F214 4.3.1 Photosynthesis By Ms Cullen

Producer (autotroph) An organism that produces complex organic compounds from simple molecules and an external source of energy, such as light. Autotrophs are considered producers in a food chain. Plants and other organisms that carry out photosynthesis are phototrophs. from the Greek autos = self and trophe = nutrition Can you remember the balanced equation for photosynthesis? 6CO2 + 6H20 C6H12O6 + 6O2

Consumer (heterotroph) A heterotroph is an organism that requires organic substrates to get its carbon for growth and development. A heterotroph is known as a consumer in the food chain. All animals are heterotrophic, as well as fungi and many bacteria. Greek heterone = (an)other and trophe = nutrition Heterotrophs depend on autotrophs for their food supply of organic materials .

Photosynthesis is a very complex metabolic process and occurs in 2 stages: The light-dependent stage The light-independent stage Both stages occur in the chloroplasts of cells.

Two palisade mesophyll cells from an Arabidopsis leaf Chloroplasts Structures found in some plant cells. Especially prevalent in palisade and spongy mesophyll tissues in leaves. Each cell will have 10 or more chloroplasts contained within it. Contain photosynthetic material, including chlorophyll. Two palisade mesophyll cells from an Arabidopsis leaf

Structure of a chloroplast A chloroplast is surrounded by 2 membranes, which form an envelope. They also contain internal membranes called lamellae which enclose fluid-filled sacs called thylakoids. In some areas the thylakoids are stacked in piles called granum. The material inside the chloroplast is called the stroma.

Complete Activity 5 Extracting Chloroplasts Using Ultrafiltration

Complete Activity 6 Hill Reaction

Photosynthetic pigments - Chlorophyll Photosynthetic pigments are substances that absorb energy from different wavelengths (colours) of light. The most common photosynthetic pigment in chloroplasts is chlorophyll. There are 2 forms chlorophyll a and chlorophyll b.

Chlorophyll absorbs blue-violet and red parts of the spectrum

Structure of chlorophyll a 11

Photosynthetic pigments Other pigments such as carotene and xanthophyll, absorb light from the blue-violet part of the spectrum

Chromatography of Photosynthetic Pigments Carry out practical and calculate Rf To calculate Rf values use the following equation: Rf = distance moved by pigment distance moved by solvent

Plant Pigments involved in Photosynthesis Using the information below can you identify your different pigments? Pigment Colour Rf Values Carotene Orangey-yellow 0.98 Pheophytin Olive green 0.81 Chlorophyll a Bluey-green 0.59 Chlorophyll b Green 0.42 Xanthophyll I Deep yellow 0.28 Xanthophyll II 0.15

Photosystems Photosynthetic pigments are arranged into structures called photosystems. Photosystems will allow the maximum absorption of light energy. The photosystems are held in place by protein embedded in the grana. Photosystem I (PSI) occur mainly on integral lamellae. Photosystem II (PSII) occur almost exclusively on the granal lamellae.

A photosystem 16

The light-dependent stage Occurs in the thylakoid membranes of the chloroplasts, where the photosynthetic pigments occur. Light energy is absorbed by the photosynthetic pigments and some of this energy is used to produce ATP (photophosphorylation). Water molecules are split to produce H+ ions, electrons and oxygen (photolysis). H+ ions and electrons are picked up by a coenzyme called NADP . This is then converted into reduced NADP. The oxygen is a waste product and is excreted.

The light-dependent stage Outputs Inputs Light ATP light-dependent stage Water reduced NADP Oxidised NADP oxygen

Photophosphorylation Means phosphorylation using light. It is the production of ATP from ADP and a phosphate group using light energy. ADP + phosphate ATP This occurs as electrons are passed along a series of electron carriers forming an electron transport chain in the thylakoid membranes. As the electron moves along it gradually loses energy. This energy is used to react the phosphate group with the ADP.

Cyclic Photophosphorylation This only involves photosystem I and results in the formation of ATP only (not reduced NADP). Light energy absorbed by PSI is passed on to electrons in chlorophyll a molecules. In each molecule 1 electron becomes so energetic that it leaves the chlorophyll molecules completely. The electron is passed along the chain of electron carriers. The energy from the electron is used to make ATP. The electron, which has lost its extra energy, returns to PSI.

Non-cyclic Phosophorylation Happens in both PSI and PSII. Electrons from PSII pass down the electron carrier chain, producing ATP by photophosphorylation. However, instead of returning to PSII, the electrons replace those lost from PSI. Electrons emitted from PSI are used to reduce NADP instead of making ATP. This requires H+ ions, these come from water being split by an enzyme in PSII and is known as photolysis: 2H2O 4H+ + 4e- + O2 H+ ions are taken up by NADP and form reduced NADP.

Non-cyclic Phosophorylation Electrons replace ones emitted from PSII when light hit it. The oxygen diffuses out of the chloroplast and eventually out of the leaf. Cyclic Phosphorylation Non-cyclic phosphorylation Is PSI involved? Is PSII involved? Where does PSI obtain replacement electrons from? Is ATP made? Is reduced NADP made?

The Z-scheme http://www.biology4all.com/resources_library/source/61a.swf 23

The light-independent stage This takes place in the stroma. It uses the ATP and reduced NADP which was produced in the light-dependent stage to produce carbohydrates form CO2. The process is also known as The Calvin Cycle.

The Calvin Cycle

The light-independent stage The enzyme rubisco (ribulose bisphosphate carboxylase-oxygenase) catalyses the reaction between carbon dioxide and RuBP (ribulose bisphosphate) The 5C RuBP when it reacts with CO2 produces a 6C molecule which immediately splits into 2 molecules of 3C called glycerate 3-phosphate (GP) 3. The reduced NADP and ATP from the light-dependent stage are now used to provide energy and phosphate groups, which change GP into TP triose phosphate. 4. TP is the first carbohydrate that is made in photosynthesis.

The light-independent stage Most of the TP is used to regenerate RUBP. The rest is converted into other carbohydrates eg glucose, fructose, sucrose, starch & cellulose.

The light-independent stage Products: Fatty acids from GP Amino acids (with addition of nitrates) from GP Hexose 6C sugars eg glucose from TP Some glucose converted to fructose Fructose and glucose can combine to form disaccharides which are translocated in phloem Hexose sugars are converted into polysaccharides eg cellulose & starch TP converted into glycerol which combines with fatty acids to form lipids

Limiting Factors

Week 11 The rate of photosynthesis at constant temperature and different light intensities

Week 11 The rate of photosynthesis at constant temperature, with raised concentrations of carbon dioxide and different light intensities

Week 11 Using an indicator solution

Week 11 Effect on relative concentrations of GP, TP and RuBP, of reducing light intensity

Week 11 Effect on relative concentrations of GP, TP, and RuBP of reducing carbon dioxide concentration

Photorespiration The enzyme rubisco is also able to catalyse the combining of oxygen with RuBP, rather than CO2. This results in loss of RuBP which could be used for carbon fixation. This will also result in the loss of CO2 from the plant. The process overall has the effect of taking in oxygen and releasing CO2, and only happens in bright light. High light intensity and high temperatures increase the rate of photorespiration. Plants growing in the tropics live in these conditions.

Photorespiration As oxygen is a competitive inhibitor of rubisco, photorespiration will increase as O2 concentration increases or as CO2 concentration decreases. In C3 plants photorespiration reduces the rate of photosynthesis. C4 plants have an alternative enzyme (PEP carboxylase) and therefore the effect of photorespiration is negligible.