• View

  • Download

Embed Size (px)

Text of Photosynthesis


Firas Corri

Photosynthesis : an overviewMethods of feeding in living organisms :1. Autotrophs : can make their food from simple materials ( i.e : plants ) 2. Heterotrophs : can`t make their own food ( i.e : animals ).

PhotosynthesisThe process of using sun light to build up complex substances from simpler ones. ( making food by using light ).

Photosynthesis need an external source of energy?Because its an endergonic reaction.

Equation of photosynthesis :Carbon dioxide + Water 6CO2 + 12H2O Sugar + Oxygen C6H12O6 + 6O2 + 6H2O2. carbon dioxide 4. chlorophyll. 2. oxygen.

Photosynthesis needs :

1. water 3. sunlight

Photosynthesis produces : 1. sugars

The site of photosynthesis- The main site of photosynthesis is the leaf. - Any green part of the plant can carry photosynthesis, because they contain chloroplast. Structure of the chloroplast :Chloroplast envelope : permeable to glucose, O2, CO2 and some ionsInner membrane Outer membraneThylakoid membranes : site of light-dep. Rxns.

Granum :A stack of thylakoid membranes

Ribosomes Lipid droplets Store energy Starch grains insolube storage carbohydrate

Stroma : Matrix of chloroplast ( site of the light-dep. Rxns )

Thylakoid space : the space inside The thylakoid membrane.

Photosynthetic pigments

Electromagnetic spectrumSun emits different types of radiations, these radiations :-

Travels in the space in the form of rhythmic waves. Have different wavelengths and energy. Together known as electromagnetic spectrum.

The following figure shows the components of electromagnetic spectrum :

Visible light : is the part of electromagnetic spectrum that can be seen by the eye

What happen when the sun light fall on a plant?

Pattern of absorption-reflection depends on the pigments the plant contain. Why do plants appear green? Because pigments inside the plant ( mostly chlorophyll ) reflect green and absorb other colours.

Photosynthetic pigmentsChlorophyll a Is the most important pigment in plants because : it is the only one that takesa direct part in photosynthesis.

accessory pigments do not participate directly in the light dep. reactions. But : borden the range of light the plant can use ( absorb light outside the range of chlorophyll-a and convey the energy to chlorophyll-a )

Accessory pigment Other chlorophylls Carotenoids Phaeophytin

Example Chl.b Carotenes, xanthophylls

colour Green - yellow Orange, yellow, brown grey

Note : none of the accessory pigments absorbs well in the green-yellow area.

Structure of chlorophyll-aChlorophyll consists of two parts :1. Porphyrin ring ( with Mg atom at the center). 2. Hydrocarbon chain

Absorption spectrum of chlorophyllAbsorption spectrum : is a graph showing the absorption of a pigment over a range of wavelengths of light. How does it measure ?


Chlorophyll sample

Chlorophyll-a absorbs light mainly in : the red-orange and blue-violet parts but little in the green part.

Action spectrumAction spectrum : is a graph showing the rate of photosynthesis over a range of wavelengths of light.

Comparing the absorption spectrum of chl. a and the action spectrum of the photosynthesis.

Rate of photosynthesis Absorption of chl.a

Compare the combined absorption spectrum of all photosynthetic pigments and the action spectrum of the photosynthesis. What you conclude?

1. The absorption spectrum of the combined photosynthetic pigments in a plant coincides very closely with the action spectrum of photosynthesis for that plant. 2. This support that these pigments harvest light for photosynthesis.

How do the photosynthetic pigments found in the chloroplast?

They found in the thylakoid membrane as clusters called photosystems. Every photosystem consists of :1. antenna complex : group of accessory pigments that gather light energy and channel it to chl-a. 2. Chlorophyll-a : gather energy and donate electrons. 3. Primary electron acceptor : accepts electrons from chl-a.

Together chl-a that donate the e- and the primary electron acceptor known as : the reaction center.

Photosystem : is the light harvesting unit of the chloroplast.

Light energy is harvested by the antenna complex and channeled to the chl-a at the reaction center.

How chlorophyll harnesses energy from sunlight?When the photosynthetic pigment absorbs the light energy : One of the pigments electrons gains the energy and excited ( raised from the ground state to a higher excited state ) In the test tube : This electron goes back to the ground state and lose energy in the form of heat and light. In the chloroplast : The excited electron is passed on to another molecule ( primary electron acceptor ) the chlorophyll is oxidized the acceptor is reduced