A2 OCR Biology - Photosynthesis

HideShow resource information
  • Created by: Jess
  • Created on: 16-04-14 19:06
What is the term that describes plants?
1 of 80
What is the equation for photosynthesis?
6CO2 + 6H20 = Glucose + 6O2
2 of 80
What is the formula for glucose?
C6 H12 O6
3 of 80
What is the coenzyme used in photosynthesis?
4 of 80
What does NADP do during photosynthesis?
Transfers hydrogen from 1 molecule to another - reducing or oxidising molecules
5 of 80
Define a coenzyme
A molecule that aids the function of an enzyme
6 of 80
What do coenzymes do (generally)?
Transfer a chemical group from one molecule to another
7 of 80
What is around the outside of chloroplasts?
A double membrane - the chloroplast envelope
8 of 80
What are thylakoids stacked up into?
9 of 80
How are the grana linked together?
By bits of thylakoid membrane called lamellae
10 of 80
What are the 3 photosynthetic pigments in chloroplasts?
Chlorophyll a/b and carotene
11 of 80
Define photosynthetic pigments
Coloured substances that absorb the light energy needed for photosynthesis, found in thylakoid membranes attached to proteins
12 of 80
Define photosystem
The protein and pigment together (photosynthetic pigments are attached to proteins in the thylakoid membranes)
13 of 80
What are the names of the 2 types of photosynthetic pigments contained in a photosystem?
Primary and accessory pigments
14 of 80
What are the primary pigments?
Reaction centres where electrons are excited during the light-dependent reaction
15 of 80
What are the accessory pigments?
They surround the primary pigments and transfer light energy to them
16 of 80
What is the difference between photosytems 1 and 2?
PSI absorbs light of wavelength 700nm / PSII absorbs light of wavelength 680nm
17 of 80
What is the stroma?
The gel-like substance contained within the inner membrane of the chloroplast and surrounding the thylakoids
18 of 80
What 3 substances are contained in the stroma?
Enzymes, sugars and organic acids
19 of 80
Where are carbohydrates stored once they have been produced by photosynthesis and not used straight away?
Stored as starch grains in the stroma
20 of 80
What are the 2 stages of photosynthesis?
The light-dependent reaction and the light-independent reaction (Calvin-Benson Cycle)
21 of 80
Where does the light-dependent reaction take place?
In the thylakoid membranes of the chloroplasts
22 of 80
Summarise what happens during the light-dependent reaction
Light energy is converted to chemical energy and used to add a phosphate group ADP --> ATP / reduces NADP --> NADPH using energy from ATP / H2O oxidised to O2
23 of 80
Where does the light-independent reaction take place?
In the stroma of the chloroplasts
24 of 80
Summarise what happens during the light-independent reaction
ATP and NADPH supplies energy and hydrogen to make glucose from CO2
25 of 80
What is the reaction for making ATP from ADP called?
26 of 80
What is the reaction that splits water into H+'s, electrons and oxygen called?
27 of 80
What are some enzymes involved in photosynthesis?
ATP synthase, rubisco
28 of 80
Why are plants green?
Green light is reflected whereas chlorophylls a and b absorb red and blue
29 of 80
Why does a plant need lots of light?
For energy for the light-dependent reaction ie. higher light intensity = more energy provided
30 of 80
At what temperature do enzymes begin to denature?
45 degrees C
31 of 80
At what temperature do enzymes become inactive?
Below 10 degrees C
32 of 80
What, other than the denaturing of enzymes happens at high temperatures?
The stomata close to avoid excessive water loss, causing photosynthesis to slow down as less CO2 is able to enter the leaft
33 of 80
What percentage of the gases in the atmosphere is made up by CO2?
0.04 %
34 of 80
At what concentration of CO2 do the stomata start to close?
35 of 80
Why is 0.4% the optimum concentration of CO2?
Gives a higher rate of photosynthesis (than the 0.04% in the atmosphere) but isn't high enough for the stomata to start to close
36 of 80
What are the limiting factors of photosynthesis?
Light intensity, CO2 concentration, temperature (and water)
37 of 80
What is the limiting factor of photosynthesis on a warm, sunny day?
CO2 concentration
38 of 80
What is the limiting factor of photosynthesis at night?
Light intensity
39 of 80
What is the 'saturation point' of a graph on limiting factors?
When the graph starts to level off as something else becomes the limiting factor
40 of 80
Why do limiting factors limit photosynthesis?
They affect the levels of GP, RuBP and TP in the Calvin-Benson cycle
41 of 80
What happens in low light intensity (technically - involving the light-in/dependent stages)?
Affects light-dependent stage first, resulting in less products (NADPH and ATP), this means that the conversion of GP to TP and RuBP will by slow, resulting in more GP building up and lower levels of TP and RuBP
42 of 80
What happens in low temperatures or hight temperatures (technically - involving the light-in/dependent stages)?
Reactions will by slower - these are all the reactions in the Calvin-Benson cycle as they are all catalysed by enzymes - resulting in the fall in levels of RuBP, GP and TP / the same will happen in higher temps as denaturing of enzymes occurs
43 of 80
What happens in low CO2 concentrations (technically - involving the light-in/dependent stages)?
The conversion of RuBP to GP is slow as there's less CO2 to combine with RuBP to make the GP, resulting in the rise of RuBP levels (as it's still being made) and the fall in levels of GP and TP (as they're used up to make RuBP)
44 of 80
What plant can be used to measure the effect of limiting factors on photosynthesis and why?
Canadian pondweed (Elodea) because the rate of O2 production can be easily measured
45 of 80
How are the photosystems linked in the thylakoid membranes?
