Short notes on Edexcel A2 Biology - Part 1

5.1 Photosynthesis

Thylakoids

• (made of) membranes ;
• (arranged as) {stacks / grana / eq} ;
• contain {pigment / chlorophyll} / eq ;
• (arranged as) quantasomes / photosystems ;

Advantage of growing crop in glasshouse rather than open field

• crops can be grown {out of season / all year round} / eq ;
• plants photosynthesise 24 hours a day / eq ;
• idea of less physical damage from {weather /animals / eq} ;
• pest control easier / eq ;
• ref to control of other named factor, eg CO2, temperature, humidity, water supply ;

Difference between abiotic and biotic factors

ref to biotic factors involve {organisms / living} abiotic are {physical / chemical / non-living} (factors) / eq ;

Using quadrat to obtain mean density of two species in an ecosystem

• ref to {several / many / more than 2} readings ;
• ref to use of random quadrat positions ;
• description of suitable process to give random positions / eq ;
• ref to {known / stated} area of quadrat ;
• number of individuals in each quadrat {counted/ recorded} / eq ;
• description of how mean density calculated using total count e.g. total number (of each species) divided by total area sampled ;

Reasons for not using all the light hitting the surface of a leaf is not used

• idea of reflection ;
• reference. to {incorrect / eq } {wavelength / colour / frequency} ;
• idea of {not hitting the {chloroplast / chlorophyll}} / it is transmitted ;
• idea of light being in excess e.g. at max. photosynthesis so more light can be used ;

Light dependant stage of photosynthesis (also see A2 revision guide page 9)

• reference to {thylakoids / thylakoid (membranes)} ; in {granum / grana} ;
• (light energy) raises energy level of electrons / {chlorophyll / electrons}excited / eq ;
• electrons released from {chlorophyll /photosystem / eq} / eq ;
• reference to electron {carrier / eq} ;

reference to series of {redox / oxidation & reduction / eq} reactions ;

• reference to energy level of electrons {falls / eq} ;
• reference to {synthesise ATP from ADP +P /phosphorylate ADP} ;
• reference to photophosphorylation ; reference to ATP {synthetase / synthase /ase} ;
• reference to {chemiosmosis / eq} ;
• idea of electrons from {photolysis / eq} used to replace those lost ;
• reference to involvement of {accessory pigments / named example} ;

Production of oxygen in light-dependent reaction of photosynthesis

• reference to energy from light ;
• reference to photolysis ;
• of water ;

Structure of chloroplast involved in ATP formation

• reference to {granum / grana} ;
• reference to (a granum is) a stack of {thylakoids / membranes} OR grana are connected by lamellae ;
• reference to (thylakoids contain) {electron carriers / eq} / chlorophyll / photosystems ;
• reference to (membranes contain) {ATPase / ATPase channel} ;
• idea that {electron carriers / ATPase /eq} are associated with {thylakoid / thylakoid membranes} ;

Why can't light independent stage of photosynthesis occur without light dependant stage

• idea that products of light- dependent stage are {needed for / used in / eq} {light-independent stage / Calvin cycle} ;
• reference to (products of light- dependent stage) are {reduced NADP / eq} and ATP ;
• reference to use of {reduced NADP / eq} for {reduction / eq} of {carbon dioxide / GP / eq} ;
• reference to use of ATP as source of energy ;

Importance of thin lamina in leaves

• idea of {fast / maximum} {gas exchange / uptake of carbon dioxide / eq};
• idea of penetration of light ;
• idea that carbon dioxide is used in the {light-independent stage / Calvin cycle / formation of GP}; OR
• idea that light is used in {light-dependent stage / photolysis / photophosphorylation /eq } ;

Importance of midrib in leaves

• transport (in xylem) of water (to the leaves) / eq ;
• transport (in phloem) of {sucrose / sugar / carbohydrates } (away from the leaves) / eq;
• (water) for {light-dependent reaction / photolysis / source of hydrogen (ions)}; OR
• idea of (transporting sugar) to make more room for more carbohydrate synthesis ;

How GALP is used to synthesise cellulose

• GALP is a 3C molecule / eq ;
• reference to conversion (of GALP) to glucose / eq;
• idea of enzymes involved in the synthesis of {glucose / cellulose} ;
• (which is) β glucose ;
• reference to formation of glycosidic bonds ;
• between C1 and C4 / these bonds are 1-4 (glycosidic bonds) ;
• by condensation ;
• reference to {straight / unbranched} (chains of glucose) ;
• reference to cellulose as a {polysaccharide / polymer of glucose / eq} ;

How GP is used to synthesise starch

• idea of conversion of GP to GALP / eq ;
• using ATP and reduced NADP / eq ;
• idea of conversion (of GALP) to {glucose /hexose} eq ;
• (which is) α glucose ;
• reference to formation of glycosidic bonds ;
• these bonds are 1-4 and 1-6 (glycosidic bonds)/ eq ;
• by condensation ;
• ref to amylose and amylopectin ;
• credit details of amylose e.g. straight chain, 1-4 bonds ;
• credit details of amylopectin eg branched, 1-4 and 1-6 bonds ;