photosynthesis Flashcards
what is photosynthesis
is a physiological process used by plants, algae and some types of bacteria to convert light energy from sunlight into chemical energy
what is autotrophic nutrition
organisms can use this chemical energy to synthesise large organic molecules , which form the building blocks of living cells, from simple inorganic molecules such as water and carbon dioxide
organisms that photosynthesise are called ? because ?
photoautotrophs
because they use light as the energy source for autotrophic nutrition
word equation for photosynthesis
carbon dioxide + water + energy from photons = glucose + oxygen
symbol equation for photosynthesis
6co2 + 6h20 = c6h12o6 + 6o2
word equation for respiration
glucose + oxygen = water + carbon dioxide + energy
symbol equation for respiration
c6h1206 + 6o2 = 6h2o +energy
describe how photosynthesis and respiration interrelate e
the products of one process are the raw materials for the other process, aerobic respiration removes oxygen from the atmosphere and adds carbon dioxide , while photosynthesis does the opposite
what is the compensation point
when photosynthesis and respiration proceed at the same point , so that there is no net gain or loss of carbohydrates
what is the compensation period
the time a plant takes to reach its compensation point
define the granum
the inner part of chloroplasts made of stacks of thylakoid membranes , where the light dependent stage of photosynthesis takes place
define stroma
fluid filled matrix of chloroplasts, where the light independent stage of photosynthesis takes place
the first stage of photosynthesis , the light dependent stage , takes place in the
grana
what are the three distinct membranes of the chloroplasts
outer
inner
thylakoid
with many grana in every chloroplast and with many chloroplasts in each photosynthetic cell, there is a huge surface area for :
- the distribution of the photosystems that contain the photosynthetic pigments that trap sunlight energy
- the electron carriers and ATP synthase enzymes needed to convert that light energy into ATP
the stroma contains
enzymes needed to catalyse the reactions of the light dependent stage starch grains oil droplets small ribosomes DNA
define photosystems
system of photosynthetic pigments found in the thylakoids of chloroplasts
define photosynthetic pigments
pigments that absorb specific wavelengths of light and traps the energy associated with the light
how do photosystems work
each pigment absorbs light of a particular wavelength and reflects other wave lengths of light . each pigment appears to our eyes and brain , the colour of the wavelength of light is reflected
the energy associated with the wavelength of light captured is funnelled down to the primary pigment reaction centre, consisting of a type of chlorophyll , at the base of the photosystem
what are the two types of chlorophyll
chlorophylls a and b
what colour do chlorophyll a appear and what colour do they absorb
appear blue green
absorb red light
what are the two types of chlorophyll a
p680
p700
describe p680
is found in photosystem 2 and its peak of absorption is light of wavelengths of 680 nm
describe p700
is found in photosystem 1 and its peak of absorption is light of wavelength 700nm
describe chlorophyll b
absorbs light of wavelengths 400-500 nm and around 640nm . it appears yellow green
name 2 accessory pigments
carotenoids
xanthophylls
describe carotenoids
they absorb blue light of wavelengths 400-500 nm , they reflect yellow and orange light
describe xanthophylls
absorb blue green light of wavelengths 375-550 nm . they reflect yellow light
what are the stages of the light dependent stage
- light harvesting at the photosystems
- photolysis of water
- photophosphorylation , the production of ATP in the presence of light
- the formation of reduced NADP
oxygen , the by product of photosynthesis , is also produced in the light dependent stage
what is photolysis
the enzyme catalysed splitting of water in the presence of light
into protons, electrons and oxygen
describe the role of water in the light dependent stage
- is the source of protons that will be used in photophosphorylation
- donates electrons to chlorophyll to replace those lost when light strike the chlorophyll
- is the source of the by product oxygen
- keeps plant cells turgid, enabling them to function
what is photophosphorylation
the generation of ATP from ADP and inorganic phosphate, in the presence of light
what are the two types of photophosphorylation
- non cyclic photophosphorylation
- cyclic photophosphorylation
what photosystems are involved, and what is produced in non cyclic photophosphorylation
PS1 and PS2
produces ATP , oxygen , reduced NAPD
what photosystems are involved , and what is produced in cyclic photophosphorylation
PS1
