Photosynthesis

Question 1

What is photosynthesis?

Answer 1

‘Synthesis from light’ - metabolic process where energy from sunlight is captured and used to convert carbon dioxide and water into sugars and oxygen.

Question 2

Why is photosynthesis so important?

Answer 2

It’s the building blocks of life, it’s energy capturing processes provide food for other organisms. Produces the oxygen we breathe by releasing it from water molecules. The synthesis of large molecules from photosynthesis can be broken down to provide metabolic energy. Provides the components needed for respiration. Also provides the foundation of food webs.

Question 3

What is the chemical formula of photosynthesis?

Answer 3

6CO2 + 6H20 + LIGHT ENERGY (Carbon dioxide and water –> C6H12O6 + 6O2 (Glucose and oxygen)

Question 4

Where do the light dependent reactions occur?

Answer 4

Thylakoids in the chloroplast.

Question 5

Where do the light independent (DARK) reactions occur?

Answer 5

Stroma in the chloroplast.

Question 6

What concludes the amount of light captured in the chloroplast?

Answer 6

The mesophyll structure - such as number and density of cell layers.

Question 7

How many chloroplasts are there roughly in each cell?

Answer 7

~20-100 per cell

Question 8

What are the inputs for the light dependent reactions?

Answer 8

Light energy and water

NADP+ and ADP+Pi from Calvin cycle

Question 9

What are the outputs of the light dependent reactions?

Answer 9

Oxygen and ATP and NADPH (Electrons) in order to function the Calvin Cycle. Hydrogen ions

Question 10

What are the inputs for the light independent reactions?

Answer 10

• CO2

- ATP and NADPH produced by the light reactions

Question 11

What are the outputs of the light independent reactions?

Answer 11

NADP+ and ADP+Pi and sugars.

Question 12

What are the sugars then used for once produced by the Calvin Cycle?

Answer 12

• Cellular respiration
• Cellulose production
• Starch production
• Other organic compounds

Question 13

What is stage 1 of photosynthesis?

Answer 13

Capturing the sun’s energy - chlorophyll a is a primary pigment in most plants and can absorb red and violet lights

Question 14

What happens in stage one?

Answer 14

• A photon of light is absorbed by a P680 chlorophyll molecule in the light harvesting molecule of Photosystem 2.
• The energy generated is passed on from each chlorophyll molecule in the antenna complex until it reaches a reaction centre in Photosystem 2.
• An electron in the chlorophyll molecules becomes excited due to high level energy. It then becomes unstable and is released into the electron transport chain.

Question 15

What happens when the electrons reach the end of Photosystem 2?

Answer 15

They are passed to a protein called plastoquinone that can donate electrons to Photosystem 1

Question 16

What is the role of water in light reactions?

Answer 16

Electron donor by photolysis whereby water molecules are split into hydrogen ions, electrons and oxygen.
Electrons replace lost electrons in PS11
Hydrogen ions are transferred to ATP synthase to produce ATP.
Oxygen is a by product.

Question 17

What is a by product of photolysis/photosynthesis?

Answer 17

Oxygen

Question 18

What is NADPH?

Answer 18

An electron carrier that can donate electrons to other molecules and therefore reduce them.

Question 19

What is the role of the electron transport chain after photosystem 2?

Answer 19

To pass the electrons excited by light through a series of oxidation-reduction reactions. Hydrogen ions are passed into the thylakoid lumen increasing the concentration in the lumen.
Due to the gradient the hydrogen ions are transferred to an ATP synthase molecule where energy is provided to combine ADP+Pi to make ATP.

Question 20

What happens when the electrons reach photosystem 1?

Answer 20

They receive energy by light absorbed by P700 chlorophyll molecules, they are transferred to a mobile carrier called ferrodoxin.

Question 21

What is the final electron acceptor after photosystem 1?

Answer 21

Ferredixin NADP Reductase, the electrons and hydrogen ions are combined with NADP+ to reduce it to NADPH.

Question 22

What is the ATP and NADPH used for in the calvin cycle?

Answer 22

To provide energy to convert carbon dioxide into glucose and other sugars.

Question 23

What are the three stages to the Calvin Cycle?

Answer 23

1. Carbon fixation
2. Reduction
3. Regeneratioon of RuBP

Question 24

What happens in the carbon fixation phase?

Answer 24

Carbon dioxide diffuses through the stomata and dissolves in water and reaches the stroma in the chloroplast.
A carbon dioxide molecule combines with a 5 carbon RuBP molecule by an enzyme called Rubisco making unstable as a 6 carbon molecule.

Question 25

What happens in the reduction phase?

Answer 25

The unstable RuBP molecule breaks down into two 3 carbon molecules called 3-phosphoglycerate. These two molecules receive energy from the hydrolysis of ATP. This results in the production of two 1,3-biphosphoglycerate molecules.

Question 26

What happens when the 1,3-biphosphoglycerate molecules are combined with an electron from NADPH?

Answer 26

They produce two molecules of Glyceraldehyde 3-phosphate (G3P). Molecules of G3P are then used to make sugars e.g. glycolysis.

Question 27

What happens in the regeneration phase of RuBP?

Answer 27

There is not enough G3P to regenrate RuBP. In the photosynthesis equation 6 Carbon dioxide molecules must be used so in order to be effective and for RuBP to be regenerated.

Question 28

How many times does the cycle have to run to make one molecule of glucose?

Answer 28

6