5.6 - Photosynthesis Flashcards
(104 cards)
1
Q
What metabolic processes do plants rely on?
A
Aerobic respiration and photosynthesis
2
Q
How are plant leaves adapted for photosynthesis
A
- Stomata on the surface of the leaf
- ## large surface area for chloroplasts on photosynthesis
3
Q
Adaptations of guard cells
A
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4
Q
How are leaves adapted for their function?
A
- Flat: large surface area for maximum light absorption
- Thin - short diffusion distance between palisade mesophyll cells and external environment (for CO2, H2O and O2)
- Palisade mesophyll cells are near the upper surface - maximises light absorption
- upper epidermal cells are transparent - allows light to reach the palisade cells mesophyll cells
- waxy transparent cuticle - allows light to enter; prevents loss of water for photosynthesis
- lower epidermis contains stomata (pores): allow gas exchange - intake of CO2 and release of O2
5
Q
2 transport vessels in plant
- What do they transport and where to in the plant?
A
- Xylem - transports H2O and minerals to leaf mesophyll cells (chloroplast) for photosynthesis
- Phloem - transports complex organic molecules made in the leaf to the rest of the plant
6
Q
How are the palisade mesophyll cells (upper layer) in a plant adapted for their function?
A
- Contain many chloroplasts - large amount of chlorophyll
- closely packed columnar cells arranged with long axis perpendicular to surface - reduces number of light absorbing cross walls and increase surface area
- Chloroplasts moved by cytoskeleton (cyclosis) - to absorb maximum light or to protect from excessive light
- Thin cells wall - reduces diffusion pathway - efficient light penetration
- Chloroplasts at periphery of cell - short diffusion pathway
- Non-pigmented vacuole - allow light penetration
7
Q
How is the spongy mesophyll (lower layer - lower of the leaf) adapted to its function?
A
- Spherical cells allow:
- Less chloroplasts
- Larger intercellular air spaces for movement of gases and H2O vapour
- Store carbohydrates as starch granules (and other organic substances, e.g. amino acids, nucleotides, lipids) made by photosynthesis - which are taken into the phloem
- Stomata opening and closing can be controlled by the guard cells
8
Q
What is an autotroph?
- What is an example of an autotroph?
A
- An organism that makes complex organic compounds (food) from organic molecules using energy (chemical or light)
- Plants are photoautotrophs
9
Q
What is a photoautotroph?
A
- An organism that makes its own food using light energy and organic materials (CO2, H2O and minerals) by photosynthesis
- e.g. plants, some bacteria and some protoctista - Algae
10
Q
What is a heterotroph?
A
- An organism that cannot make organic compounds from inorganic sources. It needs a ready made supply of organic compounds (carbon compounds)
- Heteretrophs obtain their organic compounds by consuming other organisms
- e.g. all other animals, fungi, some bacteria and protoctista
11
Q
What is the compensation point and compensation period on a graph showing rate of photosynthesis and respiration?
A
- Compensation point is when both photosynthesis and respiration are taking place at the same rate. There is not net loss or gain of carbohydrate
- The time taken to reach this point is known as the compensation period. This varies between species
12
Q
What is the endo-symbiosis theory?
A
Believed that photosynthetic bacteria were acquired by eukaryotic plant cells by endocytosis
13
Q
Evidence for endo-symbiosis
A
Chloroplast and mitochondria contain their own DNA.
They also have 70S ribosomes compared to eukaryotic 80S ribosomes
14
Q
Equation for photosynthesis
A
6CO2 + 6H2O + energy from photons —> C6H12O6 + 6O2
15
Q
Is photosynthesis exothermic or endothermic?
A
- Requires energy
- therefore reaction is endothermic
- electrons are also required
- this makes photosynthesis a reduction reaction
16
Q
What is the relationship between respiration and photosynthesis?
A
The products for one reaction the material are the materials/reactants for another reaction
- photosynthesis creates products used in respiration etc.
17
Q
Structure of thylakoids and lamellae in chloroplasts
A
- The inner membrane is folded into lamellae (thin plates) also called thylakoids
- thylakoids are staked in plates called granum (pl. grana)
- intergranal lamellae (or stroma lamellae) link different stacks of thylakoids or grana
- one granum may contain 100+ thylakoids
18
Q
Structure and function of grana
A
- Grana are where the first stage of photosynthesis takes place - the light dependent stage (LDS)
- creates a large surface area for:
- distribution of photosystems that contain photosynthetic pigments that trap sunlight
- Electron carriers and ATP synthase enzymes needed to convert light energy into ATP
- Proteins embedded in the thylakoid membrane hold the photosystems in place
19
Q
Stroma structure and function
A
- Is a fluid-filled matrix
- Contains enzymes needed for the second stage of photosynthesis - the light-independent stage (LIS)
- Also contains starch grains, oil droplets, small 70S ribosomes (similar to prokaryotic cells) and a loop of DNA.
