Gasses, Water And Waste Products Flashcards
explain why the removal of wastes is essential for continued metabolic activity
Metabolic wastes, particularly nitrogenous wastes that are the by-products of the breakdown of proteins and nucleic acids, are toxic to cells and must therefore be removed quickly. Nitrogenous wastes have the ability to change the pH of cells and interfere with membrane transport functions and may denature enzymes.
Metabolic wastes are the product of metabolic reactions. If they are not removed their concentration in the cell increases. This inhibits the reactions that produce them, interfering with normal metabolic activity.
identify the role of the kidney in the excretory system of fish and mammals
The kidney is an organ of the excretory system of both fish and mammals. It plays a central role in homeostasis, forming and excreting urine while regulating water and salt concentration in the blood. It maintains the precise balance between waste disposal and the animal’s needs for water and salt.
The role of the kidney in fish is dependant on the environment of the fish.
In marine (salt water) environments, the kidneys excrete small quantities of isotonic (same concentration as sea water) urine. This helps conserve water and excrete the excess salt they gain from their hyperosmotic environment.
In freshwater fish, the kidneys work continuously to excrete copious quantities of dilute urine, which also has a very low salt concentration. This helps to remove excess water gained from the hypo-osmotic environment.
explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes
Diffusion and osmosis are both examples of passive transport, relying on random movements of molecules. Diffusion is too slow for the normal functioning of the body and does not select for useful solutes. Osmosis only deals with the movement of water and thus would only allow water to move out of the body, not the nitrogenous wastes.
distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney
Active transport involves an expenditure of energy on the part of the organism, usually because the substance is moving against the concentration gradient, i.e. when a salt moves to an area of high salt concentration from an area of low salt concentration. Passive transport involves no expenditure of energy as the materials follow the natural concentration gradient, i.e. movement from an area of high concentration to an area of low concentration. Both diffusion and osmosis are examples of passive transport.
In the mammalian kidney, both active and passive transport processes occur.
Passive transport: Once filtration has occurred in Bowman’s capsule, water returns via the interstitial fluid from the tubule to the capillary in the process of osmosis. This occurs along the length of the tubule.
Active transport: Depending on their concentration, the ions in the blood (Na+, K+, Cl- , H+ and HCO3) can be transported to cells in the nephron tubule and then secreted by the cells into the tubule. Some poisons and certain drugs are eliminated from the body in this manner.
explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition
Filtration of the blood occurs in Bowman’s capsule where high blood pressure in the glomerulus forces all small molecules out of the blood into the capsule. Water, urea, ions (Na+, K+, Cl- , Ca2+, HCO3- ), glucose, amino acids and vitamins are all small enough to be moved into the glomerular filtrate. Blood cells and proteins are too large to be removed. This filtering process is non-selective and therefore many valuable components of the blood must be recovered by reabsorption.
Reabsorption takes place selectively at various points along the proximal tubule, loop of Henle and distal tubule.
All glucose molecules, amino acids and most vitamins are recovered, although the kidneys do not regulate their concentrations. The reabsorption of the ions Na+, K+, Cl- , Ca2+ and HCO3- occurs at different rates depending on feedback from the body. In some cases, active transport is required. Water is reabsorbed in all parts of the tubule except the ascending loop of Henle. The amount of water reabsorbed depends on feedback from the hypothalamus. If no water were reabsorbed human would soon dehydrate, losing water at a rate of around 7.5 L per hour.
The chemical composition of the body fluids is precisely regulated by the control of solute reabsorption from the glomerular filtrate.
outline the role of the hormones, aldosterone and ADH (anti-diuretic hormone), in the regulation of water and salt levels in blood
Aldosterone is a steroid hormone secreted by the adrenal gland. Its function is to regulate the transfer of sodium and potassium ions in the kidney. When sodium levels are low, aldosterone is released into the blood causing more sodium to pass from the nephron to the blood. Water then flows from the nephron into the blood by osmosis. This results in the homeostatic balance of blood pressure.
