AQA A Level Biology復(fù)習(xí)筆記2.2.3 Iodine Detects Starch Grains
Practical Skill: Using Iodine to Detect Starch Grains
- Starch is the?storage polysaccharide?of plants
- Sugars formed during?photosynthesis?are stored as starch inside?starch grains
- These starch grains are commonly found in:
- the stroma of?chloroplasts
- storage organs such as potato?tubers
- the?seeds?of cereals and legumes
- Starch grains are large enough to be seen with a?light microscope?but they first require?staining?in order to be seen?easily
- Iodine?(I2) in?potassium iodide?(KI) solution can be used to stain starch grains
- This can be done by adding a drop of potassium iodide onto the specimen (mounted on a slide) before placing a coverslip over the top
- This makes the starch grains?darker?in colour, making them easier to see
- Remember, iodine in potassium iodide solution has a light orange-brown colour but turns?blue-black?in the presence of starch
Exam Tip
Remember - only a very small amount of stain is required (usually just a drop or two will be enough)! Also, when adding a cover slip, remember to slowly lower the cover slip onto the specimen at an angle to avoid any air bubbles getting trapped (these could create ‘a(chǎn)rtefacts’ and obstruct your view of the specimen).
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