20
Q
Structure and function of membranes in chloroplast
A
- Chloroplasts are surrounded by a double membrane (known as the envelope)
- The outer membrane is highly permeable
- The inner membrane is less permeable, selectively permeable
- The inner membrane has transport proteins embedded in it
- The intermembrane space is 10-20nm wide between the inner and outer membrane
21
Q
Chloroplasts adaptations
A
Inner membrane with transport proteins - controls molecules travelling between the cell cytoplasm and the stroma
Many grana - large SA for photosynthetic pigments, electron carriers and ATP synthase enzyme needed for LDS
Photosynthetic pigments - arranged in photosystems, electron carriers and ATP synthase e enzyme needed in LDS
Proteins embedded in grana - hold photosystems in place
Fluid-filled stroma - contains enzymes needed for LIS
Grana surrounded by stroma - products made in LDS in grana can pass into stroma to be used in LIS
Chloroplast DNA and ribosomes - code for and synthesise some of the proteins needed for photosynthesis
22
Q
Structure of chlorophyll
A
- A mixture of pigments
- All contain a molecular structure consisting of a porphyrin group
- Porphyrin group contains a magnesium atom and a long hydrocarbon chain
23
Q
What pigments does chlorophyll contain?
A
Chlorophyll A and Chlorophyll B
24
Q
Different photosystems in chlorophyll a and what wavelength they absorb?
A
- P680 is found in photosystems II and it’s peak of absorption is light of wavelength 680nm
- P700 is found in photosystems I and it’s peak of absorption is light of wavelength 700nm
25
Function of photosynthetic pigments
- Absorb certain wavelengths of light
- Reflect other wavelengths (these are the colours we see)
- Arranged in photosystems in thylakoid membranes
26
Different photosynthetic pigments in in chlorophyll b and what wavelength of light they absorb?
- Chlorophyll b absorbs light of wavelength 400-500nm and around 640nm.
- It appears yellow-green
27
What are the accessory pigments in chlorophyll?
- Carotenoids
| - Xanthophylls
28
Wavelengths of light absorbed by accessory pigments
- Carotenoids: absorb blue light of wavelength 400-500nm
- They reflect yellow and orange light
- Xanthophylls: absorb blue and green light of wavelengths 375-550nm.
- They reflect yellow light
29
What method could be used to separate photosynthetic pigments in chlorophyll?
Thin Layer Chromatography
30
Info about chlorophyll a
- Is found in the Primary pigment reaction centre
| - Contains a Mg atom - when light hits this atom, a pair of electrons become excited
31
Rf values of different photosynthetic pigments
- Carotene: 0.91
- Phaeophytin: 0.63-0.75
- Chlorophyll a: 0.63
- Chlorophyll b: 0.58
- Xanthophyll: 0.32-0.53
32
Where are photosystems found in the chloroplast?
Found in the thylakoid membrane and the intergranal lamellae
33
Function of accessory pigments
These absorb light not normally absorbed by chlorophylls x then pass energy on to Chlorophyll a
34
Photosystems info
- A photosystems is a funnel shaped light-harvesting cluster of photosynthetic pigments
- Accessory pigments absorb different wavelengths of light to maximise the amount of sunlight that can be utilised
- Accessory pigments funnel energy associated with light wavelengths to the primary pigment reaction centre (Chlorophyll a)
35
ATP made in plants info
- ATP is a store of energy found in all cells
- ATP diffuses around the cell and provides energy for cellular and metabolic processes in cells
- ATP is made in the LDS from ADP + Pi (inorganic phosphate)
- ATP releases energy in the LIS when the bond between the inorganic phosphate is broken
36
Useful products of photosynthesis
- Amino acids
- Carbohydrates
- Lipids
- Nucleic Acids
37
What is the purpose of photosynthesis?
