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Photosynthesis Flashcards

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1
Q

how can ATP be hydrolysed?

A

ATP + H2O –> ADP + Pi + 30.6kJ mol-1
ADP + H2O –> AMP + Pi + 30.6kJ mol-1
AMP + H2O –> Adenosine + Pi + 14.2kJ mol-1

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2
Q

how is ATP made?

A

phosphorylation (addition of a phosphate to a compound)

Adenosine + Pi + 14.2kJ mol-1 –> AMP +H2O
AMP + Pi+ 30.6kJ mol-1 –> ADP + H2O
ADP + Pi + 30.6kJ mol-1 –> ATP + H2O

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3
Q

what is the role of ATP?

A

energy currency molecule
acts as an immediate donor of energy to various processes in cells

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4
Q

what is ATP made up of?

A

purine base, adenine
ribose sugar
3 phosphate acid molecules

ATP synthase enzyme is required to catalyse its formation from ADP, inorganic phosphae and 30.6kJ energy

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5
Q

what are common energy storage molecules?

A

glucose
sucrose
glycogen
starch
fructose
maltose

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6
Q

what happens whenenergy storage molecules are metabolised?

A

energy is released and some of he energy is incorporated into the formation of the energy currency molecule, ATP
as soon as ATP is produced, it is hydrolysed into ADP, phosphate and 30.6kJ

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7
Q

how are leaves adapted for photosynthesis?

A

leaves must be thin so that gases have a short distance to diffuse to photosynthetic cells, and light energy will be able to reach all cells

leaves must contain photosynthetic pigments to absorb light energy for photosynthesis

leaves must be accessible to CO2 via openings called stomata

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8
Q

upper epidermis description

A

consists of a single layer of thin, flat, transparent cells which allow light energy to pass through to the tissues that lie below
There may be a waxy cuticle on the surface to reduce water loss
Guard cells may also be present along with stomata

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9
Q

palisade mesophyll layer descriptions

A

Lies just below the upper epidermis
here may be 3-4 layers of cells which are long and arranged at right angles to the upper epidermis
- This reduces the number of light-absorbing cross walls on the upper part of the leaf so that maximum light is caught

Cells contain the largest number of chloroplasts per cell which contain large vacuoles with water for photosynthetic reactions n the peripheral cytoplasm

Chloroplasts are located just below the cell wall where IIh can reach them easily

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10
Q

how can chloroplasts be moved around?

A

by microtubules in the cytoplasm
- In high light intensities they are located further away from the light but in low intensities they are located near the upper part of the cell

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11
Q

how are palisade mesophyll cells adapted for photosythesis?

A

> There are long, narrow spaces between the cells so that gases can have access to the cells easily

> Palisade cells have thin walls to allow easy diffusion of gases into the cells

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12
Q

spongy mesophyll layer description

A

> cells in this layer are arranged loosely and are irregular in shape with large air spaces between them
- They present a large surface area for gaseous exchange

> There are veins in the region which contain xylem and phloem for water transport to the leaf, and transport of food away from the leaf respectively

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13
Q

lower epidermis descriptions

A

consists of a single layer of thin, flat, transparent cells, except for the guard cells which contain chloroplasts

Guard cells are adapted to open and close the stomata

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14
Q

what does the envelope enclosing the chloroplast consist of?

A

2 phospholipid membranes that are permeable to glucose, oxygen and carbon dioxide

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15
Q

what is the system of membranes running through the stroma consisting of?

A

flattened fluid filled sacs/ thylakoids which form stacks (grana) in places

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16
Q

what happens in the thylakoid membranes?

A

The thylakoid membranes present a large surface area or location of accessory pigments, primary pigments, electron carriers and transport pigments as well
-The pigments are arranged in light harvesting clusters called photosystems. The two types of photosystems are found in the thylakoid membranes

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17
Q

what happens in the stroma?

A

The stroma is the site of the light independent reactions
- It contains the enzymes required for these reactions lex. RUBISCO)
- The stroma also contains 70s ribosomes, a loop Of DNA, lipid droplets and starch grains

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18
Q

what is the function of the intermembranal space?

A

The intermemberanal space between the outer and inner membranes contains a large number of protons which are important in establishing an electrochemical gradient that enables the production of a large amount of ATP

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19
Q

what are the two types of photosystems?

