B9 Flashcards
Why is light essential for photosynthesis?
Light is a small part of the electromagnetic spectrum : 400 - 700nm. Light behaves as waves and particles, particles of light are called photons. Each photon contains a quantum of energy. Pigments absorb photons and become energised.
What is PAR?
Photosynthetically active radiation. Part of the spectrum which drives photosynthesis. Measured as a flux of photons in units of umol m2 s-1. This is called photon flux density. 1 umol of photons = 6 x 10 to the 17 photons. On a bright sunny day, PAR = 2000umol m-2 s-1
What is the absorption spectra of chlorophyll a?
Wavelengths of violet-blue and orange-red. Form of chlorophyll used in oxygenic photosynthesis. It reflects green/yellow light. It is essential as it is a primary electron donor in the ETC.
What do pigments do?
Give colour to leaves, can absorb diff wavelengths of light. Transfer energy to chlorophyll a. Part of ETC, quench excess energy.
What happens in the light phase (grana) -physical phase of photosynthesis?
Light energy absorbed by pigments is funnelled to reaction centres and used to drive the production of - ATP, NADPH. Oxygen also formed
What happens in dark phase (stroma) - chemical phase of photosynthesis?
Uses ATP and NADPH in a series of enzyme catalysed reactions to assimilate CO2 into high energy organic form.
What does the stroma have?
Appropriate enzymes and a suitable pH for the Calvin cycle
What is the thylakoids structure?
Four protein complexes which carry out e- and h+ transfer. PS1, PS2, cytochrome b6f, ATP synthase enzyme. Water is oxidised to generate O2 plus H+. H+ released into lumen by PS2. H+ diffuse down electrochemical gradient through ATP synthase and generate ATP. ETC generates NADPH.
What is the organisation of photosystems?
Each PS = 250-400 pigment molecules with a reaction centre of specialised chlorophyll a molecules. Allows for efficient energy capture. PS1 + PS2 linked by ETC and work simultaneously and continuously. Cyclic and non-cyclic light driven production of ATP
What is photophosphorylation?
Light driven production of ATP
What are the two types of photophosphorylation?
Non and cyclic
What are the two types of photophosphorylation driven by?
PMF
What happens in non-cyclic photophosphorylation?
ATP generated in an open electron transfer system, linked with oxygen evolution in PS2, electron transfer to PS1 and NADPH formation.
What happens in cyclic photophosphorylation?
ATP generated in a closed system as electron is cycled from ferredoxin to PQ and then back to PS1, via the cytochrome complex
What are the three types of photosynthesis in plants?
C3 - most plants
C4 - mostly plants of arid climates
Crassulacean acid metabolism (CAM) - mostly cacti and succulents in arid climates
What are the three phases in the Calvin cycle?
Fixation - carboxylation : CO2 linked to C skeleton using enzyme Rubisco
Reduction - carbohydrate 3C formed using reducing power of ATP + NADPH
Regeneration - CO2 acceptor ribulose-1,5-biphosphate is reformed
Net products of 1 molecule of glyceraldehyde-3-phosphate and 3 molecules of starting material
What happens in photorespiration?
Ribulose 1,5 biphosphate has O2 added to it by the enzyme (Rubisco) instead of CO2 during photosynthesis. Complex network of enzyme reactions that exchange between chloroplasts, peroxisomes, and mitochondria. Reduces efficiency of photosynthesis in C3 plants.
What happens in C4 photosynthesis?
First stable organic compounds formed are C4 acids such as oxaloacetic acid, malic acid, aspartic acid. Initial carboxylation reaction is catalysed by phosphoenol pyruvate (PEP) carboxylase and takes place in the cytoplasm of the mesophyll cells. Requires two additional ATP to regenerate PEP so has a lower quantum yield than C3.
What happens in C4 photosynthesis in the Calvin cycle?
CO2 fixed as C4 acid is imported into the bundle sheath chloroplasts from the mesophyll. In the bundle-sheath chloroplasts C4 acids are decarbocylated and the chloroplasts are enriched with CO2. This CO2 is then fixed by the rubisco reaction to give 2 x PGA which enters the Calvin cycle as in C3 photosynthesis. PEP has to be regenerated using ATP.
C4 kranz anatomy of c4 and c3 acids?
Mesophyll cells c4 acids
Bundle sheath cells c3 (PGA)
What are some characteristics of C4 plants?
No photorespiration, high productivities at warm t and high irradiance. Low CO2 compensation point, steep CO2 diffusion gradient, high water use efficiency
How many species of C4 plants are there?
3000 species, 18 families. Sugar cane, maize.
What is the Crassulacean acid metabolism (CAM)?
CAM plants open stomata at night but close during the day, CO2 enters plant at night and is fixed into organic acids in the cytoplasm. Malic acid is stored in the vacuole. During the day, stomata close, malic acid is released from vacuole and decarboxylated to liberate CO2 which is used as substrate for photosynthesis in chloroplast. CAM strategy is a water saving adaption
What are some examples of CAM plants?
30,000 species, pineapple
What is the difference in co2 incorporation in C4 vs CAM plants?
Spatial separation in C4, temporal separation in CAM
What are the end products of photosynthesis?
Sucrose, starch, fructans are important - all are made from hexose sugar. Sucrose is translocated to growing regions and storage tissues. Starch is synthesised and stored in leaves, stems, roots and seeds. In storage tissues, starch is made from sucrose and stored in amyloplasts. Fructans are found in forage grasses and other plants. They are polymers of fructose, stored in vacuoles.
What is translocation?
Sugars manufactured during photosynthesis move out of the leaf and are translocated in the assimilate stream of the phloem. Transport is bidirectional, translocation is from sources to sinks. Leaves are sources in the assimilate stream, sugars are transported to sinks and storage areas. Storage areas may be sources or sinks
What does the phloem consist of?
Sieve elements, no rigid cell walls, contain protoplasm with mitochondria. Protoplasts of contiguous sieve elements are interconnected through sieve areas of adjacent walls. Sieve plates are sieve areas with large pores that ensure protoplasmic continuity between consecutive sieve tube members.
What do the phloem parenchyma consist of?
Companion cells - provide metabolic support for sieve elements, transfer cells - solute exchange between sieve elements and leaf mesophyll.
What is the function of p proteins and arrangement?
Arranged in tubular filaments in sieve tubes and has been implicated in the phloem translocation mechanism, p protein has also been observed plugging sieve pores.
What is callose made up and what’s its function?
Glucan which becomes deposited on the surface of sieve plates. Protect and seal sieve plates.
How do we know sugars are translocated in the phloem?
Girdling or ringing (removing phloem, xylem remain intact). Experiments with aphids, fluorescent dye, 14C labelled sucrose.
How fast is phloem translocation?
50 - 500 cm h-1
What is in phloem sap?
Done
What is in phloem sap?
Most carb, small amounts of minerals, hormones, ATP
What is the phloem translocation mechanism?
Rates of flow, bidirectionality, role of living cells, most favourable hypothesis is the mass flow mechanism.
What is the mass flow mechanism?
Phloem translocation from sources to sinks. Sugars enter sieve tubes, water follows by osmosis = high turgor pressure. Sugar leaves sieve tubes, water moves into xylem, into transpiration stream
