CHAPTER 4: PHOTOSYNTHESIS + CELLULAR RESPIRATION

Question 1

photosynthesis equation

Answer 1

water and carbon dioxide in the presence of sunlight and chlorophyll form oxygen and glucose

Question 2

what is photosynthesis

Answer 2

• 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

Question 3

coenzymes ATP + NADPH

Answer 3

• 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

Question 4

light dependant reaction

Answer 4

• 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

Question 5

light independent reaction

Answer 5

• 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

Question 6

what is rubsico

Answer 6

• 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

Question 7

what is photorespiration

Answer 7

• 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

Question 8

C3 plants

Answer 8

• first step is carbon fixation of co2 by rubisco
  
  • directly enters calvin cycle
  • 35% of plant species are c3

Question 9

C4 plants

Answer 9

• 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

Question 10

CAM plants

Answer 10

• 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

Question 11

CO2 concentration
- factors affecting photosynthetic rate

Answer 11

• 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

Question 12

light intensity
- factors affecting photosynthetic rate

Answer 12

• 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)

Question 13

temperature
- factors affecting photosynthetic rate

Answer 13

• 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

Question 14

aerobic cellular respiration equation

Answer 14

glucose + oxygen → water + carbon dioxide + 30 or 32 ATP

requires oxygen

Question 15

anaerobic cellular respiration equation

Answer 15

yeast + bacteria:

• glucose → ethanol + carbon dioxide + 2ATP

animals:

• glucose → lactic acid + 2ATP

does not require oxygen

Question 16

mitochondria - role in cellular respiration

Answer 16

• site of aerobic cellular respiration
• intermembrane space
• outer membrane
• inner membrane
• matrix
• cristae
  
  • draw a diagram

Question 17

glycolysis

Answer 17

• first stage
• occurs within the cytoplasm
• glucose is broken down into pyruvic acid
  
  • releases 2ATP and 2NADH
• pyruvic acid moves via diffusion into the mitochondria to begin aerobic cellular respiration
• inputs:
  
  • glucose
  • ADP + Pi (2)
  • NAD+ (2)
• outputs
  
  • pyruvate (2)
  • ATP (2)
  • NADH (2)

Question 18

intermediate stage

Answer 18

when it moves into the mitochondria, pyruvic acid is modified into acetyle coenzyme a (Acetyl CoA)

Question 19

Kreb’s cycle

Answer 19

• • 2nd stage
  • occurs within the mitochondria matrix
  • converts acetyl CoA into the following outputs
  Inputs:
  • Acetyl CoA (× 2)
  • ADP + Pi (× 2)
  • NAD+(× 8)
  • FAD (× 2)
  Outputs:
  • CO2(× 6) — 2 during pyruvate oxidation and 4 during Krebs cycle component
  • ATP (× 2)
  • NADH (× 8) — 2 during pyruvate oxidation and 6 during Krebs cycle component
  • FADH2(× 2)

Question 20

electron transport chain

Answer 20

• final stage
• the etc consists of a series of protein complexes embedded in the cristae
• The first input of high-energy electrons to the ETC comes from loaded NADH coenzymes.
• FADH2also donates its high-energy electrons to an acceptor, but further down the chain.
• As electrons transfer from one enzyme complex to the next, the energy released is ultimately used to power the production of ATP from ADP and Pi.
  
  • energy is released from the loaded coenzymes → NADH and FADH2
• The final electron acceptor at the end of the ETC is oxygen.
• the ‘lost energy’ is used to pump H+ across membrane and into intermembrane space
• this creates a concentration gradient
  
  • H+ wants to move back
  • an enzyme located in the cristae (ATP synthase) provides a channel for them to do this
  • as H+ moves through channel, they lose energy
  • ATP synthase uses this energy to phosphorylate ADP
  • creates ATP
  • 26-28
• Inputs:
  
  • O2(× 6)
  • ADP + Pi (× 26–28)
  • NADH (× 10)
  • FADH2(× 2)
• Outputs:
  
  • H2O (× 6)
  • ATP (× 26–28)
  • NAD+(× 10)
  • FAD (× 2)

Question 21

aerobic cellular respiration vs anaerobic cellular respiration

Answer 21

• anaerobic operates without oxygen
• anaerobic takes place totally within the cytosol of cells
• anaerobic produces far less ATP per glucose molecule metabolised than that of aerobic
• anaerobic produces ATP at a rate about 100 times faster than that of aerobic
• anaerobic doesn’t involve ETC
  
  • faster rate of production enable more ATP to be produced per unit of time
• aerobic cellular respiration has a higher energy yield

Question 22

anaerobic fermentation

Answer 22

• NAD+ is continually recycled between glycolysis and the nad+ regeneration stages
• it is loaded to form NADH during glycolysis
• it is unloaded during the NAD+ regeneration stage (add on stage)

IN ANIMALS

Inputs:

• Glucose
• NAD+(× 2)
• ADP + Pi (× 2)

Outputs:

• Lactic acid
• NAD+(× 2)
• ATP (× 2)

IN YEAST/BACTERIA/PLANTS

Inputs:

• Glucose
• NAD+(× 2)
• ADP + Pi (× 2)

Outputs:

• Ethanol
• CO2
• NAD+(× 2)
• ATP (× 2)

Question 23

oxygen concentration (CR)

Answer 23

• as oxygen concentration increases, so does the rate of cellular respiration
• like w glucose concentration this eventually levels off (plateaus) due to other factors limiting the rate
  