A

Photosystem I (P700)- a pair of chlorophyll a molecule can aborb light energy at 700nm

Photosystem II (P680)- chorophyll a molecules can absorb light energy of wavelength 680nm

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20
Q

photosystems definition

A

photosynthetic pigments arranged in a funnel shape within the thylakoid membrane

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21
Q

what do accessory pigments do in photosystems?

A

transfer energy after light strikes them
the energy is transferred to a reaction centre where there are chlorophyll a molecules which absorb light energy at a peak of 700nm or 680nm

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22
Q

what happens when energy is released by accessory pigments?

A

the electrons become excited and the high energy electrons from these are then transferred along to electron acceptors and electron carriers with a subsequent production of ATP

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23
Q

how is energy released by accessory pigments?

A

when a light strikes their electrons is passed along to the reaction center

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24
Q

what is the absorption spectrum?

A

a graph which shows what wavelengths of light are absorbed by a particular pigment, and the degree to which absorbance occurs

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25
Q

what are the peak absorbances for chlorophyll a?

A

425nm (blue)
625nm (red)

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26
Q

what are he peak absorbances for chlorophyll b?

A

445nm (blue)
645nm (red)

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27
Q

what are the peak absorbances for beta carotene ?

A

445nm (blue)
475nm (green)

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28
Q

what is the range of least absorbances for all of the photosynthetic pigments?

A

525-575nm

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29
Q

what is an action spectrum?

A

a graph which shows the rate of photosynthesis of a pigment when it is exposed to different wavelengths of light
it shows how effective different wavelengths are at promoting photosynthesis

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30
Q

why does phosphorylation take place?

A

to produce ATP and reduce NADP

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31
Q

what are the two types of phosphorylation?

A

cyclic phosphorylation
non-cyclic phosphorylation

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32
Q

what happens in non-cyclic photophosphorylation?

A
  1. light strikes chloroplasts and H2O molecules split
  2. electrons from PSI and PSII become excited, move out of orbitals and leave both photosystems positively charged
  3. electrons from PSII are taken up by electron acceptor A
  4. electrons from the splitting of H2O move along electron carriers to PSII
  5. electrons from electron acceptor X move along a series of electron carriers to the+vely charged PSI
  6. electrons leave PSI and re taken to electron carrier Y then to the electron acceptor NADP
  7. NADP becomes negatively charged and reduced to NADPH
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33
Q

steps in cyclic photophosphorylation

A
  1. light striked PSI and electrons become excited, leave the photosystem and are accepted by electron acceptor X
  2. the electrons cycle back to PSII via a series of electron carriers
  3. energy released from the transfer is used to synthesize ATP
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34
Q

what will happen to the light dependent reaction if the plant is deprived of water?

A

Without water, electrons, ATP and reduced NADP production stops, therefore halting the light independent reaction. This is because Photosystem II is responsible for splitting water molecules to obtain electrons and protons.
Without water, the process cannot occur, halting the entire electron transport chain and subsequently affecting
ATP and NADPH production

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35
Q

what happens to the light dependent reaction if the plant is deprived of light?

A

without light, the light- dependent stage stops. Light
dependent reactions occur without light because there is no light energy to convert into chemical energy. These reactions produce energy in the form of ATP and NADPH, which are needed for light independent reactions. No light means no electron flow, and therefore no ATP or NADPH

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36
Q

what happens to the light dependent reaction if the plant is deprived of NADP?

A

Without NADP to accept these electrons, the electron transport chain grinds to a halt. This backup causes a cascade of negative effects.
Firstly, the flow of electrons is disrupted, preventing the generation of a proton gradient across the thy lacoid membrane. This gradient is crucial for ATP synthesis via chemiosmosis.
Consequently, the absence of NADP leads to a significant reduction or complete cessation Of ATP and NADPH production

37
Q

what is the role of water in the light dependent reactions?

A

Water serves as the primary electron donor in light dependent reactions. Through a process known as photolysis, water is split into protons and electrons. The released protons accumulate inside the thy lakoid lumen, creating a cone.
gradient. The proton gradient drives ATP synthesis through chemiosmosis as protons flow through ATP synthase.
Critically, the electrons extracted from water are essential
for replacing those lost by chlorophyll in Photosystem Is
thereby sustaining the electron transport chains

38
Q

what is the role of light in the light dependent reaction?

A

When light strikes a photosystem, it excites electrons in
the pigment molecules, particularly chlorophyll. The energy from these excited electrons is used to power the electron transport chain, which generates ATP. Light energy also provides the energy needed to split water molecules

39
Q

what is the role of NADP in the light dependent reaction?

