Autotrophic Nutrition



Autotrophic Nutrition

Autotrophic nutrition involves the use of an external en_____ source to make the complex org_____ molecules from simple in_______ substances.

Photosynthesis occurs in plants containing ch__________. It involves the formation of organic compounds, generally from carbon dioxide and water, using sunlight as an e______ source.

Chemosynthesis is performed by some b_______. The raw materials are c______ d______ and w_____ and the energy comes from the ox_______ of various in_____ compounds. E.g. the nitrifying bacteria, oxidise amm_____ to n_____ and nitrite_____ to n_____.

Q1 Look for other examples of chemosynthesis. What are the importance of these chemosynthesizers in the environment?

Photosynthesis is vital as the means of making complex organic substances available to animals, hence a photosynthesising plant at the beginning of almost* all food ch____. The oxygen released during photosynthesis is essential to support the resp_______ of other organisms and to keep a bal_____ between carbon dioxide and oxygen in our atmosphere. The appearance of photosynthesizers in the early history of the Earth is an important step leading to the evolution of aer_____ organisms.

|[pic] |

*Give an example of a food chain which is not based on green plants as the producer.

I) To MEASURE THE RATE OF PHOTOSYNTHESIS

1) by Measuring the Rate of Oxygen Released

The evolution of oxygen by aquatic plants can be measured by counting either the number of bubbles they produce per unit time, or by measuring the volume of gas produced. Q.2.0 What is/are the assumption(s) behind the methods?

2) by Measuring the Rate of Carbon Dioxide Uptake.

[pic]

A control apparatus without a green plant is used to measure the amount of carbon dioxide present in a known volume of air drawn through the apparatus. In the apparatus shown, the green plant will absorb some of the carbon dioxide passing it. Equal volumes of air are drawn through both sets of apparatus simultaneously.

Q. 2.1 Suggest a way to find the amount of CO2 taken up by the barium hydroxide solution.

Q. 2.2 The result obtained is only a measure of the ‘apparent rate of photosynthesis’. What does it mean by the ‘apparent rate of photosynthesis’ ? What further steps should be taken to find the true rate of photosynthesis?

II) SITES OF PHOTOSYNTHESIS

In plants photosynthetic pig______ are located within chloroplasts found in leaves and green stems. The chloroplasts of many of the higher plants are able to move in cytoplasmic streaming of the cell and may alter their position as the light intensity varies. Many of the green algae are motile and can swim to orientate themselves with respect to light.

A) Leaf Anatomy

[pic]

B)The Structure of the Chloroplast

In higher plants the chloroplasts are usually disc-shaped biconvex structures about 5 (m in diameter. Around the outside is a dou___ membrane enclosing a str____.

This stroma appears to have no organised structure, but contains st____ grains and enz____ which can catalyse the reduction of carbon dioxide.

Embedded in the stroma are lam____ arranged one above the other and consisting of g_____ and intergranal regions. The grana are composed of a stack of membranes with chl_______ and electron car____ attached.

[pic]

|[pic] |

a) The chloroplast pigments

All molecules absorb electromagnetic radiation. Molecules that can absorb wavelengths in the vis___ region of the spectrum are called pigments. The color of leaves comes from the wavelength or combinations of wavelengths of light refl______ off the pignents.

The two primary pigments involved in photosynthesis are chlorophyll a and chlorophyll b. These two molecules efficiently absorb light at the r__ and b___ end of the visible spectrum and not very efficiently at the middle of the spectrum. When chlorophyll a and b absorb both the blue and red light, we see what is reflected which is primarily g_____.

The existence of a number of pigments in green leaves can be demonstrated by chromat__________:

[pic][pic]

i) Chlorophylls

The green pigments called chlorophylls are the ones chiefly concerned in the photosynthetic process. Chlorophyll a and b are the most common and the only forms found in the higher plants.

