Ch9

• Organ systems of plants and animals are composed of one or more types of organs
• Plant bodies are composed of organ systems, organs, tissues, and specialized cells
• Organs are composed of one or more types of tissues
• Tissues are composed of one or more types of adherent, related cells
• Stems, roots, and leaves are the basic plant organs
• Stems are considered the fundamental organ as leaves and roots arise from stems
• Fossil evidence indicates that plants acquired stems first, followed by roots and leaves
• Shoot system and root system are the two main organ systems in plants
• Root system consists of one or more main roots, often branched
• Shoot system includes branching stems bearing buds, flowers, and fruits enclosing seeds
• Buds are young, unexpanded shoots that can develop into new branches or flowers
• Buds contain a tiny stem, miniscule leaves, and a terminal growth point
• Plasmodesmata are narrow cytoplasmic connections linking plant tissue cells
• Symplastic continuity in tissues allows for continuous cytoplasm and chemical communication
• Plasmodesmata contain an inner tube of endoplasmic reticulum and various proteins
• Plant tissues are composed of one to several types of specialized cells
• Simple tissues like parenchyma and collenchyma consist of one cell type
• Parenchyma cells store starch and have various roles like wound healing and propagation
• Collenchyma provides flexible support with unevenly thickened cell walls containing pectin
• Sclerenchyma is composed of sclereids and fibers with evenly thickened walls containing lignin
• Xylem supports plants and conducts water and minerals, while phloem transports sugars and organic compounds
• Xylem transports sugars and other organic compounds in a watery solution
• Xylem includes several types of cells: sclerenchyma, parenchyma, and pipelinelike arrays of specialized water-conducting cells with walls reinforced with lignin
• Phloem tissue contains sclerenchyma, parenchyma, and arrays of specialized food-conducting cells
• Specialized cells arise through the process of differentiation
• Specialized cells contain the same genetic material found in all cells of the same organism but differ in the sets of genes that are expressed
• Plants produce hormones like auxin, cytokinin, gibberellic acid, absicic acid, and ethylene that influence growth and development
• Internal and external signals influence cell specialization, tissue, and organ development by inducing changes in gene expression
• Differentiation in plants involves asymmetric cell divisions and chemical influences from other cells
• Plants grow by producing new cells and enlarging existing cells
• Mitosis produces new cells in plants, localized in specific regions
• Plants grow in length by the enlargement of new cells produced at their tips (apices) by apical meristems
• Primary meristems in plants generate new length-increasing tissues known as primary tissues
• Primary tissues in plants include dermal, vascular, and ground tissues
• Shoot architecture in plants is modular, composed of alternating nodes and internodes
• Secondary meristems in woody plants produce secondary tissues like wood and bark, increasing plant girth
• Cell expansion in plants involves the uptake of water into the central vacuole, accompanied by cell-wall expansion
• Expansins unlock linkages between cell-wall polysaccharides allowing cell wall stretching for cell enlargement
• Aquaporins in cell membranes increase the rate of water uptake for cell expansion
• Secondary meristems in woody plants:

  • Vascular cambium (black dashed line) and cork cambium (white dashed line)
  • Produce wood and bark
  • Increase the girth of woody plants
  • Vascular cambium forms wood to the inside and inner bark tissues to the outside
  • Cork cambium contributes to the outer bark