Lecture 12: Photosynthesis Flashcards
Discuss the importance of photosynthesis
Nearly all organisms depend on photosynthesis
- it provides the carbon source for most of the planets ecosystems
- light energy is used to make sugars from CO2 and H2O
Solar energy
Discuss the importance of solar energy
Who uses it to make organic compounds
The fundamental energy source for most of the environment is the sun.
Photoautotrophs capture the suns energy
They then use it to make organic compounds through photosynthesis
-energy from the sun is used to make complex molecules
What are photoautotrophs, what to they do?
- use simple carbohydrates eg glucose to build complex organic molecules (eg starches, also proteins and lipids)
- often called primary producers
- they create organic material from inorganic sources
- they replenish O2 in the atmosphere and are essential in the energy and carbon cycles
Photosynthesis
Why is photosynthesis important?
- It is essential for life on earth
- he conversion of solar energy to chemical energy - Responsible for the removal of 200 billion tons of carbon from the atmosphere each year
Carbon cycle:
What is humanity doing to alter the carbon cycle?
The natural ‘greenhouse’ effect is being intensified as humans alter the global carbon cycle.
- forests, soils, oceans, the atmosphere and fossil fuels are important stores of carbon
- carbon is constantly moving between these different stores that act as sinks
Chloroplasts
Plastids: what are they?
- Plastids are a group of organelles found within plants and algae
- there are many different types of plastid, each with different functions.
- they contain their own DNA
What are the different kinds of plastids? What is their function?
Chloroplast: photosynthesis
Chromoplasts: synthesis and storage of pigments
Gerontoplasts: senscene
Leucoplasts: terpene synthesis
Amyloplasts: starch storage/ gravity detection
Elainoplasts: fat storage
Proteinoplasts: protein strorage
What is the origin of plastids?
The endosymbiotic theory
- a cyanobacterium entered another cell and they entered into a symbiotic relationship
- over type genes were transferred from the cyanobacterium to the host cell
- the symbiont became an organelle
Biochemistry of photosynthesis:
Photosynthesis occurs in two broad stages:
1. Light reactions (light dependant) (energy capture)
2. Dark reactions (light independent) (carbon capture)
Photosynthesis splits water molecules apart
6co2 + 12h2o -> C6H12O6 + 6H2O + 6O2
When water molecules split to form O2, they lose electrons (e-) and H+ ions
-it is an oxidation reduction reaction (refer to slide for pic)
Photosynthesis: light reactions
What does the light reactions involve
Involves:
-The oxidation of water to oxygen
-reduction of NADP+ to NADPH
-production of ATP from ADP and Pi
Thes reactions occur in the thylakoid membranes of chloroplasts
-NADPH and ATP are used in dark reactions
Photosynthesis: Dark reactions
What does this kind of reaction involve?
Involves:
- Use of NADPH and ATP to fix CO2 into CH2O (sugar/ carbohydrate)
- they occur in the stroma matrix of the chloroplasts
- also known as the Calvin cycle
Chloroplasts
What happens in the chloroplast?
Photosynthesis occurs in the chloroplasts
- light is absorbed by chlorophyll molecules in the chloroplast
- energy from the photos of light trapped by chlorophyll molecules
- captured electrons are transferred to other compounds along an electron transport chain to form NADPH
- ATP is produced by the ATP synthase enzyme complex
Photosynthesis: Light reactions 2
Light energy is absorbed by the chlorophyll
- ATP is made from ADP + Pi
- electrons are transferred to NADP+
- the flow of electrons is coupled by the pumping of H+ across the thylakoid membrane
- as in mitochondria, the electron gradient drives a proton pump through ATP synthase to produce ATP by phosphorylation
Photosynthesis: Dark reactions 2
-CO2 is incorporated into organic molecules producing sugars
-NADPH provides some energy as electrons
-ATP provides chemical energy for some steps
NEED to look at the picture slides with diagrams
Mitochondrion vs chloroplasts
- both are ovoid in shape with a double membrane
- both are surrounded by an outer membrane and an inner membrane
- both have membranes surrounded by fluid
- in the mitochondrion, the fluid matrix is inside the inner mitochondrial membrane
- in the chloroplasts, the stroma surrounding the grana is a fluid
- fluid also occupies the lumen of each thylakoid