A

As electrons move through the electron transport chain, they lose energy. To prevent a buildup of electrons and to capture this energy, NADPT accepts these electrons. When NADP+ accepts these electrons, it becomes reduced to NADPH

40
Q

what is the role of photosynthetic pigments in light dependent reaction?

A

Chlorophyll a is the primary pigment in photosynthesis
It is the main molecule responsible for absorbing
light energy and converting it into chemical energy. It
is found in all photosynthetic organisms.

Accessory pigments are pigments that work in conjunction
with chlorophyll a. They absorb light wavelengths
that chlorophyll a cannot efficiently absorb, broadening
the spectrum of light for photosynthesis.
Absorbed energy → chlorophyll a

41
Q

what are some common photosynthetic pigments?

A

chlorophyll b
carotenids

42
Q

what is chlorophyll b?

A

a type of chlorophyll but has a different structure than chlorophyll a allowing it to absorb different wavelength of lights

43
Q

what are carotenids?

A

pigments which absorb blue and green light, which chlorophyll does not absorb efficiently
protect chlorophyll from damage by excessive light

44
Q

what is the role of the photosystems in the light dependent reaction?

A

Photosystems are protein-pigment complexes located
in the thy lakoid membranes. They consist of two main components: a light harvesting complex and
a reaction centre. The light harvesting complex consists of multiple pigment molecules, primarily chlorophyll and carotenoids which capture light energy and transfers it to the reaction centre.

Here the energy is used to excite electrons, which are
then donated to the electron transport Chain.
Photosystem I and Photosystem I are the 2
primary photosystems involved in photosynthesis, working in tandem to generate ATP and NADPH

45
Q

what is the role of the electron acceptors in the light dependent reaction?

A

Electron acceptors play a vital role in the electron
transport chain. These molecules accept electrons
from the excited molecules in the reaction centers.

As they accept electrons, they undergo reduction
and pass them on to the next acceptor in the chain.
This sequential transfer of electrons creates
an electron flow that drives the pumping of protons across the thy lakoid membrane, leading
to ATP synthesis.

46
Q

what are the useful products of the light dependent stage?

A

ATP
NADPH

47
Q

what woul happen to the light dependent reaction if theplant were exposed to blue light only?

A

Blue light is primarily absorbed by chlorophyll and
carotenoids, ashich are key pigments in photosynthesis.
It can stimulate a higher rate of electron transport, leading to increased ATP and NADPH production

48
Q

what would happen to the light dependent reaction if the plant was exposed to red light only?

A

While redlight is essential for photosynthesis, it is less
efficiently absorbed than blue light. This might result in
decreased NADPH and ATP production compared to full
sunlight. Redlight is more effective for photosystem I
which might lead to an imbalance in ATP and NADPH

49
Q

what would happen if the light dependent reaction is exposed to greenlight only?

A

Green light is reflected by Chlorophyll, making it
inefficient for photosynthesis. Very little energy will be
converted into chemical energy, leading to significantly
reduced photosynthetic activity

50
Q

what would happen if the light dependent stage was exposed to red and blue light?

A

This combination is considered ideal for photosynthesis
as it covers a broad spectrum of light absorbed
by chlorophyll.
Both Photosystem I and I will be efficiently activated, leading to balanced ATP and
NADPH production. This light combination often results in higher rates of photosynthesis and plant growth

51
Q

why will photosynthesis be highest in red and blue light?

A

Chlorophyll is the primary pigment for photosynthesis, absorbs light most efficiently in the red and blue wavelengths. The absorbed light energy is converted into chemical energy (ATP and NADPH) Which fuels the process.

A combination of red and blue light ensures maximum absorption across a broader spectrum, maximizing the efficiency of photosynthesis.

52
Q

what is the purpose of the light dependent stage?

A

The purpose of the light dependent stage is to convert light energy into chemical energy. More specifically, it produces AT P lenergy currency) and NADPH (reducing agent), which are essential for the next stage of photosynthesis, the Calvin cycle, where glucose is synthesized.

53
Q

what is the source of energy for ATP synthesis?

A

a gradient of protons established between the thylakoid lumen and the stroma of the chloroplasts

54
Q

how is an electrochemical gradient established across the thylakoid membrane?

A

the high proton concentration in the thylakoid lumen and lower proton concentration in the stroma
hence the protons in the thylakoid lumen have a high potential energy

55
Q

what is chemiosmosis?

A

the process in which protons move down an electrochemical gradient via channel proteins associated with ATP synthase

56
Q

how is ATP synthesized in chloroplasts?

