5.6 Photosynthesis

?
  • Created by: elbungay1
  • Created on: 07-04-19 11:57
What is autotrophic nutrition?
Using chemical energy to synthesise large organic molecules, which form the building blocks of living cells, from simple inorganic molecules such as water and carbon dioxide. Plants are photoautotrophs
1 of 27
What is the general equation for photosynthesis?
6CO2 + 6H2O + energy from photons ------> C6H12O6 + 6O2
2 of 27
Describe the role of carbon fixation in photosynthesis
Carbon Dioxide is converted into sugars, the carbon for synthesising all types of organic molecules is provided by carbon fixation. Endothermic so requires electrons, regulates concentration of CO2 in atmosphere and oceans
3 of 27
What is the compensation point?
Plants respire at all times but photosynthesise only during daylight. Compensation point is where there is no net gain or loss of carbohydrate, photosynthesis and respiration proceed at the same rate. Occurs twice a day
4 of 27
Describe the structure of a Chloroplast
Disc shaped with a double membrane with an intermembrane space. Filled with fluid matrix called stoma, with grana consisting of stacks of thykaloid membranes. Grana connected with interganal lamellae.
5 of 27
What are the properties of Grana
Thykaloid membranes folded into flattened disc-shaped thykaloids stacked into grana, creating a very large surface area for: distribution of photosystems that contain photosyntheic pigments that absorb light energy. Electron carriers and ATP Synthase
6 of 27
What is found in the Stroma?
Fluid-filled matrix that contains enzymes (RuBisCO) for light independent stage of photosynthesis, as well as starch grains, oil droplets, small ribosomes and DNA (codes for needed proteins)
7 of 27
What are photosynthetic pigments?
Thykaloid membranes contain photosystems which contain photosynthetic pigments, each pigment absorbs light of a particular wavelength and reflect the other wavelengths. Energy associated funnelled down to primary pigment reaction centre
8 of 27
What are Chlorophylls?
Mixture of pigments. Chlorophyll a is blue-green P(680) in Photosystem II, P(700) in PSI. Chlorophyll b appears yellow green, absorbs 400-500nm and 640nm
9 of 27
What is the role of water in the light-dependent stage?
In the presence of light energy, water splits into oxygen, protons and electrons, this is called photolysis. Source of protons for photophosphorylation, donates electrons to PSII replacing those lost, source of by-product O2, keeps plant turgid
10 of 27
What are the two types of photophosphorylation?
Non-cyclic photophosphorylation involves PSI and PSII, produces ATP, O2 and reduced NADP. Cyclic photophosphorylation involves only PSI, only produces ATP and in much smaller quantities
11 of 27
What are the similarities between cyclic and non-cyclic photophosphorylation?
Both produce ATP (in differernt quantities), both involves PSI, both use iron-containing proteins (electron carriers), embedded in thykaloid membranes.
12 of 27
Describe how ATP is produced in electron transport chain
Electrons are passed along electron carriers in thykaloid membrane and energy is released, which is used to pump protons into thykaloid space. Proton gradient forms and proton-motive force, protons diffuse down gradient through ATP Synthase
13 of 27
What is the role of NADP reductase?
After PSI, electrons accepted by electron carrier with donates it to NADP which also accepts protons forming reduced NADP, catalysed by this enzyme
14 of 27
How does Cyclic Photophosphorylation occur?
After light strikes PS1, eletcrons become excited and are accepted by electron transport chain and donated back to PSI. During trasnport a small amount of ATP is produced but there's no photolysis or reduced NADP produced
15 of 27
What is the role of carbon dioxide in the light-independent stage?
CO2 diffuses through stoma, spongy mesophyll to palisade cells into stroma. Fixation of CO2 in stoma maintains concentration gradient. Converted to organic molecules in Calvin cycle, also by-product of respiration
16 of 27
Describe the Calvin Cycle
Ribulose Bisphosphate (5C) is carbon dioxide acceptor, catalysed by RuBisCO. Unstable 6C breaks down into 2 Glycerate-3-phosphate (GP). GP reduced by NADP using ATP to produce TP. RuBP reformed by TP using ATP, 1/6 TP makes glucose
17 of 27
How many turns of the Calvin Cycle are required to form a molecule of Glucose?
Six turns of the cycle are requires to form two molecules of TP which can be used to make a molecule of glucose
18 of 27
Why does the Calvin Cycle only run during daylight?
Requires ATP and reduced NADP continuously which is derived from light dependent stage. Pumping of protons into thykaloid space increases pH in stoma to 8, optimum for RuBisCO.
19 of 27
What are the uses of triose phosphate (TP)
Forms glucose which can be converted to sucrose, starch or cellulose. Some TP is used to synthesise amino acids, fatty acids and glycerol. Most TP recycled to generate supply of RuBP.
20 of 27
Why does the rate of photosynthesis increase with increasing light intensity
Light provides energy to power first stage of photosynthesis and produce ATP and reduced NADP for the next stage. Light causes stomata to open so more gaseous exchange, meaning more transpiration.
21 of 27
How does low light intensity effect Calvin cycle?
When there is little or no light, GP cannot be reduced to TP (no rNADP or ATP), TP levels fall and GP accumulates, if TP levels fall, RuBP cannot be regenerated.
22 of 27
How does low CO2 concentration effect the Calvin Cycle?
In low CO2 levels, RuBP cannot be accept it and RuBP accumulates. GP cannot be made and therefore TP cannot be made.
23 of 27
How does Temperature effect the Calvin Cycle
From low to 25°-30°C rate of photosynthesis increases with increasing Temp. At temps above 30°C oxygen competes with CO2 for RuBisCOs active site, reducing CO2 accepted by RuBP so less TP generated, rate falls. At above 45°, enzymes may denature
24 of 27
What is water stress?
Water allows transpiration stream, cooling the plant and keeping cells turgid so they can function e.g. turgid guard cells keep stomata open for gaseous exchange. Water stress is when not enough water is avaliable
25 of 27
How does water stress affect photosynthesis?
Roots unable to replace water lost by transpiration, cells become plasmolysed. Roots produce abscisic acid causing stomatal closure blocking gaseous exchange, tissues become flaccid and leaves wilt, rate of photosynthesis greatly reduces
26 of 27
How can rate of Photosynthesis be determined?
Using a photosynthometer, gas produces by plant collected in capillary tube, volume of gas produced: length of bubble x πr^2. Rate determined by volume over time. Syringe used to reset capillary tube
27 of 27

Other cards in this set

Card 2

Front

What is the general equation for photosynthesis?

Back

6CO2 + 6H2O + energy from photons ------> C6H12O6 + 6O2

Card 3

Front

Describe the role of carbon fixation in photosynthesis

Back

Preview of the front of card 3

Card 4

Front

What is the compensation point?

Back

Preview of the front of card 4

Card 5

Front

Describe the structure of a Chloroplast

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Human, animal and plant physiology resources »