Pigments in plants

Question 1

What are pigments?

Answer 1

-They’re molecules that absorb light energy in the visible range

Question 2

What are Photons?

Answer 2

• A particle of light

- They act like a discrete bundle of energy

Question 3

What type of wavelengths have higher energy?

Answer 3

-Shorter wavelength photons have higher energy vs the longer wavelength photons which have lower energy

Question 4

What is the Photoelectric Effect?

Answer 4

• It occurs when a beam of light is able to remove electrons from certain molecules= creating an electrical current
• SO when photons transfer energy to electrons

Question 5

What is the strength of the Photoelectric effect dependent on?

Answer 5

• It depends on the wavelength of light

- SO shorter wavelengths are much more effective bc they have higher energy than longer wavelengths

Question 6

How do Chloroplasts act like photoelectric devices during photosynthesis?

Answer 6

-They absorb sunlight & transfer the excited electrons to a carrier

Question 7

What happens when a photon strikes the molecule w/ the amount of energy needed to excite an electron?

Answer 7

-The molecule will absorb the photon= raising the electron to a higher energy level

Question 8

What 2 things does whether or not the photon energy is absorbed depend on?

Answer 8

-How much energy it carries (defined by wavelength) & the chemical nature of the molecule it hits

Question 9

Why can atoms only absorb specific light photons?

Answer 9

-Bc atoms have a certain amount of available energy levels= only certain light photons can fill those remaining energy levels

Question 10

What is the Absorption Spectrum?

Answer 10

• A characteristic that each molecule has

- Which is the range & efficiency of photons it is capable of absorbing

Question 11

What are the 2 types of pigments used in green plant photosynthesis?

Answer 11

• Chlorophyll

- Cartenoids

Question 12

What are the 2 kinds of Chlorophylls found in plants?

Answer 12

• Chlorophyll a

- Chlorophyll b

Question 13

What kind of light does chlorophyll a &b absorb?

Answer 13

• Violet-blue & red light

- But NEITHER of them absorb photons w/ wavelengths between 500 & 600 nm bc these are actually reflected as green

Question 14

What is Chlorophyll a ?

Answer 14

• So it is the main photosynthetic pigment in plants & cyanobacteria
• It is the only pigment that can act directly to convert light energy to chemical energy

Question 15

What is Chlorophyll b?

Answer 15

• It acts as an accessory pigment= complements & adds to the light absoprtion of chlorophyll a
• BUT it has an absorption spectrum towards the green wavelengths= can absorb photons that chorophyll a cannot= greatly influences the proportion of photons in sunlight that plants harvest

Question 16

What is the structure of Chlorophylls?

Answer 16

• They contain a complex ring structure= Porphyrin Ring w/ alternating single & double bonds
• It has a hydrocarbon tail that anchors the molecule to hydrophobic regions of proteins embedded within the thylakoid membrane
• At the center of the ring is a magnesium atom

Question 17

What is the difference between the structures of Chlorophyll a & b?

Answer 17

-Is the substitution of –CHO (aldehyde) group in chlorophyll b for –CH3 (methyl) group in chlorophyll a

Question 18

What happens when photons excite the stucture of Chorophyll?

Answer 18

• So the photons excite the electrons in the Porphyrin ring which are then channeled away through the alternating carbon single & double bond system
• BUT electrons that ARE NOT associated w/ single atom/ bond are delocalized

Question 19

What 2 factors is the Absorption Spectrum in the Porphyin ring influenced by?

Answer 19

• Influenced by the association of chlorophyll w/ different proteins
• And the different side groups attached to the outside of the ring

Question 20

What is Action Spectrum?

Answer 20

• The relative effectiveness of different wavelengths of light in promoting photosynthesis
• It corresponds to the absorption spectrum for chlorophylls

Question 21

Why do plants only rely on chlorophyll instead of retinal pigment in our eyes?

Answer 21

-Bc chlorophyll absorbs in only 2 narrow bands w/ higher efficiency= greater energy capture rates

Question 22

What is the structure of Cartenoids?

Answer 22

-They consist of carbon rings linked to chains w/ alternating single & double bonds

Question 23

What are Cartenoids?

Answer 23

• They are a pigment that can absorb photons w/ a wide range of energies
• BUT aren’t always highly efficient in transferring the energies
• They are found in many organisms including in all the 3 domains of life

Question 24

What is the role of Cartenoids in photosynthesis?

Answer 24

• They capture light energy from light composed of wavelengths that are not efficiently absorbed by chlorophylls
• They also play a protective role by acting as general-purpose antioxidants to lessen the damage done by redox reactions that generate destructive free radicals

Question 25

How would it be possible for carrots to enhance our vision?

Answer 25

• If carrots were to have a high content of Beta-carotene
• Bc Beta-carotene consists of 2 Vitamin A molcules joined together, the oxidation of 1 of the vitamin A would produce retinal= pigment used in vertebrate vision

Question 26

What are Phycobiliproteins?

Answer 26

• They are accessory pigments found in cyanobacteria & some algae
• They can be organized to form a light-harvesting complex that can absorb green light= helps the cyanobacteria in low-light situations in oceans

Question 27

What is the structure of Phycobiliproteins?

Answer 27

-They contain a system of altenating double bonds & molecules that transfers electrons