The molecule has a porphyrin ring with a mag______ atom at its centre and a phytol (long chain alcohol) tail.

|[pic] |Absorption Spectrum |

| | |

| |The percentage absorption of different |

| |wavelengths by an extracts of a pigment is |

| |called an ab_________ spectrum. |

| | |

| |The absorption spectrum of Chlorophyll show |

| |absorption peaks at the b___-v____ and r__ |

| |ends of the visible spectrum. |

| | |

| | |

| | |

| |Action Spectrum |

| | |

| |When the rate of photosynthesis is measured |

| |for light of different wavelengths |

| | |

| |the activity is plotted against the |

| |wavelength the result is an a_____ spectrum, |

| |which corresponds very closely to the |

| |absorption spectrum of chlorophyll extracts. |

| | |

| |Q.3 What does this suggest about the role of |

| |chlorophylls in promoting photosynthesis? |

ii) Carotenoids

Carotenoids are lipid compounds widely distributed amongst plants and animals, they range in colour from yellow through orange and brown to purple.

The role of the carotenoids in the chloroplast appears to be two-fold. They ab____ light energy and tran___ it to the chlorophylls and secondly they pro____ chlorophyll against photo-oxidation. Mutant algae lacking carotenoids have been shown to die when grown in the light because their chlorophyll oxidises in its absence.

# Photosynthesis has optimized its light-absorbing capabilities by making a series of pigments covering all of the visible spectrum, called accessory pigments. These absorb light in between the red and the blue wavelength and then transfer it to chlorophyll to use in photosynthesis.

# Hydrogen carotenoids (containing only carbon and hydrogen) are called carotenes; those that also contain oxygen are called xanthophylls.

[pic]

b) Relation of pigment to habitat in Algae

It is noticeable, particularly in algae, that the type of pigment present and the habitat of the plant are closely linked. Land plants and sha____ water plants are gr____, absorbing red and blue light for photosynthesis. In deeper water red light is quickly absorbed and only the blue end of the spectrum penetrates. Here brown algae are found, with additional xanthophylls which absorb blue light. Deeper still the red algae become more common, possessing pigments that absorb mainly blue light.

III) FACTORS WHICH AFFECT THE RATE OF PHOTOSYNTHESIS

A) General Factors

a) Light Intensity

In general, increased light intensity increases the rate of photosynthesis until another factor, usually carbon dioxide, becomes lim_____. At the usual carbon dioxide levels in the atmosphere the maximum photosynthetic rate is reached in many plants, at only quarter to half full sunlight.

Leaves of many plants sh____ each other as little as possible. This arrangement is called a leaf mosaic. On the other hand, very high light intensity causes destruction of cell constituents, decolorisation of chlorophyll and ultimately even the death of the cells.

As the light intensity increases, a point is reached when the intake of carbon dioxide for photosynthesis exactly b______ its output in respiration. This is called the c__________ point. Further increase in light intensity will result in carbon dioxide being ab____ and oxygen ev____.

|Trees in woodland communities are usually s__ plants, |[pic] |

|adapted to a high light intensity. However, their | |

|seedlings are often capable of tolerating shade | |

|conditions. | |

| | |

|The shade plants usually reach their compensation | |

|point at a l_____ light intensity than the sun plants.| |

|(The compensation point for the former may be as low | |

|as 0.3 to 1.0% of maximum daylight, as compared with | |

|1.3 to 7.5% for sun plants. This is shown | |

|diagrammatically) | |

4.1 Comment on the ecological significance of the different compensation points for sun and shade plants.

4.2 Draw a table to show the morphological adaptations in sun and shade plants?

4.3 The utilisation of carbon dioxide in photosynthesis is much less temperature sensitive than the production of carbon dioxide in respiration. This fact has important bearings on glasshouse management. In seasons of low light intensity it is essential to keep temperatures at the safe minimum for the crop concerned. Explain why it is essential to do this.

4.4 How could the safe minimum temperature be defined?

b) Quality of light

The action spectrum for photosynthesis has peaks in the red and blue regions, yet the wavelengths available to a plant may vary in different habitats.

