122102
| Question | Answer |
| where does the light dependent stage of photosynthesis take place? | The thylakoid membranes |
| what is photolysis? | The splitting of water into protons, electrons and oxygen, takes place in photosystem 2 (non cyclic photophosphorylation) |
| what happens to the water once it has been photolysed? | -protons are used in chemiosmosis, are then accepted by the coenzyme NAD to form NADH used in the LIS -electrons replace those lost by the oxidised chlorophyll in photosystem 2 |
| what happens after a photon of light hits a photosystem? | The energy of the photon is transferred to tow excited electrons which are captured by electrons acceptors and are passed down a series of electron carriers (proteins containing iron) in the thylakoid membranes |
| what happens when the electrons are passed down the electron carriers? | Energy is released which allows protons to be pumped across the membranes into the thylakoid space where they accumulate. Forming a proton gradient. Protons flow down the gradients through channels associated with ATP synthase |
| what is chemiosmosis? | The flow of hydrogen ions through ATP synthase enzymes. Force drives the rotation part of the enzyme causing ATP to be produced |
| What are the products of the light dependent stage? | -Reduced NADP -ATP (by photophosphorylation) |
| what is cyclic photophosphorylation? | uses only photosystem 1, excited electrons pass to an electron acceptor and back to the chlorophyll molecule they were lose. No photolysis of water, no NADPH but small amounts of ATP |
| What can the ATP made from cyclic phosphorylation be used for? | -used in the light independent reaction -may be used in guard cells to bring in potassium ions, lowering the water potential and causing water to follow by osmosis. Guard cells swell and open the stomata |
| What is non cyclic phosphorylation? | Uses both photosystems, like strikes both causing photolysis of water and electron transfer. Produces NADPH and ATP which are taken to the stroma |
| where does the light independent stage/calvin cycle take place? | The stroma |
| What is the enzyme required for the calvin cycle? | Rubisco- fixes carbon dioxide to ribulose bisphosphate (RuBP) |
| how does co2 get to the stroma? | Diffuses into the leaf through open stomata (underside of the leaf) diffuses through air spaces in the spongy mesophyll unit it reaches the cytoplasm and the chloroplast envelope and into the stroma |
| what happens to GP? (Glycercate 3 phosphate) | GP is reduced and phosphorylated to another 3 carbon compound triose phosphate TP. (ATP and reduced NADP from the light dependent reaction are used in this process) |
| How much TP is used to regenerate Ribulose Bisphosphate? | 5 out of every 6 molecules of TP (3C), this uses ATP from the light dependent reaction to produce 3 molecules of RuBP (5C) |
| What can 1 molecule out of 6 TP be used for? | -amino acids, fatty acids, glycerol (f +g=lipids) -pairs can form hexose sugars e.g. glucose which can be isomerised to fructose. Fructose n glucose combine to make sucrose- sugar translocated in phloem sieve tubes. Hexose sugars can be polymerised to cellulose and starch |
| what is the definition of the light independent reaction? | The stage of photosynthesis where carbon dioxide is fixed and used to build complex organic molecules |
| Photosynthetic pigments | Are in the thylakoids membranes arranged in funnel-shaped structures called photo systems, held in place by proteins |
| What are the two types of chlorophyll a | P700 =1 p680=2 |
| What happens when light hits chlorophyll | Causes a pair of electrons associated with the magnesium to become excited |
| What is the primary pigment centre | The centre of the photo system made up of chlorophyll a (700 and 680) |
| Give two examples of accessory pigments | Carotene (orange) Xanthophyll (yellow) |
| What do accessory pigments do? | Absorb wavelengths that are not well absorbed by chlorophylls and pass the energy associated with that light to the chlorophyll a at the base of the photo system |
| Define the term heterotroph | Organisms that ingest and digest complex organic molecules releasing the chemical potential energy stored in them |
| What is photosynthesis? | The process whereby light energy from the sun is transformed into chemical energy and used to synthesise large organic molecules from inorganic substances |
| Why does respiration in plants and animals depend on the products of photosynthesis? | As they use oxygen, a product of photosynthesis for respiration, animals rely on photosynthesis so that light energy can be transformed to chemical potential energy which they can breakdown |
| Where does photosynthesis take place? | Takes place in the chloroplasts. It is a two stage process 1. Light dependent 2. Light independent/ Calvin cycle |
| Name the key structures in a chloroplast | -an outer membrane and inner membrane which make the envelope -stroma -grana -thylakoids -photosynthetic pigments -accessory pigments |
| Describe the outer membrane of a chloroplast | It is permeable to small ions |
| Describe the inner membrane | Less permeable to ions, has transport proteins embedded in it. It is folded into a lamellar which are in stacks. Each stack is called a granum (grana) between the grana are intergranal lamellae |
| Describe the stroma | A fluid filled matrix where the light independent stage takes place. Contains necessary enzymes such as ATP synthase, oil droplets, starch grains (store glucose) and DNA and ribosomes |
| Describe the grana | Stacks of flattened membrane compartments called thylakoids. Stage of the light dependent reaction, contains ATP synthase. Thylakoids can be seen using an electron microscope |
| How does the adaption of the inner membrane help its role? | Has transport proteins, can control what enters and exits the membrane |
| How does the adaption of the grana help its role? | Provides a large surface area for photosynthetic pigments, electron carriers ATP synthase which are required for the LDR |
| How are photosynthetic pigments arranged? | In special structures called photo systems which allow maximum absorption of light energy. Proteins embedded in the grana hold the photo systems in place |
| How does the adaption of the mitochondria and DNA in the chloroplast to help its role? | Allows the required proteins to be made for photosynthesis, using genetic instructions in the DNA and the chloroplast ribosomes to assemble proteins |
| Define the term autotroph | Organisms that use light energy or chemical energy and inorganic molecules (Caron dioxide and water) to synthesise complex organic molecules |
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