UNIT 1:Photosynthesis Process of food production by plants

What is photosynthesisThe process that occurs in green plants whereby

solar energy is converted into chemical energy and stored as organic molecules by making use of carbon dioxide, sunlight and water

Water and oxygen are formed as byproductsEquation for photosynthesis 6 CO2 + 12 H2O + Light energy

C6H12O6 + 6 O2 + 6 H2O (glucose)

Who or what can photosynthesizePhotoautotrophs can photosynthesizeIt include: green plants, cyanobacteria ,algae

and green protists

Why do plants photosynthesizeTo provide nutrients and oxygen for

heterotrophs.Heterotrophs are dependent on autotrophs,

because they cannot produce their own food

What part of the plants is responsible for photosynthesisPhotosynthesis occurs in the chloroplasts of

plants cellsThe chloroplasts are mainly concentrated in

the mesophyll cells of leavesChloroplasts contain chlorophyll- green

pigment that absorbs sunlight.Chlorophyll fill the space in the thylakoid

membrane

Raw materials of photosynthesis

Carbon dioxide water sunlight

How raw materials reach the chloroplastsWater is absorbed through the root hair into

the xylem of the roots, into the xylem of the stem, through the xylem of the leaves into the mesophyll cells and finally into the chloroplasts

Carbon dioxide diffuses from the atmosphere through the stomata, into the intercellular airspace in the leaves, and finally into the chloroplasts of the mesophyll cells

Raw materials' continuesThe chlorophyll and other pigment in the

thylakoid membrane absorb the solar energy to drive photosynthesis

Photosynthesis consists of 2 stagesLight reaction phase ( dependent on light)Dark phase/ Calvin cycle ( light

independent)

Light reaction phaseTakes place in the thylakoid membrane of

the chloroplasts.Chlorophyll absorbs solar energy from the

sun When an chlorophyll pigment absorbs light

energy, it excites the electrons, which goes from ground state to an excited state, which is instable, but can be used as potential energy

when unused excited e-fall back to the ground state, and heat are given off

Light phase continueThe electrons are excited in the photosystems

fount in the thylakoid membraneThis potential energy is then used firstly to

spilt water- into hydrogen and oxygen2H2O 2H2 + O2

Light phase continueOxygen is released as a byproduct- diffuse

through stomata into atmosphereThe hydrogen reduces NADP+ to NADPH Some energy is then used to

photophosphorylation ADP to generate ATP

ADP + P ATP

Calvin cycleCarbon dioxide diffuses through the

stomata of the leaves and finally into the stroma of the chloroplast

The carbon dioxide is accepted by a 5c molecules called ribulose biphosphate ( RuBP) which then forms an unstable 6c compound

6c compound dissociates into 2 x 3c compounds called phosphoglycerate ( PGA)

continuesPGA is then reduced to

phosphoglyceraldehyde (PGAL/G3P) by accepting a phosphate from ATP and a hydrogen electron from NADPH.

Thus changing ATP back to ADP and NADPH to NADP.

PGAL are now used for the following reactions:Some PGAL are used to make RuBP again,

so that cycle can start over againSome PGAL are used to form hexose sugars

like glucose and fructose. Which combine to form disaccharides and polysaccharides.

The carbohydrates can then be converted to other biological compounds like proteins or fats by adding mineral salts like nitrates and phosphates

Dark phase

How photosystem harvest lightThe thylakoid membrane of a chloroplasts

contain several photosystemsA photosystem consist of a protein complex

called a reaction- center complex surrounded by several light harvesting complexes

Study the diagram to understand the process of light harvesting

By MRS. T.J MkhizeGrade 10 Life science