B1Winnie7.2

Front 1

Draw the structure of a chloroplast as seen in electron microscopes

Back 1

http://micro.magnet.fsu.edu/cells/chloroplasts/images/chloroplastsfigure1.jpg

*i do not own the image

Front 2

photosynthesis consists of 2 categories of reactions, what are they?

Back 2

light-dependent and light independent reactions

Front 3

what are the four general steps of the light-dependent reactions?

Back 3

light absorption, production of ATP, production of NADP, production of oxygen.

Front 4

explain how light absorption works in the light dependent steps

Back 4

chlorophyll absorbs light and the energy from the light raises an electron in the chlorophyll moleculte to a higher energy level. the electron at higher energy level is an Excited Electrion and the chlorophyll is photoactivated. In single chlorophyll molecules the excited electron soon drops back down to its original level, re-emitting the energy.Chlorophyll is located in thylakoid membranes and is arranged in groups of hundreds of molecules called photosystems. Excited electrons from absorption of photons of light anywhere in the photosystem are passed from molecule to moleculte until they reach a special chlorophyll molecule at the reaction centre of the photosystem. This chlorophyll passes the excited electrion to a chain of electron carriers.

Front 5

what are photosystems?

Back 5

groups of hundreds of molecules in chlorophyll which play a major role in light absorption. There are two photosystems, I and II.

Front 6

what is an excited electron?

Back 6

an electron at a higher energy level.

Front 7

explain how production of ATP works as one of the light dependent steps.

Back 7

an excited electron from the reaction centre of photosystem II is passed along a chain of carriers in the thylakoid membrane (below). It gives up some of its energy each time that it passes from one carrier to the net. At one stage, enough energy is released to make a molecule of ATP. The coupling of electron transport to ATP synthesis is by chemiosmosis, in the mitochondrion. Electron flow causes a proton to be pumped across the thylaokid membrane TO the fluid space inside the thylakoid. A proton gradient is created. ATP synthase, located in the thylakoid membranes, lets the protons across the membrane down the concentration gradient and uses the energy released to synthesize ATP.

Front 8

Define non-cyclic photophosphorylation.

Back 8

The production of ATP using the energy from an excited electron from Photosystem II.

Front 9

explain how production of NADP works as one of the light dependent steps

Back 9

After releasing the energy needed to make ATP, the electron that was given away by photosystem II is accepted by photosystem I. The electron replaces one previously given away by photosystem I. With its electron replaced, photosystem I can be photoactivated by absorbing light and then give away to another excited electron. this high-energy electron passes along a short chain of carriers to NADP+ in the STROMA. NADP+ accepts two high energy electrons from the electron transport chain and one H+ ion from the stroma, to form NADPH.

Front 10

explain how production of oxygen works as one of the light dependent steps

Back 10

Photosystem Ii needes to replace the excited electrons that it gives away. The special chlorophyll molecule at the reaction centre is positively charged after giving away an electron. With the help of an enzyme at the reaction centre, water molecules in the thylakoid space are split and electrons from them are given to chlorphyll. Oxygen and H+ ions are formed as by-products. The oxygen produced in photosynthesis is all the result of photolysis of water. Oxygen is a waste product and is excreted.

Front 11

what is photolysis?

Back 11

the splitting of water molecules that only happens in the light.

Front 12

what are the four general steps to the light-independent reactions?

Back 12

the calvin cycle, carbon fixation, regeneration of RuBP, and synthesis of a carbohydrate.

Front 13

what happens in the calvin cycle?

Back 13

the light-independent reactiosn take place within the stroma of the chloroplast. The first reaction involves a Five-Carbon sugar, Ribulose Biphosphate. RuBP is also a product of the light independent reactions, which therefore form a cycle, called the Calvin cycle. There are many alternative names for the intermediate compounds in the calvin cycle.

Front 14

what are the intermediate compounds in the calvin cycle?

Back 14

glycerate 3-phosphate (a.k.a. 3-phosphoglycerate. Glycerate 3-phosphate is sometimes abbreviated as GP, which could be confused with glyceraldehyde 3-phosphate, which is a form of triose phosphate or with glucose phosphate. the abbreviation of GP should therefore be avoided.

Front 15

What happens in carbon fixation?

Back 15

carbon dioxide is an essential substrate in the light-independent reactions. It enters the chloroplast by diffusion. In the stroma of the chloroplas carbon dioxide combines with ribulose biphosphate (RuBP), a five carbon sugar, in a carboxylation reaction. The reaction is catalysed by the enzyme ribulose biphosphate carboxylase, usually called rubisco. Large amounts of rubisco are present in the stroma, because it works rather slowly and the reaction that it catalyses is a very important one.

Front 16

How does carbon dioxide enter the chloroplast?

Back 16

diffusion.

Front 17

How many carbons are in ribulose biphosphate (RuBP)?

