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9.1 Plant structure & growth. Assessment Statement . 9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant. 9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.

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assessment statement
Assessment Statement
  • 9.1.1 Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant.
  • 9.1.2 Outline three differences between the structures of dicotyledonous and monocotyledonous plants.
  • 9.1.3 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues.
  • 9.1.4 Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils.
  • 9.1.5 State that dicotyledonous plants have apical and lateral meristems.
  • 9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants.
  • 9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth.
slide3
Draw a labelled plan diagram to show the distribution of tissues in the stem of a dicotyledonous plant
slide5
Draw a labelled plan diagram to show the distribution of tissues in the leaf of a dicotyledonous plant.
relationship between the distribution of tissues in the leaf their functions1
Relationship between the distribution of tissues in the leaf & their functions
  • palisade cells contain lots of chloroplasts for absorbing light energy
  • palisade cells arranged “end-on” to ensure each cell receives maximum amount of light
  • no chloroplasts in upper epidermis to ensure light reaches palisade layer
  • chloroplasts present in spongy mesophyll cells to ‘mop up’ any unused light
  • waxy cuticle to prevent excessive water loss from epidermal cells by evaporation
  • air spaces in spongy mesophyll layer to ensure adequate supply of CO2 to photosynthesizing cells and ease of removal of O2
  • stomata located on leaf lower surface to allow gases in and out of leaf
  • presence of vascular bundle to supply water from roots & for removal of products of photosynthesis
bulbs
Bulbs
  • bulbs are underground storage structures that contain reserves of nutrients to ensure survival from season to season
  • consists of layers of fleshy leaf bases closely packed on a short stem
  • the leaf cells are packed with starch grains & other nutrients
  • E.g. onion, garlic
stem tubers
Stem tubers
  • stem tubers are swollen tip of rhizome or underground stem
  • they store carbohydrate for growth of new plants during the next season
  • the cortex cells in the stem are packed with starch grains & other nutrients
  • E.g. Irish potato
storage roots
Storage roots
  • storage roots contain stores of carbohydrate for the plant to use later
  • they are usually swollen tap roots (primary roots)
  • the cortex cells in the root are packed with starch grains & other nutrients
  • e.g. carrot, sweet potato
tendrils
Tendrils
  • tendrils are modified leaves
  • tendrils are slender stem-like structure to curl around to a support
  • they are sensitive to touch, so faster growth occurs on the opposite side
  • tendrils help support the plant
  • E.g. vine, ivy
apical and lateral meristems
Apical and lateral meristems
  • plants grow at meristemsi.e. regions of unspecialised cells that retains ability to divide & differentiate into any type of cells
  • after cytokinesis, one daughter cell differentiates & the other remains in the meristem
  • dicotyledonous plants have apical &lateralmeristems
  • apical meristems, are found at the tips of shoot & root, they result in growth in length of the plant – primary growth
  • lateral meristems, are found at the tips of cambium in the vascular bundles, they result in increase the diameter or girth of the plant – secondary growth
phototropism
Phototropism
  • phototropism is plant's response to directional light by either growing towards it or away from it
  • there are two types of phototropism:
    • positive phototropism, i.e. growth of a plant’s shoot towards light, putting the leaves in a better position for photosynthesis
    • negative phototropism, i.e. growth of a plant's roots away from light
  • phototropic responses are controlled by auxins, plant growth hormones
role of auxin in phototropism
Role of auxin in phototropism
  • auxin is a plant hormone produced by the tip of the shoot (stem)
  • auxin causes transport of hydrogen ions (H+) from cytoplasm to cell wall
  • decrease in pH due to H+ pumping breaks bonds between cell wall fibres, making cell walls flexible & extensible
  • auxin makes cells enlarge, elongate & grow
  • gene expression is also altered by auxin to promote cell growth
  • in positive phototropism, growth occur towards the source of light
  • shoot tip senses the direction of brightest light, auxin are moved to side of stem with least light i.e. darker side
  • higher concentration of auxin causes cells on dark side to elongate & grow faster than on the illuminated side - hence the shoot bends towards the source of light