plants 1-2

• Plants


  Need water and nutrients in order to grow and survive

  
• Photosynthesis


  Plants produce their own carbon source (glucose)

  
• Plants also need carbon dioxide from the air
• Plants


  • Have evolved mechanisms to ensure they can take up water and nutrients, and can be adapted to survive under dry conditions
• A large maple tree needs about 800 litres of water per day
• When plants are watered


  They survive

  
• When plants are not watered


  They die
• What plants need


  • Water
  • Nutrients
  • Light
  • Carbon dioxide

  
• Coniferous and deciduous trees


  Types of trees

  
• Water movement from soil to top of plant

  1. Water from soil ends up in the xylem of the vascular bundle

  2. Water moves up the plant, against gravity

  
• Movement of water inside root

  1. Water moving between cells

  2. Water moving through cells

  
• Roots take up water

  1. Through osmosis - movement of water from low solute (soil) to high solute (cells)

  2. Roots hairs provide increased surface area for absorption

  3. Water can move between cells (apoplast) or through cells (symplast)

  4. Water is re-directed to move via the symplast when it reaches the endodermis, allowing for control of water uptake

  5. Casparian strip inside the endodermis regulates water movement

  
• Water movement up through the xylem

  1. Water molecules adhere to each other by hydrogen bonding and to xylem vessel walls

  2. Creates a column of water internally

  3. Water travels upwards to the leaves at a rate of up to 15 metres per hour in a large tree

  
• Water loss through transpiration in the leaves


  1. Creates a "water deficit" or negative water potential inside the leaf

  2. Causes a "pull" of water into the leaf from the xylem

  3. This in turn pulls water up the xylem from the roots

  4. The "transpirational pull" is the main force that causes water to move up the plant

  
• Covering a plant in a plastic bag for 24 hours makes it easy to see the water released from the leaves into the space in the bag

  
• Stomata


  Need to stay open to take up carbon dioxide and release oxygen during photosynthesis

  
• Opening and closing of stomata

  1. Stomata open when there is lots of water, sunlight, and high potassium ion levels

  2. Stomata close when there is not enough water, it is dark, and potassium levels are low
• Stomata


  • More on the underside of leaves as they are not exposed to direct light and it is cooler
  • The guard cells regulate the stomatal opening size - larger openings mean more water loss

  
• Xerophytes


  Plants that live in the desert
• Adaptations of leaves for desert plants

  • Reduced leaf size
  • Fleshy leaves to store water
  • Closing stomata during the day, opening at night
  • Stomata located deeper inside the leaf
  • Thick waxy cuticles to retain water
  • Fewer stomata

  
• Phloem


  Transports sugar (sucrose) produced in the leaves to other parts of the plant
• Phloem sugar loading and unloading

  1. Sugar is "loaded" into phloem cells by sucrose transporters, creating high osmotic pressure that draws in water from xylem

  2. Pressure builds up, forcing the flow of sugar down the plant

  3. Sugar solution moves via "bulk flow" to reach cells that need it (e.g. growing fruit, shoots, roots), where it is "unloaded"
• Nutrients in the soil end up in food
• Xylem


  Moves water and nutrients up the plant, from roots through stems to leaves

  
• Phloem


  Moves sugar and water solution from leaves to other parts of the plant
• Xylem cells


  Tracheids and vessel elements, which are non-living and have pores
• Phloem cells


  Sieve tube elements and companion cells, which are living
• Maple syrup


  Sap from maple trees that is concentrated by boiling to 66-67% sugar
• Obtaining maple syrup


  1. Taken as "xylem sap" from trees during early spring

  2. In the Fall, sugar is transported by the phloem to the roots for storage

  3. In early spring, when temperatures are above freezing during the day, the sap is moved up through the xylem to give energy for leaves to grow

  4. Drilling holes in the trees allows xylem sap to drip due to positive pressure flow

  
• Plant nutrients


  • Macronutrients
  • Micronutrients
• Ion channels allow for nutrients to enter plant cells
• Nutrients can be provided from soil or as fertilizers
• Some plants consume insects