Plastids are double membrane bound bodies found in plants, protists, algae and absent in Animals.
Plastids are formed from colourless bodies in dividing cells termed Proplastids.
Mainly plastids are of two types
1.LEUCOPLAST 2. CHROMOPLAST
Leucoplasts :
1.They are colourless occur in the cells not exposed to sun light.
2.There function is to store food material.
3.Based on the food they store they are called
Amyloplast : Store starch
Elaioplast : store oil
Etioplast : store fat
Aleuronoplast : Store protein
CHROMOPLAST :
1.They are coloured due to the presence of coloured lipid soluble pigments in them like chlorophyll,carotene,xanthophylls etc. there colour vary from red yellow orange to brown
Occur in the cells exposed to sun light.
In tomato there is lycopene that give it red colour and in carrot the redness is due to carotene .
FUNCTIONS OF CHROMOPLAST
1.They impart colour to the flowers that make them attractive to the insects hence help in pollination.
2. Fruit colour helps to attract animals for dispersal of seed.
3.They play a main role in photosynthesis. 4.They synthesize membrane lipids
STRUCTURE AND FUNCTIONS OF CHLOROPLAST
Seen by leeuwenhoek,characterstic of all plants and green protists.
There main function is to synthesis of food and sometime they temporary store food.
1.Chloroplast is a double membrane structure the outer membrane is smooth freely permeable and have porin protein .The inner membrane is selectively perrmeable and have permease as a carrier protein. The structure of both the membranes is similar to plasma membrane.
2. Inner membrane is greatly folded but the infolds become free from it and float in the matrix as lamellae.
3. Lamellae become ovoid sac like structure called thalykoids.
4.These thalykoids piled together called grana there are 2-100 grana in each cell which are linked to one another by Frets or stroma lamellae.
5.The matrix of chloroplast called stroma have cDNA, 70S ribosomes,enzymes , lipid droplets called plastoglobules,pyrenoid (in algae protein body storing starch).