CHAPTER 4: PHOTOSYNTHESIS & CELLULAR RESPIRATION Flashcards
photosynthesis equation
water and carbon dioxide in the presence of sunlight and chlorophyll form oxygen and glucose
what is photosynthesis
- biochemical pathway
- converts sunlight energy into chemical energy
- involves 2 stages
- light dependant stage
- light independent stage
- co enzymes are used to shuttle the energy between stages
- different enzymes are needed to catalyse reactions
coenzymes ATP + NADPH
- molecules that move energy and (H+) between LD and LI stages
- exist in high energy (loaded form)
- NADPH
- ATP
- exist in low energy (unloaded form)
- NADP+
- ADP
light dependant reaction
- occurs in granum and thylakoid
- uses sunlight energy, water, NADP+ and ADP
- makes oxygen, NADPH and ATP
- energy form the sun is used to split water
- hydrogen binds to NADP+ to form NADPH
- oxygen is a waste product
- energy from the sun excites electrons which:
- provide energy to convert ADP to ATP
light independent reaction
- occurs in the stroma
- catalysed by rubsico
- inputs: carbon dioxide, ATP and NADPH
- outputs: glucose, ADP (+pi), NADP+
- hydrogen is provided by NADPH
- rubisco and energy from ATP and NADPH is used to convert carbon dioxide to glucose
- ADP and NADP+ return to the grana to be reused
what is rubisco
- an enzyme that fixes CO2
- converts inorganic carbon dioxide molecules into organic molecules
- takes CO2 gas from the air to create a solid substance
- this process is known as carbon fixation and calvin cycle
- at low temperatures, CO2 is more likely than O2 to bind to Rubisco
- at low temperatures, the rate of photorespiration in C3 plants is low and the rate of photosynthesis is high.
- as the temperature increases, more O2 and less CO2 binds to Rubisco and thus the rate of photorespiration will increase and the rate of photosynthesis will decrease
what is photorespiration
- wasteful pathway when rubisco acts on oxygen rather than carbon dioxide
- when stomata are closed, O2 accumulates bc CO2 cant enter
- more O2 and less CO2 will bind to rubisco
- rubisco can either bind to carbon dioxide or oxygen
- photorespiration will occur
- CO2, rather than glucose is made
- as temp increases rubisco prefers O2 to CO2
- majority of plants are C3 plants that don’t have adaptations to minimise photorespiration
C3 plants
- first step is carbon fixation of co2 by rubisco
- directly enters calvin cycle
- 35% of plant species are c3
C4 plants
- plants in hot and humid conditions
- minimises photorespiration by separating intial co2 fixation and calvin cycle into different cells
- PEP CARBOXYLASE: has no tendency to bind to O2 fixes atmospheric co2 to a simple 2 carbon organic acid (oxaloacetate)
- occurs in mesophyll cells
- converted to similar molecule, malic acid
- transported to bundle sheath cells
- CO2 is fixed by rubisco and made into glucose (calvin cycle occurs)
- malic acid first breaks down in the bundle sheath cells, releasing co2
- as mesophyll cells constantly pump co2 into neighbouring bundle sheath cells, increases higher concentration of cos compared to o2 around rubsico
- more likely to bind to co2 than o2
CAM plants
- minimises photorespiration and saves water by separating LI stage into 2 stage which occur at diff times, night and day
- plants in conditions that are hot and dry
- at night, cam plants open stomata → allows co2 to diffuse into leaves
- temp is lower so less evaporation occurs, minimises water loss)
- PEP CARBOXYLASE fixes CO2 to oxaloacetate which is then converted to malic acid
- during day time, CAM plants close stomata, but can still phtosynthesis
- malate is broken down to release co2
- enters calvin cycle
- the controlled release of cos maintains high concentration of co2 around rubisco
note: pep carboxylase is specific to co2
CO2 concentration
- factors affecting photosynthetic rate
- rate of photosynthesis increases with increasing concentration of carbon dioxide until a LIMITING FACTOR is reached
- enzyme may be working at their maximum rate (so no increase in p.r is possible)
- availability of essential coenzymes
- ^ limiting factors causing plateau in graph
light intensity - factors affecting photosynthetic rate
- rate of photosynthesis increases with increasing light intensity as there is more energy to drive the reaction
- the rate will plateau when another factor limits the reaction
- decreases light intensity → PS rate is slow or absent
- beyond OPTIMAL light intensity, further increase in light intensity has no effect (chlorophyll has absorbed to its maximum capacity)
temperature
- factors affecting photosynthetic rate
- rate of photosynthesis increases with increasing temperatures as the molecules are moving faster and are more likely to collide
- PS rate decreases when the enzyme catalysing the reaction begins to denature
- when the enzymes active site has changed shape
- caused by too high temperatures
- at low temp, low collision rate produces a low rate of photosynthesis
- as temp rises, rate of photosynthesis initially increases as as rate of molecular collisions increases
- once optimal temperature of the enzymes involved are exceeded, the rate of photosynthesis decreases rapidly
aerobic cellular respiration equation
glucose + oxygen → water + carbon dioxide + 30 or 32 ATP
requires oxygen
anaerobic cellular respiration equation
yeast + bacteria:
* glucose → ethanol + carbon dioxide + 2ATP
animals:
* glucose → lactic acid + 2ATP
does not require oxygen
mitochondria - role in cellular respiration
- site of aerobic cellular respiration
- intermembrane space
- outer membrane
- inner membrane
- matrix
- cristae
- draw a diagram