Photosynthesis & Respiration Flashcards
(60 cards)
1
Q
Why do plants need energy?
A
- photosynthesis
- active transport (to take in minerals via their roots)
- DNA replication
- cell division
- protein synthesis
2
Q
Why do animals need energy?
A
- muscle contraction
- maintenance of body temp
- active transport
- DNA replication
- cell division
- protein synthesis
3
Q
What is the purpose of photosynthesis?
A
light energy is used to make glucose from H2O and CO2 (light energy is converted to chemical energy in the form of glucose)
4
Q
What is the overall equation for photosynthesis?
A
6CO2 + 6H2O + energy –> C6H12O6 + 6O2
5
Q
How do animals obtain glucose?
A
by eating plants or other animals, then respire the glucose to release energy
6
Q
How do animal and plant cells release energy?
A
cells release energy from glucose by respiration
7
Q
What are the two types of respiration?
A
aerobic : respiration using O2
anaerobic : respiration without O2
8
Q
What is the overall equation for aerobic respiration?
A
C6H12O6 + 6O2 –> 6CO2 + 6H2O + energy
9
Q
In plants and yeast, what does anaerobic respiration produce?
A
ethanol and carbon dioxide and releases energy
10
Q
In humans, what does anaerobic respiration produce?
A
lactate and releases energy
11
Q
Why is ATP a good energy source?
A
- stores or releases a small, manageable amount of energy at a time, so no energy is wasted as heat
- small, soluble molecule so easily transported around cell
- easily broken down so energy released instantaneously
- quickly re-made
- can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation)
- can’t pass out of cell so cell always has an immediate supply of energy
12
Q
Define metabolic pathway.
A
a series of small reactions controlled by enzymes e.g. respiration and photosynthesis
13
Q
Define phosphorylation.
A
adding phosphate to a molecule
14
Q
Define photophosphorylation.
A
adding phosphate to a molecule using light
15
Q
Define photolysis.
A
splitting of a molecule using light energy
16
Q
Define photoionisation.
A
when light energy ‘excites’ electrons in an atom or molecule, giving them more energy and causing them to be released. The release of electrons causes the atom or molecule to become a positively-charged ion
17
Q
Define hydrolysis.
A
splitting of a molecule using water
18
Q
Define decarboxylation.
A
removal of carbon dioxide from a molecule
19
Q
Define dehydrogenation.
A
removal of hydrogen from a molecule
20
Q
What is a redox reaction?
A
reaction involving oxidation and reduction
21
Q
What is a coenzyme?
A
a molecule that aids the function of an enzyme
22
Q
How do coenzymes work?
A
by transferring a chemical group from one molecule to another
23
Q
What is the coenzyme used in photosynthesis?
A
NADP transfers hydrogen from one molecule to another - it can reduce or oxidise a molecule
24
Q
What are the enzymes used in respiration?
A
NAD and FAD transfer hydrogen from one molecule to another - they can reduce or oxidise a molecule.
Coenzyme A transfers acetate between molecules
25
Describe how the synthesis and breakdown of ATP meets the energy needs of a cell.
In the cell, ATP is synthesised from ADP and inorganic phosphate using energy from an energy-releasing reaction, e.g. respiration. The energy is stored as chemical energy in the phosphate bond. ATP synthase catalyses this reaction. ATP diffuses to the part of the cell that needs energy. Here, its broken down back into ADP and inorganic phosphate, which is catalysed by ATP hydrolase. Chemical energy is released from the phosphate bond and used by the cell.
26
Where does photosynthesis take place?
in chloroplasts of plant cells
27
What is the structure of a chloroplast?
- flattened organelle surrounded by a double membrane
- thylakoids are stacked up into grana, grana are linked by bits of thylakoid membrane called lamellae
- contain photosynthetic pigments (chlorophyll a, chlorophyll b, carotene)
28
What are photosynthetic pigments?
coloured substances that absorb light energy needed for photosynthesis (in thylakoid membranes, attached to proteins)
29
What is a photosystem?
protein and pigment
30
What wavelength of light does PSI absorb best?
