Bio U4 Photosynthesis

Question 1

Heterotroph

Answer 1

An organism that needs to take in complex organic molecules to act as a source of energy and usable carbon compounds

Question 2

Photosynthesis

Answer 2

The trapping/fixation of CO2, followed by it’s reduction to carbohydrate using hydrogen from water

6CO2+6H2O—☀️—>C6H12O6+6O2

Question 3

In plants, photosynthesis is a 2 stage process taking place in the…

Answer 3

Chloroplast

Question 4

The light dependent stage for photosynthesis in the plant occurs in the…

Answer 4

Chloroplast lamellae (thylakoid membranes)

Question 5

The light independent reaction occurs in the…

Answer 5

Chloroplast stroma

Question 6

The outer membrane of the chloroplast is …

Answer 6

Permeable to many small ions

Question 7

The inner membrane of the chloroplast …

Answer 7

Contains many transparent proteins

Question 8

The stroma

Answer 8

Fluid filled matrix which contains enzymes for the light dependent reaction - Calvin cycle

Question 9

Granum

Answer 9

Stack of thylakoids
Site of light dependent reaction
Granum provide large surface area

Question 10

Lamella

Answer 10

Connect the grana

Question 11

Photosystem

Answer 11

Collection of photosynthetic pigments

Question 12

Photosynthetic pigments

Answer 12

Substances that absorb certain wavelengths of light and reflect others
Found in the thylakoid membranes

Question 13

Chlorophyll

Answer 13

A mixture of pigments all consisting of a hydrocarbon chain and a porphysin group containing a Mg2+

Question 14

Autotroph

Answer 14

An organism that can use an external energy source and simple inorganic molecules to make complex organic molecules
Sunlight
CO2
Glucose

Question 15

Chlorophyll a (P700) (P680)

Answer 15

Both found at the centre of photosystems (primary pigment reaction centre)

Each type absorbs blue and red light

Question 16

ATP is synthesised in PHOTOphosphorylation in which there are 2 types …

Answer 16

Cyclic PHOTOphosphorylation
And
Non-cyclic PHOTOphosphorylation

Question 17

Cyclic PHOTOphosphorylation

Answer 17

Only uses photosystem 1

The exited electrons pass to an electron acceptor and BACK to the chlorophyll molecule from which they were lost

There is NO PHOTOLYSIS of water and NO GENERATION of reduced NADP

small amounts of ATP are formed

Question 18

Non-cyclic PHOTOphosphorylation

Answer 18

BOTH photosystems are needed for non-cyclic PHOTOphosphorylation

• light strikes photosystem 2, exciting a pair of electrons that leave the chlorophyll molecule from the PRIMARY pigment reaction centre
• electrons pass along a chain of electron carriers and the energy released is used to synthesis ATP
• light has also struck photosystem 1 and a pair of electrons had been lost
• these electrons, along with the protons produced at photosystem 2 by the photolysis of water join NADP with becomes reduced NADP (NADPH)

Question 19

Photosystem 2 absorbs electrons from…

Answer 19

The photolysis of water

Question 20

Photosystem 1 absorbs electrons ….

Answer 20

emitted by photosystem 2

Question 21

The Calvin Cycle

Answer 21

CO2 diffused into the stroma of a chloroplast, combines with an acceptor molecule that is a 5C sugar - Ribulose Bisphosphate (RuBP)

• enzyme needed for this reaction is Rubisco
• unstable 6C intermediate molecule breaks down into 2 molecules of the 3C compound, glycerate 3-phosphate(GP)
• GP is reduced to Triose phosphate a 3C, using ATP from PHOTOphosphorylation and hydrogen reduced from NADP - both from light dependent reactions
• Triose phosphate does not accumulate but is immediately converted I to other products
• 12 molecules of Triose phosphate are produced in the Calvin cycle
• –10 are converted to 6 molecules of RuBP
• —2 are converted to hexose

Question 22

Changing CO2

Effect on the rate of photosynthesis

Answer 22

CO2 makes up 0.04% of the gases in the atmosphere

Increasing CO2 concentration to 0.4% increases the rate of photosynthesis as it allows more CO2 to he fixed which would lead to the increase of GP and therefor TP

Above 0.4% the stomata will begin to close

Question 23

Changes in light intensity

Effect on the rate of photosynthesis

Answer 23

Light is needed to make energy for the light dependent reaction

More light would excite more electrons which take part in PHOTOphosphorylation so more ATP and NADPH will be produced and used in the Calvin cycle to convert GP to TP

Question 24

Changes in temperature

Effect on the rate of photosynthesis

Answer 24

Photosynthesis involves the enzyme rubisco

Initially as the temperature increases so does the rate of photosynthesis because molecules have more kinetic energy therefore more enzyme substrate complexes form

Above 45 degrees the enzymes denature

High temperatures also increase photorespiration so O2 is added to rubisco instead of CO2 which reduces the efficiency of photosynthesis

Question 25

How might you measure the rate of photosynthesis

Answer 25

Volume of oxygen produced in a given time

Volume of CO2 produced in a given time

Question 26

The photosynthometer

Answer 26

Can measure rate of photosynthesis under different conditions

Possible to measure the rate of O2 production by a water plant while varying light intensity or another factor

Bubbles of O2 collect in the capillary tube of the apparatus. When suitable volume of gas has been collected in a known period it can be drawn alongside the scale using a syringe - length of bubble can be measured

Length is directly proportional to volume