Q. 5.1 What would you expect to changes in the quality of light available under a woodland? What physiological adaptations are expected in the plants striving at the lower strata inside a woodland?

c) Carbon dioxide Concentration

|[pic] |Q.1 The normal CO2 concentration in air is ~0.03%. What does the figure indicates about the |

| |role of CO2 concentration in the process of photosynthesis ? |

Under bright sunlight and a temperature of 20--25°C, with a plentiful supply of water, the amount of carbon dioxide in the atmosphere (0.03%) seems likely to be the l_________ factor for most plants. Increasing the level of the gas up to 1%* shows an increase in the photosynthetic rate of most species.

*Above this level the effect depends on the species. Often there is no corresponding increase in rate and in some plants such as tomatoes the leaves may begin to die as the carbon dioxide level rises.

d) Temperature

|[pic] |Q. Comment on the relationship between the rate of photosynthesis and temperature. |

Since the ‘dark’ reaction of photosynthesis is a series of en_______-controlled reactions, it is not surprising that increasing the temperature speeds up the rate of the reaction. Photosynthesis has a Q10 of approximately two up to about 30°C, which is probably the op________ temperature for most plants for short periods (about 30 minutes). Rates at higher temperatures for longer periods soon begin to drop, probably due to en_____ destruction, accumulation of e__ products and lim_____ availability of carbon dioxide.

About 40° C the rate falls off rapidly as the enzymes are de_______. In temperate regions the range of temperature for photosynthesis for the majority of the plants is probably around 10- 35° C. Tropical species do not usually photosynthesise below about 5° C, whereas some conifers may continue to do so around freezing point.

e) Water

Less than 1% of the water absorbed by most plants is needed for photosynthesis, so it is n__ likely that its deficiency would affect the process directly. The indirect effects of water shortage however, are likely to retard photosynthesis, causing deh_______ which will affect the structure of protoplasm and hence its metabolism. The structural arrangement of the chloroplast is likely to be affected too.

*

It was originally thought that water deficit closing the stomata. would reduce carbon dioxide absorption, but there is much experimental evidence to suggest that even stomata appearing closed when viewed microscopically are still sufficiently open to admit the gas.

f) Mineral salts

Mineral salts are not directly involved as raw materials for photosynthesis, but shortage of either ir___ or mag_______ affects the rate of chlorophyll production and hence, indirectly, the photosynthetic rate. Some ions, such as potassium and some trace elements, such as molybdenum, are also required, though the exact function of some of them is obscure.

|Macronutrients are required in relatively larger amount |

|Carbon |C |Component of all organic compounds |

|Oxygen |O |supplied by air & water |

|Hydrogen |H |Component of all organic compounds |

|Nitrogen* |N |Part of chlorophyll, amino acids, proteins, nucleic acids |

|Phosphorus* |P |Used in photosynthesis and almost all aspects of growth, ATP, NADP+, nucleic acids |

|Potassium* |K |Activates enzymes, used in formation of sugar and starch |

|Calcium |Ca |Used in cell growth and division, part of cell wall |

|Magnesium# |Mg |Part of chlorophyll, activates enzymes |

|Sulfur |S |Part of amino acids and proteins |

|Micronutrients are required in trace amounts |

|Boron |B |Affects reproduction |

|Chlorine |Cl |Aids in root growth |

|Copper |Cu |Used in chlorophyll, activates enzymes |

|Iron |Fe |Used in Photosynthesis, cytochromes |

|Manganese |Mn |activates enzymes |

|Sodium |Na |Used for water movement |

|Zinc |Zn |Part of enzymes, used in auxins |

|Molybdenum |Mo |Used in nitrogen fixation |

|Nickel |Ni |Liberates Nitrogen |

|Cobalt |Co |Fixates Nitrogen |

|Silicon |Si |Makes tougher cell walls: enhances heat and drought tolerance |

g) Oxygen

It has been found that for some plants, such as wheat, the atmospheric concentration of oxygen (21%) sl___ down photosynthesis. It may be that the increased availability of oxygen speeds up the respiratory rate allowing it to compete more favourably with photosynthesis.

