Plant organs

• Plant organs


  A group of different tissues that work together to perform a common, specific function
• The bodies of flowering plants consist of different plant organs, ie. roots, stems, leaves and flowers
• Plant organs


  • Each plant organ is specialised in order to perform specific functions
• Functions of leaves


  • Capture sunlight for photosynthesis
  • Allow transpiration and gas exchange through stomata, for photosynthesis and respiration
  • Transport water and manufactured nutrients
• Lamina


  Leaf blade
• Axillary bud


  Develops in the axil, between the stem and petiole, out of which lateral branches or flowers grow
• Veins


  Consist of xylem and phloem that are continuous with the xylem and phloem of the root and stem
• Epidermis


  • Epidermal cells form the outer layer that covers a leaf, separating the internal tissues from the external environment
  • Protects against water loss via stomata and a waxy cuticle
  • Regulates gas exchange
  • Secretes metabolic compounds
• Stomata


  The pore of a stoma, with guard cells responsible for opening and closing the pore
• Stomata


  • Responsible for gas exchange, in and out of the leaf, during photosynthesis, respiration and transpiration
• Palisade mesophyll


  Elongated, thin-walled parenchyma cells situated just under the upper epidermis, containing large numbers of chloroplasts to absorb maximum sunlight for photosynthesis
• Palisade mesophyll


  • Cells are arranged longitudinally and packed tightly against one another, without intercellular spaces, to ensure the largest possible surface area is exposed to sunlight for photosynthesis
  • Cell walls are very thin for easy diffusion of gases (CO2 and O2) into and out of the cells during photosynthesis and cellular respiration
• Spongy mesophyll


  The lower mesophyll layer, with round parenchyma cells loosely packed in an irregular manner, containing large intercellular spaces connected to air chambers behind the stomata for efficient gaseous exchange
• Xylem


  Transports water absorbed from the soil through the root and stem xylem into the leaf xylem, where it moves by osmosis into the mesophyll cells for photosynthesis
• Phloem


  Transports organic nutrients manufactured during photosynthesis in the leaf to other parts of the plant