Flashcards in Photosynthesis, 5.6 Deck (52):
What is photosynthesis?
A process where plants convert light energy into chemical energy
Define autotrophic nutrition?
Organism capable of synthesizing large molecules from simple inorganic molecules.
What are phototrophs?
Autotrophs which undergo photosynthesis - produce energy from sunlight.
What is a photon?
A particle of light containing some energy
How is photosynthesis linked to respiration?
In respiration plants oxidize the molecules made in photosynthesis
What is photosynthesis an example of?
When do plants photosynthesise?
Where does photosynthesis occur?
Describe the structure of a chloroplast.
Disc shaped. Double membrane with an inter membrane space. Outer membrane highly permeable. Inner membrane less permeable. Stroma - fluid filled matrix.
Where does the light dependent stage take place?
Describe the structure of grana.
Stacks of thylakoids which contain photosystems. There is a huge surface area for - photosynthetic pigments and electron carriers.
What is a photosystem?
System of photosynthetic pigments
What is a photosynthetic pigment?
Pigment that absorbs specific wavelengths of light and traps the lights energy.
Describe the key features of the stroma
Contains enzyme needed to catalyze reactions of the light independent stage. Starch grains. Oil droplets. Small ribosomes.
What shape are photosystems?
What do the photosynthetic pigments do?
Absorb light of a particular wavelength and reflect other wavelengths
What is the primary pigment center?
A type of chlorophyll at the base of the photosystem.
What is the role of a primary pigment? And where is it located?
Absorb energy from the sun or from accessory pigments. For example chlorophyll a. At the centre of the photosystem.
What is the role of an accessory pigment? And where is it located?
Absorbs energy from the sun and passes it onto primary pigments. eg Carotenoids and Xanthophylls. At the edge of the photosystem.
Describe chlorophyll a
Two forms. Absorb red light. P680 - in Photosystem II. P700 in Photosystem I.
Describe chlorophyll b.
Appears yellow-green. Absorbs wavelengths around 400-500nm and 640nm
What is photolysis?
An enzyme that in the presence of light splits water in protons, electrons and oxygen. Oxygen is either used in respiration or released
Describe the process of NON CYCLIC PHOSPHORYLATIOn
1. Photon of light strikes PSII excites a pair of electrons
2. Energized electrons leave the chlorophyll
3. Electrons captured by electron carrier
4. Electrons replaced by electrons derived from photolysis
5. Iron is reduced when it combines with the electron and the reoxidises when it passes the electron on
6. As electrons pass along energy is released
7. Energy used to pump proteins into the thylakoid space
8. Electrons captured in PSI
9. Ferredoxin accepts electrons and passes them to NADP in the stroma
10. Protons accumulate in the thylakoid space creating a proton gradient
11. Diffuse through channels associated with ATP Synthase forming ATP
12. red. NADP is also formed
Describe the process of CYCLIC PHOSPHORYLATION
1. Light strikes PSI and excites a pair of electrons
2. Electrons escape the chlorophyll
3. Pass to an electron carrier system then back to PSI
4. Small amount of energy is generated
Why is cyclic phosphorylation different to non cyclic phosphorylation?
Only involves PSI. No photolysis of water - no oxygen produced. No red. NADP generated.
Why do guard cells only contain PSI?
Only produce ATP to actively transport K+ ions in order to lower the water potential. Water moves into the leaf via osmosis. Opens stomata.
Where does the light independent stage take place?
How does carbon dioxide enter?
Through stomata in the leaf. Diffuses through spongy mesophyll layer to the palisade layer. Through cellulose cell walls and the chloroplast to the stroma.
Describe the different stages of the Calvin Cycle.
1. Carbon Dioxide combines with RuBP (5C). Catalysed by RuBisCO.
2. RuBP is carboxylated forming 2 molecules of GP (3C)
3. GP is reduced, using hydrogens from red. NADP, to form TP (3C)
4. 10 of every 12 TP are rearranged to regenerate 6 molecules of RuBP. This requires phosphate groups (ie uses ATP)
What is the name of RuBP? How many carbons is it?
Ribulose bisphosphate. 5 Carbons
What is the name of GP? How many carbons is it?
Glycerate-3-phosphate. 3 Carbons.
What is the name of TP? How many carbons is it?
Triose phosphate. 3 Carbons.
What are some uses of triose phosphate?
Glucose converted to sucrose, starch or cellulose. Synthesis amino acids, fatty acids and glycerol.
What is a limiting factor?
Factor whose magnitude slows the rate of a natural process. The factor furthest away from its optimum.
Why is light important during photosynthesis?
Provides the energy. Needed for both stages. Light causes stomata to open - gaseous exchange. Transpiration also occurs.
What is the affect of low light on the substances involved in the Calvin Cycle?
1. GP cannot be reduced to TP
2. TP levels fall, GP accumulates
3. RuBP cannot be regenerated
What happens to the rate of photosynthesis at low light intensity?
The rate decreases
Why is carbon dioxide not usually a limiting factor?
Because there are high levels in the atmosphere
What happens if carbon dioxide levels drop below 0.01%?
1. RuBP cannot accept it, so accumulates
2. GP and TP cannot be made so levels fall
Why does temperature affect photosynthesis?
There are many enzymes involved in the Calvin Cycle
What happens to photosynthesis at low temperatures (25-30)?
As temp. increases so does the rate. Molecules are gaining kinetic energy and so are more likely to collide with the enzyme.
What happens to photosynthesis at temperatures above 30? And why?
Rate slows. Transpiration increases. Oxygen competes with carbon dioxide for RuBisCO active site - inhibits. Reduces quantity of TP and GP.
What happens to photosynthesis at temperatures above 45? And why?
Rate would slow dramatically. Enzymes involved in photosynthesis will denature. Reduce amount of GP and TP. RuBP can't be regenerated.
Why does water stress affect photosynthesis?
Transpiration stream - keeps plant cool. Turgid guard cells keep stomata open. If there's not enough water roots can't take up enough water, cells lose water and become plasmolysed. Leaves wilt.
How can the rate of photosynthesis be measured?
By oxygen produced or uptake of carbon dioxide
What are the limitations of measuring the amount of oxygen produced?
Some used in respiration. Some may be dissolved in nitrogen in gas collected.
How do we use a photosynthometer?
1. Gas given off is collected in a capillary tube
2. Gas bubbles can be measured against a scale length
3. If the radius of the capillary tube is known can calculate the volume
How is the grana adapted for its function?
Thylakoids provide a large surface area for light absorption. Contain pigments and photosystems. Contain electron transport systems
Why do heterotrophs rely on plants?
Plants produce organic materials and oxygen through photosynthesis which heterotrophs need for respiration.
What is meant by a heterotroph?
Relies on/feeds on organic molecules made by other organisms
How is light harvested in chloroplast membranes?
- Photon absorbed by pigment
- Energy passed from one pigment to another
- Energy passed to reaction centre (chlorophyll a)
- Range of pigments allow a range of wavelengths to be absorbed