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Bio > photosynthesis - unit 3 AOS 2 > Flashcards

photosynthesis - unit 3 AOS 2 Flashcards

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Biology 101 flashcards
1
Q

photosynthesis definition

A
  • the process where plants use light energy to power the production of glucose and oxygen from carbon dioxide and water.
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2
Q

autotrouph

A
  • an organism which synthesises its own food from inorganic compounds
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3
Q

heterotroph

A
  • an organism which ingests organic material by feeding on other organisms
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4
Q

photosynthesis purpose

A
  • to use the suns energy to convert inorganic substances into chemical energy in the form of glucose which can be used as an energy source for cells
  • produces oxygen, a gas that we need
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5
Q

chloroplast

A
  • a membrane bound organelle found in photoautotrophs which is the site of photosynthesis
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6
Q

chlorophyll

A
  • a green pigment found on thylakoid membranes and is responsible for absorbing light energy
  • it absorbs red, blue and purple light well but does not absorb green - it refelects
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7
Q

thylakoid

A
  • flattened sacs found in chloroplasts that are made of chlorophyl containing membranes. They are the site of the light dependent stage
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8
Q

granum

A
  • stacks of thylakoids
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9
Q

stroma

A
  • a gel like fluid which surrounds the grana and is the site of the light independent stage of photosynthesis.
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10
Q

stomata

A
  • a small poor found on the leaves surface which opens and closes to allow for gas exchange.
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11
Q

light dependent stage definition

A
  • the first stage of photosynthesis where light energy splits water molecules into oxygen and hydrogen inside thylakoid membranes
  • this stage generates the high energy coenzymes NADPH and ATP which are used in the light in-dependent stage
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12
Q

light dependent stage inputs and outputs

A

inputs: 12H2O, 12NADP+, 18ADP + Pi

outputs: 6O2, 12NADPH, 18ATP

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13
Q

light dependent stage steps

A
  1. Chlorophil captures light energy. In the thylakoid, light energy excites electrons in chlorophyl, moving along proteins. As they move, the energy in the electrons pumps H+ ions into the lumen of the thylakoid. As electrons leave, water donates electrons to replace them. This causes water to split into oxygen, 2H+ and 2e-.
  2. oxygen is released from the chlorophyl which leaves the stomata and enters the environment.
  3. The H+ ions from water and 2 electrons are used to make the coenzyme NADPH (NADP+ +2e- + H+ → NADPH). The movement of H+ ions down their concentration back into the stroma gradient generates the coenzyme ATP (ATP + Pi → ATP).
  4. the coenzymes then move onto the light independent stage.
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14
Q

light independent stage definition

A
  • the second stage of photosynthesis where CO2 is used to from C6H12O6 in the stroma of a chloroplast.
  • the stage uses the coenzymes NADPH and ATP
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15
Q

light independent stage inputs and outputs

A

inputs: 6CO2, 12NADPH, 18ATP

outputs: C6H12O6, 6H20, 12NADP+, 18ADP +pi

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16
Q

light independent stage steps - simple

A
  1. CO2 collected from stomata in leave stomata enters the Calvin Cycle
  2. CO2 undergoes carbon fixation where it is incorporated into organic molecules
  3. The Coenzyme NADPH donates hydrogen ions and electrons and ATP molecules break into ADP + Pi t release energy, facilitating further changes to carbon molecules.
  4. this creates 12 G3P molecules, two of which go into the contribution of glucose, the output of this stage
  5. leftover G3P molcuels
17
Q

the role of coenzymes on photosynthesis

A
  • coenzymes NADPH and ATP are created int he light dependent stage from NADP+ and ADP + pi. these are used in the light independent stage.
  • NADP+ acts as an electron carrier. it gets reduced to form NADPH by accepting electrons produced through the splitting of water. In the Calvin cycle, it provides electrons and protons to facilitate the formation of glucose.
  • energy from sunlight is sued to create ATP from ADP in the light dependent stage. In the Calvin cycle, ATP provides energy for reactions used to convert molecules into glucose.
18
Q

the role of enzymes in photosynthesis

A
  • ATP synthase catalyses the reaction ADP + Pi = ATP using energy from the flow of H+ down its concentration gradient
19
Q

Calvin Cycle steps - detailed

A
  1. Carbon dioxide molecules enter the Calvin cycle. The carbon from CO2 combines with a five-carbon molecule, then splits into 2 x three-carbon molecules, which continue along the cycle
  2. NADPH molecules formed in the light-dependent reactions donate their hydrogen ions and electrons, and ATP molecules break into ADP and Pi to release energy to facilitate further changes to the carbon molecules.
  3. Carbon molecules continue to change and rearrange as they move around the cycle. One specific three-carbon molecule is created and leaves the cycle, going
    on to contribute to the formation of glucose.
  4. Some of the oxygen molecules leftover from the breaking of CO2 at the beginning of the cycle combine with hydrogen ions from NADPH to create the output water.
20
Q

