Chapter 13

• Non-vascular plants

  • do not have roots but do contains simple leaves
  • they live in moist environments and are relatively small plants
• Vascular plants

  • Vascular tissue: contain vascular tissue, which transports water and nutrients around the plant body -> connects root and stem in plant, includes the xylem (transports water) and the phloem (which transports sugar)
• Xylem

  • responsible for water transport, along with minerals and other nutrients needed for growth and processes -> this occurs after water is absorbed from the soil through the root system via osmosis into root hair cells
  • consists of tubular elongated cells that allow water to pass freely
  • as xylem cell matures they die, leaving behind a hollow structure which are idea for water transport
  • dead xylem forms woody part of plant stems
• Phloem

  • transports sugars in the form of sucrose and other photosynthesis products to where it is needed in the plant body
  • phloem are living, consisting of conductive tissue composed to thin walls
  • phloem is innermost part of the bark
• Two types of phloem

  • sieve tube cells -- long thin phloem cells that have large pores through cell walls at either end, no nuclei, mitochondria, or vacuoles, it forms a channel where sugars and other products flow
  • companion cells -- these are found alongside sieve tubes, they hav nucleus and other cell organelles, they control activities of the sieve tube cells
• Photosynthesis needs necessary inputs to reach the leaves which are the photosynthetic organs of the plant - apart from taking in water and carbon dioxide - the leaves need maximum sunlight as well

  • gases such as carbon dioxide and oxygen are exchanged via stomata and the plant surface
  • organic substances produced in photosynthesis are distributed via phloem throughout root and shoot system where it is either used or stored
• Stomata

  are tiny openings in the surface (epidermis) of a plant leaf through which gas can enter or exit, found in underside of leaf

  • each stoma consists of a central pore or opening surrounded by two guard cells
• Guard cell

  Pairs of cells that open and close a stoma to control entry and exit of gases -> this can happen due to amount of water inside guard cell causing them to change shape

  • turgid guard cells (swollen with water) open the stoma because turgid guard cells bend from each other
  • guard cells shrink with lack of water, described as flaccid which closes the stoma
• Respiration occurs throughout the day and night providing plant with usable form of energy called ATP 


  Photosynthesis only occurs during sunlight hours

  • rate of photosynthesis is higher than rate of respiration during day
• Open Stomata


  • potassium ions are pumped into guard cells by active transport using energy from ATP -> creating concentration gradient causing the water to enter guard cells via osmosis
  • guard cell becomes turgid and swell as water fills, opening stoma -> gas exchange can now occur
• Close stomata 


  • during heat, guard cells pump potassium ions out, causing water to leave cell by osmosis -> makes the guard cell flaccid and closing the stoma, gas exchange will stop
• Stomata typically open at daylight and close at night, with light being the main trigger for opening
• A drop in water availability reduces photosynthesis, raising carbon dioxide levels inside the leaf, which also leads to stomatal closure
• Vascular plant exchange gases with the atmosphere via open stomata on the underside of the plant surface
• Xylem transport 


  xylem transport water and mineral nutrients from roots to leaves using

  • root pressure
  • capillary action
  • transpiration
• Water and dissolved mineral enter the root from the soil by the process of osmosis in the case of water molecules, and diffusion and active transport in the case of dissolved ions
• Transpiration 


  is the evaporation of water vapour from the plant, mainly through stomata on the underside of the leaves
• Environmental factors that affect transpiration

  • Light: increases rate of transpiration by warming leaf
  • Humidity: decrease in humidity increase rate of transpiration as evaporation rate increases
  • Wind: increase of wind increases evaporation so rate of transpiration will increase
  • Temperature: increase in temperature increases rate of transpiration
• Translocation 


  is the transport of sugars through phloem from a source (plant part that produces or releases sugars - leaves) to a sink (stores, uses sugars - roots, stems)
• In vascular plants, transport of the products of photosynthesis and some mineral nutrients occurs by translocation in the phloem, in any direction from a source to a sink. Translocation uses energy