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Flashcards in F214: Photosynthesis Deck (46)
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What are autotrophs?

Organisms that use light energy or chemical energy and CO2/H2O to synthesise complex organic molecules.

1

What are heterotrophs?

Organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them.

2

What are photo autotrophs?

Organisms that make food using energy from sunlight.

3

What is the equation for photosynthesis?

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

4

Where does photosynthesis take place?

Chloriplasts.

5

What are photosynthetic pigments?

Molecules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has it's own distinct peak of absorption.
Other wavelengths are reflected.

6

Describe the structure of chloroplasts.

Disc shaped an between 2-10 nm long.

Surrounded by a double membrane (envelope).

Intermembrane space about 10-20 nm wide between the inner and outer membrane.

Outer membrane permeable to small ions.

Inner membrane is less permeable and has transport proteins embedded in it.
Inner folded into lamellae which are stacked.
Each stack is called a granum.

Between the grana are inter grana lamellae.

7

How long is a nanometre?

One millionth of a millimetre.

8

What are the regions inside the chloroplast?

Stroma: fluid filled matrix.
Light independent stage occurs here as it has the correct enzymes.

Grana: stacks of flattened thylakoids.
Sites of light absorption and ATP synthesis during the light dependent stage of photosynthesis.

9

How are chloroplasts adapted for their role?

Inner membrane has transport proteins that control the entry/exit of substances between the cytoplasm and the Stroma.

Grana provide a large surface area for the photosynthetic pigments, electron carriers and ATP synthase enzymes in the light dependent reaction.

Photosynthetic pigments are arranged into photo systems, which allow maximum absorption of light energy.

Proteins in the grana hold the photo systems in place.

Fluid filled Stroma contain the enzymes needed for the light independent stage.

Grana are surrounded by the Stroma so the products of the LDR can pass easily into the Stroma to be used in the LIR.

10

Describe the general structure of chlorophyll.

A long hydrocarbon chain and a porphyrin group.
Porphyrin is similar to haem, but has magnesium atom not iron.

Both appear yellow green and absorb red at slightly different wavelengths (absorption peak).

Both types are found at the centre of photo systems and are known as the primary pigment reaction centre.

11

Describe the two forms of chlorophyll.

a - P680 is found in photosystem II.
Peak of absorption at a wavelength of 680nm.
Absorbs blue light at 450nm.

b - P700 is found on photosystem I.
Peak of absorption at 700nm.
Absorbs light at wavelengths between 500-640nm and appears blue green.

12

What are accessory pigments?

Carotenoids reflect yellow and orange light and absorb blue light.

They do not contain a porphyrin group and are not directly involved in the LDR.

The main carotenoid pigments are:
Carotene - orange.
Xanthophyll - yellow.

13

What is photophosphorylation?

The making of ATP from ADP and an inorganic phosphate in the presence of light.

14

What are electron carriers?

Molecules that transfer electrons.
Proteins that contain iron atoms.

15

What are electron acceptors?

Chemicals that accept electrons from another compound.
They are reduced while acting as oxidising agents.

16

Where are the photosystems embedded?

PSI is embedded mainly on the intergranal lamellae.
PSII is almost exclusively on the granal lamellae.

They trap light energy to be converted to chemical energy in the form of ATP.

17

What is photolysis?

Splitting of water in photosystem II, requires light.

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

Some of this O2 is used for aerobic respiration but most diffuses through the stomata into the air.

18

What is water a source of?

Hydrogen ions to be used in chemiosmosis to produce ATP.
They are accepted by NADP to become red NADP.

Electrons to replace those lost by the oxidised chlorophyll.

It also keeps plant cells turgid enabling them to function.

19

Describe the process of cyclic photophosphorylation.

Only uses photosystem I.
The excited electrons pass from a chlorophyll molecule to an electron acceptor and back to the chlorophyll molecule from whence they came.
Small amounts of ATP are made.

20

Describe the process of non cyclic photophosphorylation.

Both photosystems.
Light strikes PSII, exciting a pair of electrons that leave the primary pigment reaction centre.

The electrons pass along electron carriers and the energy released is used to synthesise ATP.

Light also strikes PSI and a pair of electrons are lost.

These electrons along with protons from photolysis of water at PSII join NADP to become red NADP.

The electrons from PSII replace the ones lost at PSI.

Electrons from photolysis water replace the electrons lost at PSII.

21

Describe how ATP is made in photophosphorylation.

When a photon hits a chlorophyll molecules the energy is transferred to two electrons.

These electrons are taken by electron acceptors and passed along electron carriers in the thylakoid membranes.

Energy is released as the electrons pass along the electron carriers. This pumps protons into the thylakoid space where they accumulate.

Protons move down the proton gradient through channels associated with ATP synthase enzymes.
CHEMIOSMOSIS.

This produces a force that joins ADP and an inorganic phosphate to make ATP.

The kinetic energy from the proton flow is converted to chemical energy in ATP molecules, which is used in the LIS.

22

What are electron carriers?

Proteins containing iron atoms.

23

What is chemiosmosis?

Flow of protons that joins ADP to an inorganic phosphate to make ATP.

24

What is photophosphorylation?

Using light energy to make ATP.

25

What Is the light independent stage of photosynthesis?

Where CO2 is fixed and used to build complex organic molecules.

26

Where does the light independent stage of photosynthesis take place?

The Stroma of chloroplasts.

27

Why is the light independent stage still dependent on light?

Although light is not directly used it uses products from the light dependent stage.
ATP and red NADP.

28

Describe the stages of the Calvin cycle.

CO2 diffuses into the leaf through open stomata into the Stroma.

Here CO2 combines with a 5C compound ribulose bisphosphate.
Catalysed by rubisco.
Ribulose bisphosphate is carboxylated.

This makes 2 molecules of glycerate 3 phosphate.

G3P is reduced and phosphorylated to triose phosphate.
ATP and red NADP are used from the LDR.

5/6 of TP molecules are phosphorylated using ATP from LDR to three molecules of ribulose bisphosphate.

29

How are the products of the Calvin cycle used?

Glycerate 3 phosphate can be used to make amino or fatty acids.

Pairs of triose phosphate (3C) can make 6C compounds like glucose.

Some glucose can be isomerise to make fructose.

Hexose sugars can be polymerised into other carbohydrates like cellulose or starch.