Photosynthesis Flashcards
what is the light energy in photosynthesis used for
to split strong bonds in water molecules (H2O), releasing hydrogen and oxygen
what is the waste product when splitting water molecules
Oxygen is released into the atmosphere as a waste product
state some reasons why organisms may need a constant supply of energy
To move substances across cell membranes in active transport or to move substances within cells
For muscle contraction
structure of ATP
type of nucleic acid
It is a phosphorylated nucleotide
consists of a nitrogenous base, a sugar, and three phosphate group hence triphosphate
what does the breakdown of glucose in respiration release
energy needed to phosphorylate ADP
what does the hydrolysis of ATP release
inorganic phosphate as well as a small amount of energy which can be used by the cell
ATP –> ADP + Pi
what is the removal of a phosphate group called and what is it catalysed by
dephosphorylation
catalysed by the enzyme ATPase
what 2 processes can ATP go through
is formed during respiration and can be hydrolysed to release energy for processes such as active transport, muscle contraction, and building new molecules
what is each chloroplast surrounded by
double-membrane known as the chloroplast envelope
Each of the envelope membranes is a phospholipid bilayer
what are chloroplast filled with
cytoplasm-like fluid known as the stroma
what does the stroma contain
enzymes and sugars, as well as ribosomes and chloroplast DNA
describe membrane system in the stroma
flattened fluid-filled sacs known as thylakoids, each surrounded by a thylakoid membrane
Thylakoids stack up to form structures known as grana
Grana are connected by membranous channels called lamellae which ensure the stacks of sacs are connected but distanced from each other
state the structures of a chloroplast
Chloroplast envelopes
Stroma
DNA
Ribosomes
Thylakoid membrane
Grana
Photosystems
function chloroplast envelope
double membrane encloses the chloroplast, keeping all of the components needed for photosynthesis close to each other
The transport proteins present in the inner membrane control the flow of molecules between the stroma and cytoplasm
function of stroma
The gel-like fluid contains enzymes that catalyse the reactions of photosynthesis
function of DNA in chloroplast
genes that code for some of the proteins used in photosynthesis
function of ribosomes in chloroplast
enable the translation of proteins coded by the chloroplast DNA
function of grana
large surface area, maximising the number of photosystems and allowing maximum light absorption
(granum) is formed from many layers of thylakoid membranes to increase surface area (for absorbing light)
thylakoid membranes contain chlorophyll to absorb light
electron carrier molecules in thylakoid membrane involved in ATP production
what does a photosystem do
absorbs light of a different wavelength, maximising light absorption
where does the light dependent reaction take place
across the thylakoid membrane
where does the light independent reaction take place
in the stroma
what enables the splitting of water molecules
Light energy in the light-dependent reactions in a reaction known as photolysis
what does photolysis produces
The hydrogen ions and electrons are used during the light-dependent reactions while the oxygen is given off as a waste product
2 hydrogen ions (2H+), also known as protons
2 electrons (2e-)
One atom of oxygen (O)
what process occurs in the light dependent reaction
light energy is converted into chemical energy in the form of ATP and reduced NADP
what is NADP
coenzyme; its role is to transfer hydrogen from one molecule to another
When NADP gains hydrogen, it is reduced and can be known as either reduced NADP or NADPH
how can NADPH reduce other molecules
by giving away hydrogen
what are the useful products of the light dependent reaction
ATP and NADPH transferred to the light-independent reactions within the chloroplast
what is photophosphorylation
photo = light
the addition of phosphate; in this case to ADP to form ATP
utilizing light energy from photosynthesis to convert ADP to ATP
what does non cyclic photophosphorylation produce
This produces both ATP and NADPH
what does Cyclic photophosphorylation produce only
This produces ATP only
describe electron transport chain
Electrons pass from one protein to another along the electron transport chain, releasing energy as they do so
what is chemiosmosis
The energy released as electrons pass down the electron transport chain is used to produce ATP
explain non cyclic photophosphorylation
also explain what happens to the H+ ions as electrons passed down
Light energy hits photosystem II in the thylakoid membrane
Two electrons gain energy and are said to be excited to a higher energy level
The excited electrons leave the photosystem and pass to the first protein in the electron transport chain
the electrons pass down the electron transport chain
Energy is released as the electrons pass down the electron transport chain which enables chemiosmosis to occur
H+ ions are actively pumped from a low concentration in the stroma to a high concentration in the thylakoid space
H+ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane
The movement of H+ ions causes the ATP synthase enzyme to catalyse the production of ATP
At the end of the electron transport chain the electrons from photosystem II are passed to photosystem I
Light energy also hits photosystem I, exciting another pair of electrons which leave the photosystem
