photosynthesis- chapter 11 Flashcards
what is the site of photosynthesis
The leaf is a main photosynthetic structure in eukaryotic plants.
Chloroplasts are the cellular organelles within the leaf where photosynthesis takes place.
what are the adaptations for the structure of the leaf
-A large surface area that absorbs sunlight.
-An arrangement of leaves on the plant that minimises overlapping
-Thin to keep diffusion distance short and absorb as much light as possible.
-A transparent cuticle and epidermic that let light through to the photosynthetic mesophyll cells beneath.
-Long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight.
-Numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion pathway from one.
-Stomata that open and close in response to change in light intensity
-Many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen
-A network of xylem that brings water to the leaf cells, and phloem that carries away the sugars produced during photosynthesis.
what are the three main stages of photosynthesis (brief description)
-Capturing of light energy- by chloroplasts pigments such as chlorophyll
-The light-dependent reaction, in which some of the light energy absorbed is conserved in chemical bonds. An electron flow is created by the effect of light on chlorophyll, causing water to split (photolysis) into protons, electrons and oxygen. The products are reduced NADP, ATP and oxygen.
-The light-independent reaction, in which these protons are used to produce sugars and other organic molecules.
what is the structure of the chloroplasts
-Chloroplasts vary in shape and size but are typically disc-shaped, 2-10um long, and 1um in diameter.
-Surrounded by a double membrane.
what are two distinct regions in chloroplasts which act as roles in photosynthesis
-GRANA are stacks of up to 100 disc-like structures called thylakoids where the light-dependent stage of photosynthesis takes place. Within these is the pigment chlorophyll. Some thylakoids have tubular extension that join up with thylakoids in adjacent grana, these are called intergranal lamellae.
-STROMA is the fluid-filled matric where the light-independent stage of photosynthesis takes place. Within the stromata are a number of other structures such as starch grains.
what happens in the light independant reaction (brief)
-Add an inorganic phosphate (Pi) molecule to ADP, thereby making ATP.
-To split water into H+ ions (protons) and OH-. As the splitting is caused by light, it is known as photolysis.
what is oxidation and reduction
-Oxidation is when a substance loses electrons, gains oxygen or loses hydrogen.
-Reduction is when it gains electrons, loses oxygen or gains hydrogen.
what happens in the making of ATP
-When a chlorophyll molecule absorbs light energy, it boost the energy of a pair of electrons within the molecule, raising them to a higher energy level.
-These are in an excited state and leave the chlorophyll molecule all together, this then becomes ionised so the process is known as photoionisation.
-The electrons that leave the chlorophyll are taken up by a molecule called an electron carrier.
-The chlorophyll has been oxidised, the electron carrier has been reduced.
-The electrons are now passed along a number of electron carriers in oxidation and reduction reactions.
-These electrons carriers form a transfer chain that is located in the membranes of thylakoids.
-Each new carrier is at a slightly lower energy level than the previous one in the chain, meaning the electrons lose energy at each stage.
-Some of this energy is used to combine an inorganic phosphate molecules with an ADP molecules in order to make ATP.
what is the chemiosmotic theory
-Each thylakoid is an enclosed chamber into which protons (H+) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps.
-The energy to drive this process comes from electrons released when water molecules are split by light- photolysis of water.
-The photolysis of water also produces protons which further increases their concentration inside the thylakoid space.
-This creates and maintains a concentration gradient of protons across the thylakoid member with a high concentration inside the thylakoid space and a low concentration in the stroma.
-The protons can only cross the thylakoid membrane through ATP synthase channel proteins- the rest of the membrane is impermeable to protons. These channels on the membrane surface and so are also known as stalked granules.
-As the protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP.
what is the photolysis of water
-The loss of electrons when light strikes a chlorophyll molecules leaves it short of electrons.
-These electrons then need to be replaced so it can continue absorbing light energy.
-The replacement electrons are provided from water molecules that are split using light energy.
-This photolysis of water also releases protons.
-2H2O 🡪 4H+ + 4e- + O2
-These protons pass out of the thylakoid space through the ATP synthase channels are taken up by an electron carrier called NADP meaning it becomes reduced.
-The reduced NADP is the main product of the light-dependent stage and it enters the light- independent reaction taking with it the electrons from the chlorophyll molecules.
-The reduced NADP is important because it is a further potential source of chemical energy.
-The oxygen diffuses out of the leaf as a waste product of photosynthesis.
what is the site of the light dependant reaction
takes place in the thylakoid of chloroplasts
what are the adaptations of the sight of the light dependant reaction
-Large surface area for attachment of chlorophyll, electron carriers and enzymes.
-Network of proteins in the grana hold the chlorophyll in a very precise manner to allow maximum absorption of light.
-Granal membranes have ATP synthase channels which catalyse the production of ATP. Also selectively permeable which establishes a proton gradient.
-Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light-dependent reaction.
what does the light independant reaction require and not require
This stage does not require light directly but does require the products from the light-dependent stage so will also cease when light is absent.
where does the light independant reaction take place
the stroma of the chloroplasts
explain the calvin cycle
- Carbon dioxide diffuses into the leaf and dissolves in water around the walls of the mesophyll cells and then through the cell-membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast.
- In the stroma, the carbon dioxide reacts with the 5-carbon compound ribulose bisphosphate (RuBP) a reaction catalysed by an enzyme called ribulose bisphosphate carboxylase (rubisco)
- The reaction between carbon dioxide and RuBP produces two molecules of the 3 carbon glycerate 3-phosphate (GP)
- Reduced NADP from the light-dependent reaction is used to reduce glycerate 3-phosphate to triose phosphate (TP) using energy supplied by ATP.
- The NADP is reformed and goes back to the light-dependent reaction.
- Some triose phosphate molecules are converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides.
- Most triose phosphate molecules are used to regenerate ribulose bisphosphate using ATP from the light-dependent reaction.
how is the chloroplast adapted to carry out the light-independent reaction
-Fluid of the stroma contains all the enzymes needed. Stromal fluid is membrane bound which means a chemical environment with a high concentration of enzymes and substrates.
-The stroma fluid surrounds the grana and so the products of the light-dependent reaction can readily diffuse.
-It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins involved in the light-independent reaction.
