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Osmoregulation and Excretion

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Question 1: Osmoregulation and Excretion
Diffusion refers to the random motion of molecules from a highly concentrated answer to a solution of lower attention to achieve equilibrium. Diffusion can either be easy passive or facilitated. Osmosis is the movement of the molecule from a lowly concentrated place to a region of high concentration. Simple passive is where small molecules go through the bi-lipid layer of the cell membrane whilst facilitated diffusion is dependent on carrier proteins existing in the membrane to selectively allow substances to bypass through.
Paramecium is an organism that utilizes osmosis to survive. It lives in freshwater and has a hypertonic body. To survive in this environment, it has to get rid of excess water as water moves through the membranes to its cell. If it fails to remove this water, it may swell and burst. It has two contractile vacuoles that control the excess water. The water enters the paramecium body, the contractile vacuoles swells and burst in reaching its maximum to release the water back to the surrounding.

Invertebrates utilize osmoregulation to maintain salt and water balance across cell membranes and within the body fluids in their bodies. The body fluids contain water, electrolytes, and nonelectrolytes. An electrolyte is a solute that dissociates into ions when dissolved in water while nonelectrolyte is the solute that does not dissolve in water. Both are involved in the osmotic balance. Invertebrates use simple methods to get rid of metabolic waste compared to invertebrates which have kidney and urinary systems.

Annelids have a more evolved excretory system compared to flatworms. It has structures known as nephridia which are similar to flame cells due to the presence of cilia. The excretion of metabolic waste occurs through nephridiopore. This pore is developed than flame cells as they comprise a system of tubular reabsorption done by the capillary network. Insects use the malpighian tubules for reabsorption and osmoregulation. They are convoluted to increase the surface area. Urine is secreted by cells lined in the malpighian tubules. The exchange pumps on the tubules wall transport hydrogen ions into the cell and removes sodium and potassium ions while water flows in to form the urine. The osmotic pressure is altered by the secretion of ions which allows water, electrolytes and nitrogenous waste into the tubules. The electrolytes and water are reabsorbed when insects are in a low water environment, and uric acid is removed from the body as a white powder. The ability not to dissolve waste n water enable insects to conserve water.

All vertebrates possess a paired kidney. The primary duty of the kidney is to regulate body fluids levels but not excretion. Removal of waste is only a secondary function. Terrestrial vertebrates such as humans have a urinary system which comprises of the kidneys, bladder, ureter, and urethra. The kidney filters the water in the blood and collect it as urine which moves into the ureter, accumulates in the bladder and then released out of the body through the urethra. The functioning unit of the kidney is the nephron which is a bow-shaped capsule with capillaries, glomerulus and an extended renal tube. It filters water and solutes out of the blood. Reabsorb water and conserve molecules back in the blood. It also secretes ions and other metabolic waste from the surrounding capillaries into the distal tubule.

The reabsorption of water in the kidney is controlled by the antidiuretic hormone (ADH. Increasing water absorption in the kidney which is facilitated by the ADH allows more water back into the blood hence increasing the concentration of the blood. When the blood has a lot of fluid, the hypothalamus is triggered to reduce ADH in the blood. Doing this raises the volume of water absorbed by the kidney. Therefore, the urine produced increases and become more diluted. This is referred to as the multiplier effect of mammalian kidney and the ADH. However, one might be surprised to know that even the most educated individuals in scientific did not know that DNA was a hereditary material in less than a century ago.

Question 2: DNA Structure and Function

The advanced technology has allowed various practical applications of molecular biology such as genetic screening, paternity test, fingerprint analysis in a forensic study among others. Even the most educated individuals in scientific did not know that DNA was a genetic material in less than a century ago. Some of the previous experiments on hereditary include the famous work of Gregor Mendel. He showed that traits like flower color in pea plant are not directly inherited but are dependent on the gene passed from parent to offspring. Mendel work, however, did not describe the DNA as the hereditary material but works by other scientists in the 20th century came to identify DNA as a genetic material.

Frederick Griffith, a British bacteriologist, performed several experiments using Streptococcus pneumonia bacteria and mice in 1928. His primary objectives were however not to identify the genetic material but rather to design a vaccine for pneumonia. His experiment made use of two bacteria strains namely R and S. The R strain formed rough appearing colonies (hence the name R strain) after being grown in a petri dish. The bacteria was no virulent after being injected into the subject mouse. The S strain, on the other hand, formed round colonies with smooth appearance, hence the name S strain. The smooth appearance was due to the presence of polysaccharide coat produced by the bacteria. This strain was virulent meaning it can cause a disease. Griffith injected the mouse with S bacteria that was heated to high temperatures to kill the cells, and the bacteria never killed the mouse. When the non-virulent R strain was injected into the mouse combined with the heated S bacteria, the mouse acquired pneumonia and died. Griffin, however, retrieved sample of the dead mouse’s blood and discovered that it contained living S bacteria. Griffith made a conclusion that the R-strain took a “transforming principle” from the heated S bacteria which made it ‘transform’ into a smoothly coated bacteria capable of causing disease.

