atmospheric pressure

Examples of atmospheric pressure in the following topics:

• Gas Pressure and Respiration

  • Gas pressures in the atmosphere and body determine gas exchange: both O2 and CO2 will flow from areas of high to low pressure.
  • Approximately 21 percent of atmospheric gas is oxygen.
  • Patm, the atmospheric pressure, is the sum of all of the partial pressures of the atmospheric gases added together: Patm = PN2 + PO2 + PH2O + PCO2= 760 mm Hg.
  • The pressure of the atmosphere at sea level is 760 mm Hg.
  • For this calculation, the water pressure (47 mm Hg) is subtracted from the atmospheric pressure: 760 mm Hg 47 mm Hg = 713 mm Hg, and the partial pressure of oxygen is: (760 mm Hg 47 mm Hg) 0.21 = 150 mm Hg.

• The Mechanics of Human Breathing

  • Both inhalation and exhalation depend on pressure gradients between the lungs and atmosphere, as well as the muscles in the thoracic cavity.
  • As volume decreases, pressure increases and vice versa .
  • This decrease of pressure in the thoracic cavity relative to the environment makes the cavity pressure less than the atmospheric pressure .
  • This pressure gradient between the atmosphere and the thoracic cavity allows air to rush into the lungs; inhalation occurs.
  • Air rushes out of the lungs due to the pressure gradient between the thoracic cavity and the atmosphere.

• Water and Solute Potential

  • Water potential is a measure of the potential energy in water, or the difference in potential energy between a given water sample and pure water (at atmospheric pressure and ambient temperature).
  • Water potential is denoted by the Greek letter ψ (psi) and is expressed in units of pressure (pressure is a form of energy) called megapascals (MPa).
  • The water potential in plant solutions is influenced by solute concentration, pressure, gravity, and factors called matrix effects.
  • "System" can refer to the water potential of the soil water (Ψsoil), root water (Ψroot), stem water (Ψstem), leaf water (Ψleaf), or the water in the atmosphere (Ψatmosphere), whichever aqueous system is under consideration.
  • Solutes (Ψs), pressure (Ψp), and gravity (Ψg) influence total water potential for each side of the tube (Ψtotal right or left) and, therefore, the difference between Ψtotal on each side (Δ).

• Subtropical Deserts and Chaparral

  • There are several types of deserts including high-pressure deserts, mid-continent deserts, rain-shadow deserts, and upwelling deserts.
  • In high-pressure deserts, the high atmospheric pressure enables the air to retain more moisture and there is little rainfall.
  • High-pressure deserts include the Sahara, Arabian, Thar, and Kalahari deserts, and the desert regions within the Arctic and Antarctic circles.

• Movement of Water and Minerals in the Xylem

  • Transpiration is caused by the evaporation of water at the leaf, or atmosphere interface; it creates negative pressure (tension) equivalent to –2 MPa at the leaf surface.
  • However, this value varies greatly depending on the vapor pressure deficit, which can be insignificant at high relative humidity (RH) and substantial at low RH.
  • The xylem vessels and tracheids are structurally adapted to cope with large changes in pressure.
  • The energy driving transpiration is the difference in energy between the water in the soil and the water in the atmosphere.
  • The atmosphere to which the leaf is exposed drives transpiration, but it also causes massive water loss from the plant.

• Climate and Weather

  • Climate refers to long-term, predictable atmospheric conditions, while weather refers to atmospheric conditions during a short period of time.
  • Climate refers to the long-term, predictable atmospheric conditions of a specific area .
  • In contrast, weather refers to the conditions of the atmosphere during a short period of time.
  • Climate refers to long-term, predictable atmospheric conditions of a specific area.
  • Weather, in contrast, refers to the conditions of the atmosphere during a short period of time.

• The Carbon Cycle

  • Carbon enters the atmosphere in the form of carbon dioxide via the carbon cycle and returns to organic carbon via photosynthesis.
  • The level of carbon dioxide in the atmosphere is greatly influenced by the reservoir of carbon in the oceans.
  • Carbon dioxide (CO2) from the atmosphere dissolves in water, combining with water molecules to form carbonic acid.
  • Carbon dioxide is also added to the atmosphere by the breeding and raising of livestock.
  • Carbon dioxide gas exists in the atmosphere and is dissolved in water.

• The Sulfur Cycle

  • Sulfur cycles exist between the oceans, land, and atmosphere .
  • Atmospheric sulfur is found in the form of sulfur dioxide (SO2).
  • Sulfur can also fall directly from the atmosphere in a process called fallout.
  • Sulfur may also enter the atmosphere through geothermal vents .
  • Decomposition of living organisms returns sulfates to the ocean, soil, and atmosphere.

• Transportation of Photosynthates in the Phloem

  • The multidirectional flow of phloem contrasts the flow of xylem, which is always unidirectional (soil to leaf to atmosphere).
  • Phloem STEs have reduced cytoplasmic contents and are connected by sieve plates with pores that allow for pressure-driven bulk flow, or translocation, of phloem sap.
  • This flow of water increases water pressure inside the phloem, causing the bulk flow of phloem sap from source to sink.
  • The resulting positive pressure forces the sucrose-water mixture down toward the roots, where sucrose is unloaded.

• Blood Pressure

  • Blood pressure is the pressure of blood against the blood vessel walls during the cardiac cycle; it is influenced by a variety of factors.
  • Blood pressure is the pressure of the fluid (blood) against the walls of the blood vessels.
  • Fluid will move from areas of high to low hydrostatic pressures.
  • The systolic pressure is defined as the peak pressure in the arteries during the cardiac cycle; the diastolic pressure is the lowest pressure at the resting phase of the cardiac cycle.
  • The blood pressure of the systole phase and the diastole phase gives the two readings for blood pressure .