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.
Draw a labelled plan diagram to show the distribution of tissues in the stem of a dicotyledonous plant
Draw a labelled plan diagram to show the distribution of tissues in the leaf of a dicotyledonous plant.
Differences between the structures of dicotyledonous &monocotyledonous plants
Relationship between the distribution of tissues in the leaf & their functions
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 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 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 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 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 • 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 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 • 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
any questions on plant structure & growth • Thank you