C1: Photosynthesis

Question 1

Describe how the structure of the angiosperm leaf makes them well adapted for photosynthesis

5 points

Answer 1

Large surface area - to capture the most light

Thin - light penetrates through leaf

stomata and air spaces - allow CO2 into the leaf and cells

cuticle and upper epidermis are transparent - light penetrates to the mesophyll

palisade cells are cylindrical, elongated and at right angles to the surface of the leaf - so large density of palisades can fit into the highest layer so light only travels through 3 cell walls before reaching chloroplasts

Question 2

Describe how the locatiojn shape, and movement of chloroplasts makes them well adapted for photosynthesis

3 points

Answer 2

chloroplasts have a large surface area - for maximium light absorbance

chloroplasts move and rotate within palisade cells - toward the top on dull days and the bottom on light days to avoid pigment bleaching and to maximise light absorption

higher density of chloroplasts in palisade cells than any other cell - they are at the top of the leaf and are exposed to more light

Question 3

Define Transducer and provide a biological example

Answer 3

A transducer changes energy from one form into another.

Chloroplasts converts energy in the photons of light into chemical energy made available through ATP and Biological molecules like glucose

Question 4

Name four photosynthetic pigments

Answer 4

Chlorophyll a
Chlorophyll b
b-Carotene
Xanthophyll

Question 5

What is the function of photosynthetic pigments

Answer 5

Is to absorb light energy and begin its conversion to storable chemical energy

Question 6

What two wavelength(colour) of light is absorbed the best and what two are absorbed the worst

Answer 6

Blue then Red then yellow then green

Question 7

Why is there more than one pigment ?

Answer 7

To absorb a larger range of light wavelengths

Question 8

What is the function of a photosystem

Answer 8

Store the photosynthetic pigments that absorb the light and excite electrons in the reaction centre

Question 9

Describe the stucture of a photosystem

Answer 9

Antenna complex - Is photosynthetic pigments in clusters (Chlorophyll b, b carotene and xanthophyll)

reaction centre - two chlorophyll a molecules

Question 10

How can the different pigments involved in photosynthesis be observed

Answer 10

Chromatography

Question 11

Describe the process of chromatography

4 steps

Answer 11

A mixture of unknown pigments is applied to the origin
The chromatogram is placed into a solvent and left to run.
Pigments travel up the paper in order of their solubilities.
(Larger distance more soluble )
The Rf values are calculated

Question 12

how to calculate the Rf value
and how is this useful in determaining the unkown pigments

Answer 12

distance of pigment from orgin / distance of solvent from origin

compare Rf value with known values

Question 13

Define absorbsion spectra

Answer 13

A graph showing how much light is absorbed at different wavelengths

Question 14

Define action spectra

Answer 14

A graph showing the rate of photosynthesis at different wavelemgths of light

Question 15

Describe the relationship between absorption spectra and action spectra

Answer 15

When the graphs are superimposed it shows that the pigments responsible for absorbing light are used in photosynthesis

Question 16

Name the two photosystems thier differences and state which one is first in the Z- sheme

Answer 16

PSI (P700)
PSII (P680)

They absorb light at different wavelengths PSI has an absorption peak at 700nm and PSII has an absorption peak at 680nm

PSII is first in the Z-scheme (non-cyclic photophosphorylation)

Question 17

Describe the process of exciting electrons in the photosystem

Answer 17

Photons are absorbed in the antenna complex by photosynthetic pigments their energy is moved from pigment to pigment down the photosystem to the reaction centre where the energy is passed to one of the chlorophyll a molecules, exciting one of its electrons and raises it to a higher energy level. The high energy electron leaves the chlorophyll a molecule oxidising it and moved to an electron acceptor reducing it.

Question 18

Define cyclic photophosphorylation

Answer 18

ATP can be produced by electrons that take a cylindrical pathway and are recycled back into the chlorophyll a in PSII

Question 19

Define non-cyclic photophosphorylation

Answer 19

ATP can be produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which they reduce in the stroma

Question 20

What are the two stages of photosynthesis

Answer 20

The light dependant stage (LDS)
The light independant stage (LIS)

Question 21

Define photophosphorylation

Answer 21

A reaction bonding a phosphate ion to molecule of ADP to form ATP indirectly using energy from an high energy electron thast has been excited by a photon.

