Photosynthesis & Respiration

Question 1

What is Metabolism?

Answer 1

Metabolism in living organisms is a process by which chemical substances are built up or degraded, storing or releasing energy.
Matter and energy is not created or destroyed, only changed


Question 2

What are the primary producers in Plants?

Answer 2

Primary producers (Builders!)
Plants:- photosynthesis (light builders)
Capture energy in light and use it to „FIX‟ CO2 into glucose (carbohydrate) with H2O, O2 released. Energy is stored in the bonds formed, C-H, C-C.
Photoautotrophs = Use light to “self feed”
ANABOLIC PATHWAYS (ANABOLISM)
Building up molecules e.g. starch

Question 3

What are the consumers in plants?

Answer 3

Consumers (Degraders)
Respiration
1. Plants, animals, bacteria, ALL living cells!
2. Break down large molecules to release energy to do work or build compounds themselves.
3. CO2 released from metabolism of sugars, O2 consumed.
CATABOLIC PATHWAYS (CATABOLISM)
Breaking down food for energy

Question 4

What occurs during Photosynthesis?

Answer 4

Photosynthesis
• Two major sets of reactions –Light dependent reactions
• Chloroplast (Thylakoid) membranes
–Light independent reactions
• Chloroplast stroma (liquid part)

Question 5

What is the chemical formula for photosynthesis?

Answer 5

6CO2 + 12H2O → C6H12O6 +6O2 + 6H2O
• None of the 12 waters on the left are the
same as the 6 on the right!!!
• H2O is split by light energy
• The oxygen that is given off comes from the splitting of water.


Question 6

Where does photosynthesis occur?

Answer 6

Photosynthesis occurs in the chloroplasts. Chloroplasts contain chlorophyll Chlorophyll a and chlorophyll b

Question 7

What is Electromagnetic Radiation?

Answer 7

Photons of light can collide with atoms in bio-molecules (e.g. Chlorophyll) and raise the energy of electrons (excites them!).
The ‘excited’ electrons can return to the ground state and lose their energy in heat or light of greater wavelength or lower energy (fluorescence)
The electrons may be lost from Chlorophyll which becomes oxidised (mnemonics –LEO/OIL)
And transferred to an ELECTRON ACCEPTOR MOLECULE in the thylakoid membrane . The energy is trapped and transferred!
THIS IS THE BASIS OF PHOTOSYNTHESIS.

Question 8

What are light dependent reactions?

Answer 8

• Light exists both as a wave and a particle
• Units of light mmole of photons / m2 / sec
• Wavelength of visible light 400 nm (violet- blue) to 750 nm (red)
• Visible light is just a tiny slice of the electromagnetic spectrum.
Light also behaves as particles (photons) these have energy which is inversely related to the wavelength of light.
That means that the smaller the wavelength of light the more energy it has.
So blue light (450 nm) has more energy than red light (700nm)
Photosynthesis uses visible light which provides enough energy to energize biomolecules, such as chlorophyll , but not enough to break them.

Question 9

What are two outputs of light dependent reactions?

Answer 9

Light energy harnessed by the chloroplast membranes is used to make ATP and NADPH which are energy stores. These are two outputs of the Light Dependent reactions & are used in the Light independent reactions
• ATP (adenosine-tri-phosphate)
ADP + Pi + energy = ATP (high energy)
• NADPH (nicotinamide adenine dinucleotide phosphate) NADP + 2e- + H+ = NADPH (high energy)
Making bonds takes and stores energy
Breaking bonds releases energy

Question 10

What are Photosystems I and II

Answer 10

1. Arelightharvestingcomplexes
2. Madeupof200ormoremoleculesof Chlorophyll a, b and carotenoids (all antenna molecules)
3. Reactioncentres(P680(PSII)andP700 (PSI)) Special chlorophyll molecules to which all other reaction centre molecules transfer light energy

Question 11

Describe the Electron Transport System?

Answer 11

• Move the electrons along the chloroplast membrane via electron acceptor complexes from high energy state to lower state
• Move H+ from outside of the thylakoid membrane to inside
• Sets up a H+ concentration gradient (potential energy) analogous to a „Hydro dam‟ or battery
• Concentration gradient used to produce ATP
• When H+ pass back through ATP synthase enzyme across membrane into stroma


Question 12

Describe Non-cyclic Photophosphorylation?

Answer 12

1. ATP used to split H2O, e- and H+ are generated.
2. E- is elevated to high energy level by a Photon
3. E- is passed from PS II via an electron transport chain to PSI where it is elevated to high energy level by another Photon
4. The e- is finally accepted by NADP + H+ (from split water) forming NADPH.
5. When electrons are passed down the electron transport chain from PSII to PSI they lose some energy and generate ATP from ADP + Pi
   NADPH and ATP are temporary energy stores.
   

Question 13

What is Cyclic Photophosphorylation?

Answer 13

1. PSI ONLY
2. Produces only ATP. e-’s excited and donated but cycle back to PSI losing energy.
   NO NADPH produced
   

Question 14

What is Chemiosmosis?

Answer 14

It is the mechanism of
ATP synthesis.
• PSI and PSII are embedded in the Chloroplast (thylakoid) membrane. Energy released from electron transport is used to pump protons (H+) from the stroma (outside) into the thylakoid lumen (interior).
• Concentrates H+ and reduces pH in the lumen (inside). Proton Gradient established (potential energy)!

Question 15

What is ATP synthase?

Answer 15

• Is an enzyme complex in the thylakoid membrane. Channel through which protons can leave (osmosis) and return to the stroma.
• H+ movement back into the stoma is linked to ATP synthesis from ADP + Pi.


Question 16

Where does all the energy that is produced go?

Answer 16

• ATP and NADPH produced in the light dependent reactions of photosynthesis are used in the light independent reactions (used to be called dark reaction but does not occur in the dark!)
• This is where Carbon fixation occurs CO2 is bound up to form sugar
• Also known as the Calvin Cycle
• Oxygen is a „by-product‟ of the Light reaction


Question 17

Some terms to remember

Answer 17

• 1. Thylakoids - chloroplast membranes
• 2.Grana-stacksofthylakoids
• 3. Stroma- fluid area of chloroplast where light independent reactions occur
• 4. Chlorophyll – a pigment molecule that can absorb light energy which excites an electron that is then passed on to an electron acceptor in the chloroplast membrane (Chl. is oxidised)
• 5. Photosystems (PSI & PSII) – light harvesting complexes