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photosynthesis + cellular respiration

what is the word equation for photosynthesis?

carbon dioxide + water -> glucose + oxygen

what does photosynthesis do?

convert light energy into chemical energy stored in glucose

unbalanced chemical equation for photosynthesis

CO2 + H2O -> C6H12O6 + O2

balanced chemical equation (+ over and under arrow)

6CO2 + 12H20 -> C6H1206 + 6O2 + 6H20

over arrow: light
under arrow: chlorophyll

what is chlorophyll and what is its role in photosynthesis

it is a photosynthetic pigment that absorbs light energy to drive the light dependent stage of photosynthesis

- absorbs red and blue/violet wavelengths best

where is chlorophyll found

in the thylakoid membranes inside chloroplasts (in stacks of grana)

label a chloroplast

.

where does the light dependent stage occur

in the thylakoid membranes (grana) of the chloroplast
- requires light energy

where does the light independent stage occur

in the stroma of the chloroplast

inputs of light dependent stage

light, water, ADP + Pi, NADP+
- water provides electrons and hydrogen ions through photolysis

outputs of light dependent stage

oxygen, ATP, NADPH

what happens during the light dependent stage

1. chlorophyll absorbs light energy

2. electrons become excited and move through an electron transport chain

3. water undergoes photolysis, replacing lost electrons and releasing oxygen

4. ATP and NADPH are produced

what are the inputs of the light independent stage (calvin cycle)

carbon dioxide, ATP, NADPH

what are the outputs of the light independent stage

glucose, ADP + Pi, NADP+

what happens during the light independent stage

1. the calvin cycle uses ATP and NADPH from the light dependent stage to convert carbon dioxide to glucose

2. the enzyme rubisco catalyses carbon fixation

how does light intensity affect the rate of photosynthesis

more light energy is available, so rate increases. eventually plateaus/reaches saturation point where increasing light no longer increases photosynthesis because: enzymes are working at the maximum capacity, OR another factor becomes the limiting factor

how does wavelength of light affect photosynthesis

photosynthesis occurs fastest under red and blue/violet wavelengths because chlorophyll absorbs these wavelengths strongly. green light produces lower photosynthetic rate because most green wavelengths are reflected

how does temperature affect photosynthesis

photosynthesis depends on enzymes in chloroplasts. as temperature increases towards optimum temperature, photosynthesis increases due to more enzyme-substrate collisions: above optimum temperature, enzymes denature

how does pH affect photosynthesis

photosynthetic enzymes function best at their optimal pH. if pH is too high or too low, enzymes denature

how does carbon dioxide concentration affect photosynthesis

carbon dioxide is an input of the light independent stage. increasing CO2 concentration increases photosynthetic rate until a plateau/saturation point is reached. at this point: enzymes are working at maximum capacity, OR another factor becomes the limiting factor

how does water availability affect photosynthesis

water is an input of the light dependent stage and responsible for influencing the stomata opening and closing. when water is limited, stomata close to reduce water loss, less CO2 enters the leaf, so oxygen concentration increases and photorespiration becomes more likely

how does enzyme inhibition affect photosynthesis

enzyme inhibitors interfere with enzymes involved in photosynthesis, reducing the rate of photosynthesis

what is rubisco?

the enzyme that catalyses carbon fixation during the light independent stage

what is rubisco’s role?

to bind carbon dioxide to organic molecules to begin glucose production, however it can also bind to oxygen, causing photorespiration

what is photorespiration

it occurs when rubisco binds to oxygen instead of carbon dioxide, reducing the efficiency of photosynthesis. wastes ATP and reduces glucose production

when does photorespiration occur

when temperatures are elevated, oxygen concentration is high and carbon dioxide concentration is low, rubisco has a higher affinity to bind to oxygen

what are c3 plants? (+ examples)

plants that use the standard calvin cycle where rubisco directly fixes carbon dioxide. better suited to temperate environments, e.g. wheat and rice

how do c4 plants reduce photorespiration

c4 plants use spatial adaptations to reduce photorespiration. the light dependent stage takes place in mesophyll cells, however the light independent stage takes place in bundle sheath cells, further away from the stomata where CO2 concentrations are higher as CO2 is released near rubisco

benefits of C4 plants vs C3 plants

reduced chance of photorespiration, higher photosynthetic efficiency in hot conditions, better adapted to environments with high temperatures, less affected by low CO2 concentrations

limitations of C4 plants

require extra ATP to transport carbon compounds between cells

examples of C4 plants

maize, sugarcane, corn

how do CAM plants reduce photorespiration

they temporally separate carbon fixation and the calvin cycle. at night, the stomata opens, co2 enters and carbon is stored. during the day, stomata close and stored CO2 is released for photosynthesis