By electron carriers
46 of 80
Define electron carriers
Proteins that transfer electrons
47 of 80
What is formed by the photosystem and electron carriers together?
Electron transport chain
48 of 80
What is an electron transport chain?
A chain of proteins through which excited elctrons flow
49 of 80
What process occurs during the light-dependent (1st) reaction?
50 of 80
What products are produced during the light-dependent reaction?
ATP, NADP and O2
51 of 80
STAGE 1. What occurs at the start of the light-dependent reaction?
Light energy is absorbed by PSII and excites electrons in the chlorophyll, electrons move to a higher energy level, they then move along the electron transport chain to PSI
52 of 80
What does it mean when an electron moves to a higher energy level?
It has more energy
53 of 80
STAGE 2. What occurs once excited electrons have moved along the ETC (during the light-dependent reaction)?
Electrons that have left must be replaced, light energy splits water into H+ ions and O2, O2 leaves a by-product
54 of 80
STAGE 3. What occurs once O2 has left (during the light-dependent reaction)?
Excited electrons lose energy as they move along the ETC, this energy is used to transport protons into the thylakoid, thylakoid has higher proton concentration than stroma, proton gradient across membrane formed
55 of 80
STAGE 4. What occurs on the creation of a proton gradient across the membrane of the thylakoid (during the light-dependent reaction)?
Protons move down concentration gradient into stroma via enzyme ATP synthase, energy from this combines ADP and Pi into ATP
56 of 80
STAGE 5. What occurs once light hits PSI (during the light-dependent reaction)?
Light energy absorbed by PSI, excites electrons to even higher energy level, electrons transferred to NADP with a proton from the stroma, produces NADPH
57 of 80
What is chemiosmosis?
The name of the process where the movement of H+ ions across a membrane generates ATP
58 of 80
What are the 2 types of the light-dependent reaction?
Cyclic and non-cyclic (photophosphorylation)
59 of 80
What's different about cyclic photophosphorylation compared to non-cyclic photophosphorylation?
It only uses PSI
60 of 80
Describe what happens during cyclic photophosphorylation
Electrons from chlorophyll molecule aren't passed onto NADP but are passed back to PSI via electron carriers / therefore, electrons are recycled and can repeatedly flow through PSI (ie. in a cycle)
61 of 80
What are the disadvantages of cyclic photophosphorylation?
Only produces small amounts of ATP and doesn't produce any NADP or O2
62 of 80
What is the light-independent reaction also known as?
The Calvin-Benson Cycle
63 of 80
Where does the Calvin-Benson Cycle take place
In the stroma of chloroplasts
64 of 80
What products are made by the Calvin-Benson Cycle?
TP (and GP) which go onto make useful substances / and RuBP (recycled back into the cycle)
65 of 80
Why is the Calvin-Benson Cycle also known as carbon fixation?
Because carbon from CO2 is 'fixed' into an organic molecule
66 of 80
STAGE 1: What happens when CO2 enters the leaf (light-independent reaction)?
CO2 enters leaf through stomata, diffuses into chloroplast's stroma, combined with RuBP with catalysis from rubisco (enzyme), makes unstable 6C molecule which breaks down into 2 GP (3C)
67 of 80
STAGE 2: What happens once GP has been made (light-independent reaction)?
ATP and NADP are required to make GP into TP: ATP from light-dependent reaction provides energy whilst H+ ions from NADPH are created on conversion to NADP, 2x TP is made (3C)
68 of 80
STAGE 3: What happens after TP has been made (light-independent reaction)?
5/6 TP molecules produced regenerate RuBP (starts cycle again...using energy from ATP from light-dependent reaction), 1/6 molecules create useful organic substances
69 of 80
Why is the Calvin-Benson Cycle important for a plant (other than for photosynthesis)?
It is responsible for making all of the organic substances a plant needs (from TP and GP which make carbohydrates, lipids and amino acids)
70 of 80
What products does GP make?
Amino acids / fatty acids (combined with glycerol to make lipids)
71 of 80
What produces does TP make?
Glycerol (combined with fatty acids to make lipids) / hexose sugars such as fructose, glucose and sucrose / starch / cellulose
72 of 80
What does RuBP stand for?
Ribulose bisphosphate
73 of 80
What does TP stand for?
Triose phosphate (3C)
74 of 80
What does GP stand for?
Glycerate 3-phosphate (3C)
75 of 80
What does rubisco stand for?
Ribulose bisphosphate carboxylase
76 of 80
How many times does the Calvin-Benson Cycle need to turn to make 1 hexose sugar?
6 times
77 of 80
Describe why the Calvin-Benson Cycle needs to turn 6 times to make 1 hexose sugar
1 molecule of CO2 makes 2TP (3C), 3 turns makes 6TP, 5/6 TP's regenerate RuBP, so 3 turns makes 1 TP / hexose sugar is 6C so it needs 2TP = 6 turns of the cycle
78 of 80
How much ATP and NADPH is needed for the Calvin-Benson Cycle to turn 6 times and create 1 hexose sugar?
18 ATP and 12 NADPH
79 of 80
How is a chloroplast adapted for photosynthesis?
Envelope keeps reactants close to their reactants / Thylakoids have a large SA (absorb as much light as poss) and lots of ATP synthase in their membranes / Stroma contains all enzymes, sugars and organic acids needed for light-independent reaction
80 of 80

Other cards in this set

Card 2


What is the equation for photosynthesis?


6CO2 + 6H20 = Glucose + 6O2

Card 3


What is the formula for glucose?


Preview of the front of card 3

Card 4


What is the coenzyme used in photosynthesis?


Preview of the front of card 4

Card 5


What does NADP do during photosynthesis?


Preview of the front of card 5
View more cards


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Photosynthesis resources »