Photosynthesis Flashcards
1
Q
Define autotrophs
A
Organisms that use light/ chemical energy and inorganic molecules to synthesise complex organic molecules
2
Q
Define heterotrophs
A
Organisms that inject/digest complex organic molecules which releases the chemical potential energy stored in them
3
Q
Define photosynthesis
A
The process where light energy from the sun is transformed into chemical energy that can synthesis large organic molecules from inorganic ones.
4
Q
What is the most important biochemical process?
A
Photosynthesis
5
Q
Why is photosynthesis advantageous for other organisms? 2 reasons
A
- Because it transforms light energy into chemical energy which is then available to consumers and decomposers
- It releases oxygen, from water, into the atmosphere which aerobes can use for respiration
6
Q
Name 5 organic molecules that can be synthesised from inorganic ones.
A
Carbohydrates, lipids, proteins, vitamins, nucleic acids
7
Q
What were the first life forms on Earth? Explain
A
Chemoautotrophs, which are prokaryotes that synthesise complex organic molecules with the use of energy from exergonic chemical reactions.
8
Q
Give an example of a chemoautotroph
A
Nitrifying bacteria
9
Q
How does nitrifying bacteria obtain its energy?
A
It obtains its energy by oxidising ammonia to nitrite or oxidising nitrite to nitrate
10
Q
What is an organism called when it can photosynthesise?
A
A photoautotroph
11
Q
Give 2 examples of raw inorganic molecules that photoautotrophs need to photosynthesise
A
Carbon dioxide and water
12
Q
Give an example of a photoautotroph. What kingdom is it in? Are photoautotrophs producers or consumers?
A
Algae
Protoctist
Producers
13
Q
Can heterotrophs make their own food? Explain
A
No they obtain food from other organisms and digest the complex organic molecules to simple soluble ones which can then be made into complex molecules.
14
Q
What is the scientific term for: Releasing the chemical potential energy in complex organic molecules.
What about when oxygen is used in the process?
A
Respiration
Aerobic respiration
15
Q
Where does photosynthesis take place?
A
In organelles called chloroplasts
16
Q
Define nanometre
A
One thousandth of a micrometre
17
Q
Define photosynthetic pigments
A
Molecules that absorb light energy, each pigment absorbs a range of wavelengths but has its own peak of absorption. The wavelengths that aren’t absorbed are reflected
18
Q
List 4 out of 7 things to do with the shape and structure of chloroplasts.
A
- They are disc shaped and are 2-10 um long
- The chloroplast is surrounded by a double membrane called an envelope
- There is an intermembrane space between the inner and the outer membrane
- The outer membrane is permeable to small ions
- The inner membrane is less permeable but has transport proteins embedded in it
- The inner membrane is folded to form lamellae and thylakoids which stack up to form grana
- Between the grana are intergranal lamellae
19
Q
What are the two distinct regions inside a chloroplast?
A
The stroma and the grana
20
Q
Can the stroma and grana be viewed under a light microscope or an electron microscope? What about thylakoids?
A
A light microscope
Electron
21
Q
Describe the stroma in detail
A
It is a fluid filled matrix where the light-independent stage of photosynthesis occurs. Necessary enzymes are located there and the stroma contains starch grains, oil droplets, DNA and prokaryote-type ribosomes
22
Q
Describe that grana in detail
A
The grana consists of stacks of thylakoids which is where light absorption and ATPsynthesis occurs during the light-dependent stage.
