3.5.1 photosynthesis//

AQA A level biology 3.5.1 photosynthesis

equation for photosynthesis

H2O + 6CO2 → C6H12O6 + 6O2

photosynthesis definition

process where energy form light is used to make glucose from water and carbon dioxide

* energy stored as glucose and released by respiration.
* example of a metabolic pathway

aerobic respiration

respiration using oxygen

anaerobic respiration

respiration without oxygen

products of anaerobic respiration in plants and animals

* plants- ethanol and carbon dioxide
* animals- lactate

atp

adenosine triphosphate

* base- adenine
* ribose sugar
* 3 phosphate groups

how is ATP synthesised

* via a condensation reaction between ADP and an inorganic phosphate
* energy then stored as chemical energy in the phosphate bond
* enzyme- ATP synthase

(catalyses reaction)
* AKA phosphorylation

how is ATP hydrolysed

* via a hydrolysis reaction
* ADP and inorganic then recycled and used again

ATPs properties (that makes it good energy source)

* small, soluble molecule therefore easily transported around cell
* easily broken down therefore energy release is instantaneous
* can be quickly remade
* cant pass out the cell, so cell always has immediate supply of energy

compensation point

* the particular level of light intensity at which the rate of photosynthesis matches rate of respiration

where does photosynthesis take place

in the chloroplasts of the cell

what are chloroplasts

* small flattened organelles surrounded by a double membrane
* contain thylakoids (stacked into grand)
* grant linked together by lamellae (thylakoid membrane)
* contain photosynthetic piglets (in thylakoid membrane) attached to protein (both called a photosystem)
* stroma- in inner membrane (contains enzymes, sugars an organic acids) stores starch grains

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photosystems and which light energy they absorb

* photosystem I - 700 nm
* photosystem II - 680 nm

redox

* if reduced, gains electrons
* if oxidised, loses electrons

what is a coenzyme

* a molecule that aids an enzyme
* how it works- transfers a chemical group from 1 molecule to another
* in photosynthesis- NADP (transfers hydrogen and can therefore reduce)

the light-dependant reaction

* takes place in thylakoid membrane
* light energy absorbed by chlorophyll in photosystems.
* electrons released from chlorophyll (due to light energy) - process called photoionisation and is therefore positively charged
* some energy from released e- is used to phosphorylate ADP, some used to reduce NADP from NADPH
* ATP transfers energy and NADPH transfers H to the light independent reaction
* H20 oxidised to O2
* includes cyclic and non cyclic photophosphorylation

the light-independent reaction

* takes place in stroma
* ATP and NADH (from light dependent reaction) supply energy and hydrogen to make glucose from CO2

what energy from light-dependent reaction is used for

* making ATP from ADP and inorganic phosphate
* making reduced NADPH
* photolysis- splitting water into protons, electrons and oxygen

products from non-cyclic photophosphorylation

* produces ATP, NADPH and oxygen

process of non cyclic photophosphorylation

1. light energy excites electrons in chlorophyll
2. photolysis of water produces H+, e- and O2
3. energy from excited e- makes ATP
4. energy from excited e- generates NADPH

chemiosmotic theory

the process of e- flowing down the electron transport chain and creating a H= gradient across the membrane to drive ATP synthesis.

products of cyclic photophosphorylation

* produces ATP and only uses PSI
* only makes a small amount of aTO

the Calvin cycle

* AKA light independent reaction
* makes 2x triose phosphate from CO2 and ribulose phosphate

process of the Calvin cycle

1. *forms glycerine 3-phosphate- (*CO2 enter leaf through stomata and diffuses into stroma, then combines with ribulose diphosphate (RUBP). )

* reaction catalysed with enzyme rubisco
* 2x 3C compound called glycerate 3-phosphate


2. *formation of triose phosphate*-

* products- 2x ATP →2 ADP+Pi, 2x NADPH→NADP


3. regeneration of RiBP
4. turns 6 times to make 1 hexose sugar

optimum conditions for photosynthesis

* high intensity of a certain wavelength
* temperature around 25°
* carbon discoid at 0.4%
* water- need constant supply