Lab 5: Photosynthesis

Lab  5: Photosynthesis Lab  5: Photosynthesis - Start

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Lab 5: Photosynthesis - Description

Lab. 5: Photosynthesis. Lab. 5: Photosynthesis. Leaves float in water due to presence of air (air spaces) in the leaf. . How does one get them to sink?. Lab. 5: Photosynthesis. Put leaf discs under vacuum . ID: 224831 Download Presentation

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Lab 5: Photosynthesis




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Presentations text content in Lab 5: Photosynthesis

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Lab

5: Photosynthesis

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Lab

5: Photosynthesis

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Lab

5: Photosynthesis

Leaves float in water due to presence of air (air spaces) in the leaf.

How does one get them to sink?

Slide4

Lab

5: Photosynthesis

Put leaf discs under vacuum

by placing them in an

aqueous solution inside a syringe, cover the hole of the syringe with your thumb, and then pull back on the syringe…negative pressure…sucks air out of leaf (fig 6a). Disks will sink (fig. 6b).

Slide5

Lab

5: Photosynthesis

We want

leaf discs to still be able to do photosynthesis in the solution…but you just removed the air and replaced it with water, which has little dissolved CO

2…what can we add to the water to put lots of dissolved CO2?

Slide6

Lab

5: Photosynthesis

ADD BAKING SODA…

Na

+

HCO

3

- dissociates in aqueous solution to Na+ + HCO3-

HCO

3- + H3O+ <-> H2CO3 + H2O

H2CO3 <-> H2O + CO2

Na

+

HCO

3

-

(sodium bicarbonate)

Slide7

Lab

5: Photosynthesis

Now hit them with light…what happens?

They will float after some amount of time because O2 is being produced by photosynthesis.

However, this is only an

INDIRECT

method of measuring CO2 rate…why?

Cell Respiration is occurring, using some of the O

2

and producing CO

2

gas as so you are actually also observing cell

resp

though the amount of CO

2

= O

2

used…

Slide8

Lab

5: Photosynthesis

Review…

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Lab

5: Photosynthesis

http://

www.youtube.com/watch?v

=ZnY9_wMZZWI

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Lab

5: Photosynthesis

What is the dependent variable in this experiment?

What shall we test (the independent variable)?

The time it takes for each disk to float. This is what you are measuring.

Let’s test the amount of CO

2

dissolved in the water!!!!

Slide11

Lab

5: Photosynthesis

Why is dilute soap being added in step 3?

The cuticle of the leaf is hydrophobic and prevents the leaf discs from ever sinking. The soap, as you know, is

amphiphilic

(its essentially a fatty acid). It will coat the leaf discs (tails interacts with cuticle and carboxyl head interacts with water). This will allow the discs to sink after the gas is sucked out.

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Lab

5: Photosynthesis

Why is dilute soap being added in step 3?

The “grease particle” in this case are the leaf discs…

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Lab

5: Photosynthesis

Prepare the disks…

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Lab

5: Photosynthesis

Prepare the disks…

-

One set of ten gets degassed in pure water (control)

-

One set of ten gets 0.2% bicarbonate (experimental group)

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Lab

5: Photosynthesis

Place both cups under the light source…

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Lab

5: Photosynthesis

The ET

50

is the estimated time it takes for 50% of the disks to float, which has been shown to be a reliable measure to compare between experiments if you repeat this…

The ET

50

(Estimated Time it takes for 50% of disks to float…median)

Slide17

Lab

5: Photosynthesis

Class Data

Every group should have a chart like this, but with two lines…one for pure water and one for 0.2% bicarbonate solution from which they will determine the ET

50

for both.

Slide18

Lab

5: Photosynthesis

Class Data

Trials

ET

50 – Pure Water(s)_ET50 – 0.2% bicarbonate (s)14153882420364340837143953955424410639838174163798410405

Here is our data…now what do we do to analyze it and see if there if a difference between these two groups?

Slide19

Lab

5: Photosynthesis

Class Data

ET

50

(s)

Frequency of trials

Histogram indicating the distribution of ET

50 measurements in a baby leaf spinach disk assay

Blue – pure waterGreen – 0.2% bicarbonate

Now what?

Slide20

Lab

5: Photosynthesis

Class Data

Trials

ET

50 – Pure Water(s)_ET50 – 0.2% bicarbonate (s)14153882420364340837143953955424410639838174163798410405MEANSD (σ)SE

Slide21

Lab

5: Photosynthesis

Class Data

Trials

ET

50 – Pure Water(s)_ET50 – 0.2% bicarbonate (s)14153882420364340837143953955424410639838174163798410405MEAN410387SD (σ)10.216.0SE3.605.67

And now…

Make sure you recall the meaning of the standard deviation and standard error.

Slide22

Lab

5: Photosynthesis

Class Data

Pure Water

Time (

s

)

0.2% Bicarbonate

Figure X. Mean ET

50

values for leaf disks evacuated and submerged in pure water and 0.2% bicarbonate solution. Error bars indicate standard error for eight trials (

n

=8).

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5: Photosynthesis

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5: Photosynthesis

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Lab

5: Photosynthesis


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