23
Q
How are chloroplasts adapted for their role? Name 5 out of 7 things
A
- The inner membrane can control the entry and exit of substances between the cytoplasm and the stroma because it has transport proteins
- The many grana provide a large surface area for photosynthetic pigments, electron carriers and ATP synthase enzymes during the light-dependent stage
- Photosystems, which are photosynthetic pigments arranged in a special structure, allow maximum absorption of light energy
- Proteins embedded in the grana hold the photosystems in place
- The stroma contains enzymes which are needed to catalyse the reactions in the light independent stage
- The grana is surrounded by the stroma, this allows the products from the light dependent stage to enter the light independent stage
- Chloroplasts make some of the proteins needed for photosynthesis using chloroplast DNA and ribosomes
24
Q
True or false
Photosynthetic pigments appear to be the colour of the light wavelengths that they are absorbing
A
False they appear to be the colour of the light wavelentghs that they are reflecting
25
Where are photosynthetic pigments found? And what shape is a photosystem?
In thylakoids
| They are funnel shaped
26
What is chlorophyll? And describe its molecular structure.
Chlorophyll is a mixture of pigments
It consists of a long phytol (hydrocarbon) chain and a porphyrin group which is similar to haem except it contains magnesium instead of iron
27
What happens when light hits chlorophyll?
| What are the 2 forms of chlorophyll a? And which photosystem are they found in?
A pair of electrons associated with magnesium become excited
| Chlorophyll a: P680 found in photosystem II. P700 found in photosystem I.
28
What colour does both types of chlorohyll a appear?
What colour do they absorb?
What are there absorption peaks?
Yellow green
They absorb red light but at slightly different absorption peaks
680 nm and 700 nm
29
Where are both types of chlorophyll a found in their photosystem?
What colour does chlorophyll absorb other than red light?
At what wavelength?
In the centre at a place called the primary pigment reaction centre
Blue
450 nm
30
At what wavelength does chlorophyll b absorb its light?
| What colour is it?
500 nm and 640 nm
| Blue-green
31
What colour do carotenoids absorb?
What colours do they reflect?
Do they contain a porphyrin group?
Are they directly involved in the light dependent stage?
Blue
Yellow and orange
No
No
32
What is the role of carotenoids?
| What are they?
To absorb light wavelengths that aren't well absorbed by chlorophylls and pass the energy to chlorophyll a at the base of the photosystem
They are accessory pigments
33
What are the two main pigments in carotenoids?
Carotene which is orange and xanthophyll which is yellow
34
Define photophosphorylation
Making ATP from ADP and inorganic phosphate (Pi) in the presence of light
35
Define electron carriers
Molecules that transfer electrons
36
Define electron acceptors
Chemicals that accept electrons from another compound and are reduced in the process. They act as oxidising agents.
37
Define oxidation ad reduction in terms of electron transfer
Oxidation: Loss of electrons
Reduction: Gain of electrons
38
Where does the light dependent stage of photosynthesis occur?
In the thylakoid membrane
39
What is embedded in a thylakoid membrane?
Photosystems, PSI in the intergranal lamellae and PSII in the lamellae
40
Which photosystem contains an enzyme that can split water in the presence of light?
PSII
41
What is the splitting of water called?
| What is the water split into?
Photolysis
| Protons (H+ ions), Electrons (e-) and Oxygen
42
What 2 things happen to the oxygen in PSII after photolysis?
It is used in aerobic respiration or it diffuses out of the leaves via the stomata
43
What is water a source of in plants? 2 things in detail
It is a source of hydrogen ions which can be used in chemiosmosis (when protons flow down their gradient through an ATP synthase enzyme, the flow rotates the ATP systhase headpiece, which synthesises ATP) to produce ATP. The protons are then accepted by NADP (a coenzyme) to produce reduced NADP which can be used in the light independent reaction.
It is a source of electrons which can replace those lost by the oxidised chlorophyll
44
Name 2 reasons why water is useful for plants. Name 1 reason why this benefits other organisms
1. It's a raw material needed for photosynthesis
2. It keeps plant cells turgid
1. It produces oxygen
45
Name 2 ways in which light travels.
1. It travels in waves
| 2. It travels in particles called photons
46
What happens when a photon hits a chlorophyll molecule?
The energy from the photon is passed to two electrons, causing them to get excited
47
What happens when the electrons become excited after a photon hits it?
