3.  There exists freshwater sharks which are capable of surviving in fresh water lakes and rivers. These sharks are; 1. The Bull Shark ( Carcharhinus leucas ). This shark swims up tropical rivers around the world. 2. The River Shark ( Glyphis). This shark is found in the fresh and brackish water in Asia and Australia.

4. The bull sharks are found along coastlines, bays, and harbors. They also frequent freshwater rivers. This shark swims up tropical rivers around the world (Heupel et al., 2010).

5. This shark is commonly found in the fresh and brackish water in Asia and Australia.

6.  For most shark species, they are unable to survive in fresh water because of the inhospitable surrounding environment.  The shark would die due to a process called osmosis.  Osmosis occurs when a fluid moves through a semi- permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration. This happens until there is an equal concentration of liquid on both sides of the membrane (Ballantyne & Robinson, 2010).

7.  Sharks evolved in salt water. They thus have very salty bodies.  The sharks in fresh water contain more than twice the amount of salt and chloride as more common freshwater fishes.  Because of Osmosis, these sharks would burst like an overfilled water balloon when placed in fresh water.  However, these sharks have a special adaptation to prevent this; they urinate a lot (Ballantyne & Robinson, 2010).

8.  A study conducted on the Bull Sharks in Lake Nicaragua revealed there is a lot of intake of water by these sharks.  These sharks however excrete most of this water as dilute urine.  Their rate of urination is about 20 times that of the normal saltwater sharks.  These sharks' kidneys have adapted to utilizing additional energy for this continuous excretion process. This adaptation helps these sharks survive in the freshwaters.

9.  Their ability of these sharks to tolerate freshwater is rooted in salt retention.  Sharks must retain salt inside their bodies. Without it, their cells will rupture and cause bloating and death.  Given this requirement, most sharks cannot enter fresh water. Their internal salt levels would become diluted.

10.  To prevent this, the fresh water sharks have special physiological adaptations that enable them to live in fresh water.  Their kidneys recycle the salt within their bodies and special glands. These special glands are located near their tails, also aid in salt retention (Ballantyne & Robinson, 2010).

11.  Yes. Fresh water sharks are endangered due to environmental and human activities.  The population of the river shark is at dangerous lows now.  Bull shark numbers are higher. The bull shark has an advantage because it can navigate between fresh- and saltwater environments.  The river sharks are more adapted to river and lake life. They are thus almost prisoners within their land-locked environments. These species have thus got to withstand both natural and human-induced problems.

12.  Natural problems These include; 1) Temperature, 2) Oxygen, 3) Mineral content, and 4) Turbidity changes that continue to be influenced by climate change..

13.  Human activities These involve: 1. Dam building, 2. Modifications to water for irrigation and fisheries, and 3. The introduction of pollutants into the water (Gelsleichter, 2009).

15.  Plants grow better in fresh water when compared to saltwater.  Saltwater is capable of damaging the root system of the plant.  Too much salt is also capable of interfering with the chemical process and ultimately starving the plant.

16.  If you water a fresh water plant with salt water, any moisture already in it will diffuse out and into the soil. This is because the salt water has a high solute content than the plant and will suck all of the moisture out.  When exposed to salt water, the cells of the fresh water plant lose water. The cell membrane pulls away from the cell wall. This is termed plasmolysis.

18.  The diffusion of water across a selectively permeable cell membrane is termed osmosis. The membrane is selectively permeable because virtually none of the salt crosses the membrane while the water passes freely across.  Plasmolysis results from this process of osmosis which causes the cells to lose water to the external salty environment hence resulting in the cell membrane pulling away from the cell wall (Pilizota & Shaevitz, 2013).

20.  Because of these dangers posed by excess salt concentration in the water, the salt water plants have unique physiology and adaptations that allow them to survive in this environments.  These physiological adaptations are what prevent these plants from getting dehydrated and dying (Pilizota, & Shaevitz, 2013)

21.  The cell membrane of the freshwater plants allows salt to enter the cell and accumulate in the cell vacuole. This allows the cells to accumulate a higher salt concentration than the salt concentration in the salt water.  Thus, the cells of these salt water plants do not plasmolyze. They are able to retain water which helps these plants survive in these salty environments.

22. Ballantyne, J. S., & Robinson, J. W. (2010). Freshwater elasmobranchs: a review of their physiology and biochemistry. Journal of Comparative Physiology B, 180 (4), 475-493. Gelsleichter, J. (2009). Project profile: Exposure Of Freshwater Sharks To Human Pharmaceuticals. Evaluating the risks that pharmaceutical-related pollutants pose to Caloosahatchee River wildlife: observations on the bull shark, Carcharhinus leucas. Final Report: Charlotte Harbor National Estuary Program. Heupel, M. R., Yeiser, B. G., Collins, A. B., Ortega, L., & Simpfendorfer, C. A. (2010). Long-term presence and movement patterns of juvenile bull sharks, Carcharhinus leucas, in an estuarine river system. Marine and Freshwater Research, 61 (1), 1-10. Pilizota, T., & Shaevitz, J. W. (2013). Plasmolysis and Cell Shape Depend on Solute Outer-Membrane Permeability during Hyperosmotic Shock in E. coli. Biophysical Journal, 104 (12), 2733-2742.