U3 AO3 Flashcards
What is photosynthesis?
Photosynthesis is a biological process by which photoautotrophs take light energy (from the sun) and use it too form chemical energy in the form of glucose.This glucose is then transported out the stroma for cellular respiration or for conversion into complex carbohydrates.
Where does Photosynthesis occur?
Photosynthesis occurs in the chloroplast, as light energy is absorbed by chlorophyll (the green pigment).The main cells in plants that photosynthesis are mesophylls that often contain large amounts of chloroplasts.
What is the stomata and what is its role?
the stomata are tiny pores found on the leaves surface whos opening and closing is controlled by guard cells, the stomata allows carbon dioxide diffusion and absorbtion.
Chloroplast structure
Each chloroplast is encloused in a double membrane.Within this envelope many membranous fluid filled discs called thylakoids are found.the thylakoids are found in stacks these stacks are known as grana, chlorophyll is embedded into these thylakoid membranes.
Light dependent stage process
Occurs in the thylakoid membranes
1.Light excited electrons within the chlorophyll,water previously absorbed splits into oxygen and hydrogen donating an electron to chlorophyll
2.The movement of hydrogen ions (Protons) down its concentration gradient, allows for the formation of coenzyme proton carriers NADPH and ATP
4.Oxygen becomes an output and is diffused out the plant via the stomata, or it is used as an input of aerobic cellular respiration.
5.ATP and NADPH (coenzymes) move to the stroma, where they are used for the light indpenedent stage.
*light-dependent stage traps light energy and converts it to chemical energy in the form of ATP and NADPH, if there is an absence of light, the light dependent stage cannot proceed and photosynthesis stops completely.
What are the inputs and outputs of the light-dependent stage.
Inputs
-Light
-h20
-ADP+ Pi
-NADP
Outputs
-Oxygen
-ATP
-NADPH
light independent stage process
(occurs in the stroma)
Carbon fixation
Carbon dioxide enters the calvin cycle via the stomata.Carbon fixation occurs as it binds with RuBp to form 3-PGA
Reduction
NADPH molecules formed in light dependent reaction donate their hydrogen ions and electrons, ATP breaks down into ADP + Pi these reactions release energy facilitating further changes with the glucose molecules.A specific G3P carbon molecule is formed which then goes on to contribute to the formation of glucose
Regeneration
Some oxygen molecules left over from reaction combine with hydrogens to form the output of water.NADPH and ATP are then recycled back into the light dependent stage.
The main purpose of the light-independent stage is to build inorganic carbon dioxide into energy rich reduced organic molecules,such as sugar glucose. If the glucose is not required for immediate use by a plant it is converted to starch, a plant storage polysaccharide.
Inputs and outputs of light-independent stage
Input
-Carbon dioxide
-NADPH
-ATP
Output
-Glucose
-ADP+ Pi
-NADP+
What is rubisco
Rubisco is a key enzyme in the light independent stage (calvin cycle), it has the ability to bind to carbon dioxide to conduct carbon fixation and further facilitate photosynthesis reactions, however it can also bind to oxygen and cause photorespiration too occur.
Rubisco in c3 plants process (light independent stage)
Carbon fixation:
-Rubisco uses 3 carbon dioxide molecules and 3 RuBP to produce 6 three carbon molecules (called 3-PGA)
Reduction:
-These 6 3PGA molecules are then converted by ATP and NADPH from the light dependent reactions too make 6 G3P molecules.
Regeneration:
-One G3P molecule leaves cycle to facilitate the production of glucose.The remaining G3P molecules are recycled to generate RuBP with the cycle beginning again.
What is photorespiration?
Photorespiration occurs when rubisco binds to oxygen instead of carbon dioxide, it is a wasteful process, disrupting the process of photosynthesis from occuring, meaning less glucose is produced , affecting the plants ability to survive and reproduce.
