Photosynthesis

Question 1

what is photosynthesis? what kind of organisms does it occur in? where does it occur?

Answer 1

Process that converts light energy into chemical
energy stored in organic molecules
-photoautotrophs
-Occurs in chloroplasts

Question 2

what are photoautotrophs?

Answer 2

organisms that use light energy to synthesis organic molecules from inorganic molecules

Question 3

what are the 3 major groups of autotrophs?

Answer 3

1. plants
2. algae (photosynthetic protists)
3. Cyanobacteria (photosynthetic bacteria)

Question 4

what causes the green colour in chloroplasts? where is this located?

Answer 4

colour is due to chlorophyll which is a light-absorbing
pigment located in the chloroplasts
-Pigment molecules embedded in thylakoid membrane

Question 5

name the layers of the chloroplast

Answer 5

1. outer membrane
2. intermembrane space
3. inner membrane
4. stroma
5. thykaloid membrane
6. thykaloid space

Question 6

what do the thykaloid space and the stroma have in common?

Answer 6

both are fluid filled spaces used in photosynthesis

Question 7

what kind of a process is photosynthesis? does it require energy?

Answer 7

an oxidation-reduction process

-it is an energy requiring process

Question 8

what is the formula for photosynthesis? what is happening to the starting molecules?

Answer 8

6 CO2 + 6 H2O –> C6H12O6 + 6 O2

Water molecules are split –> Lose electrons and H+ - OXIDATION
CO2 forms sugar –> gains electrons and H+ - REDUCTION

Question 9

how is CO2 reduced to glucose?

Answer 9

the light energy captured by the chloroplast provides

the energy needed to reduce CO2 to glucose

Question 10

light is a form of ….
Also known as?
how does light travel?
what is visible light?

Answer 10

energy

• electromagnetic radiation
• travels through space as waves of energy from the sun
• only small part of electromagnetic spectrum

Question 11

the shorter the wavelength the … the energy

Answer 11

greater

Question 12

what are the 3 things that can happen when light meets matter?

Answer 12

1. it can be reflected
2. it can be transmitted
3. it can be absorbed

Question 13

what are substances that absorb light? how are different wavelengths of lights absorbed?

Answer 13

pigments

-with different pigments

Question 14

what do we see when we look at a leaf?

Answer 14

we see wavelengths that the pigment molecules in the thykaloid reflect, as they only absorb some wavelengths

Question 15

what is a photon? how are they absorbed?

Answer 15

fixed quantity of light energy (discrete packets of energy)
-Photons of light energy are absorbed by pigment
molecules

Question 16

what happens when a pigment absorbs light energy?

Answer 16

-an electron is elevated from a ground state to an excited state

Question 17

what does it mean when an electron is an excited state? can electrons remain in this state? what happens when an electron changes to ground state?

Answer 17

-means it is in a higher energy state and it is unstable
-Electrons cannot remain in unstable excited state
-When electron drops back to ground state energy is
released

Question 18

what happens when a pigment absorbs light energy but is isolated from chloroplast?

Answer 18

energy is released as light or heat, and then electron is returned to ground state

Question 19

what happens when a pigment in the thykaloid membrane absorbs light energy?

Answer 19

energy not released as light or heat
-instead pigment molecules in thylakoid membrane pass
energy of excited electrons to neighboring pigment
molecules

Question 20

what is a photosystem? what are its 2 main actions?which complexes do photosystems contain? where are they found?

Answer 20

• Photosystems are functional and structural units of protein complexes involved in photosynthesis
  1. the absorption of light
  2. the transfer of energy and electrons.
• light-harvesting complexes and a reaction-center complex
• found in the thylakoid membranes of plants, algae and cyanobacteria

Question 21

what does light harvesting complex do? how does it do this/what parts are involved? what is it composed of? what is another name for it?

Answer 21

captures light energy and transfers it to the reaction center

• Accessory pigment molecules –> absorbs a photon of light
• Energy is transferred from pigment molecule to pigment molecule (within light-harvesting complex)
• Energy eventually transferred to chlorophyll A molecule in reaction center
• various pigment molecules and assoc. proteins
• antenna complex

Question 22

what is the reaction center? what does it do/how does it do this?

Answer 22

its a protein complex containing a pair of chlorophyll A molecules and a primary electron acceptor

• its chlorophyll A molecules are transferred energy from pigment molecules which it uses to boost electrons to a high energy state
• High energy electrons are transferred to primary electron acceptor (which is a protein), that then becomes reduced
• primary electron acceptor then passes electron to transport chain

Question 23

what is the Primary electron acceptor?

Answer 23

protein that captures light-excited electron from Chlorophyll A molecules and passes it to electron transport chain

Question 24

what is the thykaloid membrane?

Answer 24

double phospholipid bilayer

Question 25

what do accessory pigment molecules do?

Answer 25

absorb photons of light and the pass the energy between them

Question 26

what are the 2 types of photosystems? how are they different? what causes this difference? how are they similar?

Answer 26

1. photosystem II
2. photosystem I
   - differ slightly in which wavelengths of light they absorb most strongly
   - Difference in absorption due to differences in the pigment protein molecules associated with chlorophyll A
   - Both part of light reactions

Question 27

which wavelengths of light do the different photosystems absorb most strongly?

Answer 27

• Photosystem I absorbs 700 nm

- Photosystem II absorbs 680 nm

Question 28

what are the 2 pathways of electron transport?

Answer 28

1. Noncyclic electron flow

2. Cyclic electron flow