The excited electrons from photosystem I also pass along an electron transport chain
electrons combine with hydrogen ions from the photolysis of water and the coenzyme NADP to form NADPH
The reduced NADP and the ATP pass to the light-independent reactions
Explain cyclic photophosphorylation
same as non cyclic
Light hits only photosystem I
At the end of the electron transport chain the electrons rejoin photosystem I in a complete cycle; hence the term cyclic photophosphorylation
The ATP produced enters the light-independent reaction
what does the light independent reaction produce
Starch for storage
Sucrose for transport
Cellulose for making cell walls
what does light independent reaction require
ATP and reduced NADP from the light-dependent reactions
3 steps of light independent reaction
1) Carbon dioxide is combined with RuBP a 5-carbon (5C) compound; this yields two molecules of GP a 3-carbon (3C) compound
2) GP is reduced to (GALP), another 3C compound, in a reaction involving reduced NADP and ATP
3) RuBP is regenerated from GALP in reactions that use ATP
explain step 1 : Carbon dioxide and RuBP are combined
Carbon dioxide combines with a 5C sugar known as RuBP in a reaction catalysed by the enzyme rubisco
The resulting 6-carbon (6C) compound is unstable and splits in two
This results in two molecules of a 3C GP
explain step 2 : Reduction of GP
Energy from ATP and hydrogen from reduced NADP, both produced during the light-dependent reactions, are used to reduce the two molecules of GP to two 3C molecule known as GALP
production of useful organic molecules such as glucose, while the rest remain in the Calvin cycle to allow the regeneration of RuBP
explain step 3 : Regeneration of ribulose bisphosphate
Five sixths of the GALP molecules are used to regenerate RuBP
This process requires ATP
what does GP produce
Amino acids which can be used in protein synthesis for building polypeptides
Fatty acids which form the tails of lipid molecules such as triglycerides and phospholipids
What does GALP produce
Hexose sugars e.g. glucose
Glucose can be used by the plant in respiration while other biological molecules are used to build new plant biomass
how is NADPH formed
electrons are picked up by the coenzyme NADP along with hydrogen ions from photolysis, forming NADPH
why do indicators change colour
indicators accept the electrons instead of NADP
what colour does DCPIP and methylene blue go
blue to colourless
why may the colour of reduced solution appear green
due to the presence of chlorophyll
Method for the Hill reaction
Grind up the leaves with 20 cm3 isolation solution and blend them in a food blender for 10 seconds
Filter the resulting liquid into a clean beaker using a funnel and some filter paper
Transfer the filtered liquid into a centrifuge tube and centrifuge for 10 minutes
Discard the liquid in the centrifuge tube and keep the pellet of chloroplasts
Place 2 cm3 fresh isolation medium and the chloroplast pellet into a clean test tube, stirring with a glass rod to re-suspend the chloroplasts in the liquid; this is now the chloroplast extract
transfer the chloroplast extract to an ice-cold water bath
Place a test tube containing 0.5 cm3 chloroplast extract into a test tube rack set up at a set distance from a lamp
Add 5 cm3 DCPIP solution to the chloroplast extract and mix together using a clean glass rod
Use a pipette to immediately remove a sample of the DCPIP-chloroplast mixture and place the sample into a clean cuvette
Place the cuvette into a colorimeter and take a reading for absorbance
Repeat steps
why do we grind up leaves and blend them in food blender and put isolation solution
breaks apart the tissues of the leaf
isolation medium will prevent cell damage due to osmosis or extreme pH
why transfer filtered liquid in centrifuge tube and centrifuge
result in a pellet of chloroplasts forming at the bottom of the tube
what is liquid in centrifuge known as
supernatant
why ice cold water
The cold temperature of the water bath slows down the activity of the chloroplasts
what should happen to absorbance reading of colorimeter
The absorbance reading of the colorimeter should decrease over the 10 minute test period as the DCPIP indicator is reduced by electrons in the chloroplasts
what does the removal of one phosphate from ATP form and two phosphates
Removal of one phosphate creates ADP, and removal of two phosphates creates AMP.
describe the role of rubisco in the production of GALP in the light independent reaction
reference to RUBISCO as an {enzyme / catalyst};
in the Calvin cycle;
involved in {carbon fixation / bonding of CO2 to RuBP / reaction between COz and RuBP / eq} ;
to form GP / eg;
GP converted to GALP / eg;
using ATP and {reduced NADP / NADPH} (COz to
GALP / GP to GALP);
describe how membranes inside the chloroplast are involved in photosynthesis
site of light-dependent reaction;
credit named molecules {within / on / eq} membrane;
idea of {ATPase / eq } in (thylakoid) membranes ;
idea that (thylakoid) membranes provide a space for accumulation of H*;
reference to photophosphorylation;
suggest how GALP can be used to synthesise the cellulose in plant cell walls
reference to conversion (of GALP) to glucose / eg;
(which is) B glucose;
reference to formation of glycosidic bonds;
between C1 and Ca / 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}
describe the roles of the products of the light dependant reactions in the calvin cycle
(the products) ATP and reduced NADP
(1)
ATP is used (by the enzyme) converting
(GP to GALP / GALP to RuBP} (1)
reduced NADP used to convert GP to
GALP (1)
