengths of light at 680nm. 4. Accessory pigments such as chlorophyll b and carotenoids which surround the primary pigment absorb light other than wavelengths 680nm and 700nm and pass the energy to the primary pigment. 5. P700/ PI is involved in cyclic photophosphorylation The light energy absorbed excites electrons in P700 and the excited electrons are emitted from chlorophyll. These electrons are then captured by primary electron acceptor. 6. Electrons then flow down the electron carrier chain and the energy released is used to synthesise ATP from ADP and Pi. ATP is synthesised through chemiosmosis. 7. The electron then returns to P700 (M/J 2013 41) 10 (b) Describe how, in photosynthesis, light energy is converted into chemical energy, in the form of ATP. [8] 1. Photosynthetic pigments are arranged in light harvesting clusters called photosystems, where chlorophyll a is primary pigment.* pigment.* 2. P700, the primary pigment at reaction centre of PI absorbs wavelength of light at 700nm and P680. The primary pigment at reaction centre of PII absorbs wavelength of light at 680nm.* 3. Accessory pigments such as chlorophyll b and carotenoids which surround surround the primary pigment absorb light other than wavelengths 680nm and 700nm and pass energy to primary pigment.* 4. The light energy absorbed by (the) primary pigments excites electrons in P700 and P680 to a higher energy level. 5. The excited electrons, emitted by the pigments, are then captured by the primary electron acceptor. 6. Electrons then flow down the electron carrier chain and the energy released is used to pump H+ from the stroma into the thylakoid space. 7. The thylakoid membrane is impermeable to H+. 8. H+ gradient across the thylakoid membrane is created. g radient through ATP synthase/ ATP synthetase. 9. H+ diffuses down the concentration gradient 10. The enzyme rotates, synthesising ATP from ADP and P i. 11. In cyclic photophosphorylation, electron returns to P700.* 12. In non-cyclic photophorylation, electrons from PII are passed to PI to replace those lost in PI / electrons from water pass to PII to replace those lost in PII.* *In O/N 06, marks are awarded for this. See the immediate question below. My personal recommendation is just write down the full story. It only takes an additional 2 minutes. This is a confidential and copyright document which is restricted for the own use of the original purchaser only. Please e-mail to [email protected] [email protected] if you would like to obtain an authorised permission for the reading of this document. We appreciate your conscience in this matter.

27

(O/N 06) Describe the transfer of light energy to chemical energy in ATP during photosynthesis. 6m 1. Photosynthetic pigments are arranged in light harvesting clusters called photosystems, where chlorophyll a is primary pigment. 3. P700 , the primary pigment at reaction centre of PI absorbs wavelength of light at 700nm and P680 , the primary pigment at reaction centre of PII absorbs wavelength of light at 680nm. 2. Accessory pigments such as chlorophyll b and carotenoids which surround the primary pigment absorb light other than wavelengths 680nm and 700nm and pass energy to primary pigment. 3. The light energy absorbed excites electrons in P700 and P680 and the excited electrons are emitted from chlorophyll. They are then captured by primary electron acceptor. 5. Electrons then flow down the electron carrier chain and the energy released is used to synthesise ATP from ADP and Pi. ATP is synthesised through chemiosmosis. 6. In cyclic photophosphorylation, electron returns to P700 7. In non-cyclic photophorylation, electrons from PII are passed to PI to replace those lost in PI / electrons from water pass to PII to replace those lost in PII (M/J 11 41) Describe how non-cyclic photophosphorylation produces ATP and reduced NADP. 9m 1. Photosystem I and photosystem II are involved in non-cyclic photophosphorylation. 2. Photosynthetic pigments are arranged in light harvesting clusters called photosystems, where chlorophyll a is the primary pigment 3. Accessory pigments such as chlorophyll b and carotenoids which surround the primary pigment absorb light other than wavelengths 680nm and 700nm and pass energy to primary pigment. 4. The light energy absorbed excites electrons in P700 and P680 and the excited electrons are emitted from chlorophyll. These electrons are then captured by primary electron acceptor and pass down electron carrier chain, leaving the photosystems positively charged. 5. Electrons then flow down the electron carrier chain and the energy released is used to synthesise ATP from ADP and Pi. ATP is synthesised through chemiosmosis. 6. Electrons from PII are passed to PI to replace those lost in PI 7. Electrons from water are passed to PII to replaces those lost in PII as photolysi photolysiss occurs at PII and water is split into protons, electrons and oxygen using a water splitting enzyme. 8. Protons and electrons which are emitted from PS I combine with NADP to produce reduced NADP (O/N 12 42) Discuss the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra. 8m 1. Photosynthetic pigments are arranged in light harvesting clusters called photosystems on grana/ thylakoid, where chlorophyll a is primary pigment. 2. P700 , the primary pigment at reaction centre of PI absorbs wavelengths of light at 700nm. 3. P680 , the primary pigment at reaction centre of PII absorbs wavelengths of light at 680nm. 4. Accessory pigments such as chlorophyll b and carotenoids which surround the primary pigment absorb light other than wavelengths 680nm and 700nm and pass the energy to the primary pigment. 5. Chlorophyll a and b absorb light in red and blue/ violet region 6. Absorption peaks for chlorophyll a and b are seen in the red and blue region 7. Carotenoids absorb light in blue/ violet region 8. Diagram of absorption spectrum 9. Different combinations of pigments in different plants give a different spectra


