C1.3 Photosynthesis

Question 1

Define Photosynthesis

Answer 1

• Production of carbon compounds in cells from inorganic molecules
• Using light energy: energy is needed to build more bonds in glucose
• Release oxygen

Question 2

Chemical equation of Photosynthesis

Answer 2

6CO2 + 6H2O –> C6H12O6 + O2

Question 3

Structure of Chloroplast

Answer 3

• Stroma.
• Thylakoid.
• Granum.
• Lamella.
• Double membrane.
  Check slides.

Question 4

Site where photosynthesis happens.

Answer 4

Chloroplasts. Chlorophyll are the pigments in the chloroplasts that absorb light energy.

Question 5

Why leaves look green

Answer 5

• They reflect green light and absorb other lights.
• All 3 pigments in the chloroplast (chlorophyll a, chlorophyll b and carotenoid) are poor absorbers of green light.
• Carotenoid good absorber at blue/purple.
• Chlorophyll a is a good absorber at orange/red and purple.
• Chlorophyll b is a good absorber at yellow and blue.

Question 6

Thin-layer Chromatography of chloroplasts

Answer 6

Experiment/method to separate the different chloroplasts. Stationary phase is usually silica gel, aluminium oxide or cellulose instead of paper. Thin-layer tends to give better result.

Question 7

Limiting factors of Photosynthesis

Answer 7

• Temperature.
• Light intensity.
• CO2 concentration.

Question 8

Stages of Photosynthesis

Answer 8

Light dependent:
- Takes place in thylakoid
- Uses light to make ATP and reduced NADP
- Produces O2

Light independent:
- Takes place in the stroma
- Uses ATP and reduced NADP to form carbon compounds from CO2

Question 9

Light dependent stage of photosynthesis

Answer 9

• Begins within photosystems: molecular arrays of chlorophyll and accessory pigments within protein complexes, located in membranes.
• Arrangement of pigments allows them to absorb light energy across a range of wavelengths
• Two types of photosystems in the thylakoid membrane: photosystem I and photosystem II
• Photosystem I is most sensitive to light wavelengths of 700nm
• Photosystem II is most sensitive to light wavelengths of 680nm
• When photons of light strike the pigment molecules in the photosystem, they excite the electrons within these molecules
• Excited electrons are transferred to reaction center chlorophyll molecules
• At the reaction center, they go through a photochemical reaction, resulting in the emission of an excited electron. This process is known as photoactivation
• Electron is released by photosystem II

Question 10

Reason for having many different pigment molecules in the photosystem

Answer 10

• Only through use of a variety of pigment molecules can enough light energy be absorbed to photoactivate the central chlorophyll molecules