Core Practical 1

Question 1

What is the aim of this experiment

Answer 1

The aim of this experiment is to test and observe how the heart rate of Daphnia (Water fleas) is changed by making them absorb varying concentrations of a caffeine solution.

Question 2

What are Daphnia and why are they used

Answer 2

Daphnia are water flees
-They are abundant so can be taken with little damage to biodiversity
-They are translucent so their heart rate can be observed easily
-They are invertebrates and have a less developed nervous system, so they feel less pain

Question 3

What factors effect heart rate

Answer 3

Lowered by:
-sleeping
-stretching

Increased by:
exercise
Drinking alcohol
smoking
stress
caffeine

Question 4

What is caffeine’s effect on heart rate

Answer 4

It causes heart rate to increase

Question 5

Why was a culture of Daphnia used in our equipment

Answer 5

These are the organisms we were testing on

Question 6

Why was a container for used Daphnia used in our equipment

Answer 6

To prevent us from using the same Daphnia again (could kill it)
used Daphnia would have a higher heart rate making the results unreliable

Question 7

Why were cavity slides and 2 strands of cotton wool used in our equipment

Answer 7

To immobilize and contain the Daphnia
The cavity slide also contained the solution (stopped it from spilling)

Question 8

Why was a caffeine solution used in our equipment

Answer 8

The Daphnia would absorb the caffeine from our serial dilutions

Question 9

Why were dropping pipettes used in our equipment

Answer 9

To transfer the daphnia to our cavity slides
To make serial dilutions

Question 10

Why was distilled water used in our equipment

Answer 10

To make the serial dilutions (caffeine + distilled water)

Question 11

Why were test tubes used in our equipment

Answer 11

To contain / make the serial dilutions

Question 12

Why was a measuring cylinder used in our equipment

Answer 12

To measure out the correct volumes of caffeine solution and distilled water to make our serial dilutions

Question 13

Why was a stop clock used in our equipment

Answer 13

To measure acclimation time and the heart rate

Question 14

Why did we use paper towels / blotting paper

Answer 14

To remove excess solution

Question 15

Why was a microscope used in our equipment

Answer 15

To clearly observe the Daphnia’s heart and count the heartrate

Question 16

What was our counting method in this experiment

Answer 16

We used a pen and paper to make dots every heartbeat of the Daphnia’s in a 10s interval

Question 16

What was the independent variable

Answer 16

Concentration of the caffeine solution

0% 0.2% 0.2 % and 0.3%

Question 17

What was the dependent variable

Answer 17

The heart rate of the Daphnia in BPM

Question 17

What were some control variable in the Daphnia experiment

Answer 17

Time - 5min acclimation time + waiting 1 min intervals after measuring heartrate for 10s

Size / species / age of Daphnia - using similar sized Daphnia that came from the same batch of eggs

temperature - solutions kept at room temperature + light turned off when not in use

Question 18

What was our method in the Daphnia experiment

Answer 18

Create the serial dilutions of caffeine
Place 2 / 3 strands of cotton wool onto the cavity slide.
Take a daphnia using a dropping pipette
Place the daphnia and solution onto the cavity slide
Wait 5 min acclimation time
Turn on the microsoft light and dot on paper every time the heart beats (in 10s)
Turn of the light, dots×6 = bpm
Wait 1 min and repeat (twice) to find a mean
Place the daphnia into the used container

Repeat for each concentration

Question 19

What ethical consideration did we have to make for this experiment

Answer 19

Daphnia cant consent - minimise the experiment time

Daphnia cant express pain - Excessive caffeine not used
Extreme conditions will be avoided (e.g high temperatures / pH - chlorine kills daphnia)