PLASTIDS

PLASTIDS:

Plastid is a double membrane bounded organelle. Found ony in plant and algal cell because plastid function is food formation and food storage. As we know that plant and algal cell do photosynthesis so they have plastid. On the basis of presence or absence and type of pigment, and the stage of development plastids are classify as
1-Proplastid
2-Leucoplast
3-Chromoplast
4-Chloroplast

PROPLASTID:

Proplastids are immature,young and developing plastid. It is a self replicatting organelle. It devides and redides in merismetic cells and are distrubuted to different cell type. Depending on the structure in which they are found, intracellualr factor and exposure to light they may develop into leucoplast or chloroplast. ETIOPLAST is atype of leucoplast which on exposure ti light change into chromoplast

LEUCOPLAST:

Leucoplast is a storage organeele. Found in parenchma cells of root,stem and seed. They also classify on the basis of substance they store
1-Amyloplast(store starch)
2-Proteinoplast(stores protein)
3-Elaioplast(store lipid)

CHROMOPLAST:

It synthesize and store different pigments other then green. It is found in coloured parts of plants such as flower,fruit wall where they attract insects and thus help in pollination

CHLOROPLAST:

It is found in green parts of plant. It involves in photosynthesis> Chloroplast is discoid shape structure which consist of three parts
1-Envelope
2-Stroma
3-Thylakoid
Chloroplast is bounded by double membrane like mitochondria outer membrane contain porins therefore freely permeable to small molecules. The inner membrane is semi permeable. Between the outer and inner membrane there is intermembrane space
The ground mass of chloroplast is called STROMA. It is protenaceous, colurless substane which like mitochondria contain ribosomes,small circular DNA, all kind of RNA and various enzymes
The stroma contain chlorophyll bearing double membrane lamella that forms flattened membrane bounded sacs-like structure called THYLAKOIDS. There are two type of thylakoid
1-smaller thylakoid also known as grana lamella
2-Larger thylakoid also known as stroma lamella
Smaller thylakoid are disc like sacs which are piled over oneanother like stack of coin called GRANUM(plural:GRANA). Each granum consist of 25-50 thylakoids and there are 40-60 grana in each chloroplast. Larger thylakoid also known as INTERGRANA connects smaller thylakoid with each other. It is couorless because it don't have pigments