Ocr Biology Unit F215 - Chapter 5: Photosynthesis

Front 1

Define Autotroph

Back 1

An organism that uses an inorganic carbon source and light energy to synthesis complex organic molecules

Front 2

Define Heterotroph

Back 2

An organism that requires organic nutrients to supply it with a source of carbon. They digest complex organic molecules to release the chemical potential energy stored within them.

Front 3

Write the equation for photosynthesis

Back 3

6CO2 + 6H2O ------> C6H12O6 + 6O2

(light energy)

Front 4

Draw and annotate the structure of a chloroplast

Back 4

Front 5

Explain the structure of

a) lamellae

b) grana

c) thylakoids

d) starch grain

e) stroma

Back 5

a) sheets; in a chloroplast, the lamellae are membranes within it

b) stacks of thylakoids

c) membrane-enclosed spaces in a chloroplast where the light-dependent stage of photosynthesis takes place

d) energy store

e) the background material; where the light independent reaction takes place.

Front 6

Explain how the chloroplast is adapted to its function

Back 6

1) grana are surrounded by the stroma so the products of the light-dependent reaction can readily pass to the stroma

2) proteins embedded in the grana hold the photosystems in place

3) photosynthetic pigments are arranged in photosystems to allow maximum absorption of light energy

4) using genetic information in the chloroplast DNA, chloroplasts can make proteins needed in photosynthesis - the chloroplast ribosomes assemble the proteins

5) inner membrane controls the entry and exit of molecules

6) grana provide a large surface area for photosynthetic pigments, ATP synthase enzymes and electron carriers

7) Stroma contain enzymes needed to catalyse light independent reactions

Front 7

Define photosynthetic pigment

Back 7

A molecule that absorbs some wavelengths of light but not others and transfers the light energy to chemical energy

Front 8

What happens to the wavelengths of light that are not absorbed?

Back 8

They are reflected

Front 9

What are the majority of pigments in a chloroplast?

Back 9

Chlorophyll a +b

Front 10

What is a photosystem?

Back 10

A cluster of pigment and protein molecules that harvest light energy and channel it to chlorophyll molecules

Front 11

What is an absorption spectrum?

Back 11

A graph that shows the wavelengths of a light absorbed by a pigment

Front 12

What is an accessory pigment?

Back 12

A pigment that is different from the main light absorbing pigment - such as carotenoids, they help absorb more wavelengths of light than would be absorbed by chlorophyll alone and may also help protect chlorophyll from damage by intense light

Front 13

What happens in the light dependent stage?

Back 13

Photophosphorylation - cyclic and non-cyclic

Front 14

Define photophosphorylation

Back 14

The production of ATP using energy from light; it takes place on the thylakoid membranes of a chloroplast

Front 15

Outline what occurs in photophosphorylation

Back 15

* Light energy that hits a chlorophyll molecule transfers its energy to two electrons which become excited

* These electrons are passed along a series of electron carriers which releases energy

* This energy is used to pump hydrogen ions across the thylakoid membrane into the thylakoid space, creating a proton gradient

* The proton gradient results in the flow of H+ ions down their gradient through channels associated with ATP synthase enzymes= chemiosmosis

* Chemisomosis provides a force that allows the generation of ATP:

ADP + Pi -> ATP

Front 16

What photosystem does cyclic photophosphorylation use?

Back 16

PSI

Front 17

Outline what happens in cyclic photophosphorylation

Back 17

Light energy is absorbed by PSI and energy is transferred to electrons in chlorophyll a which become so excited that they leave the chlorophyll molecule and are passed down a series of electron carriers. This releases energy which is used to make ATP by chemiosmosis. Electrons then are returned to PSI.

Front 18

What photosystem(s) does non-cyclic photophosphorylation involve?

Back 18

PSI and PSII

Front 19

Outline what happens in non-cyclic photophosphorylation

Back 19

1) Light hits PSII, exciting two electrons that leave chlorophyll from the primary pigment reaction centre and pass along a chain of electron carriers

2) ATP is generated by photophosphorylation (see other flashcards)

3) Light energy is also absorbed by PSI, exciting two electrons which are emitted and join with protons to combine with NADP to make reduced NADP

4) Electrons from photolysis replace electrons lost in PSII and electrons from PSII replace the electrons lost in PSI.

Front 20

What is photolysis?

