Photosynthesis

Firas Corri

Photosynthesis

Methods 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 Sugar + Oxygen 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O

Photosynthesis needs : 1. water 2. carbon dioxide

3. sunlight 4. chlorophyll.

Photosynthesis produces : 1. sugars 2. oxygen.

Photosynthesis : an overview

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 ions

Granum :A stack of thylakoid membranes

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

Thylakoid membranes : site of light-dep. Rxns.

Ribosomes

Lipid droplets Store energy

Starch grains insolube storage carbohydrate

Thylakoid space : the space insideThe thylakoid membrane.

Inner membrane Outer membrane

Photosynthetic pigments Electromagnetic spectrum

Sun 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 pigments

Chlorophyll a accessory pigments

Is the most important pigment in plants do not participate directly in the

because : it is the only one that takes light dep. reactions. But : borden

a direct part in photosynthesis. 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 Example colour

Other chlorophylls Chl.b Green - yellow

Carotenoids Carotenes, xanthophylls Orange, yellow, brown

Phaeophytin grey

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

Chlorophyll consists of two parts :

1. Porphyrin ring

( with Mg atom at the center).

2. Hydrocarbon chain

Structure of chlorophyll-a

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

filter Chlorophyllsample

Action spectrumAction spectrum : is a graph showing the rate of photosynthesis

over a range of wavelengths of light.

Rate ofphotosynthesisAbsorption of chl.a

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

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.

They found in the thylakoid membrane as clusters called photosystems. Every photosystem consists of :

How do the photosynthetic pigments found in the chloroplast?

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.

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 : In the chloroplast :This electron goes back to the The excited electron is passed ground state and lose energy on to another molecule in the form of heat and light. ( primary electron acceptor )

the chlorophyll is oxidized the acceptor is reduced

How chlorophyll harnesses energy from sunlight?

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