Factors that Affect the Growth in Duckweed

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Factors that Affect the Growth in Duckweed

Introduction

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For healthy growth plants need several substances. Three important

mineral ions that can only be obtained from the soil through their

roots are nitrates, phosphates and potassium. Nitrates are essential

for making amino acids and for the 'synthesis' of proteins. Phosphates

are essential as they have an important role in reactions involved in

photosynthesis and respiration. Potassium is also important as it

helps the enzymes involved in photosynthesis and respiration to work.

The three main minerals are needed in fairly large amounts, but other

elements are required in much smaller amounts. Iron and magnesium are

the most important as they are needed to make chlorophyll.

Without photosynthesis, along with minerals, plant growth wouldn't

take place. Photosynthesis produces glucose for 'food' and takes place

in the leaves of all green plants. Glucose is combined with nitrates

(collected from the soil) to make amino acids, which are then made

into proteins. Protein amino acid contains carbon, hydrogen, oxygen

and nitrogen. Along with potassium, phosphorus and sulphur make up the

important substances that travel through the roots and up the stem.

Photosynthesis needs carbon dioxide, water, light and chlorophyll to

continue the process. Without iron and magnesium chlorophyll couldn't

be made and therefore the plant would die.

Diffusion takes place in the leaves, through the stomata. The

membranes allow substances in and out as particles from an area of

high concentration move to an area of low concentration. This takes

place in the example of NO4. There...

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...n back to the petri dish

We could do the same experiment but instead of weighing, we could

count the number of leaves. Or we could use squared paper to find the

surface area by taking a sample of 10 or 20 - this would give a good

range. Another way is to harvest 100 duckweeds, dry them in the oven,

and then weigh the dry mass of the dead duckweed. We would weigh

different samples from the same conditions every week. However, by

taking more out, the duckweed left behind have less competition for

nutrients. So we could put 100 duckweeds in 6 petri dishes with the

same concentration and would prove to be more accurate over a period

of 6 weeks. The fertiliser increases the growth up to a point. We

could put the duckweed at the bottom of a graduating tube, fill it up

with water, and measure the amount of oxygen each week.

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