Photosynthesis Flashcards
What is photosynthesis
Where organisms convert light energy into sugars
How are leaves adapted for photosynthesis
-has a large surface area so lots of sunlight can be absorbed
-lots of air spaces for efficient diffusion
-waxy cuticle preventing water loss
-has lots of veins (xylem and phloem)
-leaf is thin so short diffusion pathway for efficient diffusion
-has many chloroplast which contains chlorophyll to absorb sunlight for photosynthesis
What is autotroph and give an example
An organism that makes their own food from inorganic molecules using energy
E.g producers in an ecosystem
What is heterotroph and give an example
An organism that cannot make its own food so has to obtain organic compounds by consuming other organisms
E.g consumers or decomposers
What is a photoautotroph
An organism that photosynthesises
uses light to make food
What is a Chemoautotroph
Organism that does NOT photosynthesise
uses chemicals to make its food
What is the photosynthesis equation
Sunlight
Carbon dioxide + water > glucose + oxygen
Chlorophyll
What type of reaction is photosynthesis
-It is endothermic
-Glucose is the main product
~ transports as sucrose and stored as starch
What is the respiration equation and what type of reaction is it
Glucose + oxygen > carbon dioxide + water + energy
-it is an exothermic reaction
Define interrelationship
The products of one are the reactants of the other
What is compensation point
When photosynthesis and respiration proceed at the same rate, there is no net gain or loss of carbohydrate
Fill in the gap
Plants - - - - all day but can only - - - - in the day
- Respire
- Photosynthesise
What is the compensation point (on the graph) for rate of oxygen exchange and light intensity
Where the line crosses the x-axis
Where is the chloroplast found and how long is it
-found in plants and algae
-2-10 micrometres long
What internal structures are there in the chloroplast
-granum
-stroma
-thylakoid
-intergranal lamellae
-photosystems
what is the Granum
-Stack of thylakoids
-where light dependant stage of photosynthesis takes place
What does the grana do
-many grana in the chloroplast so there’s a huge surface area for:
~when the electron carriers and ATP synthase enzymes need to convert light energy into ATP
~distributions of the photosystems that contain the photosynthetic pigmented that trap sunlight energy
Large surface area for light absorption
Has electron carriers to convert light energy into ATP
What is the stroma
-fluid filled matrix surrounding the thylakoids
What does the stroma do
-contains enzymes to catalyse the reactions of the light dependent stage of photosynthesis
-it also contains
~starch grains
~oil droplets
~loop of DNA
~small ribosomes
What is the thylakoid
-flattened disc like sacs that form stacks (grana)
What is the intergranal lamellae
-Connects thylakoids in different grana, together
What is a photosystem
-Funnel shaped structures found within the thylakoid membrane
-contains photosynthetic pigments
-each pigment absorbs sunlight of a particular wavelength whilst reflecting other wavelengths of light
~the light energy captured is tunnelled down to the primary pigment reaction centre consisting of a type of chlorophyll at the base of the photosystem
What is chlorophyll’s
-mixture of pigments
-all have a similar molecular structure consisting of a porphyrin group which there is a magnesium atom and a long hydrocarbon chain
What are the 2 chlorophylls
Chlorophyll A
Chlorophyll B
Chlorophyll A
-2 forms
-Appear blue or green
-both absorb RED light but have different absorption peaks
P680 - found in photosystem 2 light of wavelength for absorption is 680nm
P700 - found in photosystem 1- light of wavelength absorption is 700nm
Chlorophyll B
-absorbs light of wavelengths 400-500 nm and around 640
What do accessory pigments do
-carotenoids absorb blue light of wavelengths 400-500 nm
-xanthophyll absorbs blue and green of 375 - 550nm
they reflect yellow
Where does the light dependant stage of photosynthesis take place
-In the grana and involves the photosystems
-it uses direct light energy
What are the 3 stages of light dependant stage of photosynthesis
-light harvesting at the photosystems
-photolysis of water
-phosphorylation (cyclic or non cyclic)
What are the 2 photosystems (PS)
PS1 - chlorophyll a (p700)
PS2 - chlorophyll a (p680)
What happens at the light harvesting at the photosystems stage
-light energy is funnelled down to the primary reaction centre
-has a type of chlorophyll depending on the base of the photosystem
What happens at the photolysis of water stage
-occurs in PS2
-in the presence of light, water molecule is split into protons(H+), electrons and oxygen
(The oxygen can be used in respiration if production is high or it just diffuses out of the leaf)
what happens at photo phosphorylation
- the generation of ATP from ADP and inorganic phosphate in the presence of light
- it can be cyclic or non cyclic
Non cyclic stage of phosphorylation
-light is absorbed by PS2 and is passed to the PS2 primary pigment (P680)
-2 electrons are excited to a higher energy level and are emitted from the chlorophyll molecule
-excited electrons are passed down a chain of electron carriers (electron transport chain) before being passed on to PS1
-the energy released from the ETC allows H+ ions to pass from a low conc in stroma to a high conc in the thylakoid
-the H+ then diffuses back through ATP synthase to generate ATP
-in PS2 photolysis occurs
-these electrons replace the ones that are lost from PS2 to go to PS1
-The electrons leaving PSI combine with hydrogen ions giving reduced NADP
2H+ + 2e- + NADP → reduced NADP
-The reduced NADP (NADPH) then passes to the light-independent reactions to be used in the synthesis of carbohydrates
What is electron carriers
-proteins embedded in the membrane with iron ions in it
-when the electrons bind to it, it becomes reduced
-it can then donate the electron to the next electron carrier becoming reoxidised
What is Cyclic phosphorylation and give an example
Occurs only in PS1
- produces small amounts of ATP
- e.g guard cells use this to generate ATP to actively bring potassium ions into the cells lowering the water potential so that water follows by osmosis
- causes guard cells to swell and open the stomata
What is the stages of cyclic phosphorylation
-light is absorbed and passed on through PS1 (P700)
-an electron is excited to a higher energy level and is emitted from the chlorophyll molecule
-excited electron is captured by an electron acceptor transported via electron transport chain before going back to PS1 (this process releases energy)
- energy is used to transport protons (H+) from stroma to thylakoid via proton pump
- a build up of protons in the thylakoid lumen means they diffuse back through the membrane via ATP synthase which generates ATP from ADP and P1
What photosystems are involved in cyclic and non cyclic stages
Cyclic - PS1
non cyclic - BOTH
does photolysis occur in cyclic or non cyclic
Non cyclic
What are the products of cyclic and non cyclic
Cyclic- ATP
Non cyclic- ATP, oxygen and reduced NADP
Factors affecting photosynthesis
Carbon dioxide
Light
Temperature
Water
Light intensity
As light intensity increases rate of photosynthesis increases
However if it increases too much it levels out and plateaus because there is now another factor limiting it
How light intensity affects the Calvin cycle
If it’s too LESS
GP cannot be reduced to TP
so if GP accumulates and TP levels fall RuBp cannot be regenerated
Effect of carbon dioxide on Calvin cycle
If CO2 concentrations fall below 0.01%
Then RuBp cannot accept it so it accumulates and so GP cannot be made.
So TP cannot be made
Effect of temperature on Calvin cycle
At high rates O2 competes with CO2 for RuBiSCOs active site
Lack of TP means growth rate reduced
Uses of water
Keeps guard cell turgid so they can stay open
Used as reactant
What is water stress and give examples
When water supply becomes limited for plant
E.g
Cells lose water and become plasmolysed
Rate of photosynthesis reduces greatly