A
  1. proton pumps in the thylakoid membrane actvely move protons in the lumen from the stroma/ photolysis of water also provides protons
  2. some energy is released during electron transport along carriers and is used to pump protons from the stroma into the thylakoid space
  3. energy is released as protons move through channel proteins (ATP synthase enzyme is associated with each channel protein)
  4. energy released as protons move through the channel and is used to synthesize ATP from ADP and inorganic phosphate via ATP synthase
57
Q

characteristics of cyclic photophosphorylation

A

Photosystem I alone involved
No H20 needed
Initial donor of electrons = PSI
Final donor of electrons= PSI
No O2 evolved
Synthesize extra ATP to satisfy
the energy demands of the cell
produces ATP only
Electron acceptor Y alone involved

58
Q

characteristics of non-cyclic photohosphorylation

A

Both Photosystem I and II involved
H20 needed to donate e to PSTI
Initial donor of electrons = Ha0
O2 evolved
Allows for synthesis of organic
compounds in the light- independent stage
Produces ATP, NADPH and O2
Electron acceptors x and Y involved

59
Q

Where does the Calvin’s cycle occur?

A

stroma of the chloroplast

60
Q

process of carbon fixation

A

CO2, gas diffuses into the chloroplasts along a cone. gradient.
involves CO, binding with RUBP (Ribulose Biphosphate)
which is a CO2 acceptor molecule found within the stroma Of the chloroplast
Water combines with RUBP and CO2, in a reaction catalyzed by

RUBISCO (Ribulose Biphosphate Carboxylase enzyme). This is a carbox - glation reaction and inorganic carbon is converted to an unstable six carbon compound (organic)

As fast as CO2 is accepted by RUBP, the conc. Of CO2, in the stroma decreases. This maintains a diffusion gradient between the outside of the photosynthetic cell and the stroma
- The unstable 6C compound is very quickly converted to two molecules of the 3c compound glycerate -3-phosphate (3- phosphoglycerate/ 3GPA); it is the first product of photosynthesis.

61
Q

reduction in the Calvin’s cycle

A
  • The energy of some of the ATP and the reducing power of All the NADPH from the light dependent stage and are used to convert GP to TP
  • During the reduction phase, O2 is removed from GP using energy from the splitting of some ATP molecules
    -O2 combines with hydrogen from NAAPH molecules

NADP is therefore regenerated and can be reused in the light dependent reactions
some ADP and Pi are also regenerated for use in the light dependent stage

62
Q

what is TP?

A

the first carboxylate of photosynthesis
triose phosphate/ glyceraldehyde-3-phosphate

63
Q

regeneration of RuBP

A

RUBP has to be regenerated for reuse in the calvin cycle

During the process of regeneration, 5 out of TP molecules are used along with the rest of the ATP from the light dependent stage

The TP is converted to RUP (Ribulose Phosphate)
The rest of ATP is used to convert RUP → PAUBP by phosphorylation

64
Q

formation of other carbohydrates

A
  • 1 TP Molecule out of the 6 TP molecules is used to form other carbohydrates
    ex. glucose, sucrose, starch, cellulose
65
Q

how does light intensity affect photosynthesis?

A

Affects the photolysis of water and the supply of electrons to PSII as well as the supply of protons for the reduction Of NADP

Affects the excitation of electrons in PSI and PSI, and the manufacture of ATP

Both ATP and reduced NADP are required for the reaction of the light independent stage which includes the manufacture of carbohydrates

If light intensities are low, the rate of photosynthesis is low

If light intensities increase, the rate is much higher

66
Q

how does carbon dioxide concentration affect photosynthesis?

A

Affects the light independent stage and the quantity of CO2 fixed determines the quantity of TP manufactured and the amount of Other carbohydrates synthesized

Low COs conc. means less carbohydrates manufactured and vice versa

67
Q

how does water supply affect photosynthesis?

A

If water is in low supply, less water will be split to supply electrons to photosystem II for the manufacture of ATP. There will be fewer motions to reduce NADP So the rate of photosynthesis will decrease because less ATP and reduced NADP Will be manufactured

When a dequate amounts of water are present, large amounts Of ATP and reduced NADP will ensure the rate of photosynthesis is higher

68
Q

how does the wavelength affect photosynthesis?

A
  • Highest amount of photosynthesis is in the blue and red wavelengths before more electrons become excited in the photosynthetic pigments and more ATP will be produced
  • Least amount of photosynthesis will occur when plants are exposed to the green wavelength of light
69
Q

how does oxygen affect photosynthesis?

