Lecture 2

Question 1

What effect does photosynthesis have on the environment?

Answer 1

A significant effect, completely controls the organic carbon cycle, causes fluctuations in CO2 levels due to seasonal changes in photosynthesis, uses up 120Gt of CO2 per year.

Question 2

What is the formula for photosynthesis?

Answer 2

CO2 + water + photons -> Carbohydrate + oxygen + water

Question 3

Why was early photosynthesis inefficient?

Answer 3

It used energy from other molecules to produce organic compounds.

Question 4

How did modern photosynthesis change this?

Answer 4

Oxygenic photosynthesis is more efficient and permitted the evolution of complex life.

Question 5

When did photosynthesis evolve?

Answer 5

2.4 billion years ago in unicellular cyanobacteria.

Question 6

What evidence is there for this?

Answer 6

Banded iron formations begin to form around this time due to the increase of oxygen in the atmosphere.

Question 7

What effects did photosynthesis have?

Answer 7

Converted methane into CO2 which caused a 400 million year snowball earth. Also caused the evolution of respiration and mitochondria which lead to an explosion of biodiversity.

Question 8

How is energy formed in plants?

Answer 8

Photosynthesis converts light energy onto glucose in the chloroplast which is sent to the mitochondria where respiration uses glucose to form chemical energy.

Question 9

How are photosynthesis and respiration similar?

Answer 9

Both involved the production of ATP by phosphorylation of ADP.
Both involve and electron transport change.

Question 10

How are photosynthesis and respiration different?

Answer 10

Photosynthesis is anabolic as it builds up sugars by using light to split water.
Respiration is catabolic as it breaks down sugars and produces water as waste.

Question 11

Describe the structure of ATP.

Answer 11

Adenosine triphosphate: Adenosine + 5 carbon sugar (ribose) + 3 phosphate molecules.
Addition/removal of the last phosphate molecule uses a lot of energy,

Question 12

Describe the function of NADPH.

Answer 12

Nicotinamide adeine dinucleide phosphate.

Reducing agent that gives electrons to other molecules.

Question 13

What are the 5 main structures in the chloroplast?

Answer 13

Thylakoid membranes, Granum stacks, Lamella, Stroma, Double membrane.

Question 14

What is the function of the thylakoid membranes?

Answer 14

Has an electron transport chain and ATP synthase for phosphorylation.

Question 15

What is the function of the granum stacks?

Answer 15

High S.A:Volume ratio and small internal volumes quickly accumulate ions.

Question 16

What is the function of the lamella?

Answer 16

Connects and separates thylakoid stacks (grana).

Question 17

What is the function of the stroma?

Answer 17

Appropriate enzymes and pH for the Calvin cycle.

Question 18

What does the double membrane of the chloroplast show about the origins of the chloroplast?

Answer 18

Gives evidence for symbiotic origins.

Question 19

What is the aim of the light dependent reactions?

Answer 19

Light energy hits the chloroplast causing initial production of ATP and NADPH inside thylakoids.

Question 20

What is the aim of the light independent reactions?

Answer 20

ATP+NADPH migrate into the stroma for Calvin cycle and to form sugar.

Question 21

How is ATP and NADPH produced in the light dependent reactions?

Answer 21

Electrons are excited by light energy and move to a higher energy level. As they then lose energy and return to their ground state energy is released which is used to produce ATP & NADPH.

Question 22

Where does the electron transport chain take place?

Answer 22

From molecule to molecule in the thylakoid membrane.

Question 23

Describe Photosystem 2.

Answer 23

A protein complex (20 subunits) in the granal thylakoid membranes where photosynthesis starts.

Question 24

What are the components of PS2?

Answer 24

A reaction centre, an electron acceptor and a light harvesting complex.

Question 25

How does PS2 work?

Answer 25

Light harvesting complex is filled with chlorophyll (or other pigments) that funnel light energy to reaction centre (P680). One electron from here then gets excited and passed on to the electron acceptor pheophytin.

Question 26

What happens to P680 after it loses the electron?

Answer 26

It becomes an oxidising agent and takes on an electron from water causing photolysis.

Question 27

Describe photolysis.

Answer 27

For every electron excited you need 1 photon. For every water molecule split you need 2 photons. For every oxygen molecule evolved you need 4 photons.

Question 28

What happens to the excited electron after it leaves P680?

Answer 28

Passes down the ETC: a series of proteins and protein complexes where a small amount of energy is lost at each stage. Eventually it reaches Photosystem 1.

Question 29

Describe PS1.

Answer 29

A larger, more complex protein complex integral to the intergranal thylakoid membrane.

Question 30

What happens to the electron one it reaches PS1?

Answer 30

Passed from plastocyanin (last protein in ETC) to reaction centre complexes in PS1 (P700). Electron is then re-excited with light energy and electron moves to ferredoxin where NADPH is formed.

Question 31

How is ATP produced?

Answer 31

By ATP synthase (a thylakoid membrane protein). H+ ions from photolysis, plastoquinone & cytochrome b6f create a membrane potential and the kinetic energy of H+ ions moving drives motor in ATP synthase.

Question 32

What is formed in the ETC?

Answer 32

Oxygen + 4ATP + 2NADPH

Question 33

Describe cyclic electron transport.

Answer 33

Ferredoxin passes electron back to cytochrome b6f so it can absorb more energy and force more H+ through the membrane. Excited electrons make more ATP rather than NADPH, having excess energy can become problematic.