BIOLOGY

• Insectivorous plants possess highly modified leaves that trap and digest insects to obtain needed nutrients.
• The epidermis is just behind the growing tip of roots and is covered with root hairs, which are outgrowths of the epidermal cells.
• The individual parts of flowers—carpels, stamens, petals, and sepals—are all modified leaves that have taken on reproductive functions.
• The leaf blade is connected to the stem through a narrowed portion called the petiole, or stalk, which consists mostly of vascular tissue.
• The portions of the stem between nodes are called internodes.
• Internally, roots consist largely of xylem and phloem, although many are highly modified to carry out specialized functions.
• Such roots have an abundance of parenchyma tissue.
• The spaces in the mesophyll are filled with air, from which the cells absorb carbon dioxide and into which they expel oxygen.
• Many specialized forms of leaves occur.
• Some roots are important food and storage organs, such as beets, carrots, and radishes.
• This growing point also gives rise to new leaves, which surround and protect the stem tip, or apical bud, before they expand.
• Stems increase in length through the activity of an apical meristem at the stem tip.
• The function of roots is to anchor the plants substrate and to absorb water and minerals.
• A vascular network runs through the mesophyll, providing the cell walls with water and removing the food products of photosynthesis to other parts of the plants.
• The primary photosynthetic organ of most plants, leaves are usually flattened blades that consist, internally, mostly of parenchyma tissue called the mesophyll, which is made up of loosely arranged cells with spaces between them.
• Appendages called stipules are often present at the base of the petiole.
• Apical buds of deciduous trees, which lose their leaves during part of the year, are usually protected by modified leaves called bud scales.
• Stems are usually above ground, grow upward, and bear leaves, which are attached in a regular pattern at nodes along the stem.
• The mesophyll is bounded by the upper and lower surface of the leaf blade, which is covered by epidermal tissue.
• Some leaves are modified as spines, which help protect plants from predators.
• The root hairs increase the surface area of the roots and serve as the surface through which water and nutrients are absorbed.
• Epidermal cells vary greatly in function and structure.
• Vessels usually are shorter and broader than tracheids, and in addition to pits they have perforation through which water and dissolved nutrients may freely pass.
• The phloem, or food-conducting tissue, consists of cells that are living at maturity.
• The cells of parenchyma tissue carry out many specialized physiological functions, such as photosynthesis, storage, secretion, and wound healing.
• The parenchyma tissue is found throughout the plants and is living and capable of cell division at maturity.
• Although the sieve elements contain cytoplasm at maturity, the nucleus and other organelles are lacking.
• Associated with the sieve elements are companion cells that do contain nuclei and that are responsible for manufacturing and secreting substances into the sieve elements and removing waste products from them.
• Two types of sieve elements occur: sieve cells, with narrow pores in rather uniform clusters on the cell walls, and sieve-tube members, with larger pores on some walls of the cell than on others.
• The dermal system consists of the epidermis, or outermost layer, of the plants body.
• Collenchyma tissue is made up of cells with unevenly thickened primary cell walls and is pliable, functioning as support tissue in young, growing portions of plants.
• Sclerenchyma tissue consists of cells that lack protoplasts at maturity and have thick secondary walls usually containing lignin.
• The xylem also stores food and helps support the plants.
• These organs all contain the three kinds of tissue systems mentioned above, but they differ in the way the cells are specialized to carry out different functions.
• The body of a vascular plants is organized into three general kinds of organs, stems, and leaves.
• Elongated cells, with tapered ends and secondary walls, both types lack cytoplasm and are dead at maturity.
• The epidermis forms the skin of the plants, covering the leaves, flowers, roots, fruits, and seeds.
• The principal cells of phloem, the sieve elements, are so called because of the clusters of pores in their walls through which the protoplasts of adjoining cells are connected.
• The vascular tissue system consists of two kinds of conducting tissues: the xylem, responsible for conduction of water and dissolved mineral nutrients, and the phloem, responsible for conduction of food.
• The ground, or fundamental, tissue systems of plants consist of three types of tissue: parenchyma, collenchyma, and sclerenchyma.