  • rate of supply of electrons via the ETC has reached its maximum, so no further increase in cellular respiration rate can occur

Question 24

glucose concentration (CR)

Answer 24

• increase in glucose conentration lead to an increase in the rate of cellular respiration
• this rate eventually plateaus from rate limiting factors
  
  • the active sites of the first rate-determining enzyme in the cellylar respiration pathway are saturated with substrates (the glucose)
  • so, no further increase in the amount of carbon dioxide can occur

Question 25

temperature (CR)

Answer 25

• at low temp, collisions between substratr and enzyme are less frequent
  
  • rate of respiration decreases
  • as temp. increases further, respiration rate increases until optimal temp. is reached
  • as temp increases above optimal, heat denaturation befins
    
    • causes steep decline in respiration rate

Question 26

define biofuel

Answer 26

• comes from biomass, which are organic materials from plants or animals that can be used for fuel production
• renewable source of energy
• contains stored energy from the sun and plants
• when burnt, heat is released allowing for electricity

Question 27

substances that can be used as biomass

Answer 27

• animal fat
• garbage
• landfill gas
• crops

Question 28

landfill gas

Answer 28

• fermentation by bacteria and fungi decomposes dead plants and animals (biomass)
• produced methane which is collected and purified to be used as fuel
• used for electricity for cooking or lighting

Question 29

bioethanol

Answer 29

• ethanol-based fuel that comes from sugars in photosynthetic plants
• These sugars are a product of photosynthesis and are then able to be fermented by bacteria to produce ethanol as a by-product
• E10 - 10% ethanol

Question 30

biodiesel

Answer 30

• are made from animal fats, recycled cooking oil, and vegetable oils
• B5 - 5% biodiesel

Question 31

advantages of using biomass

Answer 31

• renewable because we will always have the sources of biomass such as crops, manure, and garbage
• cost-effective → energy harnessed from biomass is inexpensive compared to coal and oil
• available in large quantities all over the world

Question 32

diasdvantages of using biomass

Answer 32

• expensive → extraction and storage of biomass can be expensive
• requires space → big areas are required for all the different processes involved in harnessing energy from biomass
  
  • large areas are required for storage.

Question 33

how can CRISPR Cas9 be used to improve crop yield

Answer 33

• target certain genes that impact crop yield
  
  • insert genes to improve crop yield
  • knocking out genes that have a negative effect
• improved outcome of photosynthesis efficiency + speed
• → more crop yield for C3 plants
• → more food for consumers
• → being able to produce crops even when it is out of season

Question 34

how can CRISPR-Cas9 be used to increase the efficiency of photosynthesis

Answer 34

• rubisco is an enzyme (produced by transcription and translation)
• these genes are a target site for genome editing
• CRISPR Cas9 can be used to alter the genes that code for Rubisco to make it less likely to bind with oxygen
  
  • delete genes that increase the binding of rubisco with oxygen
  • insert genes that would promote rubisco to bind to carbon dioxide
• makes it more efficient → likely to bind with CO2 for carbon fixation for photosynthesis to occur
  
  • reduce photorespiration

Question 35

how can CRISPR Cas9 be used to improve crop quality

Answer 35

• used to alter the gluten and nutrient content, storage quality and visual appearance of crops
  
  • eg. alter the a-gliadin gene in cereal crops (responsible for making gluten proteins)
    
    • removing the gene enables people w coeliac to eat it
  • eg, increasing the amount of amylose and reducing amount of starch in the rice by editing their genes
    
    • nutrient quality increases

Question 36

how can CRISPR Cas9 be used to improve biotic + abiotic stress factors

Answer 36

• CRISPR Cas9 can be used to increase crop resistance to biotic factors
  
  • virus, bacteria, and pests
• increase crop resistance to abiotic factors
  
  • drought, salt tolerance, stress, herbicides

Question 37

benefits of using CRISPR-Cas9 over other methods to increase crop yield

Answer 37

• simultaneous editing of multiple target sites.
• CRISPR-Cas9 offers an easier, more versatile, and accurate form of genetic modification
• can perform mutations to a specific site within the targeted gene, making the effects on the plants more significant as it can be programmed to target specific segments of genetic code or edit DNA with greater accuracy.
• Traditional gene-editing techniques had a negative effect on crop yields. with a decrease in crop yield, size, and mass
• CRISPR-Cas9 could eliminate these negative side effects and improve these yield-related traits.
• CRISPR-Cas9 can be used to target certain genes that impact crop yield; such as by inserting genes to improve yield or knocking out genes that have a negative effect.

Question 38

impact of water availability on the rate of photosynthesis

Answer 38

• low water levels: stomata close resulting in a decreased rate of photosynthesis
• closed stomata prevent the uptake of carbon dioxide needed for the calvin cycle

Question 39

what are accessory pigments

Answer 39

• pigments that can absorb light at different wavelengths
• can extend absorption spectrum of photosynthesis

Question 40

coloured light affecting rate of photosynthesis

Answer 40

• chlorophyll best absorbs violet, blue and red light
• in plants with photosynthesis, the rate is highest in these coloured lights
• absorbs less light of green wavelength

Question 41

controlled variables for photosynthesis experiments

Answer 41

• same wavelength of light
• temperature
• humidity
• pH of soil
• number of seeds for each plant
• the volume of water applied to plants.