5.6 - E - Photosynthesis Flashcards
What is photosynthesis?
The physiological process that converts light energy from sunlight into chemical energy, used by autotrophs such as plants and algae.
What are photoautotrophs?
Organisms that photosynthesise
What is the equation for photosynthesis?
6CO2 + 6H2O + energy from photons = (with chlorophyll) C6H12O6 + 6O2
What is a photon?
What does it contain?
A particle of light, each photon contains an amount (a quantum) of energy
What is the main product of photosynthesis?
Monosaccharide sugar, which can be converted to disaccharides for transport and then starch for storage
What is carbon fixation?
The process by which carbon dioxide is converted into sugars. Photosynthesis is an example of this. The carbon for synthesising all types of organic molecule is providing by carbon fixation. It’s endothermic and so needs energy. It also needs electrons, the addition of this is a reduction reaction.
Why is carbon fixation important?
It helps regulate the concentration of carbon dioxide in the atmosphere and oceans.
What is the equation for respiration?
C6H12O6 + 6O2 = 6H2O +6CO2 + energy
Explain how photosynthesis and respiration interrelate
Sunlight energy impacts photosynthesis in photoautotrophs.
They release carbohydrates and oxygen which is taken up by respiration in all living organisms. They release carbon dioxide and water which is taken up by the photoautotrophs. The cycle repeats.
What are heterotrophs?
Non-photosynthetic organisms
Eg: fungi, animals
What type of reaction is respiration?
Exothermic
What is the compensation point?
When photosynthesis and respiration proceed at the same rate 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. This is different for different plant species.
How are leaves adapted for photosynthesis?
Flat and large surface for maximum light absorption,
Stomata open and close for gases and water,
Air gaps allow diffusion,
The vascular bundle pushes the palisade cells to the top of the leaf, closer to the sun,
Thin – short diffusion distance between palisade mesophyll cells and external environment
How is the vascular bundle adapted to optimise the rate of photosynthesis?
Xylem - transports water and minerals to chloroplasts for photosynthesis.
Phloem - transports organic molecules made in the leaf to the rest of the plant.
How is the waxy cuticle adapted to optimise the rate of photosynthesis?
It acts as a waterproof barrier to prevent excessive evaporation from the upper surface of the leaf
How is the upper epidermis adapted to optimise the rate of photosynthesis?
They are transparent, allowing light to enter the leaf
How are palisade cells adapted to optimise the rate of photosynthesis?
They are the main site for photosynthesis.
They have the most chloroplasts and therefore lots of chlorophyll.
A large vacuole forces chloroplasts (non-pigmented) to the edge of the cell, allowing light penetration - shorter distance.
Thin cell walls.
Chloroplasts move by the cytoskeleton to absorb max light or protect from too much.
Closely packed - increase surface area
What are palisade cells also known as?
Palisade parenchyma
How is the spongy mesophyll adapted to optimise the rate of photosynthesis?
Spherical cells - less chloroplasts, large air spaces for gas movement - better diffusion.
They store carbs made by photosynthesis taken into the phloem.
How is the lower epidermis adapted to optimise the rate of photosynthesis?
Guard cells control diffusion by controlling stomata
What is the difference between respiration and photosynthesis in plants?
Plants respite all the time, but only photosynthesis during daylight
Explain the evolution of chloroplasts
It is believed that photosynthetic bacteria were acquired by eukaryotic cells by endocytosis to produce the first plant cell.
This is called the endosymbiont theory. They were then passed on to the next generation.
Describe the size and shape of a chloroplast
Size varies, but is usually between 2 and 10 micrometers.
They are usually disc shaped.
Describe the membrane surrounding chloroplasts
Chloroplasts are surrounded by a double membrane (the envelope.)
The outer membrane is highly permeable.
The inner membrane is less permeable and has transport proteins embedded in it.
The intermembrane space is 10-20 micrometers wide between the 2 membranes.
What is a granum?
The inner part of chloroplasts made of stacks of thylakoid membranes, where the light-dependent stage of photosynthesis takes place - the first stage of photosynthesis.
They create a huge surface area for:
Distribution of photosystems that contain photosynthetic pigments that trap sunlight.
Electron carriers and ATP synthase enzymes needed to convert light energy into ATP.
