Lecture Notes: Nutrient and Gas Requirements

Overview

• Discussion on nutrient and gas requirements
• Examination of xylem and phloem structures
• Respiratory and circulatory systems in various organisms

Gas Exchange in Fish

• Gills: Paired respiratory organ in fish and some amphibians
  • Oxygen extracted from water flowing over surfaces within/attached to the pharynx
  • Water flows into gill slits on the fish's side
  • Deoxygenated blood moves into secondary lamellae
  • Oxygen absorbed into lamellae and blood, CO2 released
  • Blood pumped by heart, similar to humans
  • High surface area (SA) increases gas exchange rate

Trachea and Gas Exchange in Insects

• Trachea: Tube extending from larynx to bronchial tubes, conveys air to/from the lungs
• Insects: Gas exchange occurs directly on cells
  • Air enters through spiracles
  • Flows into trachea, then small branching structures reaching every cell
  • Oxygen/water diffuse in, CO2 diffuses out
  • Movement by passive diffusion or active ventilation (larger insects)

Digestive System Overview

• Mouth: Physical digestion via chewing, increases SA for chemical digestion
• Oesophagus: Bolus and breakdown of starch
• Stomach: Physical churning and gastric juices breakdown food
• Small Intestine: Three regions, releases pancreatic juices, nutrient absorption
• Large Intestine: Absorbs water, ions, aids metabolism; beneficial bacteria digest substances
  • Vitamins A and K absorbed into bloodstream

Xylem Structure

• Vessels: Long, water-filled tubes of elongated end-to-end cells
  • As cells mature, strengthened with lignin, become rigid
  • Hollow lignin tubes formed after cell death
  • Pits, perforations allow sideways movement between vessels
• Tracheids: Single, large, tapering water-filled cells in xylem tissue
  • Lose nucleus and cytoplasm, form continuous tubes
  • Water transferred horizontally through adjoining pits

Phloem Structure

• Components: Sieve tubes, companion cells, parenchyma, sclerenchyma
  • Sieve Tubes: Living cells, thin cell walls, perforated by sieve plates
  • Companion Cells: Enable sugar transportation
  • Parenchyma Cells: Provide structure to vascular tissue
  • Sclerenchyma Cells: Provide structural support

Circulatory Systems in Animals

• Fish: Single circuit blood flow
  • Blood flows from gills to capillaries without passing through heart
  • Two-chambered heart
• Insects: Open circulatory system
  • Dissolved nutrients travel directly to tissues
  • Dorsal Vessel: Transports material from abdomen to head
    • Aorta leads to head, empties, travels through organism

Important Concepts

• Differences between xylem and phloem structures
• Differences in respiratory and circulatory systems across organisms
• Macroscopic structures in animals, fish vs. mammals
• Single vs. double circulatory systems