Antidiuretic hormone (ADH or vasopressin) controls water reabsorption in the nephron. When levels of fluid in the blood drop, the hypothalamus causes the pituitary to release ADH. This increases the permeability of the collecting ducts to water, allowing more water to be absorbed from the urine into the blood. The resulting urine is more concentrated. When there is too much fluid in the blood, sensors in the heart cause the hypothalamus to reduce the production of ADH in the pituitary, decreasing the amount of water reabsorbed in the kidney. This results in a lower blood volume and larger quantities of more dilute urine.
define enantiostasis as the maintenance of metabolic and physiological functions in response to variations in the environment and discuss its importance to estuarine organisms in maintaining appropriate salt concentrations
Enantiostasis is the maintenance of normal metabolic and physiological functioning, in the absence of homeostasis, in an organism experiencing variations in its environment.
All organisms living in an estuary experience large changes in salt concentration in their environment over a relatively short time span, with the tidal movement and mixing of fresh and salt water. Organisms that must tolerate wide fluctuations of salinity are said to be euryhaline.
One strategy to withstand such changes in salt concentration is to allow the body’s osmotic pressure to vary with that of the environment. Organisms that do this, and therefore do not maintain homeostasis, are said to be osmoconformers. Most marine invertebrates are osmoconformers. In contrast, marine mammals and most fish are osmoregulators, maintaining homeostasis regardless of the osmotic pressure of the environment.
However, as the salt concentration of body fluids in an osmoconformer changes, various body functions are affected, such as the activity of enzymes. For normal functioning to be maintained, another body function must be changed in a way that compensates for the change in enzyme activity.
One example of enantiostasis is when a change in salt concentration in the body fluid, which reduces the efficiency of an enzyme, is compensated for by a change in pH, which increases the efficiency of the same enzyme.
Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss
You will recall from the Preliminary course that the leaves of plants contain stomates or small pores that allow the exchange of gases essential for respiration and photosynthesis. These gases include water vapour, as well as oxygen and carbon dioxide. If stomates are open, there will be a loss of water by transpiration and evaporation. Plants in arid areas have to balance the need for CO2 with the need to conserve water.
Adaptations of Australian xerophytes (plants adapted to dry conditions) include:
hard leathery, needle-shaped leaves with reduced surface areas such as in Hakea sericea (needlebush) and coastal tea trees
use of phyllodes for photosynthesis rather than leaves that would lose water by transpiration, as in many acacias
some salt bushes, e.g. Atriplex, change the reflectiveness of their leaves during leaf development so that they have highly reflective leaves during summer
Eucalypts avoid high radiation in the middle of the day by hanging their leaves vertically to present less surface area to sun
heat loss is greater for small leaves or highly dissected leaves than it is for larger leaves and many Acacias have fronds of bipinnate leaves
waxy cuticle prevents evaporation in many Eucalypts.
perform a first-hand investigation of the structure of a mammalian kidney by dissection, use of a model or visual resource and identify the regions involved in the excretion of waste products
Use the diagram below as a visual resource to identify the regions of the kidney, or use the models provided on these Internet sites.
Video of kidney dissected (external website) Broward Community College Ft. Lauderdale, Florida, USA
Before starting, consider safe working practices. Carry out a risk assessment by listing any potential dangers involved in this procedure and then say how you will avoid these dangers.
If a mammalian kidney, such as a sheep’s kidney, is available, perform a dissection of it.
Kidney disection
Identify the parts of the kidney using the diagram above as a guide.
explain why the concentration of water in cells should be maintained within a narrow range for optimal function
Water is the solvent for metabolic reactions in living cells. Many molecules and all ions important for the life of the cell are carried in an aqueous solution and these diffuse to reaction sites through the water in the cell.
Metabolic reactions within the cell can occur only in solution where water is the solvent. It is critical for proper functioning of these reactions that the amount and concentration of water in the cell be kept constant. Most cells die when the water content is changed significantly.