Proteins embedded in the thylakoid membrane hold the photosystems in place.
What is the plural of a granum?
Grana
What is a stroma?
Fluid-filled matrix of chloroplasts. It contains enzymes needed for the second stage of photosynthesis - the light-independent stage.
It also contains starch grains, oil droplets, small ribosomes (similar to prokaryotic cells) and a loop of DNA.
Define the term photosynthetic pigment
Absorb certain wavelengths of light and traps the energy associated with the light.
Reflect other wavelengths (these are the colours we see).
Arranged in photosystems in thylakoid membranes.
What are the 4 photosynthetic pigments?
Chlorophyll a,
Chlorophyll b,
Carotene,
Xanthophyll
What is a photosytem?
A system of photosynthetic pigments found in thylakoids of chloroplasts; each photosytem contains about 300 molecules of chlorophyll that trap photons and pass their energy to a PPRC, a molecule of chlorophyll a, during the light-independent stage of photosynthesis.
What are thylakoids?
Flattened membrane-bound sacs found inside chloroplasts; they contain photosynthetic pigments/photosystems and are the sire of the light-dependent stage of photosynthesis.
What is the first stage of photosynthesis and where does it take place?
The light-dependent stage
The grana
What connects thylakoids in different grana together?
Intergranal lamellae/intergranal thylakoids
What are chlorophylls?
A mixture of pigments. They all have a similar molecular structure consisting of a porphyrin group, in which there is a magnesium atom and a long hydrocarbon chain.
What are the 2 types of chlorophyll a, where are they found and what is their peak absorption wavelength?
P680 - found in photosystem II - 680nm
P700 - found in photosystem I - 700nm
What colour do both chlorophyll a’s appear?
Blue-green
At what wavelengths do chlorophyll b absorb light and what colour does it appear?
400-500nm and 640nm
Yellow
What colours do carotenoids absorb and reflect and at what wavelengths?
Absorb blue light
Reflect orange and yellow light
400-500nm
What colours do xanthophylls absorb and reflect and at wha wavelengths?
Absorb green and blue
Reflect yellow
375-550nm
What are the 3 parts of a nucleotide?
Base
Ribose Sugar
Phosphate
Describe ATP and its role in photosynthesis
ATP is a store of energy found in all cells
ATP diffuses around the cell and provides energy for cellular processes
ATP is made in the LDS from ADP + Pi (inorganic phosphate)
ATP releases energy in the LIS when the BOND between the inorganic phosphate groups is broken
What is phosphorylation?
Adding a phosphate molecule
What does photophosphorylation mean?
Photo - light
Phosphorylation - adding a phosphate molecule
What does NADP stand for?
Nicotinamide Adenine Dinucleotide Phosphate
What is NADP and what does it do?
It’s a coenzyme and electron and hydrogen carrier.
It can accept electrons and protons and becomes reduced.
It is also a ‘store’ of energy in the form of ‘reducing power’ which can drive biosynthetic reactions in LIS.
List the 4 ways that reduced NADP can be written
Reduced NADP
NADPH
NADPH2
NADPH + H+
Where does the light-dependent stage of photosynthesis occur?
In the grana or chloroplasts
What does the light-dependent stage consist of?
Light harvesting at the photosystems
Photolysis of water
Photophosphorylation - the production of ATP in the presence of light
The formation of reduced NADP
What does hydrolysis mean?
Hydro - water
Lysis - splitting
The splitting of water
What does photolysis mean?
Photo - light
Lysis - splitting
Splitting molecules by the use of light
List and explain the 2 types of photosystem
Photosystem I (PSI) - the pigment at the primary reaction centre is a type of chlorophyll a, which has a peak absorption of red light of wavelength 700nm (P700). Photosystem II (PSII) - the pigment at the primary reaction centre is also a type of chlorophyll a, but this has a peak absorption of red light of wavelength 680nm (P680).
What is the equation for photolysis?
2H2O -> 4H+ + 4E- + O2
List the 4 roles of water in photosynthesis
It’s the source or protons (hydrogen ions) that will be used in photophosphorylation.
It donates electrons to chlorophyll to replace those lost when light strikes chlorophyll.
