Required practical: Photosynthesis Flashcards

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1
Q

Step 1

A

Place a boiling tube with sodium hydrogen carbonate solution 10cm away from an LED light source

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2
Q

Step 2

A

Place a piece of pondweed with the end cut at the top into the tube

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3
Q

Step 3

A

Place a funnel and measuring cylinder at the top of the boiling tube

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4
Q

Step 4

A

Calculate the volume of gas produced (bubbles) in the measuring cylinder in a minute
Use a stop watch to time it for a minute

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5
Q

Step 5

A

Repeat experiment 2 more times and calculate the mean volume of oxygen gas

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6
Q

Step 6

A

Repeat whole experiment, but moving the tube 10cm back each time until it’s 40cm away

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7
Q

Why use an LED light?

A

Normal light bulbs produces heat energy. This affects the rate of photosynthesis
We are trying to measure the affect of light energy on photosynthesis

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8
Q

Why calculate volume of oxygen rather than bubbles propounded?

A

Bubbles may be too quick to count accurately

Some bubbles are different sizes

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9
Q

The inverse square law

A

If you plot these results on a graph then:
When you double the distance, the number of bubbles produced per minute falls by 4 times.
If at 10 cm away it produced 20cm³ of oxygen, then at 20 cm away it would produce 5cm³ of oxygen

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10
Q

Why does the inverse square law happen?

A

If the distance is doubled, the light intensity falls by 4 times.
Causes the volume of oxygen produced to decrease by 4 times because rate of photosynthesis falls

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11
Q

Why do we use sodium hydrogen carbonate?

A

Releases carbon dioxide = needed for photosynthesis

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