2.9 Photosynthesis

Question 1

what is photosynthesis?

Answer 1

the process by which cells synthesise organic compounds (eg. glucose) from inorganic molecules (CO2 + H2O) in the presence of sunlight

Question 2

what does photosynthesis require?

Answer 2

requires photosynthetic pigment (chlorophyll) and only occurs in certain organisms

Question 3

what is the equation for photosynthesis?

Answer 3

6CO2 + 12H2O -> C6H12O6 +6O2 + 6H2O

Question 4

What is chlorophyll? (2)

Answer 4

A green pigment found in photosynthetic organisms responsible for light absorption
When it absorbs light it releases electrons which are used to synthesis ATP

Question 5

Collectively, what does chlorophyll absorb? (2)

Answer 5

• chlorophyll absorbs light moist strongly in blue portion of the visible spectrum, followed by the red portion
• chlorophyll reflects light most strongly in the green portion of the visible spectrum (why green colours of leaves)

Question 6

What is the absorption spectrum?

Answer 6

It indicated the wavelength of light absorbed by each pigment

Question 7

What is the action spectrum?

Answer 7

Indicates the overall rate of photosynthesis at each wavelength of light

Question 8

What kind of correlation is there between the cumulative absorption spectra of all pigments and the action pigments?

Answer 8

Strong

Question 9

What are the steps of photosynthesis? (2)

Answer 9

• the light dependent reaction convert light energy from the sun into chemical energy
• the light independent reactions use the chemical energy to synthesis e organic compounds

Question 10

What are the processes of light dependent reaction? (3)

Answer 10

• light is absorbed by chlorophyll, which results in the production of ATP
• light is also absorbed by water which is split (photolysis) to produce oxygen and hydrogen
• the hydrogen and ATP are sued in the light independent reactions, the oxygen is released from the stomata as a waste product

Question 11

What are the processes of light independent reaction? (3)

Answer 11

• ATP and hydrogen (carried by NADPH) are transferred to the site of the light independent reactions
• the hydrogen is combined with carbon dioxide to form complex organism compounds (eg. Carbs, amino acids)
• the ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together

Question 12

What are different types of pigments which absorb light? (3)

Answer 12

Chlorophylls, xanophyll and carotenes

Question 13

What the process chromatography? (3)

Answer 13

• a mixture is dissolves in a fluid (mobile phase) and passed through a static material (stationary phase)
• the different components of the mixture travel at different=fervent speeds, causing them to separate
• a retardation factor can then be calculated at different speeds (Rf value= distance component travels / distance solvent travels)

Question 14

What are the 2 most common techniques for separating photosynthetic pigments?

Answer 14

• paper chromatography - uses paper (cellulose) as the stationary bed
• thin layer chromatography - uses thin layer of absorbent which runs faster and has better separation

Question 15

What is the law of limiting factors?

Answer 15

States that when a chemical process depends on more then one essential condition being favourable, the rate if reaction will be limited by the factor that is nearest its minimum value

Question 16

How can temperature become a limiting factor? (3)

Answer 16

• photosynthesis is controlled by enzymes, which are sensitive to temperature fluctuations
• as temperature increases reaction rate will increases, as reactants have greater kinetic energy and more collisions result
• above a certain temperature the rate of photosynthesis will decrease as essential enzymes begin to denature

Question 17

How can light intensity become a limiting factor? (4)

Answer 17

• light is absorbed by chlorophyll which convert the radiant energy into chemical energy (ATP)
• as light intensity increases reaction rate will increase as more chlorophyll are being photo-activated
• at a certain light intensity photosynthetic rate will plateau, as available chlorophyll are saturated with light
• different wavelengths of light will have different effects in the rate of photosynthesis

Question 18

How can carbon dioxide become a limiting factor? (3)

Answer 18

• carbon dioxide is involved in the fixation of carbon atoms to from organic molecules
• as carbon dioxide concentration increases reaction rate will increase, as more concentrations of CO2 -
• at a certain concentration of CO2 photosynthetic rate will plateau as the enzymes responsible for carbon fixation are saturated

Question 19

How can CO2 uptake be used to measure rate of photosynthesis? (5)

Answer 19

• CO2 uptake measured by placing leaf tissue in an enclosed space with water
• water we of dissolved carbon dioxide can initially be produced by boiling and cooling water
• carbon dioxide interacts with the water molecules produced by bio carbonate and hydrogen ions which change the pH (increase acidity)
• increased uptake of CO2 by the plant will lower the concentration in solution and increase the alkalinity (with probe)
  (Or CO2 levels may be monitored is data logger)

Question 20

How can O2 production be used to measure rate of photosynthesis? (4)

Answer 20

• oxygen production can be measures by submerging a plant in an enclosed water-filled space attached to a sealed gas syringe
• any oxygen gas produced will bubble out of solution and can be measured by change in meniscus level on the syringe
• or oxygen production could be measured by the time taken for submerged lead discs to surface
• oxygen levels can also be measured with a data logger if the appropriate probe is available

Question 21

How can biomass (indirect) be used to measure rate of photosynthesis? (5)

Answer 21

• glucose production can be indirectly measured by a change in the plants biomass(weight)
• this requires the plant tissue to be completely dehydrated prior to weighing to ensure the change in biomass represents organic matter and not water content
• an alternative method to measuring glucose production is to determine he change in starch levels (glucose is stored as starch)
• starch can be identified via iodine staining (turns starch solution purple) and quantitated suing a colorimeter

Question 22

How are oceans oxygenated? (3)

Answer 22

• earth’s oceans initially has high levels of dissolved iron (released from the crust by underwater volcanic vents)
• when the iron reacts with oxygen gas it undergoes a chemical reaction to from an insolubleprecipitate (iron oxide)
• when iron in the ocean was completely consumed, oxygen gas started accumulating in the atmosphere

Question 23

How are atmosphere oxygenated? (2)

Answer 23

• for the first 2 billion yrs after the earth was formed its atmosphere was anoxic (oxygen-free)
• the current concentration of oxygen gas within the atmosphere is approximately 20%

Question 24

How are rock deposition oxygenated?

Answer 24

• the reaction between dissolved iron and oxygen gas created oceanic deposits called banned iron formations
• these deposits are not commonly found in oceanic sedimentary rock younger than 1.8 billion yrs old
  -> this likely reflects the time when oxygen levels caused the near complete consumption of dissolves iron levels
• as BIF deposition slowed in oceans, iron rich layers started to door on land due to the rise in atmospheric O2 lvl

Question 25

How is biological life oxygenated? (2)

Answer 25

• free oxygen is toxic to obligate anaerobes and an increase in O2 levels may have wiped out many of these species
• conversely, rising O2 lvls was critical determinant to the evolution of aerobically respiring organisms