Back 17

Five carbons

Front 18

What is the product of carbon fixation?

Back 18

The product of the reaction is a six-carbon compound, which immediately splits to form two molecules of glycerate 3 phosphate. This is therefor ethe first product of carbon fixation.

Front 19

How does regeneration of RuBP work in the light-independent steps?

Back 19

For carbon fixation to continue, one RuBP molecule must be produced to replace each one that is used. Triose phosphate is used to regenerate RuBP. Five molecules of triose phosphate are converted by a series of reactions into three molecules of RuBP. This process requires the use of energy in the form of ATP.
For every six molecules of triose phosphate formed in the light-independent reactions, five must be converted to RuBP.

Front 20

How does synthesis of a carbohydrate work in the light-independent steps?

Back 20

Glycerate 3-phosphate, formed in the carbon fixation reaction, is an organic acid. It is converted into a carbohydrate by a reduction reaction. Hydrogen is needed to carry out this reaction and is supplied by NADPH. Energy is also needed and is supplied by ATP. NADPH and ATP arep roduced in the light-dependent reactions of photosynthesis. Glycerate 3-phosphate is reduced to a three-carbon sugar, triose phosphate (TP). Linking together two triose phosphate molecules together produces glucose phosphate. Starch, the storage form of carbohydrate in plants, is formed in the tstroma by condensation of many molecules of glucose phosphate.

Front 21

Explain the relationship between the structure of a chloroplast and its function.

Back 21

Thylakoids have a large surface area for light absorption.
The small space inside thylakoids allows for accumulation of protons.
The fluid in the stroma allows for enzymes of the Calvin Cycle.

Front 22

Draw the action spectrum of photosynthesis.

Back 22

http://www.cartage.org.lb/en/themes/sciences/BotanicalSciences/Photosynthesis/Photosynthesis/absorspect.gif

*i do not own this picture.
-notice that it starts from 400. Your IB Book has a better diagram on page 77.

Front 23

Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants.

Back 23

The action spectrum of photosynthesis is explained by considering the light-absorbing properties of the photosynthetic pigments. Most pigments absorb some wavelengths better than others. The figure (pg. 77) shows the percentage of the wavelengths of visible light that are absorbed by two common forms of chlorophyll. This graph is called the absorption spectrum of these pigments. The graph shows strong similarities with the action spectrum for photosynthesis.
-the greatest absorption is in the violet-blue range.
-there is also a high leel of absorption in the red range of the spectrum.
-There is least absorption in the yellow-green range of the spectrum. most of this light is reflected.
THere are some differences between the action spectrum and the absorption spectra. Whereas little light is absorbed by chlorophylls in the green to yellow range there is some photosynthesis. This is due to accessory pigments, including xanthophylls and carotene, which absorb wavelengths that chlorphyll cannot.

Front 24

Explain the concept of limiting factors with reference to light intensity, temperature and concentration of carbon dioxide.

Back 24

Light intensity, carbon dioxide concentration and temperature are three factors that can determine the rate of photosynthesis. If the level of one of these factors is changed, the rate of photosynthesis changes. Usually, only changes to one of the factors will affect the rate of photosynthesis in a plant at a particular time. This is the factor that is nearest to its minimum and is called the limiting factor. changing the limiting factor increases or decreases the rate, but changes to the other factors have no effect. This is because photosynthesis is a complex process involving many steps. The overall rate of photosynthesis in a plant is determined by the rate of whichever step is proceeding most slowly at a particular time. This is called the rate-limiting step. The three limiting factors affect different rate-limiting steps.

Front 25

Explain the effect of light intensity on the rate of photosynthesis

Back 25

At low light intensities, there is a shortage of products of hte light-dependent reactions-NADPH and ATp. The rate -limiting step in the calvin cycle is the point where glycerate 3-phosphate is reduced. At high light intensities osome other factor is limiting. Unless a plant is heavily shaded, or the sun is rising or setting, light intensity is not usually the limiting factor.

Front 26

Explain the effect of carbon dioxide concentration on the rate of photosynthesis

Back 26

At low and medium CO2 concentrations, the rate-limiting step in the calvin cycle is the point where CO2 is fixed to produced glycerate 3-phosphate. RuBP and NADPH accumulate. At high CO2 concentrations some other factor is limiting.
Becase the level of carbon dioxide in the atmosphere is never very high, carbon dioxide is often the limiting factor.

Front 27

Explain the effect of temperature on the rate of photosynthesis

Back 27

At low temperatures, all of the enzymes that catalyse the reactions of the Calvin Cycle work slowly. NADPH accumulates.
At intermediate temperatures, some other factor is limiting.
At high temperatures, RuBP carboxylase does not work effectively, so the rate lmiting step in the calvin cycle is the point where carbon dioxide is fixed. NADPH accumulates.