Trabalhos Do Carrio

What is the effect of different caffeine concentrations on the heartbeat of Daphnia

Background

Daphnia are members of the Cladocera order, which is an order of crustaceans more commonly known as water fleas. Daphnia measure from 0.20 – 0.50 mm in length, depending on the type of Daphnia. Their carapaces are translucent allowing easy observation of their feeding mechanism the movement of the eyes, and their circulatory system through microscopes. Its average heartbeat is 180 bpm, which can be seen behind its head through a microscope.

When caffeine enters the body it stimulates receptors in cells in the ventricles to increase the rate of contraction and therefore increasing the heart beat. Its effects are similar of those of adrenaline and noradrenaline though affects the heart rate through a different mechanism. In humans, 200 mg of caffeine can increase the human heart rate 5-20 bpm.

Research Question

What is the effect of a caffeine concentration of 0.01000, 0.00500, 0.00300, 0.00150, and 0.00075 (± 0.00001) in a 50.0cm3 (± 0.1cm3) solution of distilled water 60 seconds (±0.001seconds) on the heart rate of a Daphnia Magna?

Hypothesis

In higher concentrations the heart rate will beat more times per 60 seconds. At a lower caffeine concentration, the Daphnia’s heart rate will beat less times per 60 seconds due to the decreased effect caffeine will have on the Daphnia’s heart rate.

Variables

Independent – Caffeine concentration of 0.010000, 0.005000, 0.002500, 0.001250, and 0.000625 (± 0.000001)

Dependent – Heart Rate – beats/60s (± 0.01 seconds)

Control:

What is controlled? Why does it need to be controlled? How is it controlled?

Heart rate in Distilled water – control solution This will be used as the control solution. This serves the purpose of having a figure to compare the other concentrations to, in order to be sure whether caffeine has any effect on the heart rate of the daphnia. Count the heart rate beats of a daphnia in 60 seconds in a neutral water solution (distilled water).

Light intensity A higher light intensity has the effect of heating up the water on the slide…

Age and sex of Daphnia An older flea’s heart rate may be slower than a younger Daphnia. Females and males may also have different average heart rates One can verify with the provider of Daphnia whether they were created in the same batch and thus have roughly the same age and whether they are female or male. Males are usually smaller in size.

Apparatus

At least 20-40 Daphnia Magna

Low intensity Microscope

A 50 mg caffeine tablet

100ml3 measuring cylinder

6 Welled slides

6 Pipettes

1 hand tally counter

1 Pestle and Martor

1 Stopwatch

6 Syringes

Method

Crush the 50mg caffeine tablet with a marter and pestle into a fine powder.

Add 50ml3 of distilled water – measured in a measuring cylinder – to the caffeine tablet powder.

This mixture creates a solution of a 0.010000g/cm3 concentration of caffeine.

Use a syringe to retrieve 25cm3 of the 0.010000g/cm3 solution, measured in a beaker.

After having added the retrieved solution into a new beaker, add 25cm3 of distilled water in order to dilute the previous solution

This mixture creates a solution of a 0.005000 g/cm3.

Dilute the solution three more times by repeating steps 4-5, creating solutions with the concentrations 0.002500, 0.001250, and 0.000625.

Using a pipette, place a drop of the first concentration, 0.010000g/cm3 on a welled slide.

Using a different pipette, pick up a daphnia from the container with daphnia and place it on the well slide.

Remove any excess fluid from the slide using a pipette, in order to constrict the daphnia’s movement

Place the welled slide under a microscope using the x4 magnification lense

Be sure to see the Daphnia’s heart rate clearly before proceeding to counting of the beats.

The stopwatch must then be started simultaneously as the counting starts. Use a hand tally counter to count the heart rate. If none is available, count the heart rate by making dots with a pen on a piece of paper.

Record your data on a table of raw data.

Redo steps 8-14 for each concentration.

Do 4 more trials in order to create a greater sample of data.

Data Collection

Concentration of Caffeine

(±0.000001g/cm3) Heart Rate of Daphnia ±5 Bpm (±0.01s)

Trial 1

Trial 2

Trial 3

Trial 4 Trial 5

0.010000 201 223 196 220 216

0.005000 187 175 190 184 195

0.002500 156 181 176 179 183

0.001250 182 173 174 167 171

0.000625 168 168 172 163 166

0.000000 (H2O) 160 169 158 172 167

Sample Calculations

The Mean of each concentration ill be found using the following method:

Mean=Σx/n,