Photosynthesis Flashcards
(37 cards)
What is photosynthesis
The process of making glucose from carbon dioxide, water and light energy
What does it mean if an organism is chemosynthetic?
An organism that is chemosynthetic is one which doesn’t require the use of light energy to form carbohydrates
Where in plants does photosynthesis occur?
Photosynthesis occurs in plant structures known as chloroplast which contain chlorophyll (light-sensitive pigments)
Where is chlorophyll found in green leaves?
In green leaves, chlorophyll is found right under the epidermis within the palisade mesophyll cells and the spongy mesophyll cells (less frequent).
Describe the structural makeup of green leaves
- The outer layers of the leaves are called cuticles (waxy layer)
- under the cuticle is another layer (plant skin) known as the upper epidermis
- The inner layer as a whole is called the mesophyll which consists of palisade mesophyll (cells are tightly packed) and spongy mesophyll (pores)
- Chloroplasts are found within mostly the palisade mesophyll and less frequently within the sponge mesophyll
( ROUND PORES) - The lower epidermis (plant skin)
- In the lower epidermis are guard cells and stroma which regulate the entrance and exit of different molecules in and out of the leaf
- another cuticle under the cuticle
What are thylakoids?
Thylakoids are small stacks of disk-like structures found within chloroplasts
What is the difference between stroma and lumen?
Lumer is the internal space of thylakoids and stroma is the aqueous medium in which all plant structures are suspended within
Where is chlorophyll found?
Chlorophyll is found bound to thylakoid membranes
What is the main significance of chlorophyll (function)?
The main significance of chlorophyll in plants is to give them their green colour and also give them their ability to absorb light energy
What are the two main forms of chlorophyll?
1) Chlorophyll a
2) Chlorophyll b
What are pigments?
Pigments define the electromagnetic wavelength at which a plant may absorb light energy. Plant pigments absorb light mostly within the visible spectrum.
What are the different stages of the series of reactions which take place during photosynthesis?
The two stages which photosynthetic reactions are split into include:
1) “light-dependent reactions”: reactions which require the use of light
- Energy harvesting stage
2) Dark reactions: those reactions which take place with or without the presence of light (Calvin cycle)
- Where carbon is “fixed” or combined using the harvested energy to form glucose molecules
Break down the two major stages of photosynthetic reactions into 3 steps each
Light-dependent reactions:
1)Capturing light
2)Transfering light to energy carriers
3)Converting into ATP and NADH
Dark reactions: (Calvin cycle)
1) Carbon fixation
2) Reduction of PGA
3) Regeneration RuBP
What happens during the first step of the light-dependent reactions?
First, a photon of light hits a chlorophyll molecule in the reaction center of the antenna system. From the electron center, the primary electron acceptor oxidizes the reaction center to gain the electron.
What is a photon?
A photon refers to a wave of light energy which strikes chlorophyll molecules bound to thylakoid membranes.
What is the antenna system?
The antenna system consists of a bunch of pigments including chlorophyll a, b and accessory pigments referred to the reaction center as a whole. The pigment which makes up of the reaction center converts the light energy which strikes the chloroplast into electrons. Along with this, a primary electron acceptor.
What are the two main proteins directly associated with the antenna system?
the two main proteins include Photosystem II and Photosystem I
What happens during the second step of light-dependent reactions?
The second step of the light-dependent reaction being the transfer of electrons by electron carriers starts with photosystem II. This complex is used to perform photolysis which splits 2 water molecules removing electrons, and releasing H+ ions into the thylakoid lumen. This creates a chemiosmotic gradient of protons in the lumen compared to protons in the stroma. Electrons removed during photolysis are transferred from photosystem I to photosystem II and so on throughout a chain of proteins and metal ion energy carriers. This is known as the elctron transport chain. While moving through the electron transport chain, energy is consistently used at each complex to pump H+ ions into the lumen or lost to heat. The chemiosomotic gradient result in the production of ATP molecules at end of the electron transport chain. At photosystem I, electrons are recharged by more light energy, similar to photosystem II. From photosystem I, an energy carrier called ferredoxin carries the excited electron the NADP reductase in which reduction takes place and 2 NADPH molecules are produced.
What is photolysis?
Photolysis in cellular respiration refers to the use of light energy to split water molecules removing electrons, releasing protons (H+) and creating the bi-product oxygen.
Describe what happens in the last step of light dependent reactions during photosynthesis
In the final step which consists of transforming the photon energy into chemical energy, ATP is produced through phosphorylation at the end of the ETC when protons come down the ATP synthase. After electrons are recharged in photosystem I, some of the energy is used to reduce NADP in the NADP reductase which attaches H+ ions from the stroma.
State the order in which each structure involved in the light-dependent reactions is found embedded in the thylakoid membrane
1) photosystem I
2) ETC
3) photosystem II
4) NADP reductase
5) ATP synthase
Where are the ATP and NADPH produced during the light-dependent reactions?
In the stroma
Where are protons pumped to using energy from electrons passing through the ETC?
The Lumen (inner thylakoid space)
What is the proton motive force which drives chemiosmosis and the production of ATP?
The proton motive force which drives the chemiosmosis of protons from the stroma to the lumen in photosystem II is the chemiosmotic gradient created by the proton pump increasing the concentration of hydrogen atoms in the lumen.
