Photosynthesis Photosynthesis, Transpiration, and Surface ...
Photosynthesis
Transcript of Photosynthesis
PhotosynthesisPhotosynthesis
Photosynthesis
Method of converting sun energy into chemical energy usable by cells
done by autotrophs takes place in specialized
structures inside plant cells called chloroplasts
1. Capturing light energy2. Using captured energy to make ATP and NADP+
(energy carrying co-enzyme like NAD. It is reduced by 2 H atoms to NADPH+ + H+)
3. Using ATP and energy from NADPH to synthesize molecules like glucose.
first 2 steps require sunlight (light dependant) and occur in chlorophyll
last step does not necessarily need sunlight (light independent) and takes place in stroma
3 Steps of Photosynthesis
Light-Dependent Phases
occurs in thylakoid membrane light energy converted to chemical energy of
ATP & NADPH (reduced NADP = NADPH) photosystems (highly organized light capturing
complexes) are found in thylakoid membranes and made of 2 parts:
antenna complex – system of chlorophyll molecules and pigments that transfers energy to reaction centre
reaction centre – protein complex containing chlorophyll a that absorbs energy from antenna complex and raises it to high energy level to start photosynthesis
there are 2 kinds of photosytems (I and II) depending on which wavelength of light chlorophyll a absorbs
Steps in Light Dependent Reactions
1. Photoexcitation: Sunlight hits leaf and some energy passes into stroma
then absorbed by antenna complex of photosystem II and passed along to chlorophyll a.
2. Electron Transport: An electon gets boosted to a higher level and passed
along a ETC (like in cellular respiration) in thylakloid membrane.
This energy boost also causes H2O to split which releases H+ ions and O2 which is vital to other living things.
e- passes through several carriers via redox reactions releasing energy as they pass through the proteins. H+ ions are pumped from stroma into intermembrane space which creates electrochemical gradient.
3. Chemiosmosis: H+ ions move through ATPase complex back into stroma
converting ADP to ATP a process called photophosphorylation. It takes 4 H+ to make 1 ATP.
At same time light of a different wavelength is also striking photosystem 1. e- from P1 pass through another ETC, then move to enzyme NADP reductase that reduces NADP to NADPH which moves to Light Independent Phase.
Reactants: H2O, sunlight
Products: ½ O2, NADPH, ATP
YouTube - Light (Dependant) Reactions of Photosynthesis Animation
2. Light Independent Reactions (the Calvin Cycle)
ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.
called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)
occur in stroma don’t require light also known as C3 Cycle
Steps in Light Independent Phase:
1. Carbon Fixation CO2 molecule combines with 5C molecule called
RuBisCO (ribulose biphosphate) to produce 2, 3C molecules called 3-PGA (3-phosphoglycerate).
2. Reduction Reactions 3-PGA phorphorylated by ATP then reduced by NADPH
to produce G3P (glycerate 3-phosphate).3. RuBisCO Regeneration G3P phosphorylated by ATP to re-create RuBisCO to
restart the cycle. For every 2 G3P, 1 molecule glucose is removed from cycle, so need 6 CO2 to create 1 glucose.
Other Methods of Carbon Fixation
Type of carbon fixation
Stomata open
Advantages Examples
C3 dayUses fewer
ATPMost plants
C4day Faster
photosynthesisCorn, sugar
cane, grasses…
CAMnight Water
efficiency
Succulents, cacti, orchids, pineapple…