Photosyntesis

Question 1

What is photosynthesis

Answer 1

It is vital because it produces food and oxygen

Mostly takes place in the leaves

Equation = 6CO2 + 6H2O + Light ————> C6 H12 O6 + 6O2

Question 2

What are the main events in photosynthesis

Answer 2

Light energy is absorbed by chlorophyll

Water is split using absorbed sunlight energy

Products of splitting water are electrons (passed to chlorophyll ), protons (stored in the chloroplast) and oxygen gas (released or used in respiration)

Sunlight energy is used to form high - energy electrons in chlorophyll

High energy electrons, stored protons (hydrogen ions ) are used to make glucose

Question 3

What are the sources of light, co2 and water

Answer 3

Sunlight is the normal source of light

Co2 comes from th atmosphere or from respiration in leaf

Water comes from the soil

Question 4

The light stage

Answer 4

“The light stage requires light and takes place in the chloroplasts”

1. Light energy is absorbed by a range of pigments in the chloroplast
2. The absorbed is transferred to a special chlorophyll, where it energised electrons
3. The energised electrons my return to chlorophyll using their energy to make ATP

4 . The energised electrons may be taken away from chlorophyll and combined with NADP+ and H+

5. Water is split to produce:
   - electrons which replace those lost by chlorophyll
   - protons (H+) help form NADPH
   - oxygen, used in respiration

Question 5

Pathway 1 and 2 of light stage

Answer 5

In pathway 1 an electron from chlorophyll flows along a sequence of electron acceptors.

• The electrons return back to chlorophyll molecule
• The electrons loose energy as they flow along pathway 1. This energy is used to convert ADP to ATP

In pathway 2 a pair of electrons leave chlorophyll and pass along a series of electron carriers

• They join with NADP+ to form NADP-
• The chlorropyll is now short of 2 electrons. Regains electrons when water is split using light energy
• Hydrogen ions formed when water is split are stored in chloroplasts
• one combines with NADP- to form NADPH
• As they flow from acceptor to acceptor they loose energy which converts ADP to ATP

Question 6

What are the end products of the light stage?

Answer 6

ATP, NADPH and oxygen

ATP and NADPH are used in the dark stage

Question 7

The dark stage

Answer 7

” The dark stage does not require light and takes place in the chloroplasts”

1. NADPH releases H+ and 2 electrons
2. Co2 combines with the H+ and electrons
3. Energy I provided by converting ATP to ATP
4. Glucose is made
   5 . ADP and NADP+ return to the light stage