700nm
31
What wavelength o flight does PSII absorb best?
680nm
32
What does the stroma contain?
enzymes, sugars, organic acids
33
How are carbs stored when they're produced by photosynthesis and not used straight away?
carbs stored as starch grains in the stroma
34
Where does the LDR take place?
thylakoid membranes
35
What are electron carriers?
proteins that transfer electrons
36
What is an electron transport chain?
photosystems and electron carriers form an ETC - chain of proteins through which excited electrons flow
37
Describe the steps in the LDR (non-cyclic photophosphorylation).
1. Light energy is absorbed by PSII and excites electrons in the chlorophyll. The electrons move to a higher energy level (they have more energy). High-energy electrons are released from the chlorophyll (chlorophyll is photoionised) and move down the ETC to PSI.
2. As excited electrons from chlorophyll leave PSII to move down ETC, they must be replaced. Light energy splits water into protons (H+ ions), electrons and oxygen - photolysis. (so O2 in photosynthesis comes from water and is made in LDR)
H2O --> 2H+ + 1/2O2
3. Excited electrons lose energy as they move down the ETC. Energy used to transport protons into the thylakoid, so that there's a higher concentration of protons than in the stroma, forming a proton gradient across the thylakoid membrane. Protons move down their conc gradient, into stroma, via the enzyme ATP synthase, which is embedded in the thylakoid membrane. Energy from this movement combines ADP and inorganic phosphate to form ATP.
4. Light energy is absorbed by PSI, which excites electrons again to an even higher energy level. Finally, electrons are transferred to NADP, along with a proton from the stroma, to form reduced NADP.
38
What is chemiosmosis?
the process of electrons flowing down the ETC and creating a proton gradient across the membrane to drive ATP synthesis. (described by the chemiosmostic theory)
39
What is cyclic photophosphorylation?
Only uses PSI. Electrons from the chlorophyll molecule aren't passed onto NADP, but are passed back to PSI via electron carriers, so electrons are recycled and can repeatedly flow through PSI. Doesn't produce any reduced NADP or O2 - only produces small amounts of ATP.
40
Where does the light-independent reaction (Calvin Cycle) take place?
stroma
41
Why is the Calvin Cycle also known as carbon dioxide fixation?
carbon from CO2 is 'fixed' into an organic molecule
42
Describe the steps in the Calvin Cycle.
1. CO2 enters the leaf through stomata and diffuses into stroma where its combined with RuBP (ribulose bisphosphate), a 5C compound. This reaction is catalysed by the enzyme rubisco. This gives an unstable 6C compound, which quickly breaks down into two molecules of GP (glycerate 3-phosphate), a 3C compound.
2. Hydrolysis of 2 ATP (from LDR) provides energy to turn GP into 2 molecules of TP (triose phosphate), 3C compound. Reaction also requires H+ ions from 2 reduced NADP (from LDR). Reduced NADP is oxidised to NAD. GP is reduced to TP. Some TP is converted into useful organic compounds (glucose) and some continues in Calvin cycle to regenerate RuBP.
3. Five out of every six molecules of TP are used to regenerate RuBP. Regenerating RuBP uses the rest of the ATP produced by the LDR.
43
How are carbohydrates produced from Calvin cycle?
Carbohydrates - hexose sugars (glucose) are made by joint two TP molecules together and larger carbs (sucrose, starch, cellulose) are made by joining hexose sugars together in different ways
44
How are lipids produced from the Calvin cycle?
Lipids - made using glycerol (synthesised from TP) and fatty acids (synthesised from GP)
45
How are amino acids produced from the Calvin cycle?
Amino acids - some are made from GP
46
How many times does the Calvin cycle need to turn to make one hexose sugar?
The cycle must turn six times to produce two molecules of TP that can be used to make one hexose sugar
47
How much ATP and reduced NADP is needed for six turns of the cycle?