why are CAM plants best suited to dry environments

because they keep stomata closed during the day, reducing water loss through transpiration

what are the benefits of CAM plants vs C3 plants

excellent water conservation, reduced chance of photorespiration, survive in extremely dry conditions, less affected by low water availability

limitations of CAM plants

slower growth rate, lower photosynthetic rate, limited CO2 intake because stomata only open at night

examples of CAM plants

cacti, pineapple, succulents

what is CRISPR-Cas 9

a gene editing technology that allows scientists to make precise changes to dna

how does CRISPR increase photosynthetic efficiency and crop yield

modify rubisco to have a higher affinity for CO2 than O2, bypass photorespiration, edit chloroplast function to increase photosynthetic output, modify stomata to reduce water stress

what steps are involved in using CRISPR-Cas9 to improve photosynthesis

1. understand the photosynthetic process of the crop species

2. identify genes affecting photosynthesis and growth

3. use computer modelling to identify inefficiencies

4. use CRISPR-Cas9 to edit genes responsible for the inefficiencies

what are the advantages of CRISPR-Cas9 compared with older models

highly precise, fewer negative side effects, can modify existing DNA

what is cellular respiration? what is its purpose?

cellular respiration is the process of breaking down high-energy organic molecules (such as glucose) to produce ATP

what is the word equation for aerobic cellular respiration

glucose + oxygen -> carbon dioxide + water + ATP

balanced equation for aerobic cellular respiration including ATP

C6H12O6 + 6O2 -> 6CO2 + 6H20 + 30 or 32 ATP

what is ATP

ATP is the main energy carrier in cells

label a mitochondrion

.

what is the function of the cristae

cristae are the folds of the inner mitochondrial membrane that increase surface area for the electron transport chain and ATP production

what are the 3 stages of aerobic cellular respiration

1. glycolysis
   + link reaction

2. krebs cycle (citric acid cycle)

3. electron transport chain

where does glycolysis occur

in the cytosol

what happens during glycolysis

1. 1x glucose is split into 2x pyruvate

2. electrons and hydrogen ions are transferred to NAD+, forming NADH

3. 2 net ATP produced

inputs of glycolysis

1 glucose, ADP + Pi, NAD+ + H+

outputs of glycolysis

2 pyruvate, 2 net ATP, NADH

what is the link reaction

connects glycolysis to the krebs cycle. pyruvate is transported to the mitochondrial matrix, where:

1. each pyruvate is oxidised

2. carbon dioxide is released

3. NADH is produced

4. an acetyl group combines with coenzyme A to form acetyl-CoA, which enters the krebs cycle

where does the krebs cycle (citric acid cycle) occur

in the mitochondrial matrix

what happens during the krebs cycle

in each turn of the krebs cycle:

1. 1x acetyl-CoA enters

2. 1 ATP is produced

3. electron carriers become charged

   • 3 NADH

   • 1 FADH2

4. 2 CO2 are released

because one glucose produces 2x acetyl-CoA, the cycle turns twice per glucose

inputs of krebs cycle

2 acetyl-CoA, ADP + Pi, NAD+ + H+, FAD + H+

outputs of krebs cycle

4CO2, 2 ATP, NADH, FADH2

where does the electron transport chain occur

on the cristae

what happens during the electron transport chain?

1. NADH and FADH2 donate electrons to the electron transport chain

2. electrons move through a chain of cytochromes and enzymes embedded in the inner membrane

3. energy released pumps hydrogen ions out of the mitochondrial matrix, creating a proton gradient

4. hydrogen ions move back through ATP synthase, producing ATP from ADP + Pi

5. oxygen acts as the final electron acceptor, combining with hydrogen to form water

6. produces 26 or 28 ATP

inputs of electron transport chain

O2, ADP + Pi, NADH, FADH2

outputs of electron transport chain

H20, 26 or 28 ATP, NAD+ + H+, FAD + H+

what is anaerobic respiration

a metabolic process that occurs in the absence of oxygen, to generate ATP from glucose

why does anaerobic respiration occur

occurs in the absence of oxygen. without oxygen, the E.T.C cannot be used, so glycolysis is followed by fermentation to allow ATP production to continue

why is glycolysis important in anaerobic fermentation

because it produces 2 net ATP, 2 pyruvate and 2 NADH (which is recycled back into NAD+, allowing glycolysis to continue)

products of anaerobic fermentation in animals

pyruvate -> lactic acid

products of anaerobic fermentation in yeast and plants

pyruvate -> ethanol + CO2

what factors affect the rate of cellular respiration

temperature, pH, glucose concentration, oxygen concentration, enzyme inhibition

how does temperature affect the rate of cellular respiration

• below optimum temperature: substrates have less kinetic energy, so therefore fewer enzyme-substrate collisions and ATP production decreases

