how would you test the presence of starch in leaves
Answers
sᴛᴀʀᴄʜ ᴛᴇsᴛɪɴɢ
ɪᴏᴅɪɴᴇ sᴏʟᴜᴛɪᴏɴ ɪs ᴜsᴇᴅ ᴛᴏ ᴛᴇsᴛ ʟᴇᴀᴠᴇs ғᴏʀ ᴛʜᴇ ᴘʀᴇsᴇɴᴄᴇ ᴏғ sᴛᴀʀᴄʜ. ʏᴏᴜ ɴᴇᴇᴅ ᴛᴏ: ʜᴇᴀᴛ ᴀ ᴘʟᴀɴᴛ ʟᴇᴀғ ɪɴ ʙᴏɪʟɪɴɢ ᴡᴀᴛᴇʀ ғᴏʀ 30 sᴇᴄᴏɴᴅs (ᴛʜɪs sᴛᴏᴘs ɪᴛs ᴄʜᴇᴍɪᴄᴀʟ ʀᴇᴀᴄᴛɪᴏɴs) ʜᴇᴀᴛ ɪᴛ ɪɴ ʙᴏɪʟɪɴɢ ᴇᴛʜᴀɴᴏʟ ғᴏʀ ᴀ ғᴇᴡ ᴍɪɴᴜᴛᴇs (ᴛʜɪs ʀᴇᴍᴏᴠᴇs ᴍᴏsᴛ ᴏғ ɪᴛs ᴄᴏʟᴏᴜʀ)
Requirements:
- Sample plants
- Glass jar or beaker
- Stove and saucepan
- Iodine solution
- Ethyl alcohol
- Tweezer
Procedure:
Set up one plant on a sunny windowsill and another in a dark room for 24 hours
After 24 hours, fill a beaker with ethyl alcohol and place it in a saucepan full of water
Continue heating the pan until ethyl alcohol starts boiling and then take it off from the heat
With the help of tweezers, dip each of the leaves in hot water for a minute
Now, dip the leaves in the beaker holding ethyl alcohol for 120 seconds or till they change their color to almost white
Place each of them in a shallow dish
Cover these leaves with some drops of iodine solution and observe
Observation:
Alcohol breaks down the chlorophyll and hot water kills the leaf. Hence, the leaf is no more green in color
When leaves are treated with iodine, one of them turns its colour to blue-black due to the presence of starch with iodine as an indicator. The other leaf turns its colour to reddish-brown
The leaf that was kept in light turns blue-black in colour indicating the leaf has been carrying out photosynthesis, producing starch
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