GT BSCS Chapter 3 Exchanging Materials with the Environment

The Plasma Membrane The plasma (cell) membrane is the edge of life, the boundary that separates the living cell from its nonliving surroundings. It regulates what enters and exits the cell.

Semi-Permeable This bilipid layer is semipermeable, meaning that some molecules are allowed to pass freely (diffuse) through the membrane.

Osmosis and Diffusion Two mechanisms for moving materials: 1.Diffusion- movement of materials from an area of high concentration to an area of low concentration. 2.Osmosis – diffusion of water.

Diffusion

Materials move along a concentration gradient. Concentration gradient = a difference in concentration of molecules across a distance. This is a passive process- no energy is needed. In its simplest form, diffusion is the transport of a material or chemical by molecular motion.

Osmosis Diffusion of water through a selectively permeable membrane. From high solute concentration to low solute concentration. From high water concentration to low water concentration

Hypertonic, Hypotonic, and Isotonic Solutions The concentration of solute in the solution can be equal to the concentration of solute in the cells. The cell is in an isotonic solution. (iso = same as normal) The concentration of solute in the solution can be greater than the concentration of solute in the cells. The cell is in an hypertonic solution. (hyper = more than normal) The concentration of solute in the solution can be less than the concentration of solute in the cells. The cell is in an hypotonic solution. (hypo = less than normal)

Osmosis

Gas Exchange Oxygen (O 2 ) is essential for cellular respiration. Carbon Dioxide (CO 2 ) is released as a by- product of cellular respiration. How gas exchange occurs depends on the organism’s environment. No matter what the environment, the gas exchange actually occurs by diffusion

Aquatic Organisms Diffusion must happen in water. So, organisms in water are in direct contact with the water. Many have gills for gas exchange. Gills have a huge surface area.

Aquatic Organisms Surface area is very important for gas exchange. The greater the surface area, the more efficient the gas exchange. Gills have tiny filaments that make the surface area huge. Each filament is surrounded by capillaries, where gas exchange occurs.

Terrestrial Organisms On Land- because organisms must have water for gas exchange, they must have moist membranes. Although, the oxygen concentration in the air is much higher than in water, land organisms are always battling the tendency to dry out.

When breathing out, water is lost. So, many land organisms have evolved mechanisms for internal gas exchange (lungs). Lungs are not as efficient as gills, but water loss is minimized.

Lungs Oxygen comes in through the mouth and nose. The oxygen moves past the epiglottis into the trachea (windpipe.) The trachea is made of rings of cartilage.

The oxygen then moves into the bronchi (branches of trachea that go to each lung). The bronchi continue to branch into smaller and smaller tubes (bronchioles) And end in little sacs called alveoli – where gas exchange occurs.

Alveoli The oxygen enters the alveoli and diffuses into the bloodstream through the capillaries that surround each alveoli.

Gas Exchange in Plants Plants have small openings in the leaf known as stomates. Each stomate is surrounded by a guard cell- which acts as a gate.

When the guard cells are swollen with water, they bend apart and open the stomate. This allows carbon dioxide to diffuse in and water vapor and oxygen to exit. This is called transpiration.

If a plant loses more water than it can take in via the roots, it wilts. One protective mechanism is that the guard cells shrink when they lose water and close.

Waste Removal Organisms in fresh water must rid themselves of excess water. Paramecium, a freshwater unicellular organism, uses a contractile vacuole to squeeze out water.

Homeostasis Other products must be removed as well. Waste products = excess salts, carbon dioxide, etc. Exchanging materials is critical for maintaining homeostasis (a balance of the internal with the external environment of an organism.)

Waste Removal Simple organisms can remove products through their cells. In more complex organisms, special organs have evolved to remove these products.

Ammonia In fish, the gills remove the CO 2. Waste products containing nitrogen must also be removed. This waste product is ammonia. These ammonia wastes are from the metabolism of proteins and nucleic acids and are toxic.

Organisms in water can excrete ammonia directly into the water. Some organisms convert the ammonia to urea which is not as toxic. Urea, when diluted with water, can be safely excreted from the body. Humans, other mammals, some fishes, and amphibians excrete urea. Urea

Uric Acid Ammonia can also be converted to Uric acid, the most concentrated form of nitrogenous waste. Birds and many desert reptiles excrete uric acid, since it prevents water loss.

Human Urinary System Excretory System Functions 1.Collect water and filter body fluids. 2.Remove and concentrate waste products from body fluids and return other substances to body fluids as necessary for homeostasis. 3.Eliminate excretory products from the body.

Anatomy of Urinary System The urinary system is made- up of the kidneys, ureters, bladder, and urethra. The nephron is the kidney's functional unit.

What happens to the wastes? Waste is filtered from the blood and collected as urine in each kidney. Urine leaves the kidneys by ureters, and collects in the bladder. The bladder can distend to store urine that eventually leaves through the urethra.

Nephrons The nephron has three functions: 1.Filtration of water and wastes from the blood. 2.Reabsorption of water and conserved molecules back into the blood. 3.Secretion of waste products.

Functions of Nephrons Filtration Blood from the renal artery enters the glomerulus. Blood pressure forces the plasma of the blood, containing both waste material and useful material, into the Bowman’s capsule. This material is called filtrate.

Reabsorption Useful materials contained within the filtrate are reabsorbed by the capillary network that surrounds the renal tubule Reabsorption of water occurs by osmosis Reabsorption of glucose, sodium, amino acids, etc occurs by active transport

Secretion Fluid that remains in the renal tubule after reabsorbtion is urine Path of urine: collecting duct -> pelvis -> ureter -> urinary bladder -> urethra

Aldosterone Some products are regulated by hormones. The reabsorption of sodium and potassium in the distal tubule and the collecting tubules is regulated by the hormone aldosterone. Aldosterone, released by the adrenal gland, is released when potassium levels in the blood are too high.

Antidiuretic hormone (ADH) regulates the amount of water that is reabsorbed. The release of ADH (from the posterior lobe of the pituitary gland) is regulated by the osmotic pressure of the blood. ADH

Blood Pressure This means that if there is not enough water in the blood the osmotic pressure (blood pressure) drops and more water is retained and If there is too much water in the blood the osmotic pressure increases and more water is secreted.

Kidneys Kidneys perform a number of homeostatic functions: 1.Maintain volume of fluids outside the cells (extracellular). 2.Maintain ionic balance in this fluid. 3.Maintain pH and concentration of the extracellular fluid. 4.Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.