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Photosynthesis and cellular respiration
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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