photosynthesis Flashcards
1
Q
What is a photoautotroph?
A
Organisms that use light energy & inorganic molecules to synthesis complex organic molecules
2
Q
What is an autotroph?
A
Organisms that use light energy or chemical energy & inorganic molecules to synthesise complex organic molecules
3
Q
What is a chemoautotroph?
A
Prokaryotes that synthesise complex organic molecules, using energy derived from exergonic chemical reactions.
4
Q
which of these autotrophs and heterotrophs respire?
A
both
5
Q
do autotrophs or heterotrophs synthesise organic molecules?
A
autotrophs
6
Q
do autotrophs or heterotrophs use light energy?
A
autotrophs
7
Q
do autotrophs or heterotrophs hydrolyse complex organic molecules?
A
both
8
Q
examples of autotrophs?
A
plants, algae, some bacteria
9
Q
examples of heterotrophs
A
some bacteria, some protocists, fungi, animals
10
Q
what is a heterotroph?
A
Organisms that ingest & digest complex organic molecules, releasing the chemical potential energy stored in them.
11
Q
how does carbon dioxide diffuse into the leaf?
A
through the stomata
12
Q
where are stomata located?
A
pores on the underside of the leaf
13
Q
where does most of photosynthesis take place and what do they contain?
A
in the palisade mesophyll layer , which contains a large number of chloroplasts.
14
Q
what does the spongy mesophyll contain and why?
A
Lots of air spaces so that the carbon dioxide can get to the cells needed for photosynthesis.
15
Q
what does the photosynthesising cells produce and this diffuses from where?
A
produce oxygen, which diffuses out through the stomata
16
Q
where does water for photosynthesis come from and how is it transported?
A
through the roots and transported to the leaf by the xylem
17
Q
what do phloem vessels transport?
A
sucrose made by photosynthesis
18
Q
structure of a leaf
A
19
Q
A
20
Q
what are the adaptations to allow for gas exchange for photosynthesis?
A
- Leaf is very thin.
- Stomata -allow carbon dioxide in and oxygen out.
- Inside the leaf, a large surface area is produced by the spongy & palisade mesophyll.
- The spongy mesophyll has large air spaces with thin moist cell walls allowing gases to move easily within the leaf.
- The cells of the palisade mesophyll are vertical and have thin cellulose cell walls to allow rapid diffusion of carbon dioxide.
21
Q
Label the structure of a chloroplast?
A
22
Q
what are chloroplasts surrounded by?
A
a double membrane called the chloroplast envelope
23
Q
what is the fluid filled structure in the chloroplast and what is its role?
A
the stroma, it carries out light independent reactions.
contains starch grains, enzymes and lipid droplets.
24
Q
what is in the structure of a stroma?
A
disc-like structures called thylakoids
25
how are thylakoids arranged in the chloroplasts?
stacked together in groups of up to 100 to form grana
26
what occurs in the grana?
light dependent reactions of photosynthesis
27
what do chloroplasts contain and why?
DNA and Ribosomes, allow them to make their own proteins
28
what is a photosynthetic pigment?
a substance whose molecule absorbs some colour or wavelengths of light energy for photosynthesis
29
what is the inner membrane of the photosynthesis used for?
controls the entry and exit of substances between the cytoplasm and stroma
30
why do chloroplasts have many grana?
Large surface area for photosynthetic pigments, electron carriers & ATP synthase enzyme.
31
what do photosynthetic pigments do?
Allow maximum absorption of light energy
32
why are proteins embedded in the grana
to hold photosystems in place
33
why is the grana surrounded by stroma?
so that products of light dependent stage can pass into stroma for use in light independent stage
34
photosynthesis equation
6H2O + 6CO2 ----------> C6H12O6+ 6O2
35
what is wavelength defined as?
the distance from peak to peak (or trough to trough) of a waveform of light
36
how is white light separated?
into different colours/wavelengths of light
37
where is light energy absorbed?
photosynthetic pigments on the thylakoid membrane. These are molecules that can absorb some wavelengths of light.
