Biology B4 (organisations of plants)

• Plant tissues


  Differentiated cells that form the organs of plants
• Plant organ system


  • Leaves, stems and roots transport substances around the plant
• Epidermal tissues


  • Cover the surface and protect the plant
  • Often secrete a waxy substance that waterproofs the surface of the leaf
• Palisade mesophyll tissue


  • Contains lots of chloroplasts which carry out photosynthesis
• Spongy mesophyll tissue


  • Contains some chloroplasts for photosynthesis
  • Has big air spaces and a large surface area to make diffusion of gases easier
• Xylem tissue


  • Transports water and mineral ions from the roots to the stems and leaves
  • Composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream
• Phloem tissue


  • Transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage
  • Movement of food molecules through phloem tissue is called translocation
  • Composed of tubes of elongated cells
  • Cell sap can move from one phloem cell to the next through pores in the end walls
• Guard cells


  • Control the opening and closing of stomata to regulate gas exchange and water loss
  • In light, guard cells take up water by osmosis and become turgid, pulling the pore open
  • In darkness, water is lost and the pore closes
• In bright light


  Transpiration increases
• At higher temperatures

  Transpiration is faster
• In windy conditions

  Transpiration is faster
• In humid conditions


  Transpiration is slower
• Transpiration


  1. Water evaporates from the surface of spongy and palisade cells inside the leaf

  2. Water diffuses out of the leaf

  3. More water is drawn up from the xylem to replace what's lost

  4. The continuous xylem tubes act like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves
• Plant Tissues

  • Plants are multicellular organisms
  • They contain differentiated cells, tissues and organs
  • Leaves, stems and roots are plant organs
  • They form a plant organ system for the transport of substances around the plant
• Epidermal tissues


  • Cover the surface and protect
  • Secrete a waxy substance that waterproofs the surface of the leaf
• Palisade mesophyll tissue


  • Contains lots of chloroplasts
  • Carries out photosynthesis
• Spongy mesophyll tissue


  • Contains some chloroplasts for photosynthesis
  • Has big air spaces
  • Has a large surface area to make diffusion of gases easier
• Thin, waxy cuticle


  To protect the leaf without blocking out light
• Thin epidermis


  To allow more light to reach the palisade cells
• Palisade cells on the top surface


  To absorb light
• Many chloroplasts in the palisade cells


  To increase absorption of light
• Spongy mesophyll inside the leaf

  Air spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area
• Xylem tissue

  • Transports water and mineral ions from the roots to the stems and leaves
  • Composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream
• Phloem tissue

  • Transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage
  • Movement of food molecules through phloem tissue is called translocation
  • Composed of tubes of elongated cells
  • Cell sap can move from one phloem cell to the next through pores in the end walls
• Guard cells


  • Control gas exchange and water loss
  • Opening and closing of the stomata is controlled by the guard cells
  • In light, guard cells take up water by osmosis and become turgid, pulling the inner walls apart to open the pore
  • In darkness water is lost and the inner walls move together closing the pore
• Light


  In bright light transpiration increases
• Temperature


  Transpiration is faster in higher temperatures
• Wind


  Transpiration is faster in windy conditions
• Humidity


  Transpiration is slower in humid conditions
• Transpiration


  1. Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf

  2. More water is drawn out of the xylem cells inside the leaf to replace what's lost

  3. The xylem cells make a continuous tube from the leaf, down the stem to the roots, acting like a drinking straw to produce a flow of water and dissolved minerals from roots to leaves
• Root hair cells


  • Adapted for the efficient uptake of water by osmosis, and mineral ions by active transport
  • Contain lots of mitochondria, which release energy from glucose during respiration to provide the energy needed for active transport
• Evaporation


  The process of a liquid turning into a gas or vapor. For example, when water on the surface of spongy and palisade cells inside the leaf evaporates, it turns into water vapor and diffuses out of the leaf.
• Condensation


  The process of a gas or vapor turning back into a liquid. For example, when water vapor cools down and turns back into tiny water droplets, which then form clouds.
• Spongy and palisade cells


  Cells inside the leaf responsible for photosynthesis, where water evaporation occurs.
• Transpiration


  The process of water movement from the roots to the leaves through the xylem cells, driven by the evaporation of water on the surface of spongy and palisade cells inside the leaf.
• Xylem cells


  Specialized cells that transport water and dissolved minerals from roots to leaves, forming a continuous tube from the leaf down to the roots.
• Photosynthesis


  The process by which plants convert light energy into chemical energy to fuel their growth. This process occurs in the spongy and palisade cells of the leaf, which contain chloroplasts that contain the pigment chlorophyll and allow the cells to absorb light energy and convert it into chemical energy.