2.9 (Energy Metabolism)

Question 1

Define photosynthesis.

Answer 1

• Photosynthesis is the production of carbon compounds in cells using light energy.
• The process in which cells synthesize organic compounds (eg. glucose) from inorganic compounds (H2O + CO2) in the presence of sunlight.

Question 2

State the chemical equation for photosynthesis.

Answer 2

6CO2 + H2O ———> C6H12O6 + 6O2

Question 3

Define visible light.

Answer 3

Electromagnetic radiation in the range of 400-700nm, which can be detected by the eye and used by plants.

Question 4

State the relationship between wavelength and energy.

Answer 4

The shorter the wavelengths, the more energy there is. The longer the wavelengths, the less energy there is.

Question 5

State the range of wavelengths that fall within the visible spectrum.

Answer 5

Visible light range from 700 nm - 400 nm. The colors from long to short wavelengths are red, orange, yellow, green, blue, indigo, and violet

Question 6

Define pigment

Answer 6

Substances, often proteins, which absorbs light and therefore color appears to us the ones that the pigment doesn’t absorb

Question 7

State the primary and accessory pigments found in chloroplasts.

Answer 7

• The primary pigment in the chloroplast is the chlorophyll (green).
  
  • Chlorophyll-A is the most abundant and has a darker green.
  • Chlorophyll-B is the less abundant and has a lighter green.
• Carotenes are orange.
• Protective pigments (red, violet, blue) attracts pollinators and protects DNA from UV light.

Question 8

Explain why plants are green.

Answer 8

Sunlight contains all the wavelengths of visible light. The main photosynthetic pigment in plants is the chlorophyll, which appears green because it reflects light most strongly in the green portion of the spectrum. Chlorophyll absorbs light most strongly in the blue portion followed by the red portion of the spectrum.

Question 9

​Define photolysis.

Answer 9

• Photolysis means water splitting. During photosynthesis, light energy is used to split water molecules as represented by the following equation: 2H2O → 4H+ + 4e- + O2

Question 10

State the equation for photolysis.

Answer 10

2H2O → 4H+ + 4e- + O2

Question 11

State that the oxygen produced in photolysis is a waste product of photosynthesis

Answer 11

Oxygen (O2) is released as a waste product in this process. The H+ and e- continue on in the photosynthesis light reactions.

Question 12

State the energy conversion that occurs during photosynthesis.

Answer 12

Energy can’t be created/destroyed. The energy in the form of light is converted into chemical energy in the bonds of carbohydrates.

Question 13

Define “limiting factor.”

Answer 13

A limiting factor is a variable of a system that can limit the rate of a reaction.
Either the amount of light, temperature or CO2 concentration will limit the rate of photosynthesis. Whichever of the three is furthest from its optimal will be the limiting factor.

Question 14

Explain how the following factors limit the rate of photosynthesis: temperature, light intensity, CO2 concentration.

Answer 14

Temperature

• Photosynthesis is an enzyme-catalyzed reaction, and like with other enzyme reactions, photosynthesis rate will increase as the temperature is raised until an optimal temperature is reached.
• After the optimum, the rate of photosynthesis abruptly declines with further increase of temperature. The decline is because most enzymes involved in photosynthesis rapidly denature at higher temperatures.

Light intensity
- Without enough light, a plant cannot perform photosynthesis because light energy is required in the light dependent reactions.
Increasing the light intensity will increase the rate of photosynthesis. - -
- However, at a certain point the photosynthetic rate will plateau. The leveling off is because all available chlorophyll pigments are being used.

CO2 concentration

• Without carbon dioxide, a plant cannot perform photosynthesis because CO2 is required in the light independent reactions.
• Increasing carbon dioxide concentration will increases the rate of photosynthesis.
• However, at a certain point the photosynthetic rate will plateau. The leveling off is because all enzymes used in the reactions are being used.

Question 15

State that (some) prokaryotes, algae and plants carry out photosynthesis.

Answer 15

Prokaryotes were the first to perform photosynthesis around 3.5 billion years ago, they became a part of the algae and plants million of years later.

Question 16

Define and state evidence for the “Great Oxidation Event.”

Answer 16

The rise in oxygen concentration to 2% about 2.4 billion years ago is known as the Great Oxidation Event.
* Banded ion formation in rocks dated between 2.4-2.2 BYO.
* Only when iron dissolved in ancient oceans where it was exposed to oxygen resulted in rusting.
Due to no other significant sources of oxygen are known, scientists attribute the rise in atmosphere O2 to biological synthesis.

Question 17

Distinguish between an action spectrum and an absorption spectrum.

Answer 17

Action: Overall rate of photosynthesis acting at each wavelength
Absorption: wavelength of light absorbed by each pigment.

Question 18

Describe the shape of the curve for an absorption spectrum.

Answer 18

Both absorption and action displays peak at the blue (~450nm) and red (~670nm)
Both displays a drop at green/yellow region (~550nm)

Question 19

Describe the shape of the curve for an action spectrum.

Answer 19

Both absorption and action displays peak at the blue (~450nm) and red (~670nm)
Both displays a drop at green/yellow region (~550nm)

Question 20

​List mechanism for measuring the rate of photosynthesis.

Answer 20

Measuring the uptake of CO2

• immobilized algae in hydrogen carbonate indicator solution
• monitor the CO2 concentration using a CO2 sensor

Measuring the production of O2

• counting bubbles formed
• measuring water displacement by O2 gas formed
• floating leaf disk

Measuring the increase in dry mass
- harvest plants and record how much mass they have accumulated as a proxy measure for carbohydrate formation

Question 21

Outline the process of separating pigments using chromatography

Answer 21

1) Place a line of pigment extract from leaf tissue on one end of the filter paper and dip it in an inorganic substance.
2) As the solvent moves up the semi-polar paper, the pigments get moved as well. The components that adhere more strongly to the other paper travels more slowly compared to those which are less adhesive.

Question 22

Calculate the Rf value for pigments using pigment chromatography.

Answer 22

Rf value: (distance of pigment traveled)/(distance solvent traveled).