They are captured by electron acceptors and passed along a series of electron carriers which are embedded in the thylakoid membrane
48
What are the electron carriers?
Proteins that contain iron atoms
49
In photosynthesis, what happens as the electrons are passed along the chain of electron carriers?
Energy is released which is used to pump protons across the thylakoid membrane and into the thylakoid space. The protons accumulate here.
50
What happens as the protons accumulate in the thylakoid space? What is the result of this?
It forms a proton gradient across the thylakoid membrane.
This causes the protons to flow down their gradient by flowing through ATP synthase enzymes. The protons flowing through is chemiosmosis which results in ATP molecules.
51
How is ATP made via chemiosmosis?
| What is the ATP used for in photosynthesis?
It's made because the kinetic energy from the protons is used to synthesis ATP, which converts the energy into chemical energy
ATP is used in the light independent stage
52
What is the process called when ATP is made from chemiosmosis using light energy?
Photophosphorylation
53
What are the two types of photophosphorylation?
Cyclic photophosphorylation
| Non-cyclic photophosphorylation
54
Describe in detail everything about cyclic photophosphorylation
It only uses PSI with P700 in it. The excited electrons pass to an electron acceptor and then back to PSI in the chlorophyll molecule. No photolysis occurs and no reduced NADP is formed. Small amounts of ATP are made which can be used in the light independent reaction or it can be used in guard cells to actively bring in potassium ions which reduces the water potential. This causes water to flow in via osmosis so that the guard cells swell and open the stomata.
55
What photosystem is found in a guard cell?
PSI so only cyclic photophosphorylation occurs
56
Describe in detail everything about non-cyclic photophosphorylation.
Both PSI and PSII are involved. Light strikes PSII, exciting the electrons causing them to leave the chlorophyll and the primary pigment reaction centre. The electrons pass along the chain of electron carriers, releasing energy for the synthesis of ATP. The light that has struck PSI causes the electrons and protons (from photolysis in PSII) to join NADP, forming reduced NADP in the stroma which is then used in the light independent stage. But first, the protons take part in chemiosmosis. The electrons from the oxidised PSII (due to loss of electrons) replace those lost from PSI. The electrons from photolysis replace those from the oxidised PSII.
57
Define the light independent stage
The light independent stage is when carbon dioxide is fixed and used to build complex organic molecules
58
Where does the light independent stage occur?
In the stroma
59
What is the light independent stage also called?
The Calvin cycle
60
Can the light independent stage of photosynthesis still occur if there is no light?
No because the products from the light dependent stage are needed for the light independent stage
61
List the 5 stages of the Calvin cycle.
1. Carbon dioxide diffuses into the leaf via stomata and then diffuses through a spongy mesophyll layer. It then diffuses through the cellulose walls and cell surface membranes of the palisade mesophyll layer. Once in the cell, it diffuses through the cytoplasm and chloroplast envelope to end up in the stroma
2. Once in the stroma, carbon dioxide combines with ribulose bisphosphate, a 5 carbon compound and carbon dioxide acceptor. Ribulose bisphosphate carboxylase-oxygenase catalyses this (also called rubisco). RuBP is now carboxylated
3. This reaction produces two molecules of glycerate 3-phosphate, a 3 carbon compound. CO2 is now fixed
4. GP is phosphorylated to produce triose phosphate, a 3 carbon compound. ATP and reduced NADP are used in the process
5. TP is then recycled via phosphorylation to produce 3 molecules of RuBP. ATP is used
62
List the abbreviations for all the molecules in the Calvin cycle. There are 3 of them
RuBP
GP
TP
63
List 7 ways in which the products of the Calvin cycle can be used.
