Photosynthesis Flashcards
Where does photosynthesis take place?
Leaf is main structure, occurs in chloroplasts.
How are leaves adapted to bring together the three raw materials of photosynthesis? (9)
-A large SA (sunlight) -An arrangement of leaves on the plant that minimises overlapping (no shadow) -Thin, as most light is absorbed in the first few mm of leaf. Diffusion distance short. -Transparent cuticle and epidermis that let light through to photosynthetic mesophyll cells beneath. -Long, narrow upper mesophyll cells packed with chloroplasts. -Numerous stomata for gaseous exchange. -Stomata that open and close in response to changes in light intensity. -Many air spaces in lower mesophyll layer to allow diffusion of CO2 and O2. -A network of xylem that brings water to the leaf cells, and phloem that carries away the sugars produced in photosynthesis.
Overall photosynthesis equation.
6CO2 + 6H2O = (light)= C6H12O6(glucose) + 6O2
Describe the structure of a leaf.
Structure of chloroplast.
What are the 3 main stages of photosynthesis?
- CAPTURING OF LIGHT ENERGY by chloroplast pigments such as chlorophyll.
- THE LIGHT DEPENDENT REACTION,
- THE LIGHT INDEPENDENT REACTION,
Describe (simply) the light dependent reaction.
in which light energy is converted into chemical energy. During the process an electron flow is created by effect of light on chlorophyll and this causes water to split (photolysis) into protons, electrons and O2.
Describe (simply) the light independent reaction.
in which these protons (hydrogen ions) are used to reduce carbon dioxide to produce sugars and other organic molecules.
What is light energy used for in the light dependent reaction?
- to add an inorganic phosphate (Pi) molecule to ADP, thereby making ATP.
- to split water into H+ ions (protons) and OH- ions. PHOTOLYSIS
What are the main features of a chloroplast?
Double membrane
- The grana
- the stroma
Describe the grana.
Stacks of up to 100 disk like strcutures called thylakoid where the light dependent satge of photosynt. takes place. Within thylakoids is chlorophyll. Lamella joins adjacent thylakoids.
Describe the stroma.
The stroma is a fluid- filled matrix where the light idendent stage of photosynt. takes place. Starch grains within stroma.
Describe how ATP is made in the light dependent reaction.
Light energy is absorbed by PSII, the light energy excites electrons in chlorophyl molecule the electrons move to a higher energy level.
These electrons are said to be in an excited state, they leave the chlrophyll molecule. (Chlorophyll oxidised)
Taken up by an electron carrier molecule. (REDUCED)
Electrons passed along a number of electron carriers in a series of ox-red reaction. These electon carriers form a transfer chain that is located in themembranes of the thlakoids.
Each new carrier is at a slightly lower energy level than the last so electrons lose energy. Electrons move along electron transport chain to PSI.
The energy lost is used to transport protons into the thylakoid so that the thylakoid has a higher concentration of protons that the stroma.
This forms a proton gradient across the membrane.
Protons move down their conc. gradient, into the stroma, via ATP synthase. The energy from this movement comines ADP and inorganic phophate to form ATP.
Describe photolysis of water.
Chlorophyll short of electrons (from light hiiting), to continue absorbing light energy, these electrons must be replaced.
Electrons provided by water molecules that are split using light energy.
Also yields H+ ions (protons)
2H2O = 4H+ + 4e- + O2
What happens to the hydrogen in photolysis of water? How does this happen?
Taken up by electron carrier called NADP, NADP is reduced (NADPH):
Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level.
Finally, the electrons are transferred to NADP, along with a proton from the stroma, to form reduced NADP.
What happens to the reduced NADP and why is it important?
It goes into the light independent reaction along with the electrons from chlorophyll molecules.
Important because it is a further potential source of energy to the plant.
What is the O2 by product from photolysis used for?
RESPIRATION OR DIFFUSES OUT OF PLANT AS A WASTE PRODUCT OF PHOTOSYNTHESIS.
Where does the light dependent reaction take place?
THYLAKOIDS
How are chloroplasts adapted to their function of capturing sunlight and carrying out the light dependent reaction?
- Thlakoid membranes provide a large SA for attachement of chlorophyll, electron carriers and enzymes that carry out the light dependent reaction.
- A network of proteins in the grana hold the chlorophyll in a very precise manner that allows maximum absorption of light.
- The granal membranes have enzymes attached to the,, which help manufacture ATP.
- Chloroplasts contain both DNA and ribosomes o they can quickl yand easily manufacture some of the proteins needefor the light dependent reaction.
Why is the light independent reaction called so?
Does not require light directly.
Describe the Calvin cycle.
- CO2 from atmosphere diffuses into stroma.
- In the stroma, CO2 combines with 5-carbon compound RIBULOSE BIPHOSPHATE (RuBP) using enzyme ribulase.
- The combination of CO2 and RuBP produces two molecules of 3- carbon GLYCERATE 3-PHOSPHATE (GP).
- ATP and NADPH from light dependent are used to reduce the activated GP toTRIOSE PHOSPHATE (TP)
- The NADP is reformed and goes back to the light dependent reaction to be reduced agan by accepting more hydrogen.
- SOme trios phosphate molecules are converted to useful organic substances, such as glucose.
- Most triose phosphate molecules are used to regenerate ribulose biphosphate using ATP from the light dependent reaction.
