biology: transport systems

• Gas movement in leaves


  Largely local and occurs via simple diffusion
• Gas exchange in plants


  Occurs through stomata and lenticels
• Opening of stomata


  1. Guard cells fill with water

  2. Guard cells bend outwards

  3. Stoma opens

  4. Allows for gas exchange
• Closing of stomata


  1. Water is lost from guard cells

  2. Guard cells straighten

  3. Stoma closes

  4. Prevents gas exchange and water loss
• Plants


  Have to balance their requirement for gas exchange and the necessity for water conservation
• Stomata open in light and close in the dark
• Lenticels


  Pores through which gaseous exchange occurs in the woody parts of plants, such as the trunks and branches of trees and woody shrubs
• Epidermal cells are located on the upper and lower surfaces of the leaf. It allows sunlight to penetrate, prevents water loss and provides protection.
• Palisade cells are located on the upper part of the leaf. They hold chloroplasts containing chlorophyll as small dots for photosynthesis.
• Guard cells control the opening and closing of the stroma for gas exchange.
• Spongy cells also contain chloroplasts, however, they are located on the underside of the leaf and are loosely packed to allow air movement.
• Phloem cells are located in the bottom main vein and transport plant products.
• Xylem cells are located in the upper main vein and transport water and minerals
• Gas exchange occurs in all animals and involves the movement of gases between the internal and external environments by diffusion across cell membranes. The respiratory system enables the exchange of gases between an organism and its environment. It contains organs made up of specialised tissues that allow an organism to take in oxygen and to remove carbon dioxide from its body.
• Alveoli have thin walls with a large surface area allowing rapid diffusion of gases. Oxygen diffuses from the alveoli into capillaries surrounding them while carbon dioxide moves in the opposite direction.
• The lungs are two sponge-like structures where gas exchange takes place. Air is drawn into the trachea through the mouth or nose during breathing. This air passes down the windpipe (trachea) and enters the bronchi which branch out into smaller tubes called bronchioles. These end at tiny sacs called alveoli.
• Oxygenated blood leaves the lungs via pulmonary veins and travels to the heart. Deoxygenated blood returns to the lungs via pulmonary arteries.
• Vascular tissue


  Arranged in vascular bundles made up of xylem and phloem tissue
• Xylem tissue


  Transports water and mineral ions from the roots through the stem to the leaves
• Xylem tissue


  • Composed of xylem vessels and xylem tracheids
  • Xylem vessels are long, thin, continuous tubes composed of dead tissue with lignin-strengthened walls
  • Water molecules and dissolved ions pass from one tracheid to the other through the many small holes called pits
  • Lignin prevents the vessels from collapsing, and helps the easy movement of water and dissolved substances
• The transpiration-cohesion-tension theory currently explains the movement of substances up the xylem vessels. This theory has at its core the evaporation of water from the leaves (transpiration) creating a suction pull of water up the stem from the roots. Water evaporates from the leaves and creates tension, which pulls more water from the veins and then up the xylem vessel.
• Cohesion between water molecules and adhesion between the water molecules and the walls of the xylem maintain the column of water. Cohesive forces cause the water molecules to stick together with positive and negative ends of molecules attracted to each other (polarity). Adhesive forces between the water molecules and the walls of the xylem vessel cause the water to rise up the sides. When molecules of water are pulled up, other molecules follow. A small amount of root pressure forces the water already present in the xylem vessel upwards.
• Cohesion: Water molecules are attracted to each other

  Adhesion: Water molecules stick to the wall of the xylem vessel

  Water moves up with an osmotic pull

  Xylem: unidirectional movement of water (one way) up from the root towards the leaf for photosynthesis.

  Phloem: bidirectional movement of water
• Epithelial Tissue


  Lining of organs, glands, and other body surfaces. Examples: skin, respiratory tract lining, gastrointestinal tract lining.
• Connective Tissue


  Provides support, structure, and protection to the body. Examples: bones, tendons, ligaments, cartilage, blood, and fat.
• Muscle Tissue


  Enables movement and contraction. Examples: skeletal, smooth, and cardiac muscle.
• Nervous Tissue


  Transmits and processes information. Examples: neurons and glial cells.
• Nervous System


  Controls and coordinates body functions through electrical and chemical signals. Examples: brain, spinal cord, and peripheral nerves.
• Circulatory System


  Transports oxygen and nutrients to cells and removes waste products. Examples: heart, arteries, veins, and capillaries.
• Digestive System


  Breaks down food into nutrients for energy and growth. Examples: mouth, esophagus, stomach, small intestine, and large intestine.
• Respiratory System


  Brings oxygen into the body and removes carbon dioxide. Examples: nose, mouth, trachea, bronchi, lungs, and diaphragm.
• Urinary System


  Filters waste and excess substances from the blood and excretes them in the urine. Examples: kidneys, ureters, bladder, and urethra.
• EBB #2

  Sonnet 1

  “The sweet, sad years, the melancholy years, Those of my own life, who by turns had flung / A shadow across me.”

  Personification
• EBB #2

  Sonnet 1

  “Guess now who holds thee? ‘—Death,’ I said. But there, / The silver answer rang … ‘Not Death, but Love.’”