1. NADP can be reused for the light dependent reaction
2. GP can be used to make amino/ fatty acids
3. 2 TP molecules can combine to form hexose sugars like glucose
4. Glucose can be isomerised to form fructose
5. Glucose and fructose (made from TP) can combine to form sucrose, a disaccharide that is translocated in the phloem
6. The hexose sugars can be polymerised into other polysaccharide carbohydrates like cellulose and starch
7. TP can be converted to glycerol which can be combined with fatty acids to form lipids
64
Define limiting factor in terms of metabolic processes
The factor that is present at the lowest or least favourable value. It must limit the metabolic process
65
If a plant is in a constant temperature but in different light intensities, what factor affects the rate of photosynthesis?
The varying light intensities.
66
If a plant is in suitable conditions but in low light intensities, what is the limiting factor and why?
The light intensity because if the intensity increased then so would the rate of photosynthesis so it must be limiting the process
67
If light was the limiting factor for a plant but it was then subjected to high light intensities, would light still be the limiting factor? Explain
No, because the light would no longer affect the rate of photosynthesis as it has plateaued and another factor would now be the limiting factor.
68
If carbon dioxide was the limiting factor, but the concentration of it is increased, what will happen? Explain
It will initially increase the rate of photosynthesis but then the rate will plateau and another factor, e.g. temperature, would limit the process
69
If temperature was the limiting factor, but you increased it. Would the rate of photosynthesis increase and then plateau?
Yes but if it's increased too much then enzymes will be denatured and the rate of photosynthesis will decrease.
70
How can you increase the carbon dioxide concentration in a green house?
Burn methane or introduce oil fired heaters
71
Is the rate of photosynthesis directly proportional to the limiting factor?
Yes, as the limiting factor increases, so does the rate of photosynthesis
72
What are the three main effects of light on a plant?
It causes the stomata to open, allowing oxygen to diffuse in
It excites electrons by getting trapped in the chlorophyll
It splits water molecules to produce protons
73
What is a posh term for the reactions in the light dependent stage?
Photochemical reactions
74
Are photochemical reactions influenced by temperature?
| What about the enzyme catalysed reactions in the Calvin cycle?
Not really
| Yes
75
At what temperatures does the rate of photosynthesis double when increased by 10oC?
At what temperature does the rate of photosynthesis plateau?
Between 0 oC and 25 oC
| 25 oC
76
List 3 main problems for a plant if the temperature rises too high
Enzymes are denatured preventing the Calvin cycle from occurring
Oxygen more successfully combines with rubisco's active site, preventing it from accepting carbon dioxide
More water loss, causing the stomata to close, decreasing the carbon dioxide intake.
77
Define photosynthometer
An apparatus that is used to measure the rate of photosynthesis by collecting and measuring the volume of oxygen produced within a specific time
78
When answering data based questions, what word should you never use? List 4 words to use instead.
Don't use amount
| Use: volume of gas, length of time, intensity of light and concentration of a solution
79
Name 3 ways in which you could measure the rate of photosynthesis. What is the usual way of measuring it?
Measure the volume of oxygen produced per unit time
Measure the rate of uptake of carbon dioxide
Measure the rate of increase in dry mass
The usual way is by measuring oxygen
80
Name 2 limitations of measuring photosynthesis via the amount of oxygen produced
1. Some of the oxygen may be used in respiration and therefore not secreted
2. The gas collected could contain nitrogen in it
81
What is another name for a photosynthometer?
An Audus microburette
82
What is the formula for measuring the volume of gas collected when using a photosynthometer?
Volume of gas collected= length of bubble X pieR2
83
Why should a photosynthometer experiment be carried out in a water bath? What should be added to the water in the test tube and why? And what should the light in the room be like?
To keep the temperature constant
Sodium hydrogencarbonate solution to provide carbon dioxide
The room should be dim so that you can manipulate the light intensity with a lamp
84
Describe the procedure in detail for a photosynthometer experiment
1. Fill the apparatus and barrel of the syringe with water. Then push the syringe plunger to gently push water into the capillary tubing making sure there are no air bubbles.
