Plant structure and growth Topic 9.1
Assessment Statements • 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 modification 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.
Seeded vascular plants • Gymnosperms – have seeds that do not develop within an enclosed structure • Angiosperms – have seeds that develop within a protective structure
Meristematic tissue • All 3 tissue types derive from meristematic tissue • Composed of aggregates of small cells that have the same function as stem cells in animals • When these cells divide, one cell remains meristematic (initial) while the other (derivative) is free to differentiate and become part of the plant body
Root tissue • Absorbs mineral ions and water from the soil • Anchor the plant • Provide food storage epidermis cortex xylem endodermis phloem
Stem tissue • Plant region where leaves are attached • Area where leaf joins is called a node and the area between two nodes is called the internode
Leaf tissue Upper epidermis • Involved in photosynthesis • Consist of the blade and a stalk called the petiole that attaches the blade to the stem Cuticle (wax) Palisade mesophyll xylem Spongy mesophyll phloem Vascular bundle Stomatal pores
Functions of tissues in relation to their position in the leaf • The palisade mesophyll is located in the upper portion of the leaf where light is most available. The cells of this region are chloroplast rich, thus allowing for maximal photosynthesis. • Veins are distributed throughout the leaf so as to transport raw materials and products of photosynthesis. The veins occur roughly in the middle of the leaf so as to be near all cells. • The spongy mesophyll is located just superior to the stomata allowing continuous channels for gas exchange. • The stomatal pores are on the bottom of the leaf. This area receives less light with a resulting lower temperature. The lower temperature minimizes water loss from the pores and the plant.
Meristems • Plants show growth throughout their entire life • Continual pattern of growth is referred to as indeterminate • Some plants are annuals and complete their life cycle in one year • Other plants are biennials and take two years to complete their life cycle • Perennials live many years and when they die it is usually due to infection or some environmental factor • Reason for indeterminate growth is due to meristematic tissue
Dicot meristematic tissue: apical and lateral • Apical meristems • Occurs at tips of roots and stems • Produces primary tissues and causes primary growth which allows the root to extend throughout the soil • Allows stem to grow longer • Herbaceeous, non-woody stems and roots • Lateral meristems • Allow growth in thickness of plants • Woody plants • Two types • Vascular cambium produces xylem/phloem and secondary xylem which produces wood • Cork cambium produces cork cells of outer bark
Phototropism • Tropisms are growth or movement responses to directional external stimuli • may be positive (towards stimulus) or negative (away from stimulus) • Common stimuli: chemicals, gravity, touch, and light • Phototropism means plant growth in response to light • Plant stems exhibit positive phototropism and roots demonstrate negative phototropism
Auxins • Auxins are plant hormones that cause the positive phototropism of plant shoots and seedlings • found in the embryos of seeds, the meristems of apical buds and young leaves • Work only on plant cells that have auxin receptors • Increase flexibility of plant which enables cell elongation on the side of the shoot necessary to cause growth towards the light • Auxin is redistributed to the stem side away from the light source causing a curvature toward the light source • Called indoleacetic acid (IAA)