Back 20

The splitting of a water molecule using energy from light

2H2O -> 4H+ + 4e- + O2

Front 21

What provides the protons in non-cyclic photophosphorylation ? Explain the uses of the products of photolysis.

Back 21

PSII contains an enzyme that splits water when activated by light (photolysis)

2H2O -> 4H+ + 4e- + O2

PROTONS - are used in chemiosmosis and the reduction of NADP - it is accepted by coenzyme NADP to be used in the light dependent reaction

ELECTRONS - Are used to replace electrons lost in PSII

OXYGEN - Used for aerobic respiration or diffuses out of the stomata

Front 22

Draw the Calvin cycle

Back 22

Front 23

Explain the Calvin cycle

Back 23

1) CO2 diffuses into the leaf through open stomata. In the stroma, it combines with 5C RuBP to from an intermediate 6C compound that immediately splits to form two molecules of 3C Glycerate phosphate. The carbon fixing is catalysed by Rubisco.

2) ATP and Reduced NADP from the light dependent reaction are now used to provide a phosphate and energy to change GP to 2x TP.

3) 5/6 of the TP go on to regenerate three molecules RuBP

Front 24

What can the products of the Calvin cycle be used for?

Back 24

TRIOSE PHOSPHATE

*5/6 regenerates RuBP

* Can be converted to glycerol and can then be combined with fatty acids made from GP to form lipids

* Can be paired up to form hexose sugars such as glucose

GLYCERATE PHOSPHATE

* Used to make fatty acids and amino acids

Front 25

What are the limiting factors of photosynthesis?

Back 25

- Light intensity

- CO2 conc

- Temperature

Front 26

How does light intensity affect the rate of photosynthesis?

Back 26

As light intensity increases, the rate of photosynthesis increases up to a certain point

Front 27

What does light do and how does this affect photosynthesis?

Back 27

* Opens the stomata so CO2 diffuses in (CO2 is used in the Calvin cycle)

* Light is trapped by chlorophyll to excite electrons (these electrons are used in photophosphorylation)

* Causes the splitting of water to produce protons (used in photophosphorylation)

Front 28

Draw and annotate a graph of show how light intensity is a limiting factor

Back 28

Light intensity is a limiting factor.

You reach a point where increasing the light intensity has no effect on the rate of photosynthesis as something else becomes the limiting factor (ex CO2 concentration)

Front 29

Describe how CO2 is used in photosynthesis

Back 29

Plants absorb CO2 through diffusion into the stomata. During daylight, CO2 is being used in the Calvin cycle so the concentration of CO2 inside the leaf is lower than the concentration of CO2 outside the leaf so there is a gradient which keeps CO2 moving into the leaf.

Front 30

How does temperature affect the kinetic energy of molecules?

Back 30

A higher temperature increases the movement of molecules which mean there are more frequent collisions and that they collide with more energy. This increases the rate of the reaction.

Front 31

What stage of photosynthesis does temperature affect?

Back 31

Light independent - affects the enzyme catalysed reactions

Front 32

How does temperature affect Rubisco?

Back 32

At high temperatures it stops it binding CO2 and RuBP but instead O2 + RuBP = photorespiration

Front 33

How does temperature affect the stomata?

Back 33

Higher temperatures = more water loss from the stomata which induces a stress responses that closes the stomata, so CO2 availability is limited.

Front 34

Explain, in terms of chemicals, how light affects the Calvin Cycle

Back 34

Although the calvin cycle doesn't directly use light, it uses ATP and NADP from the light-dependent reaction to convert GP to TP. So if the light stops, the light dependednt stage stops and the supply of ATP and NADP to the Calvin cycle stops. GP can no longer be converted to TP and so builds up - the Calvin cycle stops when all TP is used up.

Front 35

Explain, in terms of chemicals, how CO2 supply affects the calvin cycle

Back 35

A short supply of CO2 means less GP is made and so less TP is made.

There is less CO2 to bind with RuBP so it builds up.

RuBP must be replaced by TP, there is less TP avaliable to convert to RuBP and other amino acids/ lipids.

The plant prioritises RuBP replacement/

Front 36

What can you do to measure the rate of photosynthesis?

Back 36

- Measure volume of O2 produced per unit time

-Measure uptake of CO2

- Measure rate of increase of dry mass of a plant