Photosynthesis

Question 1

Give the overall equation for photosynthesis

Answer 1

6CO2 + 6H20 —> C6H12O6 + 6O2

Question 2

How is a carbohydrate formed?

Answer 2

CO2 is reduced as hydrogen and electrons from water are added to it

Question 3

What kind of energy input is needed to break the bonds in photosynthesis?

Answer 3

Light energy

Question 4

Why does carbohydrate act as a storage of energy?

Answer 4

Because more energy is needed to break the bonds of water than is given out in the by bond formation in the carbohydrate

This energy can then be released via oxidation at another time

Question 5

Give examples of why plants need energy

Answer 5

• Photosynthesis
• Active transport
• DNA replication
• Cell division
• Protein synthesis

Question 6

What is the immediate source of energy in a cell?

Answer 6

ATP

Question 7

Where is the energy stored in ATP?

Answer 7

In the phosphate bond

Question 8

What makes up ATP?

Answer 8

ADP + an inorganic phosphate

Question 9

What enzyme catalyses the breakdown of ATP?

Answer 9

ATPase

Question 10

What is ATP made up?

Answer 10

Adenine, ribose sugar and three phosphate groups

Question 11

What enzyme catalyses the formation of ATP?

Answer 11

ATP synthase

Question 12

Where does the energy come from to form ATP?

Answer 12

From glucose in respiration

Question 13

What type of reaction is it going from ADP to ATP?

Answer 13

Phosphorylation

Question 14

What type of reaction is it going from ATP to ADP?

Answer 14

Hydrolysis

Question 15

Why is ATP a good source of energy?

Answer 15

The energy can be released very quickly via hydrolysis

Question 16

What is a coenzyme?

How do they work?

Give an example

Answer 16

A molecule that aids the function of an enzyme

They transfer a chemical group from one molecule to another

NADP - Transfers hydrogen from one molecule to another in photosynthesis

Question 17

Give examples of uses of glucose

Answer 17

• Energy source
• Converted into starch
• Cellulose
• Fats
• amino acids/proteins
• nucleic acids

Question 18

Describe the structure of chloroplasts

Answer 18

• Small, flattened organelles found in plant cells
• Double membrane called the chloroplast envelope
• Contain thylakoids (fluid-filled sacs) which are stacked up into structures called grana (singular -granum)
• Grana are linked together by bits of thylakoid membrane called lamellae (singular - lamella)
• Chloroplasts contain photosynthetic pigments such as chlorophyll a
• These pigments are found in the thylakoid membranes attached to proteins
• Within the inner membrane of the chloroplast and surrounding the thylakoids is a gel-like substance called the stroma
• Stroma contains enzymes, sugars, organic acids and oil droplets which store non-carbohydrate organic material)

Question 19

Two stages of photosynthesis

Answer 19

Light-dependent reaction

Light-independent reaction

Question 20

Describe the light-dependent reaction

Answer 20

• Happens in the thylakoid membranes
• Starts in PSII chlorophyll
• Energy from light raises two electrons in each chlorophyll to a higher energy level
• The chlorophyll molecules are now in an excited state
• The electrons leave the chlorophyll molecule and pass along a series of electron carrier molecules which are embedded in the thylakoid membrane. This forms the electron transport chain
• The electrons from PSII pass along from one carrier to the next in a series of oxidation and reduction reactions, losing energy which is then used in the synthesis of ATP using photophosphorylation
• The electrons from the PSII chlorophyll replace those lost from the PSI chlorophyll when it’s electrons became excited and left
• The electrons from the PSII chlorophyll are replaced by the photolysis of water to produce oxygen, hydrogen and electrons
• The hydrogen ion concentration has increased
• The electrons from the PSI chlorophyll pass along the ETC and combine with the co-enzyme NADP and hydrogen ions from the water to form reduced NADP

Question 21

Describe the light-independent reaction

Answer 21

• Takes place in the stroma of the chloroplasts
• Calvin cycle:
• Carbon dioxide combines with a 5-carbon compound called RuBP. This reaction is catalysed by the enzyme RuBISCO. The process is called carbon fixation
• The 6-carbon compound formed is unstable and immediately breaks down into two 3-carbon compounds, GP
• GP is reduced to form a 3-carbon sugar phosphate called GALP. Hydrogen used to reduce GP comes from the light-independent reaction as does the energy in the form of ATP
• 2 of the 12 GALPs formed are used to form hexose, a 6-carbon sugar, which can be converted into other organic compounds such as amino acids or lipids
• 10 out of every 12 GALPs are used to recreate RuBP
• This happens as the 10 GALP molecules form 6 lots of 5-carbon compounds which are then phosphorylated, using ATP, to RuBP

Question 22

How is the structure of a chloroplast adapted for photosynthesis?

Answer 22

• Chloroplast envelope keeps reactants in photosynthesis close to their reaction sites
• Thylakoids have large surface area to allow as much light energy to be absorbed as possible
• Many ATP synthase molecules present in the thylakoid membrane to produce ATP
• Stroma contains enzymes, sugars and organic acids used in the light-independent reaction