Plant tissues/organs

• Photosynthesis takes place in leaves
• The leaf is a plant organ that contains different tissues
• Epidermal cells


  Very thin cells that form the upper and lower epidermis of the leaf
• Upper epidermis


  • Transparent to allow light to pass through
  • Covered with a waxy cuticle to reduce water evaporation
• Lower epidermis


  • Contains tiny pores called stomata that allow carbon dioxide in and oxygen out
  • Has guard cells on either side of the stomata
• Palisade mesophyll


  Packed full of chloroplasts that contain chlorophyll to absorb light energy for photosynthesis
• Spongy mesophyll


  • Full of air spaces that allow carbon dioxide to diffuse to the palisade cells and oxygen to diffuse out
• Xylem


  Transports water and dissolved mineral ions from the roots to the stem and leaves
• Phloem


  Transports dissolved sugars produced by photosynthesis from the leaves to the rest of the plant
• Translocation


  The movement of sugars through phloem tissue
• Meristem tissue


  Contains stem cells that can differentiate into different types of plant tissue
• Meristem tissue is found at growing tips such as shoots and roots
• Plant tissues


  • Plant cells, tissues and organs are adapted to their functions
  • The stem, root and leaves form an organ system that transports substances into, around and out of a plant
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Plant transport tissues


  • Xylem
  • Phloem
• Transpiration


  The loss of water from leaves by evaporation through the stomata
• Closing the stomata helps to control water loss
• Plant tissues


  • Epidermis
  • Palisade mesophyll
  • Spongy mesophyll
• Palisade mesophyll


  Plant tissue containing closely packed cells in the upper layer of a leaf
• Chloroplast


  Contains the green pigment chlorophyll; the site of photosynthesis
• Spongy mesophyll


  The plant tissue in a leaf which has loosely packed cells and air spaces between them to allow gas exchange
• Gases dissolve in the water layer covering the spongy mesophyll cells as they move into and out of the cells
• When the plant is photosynthesising during the day, the features of the spongy mesophyll allow carbon dioxide to diffuse into the cells, and oxygen to diffuse out of them
• Gases enter the leaf through small pores called stomata
• As the stomata open, water is lost by the process of transpiration
• Plant cells, tissues and organs


  Adapted to their functions
• Stem, root and leaves


  • Form an organ system that transports substances into, around and out of a plant
• Xylem


  Transports water and minerals
• Phloem


  Transports sugars and amino acids dissolved in water
• Root


  • Xylem forms a central column, provides solid support
  • Phloem is towards the centre, outside the xylem
• Stem


  • Transport tissues of xylem and phloem are grouped into vascular bundles
• Leaves


  • Main organ of photosynthesis
  • Adapted for gas exchange and photosynthesis
• Leaf adaptations


  • Large surface area for maximum absorption of light and carbon dioxide
  • Thin, flattened blade so water and gases have limited distance to diffuse
  • Vascular tissue in midrib and veins to transport water, minerals, glucose and other photosynthesis products
  • Air spaces between cells for diffusion of gases
• Plant cells, tissues and organs


  Adapted to their functions
• Stem, root and leaves


  • Form an organ system that transports substances into, around and out of a plant
• Xylem


  Narrow, hollow, dead tubes with lignin, responsible for the transport of water and minerals in plants
• Xylem vessels


  Specialised cells that make up most of the xylem in a mature flowering plant or tree
• Xylem vessels


  • Lose their end walls so the xylem forms a continuous, hollow tube
  • Become strengthened by a chemical called lignin
• Transport in the xylem is a physical process and does not require energy
• Phloem


  The tissue in plants that transports the products of photosynthesis, including sugars and amino acids