B) Limiting Factors

Photosynthesis is a complex process, involving a great many steps and subrates. If any one of these slows down or is scarce then it may hold up the rest of the process and it is called a limiting factor.

[pic]

Q. The effect of different light intensity on the photosynthetic rate of an intact leaf of a flowering plant measured at two different concentrations of carbon dioxide (300 and 600 parts per million (ppm) was studied and the results summarized in the following table:

Photosynthetic rate (Net C02 fixed in mg per 100 cm2 leaf area per hour)

|Light intensity (kilolux) |300 ppm C02 |600 ppm C02 |

|0 |-2.0 |-2.0 |

|4 |1.5 |2.4 |

|8 |5.0 |6.8 |

|14 |10.4 |13.4 |

|18 |14.0 |17.8 |

|22 |15.0 |22.3 |

|28 |15.0 |29.0 |

|32 |15.0 |30.0 |

|50 |15.0 |30.0 |

|80 |15.0 |30.0 |

a) Present the results in graphical form. 5m

b) Describe how the light intensity affects the rate of photosynthesis of the leaf. 3m

c) How does the performance of the leaf differ when put into the two different carbon dioxide concentrations? 4m

d) Account for the photosynthetic rate at zero light intensity. Identify and explain the points at which there is no net fixation of carbon dioxide by the leaf. 4m

e) With light intensity at 10 kilolux and CO2 concentration at 300 ppm, explain how you would expect the photosynthetic rate of the leaf to change under

i) light wind, and

ii) moderate water deficiency conditions. 4m

IV) THE PROCESS OF PHOTOSYNTHESIS

Put in a very simplified form the photosynthetic process begins with the absorption of l____ energy by the chloroplast pig______ and this energy is then used to split w____. The h______ obtained is used to reduce c_____ d______ forming carbohydrate, o_____ is evolved as a waste product.

A) The Evidence for Light and Dark reactions

Chemical reactions are affected by temperature; a 10(C rise will approximately double the rate. Photochemical reactions are not much affected by temperature. Photosynthesis is affected by intensity of li____ and temp________, suggesting both photochemical and chem____ stages in the process.

In the light, isolated chloroplasts were found to accumulate ATP and reduce a hydrogen acceptor NADPH, Oxygen is also evolved. In the dark, chloroplasts will synthesise carbo________ if supplied with ATP, NADPH and carbon dioxide.

[pic]

B) The light (dependent) Reaction

The light reaction consists of the photochemical spl_____ of water, providing h_______ atoms for the re_______ of carbon dioxide in the dark reaction and, secondly, the formation of an e_____ store in ATP, which can be used to power the dark reaction. The production of ATP by photochemical means is called photo-phosphorylation.

➢ The light reaction begins with the absorption of light by chlorophyll. An 'ex_____' electron of the chlorophyll is elevated to a h______ energy level than the normal ground state #1.

➢ the excited electron is 'picked up' by an electron acc_____. the excess energy it possesses is available for use by the cell to make ATP either in Cy___ phosphorylation or Non-cyclic Photo-p______________.

*If the electron merely lost energy and fell back into the chlorophyll molecule it would fluoresce.--- A chlorophyll extract shows a blood red fluorescence in reflected light.

Cyclic and Non-cyclic Photophosphorylation

◆ In cyclic p________________ the e______ electrons are picked up by an electron a________.

◆ The e_____ e_____ are passed from the acc_______to the cy__________ and then back to ch_________.

◆ As the e______ electrons pass along the cyto________, energy is released and used up in the synthesis of ___. By the time the electron returns to the chlorophyll molecule it has lost all its excess energy and is back to its normal ground state.

