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Biology U3/4 > Chapter 4: Photosynthesis and Cellular Respiration > Flashcards

Chapter 4: Photosynthesis and Cellular Respiration Flashcards

1
Q

Outline the light dependent stage of photosynthesis

A
  • Occurs in thylakoids and grana
  • Inputs → Water (H2O), NADP+ and ADP + Pi
  • Outputs → Oxygen (O2), NADPH and ATP
  • Energy is provided by light
  • Chlorophyll absorbs light energy
  • Sunlight energy excites electrons, providing energy to convert ADP to ATP
  • Sunlight energy is used to split water
    • Hydrogen binds to NADP+ to form NADPH
    • Oxygen is a waste product that will diffuse out through the plasma membrane

NOTE: The light dependent stage is the same for all three plant types; C3, C4 and CAM.

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2
Q

Outline the light independent stage of photosynthesis

A
  • Occurs in the stroma
  • Inputs → ATP, NADPH and CO2
  • Outputs → ADP + Pi, NADP+ and glucose
  • Energy is provided by ATP molecules
  • Rubisco, along with energy from ATP and NADPH, is used to convert carbon dioxide to glucose
  • ADP + Pi and NADP+ is returned to the grana to be reused

NOTE: The synthesis of glucose is an anabolic reaction as ATP is being used.

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3
Q

Explain Rubisco

A
  • Enzyme in C3 plants that bring carbon dioxide from the air into the Calvin cycle where glucose is made
    • Earth’s most abundant enzyme
  • Rubisco works most efficiently in
    • High levels of carbon dioxide
    • Low oxygen levels
    • Moderate temperatures
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4
Q

Explain the issues faced by CAM and C4 plants (desert and tropical plants)

A
  • These plants are generally in hot and dry areas where water is scarce
  • Limited water results in closed stomata leading to an accumulation of oxygen, hence, an increased rate of photorespiration as rubisco will bind to oxygen rather than CO2
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5
Q

Explain photorespiration

A
  • Photorespiration occurs when plants take up oxygen instead of carbon dioxide resulting in a decreased rate of photosynthesis
  • Photorespiration occurs as temperatures increase or as conditions dry out
    • This is because stomata remain closed (to prevent water loss) resulting in the accumulation of oxygen as carbon dioxide cannot enter
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6
Q

Explain how C4 plants have adapted to avoid photorespiration

A
  • Plants in warm and tropical environments (e.g. corn and sugar cane)
  • Initial CO2 fixation and the calvin cycle are separated into different cells
  • PEP carboxylase fixes carbon dioxide (converts it into a similar molecule, malic acid) in leaf mesophyll cells
  • Glucose production via the Calvin cycle occurs in bundle sheath cells
    • Malic acid breaks down in bundle sheath cells releasing CO2
    • CO2 concentration increases allowing Rubisco to bind to it
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7
Q

Explain how the structure of C4 plants facilitate the adaptations they have to minimise photorespiration

A
  • Bundle-sheath cells are surrounded by mesophyll cells for the efficient transfer of malic acid
  • Stomata are adjacent to mesophyll cells for fast initial carbon fixation
  • Less air pockets to store gases exchanged in photosynthesis
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8
Q

Explain how CAM plants have adapted to avoid photorespiration

A
  • Plants in hot and arid environments (e.g. cacti and orchids)
  • Initial CO2 fixation occurs at night and the calvin cycle occurs during the day
  • Night: CAM plants open their stomata allowing CO2 to enter
    • PEP carboxylase fixes CO2 into malic acid (or other organic acids)
    • Malic acid is stored in vacuoles in mesophyll cells
  • DAY: CAM plants close their stomata to prevent water loss
    • Malic acid is released from storage and is broken down to release CO2
    • CO2 concentration increases allowing Rubisco to bind to carbon dioxide

NOTE: Both stages take place in leaf mesophyll cells.

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9
Q

Explain how CAM plants photosynthesise when water is available and their stomata are open

A
  • They revert back to the C3 process of photosynthesis
  • Carbon fixation is not split up
  • The light dependent and light independent stage both occur during the day
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10
Q

Explain why PEP carboxylase is able to avoid photorespiration

A
  • PEP carboxylase only binds to carbon dioxide at its active site (photorespiration cannot occur)
  • Not capable of binding oxygen
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11
Q

Explain the importance of maximising photosynthetic efficiency

A
  • Maximising photosynthetic efficiency increases glucose production and allows for the conservation of energy
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12
Q

Explain how light availability can affect the rate of photosynthesis

A
  • The rate of photosynthesis increases as light availability increases until a maximum point is reached
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13
Q

Explain how water availability can affect the rate of photosynthesis

A
  • When water is scarce, stomata close resulting in a decreased rate of photosynthesis
  • This is because closed stomata prevent the uptake of carbon dioxide needed for the calvin cycle
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14
Q

Explain how carbon dioxide concentration can affect the rate of photosynthesis

A
  • The rate of photosynthesis increases as carbon dioxide concentration increases until a limiting factor is reached
  • E.g. Rubisco or PEP carboxylase may already be working at their maximum rate
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15
Q

Explain why temperature affects the rate of photosynthesis

A
  • The rate of photosynthesis increases as temperature increases until a maximum point is reached
  • This is because molecules are moving faster and are more likely to collide

NOTE: Temperature also influences whether stomata are open or closed. High temperatures = closed stomata = decreased rate of photosynthesis.