38
pigments and wavelength
different pigments absorb different wavelengths of light energy
39
what does an absorption spectrum do?
a graph to show the absorbance of different wavelengths of light by a pigment
40
what is an action spectrum?
a graph of the rate of photosynthesis at different wavelengths of light
41
what structural groups do plant photosynthetic pigments fall into?
- chlorophylls
- carotenoids
42
photosynthetic pigments can ACT as?
- primary pigments
- accessory pigments
43
where are the primary and accessory pigments arranged?
in light harvesting clusters in the thylakoid membrane called photosystems
44
what wavelengths do chlorophyll b absorb?
500nm and 640nm (blue-green)
45
what light do carotenoids absorb?
blue light (appears yellow - orange)
46
what are the main carotenoid pigments?
- carotene (orange)
- xanthophyll (yellow)
47
what is at the centre of the photosystems?
primary pigment molecule called chlorophyll a.
Absorbs red light and blue light energy (appears green)
48
how many photosystems exist in a chloroplast?
two
49
photosystem I
The primary pigment (chlorophyll a) in photosystem 1 has a peak absorption of 700nm (P700). Mainly found on the intergranal lamellae
50
Photosystem II
The primary pigment (chlorophyll a) of photosystem 2 has a peak absorption of 680nm (P680). Almost exclusively found on the granal lamellae.
51
What does light dependent mean?
light energy is needed
52
what does light independent mean?
light energy is not needed
53
where does the light dependent stage of photosynthesis take place?
in the grana of the chloroplast
54
what are the stages of light harvesting and the photosystems?
- Light energy shines on a leaf.
- Photons of light are absorbed by the accessory pigment molecules.
- A pair of electrons from the accessory pigment are excited and then return to the pigment.
- Photons (light energy) passed from one pigment to another.
- Photons (light energy) passed to reaction centre (chlorophyll a) of the primary pigment
55
what occurs to the light energy in a photosystem?
light is passed from molecule to molecule in a chain to the reaction centre (chlorophyll A)
accessory pigments are needed
56
photophosphorylation equation
ADP + Pi combines to form ATP, using light energy
57
what is photosystem I involved in?
cyclic and non cyclic photophosphorylation
58
what is photosystem II involved in?
non cyclic photophosphorylation
59
what are the stages of cyclic photophosphorylation?
- Light energy strikes PSI (P700) and a pair of electrons from the magnesium atom in the chlorophyll a is excited and emitted.
- The electrons leave the electron shell and are caught by an electron acceptor.
- They are then passed ALONG a series of electron carriers embedded in the thylakoid membrane, releasing energy until it returns to the chlorophyll a.
- The energy released is used to synthesise ATP (ADP + Pi) by CHEMIOSMOSIS
60
what are non cyclic photophosphorylation?
also called the z-scheme
- electrons do not return to the chlorophyll a molecule
- they must be replaced from somewhere else - from photolysis
61
what is photolysis?
the splitting of water into electrons, oxygen and protons
62
sequence of events in non cyclic photophosphorylation
- Photolysis of water - the splitting of water into protons (H+), electrons and oxygen catalysed by a water - splitting enzyme.
(2H20 4H+ + 4e- +O2).
- The light energy strikes PSII (P680) and a pair of electrons is excited.
- The excited electrons are emitted from the chlorophyll a molecule.
- They pass along a chain of electron carriers and energy is released, which is used to synthesise ATP by CHEMIOSMOSIS.
- *The electrons are then passed to PSI (P700) and NOT returned to the original pigment molecule, and reduce it (OIL RIG).
- Light energy has also struck PSI and a pair of electrons has been lost – replaced by those from PSII*.
- The electrons lost from PSII are replaced by ones from the photolysis of water.
- The electrons and the hydrogen ions (from the photolysis of water) combine with NADP to form reduced NADP (in the presence of NADP reductase).
63
chemiosmosis stages
- Energy is released as electrons pass along the chain of electron carriers in the thylakoid membrane.