It’s the source of the by-product: oxygen.
It keeps plant cells turgid, enabling them to function.
Define photophosphorylation
The generation or ATP from ADP and inorganic phosphate, in the presence of light.
List and explain the 2 types of photophosphorylation
Non-cyclic photophosphorylation involves PSI and PSII. It produces ATP, oxygen and reduced NADP.
Cyclic photophosphorylation involves only PSI. It produces ATP but in smaller quantities than are made in non-cyclic photophosphorylation.
Both types involve iron-containing proteins embedded in the thylakoid membranes that accept and donate electrons and form an electron transport system.
What are electron carriers?
Molecules that can accept one or more electrons then donate those electrons to another carrier. Proteins embedded in thylakoid membranes are electron carriers, and form an electron transport chain or system. Ferredoxin, NAD and NADP are also electron carriers.
Describe how photosynthetic pigments are arranged into photosystems
In funnel-shaped light-harvesting clusters held in place in the thylakoid membrane by proteins
What is an absorbance spectrum?
A graph that shows which wavelengths of light are absorbed by a pigment
What is an action spectrum?
A graph which shows the wavelengths of light that are actually used in photosynthesis
Explain the link between the absorption spectra and the action spectra
The aborsbance spectra and action spectra closely match each other, suggesting these wavelengths of light are used in photosynthesis
Describe the steps in non-cyclic photophosphorylation
That shit with the 2 photosystems and 2 electrons and electron carriers and acceptors n shit makes NADPH and ATP
Where does cyclic photophosphorylation take place?
In chloroplasts in guard cells.
Only ATP is made which actively brings potassium ions into the cells.
What is different about respiration and photosynthesis in plants?
Plants respire all the time but only photosynthesise during daylight
Explain what happens in cyclic photophosphorylation
ATP is produced
No photolysis
No reduced NADP
Guard cells contain PSI only, producing ATP to pump K+ into the cells.
This causes guard cells to swell and open the stomata.
Who worked out the stages of the light independent reactions?
Melvin Calvin between 1946 and 1953
What are the products of the light dependent reactions?
ATP and NADPH
Where does the light dependent stage (LIS) occur?
In the thylakoid membrane
What is the main source of electrons in the Light-independent stage?
Water
Where does photolysis take place?
In the PSII - the enzyme attached to it
How do protons accumulate inside the thylakoid space?
Pumped across the thylakoid membrane using energy released
from electrons in the etc
What is the Calvin cycle?
A metabolic pathway of the light-independent stage of photosynthesis, occurring (in eukaryotic cells) in the stroma of chloroplasts where carbon dioxide is fixed, with the products of the light-dependent stage, to make organic compounds. The Calvin cycle also occurs in many photoautotrophic bacteria.
Explain GANT TAR
GP + ATP + NADPH -> TP
TP + ATP -> RuBP
Explain the Calvin Cycle
Shit happens
What are the uses of triose phosphate (TP)
Some are used to synthesise organic compounds
Eg:
Some glucose is converted to sucrose, some to starch and some to cellulose.
Some TP is used to synthesise amino acids, fatty acids and glycerol.
The rest of the TP is recycled to regenerate the supply of RuBP. 5 molecules of the 3-carbon compound TP interact to form 3 molecules of the 5-carbon compound RuBP.
Define light intensity
Level of light
Define water stress
The condition a plant will experience when water supply becomes limiting
What is light intensity and rate of photosynthesis measured in?
Arbitrary units
Explain the effect of decreasing light intensity in the Calvin cycle
If there is little or no light:
GP cannot be reduced to TP
TP levels fall and GP accumulates
If TP levels fall, RuBP cannot be regenerated
Explain the effect of decreasing carbon dioxide concentration on the Calvin cycle
If carbon dioxide concentration falls below 0.01%:
RuBP cannot accept it, and accumulates
GP cannot be made
Therefore, TP cannot be made
What happens to a plant under water stress?
The roots are unable to take up enough water to replace that lost via transpiration.
Cells lose water and become plasmolysed.
Plant roots produce abscisic acid that, when translocated to leaves, causes stomata to close, reducing gaseous exchange.
Tissues become flaccid and leaves wilt.
The rate of photosynthesis greatly reduces.