1. Cyclic Photophosphorylation

|Light Reaction -- Cyclic Photophosphorylation |Dark Reaction |

| | |

|e- acceptor | |

|cytochromes | |

|excited e- | |

| | |

|ADP + Pi | |

| | |

| |ATP |

|e- | |

| | |

|Light | |

2. Non-Cyclic Photophosphorylation

◆ In n___-c_____ p_______________ the excited electrons emitted by chlorophyll are picked up by an electron acc______.

◆ Water tends to sp___ spontaneously into H + and OH- ions. Some of the H + ions from the water and the excited electrons combine with h________ acceptor NADP+ which is then re______ (NADPH + H+).

◆ In its reduced state NADPH enters the d___ reaction of photosynthesis, providing h_______ for the red______ of carbon dioxide. After passing on its hydrogen the NADP+ can be recy___ and used again.

◆ The hydroxyl ions from the water pass e______ back to chlorophyll via the cy________ (Electron Transport Chain) with consequent production of A___. The hydroxyl ions which have passed on electrons rearrange forming water and o______.

2 H2O 2H+ + 2OH-

4OH- 2H2O + O2 + 4 e-

This process is non-c_____, since electrons (and protons) are accepted by N____ and replaced from w_____.

|Light Reaction -- Non-Cyclic Photophosphorylation |Dark Reaction |

| | |

|NADP+ |NADPH + H+ |

| | |

|2 H+ | |

| | |

|2e- | |

| | |

|excited e- | |

|Light | |

| | |

| | |

| | |

|2e- | |

| | |

|ADP + Pi |ATP |

| | |

|2e- | |

|2OH- + 2 H+ 2H2O | |

|O2 | |

C) The Dark Reaction / the Calvin Cycle

a) The Calvin Apparatus and the elucidation of the dark reaction.

|[pic] |The individual steps of the reduction of carbon dioxide and |

| |synthesis of carbohydrates were traced by Dr Melvin Calvin, using |

| |a unicellular green algae.. |

| | |

| |They supplied CO2 with radioactive isotope 14C to an illuminated |

| |suspension of the alga. The algae were exposed to radioactive |

| |carbon for a known length of time --from a few seconds to a few |

| |minutes, they then killed them rapidly in boiling methanol. |

| | |

| |Using chromatography and exposing the chromatogram to sensitive |

| |photographic film they were able to discover into what substances |

| |the 14C had been incorporated. |

They found that after about five seconds exposure to 14CO2 the radioactive carbon was mainly in a 3-carbon compound, phosphoglyceric acid (PGA). After thirty seconds it was chiefly in two 3-carbon sugar phosphate (triose phosphate), phosphoglyceraldehyde (PGAL) and dihydroxyacetone phosphate. Finally after about ninety seconds the carbon dioxide was incorporated into pentoses and hexoses.

b) Biochemistry of the Dark reaction

It is the series of enz_______ steps by which carbon dioxide is re_____ to sugars. Its occurs in the st______ of the chloroplast. The dark reaction does NOT actually require darkness; it is merely light-in-_________. However, it relies on the light reaction to provide re_______ power and en______(ATP).

CO2

+

ATP

ADP

ADP

ATP NADPH + H+

NADP+

Glucose and other sugars

To synthesise a glucose molecule, ____ turns of the Calvin Cycle is required. The Calvin Cycle can be summarized into four major steps:

1. Carbon fixation / Carboxylation

A molecule of CO2 combines with r_________ b___________ (RuBp), a __-carbon sugar to form a 6- carbon compound which presumably breaks into two __-carbon p____________ acid (PGA) immediately.

2. Reduction

Each PGA is ph___________ by ATP and then re_____ by NADPH to form p_________________(PGAL).

3. Product Formation

Some of the p_________________ (PGAL) become channelled into formation of product such as glucose.

4. Regeneration of RuBp

Some of the PGAL is reorganized to become r_________ b___________ (RuBp) again. This is important for maintaining a sufficient concentration of r_________ b___________ for continuing fixation of CO2.