Question 22

Describe the path of electrons in cyclic photophosphorylation

Answer 22

PSI absorbs photons, the energy excites electrons in chlorophyll a (reaction centre). These electrons are emitted and picked up by an electron acceptor, which passes them down a chain of electron carriers back to PSI. The energy released as electrons pass through the ETC phosphorylates ADP to ATP

Question 23

Describe the path of electrons and protons in non cyclic photophosphorylation

Answer 23

A photon of light is absorbed by a pigment in the antennae complex of PSII. The energy is passed to the reaction centre where an electron from each of the chlorophyll a molecule is excited. These excited electrons reduce an electron acceptor leaving the oxidised chlorophyll a.
The photolysis of water results in the reduction of this chlorophyll by the electrons produced.

Electrons are passed along an series of electron carriers, powering one proton pump so protons move from the stroma into the thylakoid space. An electrochemical gradient is established and Chemiosmosis occurs resulting in the synthesis of ATP.

A photon of light hits PSI and the same process occurs as in section PSII. However, this time the electron acceptor passes the electron to NADP, protons from the photolysis of water also pass into the stroma and together they form reduced NADP

Question 24

Define photolysis

Answer 24

The breakdown of water into electrons protons and oxygen

Question 25

Describe the use of the photolysis of water

Answer 25

The electrons are used to reduce chlorophyll a in PSII

Protons and electrons are used to reduce NADP in stroma

Oxygen is waste product and is released via the stomata

Question 26

Name three factors that maintain the electrochemical gradient between the thylakoid space and stroma

Answer 26

Proton pumps in the ETC pump protons from stroma to T space
Photolysis of water in the thylakoid space
Removal of protons in the stroma by the formation of reduced NADP

Question 27

What is the independant stage also called

Answer 27

Calvin cycle

Question 28

Describe the calvin cycle

Answer 28

5C Ribulose bisphospahte (RuBP) combines with carbon dioxide catalysed by the emzyme Ribisco to form a 6C compound
6C compound is unstable and breaksdown into two 3C Glycerate-3-phosphate (GP) molecules
Each GP is reduced to 3C Triose phosphate (TP) by reduced NADP and ATP
1C from TP contributes to the formation of the products of the calvin cycle
remaining TP is Phosphorylated by ATP to RuBP which is regernerated

Question 29

What are the possible products of the calvin cycle

Answer 29

Glucose
Lipids
Amino Acids {with the addition of nitrogen obtained
from nitrates}

Question 30

What is the function of ATP and reduced NADP in the calvin cycle

Answer 30

To reduce GP to TP

Question 31

Define limiting factor

Answer 31

A factor that limits the rate of a physical process by being in short supply, any change in the amount of this factor will therefore effect the rate.

Question 32

What 4 factors do plants need for photosynthesis

Answer 32

The reactants CO2 and water
light at a high enough intensity and suitible wavelengths
a suitible temperature
water

Question 33

What is the role of inorganic nutrients such as N and Mg
and what happens if they are in short supply

Answer 33

Nitrogen is needed for the synthesis of proteins, nucleic acids and chlorophyll
a difficiency will result in reduced growth of all organs and chlorosis

magnesium is a component in chlorphyll
a difficiency will result in reduced growth and chlorosis

chlorosis = yellowing of leaves

Question 34

What factor is usually the limiting factor in terrestrial plants and why

Answer 34

CO2 as it has a 0.04% concentration in the athmosphere and the photosunthesis of most terrestrial plants is most efficient at 0.1%

Question 35

what happens if the limiting factor of light intensity is increased

Answer 35

Rate increases initially
until light is no longer a limiting factor so graph platues
further increase results in the bleaching of pigments so rate decreases

Question 36

Define the light compensation point

Answer 36

The light intensity at which a plant has no net gas exchange as the volume of gasses used and produced in photosynthesis and respiration are equal

Question 37

When limiting factors combine which one is the limiting factor

Answer 37

the one closest to its minimium value

Question 38

Name three inorganic forms of nitrogen

Answer 38

Ammonium , NH4+.
Nitrate , NO3-.
Nitrite , NO2-.

nitrogen is largely taken up by roots as nitrates. Although Rhizobium in the root noodles delivers NH4+ to the plant.