2. Cut a piece of Elodea (canadian pondweed) and make sure bubbles of gas are emerging from the cut end, then place the pondweed, with the cut end facing upwards, into a test tube full of the water from the pond.
3. Add 2 drops of sodium hydrogencarbonate solution and make sure the water bath is at 20 oC.
4. Place a light source at a specific distance from the water bath so you can work out the light intensity.
5. Calculate the light intensity using I= 1/d2 (d being distance)
6. Leave the plant to acclimatise and then position the capillary tube over the cut end for a set time, pull the plunger until the gas is next to the scale. Note the length of the bubble. Repeat 4 times
7. Change the light intensities an write the results in a table.
85
Define dicotyledons
A flowering plant that bears 2 cotyledons
86
Define cotyledons
They act as the first leaves and it's where the seeds store food
87
How can you measure the effects of temperature on the rate of photosynthesis?
You can use a photosynthometer to measure the rate and you can regularly change the temperature of the water bath at set intervals but keep every other variable constant
88
How can you measure the effects of carbon dioxide concentration on the rate of photosynthesis?
Use a photosynthometer to measure the rate but vary the amount of sodium hydrogencarbonate solution you add. Measure the volume of gas at set time intervals and keep all other variable constant
89
How can you measure the rate of photosynthesis using leaf discs?
You can do this by cutting circular discs of leaf, via a drinking straw, from cress cotyledons. Place the discs into a syringe and half fill the syringe with diluted sodium hydrogencarbonate solution. Gently pull the plunger to pull the air out of the spongy mesophyll. The air is replaced with sodium hydrogencarbonate, increasing the discs' densities, causing them to sink. Transfer the contents to a small beaker that is illuminated and time how long it take for a disc to rise. Divide 1 by the time (1/t) to find out the rate. Repeat this procedure at different light intensities.
90
How does light intensity affect levels of RuBP, GP and TP if it's the limiting factor?
The more light, the more products (ATP and reduced NADP) will be made from the light dependent reaction. This means that more molecules of GP will be reduced to TP, subsequently meaning there will be low levels of GP but high levels of TP and RuBP.
The less light, the less products will be made as the light dependent stage will cease. This means that GP won't be reduced, causing it to accumulate. Consequently, less molecules of TP will be synthesised and in turn less molecules of RuBP
91
How does carbon dioxide affect levels of RuBP, GP and TP if it's the limiting factor?
The more carbon dioxide present, the more carbon dioxide fixation will occur, meaning more GP will be produced and subsequently more TP. Although RuBP will be regenerated, there will still be less of it in relation to GP and TP as it's being used for carbon dioxide fixation.
When there is a high concentration of CO2, the stomata open, but if too much water is lost via transpiration then they close. When they close the CO2 concentration will fall, meaning RuBP will accumulate as it isn't fixating CO2, this means that less GP will be synthesised from RuBP and CO2 and consequently less TP.
92
How does temperature affect levels of RuBP, GP and TP if it's the limiting factor?
Increasing the temperature, will increase the rate of photosynthesis in the light independent reaction but it won't affect the light dependent reaction. This means there will be high levels of RuBP and TP but low levels of GP as it is being reduced.
If temperatures rise too high then rubisco oxygenates oxygen more than it carboxylates CO2 (this is photorespiration) because oxygen more successfully competes with the active site of rubisco. This means there are lower levels of GP and TP but higher levels of RuBP. It also means that reduced NADP and ATP dissipates and is wasted.
If the temperature rises even further then proteins may be damaged and stomata may close due to too much transpiration.
93
GB: How did scientists discover that the oxygen was produced from water?
They discovered this by using radioactive isotopes. They gave the plant carbon dioxide containing radioactive oxygen and normal oxygen was produced. They also gave a plant water, containing radioactive oxygen and radioactive oxygen was produced from the plant.
94
GB: Why is photosystem II used before photosystem I?
Because photosystem I was discovered first by scientists but photosystem II is actually used first in the reaction.
