Assessment Statement Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant Outline three differences between the structures of dicotyledonous and monocotyledonous plants Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils State that dicotyledonous plants have apical and lateral meristems Compare growth due to apical and lateral meristems in dicotyledonous plants 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

StructureFunction Epidermis Thin layer of cells for protection Xylem For transport of water & mineral ions Phloem For translocation of organic nutrients such as amino acids & sucrose Pith Storage and support Cambium layer of actively dividing cells (lateral meristem ) for the secondary growth Cortex Packaging tissue for storage and support

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 MonocotyledonsDicotyledons Parallel veins in narrow leaves Branching, net-like veins in broad leaves Embryo has ONE cotyledon Embryo has TWO cotyledons Flower parts (sepals & petals) arranged in threes Flower parts (sepals & petals) arranged in fours or fives Fibrous adventitious roots Tap root with lateral branches Vascular bundles scatted throughout the cortex Vascular bundles arranged in a ring around edge E.g. maize, wheat, oat E.g. bean, daisy, sunflower, pea

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 CO 2 to photosynthesizing cells and ease of removal of O 2 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

Modifications of roots, stems and leaves for different functions

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 meristems i.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 & lateral meristems 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