The rough endoplasmic reticulum (RER) and the Golgi apparatus are the cellular structures involved in protein synthesis and secretion. The rough endoplasmic reticulum comprises of ribosomes which are structures where messenger RNA and protein synthesis are contained. Once the proteins are formed, they are stored in the RER before being moved to the Golgi apparatus. The proteins are chemically transformed in the Golgi apparatus and later put into vesicles that will detach from the organelle. The vesicles then join with the plasma membrane in a process known as exocytosis and its content released out of the cell.

Transcription is the copying of DNA to mRNA. It carries the needed information for protein synthesis. The process has two steps. First, there is the formation of the pre-messenger RNA with RNA polymerase enzymes being involved. The process is dependent on Watson - Crick Model of base pairing, and the formation of a single strand of RNA is the reverse – complement of the original DNA sequence. The second step involves Pre-messenger RNA edit to design the desired mRNA molecule through the RNA slicing.

Translation is the final step on DNA to protein way. The mRNA template directs the formation of protein. The mRNA template is read in accordance to the genetic code that relates the sequence of the DNA to that of amino acid in proteins. The bases in the nucleotide of mRNA are grouped into three to form a codon with each codon specifying a particular amino acid. The sequence of mRNA form a template that chains several amino acids to form a protein.

Question 3: Structural Materials and Terrestrial Locomotion

Locomotion is a fundamental aspect of the survival of many species with the terrestrial habitats being one of the areas where the movement for long distances is required.

Terms Definition

Stress: it is the force applied per unit and can be categorized as tensile, compressive or shear.

Strain: it is the change in the bone dimension in relative to length, angulation or width.

Stiffness is the amount of strength that is necessary to deform a structure

Plastic is a synthetic material made from a wide range of polymers and can be molded into different shapes while soft and into a rigid or elastic form

Elastic is a connective tissue that contains a protein called elastin

Spider milk protein is a fibrous material with large proteins. The silk contain tensile strengths that can be compared to steel. It is two to three times tougher that synthetic fibers of nylon and rayon.

Locomotion in the terrestrial environment can take place in a variety of substrates such as leaf litter, soil, rocks, and debris flowing in response to stress. There are three basic types of locomotion in the terrestrial animals’ namely legged, limbless locomotion and rolling. Legged is the movement by appendages, limbless is the movement without legs where the body itself is usually used as the propulsive structure. Rolling is the rotation of the body over the substrate. Identifying the different principles of locomotion in the terrestrial environment requires the understanding of the interaction between the organism and its environment. To walk, run or crawl on complex substrates, terrestrial animals are required to generate a forward push to progress and a vertical thrust to maintain the gravity.

Muscles vary in the architecture and that architecture translate to its function. The critical purpose of the muscle is to shorten or lengthen when the generation of tension is required thereby performing mechanical work. They contain elastic elements that enhance their versatility. The arrangement of elasticity consists of contractile elements which are muscles and fibers and elastic elements such as titin and perimysium. The arrangement of muscles and tendons determine the speed of movement. Other properties that differentiate the mode by which an animal move is the strength of the muscles and tendons, their stiffness, and elasticity .

The mechanism of such mammals like cat, giraffe, horse, and humans can get complicated and involve the use tendons and the back to store energy for enhancing transcription. The giraffe, for example, moves both of its legs on one side and then a similar move of both legs on the other side. Sometimes the hind legs move first creating a slight lag. Cat dogs and many other hoofed animals use the diagonal walk. The front left and the right back legs move forward followed by the front right and left back and so on.

Question 4: Tides and Intertidal Animals

The force of gravity mainly causes tides. The gravitational attraction of the moon on the earth creates the tidal bulge. If there are no other forces involved, the shores will experience one high tide in one rotation of the earth. Inertia, which is described as the tendency of a moving object to remain in motion also influence the earth’s oceans. As the moon moves round the earth, the earth moves slightly around, and this movement causes a centrifugal force on the ocean. This force result to the bulging of the ocean on the opposite side that face the moon. Although the moon has a stronger gravitational force enough to attract oceans into bulging on the side of the earth’s facing the moon, it fails to overcome the inertia on the opposite side of the earth. Due to this, the world’s oceans experience double bulging when on the side of the earth nearest to the moon, and once they are on the side farthest from the moon.

The intertidal zone, also referred as the littoral zone is dived into vertical zones namely; the spray zone, the high tide zone, middle tide zone, and the low tide zone.

Spray zone: this zone is also known as the upper littoral, the supralittoral fringe, the splash zone or the Barnacle belt. It is mostly dry, but is covered with salt water on high tides. The area only experiences flooding during storms and exceptionally high tides. Animals in this area can stay under the sun since they have adapted to land and can feed off things like particles in the sand. Organisms in this area include lice, barnacles, and isopods.

