Topic 5. Photosynthesis Flashcards
What are autotrophs?
organisms that use light or chemical energy to synthesise complex organic molecules from inorganic molecules
What are chemoautotrophs?
- autotrophs which use energy derived from chemical reactions
- mainly bacteria
What are some examples of chemoautotrophs?
- nitrifying bacteria
- Nitrosomonas (ammonium ions to nitrites)
- Nitrobacter (Nitrites to nitrates)
What are photoautotrophs?
- use energy derived from sunlight to convert carbon dioxide and water (inorganic molecules) to complex organic molecules e.g. glucose during photosynthesis
What are examples of photoautotrophs?
- plants
- cyanobacteria
- protoctists such as algae and seaweeds
What are heterotrophs?
- organisms that ingest and digest complex organic molecules, releasing chemical potential energy stored within them
What are some examples of heterotrophs?
- animals
- fungi
- some bacteria
Is photosynthesis endothermic or exothermic?
endothermic - more energy used to make bonds than is released
What is photosynthesis?
- a process which uses the sun’s energy to create complex organic molecules such as glucose
What is needed for photosynthesis?
- water
- sunlight
- CO2
What are the products of photosynthesis?
- O2
- Glucose
How is water taken up for photosynthesis?
absorbed from the roots
How is CO2 taken up for photosynthesis?
enters through the stomata of the leaves
How is sunlight absorbed for photosynthesis?
Chlorophyll - traps light energy to make food
What is glucose stored as in plants?
starch
What is O2 released as in photosynthesis?
a bi-product
Where does photosynthesis occur in plants?
organelles called chloroplasts
What are the two stages of photosynthesis?
- Light Dependent Stage
- Ligth Independent Stage
Where does the Light Dependent Stage (LDS) occur?
Grana
Where does the Light Independent Stage (LIS) occur?
Stroma
What are the adaptations of chloroplasts?
- large s/a to absorb sunlight
- ribosomes to make proteins
- loops of DNA to code for some of the proteins needed for photosynthesis
- stroma contains lipid droplets and starch grains to store products of photosynthesis
- stroma contains enzymes for LIS
- Photosynthetic pigments for LDS in photosystems
What is the internal structure of a chloroplast?
- intergranal membranes called thylakoids and lamellae contain photosystems for LDS
- Thylakoids are flattened membrane discs which form stacks called grana (singular granum)
- Lamellae are the network of thin membranes which connect grana
What are photosynthetic pigments?
molecules that absorb light energy at a range of wavelengths in the visible region
What is unique about each photosynthetic pigment?
each has its own distinct peak of absorption (wavelength of light)
Why is the colour of each photosynthetic pigment important?
each pigment is the colour of the wavelength of light that it reflects
How are photosynthetic pigments used in photosynthesis?
- by acting together they capture as much light energy as possible
- absorb as much of the visible spectrum as possible
- they are used in the LDS of photosynthesis
What colour is Chlorophyll a?
blue-green
What type of pigment is Chlorophyll a?
Primary
Where in the Photosystem is Chlorophyll a located?
Reaction centre
What are the three accessory pigments?
Chlorophyll b, Carotene, Xanthophyll
What colour is Chlorophyll b?
yellow-green
What colour is carotene?
Orange
What colour is Xanthophyll?
yellow
Where are the three accessory pigments found?
Light harvesting system/region
How are photosynthetic pigments arranged?
In funnel-shaped structures called photosystems
Where are photosystems found?
embedded in thylakoid membranes and lamellae membranes
What type of Chlorophyll a is found in PSI?
P700
What is the peak absorption of PSI?
700 nm
What is the main location of PSI?
Intergranal lamallae
What type of Chlorophyll a is found in PSII?
P680
What is the peak absorption of PSII?
680nm
What is the main location of PSII?
grana (thylakoids)
In what order do the photosynthetic pigments absorb light energy in a photosystem?
- accessory pigments absorb light energy and transfer it to primary pigments
- light energy passes through accessory pigments first
What is the significance of the magnesium atom found in Chlorophyll a?
- contains two electrons
- electons become excited when they absorb light energy
What are the two distinct pathways of the LDS?
- Cyclic photophosphorylation
- Non-Cyclic photophosphorylation
What is phosphorylation?
adding a phosphate
What is released from Cyclic photophosphorylation?
ATP
What is released from Non-Cyclic photophosphorylation?
- ATP
- Reduced NADP
- O2
What are the three importnat types of reaction that occur during the LDS?
1) Photophosphorylation
2) Photolysis
3) Oxidation - Reduction reactions
What happens during photophosphorylation?
- light energy used to add a phosphate ion onto ADP to make ATP
- (using light energy to phosphyorylate ADP)
What is Photolysis?
- the splitting of water in the presence of light
- water –> electron + oxygen + proton
What are the thylakoid and lamellae membrane proteins involved in photophosphorylation?
- electron acceptors
- electron carriers
What is the role of electron acceptors during photosynthesis?
accept electrons from Chlorophyll a
What happens to the electrons accepted from Chlorophyll a?
- passed down a series of electron carriers
What happens to electron carriers when they accept electrons?
they become reduced
What happens to electron carriers when they pass electrons on to the next carrier?
they are oxidised
What type of reactions are the Oxidation - Reduction reactions during the LDS of photosynthesis?
- redox reactions
What do the redox reactions release?
energy which is used to make ATP