2 key factors impacting whether rubisco binds to carbon dioxide or oxygen include:
-Substrate concentration:the more substrate present (carbon dioxide), the greater chance that rubisco is likely too bind.To increase substrate concentration the stomata opens allowing carbon dioxide into the plant, and oxygen and water to stimultaneously diffuse out.When a plan needs to conserve water however it closes its stomata, this can lead to a build up of oxygen, increasing the likelyhood of Rubisco binding with carbon and the intiation of Photorespiration
-Temperature:At regular or low temperatures rubisco is more likely too bind with carbon dioxide, however when temperatures are higher rubiscos affinity changes and it becomes more likely too bind with oxygen intiating photo respiration instead.
What are C3 plants
what we consider “Normal” plants.In C3 plants rubisco is responsible for fixing carbon dioxide into 3 carbon compounds which cycles through the pathway all occuring within a mesophyl cell.
Examples of C3 plants include; trees,wheat,rice,majority or fruits,nuts and vegetables.
What is a C4 plant and how does it seperate its carbon cycle
In C4 plants the initial carbon fixation process and the calvin cycle are seperated into 2 seperate cells.Carbon fixation occurs in mesophyll cells however the remainder of the calvin cycle occurs in specialised bundle sheath cells.This means that C4 plants have an additional biochemical pathway compared to C3 plants with adaptions too prevent photorespiration.
Examples of C4 plants include: (sugarcane,corn and switchgrass)
C4 plant calvin cycle process
(Occurs in mesophyll cell)
-Carbon dioxide (CO2) enters mesophyll cells and is fixed by the enzyme pep carboxylase, the CO2 molecule binds with the three carbon molecule (PEP) and forms a 4 carbon molecule (oxaloacetate),(pep carboxylase enzyme responsible for carbon fixation in c4 plants has no affinity to bind with O2)
-Oxaloacetate is then converted to the four carbon molecule malate and is transported to bundle sheath cells
(occurs in bundle sheath cells)
-inside bundle sheath cells, malate breaks down and releases CO2 -Carbon dioxide enters the calvin cycle in exactly the same way as c3 photosynthesis
-pyruvate is then formed from the breakdown of malate and is transported back to the mesophyll cell and converted to another molecule, PEP, with the help of ATP
-PEP is then ready to contribute to the fixation of CO2 and production of oxaloacetate and the cycle continues all over again
What are CAM plants
CAM plants seperate the stages of the calvin cycle such as carbon fixation over time.CAM plants open their stomata at night and keep it closed during the day to prevent water loss.
Examples of CAM plants include;cacti,vanilla,orchids and pineapples
CAM plants calvin cycle
-At night CAM plants open up there stomata to bring in CO2, the CO2 is then fixed into a 4-carbon molecule (oxaloacetate) by the enzyme PEP carboxylase
-Oxaloacetate is then converted to malate which is stored inside vacuoles within the mesophyll cell until the daytime
-During the daytime, CAM plants dont open their stomata to prevent water loss
-Malate is transported out of the vacuole and broken down to release CO2
-CO2 is then free to enter the calvin cycle.
How does light effect photosynthesis
Light is an input of the light dependent stage of photosynthesis,without it photosynthesis cannot occur.As the amount of light is increased so is the rate of photosynthesis
How do different colours of light effect photosynthesis?
-Photosynthesis occurs the most when a plant is exposed to purple or red light
-Occurs relatively the least when exposed to green light.
What causes the plateau seen in photosynthesis graphs
-The maximum mate has been reached since all enzymes in the chloroplasts are operating at their full capacity, that even all inputs were unlimited this would not increase unless their were more enzymes
-One of the other inputs or requirements for photosynthesis is a limiting factor, which is restricting the reaction from hitting a higher reaction rate.
How does temperature effect photosynthesis?
Enzymes catalyse photosynthesis reactions, this means photosynthesis occurs optimally when enzymes are working at their optimal temperature, and that in general increasing temperature will increase reaction rat.
How does pH effect photosynthesis?
Similar to temperature enzymes involved in photosynthesis function best at their optimal temperature, this means that at their optimal temperature photosynthesis will occur its fastest.
