C1.3 Photosynthesis

Question 1

how is light energy is converted to chemical energy in carbon compounds?

Answer 1

it is converted via photosynthesis

Question 2

define photosynthesis

Answer 2

the production of carbon compounds in cells from inorganic molecules using light energy and releasing oxygen

Question 3

what are three reasons why living organisms need energy for cell activities?

Answer 3

1. metabolic reactions (reactions don’t occur automatically, they need energy)
2. transport (moving substances across membranes)
3. mechanical work (moving muscles)

Question 4

what is sunlight?

Answer 4

it is the principal energy source in most ecosystems

Question 5

State the chemical equation for photosynthesis

Answer 5

Question 6

Outline the source of the atoms used to form glucose during photosynthesis

Answer 6

During photosynthesis, the atoms used to form glucose come from carbon dioxide and water

• The carbon atoms in glucose come from carbon dioxide
• The hydrogen atoms in glucose come from water

Question 7

Define photolysis

Answer 7

the process of splitting water molecules using light energy during photosynthesis

• it releases oxygen

Question 8

State the source of the oxygen produced as a by-product in photosynthesis

Answer 8

Oxygen in photosynthesis is a by-product from splitting water molecules

Question 9

where does photosynthesis happen in cells?

Answer 9

in chloroplasts

Question 10

how could you increase the rate of photosynthesis in plants?

Answer 10

• increase water
• increase carbon dioxide
• increase light
• increase temperature

but all to a CERTAIN POINT

Question 11

structure of the chloroplast?

Answer 11

Question 12

Outline the process of separating pigments using chromatography

Answer 12

1. Crush leaves using propanone/acetone to dissolve pigment out
2. Place spot of pigment solution at the bottom of the chromatography paper
3. Dip it in solvent
4. As solvent passes through, it will separate out the pigments into different layer as they travel at different rates across the paper
5. Calculate the Rf value

Question 13

Identify pigments that result from chromatography by color and calculated Rf value

Answer 13

you can identify pigments that result from chromatography by color and calculated Rf value by comparing the Rf value to known published values

Question 14

how to calculate Rf value?

Answer 14

distance traveled by the component / distance traveled by the solvent

Question 15

State the range of wavelengths that fall within the visible spectrum

Answer 15

400 to 700 nanometers (nm)

• violet has the shortest wavelength (380~450nm)
• red has the longest wavelength (620~750nm)

Question 16

Outline the function of pigments

Answer 16

pigments = colored materials that absorb and reflect different wavelengths of light

• these pigments give things their color

Question 17

State the primary and accessory pigments found in chloroplasts

Answer 17

• primary = green
  (they look green BC they reflect green light while absorbing other lights)
• accessory = carotenoids
  (they help to maximize the rate of photosynthesis by absorbing other wavelengths)

Question 18

why do most plants look green?

Answer 18

because they reflect green light and absorb other lights

Question 19

Sketch the chlorophyll pigment absorption spectrum

(including both wavelengths and colours of light on the X-axis)

Answer 19

Question 20

Compare and contrast the action spectrum and absorption spectrum

Answer 20

an absorption spectrum shows the wavelengths of light that a pigment absorbs

an action spectrum shows the rate of photosynthesis at different wavelengths of light (good for showing which wavelengths are most efficient for photosynthesis)

• similarity = both graphs have two main peaks (one in the blue-violet region, one in the red region)

Question 21

Explain the shape of the curve of the photosynthesis action spectrum

Answer 21

the shape is characterized by two peaks and a trough

• the peaks indicate the wavelengths that chlorophyll and accessory pigments absorb most efficiently
• the trough represents green light

Question 22

Outline a technique for calculating the rate of photosynthesis by measuring oxygen production

Answer 22

• you can use a water plant
• it ensures that the oxygen produced as a result of photosynthesis can be counted as bubbles OR in a measuring cylinder / gas syringe

Question 23

Define “limiting factor”

Answer 23

it is a factor that restricts the rate of a reaction when present in a low amount

Question 24

limiting factors of photosynthesis?

Answer 24

• temperature
• light intensity
• carbon dioxide concentration

Question 25

Explain how temperature limits the rate of photosynthesis

Answer 25

it limits by **impacting the frequency of successful enzyme-substrate collisions** - At low temp: LOW respiration rate, insufficient kinetic energy for collision (**limiting factor**) - At too high temp: LOW respiration rate, so enzymes denature and loose functionality

Question 26

Explain how light intensity limits the rate of photosynthesis

Answer 26

- Light intensity = required for the photoactivation of pigments and production of ATP - Increasing intensity = high rates of photosynthesis until all pigments are photo-activated (results in **plateau**) - too little light intensity = not enough sunlight means the plant can't photosynthesize as fast / as much (**limiting factor**)

Question 27

Explain how carbon dioxide concentration limits the rate of photosynthesis

Answer 27

- increasing = higher rates of photosynthesis until all enzymes are saturated - not enough carbon dioxide: photosynthesis may not be able to occur since carbon dioxide is a key reactant (**limiting factor**)

Question 28

Identify: - manipulated (independent) - responding (dependent) - controlled variables in experiments testing limiting factors on the rate of photosynthesis

Answer 28

Independent: light intensity, carbon dioxide conc, temp Dependent: rate of photosynthesis Control: plant species, pH, water availability

Question 28

Outline techniques for measuring the rate of photosynthesis while manipulating either temperature, light intensity, or CO2 concentration

Answer 28

- Temp: running a process in a water bath or chiller - Light intensity: Regulated by controlling distance of light - CO2 concentration: Using baking soda tablets

Question 29

State the source of atmospheric carbon dioxide beyond the historical average of about 300 ppm

Answer 29

source = Anthropogenic activities (Humans)

Question 30

Compare enclosed greenhouse and FACE experiments

Answer 30

**Enclosed Greenhouse**: - Carbon levels can be artificially increased by adding co2 from tanks - Acts as a closed system, allowing for controlled variables (temp and light) - Conditions don't reflect those in natural environment - Only houses small plants **FACE**: - FACE = free air CO2 enrichment - Placement of pipes emit CO2 around experimental area - CO2 flow monitored by sensors, allows for adjustments - Represents open system - Certain conditions can not be controlled (sunlight)

Question 31

List the questions that are addressed in carbon dioxide enrichment experiments

Answer 31

- How does carbon dioxide concentration affect photosynthesis? - How can we predict future plant growth and photosynthesis? - How will carbon dioxide enrichment impact ecosystems? - How can carbon dioxide enrichment impact food security?