plant structures and their functions

• Photosynthesis

  6CO2 + 6H2O (+ light energy) > C6H12O6 + 6O2Carbon Dioxide + Water (+ light energy) > Glucose + Oxygen
• Factors needed for photosynthesis

  water, sun, carbon dioxide, minerals, chlorophyll
• root hair cells

  Cells in the epithelium of roots that have long extensions to increase surface area for the absorption of water and minerals.
• Phloem


  carries iron and food from leaf to roots
• Xylem


  carries water from roots to leaves
• Transpiration

  Evaporation and diffusion of water from the leaves of a plant
• Stomata


  Tiny pores on the surface of a plant, surrounded by guard cells, allow CO2, H2O and water vapour in transpiration to diffuse in and out
• adaptations of leaves

  • broad = large surface area exposed to light
  • palisade layer = chloroplasts near to top
  • upper epidermis = transparent so light can get through to palisade layer
  • xylem and phloem = provide water and take away glucose produced
  • waxy cuticle = reduce water loss
• adaptations of plants

  small leaves = reduces surface area for waterloss

  • curled leaves = traps watervapour near to surface and reduce diffusion-
  • thick waxy cuticles = reduce water loss-
  • fleshy stem = stores water-
  • fewer stomata or stomata which open at night - reduce water loss
• Phototropism


  A growth response towards light
• Geotropism


  response to earth's gravity, as the growing of roots downward in the ground
• Auxin

  a plant hormone that promotes root formation and bud growth
• Uses of plant hormones

  • selective weedkiller = auxin disrupts growth patterns-
  • growing from cuttings and root powder = produce roots rapidly
  • controlling flower and fruit formation = gibberellins stimulate seed germination, stem growth and flowering, improve fruit quality
  • producing seedless fruit = gibberellins to unpollinated fruit
  • ethene ripens fruit
• Producers

  Plants and algae are the main producers of food, which they synthesise from sunlight in a process called photosynthesis
• Photosynthesis

  The process where plants and algae synthesise food from sunlight
• Photosynthesis is an endothermic reaction, meaning that it takes in more energy than it releases

  
• Chloroplasts

  The organelles in leaves where light energy is transferred to
• Photosynthesis

  Carbon dioxide + water → glucose + oxygen

  
• Chemical symbols

  • Carbon dioxide: CO2
  • Water: H2O
  • Oxygen: O2
  • Glucose: C6H12O6
• Factors affecting rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration

  
• Limiting factor

  An environmental condition that restricts any increase in the rate of photosynthesis, despite increases in other factors

  
• Measuring rate of photosynthesis using pondweed

  1. Place pondweed in sealed test tube with capillary tube

  2. Measure distance bubble moves in capillary tube to calculate oxygen produced

  3. Vary factors like temperature and light intensity

  
• Light intensity

  Directly proportional to rate of photosynthesis

  
• Inverse square law

  Light intensity is inversely proportional to the square of the distance from the light source
• Root hair cells

  • Large surface area from root hairs
  • Large permanent vacuole
  • Mitochondria for active transport of mineral ions
• Xylem cells

  • Become lignified and hollow to transport water and mineral ions
  • Lignin deposited in spirals to withstand pressure
• Phloem cells

  • Have sieve plates to allow movement of substances
  • Remain alive with energy from companion cells to transport sucrose
• Transpiration

  The loss of water vapour from leaves and stems
• Guard cells

  • Kidney-shaped with thin outer walls and thick inner walls
  • Open and close stomata when plant has lots of water available
• Translocation

  The movement of food substances like sucrose made in the leaves up or down the phloem
• Leaf surfaces

  • Water molecules are attracted to each other, when some molecules leave the plant the rest are pulled up through the xylem
  • This results in more water being taken up from the soil resulting in a continuous transpiration stream through the plant
• Guard cells

  • They close and open stomata
  • They are kidney shaped
  • They have thin outer walls and thick inner walls
  • When lots of water is available to the plant, the cells fill and change shape, opening stomata (they are also light sensitive)
  • This allows gases to be exchanged and more water to leave the plant via evaporation
  • More stomata are found on the bottom of the leaf, allowing gases to be exchanged whilst minimising water loss by evaporation as the lower surface is shaded and cooler
• Translocation

  The movement of food substances (such as sucrose) made in the leaves up or down the phloem, for use immediately or storage
• Translocation only occurs in the phloem, not the xylem or any other tissues in the plant
• Sources

  The places where sucrose is made
• Sinks

  The places where sucrose is used or stored
• The location of the sources and sinks can depend on the season
• Stomata

  • They are able to close to minimise water loss and open to increase evaporation and transpiration
  • They also allow gas exchange to occur when they are open
• Chlorophyll

  • It is green, which is the most efficient colour for absorbing light
• Leaf thinness

  • Means that carbon dioxide only has a short distance to travel to enter the leaf (and work in photosynthesis) and oxygen only has a short distance to diffuse out