Bicol University College of Science Department of Biology
LABORATORY ACTIVITY 2
OSMOREGULATION
Date performed: January 18, 2011
Performed by: Zarieh Dawn L. Novela BS Biology 3A
INTRODUCTION The earthworm belongs to the phylum Annelida. This group of higher invertebrates possesses a number of highly developed organs and organ-systems for performing various vital functions. One of the most important is nephridia where in one of its function is the regulation of osmotic pressure in the body in order to maintain constant water.
OBJECTIVES •
Observe the effect of salinity on changes in the volume and weight of earthworms
•
Use the earthworms as model for explaining basic osmoregulatory mechanisms
MATERIALS AND METHOD I. Preparation A. Earthworm 1. Collect at least 30 earthworms (of more or less the same size) for this experiment. The best time to hunt for worms is on a damp night when it is not too cold. Use a flashlight to help locate them in patches of grass, in parks or fields, or in lawns. You may have plenty in your garden. Usually, you will find them stretched out in the surface of the ground with their posterior ends inside their burrows. They may pop back into the ground when you appear. 2. If you collect during the day, you may dig for them preferably at places where the soil is loose. Digging for worms, however, is not equally successful in the different parts of the garden or field. There are some areas where one will find many worms and others where worms will be quite scarce. It is preferable to dig for worms after heavy rain. Heavy rain drives the worms to the surface where they may be seen crawling on the ground. Actually, worms come up from their flooded burrows below the ground. It is also suggested that you record your field observations of the worms’ behavior. 3. Bring the worms to the laboratory in an uncovered can or glass jar, or a box containing some damp soil and some moist leaves or grass. 4. When you reach home, tumble them on paper towels to remove excess soil. 5. In groups of five, place them in separate containers with rain or aged tap water (with the heavy chlorine removed). Time your preparation so that after the sixth hour, you are to start with the experiment in the laboratory.
B. Reagents •
Six salt solutions of the following concentrations: 0.03 M, 006 M, 0.09 M, 0.12 M, 0.14 M and 0.15 M.
Note: you will be immersing the worms in these different media and observing for their osmoregulatory responses. You will use five containers with five worms each. The worms in the
sixth container are extras for possible replacements if death takes place during the six hours of immersion in tap water.
II. Experiment Proper 1. Weigh the worms in groups of five and place them in separate containers with aged tap water. 2. Weigh at the end of 15 and 30 minutes. If the weights are fairly constant already, determine the volume of each group by volume displacement in a graduated cylinder containing water. 3. After you have determined the weight and volume of each group, transfer each group to a different dish containing one of the salt solutions. 4. Weigh the worms at 20-minute intervals within the 100 minutes of immersion. At the end of the experiment, determine their volume. 5. Record your results in the table below. 6. Using graphs show the relationship between osmotic concentration of the medium and the weight and volume changes exhibited by the animals throughout the duration of the experiment. For this, plot weight or volume change against time with a color or symbol legend for the different experimental groups. 7. Similarly, make graphs to depict the relationship between percentage weight change or percentage volume change through time and the osmotic concentration of the medium.
RESULTS AND DISCUSSION We have collected earthworms and grouped it into 5 and placed it in different containers with different salt concentration. This was to observe the osmoregulatory response of earthworms. 0.09 M NaCl Moles of solute = (molarity)(liter of solution) = (0.09 M) (0.05 L) `
= 0.0045 moles of NaCl
Mass of NaCl = (0.0045 moles NaCl) (1 mole NaCl / 58.44 g NaCl) = 0.00007.7 g of NaCl
*0.06 M NaCl
*0.03 M NaCl
M1V1 = M2V2
M1V1 = M2V2
V1 = M2V2 / M1
V1 = M2V2 / M1
= (0.06 M)(50 ml) / (0.09 M)
= (0.03 M)(50 ml) / (0.09 M)
= 33.33 ml
= 16.67 ml
*0.012 M NaCl
*0.015 M NaCl
M1V1 = M2V2
M1V1 = M2V2
V1 = M2V2 / M1
V1 = M2V2 / M1
= (0.012 M)(50 ml) / (0.09 M)
= (0.015 M)(50 ml) / (0.03 M)
= 6.67 ml
= 8.33 ml
0.03 M
0.06 M
0.09 M
0.012 M
When the earthworms were placed in different media, 0.012 M
we observed that they furiously wriggle out of the Petri dish as if they were being drowned.