• at the optimum temperature: enzymes function at their highest rate, causing the greatest ATP production

• above the optimum temperature: enzymes denature, changing shape and reducing respiration rate dramatically

how does pH affect the rate of cellular respiration

respiration enzymes have optimal pH at which they function most efficiently

• if pH becomes too acidic or basic, enzymes denature

how does glucose concentration affect the rate of cellular respiration

• increasing glucose concentration increases the rate of respiration because more substrate is available for enzymes

• eventually reaches saturation point, meaning all active sites are occupied

  • at this point, increasing glucose no longer increases respiration, causing the graph to plateau

how does oxygen concentration affect the rate of cellular respiration

increasing oxygen concentration increases aerobic respiration and ATP production until it plateaus because enzymes are working at maximum capacity

what is enzyme inhibition

when a molecule (enzyme inhibitor) interferes with enzyme activity, reducing the rate of cellular respiration and ATP production

what is a competitive inhibitor

binds to the enzyme’s active site, preventing the substrate from binding

• its effects can be reduced by increasing substrate concentration, allowing substrates to outcompete the inhibitor

what is a non competitive inhibitor

binds to an allosteric site rather than the active site, causing conformational shape change in the enzyme, altering the active site

• increasing the substrate concentration does not overcome inhibition

what is reversible inhibition

an inhibitor temporarily binds to an enzyme and can later detach

what is irreversible inhibition

an inhibitor binds permanently to an enzyme, preventing it from functioning

what is end-product inhibition

the final product of a metabolic pathway inhibits an earlier enzyme in the pathway

• prevents overproduction and helps regulate metabolism

what is biomass

organic material from living or recently living organisms that can be used to produce fuel

• plant mass

what is biofuel

a renewable fuel made from biomass

• alternative to non-renewable fossil fuels

  • bioethanol

  • biodiesel

what is renewable energy

sources that can be continuously replenished naturally

• biofuels are renewable because biomass can be continuously produced through agriculture and forestry

what is a non-renewable fuel

a fuel source that cannot be replenished quickly enough for human use

• coal

• oil

• natural gas

known as fossil fuels

why are biofuels considered carbon neutral

because the carbon dioxide released during combustion was originally absorbed during photosynthesis

• carbon cycles back into the atmosphere and can be reused by plants

difference between bioethanol and biodiesel

bioethanol: made from plant sugars and starches, produced through fermentation

biodiesel: made from natural oils and fats, produced from vegetable oils or animal fats reacting with short-chain alcohols (e.g. ethanol)

1st step in making bioethanol

deconstruction - biomass is broken down to increase surface area by damaging the cell wall and cellulose

• crushing

• acids

• enzymes

2nd step in making bioethanol

digestion by enzymes (hydrolysis) - enzymes break starch and cellulose into glucose and sugars

3rd step in making bioethanol

ethanol fermentation - yeast anaerobically ferments sugar, producing ethanol

4th step in making bioethanol

purification and dehydration - water is removed through distillation, purifying ethanol into usable fuel

all 4 steps of making bioethanol in order

deconstruction, hydrolysis, fermentation, purification

applications of biofuels

transportation, energy generation

advantages of biofuels

renewable, lower reliance on fossil fuels, carbon neutral

disadvantages of biofuels

large land requirements, deforestation risk, expensive producing

what is an independent variable

the variable that is deliberately changed by the experimenter to test its effect

• variable being tested

what is a dependent variable

variable that is measured or observed in response to changes in the independent variable

what is a controlled variable

variables that are kept constant to ensure a fair test, and prevent other factors from affecting results

what is a control group

does not receive the experimental treatment and is used as a baseline for comparison

what is an aim in an experiment

a statement describing the purpose of the experiment

• to investigate the effect of [IV] on [DV]

what is hypothesis

a testable prediction based on scientific knowledge

if … then

what is a conclusion in an experiment

summarises the results, patters/trends in data, whether the hypothesis was supported

what is a personal error

an error caused by human mistakes during an experiment

what is a systematic error

an error caused by faulty equipment or consistent bias. causes measurements to be consistently too high or too low, reducing accuracy

what is a random error

unpredictable variation that causes results to vary randomly, reducing precision