produces ATP but smaller quantities than are made by non cyclic photophosphorylation
describe the non cyclic photophosphorylation steps
1-when a photon of light strikes PS2 its energy is channelled to the primary pigment reaction centre
2- the light energy excites a pair of electrons inside the chlorophyll molecule
3-the energised electrons escape from the chlorophyll molecule and are captured by an electron carrier, which is a protein with iron at its centre , embedded in the thylakoid membrane
4- these electrons are replaced by electron derived from photolysis
5-when this iron ion combines with an electron it becomes reduced Fe2 , it can then donate the electron , becoming reoxidised Fe3, to the next electron carrier in the chain
6-as electrons are passed along the chain of electron carriers embedded in the thylakoid membrane at each step some energy associated with the electron is released
7- this energy is used to pump protons across the thylakoid membrane into the thylakoid space
8- eventually the electrons are captured by another molecule of chlorophyll a in PS1 . these electrons replace those lost from PS1 due to excitation by light energy
9-v a protein ion sulfur complex called ferredoxin accepts the electron from PS1 and passes them to NADP in the stroma
10- as protons accumulate in the thylakoid space , a proton gradient forms across the membrane
11- protons diffuse down their concentration gradient through special channels in the membrane associated with ATP synthase enzymes and , as they do so, the flow of protons causes ADP and inorganic phosphate to join , forming ATP
12- as the protons pass through the channels they are accepted , along with electrons , by NADP which becomes reduced . the reduction of NADP is catalysed by the enzyme NADP reductase
describe cyclic photophosphorylation
uses only photosystem 1 . as light strikes a pair of electrons in the chlorophyll molecule at the reaction centre gain energy and become excited . they escape from the chlorophyll and pass to an electron carrier system and then pass back to PS1
during the passage of electrons along the electron carriers , a small amount of ATP is generated . however no photolysis of water occurs , so no protons or oxygen are produced . no reduced NAD is generated
chloroplasts in guard cells contain only PS1. they produce only ATP which actively brings potassium ions into the cells ,lowering the water potential so that water follows by osmosis , this causes the guard cells to swell and open the stoma
the light independent stage of photosynthesis takes place in the
stoma in the chloroplasts
define the calvin cycle
metabolic pathway of the light independent stage of photosynthesis , occurring in the stroma of chloroplast where carbon dioxide is fixed with the products of the light dependent stage to make organic products
describe the steps of the calvin cycle
1- at atmospheric carbon dioxide molecule
2- combines with RuBP
3- RuBP serves as a carbon dioxide acceptor , the reaction is catalysed by rubisco
4- this forms a 6c sugar that quickly splits to form 2 molecules of GP , a 3c compound
5-that combine with ATP and reduced NAD from the light dependent stage
6- and forms 2 molecules of TP and NADP anf ADP+ P
7- one out of 6 molecules make hexose sugar and 5 out of 6 molecules makes RuBP that is combined with co2 again
when does the calvin cycle run
during the day
what are the uses of triose phosphate (TP)
- some glucose is converted to sucrose , some starch and some to cellulose
- some TP is used to synthesis amino acids, fatty acids and glycerol
the rest of TP is recycled to regenerate the supply of RuBP
what are the factors affecting photosynthesis
light intensity
carbon dioxide concentration
temperature
define limiting factor
a factors whose magnitude slows down the rate of a natural process
describe light intensity as a factor affecting photosynthesis
light provides the energy to power the first stage of photosynthesis and produce ATP and reduced NADP needed for the next stage . light also causes stomata to open so that gaseous exchange can occur. when stomata are open transpiration can also occur and this leads to uptake of water and delivery to leaves
at a constant favourable temperature and constant suitable carbon dioxide concentration , light intensity is the limiting factor . when light intensity is low , the rate of photosynthesis is low. as light intensity increases , the rate of photosynthesis increases
the effect of little or no light intensity on the calvin cycle
1- GP cannot be reduced to TP
2- TP levels fall and GP accumulates
3- if TP levels fall, RuBP cannot be regenerated
the effect on the calvin cycle if the carbon dioxide levels fall below 0.01%
1-RuBP cannot accept it , and accumulate
2- GP cannot be made
3- therefore TP cannot be made