RUBISCO enzyme

A
  • the key enzyme in the light independent stage
  • it is involved in carbon fixation, fixing carbon form inorganic CO2 into organic molecules.
21
Q

photorespiration

A
  • sometimes, rather than using cO2 as a substrate, RUBISCO uses oxygen
  • this takes place when there is low CO2 concentration and high O2 concentration.
  • the process of photorespiration is wasteful in plants
  • less glucose is produced, negatively impacting the plants ability to grow
  • photorespiration can arise in plants due to increased temperature and dry conditions
22
Q

factors impacting whether photorespiration occurs

A

temperature - when the temperature is low, RUBISCOs is more likely to bind to CO2. As the temperature increases RUBISCO loses its ability to distinguish between CO2 and O2, meaning it can be likely to bind to O2 instead, causing photorespiration.

dry conditions: when conditions become dry and water availability decreases C3 plants close their stomata to prevent water loss. this blocks the entry of CO2 and limits the exiting of O2. This creates a high oxygen and low carbon dioxide environment in leaf mesophyll cells, in which the Rubisco enzyme will increasingly bind oxygen rather than bind carbon dioxide.

23
Q

C4 adaptations

A
  • the light independent stage is separated over two different cells
  • carbon fixation occurs in mesophyll cells and the rest of the Calvin cycle occurs in bindle sheath cells to produce glucose
  • in the mesophyll cells, PEP carboxylase is used instead of RUBISCO as it can only bind to CO2 molecules. This forms a 4 carbon molecule which is turned into malic acid
  • in the bundle sheath cell, malate is broken down, releasing CO2 which enter the calvin cycle as normal
  • the constant supply of CO2 from mesophyll cells into bundle sheath cells keeps the concentration of CO2 higher than O2
  • this prevents photorespiration from occurring
24
Q

adaptations in CAM plants

A
  • the light independent stage is separated over day and night
  • the carbon fixation stage takes place at night when the stomata are open
  • the Calvin cycle occurs only at day time
  • CO2 enters though the stomata at night time and PEP carboxylase used CO2 to create 4 caron molecules such as malate which are stored in the Vacuoles of mesophyll cell
  • to prevent water loss, plants do not open their stomata during the day
  • malic acid is released from storage and broken down into CO2, creating a higher concentration of CO2 compared to O2
  • this prevents photorespiration from occurring
25
Q

C4 plants

A
26
Q

disadvantages of C4 and CAM photosynthesis

A
  • it requires more ATP to cycle PEP
  • they use more energy to undertake photosynthesis compared to C3 plants
  • CAM plants can prevent water loss
27
Q

factors affecting the rate of photosynthesis - pH

A
  • enzymes have an optimal pH
  • above or below this pH, the enzymes will begin to denature, slowing down the rate of photosynthesis.
28
Q

factors affecting the rate of photosynthesis - temperature

A
  • as temperature increases, so does the rate pf photosynthesis up until a certain point
  • this is due to increased collisions between reactants and enzymes
  • above the enzymes optimal temperature, the enzymes will begin to denature, slowing down photosynthesis.
  • if temperature increases too much above the optimal temperature, RUBISCO will be more likely to bond to oxygen instead of carbon dioxide, which initiates photorespiration.
29
Q

factors affecting the rate of photosynthesis - light

A
  • as light increases, the rate of photosynthesis increases, to a certain point
  • light is responsible for electron movement in the light dependent stage
  • it will eventually plateau either becase the maximum rate of photosynthesis has been reached, or because of o the other inputs is limited.
30
Q

factors affecting the rate of photosynthesis - CO2 concentration

A
  • as CO2 concentration increases, the rate of photosynthesis will increase to a certain point
  • this is because CO2 is an input
  • it will begin to plateau either because enzymes are working at their maximum rate or because another factor has become limiting.
  • increased CO2 means RUBISCO is more likely to bind to it rather than O2
31
Q

factors affecting the rate of photosynthesis - water

A
  • as water availability increases, so does the rate of photosynthesis as the stomata is more likely to be open.
    this is because water is an input of photosynthesis.
  • when water is low, plants close their stomata to prevent water loss. this prevents the uptake of CO2 for the Calvin cycle, slowing down the rate of photosynthesis.
  • C4 and CAM plants are not affected unless it is extreme
32
Q

reasons why the rate of photosynthesis may plateau

A
  • enzymes could be working at their optimal rate
  • enzyme catalysed systems are fully saturated
  • another factor (input) has become the limiting factor
33
Q

CRISPR Cas-9 to improve photosynthesis efficiencies

A
  • it can be used to knockout sections of genes that result of RUNISCO binding to oxygen instead of carbon dioxide.
  • this reduces the likelihood of photorespiration occurring, thus improving efficiency and maximising the production of glucose.
34
Q

Crispr to improve crop yields

A
  • Crispr technologies can be used to edit a plants genome in order to achieve desired traits that combat different abiotic and biotic stresses.
  • can improve frost, drought and heat tolerance
  • improve disease resistance
  • improve herbicide resistance
  • adjust stomata to improve CO2 uptake
  • improve light capture in chloroplasts
35
Q

Crispr to improve crop quality

A
  • Crispr can be used to improve shelf life, and enhance nutrients, improving the quality of the crop

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