A
  • Both CO, and O2 compete for the active site of RUBISCO
  • RUBISCO can catalyze a reaction between RUBP+ CO2, and between RUBP+ O2 under different conditions
  • In the presence Of light, if CO2 levels are high, O, levels low and temp. is low., CO2 fixation is favoured
  • When light intensities are high.CO, levels are low, O, levels high, and temp. is high, photorespiration is favoured in which 1GP molecule is produced, along with a molecule of 2-phospho glycolate
  • Phosphorglycolate enters mitochondria and is used to produce CO2
    Photorespiration makes photosynthesis 30-401. efficient2
70
Q

how does temperature affect photosynthesis?

A

Affects the rate of photosynthesis since enzyme - controlled reactions in the light independent stage are affected by temperature

At low temperatures, there is less kinetic energy available, also less energy available for activation energy, and the rates are lower

When temperatures increase, rates increase due to increased kinetic energy

If temperatures go too high, enzymes become denatured and reactions slow considerably

71
Q

how does pH affect photosynthesis?

A

Affects the enzymes involved by altering the shape of the enzyme and its active site

72
Q

what is the law of limiting factors?

A

When a process is affected by more than one factors, its rate is determined by the factor which is closest to its minimum to value.

73
Q

what is a greenhouse?

A

structure in which plants are grown under controlled environments

74
Q

characteristics of greenhouse

A

glass or plastic roof and walls
plants are exposed to natural light inside the greenhouse
air heats up due to incoming solar radiation
artificial lighting can be used in temperate countries

75
Q

what is the temperature of cool greenhouses?

A

7-10 degrees

76
Q

temperature of warm greenhouses

A

10-13 degrees

77
Q

temperature of tropical greenhouses

A

16-21 degrees

78
Q

why will wilting occur in a greenhouse?

A

soll is dry (use irrigation, hydroponics)
2.high temperatures in greenhouse l use thermostat, ventilation system)
3. extremes of light (use shade netting)
4. too much fertilizer I supply more water)
S. diseases damage plant tissues I chemicals to remove pathogens)

79
Q

how is CO2 obtained by greenhouses?

A

burning C based fuels
- increases temperature and emits So2 and NO2

80
Q

carbon dioxide in greenhouses

A

If CO. concentrations are increased, this can improve the yield of fruits, promote flowering, improve strength of stems, increase size of flowers

As CO2 conc. increases from 340→1000 ppm, net photosynthesis increases

Most crops show increases in photosynthesis by about 50s. when CO2 conc. rises to 1000 ppm.

↳ The saturation point for COa conc. for most crops is reached at 1000-1300ppm
CO, under ideal conditions

81
Q

what level of CO2 is reccommended for groing seedlings?

A

a lower level of CO2 because higher levels would kill the plant

82
Q

pros of greenhouses

A

increased profits from growing crops
can control climatic conditions
control over pests, weeds, diseases
no dependence on external climate
consistent supply of nutrients and water
can grow exotic plants

83
Q

cons of greenhouses

A

operational costs are high
costly to set up controls and maintain them
high level of monitoring required
lack of pollination
can be space-consuming

84
Q

what is a hydroponic system?

A

plants are grown in an inert growing medium such as gravel, sand, coconuts etc

85
Q

pros of hydroponics

A

water system constantly recycles water in a closed system
less use of chemicals higher yield than conventional methods
plants grow in a short time
initial temp, pH, CO2 conc, water supply are carefully controlled

86
Q

cons of hydroponics

A

diseases can be spread rapidly
pH control is important to detect changes produced by microorganisms
higher operative costs
plants that need agents of pollination cannot grow here
water loss can occur through evaporation and leaks in pipes

87
Q

what is a growth chamber?

A

A growth chamber can range from a simple, lighted cabinet to a larger structure which provides rigorous control of several environmental factors

88
Q

uses of growth chambers

A

to obtain plant material
to permit the selection of environmental conditions appropriate to a given plant species without regard for the season
to permit environmental manpulation as an experimental variable
to permit plant pathologists to fight plant diseases
to make predictions about the yield nd survivability of crops

89
Q

problems involved in growth chambers

A

expensive to maintain
humidity has to be carefully controlled to prevent buildup of moles
problems can occur in the operation of the controls
fresh air must be changed every two hours to prevent a build up of excess CO2 at night and depletion during the day

Biology (5 decks)

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