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16
Q

Outline the three interconnected stages of aerobic cellular respiration

A
  • Glycolysis → one glucose molecule is split into two pyruvate molecules
    • Does not require oxygen
    • Occurs in the cytosol
  • Krebs cycle → further breakdown of pyruvate resulting in the formation of NADH and FADH2coenzymes
    • Does not require oxygen
    • Occurs in the mitochondrial matrix
  • Electron transport chain → energy from electrons (via loaded coenzymes) used to make ATP
    • Requires oxygen
    • Occurs in the cristae (inner mitochondrial membrane)
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17
Q

State the inputs and outputs of glycolysis

A
  • Inputs → Glucose, NAD+ (2) and ADP + Pi (2)
  • Outputs → Pyruvate (2), NADH (2) and ATP (2)
18
Q

Explain pyruvate oxidation

A
  • Before pyruvate enters the Krebs cycle, pyruvate oxidation occurs
  • Pyruvate moves into the mitochondria and is modified into acetyle coenzyme a (acetyl-CoA)
19
Q

State the inputs and outputs of the Krebs cycle

A
  • Inputs → Pyruvate, NAD+, FAD and ADP + Pi
  • Outputs → CO2, NADH, FADH2 and ATP
20
Q

State the inputs and outputs of the electron transport chain

A
  • Inputs → O2, NADH, FADH2 and ADP + Pi
  • Outputs → H2O, NAD+, FAD and ATP
21
Q

State how much ATP is made in each stage of cellular respiration (+ net yield)

A
  • Glycolysis → 2
  • Krebs cycle → 2
  • Electron transport chain → 26-28
  • Net → 30-32
22
Q

Explain why ATP is produced and not just glucose

A
  • Glucose has greater chemical energy content than ATP, however, the direct use of glucose leads to the production of excessive heat and waste
  • ATP is a more useable form of energy as its energy can be released in a single step (energy isinstantlyavailable for use by cells)
  • Release of energy from glucose involves a multistep pathway that is about 100 times slower than that for ATP energy release
23
Q

State the cellular location and ATP output of fermentation

A
  • Anaerobic fermentation occurs in the cytoplasm (usually of human skeletal muscle cells) when oxygen supply from aerobic cellular respiration cannot keep up with the demand for ATP
  • Produces a net of 2 ATP molecules
24
Q

State the equation for lactic acid fermentation in animals

A

Glucose → Lactic acid + 2ATP

25
Q

State the inputs (reactants) and outputs (products) of lactic acid fermentation in animals

A
  • Inputs → Glucose, NAD+ and ADP + Pi
  • Outputs → Lactic acid, NAD+ and ATP
26
Q

State the equation for ethanol fermentation in yeasts

A

Glucose → Ethanol + CO2 + 2ATP

27
Q

State the inputs (reactants) and outputs (products) of fermentation in yeasts

A
  • Inputs → Glucose, NAD+ and ADP + Pi
  • Outputs → Ethanol, CO2, NAD+ and ATP
28
Q

State how glucose and oxygen availability affects the rate of cellular respiration using the term limiting factor

A
  • As glucose and oxygen availability increases, the rate of cellular respiration increases
  • This rate eventually levels off from limiting factors
29
Q

Explain the difference between aerobic and anaerobic cellular respiration

A
  • Anaerobic operates without oxygen
  • Anaerobic takes place totally within the cytosol of cells
  • Anaerobic produces less ATP per glucose molecule
  • Anaerobic does not involve ETC
  • Anaerobic produces ATP quicker (about 100 times faster)
  • Anaerobic takes up more glucose to get the same amount of energy (as aerobic, therefore more wasteful)

NOTE: Anaerobic cellular respiration occurs at a faster rate enabling more ATP to be produced per unit of time.

30
Q

Describe two ways CRISPR-Cas9 could improve crop yield

A
  • Target certain genes that impact crop yield by either inserting advantageous genes or removing disadvantageous genes
  • This improves photosynthetic efficiency and speed allowing for higher crop yield
31
Q

Describe one potential way CRISPR-Cas9 could be used to increase the efficiency of photosynthesis

A
  • Genes that code for Rubisco can be edited to make it less likely to bind with oxygen (reduce photorespiration)
  • Delete genes that increase the binding of Rubisco and oxygen
  • Insert genes that would promote Rubisco to bind with carbon dioxide
  • This reduces the likelihood of photorespiration and therefore improve photosynthetic efficiency
32
Q

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

A
  • More precise than traditional methods
  • Able to edit multiple target genes simultaneously
  • Can knock out certain genes
  • Can insert certain genes
33
Q

Define biofuel

A
  • Any source of energy made up of from biomass (organic material)
34
Q

List 3 substances that can be used as biomass

A
  • Wood, ethanol and waste
35
Q

Describe how biomass can be converted to biofuel using fermentation

A
  • Microorganisms (e.g. bacteria and yeast) metabolize plant sugars and produce ethanol
36
Q

List advantages and disadvantages biofuel has over other fuel types

A
  • Advantages
    • It is a renewable energy source
    • Causes less pollution
    • Many ways to apply it and use for energy
  • Disadvantages
    • Extraction and storage of biomass can be expensive
    • Large areas are required for the different processes involved in harnessing energy from biomass
37
Q

Chloroplasts

A
  • Chloroplasts are present in all plants but not all plant cells (e.g. roots and onion epidermal cells)
  • Most abundant in shaded regions, allowing plants to maximise limited light availability
38
Q

Explain the function of photosynthesis

A
  • Converts light energy into chemical energy stored as glucose
  • Glucose provides energy to produce ATP, which the cell can use for energy and to catalyse reactions
39
Q

C3 plants

A
  • C3 plants comprise about 85% of terrestrial plants worldwide
  • Cool to temperate conditions
  • Carbon fixation occurs only once
40
Q

State the optimal wavelengths of light for photsynthesis

A
  • Plants with chlorpohyll best absorbs violet, blue and red light
  • They absorbs less light of green wavelength

Biology U3/4 (12 decks)

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