CHECKPOINT I Which method should be used to separate 1. grass from a bunch of spinach leaves? 2. stone pieces from a bowl of wheat? 3. dead insects from flour? 4. pieces of paper from cardboard pieces? 5. pebbles from sand?
Answers
1. Hand Picking
Activity 2 :
Bring a packet of grain purchased from a shop to the classroom. Now, spread the grain on a sheet of paper. Do you find only one kind of grain on the sheet of paper? Are there pieces of stone, husks, broken grain and particles of any other grain in it? Now, remove with your hand the pieces of stone, husks and other grains from it.
This method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses2. Threshing
You must have seen bundles of wheat or paddy stalks lying in fields after harvesting the crop. Stalks are dried in the sun before the grain is separated from them. Each stalk has many grain seeds attached to it. Imagine the number of grain seeds in hundreds of bundles of stalk lying in the field! How does the farmer separate grain seeds from those bundles of stalks?
One may pluck mangoes or guavas from the trees. But, grain seeds are much smaller than mangoes or guavas. So, plucking them from their stalks would be impossible. How does one separate grain seeds from their stalks?
The process that is used to separate grain from stalks is threshing.
In this process, the stalks are beaten to free the grain seeds (Fig. 3). Sometimes, threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.