28

(O/N 12 43) Outline the process of the photolysis of water and des cribe what happens to the products of photolysis. 10m 1. PII absorbs light 2. Enzyme in PII involved 3. To break down water 4. 5. Oxygen is produced 6. Used by cells for aerobic respiration 7. Or released out of plant through stomata 8. Protons used to reduce NADP 9. With electrons from PI 10. Reduced NADP used in light independent stage 11. To convert GP to TP 12. Electrons used in ETC 13. To release energy for photophosphorylation 14. To produce ATP 15. Electrons from PII go to PI 16. Ref re-stabilise PI

Absorption spectrum and action spectrum are related because the rate of photosynthesis depends on the effectiveness of different pigments in absorbing light.

Photosynthetic pigments fall into 2 categories: primary pigments and accessory pigments. The primary pigments are 2 forms of chlorophyll a with slightly different absorption peaks. The accessory pigments include other forms of chlorophyll a, chlorophyll b and the carotenoids.

8.3: Essays- Calvin Cycle (M/J 04) (M/J 41 11) Outline the main features of the Calvin Cycle. 9m 1. RuBP (5C) combines with carbon dioxide using rubisco to form an unstable 6C compound, which immediately splits into 2 molecules of GP. 2. GP is converted to TP by ATP and reduced NADP which are produced from light dependent stage. 3. TP used to form glucose/ carbohydrates/ lipids/ amino acids 4. TP is also used in the regeneration of RuBP, using ATP as a source of phosphate 5. Calvin cycle is a light independent reaction and occurs in the stroma.


29

8.4: Essays- C4 Plants (M/J 13 41) Explain how the physiology of t he leaves of a C4 plant is adapted for efficient carbon fi xation at high temperatures. [7] 1. In C3 plants, rubisco combines with oxygen at high temperature 2. Causing less rubisco to combine with CO2 3. In C4 plants such as maize, there is a spatial separation of light-dependent stage from carbon fixation 4. rubisco/RuBP present in bundle sheath cells 5. Kept away from oxygen/air 6. Mesophyll cells absorb CO2 7. Enzyme PEP carboxylase catalyses the combination of CO2 with PEP to form oxaloacetate 8. Oxaloacetate is converted to malate. CO2 is removed from malate in bundle sheath cells. 9. CO2 released combine with RuBP by rubisco 10. photorespiration is avoided/reduced 11. High optimum temperature of enzymes are involved 12. Calvin cycle can continue

8.5: Essays- NADP (M/J 04) Explain the role of NADP in photosynthesis 6m 1. NADP is a coenzyme. 2. They become reduced during non-cyclic phosphorylation. 3. They carry protons and electrons 4. from photosystem I on the thylakoid membrane to the stroma for reactions in the Calvin cycle. 5. NAPD is regenerated when converting GP to TP. (O/N 07) Explain briefly how reduced NADP is formed in the light-dependent stage of photosynthesis and is used in the light-independent stage. 6m 1. Photolysis of water releases H +. This occurs at PS II. 2. Electrons is released by P700/ PI during non-cyclic photophosphorylation 3. Both protons and electrons combine with NADP

4. 5. 6. 7.

Reduced NADP Reduces GP/ PGA To TP ATP used NADP regenerated/ oxidised


30

CIE A2 Biology Notes Photosynthesis

Recommend Documents