Experimental evidence for cyclical pathways

The three graphs below show the results of experiments originally carried out by M. Calvin, and others in the 1950s. The experiments were designed to investigate the process of photosynthetic reduction of carbon dioxide in the green alga Scenedesmus..

[pic]

[pic] [pic]

The results of experiments to investigate the photoreduction of CO2 containing the radioactive 14C:

a) The percentage of radioactivity incorporated into different compounds during the first few seconds and minutes of photosynthesis in the alga Scenedesmus.

b) The changes in the level of radioactivity in phosphoglyceric acid (PGA) and ribulose bisphosphate (RuBP) in Scenedesmus when the light is switched on and off.

c) The changes in the level of radioactivity in phosphoglyceric acid (PGA) and ribulose bisphosphate (RuBP) following a reduction in the concentration of carbon dioxide.

a Why was an algal suspension rather than a leaf used for these experiments ?

b The graph in a) shows the percentage of total radioactivity from 14C that was incorporated into the compounds which became most heavily labelled during the first few seconds and the first few minutes of photosynthesis. How do these results support the hypothesis that phosphoglyceric acid (PGA) is a very early product of carbon dioxide reduction ?

c The graph shows a fall in the level of radioactivity found in sugar phosphates after approximately two minutes of photosynthesis. Why should this occur ?

The graph in figure b) shows the changes in the level of radioactivity in phosphoglyceric acid and in ribulose bisphosphate which occur when the light illuminating the algal suspension is switched on and off. (Note that the level of radioactivity is expressed in different ways in graphs a and b.)

d Why are the levels of PGA and RuBP in a 'steady state' in the light ?

e Why is there a rapid change in the levels of radioactivity when the illumination is switched off?

f Why does this change take the form of an increase in PGA and a decrease in RuBP?

g How do the results provide evidence that PGA is converted to RuBP?

Graph c shows the changes in the levels of radioactive carbon in PGA and RuBP which occur when the carbon dioxide concentration is reduced from 4 per cent to 0.03 per cent.

h Why does the level of PGA fall?

i Why does the level of RuBP rise ?

j Explain how the oscillations in PGA and RuBP shown in both graphs b and c support the hypothesis that a cyclic series of reactions is involved in carbon dioxide reduction.

V) A Summary of Photosynthetic Reactions

[pic]

| |Light reactions |Dark reactions |

|Location |Thylakoids / lamellae |S______ |

|Reactions |Ph____chemical, i.e. requires light. |Do not require l____. |

| | | |

| | | |

| |Light energy causes the flow of e______ from electron ‘donors’ to |Carbon dioxide is fi___ when it is accepted by a 5C- compound |

| |electron 'acceptors', along a cy___ or n__-c____ pathway. |r______ biphosphate (RuBP), to form two molecules of a |

| | |3C-compound p__________ acid (PGA), the f___ identifiable |

| | |product of photosynthesis. |

| |C________ emit electrons when they absorb light energy. W____ acts | |

| |as an electron d___ to the non-cyclic pathway. Electron flow results| |

| |in production of ATP (photo-phos_________) and r_________ power |A ser____ of reactions occurs in which the carbon dioxide |

| |NADPH |acceptor ________________ is regenerated and some PGA is |

| | |converted into a su___. |

|Overall equation | | |

| |2H2O + 2NADP+ O2 + 2NADPH + 2H+ |2NADPH + 2H+ 2NADP+ |

| | | |

| |ADP + Pi ATP (variable amount) |CO2 + [2H] sugar (+ water) |

| | | |

| | |ATP ADP + Pi |

| | | |

|Results |Light energy is converted to c________energy in ATP such as and |C_____ d_______ is reduced to car_________, using the chemical|

| |NADPH. |e_______ in ATP and hydrogen in NADPH. |

| |Water is split into h_______ and o______, and H________ is passed to| |

| |NADPH and oxygen is a w_____ product. | |

| | | |

|Combined equation | |

| |H2O + CO2 [CH2O] + O2 |

| | |

VI) THE FATE OF THE PRODUCTS OF PHOTOSYNTHESIS

The triose phosphate formed by the dark reaction can pass along different pathways to form c____________, p______ or l_____, or it may be used as a respiratory substrate.