To create complex organic molecules
38
Describe the absorbance spectrum of the different photosystem pigments
(3 Marks)
- Wavelengths of light around 430 and 500nm are absorbed by carotenoids (blue light)
- Wavelengths of light between 530 and 620 are not absorbed by any pigments (yellow light)
- Wavelengths of light between 670 and 700nm are absorbed well (red light)
39
Light dependent reaction
- Adding a phosphate molecule is phosphorylation
- In this case light is used as an energy source
- So the process is called photophosphorylation
- ATP + H2O(catalyst)—> ADP + Pi + energy
40
Equation for the reaction in the light dependent reaction
ATP + H2O(catalyst) —> ADP + Pi + energy
41
What is NADH?
- Nicotinamide Adenine Dinucleotide Phosphate
| - Phosphorylated NADH
42
Function of NADPH
- Is a coenzyme
- Can accept electrons and protons and becomes reduced
- Id also a store of energy in the form of “reducing power” which drives bio synthetic reactions in LIS (Light Independent Stage)
43
Different forms NADPH can be written
- NADPH (main)
- Reduced NADP
- NADPH2
- NADPH + H+
44
Describe how photosynthetic pigments are arranged into photosystems
- They are found in the thylakoid membrane
- In funnel-shaped light-harvesting cluster held in place in the thylakoid membrane by proteins
- Funnel is embedded in the thylakoid membrane
- Primary pigments are at the bottom of the funnel
- Accessory pigments are scattered throughout the rest of the funnel
45
What is an action spectrum?
A graph that shows the wavelengths of light that are actually used in photosynthesis
46
What is an absorption spectrum?
A graph that shows which wavelengths of light are being absorbed by a pigment
47
Explain the link between the absorption spectra and the action spectra
- The absorption spectra and the action spectra closely match each other
- This suggests that the absorbed wavelengths of light are used in photosynthesis
48
Where does the light dependent stage take place in the chloroplast?
The thylakoid membrane
49
Which inorganic ion do electrons from chlorophyll A to be transported to the ETC come from?
Magnesium ion, Mg2+ ion
50
Where does the LDS (Light Dependent Stage Occur) in the chloroplast?
Occurs in the grana (thylakoids of chloroplasts)
51
What is required in the LDS?
Involves the photosystems
52
Where is photosystem 1 found
In the intergranal lamellae
53
Where is photosystem 2 found
Found in the thylakoid membrane
54
Stages of the LDS
1. Light harvesting at the photosystems
2. Photolysis of water
3. Photophosphorylation - the production of ATP in the presence of light
4. The formation of reduced NADP
- Oxygen, the by-product of photosynthesis, is also produced in the LDS
55
Granum definition
Inner part of chloroplasts made of stacks of thylakoid membranes, where the light-dependent stage of photosynthesis takes place
56
Photosynthetic pigment def
- Pigment that absorbs specific wavelengths of light and traps the energy associated with the light
- Such pigments include chlorophyll a and b, carotenoids and xanthophyll
57
Photosystem def
A funnel-shaped light harvesting cluster of photosynthetic pigments
58
Stroma def
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59
Thylakoid def
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60
Info about Photosystem 1 (PSI)
- The pigment at the primary reaction centre is a type of chlorophyll a
- this has a peak absorption of red light of wavelength 700nm (P700)
61
Info about photosystem 2 (PSII)
- The pigment at the primary reaction centre is also a type of chlorophyll a
- This has a peak absorption of red light at wavelength 680nm (P680)
62
How is water present in photosynthesis
- Is present in LDS
- Is present in Photosystem 2 reaction
- Undergoes photolysis to produce oxygen, H+ and electrons
63
Use of water in the LDS
- The source of protons (hydrogen ions) that will be used in photophosphorylation
- Donates electrons to chlorophyll to replace those lost when light strikes chlorophyll
- Is the source of the by-product, which is oxygen
- Keeps plant cells turgid - enables them to function
64
Equation for the photolysis in the LDS
2H2O —> 4H+ + 4e- + O2
65
Use of oxygen in photolysis
Used by plant cells for aerobic respiration
66
What is photophosphorylation
The generation of ATP from ADP and inorganic phosphate, in the presence of light
67
What are the two types of photophosphorylation?
Non-cyclic phosphorylation
| Cyclic photophosphorylation
68
Info about non-cyclic photophosphorylation
- Involves Photosystem 1 and Photosystem 2.
| - Produces ATP, Oxygen and reduced NADP (NADPH)
69
Info about Cyclic photophosphorylation
- Only involves Photosystem
| - Produces ATP but in smaller quantities than are made by non-cyclic photophosphorylation
70
Non-cyclic photophosphorylation mechanism/ Z scheme mechanism
1. When a photon of light strikes Photosystem 2 (P680), its energy is channelled to the primary pigment reaction centre
2. The light energy excites a pair of electrons inside the chlorophyll molecule
3. The energised electrons escape from the chlorophyll molecule and are captured by an electron carrier
- The electron carrier is a protein with iron at its centre, embedded in the thylakoid membrane
4.