18 ATP and 12 reduced NADP from the LDR
48
What are the optimum conditions for photosynthesis?
- High light intensity of a certain wavelength: light needed to provide energy for the LDR, higher light intensity = more energy. Photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb red and blue light in sunlight (green is reflected)
- Temp around 25°C. Photosynthesis involves enzymes (ATP synthase, rubisco). If temp falls below 10°C enzymes become inactive, if temp is more than 45°C they may start to denature. At high temps stomata close to reduce water loss, causing photosynthesis to slow down because less CO2 enters the leaf when stomata are closed.
- Carbon dioxide at 0.4%. CO2 makes up 0.04% of gases in the atmosphere. Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and stomata start to close.
- constant supply of water - too little and photosynthesis has to stop but too much and soil becomes waterlogged (reducing uptake of minerals such as magnesium, which is needed to make chlorophyll a)
49
What is a limiting factor?
anything in short supply that prevents photosynthesis occurring at its maximum rate
50
Name 3 factors that limit photosynthesis.
- light
- temp
- CO2
51
On a warm, sunny, windless day what would be the limiting factor?
CO2
52
At night, what is the limiting factor?
light intensity
53
What is the saturation point?
where a factor is no longer limiting the reaction - something else has become the limiting factor
54
How are conditions in glasshouses controlled to increase yields?
- CO2 is added to the air e.g. by burning a small amount of propane in a CO2 generator
- light can get in through the glass and lamps provide light at night-time
- temp - glasshouses trap heat energy from sunlight, which warms the air. Heaters and cooling systems used to keep a constant optimum temp, and air circulation systems make sure temp is even throughout the glasshouse
55
How can the presence of pigments in a leaf be determined?
thin layer chromatography (TLC) used to compare pigments in different plants
56
What is the mobile phase?
where molecules can move - liquid solvent
57
What is the stationary phase?
where molecules can't move - solid (glass) plate with a thin layer of gel (silica gel) on top
58
How do you calculate the Rf value?
Rf value = distance travelled by spot/distance travelled by solvent
59
Describe the method using TLC to compare the pigments present in shade-tolerant plants and shade-intolerant plants.
1. grind up several leaves from the shade-tolerant plant with some anhydrous sodium sulfate, then add a few drops of propanone
2. transfer liquid to a test tube, add some petroleum ether and gently shake the tube - 2 distinct layers form in the liquid - top layer is the pigments mixed in with the petroleum ether
3. transfer some liquid from top layer into a second test tube with some anhydrous sodium sulfate
4. draw a horizontal pencil line near the bottom of the TLC plate. Build up a single concentrated spot of the liquid from step 3 on the line by applying several drops and ensuring each one is dry before the next is added. This is the point of origin.
5. once point of origin is completely dry, put the plate into a small glass container with some prepared solvent (e.g. mixture of propanone, cyclohexane and petroleum ether) - just enough so the point of origin is a little but above the solvent. Put a lid on container and leave plate to develop. As solvent spreads up plate, different pigments move with it, but at different rates - so they separate.
6. when solvent has nearly reached the top, take the plate out and mark the solvent front (furthest point solvent has reached) with a pencil and leave plate to dry in a well-ventilated place
7. should be several new coloured spots on the chromatography plate between the point of origin and the solvent front - these are the separated pigments. Calculate Rf values of pigments and look them up in a database to identify them.
8. repeat process for shade-intolerant plant and compare pigments present in their leaves.
60
How are the pigments different in shade-tolerant and shade-intolerant plants?
shade-tolerant plants can adapt to light conditions in their environment by having a different proportion of photosynthetic pigments, which allows plant to make best use of light available. Mixture of non-photosynthetic pigments is likely to be different e.g. chloroplasts of shade-tolerant plants are adapted for photosynthesis in low light conditions, but really sensitive to higher levels of light, these plants produce dark red and purple pigments called anthocyanins, which are thought to protect their chloroplasts from brief exposure to higher light levels.
