AQA A Level Biology復習筆記2.2.3 Iodine Detects Starch Grains

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年6月28日上午10:18

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 ‘artefacts’ and obstruct your view of the specimen).

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