71
Cyclic photophosphorylation mechanism
- Only uses Photosystem 1 (P700)
| - …
72
Calvin cycle def
- Metabolic pathway of the light-dependent stage of photosynthesis, occurring (in eukaryotic cells) in the stroma of chloroplasts
- Carbon dioxide is fixed, with the products of the light-dependent stage, to make organic compounds
- The Calvin Cycle also occurs in many autotrophic bacteria
73
Glycerate-3-phosphate def
An intermediate compound in the Calvin cycle
74
Ribulose biphosphate (RuBP) def
- A five carbon compound present in chloroplasts
| - It is a CO2 acceptor
75
Triose phosphate def
- A three carbon compound, and the product of the Calvin cycle
- Can be used to make other large organic molecules
76
Where does the light independent stage take place in the chloroplast
Takes place in the stroma of chloroplasts
77
Light Independent Stage info
- Doesn’t directly use light energy
- Uses the products of the Light Dependent stage
- If plant isn’t illuminated, the light independent reaction will soon cease
- As ATP and hydrogen are not available to reduce the carbon dioxide and synthesis large complex organic molecules
78
What happens to Light Independent reaction if the plant isn’t illuminated
- The plant won’t have light present for the Light Dependent reaction
- This means that no ATP and Hydrogen (from NADPH) is available to reduce the CO2
- So there is no synthesis of large complex organic molecukes
79
Role of CO2 in LIS
Source of carbon for the production of all organic molecule found in all carbon-based life forms
80
Calvin cycle mechanism
1. CO2 combines with a carbon dioxide acceptor, a five-carbon compound called Ribulose Bisphosphate (RuBP)
2. This reaction is catalysed by the enzyme RuBisCO
3. RuBP, by accepting the carbonyl (COO-) group, becomes carboxylated
4. This forms an unstable intermediate six-carbon compound that immediately breaks down
5. The product of this reaction is two molecules of a three-carbon compound, GP (glycerate-3-phosphate)
6. The CO2 has now been fixed
7. GP is then reduced
Etc…
81
Uses of TP produced in the Calvin cycle
- Some glucose is converted to sucrose, some to starch and cellulose
- Used to synthesise amino acids, fatty acids and glycerol
- Rest of the TP is used to regenerate the supply of RuBP (Ribulose Bisphosphate)
82
How does increasing light intensity affect rate of photoysnthesis?
Increases rate of photosynthesis, until it plateaus to maximum rate (Vmax of Rubisco enzyme)
83
Effect of increased CO2 concentration on rate of photosynthesis
Increases rate of photosynthesis, plateaus to Vmax/ max rate of photosynthesis
84
Effect of changing light intensity on the Calvin cycle
- LDS cannot occur to produce NADPH and ATP
- GP cannot be reduced to TP
- TP levels fall
- GP levels accumulate
- If TP levels fall, RuBP cannot be regenerated
85
Effect of increasing light intensity on rate of photosynthesis
- Increases rate of photosynthesis, until rate plateaus to a maximum rate
86
Limiting factors of photosynthesis
- Carbon dioxide concentration/availability
- Light intensity
- Temperature
- Water availability
- Turgidity of cells
-
87
Water stress def
The condition a plant will experiment when water supply becomes limiting
88
Light intensity def
The level of light
89
Effect of decreased CO2 concentration/availability on the Calvin cycle
- RuBP accepts less CO2, so it accumulates
- Less GP can be made
- Therefore, less TP can be made
90
Effect of temperature on rate of photosynthesis
- From 25-30 Degrees, rate increases
- At temperatures above 30 Degrees, there is competition for Rubisco’s active site.
