Section #-/Group #-- Biology 142-Spring 2018 Homework Set 6 (10 points) 1. (1 pt

Question

Section #-/Group #-- Biology 142-Spring 2018 Homework Set 6 (10 points) 1. (1 pt.) A stalk of celery is placed into a cup containing fresh water. Water will move from the (circle one) celery cells / cup of fresh water and into the [circle one] celery cells / cup of fresh water. 2. (1 pt) In the example above, the internal environment of the celery cells is (circle one) hypotonic / hypertonic/ isotonic relative to the cup of fresh water 3. Regardless of what type of nitrogenous waste an animal excretes, ammonia, urea, uric acid, there are trade-offs among water conservation, energy expended, toxicity levels (2 pts.) What is one disadvantage animals face in making uric acid? What is one reason they would pay this price (ie. a benefit for uric acid their environment or reproductive strategies)? (1 pt.) Why do saltwater fish NOT have the benefit of excreting ammonia directly into the water? 4. (1 pt.) Given the following graph of environmental vs body fluid osmolarity, which line represents an osmoconformer? Line A or Line B Line A Line B Environmental Osmolarity

Explanation / Answer

1. Water will move from the cup of fresh water and into the celery cells because of endosmosis.

2. The internal environment of the cells is hypertonic relative to the cup of freshwater.

3. One disadvantage: The animals that excrete nitrogen in the form of uric acid are known as uricotelic animals. Biggest disandvantage of this excretory mechanism is it's an expensive metabolic strategy, or in other words, uric acid formation requires more energy in comparison to excreting in the form of ammonia or urea.

One environmental or reproductive benefit: Formation of uric acid requires very less water by the organism as it is almost insoluble in the water. Thus, its environmental benefit is it helps in conserving water.

Saltwater is not benefitted by excreting ammonia directly into the water because formation of ammonia requires maximum water by the body in comparison to excreting in the form of urea or uric acid. Thus, ammonia formation leads to more water requirement and less water conservation.

4. Osmoconformer word is basically used for the aquatic organisms, in which the internal osmolarity matches with the surrounding environment.

Line A in the given graph shows that as environmental osmolarity is increasing body fluid osmolarity is also increasing. Thus, Line A shows osmoconformity.

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