Chapter 10 - Photosynthesis Flashcards
Types of organims who use energy
Autotrophs: use energy from the sun to make organic molecules
- All plants are photoautotrophs as light is their main source of energy
Heterotrophs: obtain organic food molecules by eating other organisms or substances derived from them
- Most are known as decomposers
Stomata
micro pores which are surrounded by guard cells in the surface of leaves allowing gaseous exchange
Chlorophyll
green pigment located within the thylakoid disks of chloroplasts which absorb light energy and convert to chemical energy
Photosynthesis
the process transforming sunlight energy into chemical energy in the form of 3 carbon molecules which are transformed into sugar
3 stages:
- light dependent
- calvin cycle
Stages of Photosynthesis: light dependent
first stage which occurs in the thylakoid membrane and converts solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process
- Water is split, providing electrons and protons and giving of O2
- Light absorbed drives a transfer of electrons and hydrogen ions to an acceptor converting NADP+ to NADPH
- generates ATP through photophosphorylation
Stage of Photosynthesis: Calvin Cycle
the second stage involving fixation of atmospherically carbon dioxide and reduction of the fixed carbon into carbohydrates occurring in the stroma
- 3 cycles bring in 3 Co2 molecules to produce 1x G3P molecule(6 cycles in total)
- CO2 from air is incorporated through carbon fixation
- Co2 reduced to 3-PGA by addition of electrons, oxidizing NADPH back to NADP+
- ATP converts CO2 to G3P
Photophosphorylation
the process of generating ATP by means of chemiosmosis(PMF) across the thylakoid membrane
Photons
not tangible objects but waves of light which behavior like objects in that they have fixed quantities of energy
- Amount of energy is inversely related to wavelength; the shorter it is, the greater the energy
Pigment
substances that absorb visible light
- If a pigment is illuminated with green light it is because it’s the colour most reflected or transmitted by the pigment
Electrons being Excited
- When molecules absorb a photon of light, the molecules electrons is elevated to an orbital where it has more potential energy
- The only photon absorbed is those with energy exactly equal to the energy difference between ground state and excited state
- Once excited, an electron cannot remain there for long as it is unstable and drop back down to ground state, releasing excess energy as heat
Photosystem
a light capturing unit in the thylakoid membrane which consists of a reaction centred complex surrounded by several light harvesting complexes
- Different types which absorb light at different wavelengths
- When a photon is absorbed, energy is transferred from pigment molecule to pigment molecule within the complex until it reaches the reaction center complex - the light energy is used to boost one of their electrons to a higher level and is transferred to an electron acceptor; reducing it
Photosystem I: 700nm
Photosystem II: 680nm
Components of Photosystem
Reaction-center complex: an organized association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor
Light Harvesting Complexes: consist of various pigment molecules bound to proteins enabling the photosystem to harvest light over a larger surface area
Types of Electron Flow
Linear Electron Flow: the route of electrons during the light reaction involving light stimulating both photosystems in order to produce ATP, NADPH and O2
Cyclic electron flow: an alternative route of electron flow which only uses PS I and produces ATP but not O2 or NADPH
- Generates a surplus of ATP required to satisfy the higher demands of the calvin cycle
Steps in Linear Flow
- Photon of light strikes one of the pigment molecule in PSII, boosting an electron to a higher energy level stimulating a chain reaction until it reaches RCC where its transferred to Primary Electron acceptor
- An enzyme catalyzes the splitting of water and electrons replace ones lost in PSII, H move into thylakoid space and O combines to form O2 and is released
- photoexcited electron passes from PSII to PS I through ETC which carries out redox reactions that release free energy used to pump protons into the thylakoid space creating PMF
- Light energy has been transferred to PS I RCC resulting in Photoexcited electrons passed down a series of redox reactions from primary electron acceptor of PS I to a secondary ETC
- this reduces NADP+ into NADPH in the stroma
- build up of H+ in thylakoid space then creates PMF to go down ATP synthase
Calvin Cycle
- Takes place in the stroma
- Is anabolic, building carbs from smaller molecules and consuming energy
- The cycle spends 9 ATP and consumes 6 NADPH for a net synthesis of 1x G3P molecule(3 cycles/1 turn)
3 phases:
- carbon fixation
- reduction
- Regeneration