module 2

• One of the most essential events in everyday life of a living organism is the exchange of gases. This process is important as it keeps organism alive.
• Carbon dioxide, as a waste product during this process is removed from most animal systems and substituted by oxygen. Plants on the other hand uses carbon dioxide in photosynthesis to produce oxygen which will be used by animals and plants for respiration.
• Gas exchange is responsible for the presence of oxygen and carbon dioxide in the air.
• Carbon dioxide may appear to be a waste product of respiration in plant cells, but carbon dioxide may be considered to be a by-product because it is used in photosynthesis.
• Plant cells must have carbon dioxide available in them while the oxygen gas must be eliminated.
• Gas exchange is an important process in the metabolism of energy, and gas exchange is an essential prerequisite for life.
• Diffusion


  The movement of molecules in the direction following the concentration gradient, from a region of greater concentration to a region of lower concentration
• Diffusion through a moist membrane is the fundamental process of gas exchange.
• Plants


  • Water moves through the tissues of aquatic plants and provides the means for the exchange of carbon
  • Air enters the tissues of terrestrial plants, and the gases diffuse through the moisture that bathes the inner cells
• Gases do not pass through the leaf cuticle; they pass through pores called stomata in the epidermis.
• On the lower surface of the leaf, stomata are numerous and usually open during the day when the rate of photosynthesis is highest.
• The opening and closure of stomata are due to physiological changes in the surrounding guard cells.
• Animals


  • Oxygen and carbon dioxide diffuses across moist membranes
  • The exchange happens directly with the environment in simple animals
  • The exchange between the environment and the blood happens with complex organisms, such as mammals
  • The blood transports oxygen to deeply embedded cells and transports carbon dioxide out of the body
• Oxygen and carbon dioxide transfer in animals

  • Earthworms - directly through their skin
  • Terrestrial arthropods - through spiracles and tracheae
• Terrestrial vertebrates


  • Have well-developed respiratory systems with lungs
  • Frogs swallow air, where oxygen diffuses the blood to bind with hemoglobin in the red blood cells
  • Amphibians can exchange gases through their skin
  • Reptiles have folded lungs, with rib muscles aiding the expansion of the lungs
  • Birds have air sacs in their lungs, with the rib cage spreading apart when inhaling to create a partial vacuum
  • Mammalian lungs have millions of microscopic air sacs called alveoli, with a rich network of blood vessels surrounding each alveolus
• Mammalian respiratory system


  • Has a dome-shaped diaphragm that separates the thorax from the abdomen, providing a separate chest cavity for breathing and blood circulating
  • The diaphragm contracts and flattens to create a partial vacuum in the lungs during inhalation, causing the lungs to fill with air and gas exchange to occur
• Gas exchange between the external atmosphere and the circulatory system of an organism is the primary feature of the respiratory system.
• This exchange combines the oxygenation of blood with the removal of carbon dioxide and other metabolic waste from circulation in humans and other mammals.
• Gas exchange in the lungs


  • Occurs at the molecular level in the alveoli-tiny sacs that are the essential functional part of the lungs
  • The alveolar epithelial tissue is extremely thin and permeable, facilitating the exchange of gas between the air inside the lungs and the blood stream capillaries
  • Air moves due to variations in pressure, where air flows from high-pressure areas to low-pressure areas
• Key respiratory system organs


  • Provide oxygen for cellular respiration to body tissues
  • Extract carbon dioxide from the waste product
  • Help preserve acid-base balance
• Parts of the respiratory system


  • Mouth and nose
  • Sinuses
  • Pharynx (throat)
  • Trachea
  • Bronchial tubes
  • Lungs
• From the lungs, the bloodstream delivers oxygen to all organs and other tissues.
• Muscles and bones that help move air in and out of the lungs


  • Diaphragm
  • Ribs
• Other components of the respiratory system


  • Alveoli
  • Bronchioles
  • Capillaries
  • Lung lobes
  • Pleura
  • Cilia
  • Epiglottis
  • Larynx (voice box)
• Multicellular organisms need to supply every cell with oxygen, water and nutrients and to achieve this they need a transport mechanism otherwise diffusion will be too long. The development of a transport system is thus directly related to an organism's surface area:volume ratio. Organisms which have a very large surface area:volume ratio e.g. protozoans, may depend upon diffusion, but as an organism grows bigger, the surface area to volume ratio reduces and this makes a specialised transport mechanism necessary.
• Plants need a transport system to supply raw materials for photosynthesis to the leaves and to deliver the sugar made to other areas of the plant for use or storage.
• Xylem


  A tissue composed of dead, hollowed-out cells that form a web of pipes. The walls of xylem cells are lignified (strengthened with a material called lignin). This allows the xylem to tolerate pressure changes as water flows through the plant. Transport in the xylem is a physical process. It does not require energy.
• Phloem


  Living cells adapted for transport. Sieve tubes are specialized for transport and contain no nuclei. Companion cells supply the energy for the sieve cells. The end walls of the sieve cells have pores from which sugar is transferred from cell to cell.
• In the root, the xylem forms a central axis, forming a strong support. The phloem is in the middle, above the xylem.
• In the stem, the transport tissues of the xylem and phloem are organized into vascular bundles.
• Water entry into root hair cells

  1. Water enters root hair cells by osmosis down a concentration gradient

  2. Water then moves from cell to cell through the root cortex by osmosis

  3. Water enters the xylem vessels in the center of the root
• Water movement in xylem


  1. Water molecules move up the xylem vessels to the leaves

  2. Water exits the xylem vessels and moves from cell to cell

  3. Some water evaporates into the surrounding air spaces inside the leaf and then diffuses out through the stomata into the surrounding air
• Transpiration


  The loss of water from the leaves of a plant
• Transpiration stream


  The resulting flow of water through the plant
• Open circulatory system


  The blood vessels carry all fluids to the cavity. When the animal moves, the blood inside the cavity moves freely in both directions throughout the body. Blood bathes the body immediately, delivering oxygen and eliminating waste from the bloodstream.
• Closed circulatory system


  Blood never leaves the blood vessels. Instead, it is continually moved from one blood vessel to another without entering the cavity. Blood is transported in one direction, supplying oxygen and nutrients to cells and removing waste materials.
• Parts of the human circulatory system


  • Heart
  • Arteries
  • Veins
  • Blood
• Pulmonary circulation


  1. Deoxygenated blood exits the heart from the right ventricle and is transferred through the pulmonary artery to the lungs

  2. Oxygen diffuses through the alveoli, and then to the blood and returns to the left atrium of the heart through the pulmonary vein
• Systemic circulation


  1. Blood exits from the left ventricle to the aorta, the body's largest artery

  2. Arteries supply all of the body's organs

  3. Arteries branch to the capillaries where oxygen diffuses from the blood to the cells, and the waste and carbon dioxide diffuses from the cells and into the blood

  4. Deoxygenated blood in the capillaries travels to the veins that converge into the veins, where the blood is transferred back to the heart