- This is used to pump protons (H+) across the thylakoid membrane into the thylakoid space.
- Proton gradient formed.
- Protons flow down their gradient, through a protein channel associated with ATP synthase.
- The proton motive force phosphorylates ADP to form ATP. i.e. Kinetic energy from the proton flow is converted to chemical potential energy.
- ATP is used in the light-independent stage of photosynthesis.
64
what photosystems involved in cyclic and non-cyclic
cyclic: I
non-cyclic: I & II
65
do photolysis of water occur in cyclic or non-cyclic?
non-cyclic
66
what products are formed in both cyclic and non-cyclic?
cyclic - atp
non-cyclic: atp, reduced NADP, oxygen
67
non-cyclic photophosphorylation overview diagram
68
the light-independent stage overview?
- ATP and reduced NADP from the light dependent reaction are used to reduce CO2 and produce carbohydrates.
- Takes place in the stroma of chloroplasts
- Takes place in a series of enzyme catalsed reactions called the Calvin cycle
69
what are the stages that co2 takes from the atmosphere to stroma?
70
what are the stages of the Calvin cycle?
- CO2 diffuses into the leaf through the stomata In the chloroplast stroma
- CO2 combines with a 5C sugar called ribulose bisphosphate (RuBP). This is catalysed by the enzyme ribulose bisphosphate carboxylase (RUBISCO) to form an unstable 6C intermediate.
- This immediately breaks down into 2 molecules of a 3C sugar called glycerate 3 phosphate.
- In the presence of ATP and reduced NADP, from the light dependent reactions, GP is phosphorylated and reduced to two molecules of triose phosphate.
- The NADP then returns to the light dependent stage to accept more hydrogens. Five out of six molecules out of every TP are recycled to RuBP by phosphorylation, using phosphates supplied by ATP from the light dependent reactions.
- Two triose phosphate molecules can condense to form hexose sugar.
71
how many TP molecules are needed to form a glucose molecule?
pairs of TP can be combined to from glucose
72
what are the 4 possible fates of this glucose?
Glucose is isomerised to fructose, Glucose and fructose can combine to form sucrose, Glucose can polymerise to form carbohydrates e.g. starch and cellulose
73
what other molecule can be formed form TP?
TP can be converted to glycerol
74
what 2 molecules are formed form GP?
GP can be converted into amino acids and fatty acids
75
how are lipids formed?
glycerol can combine with fatty acids formed from GP to make lipids
76
how did Melvin calico work out the cycle? (lollipop experiment)
- Algae grown in thin transparent “lollipop”
- Radioactive 14C injected in the form of hydrogencarbonate which becomes incorporated into the compounds of the Calvin cycle
- At intervals, samples are rapidly run into boiling ethanol to kill cells and denature the enzymes immediately.
- Compounds in algae separated by chromatography and identified
77
limiting factor
A limiting factor for a metabolic process is the factor that is present at the lowest or least favourable value.
78
what are the main limiting factors?
- light intensity
- temperature
- co₂ concentrarion
- water
79
low light intensity affect on photosynthesis
the limiting factor is the light intensity, therefore the rate of photosynthesis is directly proportional to the light intensity
80
high light intensities and photosynthesis
At high light intensities, other factors will become limiting and the rate of photosynthesis will plateau.
81
the three main effects on light?
- Causes the stomata to open so CO2 can enter leaf.
- Trapped by chlorophyll where electrons excited.
- Splits water to produce protons (Hydrogen ions).
82
what are the effects of light intensity on the Calvin cycle?
- an increase in light intensity increase rate
- more light energy available to excite electrons
- more ATP produced and more reduced NADP produced
- both used in light independent reactions
83
ATP & reduced NADP light intensity effects
increased LI - Increase
Decreased LI - decrease
84
TP light intensity effects
Increase LI - INCREASE
Decrease LI - DECREASE
85
GP light intensity effects
increase LI - decrease
decreased LI - increase
86
RuBP light intensity effects
Increased LI - increase
Decreased LI - decrease
87
why will levels of RuBP in the chloroplasts drop when light intensity falls?
