5.6.2 Chloroplast structure and function Flashcards
What are chloroplasts
Organelles in plant cells where photosynthesis takes place
How big are chloroplasts
2-10μm in diameter (larger than mitochondria)
What is each chloroplast surrounded by, and describe the structure/function of this
Each chloroplast is surrounded by a double membrane envelope:
Each of the envelope is a phospholipid bilayer.
The outer membrane is permeable to a range of ions and small molecules.
The inner membrane contains transport proteins that only allow certain molecules or ions to enter or leave the chloroplast
What are chloroplasts filled with
Cytosol-like fluid known as the stroma
CO2, sugars, enzymes, and other molecules are dissolved in the stroma
What are the seperate system of membranes known as that are found in the stroma
This membrane system consists of a series of flattened fluid-filled sacs known as thylakoids
What do thylakoid membranes contain
Pigments, enzymes, and electron carriers
What do thykakoids stack up to form?
Structures known as grana - singular = granum
What are grana connected by?
They are connected by membranous channels called stroma lamellae
What do stroma lamellae ensure?
The stacks of sacs are connected but distanced from eachother = ensuring a large surface area
What does the membrane system in chloroplasts provide?
Provide a large number of pigment molecules that ensure as much light as necessary is absorbed
How are pigments arranged in chloroplasts?
In light-harvesting clusters known as photosystems.
In photosystems, the different pigment molecules are arranged in funnel-like structures in the thylakoid membrane (each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre)
What does the stroma also contain other than grana.
Ribosomes, a loop of DNA, and starch grains.
Loop of DNA codes for some of the chloroplast proteins. The proteins coded for by this loop of DNA are produced at the 70S ribosomes. Sugars formed during photosynthesis are store as starch inside starch grains
What are the two stages of photosynthesis?
Light dependent stage - LDR
Light independent stage - LIR
Where does the light dependent stage take place?
On the thylakoid membranes of the grana. Light becomes trapped within the reaction centres of the grana
Where does the light independent stage take place?
In the stroma
How is the stroma adapted to carry out photosynthesis?
The gel-like fluid contains enzymes that catalyse the reactions of the light-independent stage.
The stroma surrounds the grana and membranes, making the transport of the products from the LDR into the stroma rapid.
How is the grana adapted to carry out photosynthesis?
The granal stacks create a large surface area for the presence of many photosystems which allows for the maximum absorption of light. It also provides more membrane space for electron carriers and ATP synthase enzymes.
How is DNA adapted to carry out photosynthesis?
The chloroplast DNA (cpDNA) contains genes that code for some of the proteins and enzymes used in photosynthesis
How are ribosomes adapted to carry out photosynthesis
The presence of ribosomes allows for the translation of proteins coded by cpDNA
How is the inner membrane of the chloroplast envelope adapted to carry out photosynthesis?
The selective transport proteins present in the inner membrane control the flow of molecules between the stroma and cytosol (cytoplasm of the plant cell)
