7-8

• Xylem tissue


  Vascular tissue that transports water and minerals from roots to stems and leaves
• Phloem tissue


  Vascular tissue that transports food materials from leaves to roots and stems
• Cross-section of a stem shows xylem and phloem tissues in the vascular bundle
• Cross-section of a root shows xylem and phloem tissues
• Cross-section of a leaf shows xylem and phloem tissues
• Root hairs


  Increase the surface area of root cells, increasing the rate of absorption of water via osmosis and mineral ions via active transport
• Water movement pathway


  1. Roots → stem + leaves via xylem

  2. Leaves → roots + stem via phloem
• Leaving plants in sunlight with red or blue dye shows the dye moving through the xylem vessels
• Cutting cross-sections of celery stalks without staining does not allow identification of xylem vessels, but adding dyes stains the xylem vessels
• Water is transported from roots to leaves through xylem vessels
• Transpiration


  Loss of water vapour from plant leaves by evaporation of water from the surface of mesophyll cells and diffusion of water vapour through the stomata
• Transpiration stream


  Transpiration 'pulls' on water in xylem, with water molecules held together by cohesion and pulled as a continuous water column
• Factors affecting transpiration
• Translocation


  Movement of sucrose and amino acids in phloem vessels from source (regions of production) to sink (regions of storage, respiration or growth)
• Glucose, fructose and sucrose are transported in the phloem
• Arteries pump blood away from the heart, while veins return blood to the heart
• Double circulation

  1. Blood travels to the lungs (pulmonary circulation)

  2. Blood travels to the body tissues (systemic circulation)
• Advantages of double circulation include faster delivery of oxygen and nutrients to body cells
• Coronary heart disease is caused by blockage of the coronary arteries that supply the heart muscle with oxygen and nutrients
• Arteries

  • Thick outer wall, smooth lining, small lumen to withstand high pressure blood flow

  Carry oxygenated blood away from the heart
• Capillaries

  • Very small lumen, allow slow flow of blood within tissues for gas and nutrient exchange
• Veins


  • Fairly thin outer wall, contain valves, carry deoxygenated blood towards the heart
• Plasma, red blood cells, white blood cells and platelets are the main components of blood
• The intercostal muscles control rib movement for inhalation and exhalation
• The alveoli in the lungs have a large surface area, thin walls and good blood supply to facilitate gas exchange
• Inspired air has 21% oxygen, while expired air has 16% oxygen due to oxygen absorption during gas exchange
• Mucus and cilia in the respiratory system trap particles and push them out of the lungs
• Exercise increases breathing frequency and depth


  To remove more CO2 and repay oxygen debt
• Tobacco smoking causes COPD, lung cancer and coronary heart disease
• Anaerobic respiration in muscles produces lactic acid, while anaerobic respiration in yeast produces alcohol and CO2
• Aerobic respiration uses oxygen to break down glucose and release a large amount of energy, while anaerobic respiration does not use oxygen and releases much less energy