- Light dependent stage (LDS) will stop.
- Light independent stage stops as it needs products from LDS.
- GP not reduced to TP.
- GP accumulates and levels of TP fall.
- Lowers the concentration of RuBP, reducing fixation of CO2 and formation of more GP.
88
light dependent and light independents are/aren't temp dependent?
Light dependent: NOT temp dependent
Light- independent: are temp dependent
89
affects of temperature on photosynthesis
- These reactions have an optimum temperature (about 25o C)
- Between 0oC and 25oC, the rate of photosynthesis doubles for each 10oC rise in temperature.
- Above 25oC the rate plateaus off and then falls.
90
Why does an increase in temperature increase photosynthesis?
- More kinetic energy so more successful collisions (between S and AS) which increases the rate up to 25oC.
- Above 25oC RUBISCO works less efficiently.
- OXYGEN competes more successfully for the active site of RUBISCO and prevents it from binding to CO2.
ATP and reduced NADP from light-dependent stage is wasted.
PHOTORESPIRATION exceeds photosynthesis so rate of photosynthesis goes down.
- Very high temperatures can damage proteins involved in photosynthesis.
91
why does an increase in temp NOT affect the light dependent stage?
not enzyme catalysed
92
Which proteins, besides enzymes, involved in photosynthesis may be damaged by high temperatures and how are they damaged?
electron carriers, proteins that hold photosystems in place. High temps break the H bonds and ionic bonds and disrupts the 3D shape/tertiary structure of proteins/changes shape of active site/no longer complementary shape to substrate so ESC don’t form. formed/Calvin cycle stops.
93
explain how stomatal closure leads to a reduction in the rate of photosynthesis?
Less CO2 enters the leaf so G-3-P not formed/Calvin cycle stops.
94
CO₂ Concentration what makes it limiting
- Atmospheric levels of CO2 are relatively low at 0.03 – 0.06%.
- At constant light intensities and temperature, the rate of photosynthesis initially increases with an increasing concentration of CO2.
- CO2 concentrations becomes limiting when light levels increase, therefore an increase in it’s levels will increase the rate of photosynthesis (productivity).
- It is not just the concentration that is limiting, but the rate at which it can diffuse into the leaf.
95
What is the hill reaction?
Robert hill demonstrated that isolated chloroplasts in light had "reducing power" and could produce oxygen from water in the presence of an oxidising agent.
- this was demonstrated using a redox reagent
96
what is the reagent used in hill reaction?
DCPIP, and acts as a substitute for the plant's NADP
97
what did the hill reaction show?
- He showed that isolated chloroplasts absorb light and split water, generating hydrogen ions and electrons.
- The electrons and hydrogen ions combine to reduce DCPIP from blue to colourless.
- This reaction can be monitored spectrophotometrically @ 600 nm
98
what is the photolysis of water equation?
H2O --> 2H+ + 2e- + ½ O2
99
photolysis of water waste products?
oxygen is a waste product f this process
The H ions combine with electrons from PSI and NADP to give red NADP
The photolysis of water can be demonstrated by the Hill reaction.
100
what is the change in colour in DCPIP?
oxidised DCPIP - BLUE
REDUCED DCPIP - CLEAR/COLOURLESS
101
what does the hill experiment conclude?
- From this experiment it was concluded that chloroplasts have reducing power
- And hydrogen ions and electrons are produced which combine to reduce DCPIP or NADP
102
what is the primary pigment?
a particular chlorophyll molecule (chlorophyll a)
103
what is the reaction centre?
contains the primary pigment. Energy is transferred to the reaction centre
104
what is the accessory pigments?
the remaining pigment molecules in the photosystem that absorb light energy. From the antenna complex
105
What is the antenna complex?
accessory pigments held together by proteins that act as a framework. Hold the pigment molecules in the best positions to allow energy transfer between them
