Lecture 4

• There are three tissue systems in vascular plants: dermal tissue, vascular tissue, and ground tissue
• Dermal tissue is a single layer on the outside of the organism, it secretes the cuticle
• Vascular tissue are the xylem and phloem which support and supply the plant
• Ground tissue is the bulk of young plants, it fills the space between the dermal and vascular tissues
• Ground tissue is mostly parenchyma which functions in storage, photosynthesis and support of plants
• The epidermis is dermal tissue
• Parenchyma, collenchyma, and sclerenchyma are ground tissues
• Tracheids and vessel elements, and sieve elements are vascular tissues
• Epidermal cells are the outermost cells, they are a single layer that covers the leaves, stems and roots of non-woody plants or plant parts
• Epidermal cells waterproof plants, protect plants from pathogens such as viruses, bacteria and fungi
• Epidermal cells can have specialized roles such as trichomes, nectary and guard cells
• The cuticle is formed by epidermal cells, the outermost part is wax
• The cuticle protects the plant from water loss, pathogens and ultraviolet radiation
• The wax on chamomile flowers is arranged to give it it's white colour
• The wax on pitcher plants is arranged to help it capture its prey
• Guard cells open and close to allow for gas exchange
• Trichomes are hairs that protect plants from harm
• Secretory trichomes secrete oils to defend against insects
• A nectary produces nectar
• Parenchyma cells have many often specialized functions including most metabolic processes such as photosynthesis, storage, secretion, and food storage
• Parenchyma cells are a type of ground tissue when in the stem and roots
• Parenchyma cells usually lack a secondary wall
• Parenchyma cells can often divide and differentiate at maturity
• Examples of parenchyma cells include fruit flesh, endosperm, pith and cortex of stems and roots, and chloroplast containing cells inside leaves
• Collenchyma cells provide support, especially to young and growing organs
• Collenchyma cells are a type of ground tissue
• Collenchyma cells have a thick and uneven primary wall
• Collenchyma cells do not have a secondary wall which allows them to expand
• Collenchyma cells always occur just below the epidermis
• Collenchyma cells often occur in strands
• Collenchyma cells are alive at maturity and can elongate
• Examples of collenchyma cells include the celery leaf midrib and petiole
• The ribs we feel on a celery stalk are each underlayed by a strand of collenchyma
• Sclerenchyma cells provide support and protection to tissues that are no longer elongating
• Sclerenchyma cells are a type of ground tissue
• Sclerenchyma cells have a thick secondary wall with lignin
• Sclerenchyma cells cannot elongate at maturity and may be dead
• Sclerenchyma cells have two forms: fibers and sclereids
• Sclereids are boxier and irregular in shape, they have very thick lignified secondary walls
• Sclereids give nutshells their hardness and give pears their grittiness