Photosynthesis

 

WHAT IS PHOTOSYNTHESIS

DEFINITION

Photosynthesis is defined as *The  process by which  green plants prepare there food by using carbon dioxide (CO2) and water (H2O) in the presence of sunlight and photosynthetic pigments(carotenoids and chlorophyll).

Photosynthesis is a redox reaction means molecule oxidized and reduced respectively.

Photosynthesis ocuurs in green plants,bacteria and in some protists like algae etc.

It is energy storing process.

Autotropic organisms(which make their own food) carry out photosynthesis to make organic food molecule to fulfill their energy requirements.

Overall photosynthesis reaction:

6CO2 + 12 H20 + sunlight+photosynthetic pigments = C6H1206 (GLUCOSE)(product) + 6H2O(Regenerated by product) + 6O2 ( By product).

It is a redox reaction.

The water and carbon dioxide are reactants while glucose and oxygen are products.

In this reaction Carbon dioxide reduced to sugar.

While water is oxidized to by products oxygen.

REQUIREMENTS FOR PHOTOSYNTHESIS:

For organism to prepare food through photosynthesis reaction they require four important things which are given below;

1-Sunlight

2-Carbon dioxide

3-Water

4-Photosynthetic pigments ( Carotenoids and chlorophyll).

Now we will explain in detail the role of these four things in photoyntesis.

1-ROLE OF SUNLIGHT IN PHOTOSYNTHESIS:

Sunlight is the main source of energy maintaining all life forms on Earth.

Sunlight is the kind of energy travels in form of electromagnetic waves of different wavelengths.

The sunlight act as beam of particles of different wavelengths and frequencies also called as PHOTONS.

There is a wide range of sunlight wavelngths for making organic food molecule ranging from gamma rays(most energetic ) to radio waves (less energetic).

Wavelength and energy of light are inversely proportional it means like the wave which has more wavelength will be less energetic.

The portion of sunlight which is best for use in photosynthesis is called as visible spectrum having wavelength ranges from 390nm to 760 nm.

WHY PLANTS NOT USE UV RAYS

Plants donot use uv portion of sunlight because it is so energetic and can destroy plants cells so visible spectrum is less energetic than uv rays and it is good to be use in photosynthetic reaction instead of Uv rays.

About forty percent sunlight enters into atmosphere but plants capture only 1 % of sunlight for photosynthetic reaction.

Visible spectrum has right amount of energy to be absorbed by photosyenthetic pigments for photosynthesis.

Visible spectrum reflects seven lights of different wavelength,energy,frequency and wavelength.

          VIOLET  (390-420nm)(most energetic)(short wavelength)

          INDIGO (420-460nm)

         BLUE(460-510nm)

          GREEN(510-580nm)

        YELLOW (580-600nm)

        ORANGE (600-630nm)

         RED      (630-760nm) (less energetic)(longer wavelength)

2-ROLE OF CARBON DIOXIDE IN PHOTOSYNTHESIS:

Carbon dioxide is one of the raw material of the photosynthetic reaction where it act as a carbon source for the synthesis of organic compounds in photosyntheis.

Air contains about 0.03-0.04 % of carbon dioxide.

Plants are called as autotrophs because they use low energy inorganic compound carbon dioxide for synthesis of high energy organic compound Glucose (carbohydrate) by their own.

Carbon dioxide act as reactant in photosynthetic reaction and reduced into organic food molecule glucose by reduction process.

Photosynthesis process increase by increasing carbon dioxide concentration but upto 1% limit.

If carbon dioxide concentration increases from 1 % then photosynthesis process slow down because of stomatal closing.

3-ROLE OF WATER (H2O) IN PHOTOSYNTHESIS:

Water is one of the raw material important for photosynthetic reaction.

Water act as reactant in photosynthetic reaction.

It also act as Hydrogen and electron donor in photosynthesis.

During light reaction of photosynthesis water molecules breakdown this process is called photlysis and release two electrons which compensate the photo excited electrons lost by the chlorophyll a molecule present in the reaction center of photosystem PS-2 (680nm).

water oxidized into by product oxygen through oxidation confirmed by vein neil in 1930 and supported by robert hill in 1937.

4-ROLE OF PHOTOSYNTHETIC PIGMENTS IN PHOTOSYNTHESIS:

Photosynthetic organisms contain different pigments which absorb sunlight.

What is pigment:

Pigment is any substance which absorb sunlight energy for use in food synthesizing process.

Algae and bacteria has different type of pigments than higher plants.

In bacteria photosyenthetic pigments present in cytoplasm while in higher plants they are embedded in thalakoid membrane within chloroplast.

Higher plants has two type of photosynthtic pigments which are explained below:

1- CHLOROPHYLL:

The type of pigment embedded in thylakoid membrane of chloroplast which capture visible portion of sunlight and prepare food.

There are various type of chlorophylls

    Chlorophyll a  present in all green plants.

    Chlorophyll b present in all higher plants and algae.

    Chlorophyll c,d,e present only in algae.

    Bacteriophyll present only in bacteria.

Chlorophyll mostly absorb violet, blue ,red and orange light and reflects green light therefore leaves appears green in colour.

Higher plants have two type of chlorophyll.

Chlorophyll a having methyl group its formula is C55H72O5N4Mg

Chlorophyll b having carbonyl group its formula is C55H70O6N4Mg

Structure of chlorophyll:

Its having two parts:

Head part: It contain central magnesium atom sorrounded by four nitrogen rings (pyrole rings) .There four rings collectively called as porphyrin ring.

This part is hydrophilic (water loving).

This part lies on surface of thylakoid membrane.

Tail part: This part contain long hydrocarbon chain called as phytole chain which is hydrophobic (water hating).This part is embedded in thylakoid membrane.

2-CAROTENOIDS:

It is also photosynthetic pigment.

It is lipid in nature.

It is also called as accesory pigments because it capture light first then it transfer it to chlorophyll b and then chlorophyll a.

It includes carotenoids and xynthophylls.

It is usually brown,yellow,orange and red in colour.

They convert low intensity light into higher intensity but it inverse is not possible.

They also protect chlorophyll from oxidation by oxygen (produce during photosynthesis).

IMPORTANT MCQS IN THIS TOPIC:

1-During photosynthesis carbon is oxidized or reduce:

Answer: REDUCED

2-Photosynthetic pigments present in _in bacteria:

Answer: CYTOPLASM

3-The photosynthetic pigments capture _portion of sunlight:

Answer: VISIBLE SPECTRUM (390-760nm)

4-The life on earth possible because of _electrons:

Answer: 2 electrons

5-_is the regenrated by product in photosynthesis:

Answer: WATER

6-Carbon dioxide is reduced in _phase of photosynthesis:

Answer: DARK REACTION (CALVIN CYCLE)

7-_% carbon dioxide present in atmosphere:

Answer: 0.03-0.04

8-Chlorophyll a has _functional group:

Answer: METHYL GROUP (CH3)

9-The formula of chlorophyll b is :

Answer: C55H70O6N4Mg

10-The chlorophyll has _central atom:

Answer: MAGNESIUM AS A CENTRAL ATOME

11-Chlorophyll b is present in:

Answer: ALGAE AND PLANTS

12-Photosynthesis energy _process:

Answer: CONSERVATION OR STORING

IN SHA ALLAH NEXT BLOG WILL BE ON LIGHT DEPENDENT REACTION.

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