what are the effects of changing temperature on the calvin cycle
- from low temperatures to temperature of 25-30 degrees , if plant shave enough water and carbon dioxide and a sufficient light intensity , the rate of photosynthesis increases as temperature increases
- as temperatures above 30 degrees , for most plants , growth rates may reduce due to photorespiration ; oxygen competes with carbon dioxide for the enzyme rubiscos active site . this reduces the amount of carbon dioxide being accepted by RuBP and subsequently reduces the quantity of GP and therefore of TP being produced , whilst initially causing an accumulation of RuBP . however , due to the lack of TP, RuBP cannot be regenerated
- at temperatures above 45 degrees , enzymes involved in photosynthesis may be denatured . this would reduce the concentrations of GP and TP , and eventually of RuBP as it could not be regenerated due to lack of TP
what are the steps if there is not enough water available to the plant (water stress)
1- the roots are unable to take up enough water to replace that lost via transpiration
2- cells lose water and become plasmolysed
3- plant roots produce abscisic acid that, when translocated to leaves , causes stomata to close, reducing gaseous exchange
4-tissues become flaccid and leaves wilt
5- the rate of photosynthesis greatly reduces
what is water stress
the condition a plant will experience when water supply becomes limiting
how to measure the rate of photosynthesis
- rate of uptake of raw materials , c02
- rate of production of the by product , oxygen
need to measure the quantity taken or produced per unit time
in school labs , the rate of photosynthesis is often found by measuring the volume of oxygen produced per minute by an aquatic plant. what are the limitations of this
- some of the oxygen produced by the plant will be used for respiration
- there may be some dissolved nitrogen in the gas collected
describe the setting up and using a photosynthometer
it is set up so that it is air tight and there are no air bubbles in the capillary tubing . gas given off by the plant , over a known period of time , collects in the flared end of the capillary tube. as the experimenter manipulates the syringe , the gas bubbles can be moved into part of the capillary tube against the scale and its length measured , if the radius of the tube bore is known , then the length can be converted to volume
= length of bubble x πr2
what is the equation for volume of gas collected
length of bubble x πr2
what are the units for light intensity
lux
how to investigate the effect of light intensity on the rate of photosynthesis
( investigation 1 )
1- remove the plunger from the syringe and allow a gentle stream of tap water into the barrel of the syringe , until the whole barrel and plastic tube is full of water
2-replace the syringe plunger and gently push water out of the flared end of the tube until there are no air bubbles in the water of the capillary tube
3- cut a 7 cm length if well illuminated elodea and make sure that the bubbles of gas are emerging from the cut stem. place this piece of elodea , cut end upwards , into a boiling tube containing some of the water in which it has been kept in and add two drops of the hydrogencarbonate solution to it
4- stand the boiling tube in a beaker of water at around 25 degrees
5- place the light source as close as possible to the beaker . measure and record the distance
6- leave the apparatus with the capillary tube over the cut end of the plant stem and after a known period of time , gently pul the syringe plunger and bring the oxygen bubble into the tube against the scale
7- repeat twice more
8- move the light source further away form the plant and measure the distance, repeat 5 an d 6
9- plot graph
how to investigate the effect of light intensity on the rate of photosynthesis
( investigation 2 )
1- use a straw to cut several leaf discs from cress cotyledons
2- place 6 or 8 discs into a 10cm3 syringe and half fill the syringe with a dilute solution of sodium hydrogencarbonate
3- hold the syringe upwards , place your finger over the end of the syringe and gently pull on the plunger . this causes air to leave the spongly mesophyll layer of the leaf discs . the air is replaced by the sodium hydrogencarbonate solution that enters the discs , making them more dense . they sink to the bottom of the syringe
4- once all the discs are have sunk , transfer the contents into a small beaker .
5- place the beaker of the discs directlt under a lamp and measure the time taken for one leaf disc to float to the top . as the discs carry out photosynthesis , oxygen produced collects in the spongy mesophyll and displaces the sodium hydrogencarbonate making the discs less dense and more buoyant
6- repeat these steps 2 more times and find the mean rate of photosynethesis
7-
