F2144 -3- Photosynthesis

Question 0

Photolysis

Answer 0

Enzyme-catalysed reaction where water molecules are split, using light energy. It occurs in photosystem 2, during the LIGHT-DEPENDENT stage of photosynthesis.

Question 1

Define Photophosphorylation

Answer 1

Formation of ATP in the presence of light energy. It takes place in the thylakoid membranes of chloroplasts, during the LIGHT-DEPENDENT stage of photosynthesis. There are 2 types:
•Cyclic photophosphorylation
•Non-cyclic photophosphorylation

Question 2

Photosynthetic Pigments

Answer 2

Chemicals that absorb light energy are photosynthetic pigments. They are found in thylakoid membranes, in photosystems. Each pigment absorbs energy associated with light of a specific wavelength. Examples include chlorophyll a, chlorophyll b, carotenoids and xanthophylls.

Question 3

Photosystems

Answer 3

Group of photosynthetic pigments in the thylakoid membrane. Consists of primary reaction centre and accessory pigments.

Question 4

Primary pigment reaction centre

Answer 4

The primary photosynthetic pigments in a photosystem act as reaction centres. In Photosystem 1 the primary pigment reaction centre is a molecule of chlorophyll a that has a peak absorption of 680nm. This means that it’s greatest absorption is of light of wavelength 680nm. In Photosysystem 2 the primary pigment reaction centre is a molecule of chlorophyll a that has an absorption peak of 700nm

Question 5

• Photosystem 1

* Photosystem 2

Answer 5

• Photosystem 1 - Primary pigment reaction centre P680 (chlorophyll a)
• Photosystem 2 - Primary pigment reaction centre P700 (chlorophyll a)

Question 6

Chlorophyll a and b

Answer 6

• Chlorophyll a is a primary pigment, coming in 2 forms: P680 or P700, corresponding to it’s peak wavelength absorption.
• Chlorophyll b is just an accessory pigment.

Question 7

Accessory pigments

Answer 7

Accessory pigments are other pigments in the photosystem that absorb certain wavelengths of light. They are not directly involved in the light-dependent reaction. The accessory pigments absorb light wavelengths that are not well absorbed by chlorophylls and pass the energy associated with that light to the chlorophyll a at the base of the photosystem. Carotene (orange) and xanthophyll (yellow) are the main carotenoid pigments.

Question 8

Photoautotroph

Answer 8

Organism that makes it’s own food using simple inorganic molecules, such as carbon dioxide and water, using LIGHT ENERGY.

Question 9

Chloroplasts

Answer 9

Organelles, in plant and some protoctist cells, where photosynthesis occurs

Question 10

Heterotroph

Answer 10

Organisms ingest and digest complex organic molecules, releasing the chemical potential energy stored in them.