a) The carbohydrate pathway

The first stage is the conversion of t____ phosphate (PGAL) to f______ diphosphate. One phosphate is removed to form fructose-6-phosphate and the molecule is then rearranged giving g______-6-phosphate. By removal of the phosphate and c___________ of the sugar molecules, disaccharides such as s_____ and polysaccharides such as c________ and s_______ may be produced.

Carbohydrate is usually passed around the body of the higher plants as sucrose in the phloem. Arriving at its destination it may be used as a respiratory substrate in an actively growing region or stored, usually as starch an insoluble polysaccharide, in roots and stems, particularly perennating organs.

triose phosphate

fructose 1,6 diphosphate

fructose phosphate

sucrose glucose phosphate cellulose

starch

b) The pathway to amino acids and protein

In order to make protein, a source of n______ is required. For higher plants this is provided mainly by n_____ taken from the soil. Nitrate is reduced to n_____ and then to ammonia.

The a________ could then be taken up by (-ketoglutaric acid of the Krebs cycle, ultimately forming glutamic acid. Using glutamic acid as an initial donor of am___ groups, a variety of amino acids could be built up by trans________ enzymes.

Triose phosphate

Proteins

Pyruvic acid

Acetyl CO A other

amino acids

Krebs cycle transamination

Glutamic acid

d) The pathway to lipids

The synthesis of lipids requires the formation of g_______ and f____ acids, and their combination by con________. Glycerol can be obtained from conversion of tri___ phosphate (TP)

The f____ acid chains are build up by adding 2-carbon residues ( from acetyl COA) repeatedly to produce chains of varying length and finally combined with glycerol, either as phospholipids or true lipids.

The products of Calvin cycle

+

VII) PHOTOSYNTHETIC BACTERIA

Some autotrophic bacteria are ph___________. They contain a pigment called bacteriochlorophyll, which is similar to the chlorophylls of other plants, except that it has the ability to absorb infra red light as well as the blue-violet end of the visible spectrum. The light energy absorbed by the pigment is used by the bacteria to split hydrogen s_______ instead of water.

The hydrogen reduces carbon dioxide as a preliminary to the production of complex organic molecules, while the sulphur is sometimes deposited in the bacterial cells. The bacteria are called the green or the purple sulphur bacteria, depending on the type of b________chlorophyll they contain. They are found in the anaerobic conditions in the mud at the bottom of ponds and lakes where hydrogen sulphide is plentiful.

End

-----------------------

Lamellae of granal and intergranal regions bear p__________ pigments and present a large surface a___ for the absorption of l____.

Double membrane bounds the ch________; allow inward movement of C__, water and minerals and outward m________ of su___ etc.

Intergranal and granal lamellae bear cytochromes and other e______ carriers associated with the l____-dependent reactions; lamellae act as convenient surf____ for spacing of mole____ involved in electron flow

Stroma - fluid-filled containing en_____ of light-I__________ stage of photosynthesis;

Chlorophyll

Cytochromes

Chlorophyll

Ribulose biphosphate

RuBp (5C)

Phosphoglyceric acid

2 x PGA (3C)

Diphosphoglyceric acid

DPGA (3C)

Phosphoglyceraldehyde

PGAL (3C)

Phosphoglyceraldehyde

( triose phosphate )

PGAL (3C)

The Calvin Cycle

citric acid (6C)

(-ketoglutaric acid (5C)

oxaloacetic acid (5C)

4-C intermediates

carbon dioxide

RuBP

PGA

RuP

Krebs cycle

TP

glucose, sucrose, starch and other polysaccharides

nucleotides, nucleic acids

gIycerol

amino acids and proteins

fatty acids

fats

pyruvic acid

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download