Plant Organisation

• Plant Tissues

  1: Epidermal tissue - Cover and protect the plant.

  2: Palisade mesophyll - Composed of cells with lots of chloroplasts for photosynthesis.

  3: Spongy mesophyll - Contains internal air spaces that increase surface area to volume ratio for diffusion of gases.

  4: Xylem - Transport water and mineral ions from the roots to the leaves for photosynthesis.

  5: Phloem - Transport dissolved sugars from the leaves to the rest of the plant.

  6: Meristem tissue - At the tips of roots and shoots; made up of cells that grow and differentiate into any type of cell needed.
• Plant Organs

  Specialised tissues in a plant are arranged to form organs, including:

  1: Leaves - Carry out photosynthesis.

  2: Stem - Transport substances around the plant; Support leaves.

  3: Roots - Take in water from the soil by osmosis and mineral ions from the soil by active transport.
• Structure of Leaf

  Upper Epidermis.

  Palisade Mesophyll.

  Spongy Mesophyll.

  Lower Epidermis.

  Guard Cells.

  Stomata.

  Xylem and Phloem.

  
• Upper Epidermis

  Thin and transparent to allow light to enter the palisade mesophyll for photosynthesis.

  Covered in waxy cuticle that prevents water from evaporating.
• Palisade mesophyll

  Cells are tightly packed with lots of chloroplasts to maximise photosynthesis.
• Spongy mesophyll

  Contain internal air spaces that increase surface area: volume ratio for diffusion of gases.
• Lower Epidermis

  Contains the guard cells and stomata for gas exchange and transpiration.
• Guard cells

  Control opening and closing of stomata.
• Stomata

  Where gas exchange takes place; carbon dioxide from air enters leaf via stomata and travels into palisade mesophyll for photosynthesis; oxygen produced as a waste product and leaves leaf via the stomata.

  Also where water is evaporated from.
• Xylem

  Transports water from the roots to the leaves for photosynthesis and for transpiration from the stomata.
• Phloem

  Transports dissolved sugars around the plant.
• Vascular bundles

  Contain the transport vessels, xylem and phloem.

  
• Transpiration

  Loss of water vapour from plant leaves by evaporation of water at mesophyll cells followed by diffusion of water vapour through the stomata.
• Factors affecting transpiration

  Air movement - when high, there is more transpiration as water vapour is removed from the air setting up a concentration gradient between the leaf and the air.

  Humidity - when high, there is less transpiration as the air is saturated with water vapour creating a weaker concentration gradient.

  Light intensity - when high, there is more transpiration as the guard cells respond to light.

  Temperature - when high, there is more transpiration as particles have more kinetic energy so water molecules diffuse faster.
• Investigating transpiration

  1: Cut a shoot underwater to prevent air entering xylem then place in tube.

  2: Set up apparatus, ensuring it is airtight then dry leaves of the shoot.

  3: Remove capillary tube to allow a single air bubble to form then place tube back.

  4: Set up environmental factor (airflow/humidity/light intensity/temperature) then leave plant to adapt to environment for 5 minutes.

  5: Record bubble's starting location, leave for a set period of time then record ending location.

  6: Change the intensity of the factor being tested, reset bubble by opening tap then repeat.
• Transpiration and stomata

  When availability of water is high, guard cells become turgid due to osmosis, causing stomata to open and water to be lost via transpiration.

  When less water is available, guard cells lose water by osmosis and become flaccid, closing stomata and stopping water loss via transpiration.

  Stomata tend to be on the underside of the leaf where it is shaded so there is less transpiration.
• Translocation

  Transport of dissolved sugars by the phloem from regions of production to regions of storage or use
• Factors affecting translocation

  During winter when plants have no leaves, phloem transports sugars from storage organs to other parts so respiration can continue without photosynthesis.

  The same occurs when a plant is growing.

  After the plant has regrown, leaves are photosynthesising again and producing more sugars so they are stored as starch again until needed.