ds would really like some help with his science homework please?

[avenanap]

" a green leaf was bolied in water to soften it and then boiled in ethanol. It was washed with water and some brown iodine solution was dropped on to it. The extra iodine solution was washed away. When the iodine was added to the leaf, it turned blue/black. What does this mean?"

Thankyou.

there is starch in the leaf as a result of photosynthesis

Yes, I would have said it indicates starch.

So does the iodine show up the starch?

The iodine and the starch react together chemicaly to produce something which is blue/black in colour. It is a classic test for starch.

Was I seriously not very well educated whilst at primary school or is this not a question that a 9 year old should be answering?

I'm sure I learned it at secondary school. But not sure whether they do it now at primary. Things have changed a lot since I was at school (well I am old!)

c) a plant with green leaves was put in the dark for 2 days then a leaf was tested with iodine. What result would you expect and why? (last one, he's done the rest)

It is the classical test for photosynthesis.

the green bits of plants, in the presence of light carry out the following chemical reaction

Carbondioxide + water -> glucose + oxygen.

The plant then converts the glucose onto startch for storage.

The leaf is boiled in ethanol do that the green chorophyll is remove. the starch turns the brown iodine black (another chemical reaction.

What has been shown is that a green leaf produces starch.

(No child has ever learned anythung from this experiment ever in the history of schooling....they get so wrapped up in what they do they can never 'get' why they are doing it )

for the answer to c, plants need light to carry out photosynthesis, if there is no light what do you think will be the result?

I would think that no blue/black colour would appear - the iodine would stay brown. This is because the plant needs light for photosynthesis. In the dark it cannot photosynthesise, and therefore cannot produce starch.

You know, ds has just said that they have never done the experiment!!! God knows why he's been sent home with this. And he's just corrected my grammar .

Thankyou, thankyou, thankyou.

quite right, so much! take a gold star!

Ooh, don't mind if I do!

(You can tell that MB is a science teacher, can't you? )

Bloody hell, you should read the next one! I can do this ???? May be back in a bit.

Feel free!

We've managed it. Thankyou for all of your help.

Well done, you and your ds!