Table 1. Weight of earthworms while immersed in media of varying salinity Weight of worms in media or varying concentration
Length of exposure, min
0.03 M
0.06 M
0.09 M
0.12 M
0.15 M
0
6.12 g
6.12 g
6.12 g
6.12 g
6.12 g
20
6.53 g
6.97 g
5.75 g
6.65 g
6.12 g
40
7.21 g
6.77 g
5.73 g
6.35 g
5.97 g
60
7g
6.22 g
5.71 g
6.25 g
6g
80
7.6 g
6.18 g
5.65 g
6g
5.75 g
100
7.5 g
6.37 g
5.64 g
6g
5.75 g
Weight of earthworms while immersed in media of varying salinity 8
weight in grams
7.5 0.03 M 7
0.06 M 0.09 M
6.5
0.12 M 6 0.15 M 5.5 0
20
40
60
80
100
Table 2. Volume of earthworms in different media at start and end of experiment Volume of worms in media
Length of exposure, min
0.03 M
0.06 M
0.09 M
0.12 M
0.15 M
0
3 ml
5 ml
5 ml
9 ml
6 ml
100
9 ml
3.5 ml
5 ml
4.6 ml
4.2 ml
Let us study the anatomy and morphology of an earthworm. Partitions divide their body into a series of coelomic chambers, each with repeats of muscles, blood vessels, branching nerves, and other organs. The gut extends through all chambers, from mouth to anus. As in all annelids, an earthworm’s body is enclosed in a flexible cuticle of secreted material. The permeable cuticle is good for gas exchange but not for conserving water. That is one reason annelids cannot venture from aquatic habitats or moist habitats on land. Annelids contain a system of nephridia, a series of units that control the volume and composition of the fluids. Usually, each unit has a funnel that collects excess fluid from one coelomic chamber and drains it into a small tube in the chamber behind it. The tubes lead to a bladder, which delivers fluid to a pore at the surface in the body wall of the next coelomic chamber.
Looking at the graph above, it is observable that from the initial weight of 6.12 grams, the weight of earthworms placed in 0.09 M, 0.012 M, and 0.015 M of salt solution decreases. In contrast, those in 0.06 M and 0.03 M solution increases. 0.06 M and 0.03 M salt solution are hypotonic solutions, that is, it has a lower concentration of solute than that of earthworms, therefore, the water moves in the body of the organism resulting to the increase of its weight. In the case of 0.09 M salt solution, there should neither decrease nor increase in the weight of the earthworm since this is isotonic. On the other hand, 0.012 M and 0.015 M salt solution are hypertonic solutions, that is, it has higher concentration of solute than that of the organism, causing it to release water from its body. These are all for the balance of water content of the organism.
Guide Questions: 1. What determines the salt concentration of the soil? What is the effect of rainfall on the soil? On the behavior of earthworms? What mechanisms are of survival value to the earthworms in variable environments?
2. What response in the weight and volume of the earthworms do the different salt solutions evoke? Depending on the salinity of the media, the weight and volume of the earthworms could increase, decrease or no change.
3. Compare the water exchanges in the worms exposed to varying saline media. What is the regulatory role of these exchanges? The hypotonic solutions causes increase in weight and volume in earthworm, while the hypertonic solutions causes decease in weight in earthworm. There would be consistent weight and volume in earthworm in an isotonic solution.
4. What are the osmoregulatory organs or structures of the earthworm? Nephridia
5. Why ionic regulation, volume regulation, and osmoregulation are inextricably associated with each other? Those variables are directly proportional to each other. And also they are regulated by the same organ of an organism, which is nephridium in earthworms.
6. Aside from osmoregulation, what is the other reason for the earthworm to crawl to the surface at night? Do they have eyes? They crawl to the surface at night taking advantage since the sun won’t dry them therefore they will get enough oxygen. Earthworms don't have eyes, but they do have light-sensitive cells scattered in their outer skin. These cells don't enable earthworms to
see images, or forms, but they do give their skin the capacity to detect light and changes in light intensity.