- O2 compete with CO2 for Rubisco’s active site
- Therefore oxygen acts as a competitive inhibitor for Rubisco, prevent CO2 binding
- O2 causes photorespiration - decreases rate of photosynthesis
- This reduces TP production, and therefore other products (e.g. RuBP cannot be regenerated)
- At temperatures above 45 Degrees, enzymes involved in photosynthesis (e.g. Rubisco) will be denatured
- So the rate of photosynthesis will decreases rapidly
91
Mechanism of water stress
| 5 points
- If not enough water is available:
1. The roots are unable to take up enough water to replace that lost via transpiration
2. Cells lose water and become plasmolysed
3. Plant roots produce abscisic acid that, when transloacted to leaves, causes stomata to close
4. This reduced gaseous exchange
5. Tissues become flaccid and leaves wilt
6. The rate of photosynthesis greatly reduces
92
Explain why the theoretical rate of photosynthesis is not achieved at higher light intensities.
(2 Marks)
- At higher light intensities, there may be a limiting factor, including
- CO2 concentration -
- required for Calvin cycle to react with RuBP
- Temperature -
Calvin cycle is dependent on enzymes, e.g. Rubisco.
- The activity of Rubisco can be mediated by temperature, higher kinetic energy = more enzyme activity
93
The leaf of a plant that is adapted to living in shade will differ from the leaf of a plant that is adapted to living in sunlight.
Suggest one way in which the structure of these leaves will differ.
- more chloroplasts on leaves
- more grana/thylakoids in chloroplast
- larger surface of leaves - more light absorption for photosynthesis
94
Plants are autotrophs. Most other organisms are heterotrophs.
Outline the way in which heterotrophic organisms are dependent on plants.
(3 Marks)
- Animals eat and obtain organic materials from plants
- Plants produce organic molecules during photosynthesis/Calvin Cycle/LDS
- Plants produce oxygen as a byproduct of photosynthesis/during photolysis
- Oxygen is used by animals for aerobic respiration in the mitochondria to produce ATP
95
What is the product of the Calvin cycle?
| - What is it used for?
- Triose Phosphate
| - Used for production of complex organic molecules
96
Suggest why there are always only low levels of RuBP in the stroma of chloroplasts
- RuBP is always being recycled - reacts with CO2 to produce GP
- Excess RuBP not needed in the stroma, no further metabolic uses
97
Suggest how a lack of nitrate ions in the soil can affect the levels of Rubisco in plants
- Enzymes are proteins - made of amino acids and polypeptide chains
- Less nitrates = less Rubisco produced
98
Outline the importance of photosynthetic pigments in plants.
| 3 Marks
- Absorb light energy/photons
- Electrons raised to higher energy level
- Accessory pigments pass energy to primary pigments
- prinary pigments become oxidised - electrons passed to ETC
- Energy absorbed used in light-dependent reaction - production of ATP/NADPH, etc.
99
Suggest two ways in which the ultrastructure of the chloroplast can be altered by high temperatures.
For each suggestion, explain the effect it will have on photosynthesis.
(4 Marks)
- Damage to thylakoid membranes in chloroplast
- reduces amount of sites for photosystems
- reduces light capture
- reduces activity of LDS
- Damage to chlorophyll
- reduction in pigment
- reduction in light absorbed for LDS
- reduces activity of LDS
- damage to outer membrane
- causes release of enzymes
- which will reduce activity of light independent stage / Calvin cycle
- damage to inner membranes in chloroplast / reduction in
reaction sites for electron transfer ✓
- which will reduce, photophosphorylation / ATP production
in the light dependent stage
100
Function of energized electrons in photosynthesis
| How do they become energized?
- Provide energy for H+ ion transport
- Used to reduce NADP to NADPH
- flow of H+ ions through ATP synthase produces ATP
- they absorb wavelengths of light in the photosystems (1 and 2)
101
Where do protons/H+ ions accuumulate in chloroplast during photosynthesis?
What does this allow?
- accumulate inside the thylakoid space
- The concentration gradient between the inside and outside of the thylakoids produces the proton motive force that propels H+ ions across ATP synthase
102
Role of water in photosynthesis
- Used in photolysis in Photosystem 2 (P680)
- Water broken apart by light energy into H+ ions O2 and electrons
- H+ ions used in electron transport chain as part of proton motoive force to produce ATP at ATP synthase
103
List differences between cylic and non-cyclic photophosphorylation.
Name things that occur in both.
Cylic:
the same electron returns to the photosystem
electrons leave only photosystem 1
Non-Cyclic:
electrons leave photosystem 1 and 2
an electron from a water molecule replaces the electron lost from the photosystem
Both:
an electron leaves photosystem 1
ATP is produced
electrons are passed along the ETC
104
Use of NADPH from LDS in the LIS
Reduction of GP to TP
NADPH is split into NADP and H+
H+ is used to reduce GP to TP