High tide zones: it I also referred to as the upper mid-littoral zone and the high intertidal zone. It is only flooded during the high tide only. Animals in this area must be adapted to harsh environments like the rough waves. Many sea creatures have unique features like shells that allow them to survive in these conditions. The shells act like a protection and a shield from the waves. Clinging is another adaptation of animals in this zone. Creatures like limpets cling to rocks to prevent water from pushing it away. Organisms in this area include the crabs, sea stars and the limpets.

Middle Tide Zone: also referred to as the lower mid-littoral zone. This zone is turbulent and is covered and uncovered twice a day with salt water from the tides. Animals in this area are adapted to living in lots of light or lots of water. For example, anemones are able to stay underwater by absorbing the water while in water. Organisms in this area include crabs, mussels, snails, and sponges.

Low Tide Zone: it is also known as the lower littoral zone. It is generally a region under water. The area is only made visible when the tide is usually low. Organisms in this area are not adapted to long dryness periods or very high temperatures. Since animals in this zone live underwater mostly, they have adaptations that enable them to breathe underwater. They also have sharp teeth that that help them scrape food from rocks. The animals include the gumboot chitin, sea stars, and the purple sea urchin.

The organisms living in the intertidal zone are prey to many that capture and feed on them. When the tide sets in, littoral microorganisms are preyed upon by sea animals, and when the tide is out, they become prey to the land animals like humans. The animals that feed on these “small food” employ some strategies that enable them to get the small food. The mechanisms include:

Lunge feeding: this is a kind of inverted suction feeding .the animal accelerates to acquire adequate velocity to fold its flexible throat around the amount of water meant to swallow. The water then flows back through the baleens restricting the food particles. The functional adaptation of this feeding mechanism is the elastic and muscular buccal rills. An example of an animal that feeds on this mechanism is the baleen whale

Sanction feeding: this is the ingesting of the prey item in fluids when the prey is sucked into the predator’s mouth.

Pivot feeding: this method involves the moving of the mouth while targeting the prey by an upward turn of the head which is precisely pivoting of the neck joint. Seahorses and sea dragons use this mechanism.

Question 5: Fossil Evidence for “Warm-bloodedness”

Terms definition

Endotherms are animals that produce their heat

Homeotherms are animals having a constant body temperature

Poikilotherms are animals that adjust their body temperatures depending on the nature of the environment

Exotherms are those animals that primarily gain heat through the environment

Dinosaurs were once classified as cold-blooded creatures of the Mesozoic era. However, several recent research on their bone tissues structures and growth rate have strongly indicated that they might have been warm-blooded. However, this has a topic debated by paleontologists having different views. Some even argue that dinosaurs fell between ectothermic (cold-blooded) and endotherm (warm-blooded) suggesting that they were mesotherms (intermediate blooded). For decades, researchers have debated the thermoregulation of dinosaurs and other early ancestors of the mammals. Recent studies show that they could have been warm-blooded and therefore a new description of how they existed and died could be developed.

In a journal, Nature scientists in Spain published a report that dinosaur had a high metabolic rate to allow fast growth which is a characteristic of warm-bloodedness. They also discovered tree-like growth rings on mammals’ bones; a feature previously associated with cold-blooded creatures and dinosaurs only. Paleontologists for a long period have used the ring-like markings on bones of cold-blooded animals including the dinosaurs to indicate halts in growth probably due to cold periods or food scarcity. Koehler and the research team assessed various species of mammals and found 41 of the subject mammals had these rings. This study puts off the strongest argument that ties dinosaur to the cold-blooded group of animals. The team also analyzed the bone tissue and found that the accelerated growth rate in mammals relates to the high metabolic rate. They then found that the tissue of the dinosaur was indistinguishable from those of the mammals studied. This indicates that the dinosaurs not only grew fast but also had a high rate of metabolism indicating the warm-bloodedness.

Works Cited

"Dinosaurs May Have Been Warm-Blooded: Study." Phys.Org, 2012,

"Transcription And Translation." National Human Genome Research Institute (NHGRI), 2014,

Carter, M. I., and P. S. Hinton. "Physical activity and bone health." Missouri medicine 111.1 (2014): 59-64.

Ding, Yang, et al. "Comparative studies reveal principles of movement on and within granular media." Natural Locomotion in Fluids and on Surfaces. Springer, New York, NY, 2012. 281-292.

Gordon, Malcolm S., et al. Animal Locomotion: Physical Principles and Adaptations. CRC Press, 2017.

Kohlmeyer, Jan, and Erika Kohlmeyer. Marine mycology: the higher fungi. Elsevier, 2013.

Weis, Judith S. "Osmoregulation and Excretion." Physiological, Developmental and Behavioral Effects of Marine Pollution. Springer Netherlands, 2014. 97-125.

October 26, 2021




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