Plants: Forms and Functions [BIOLOGY]

• Major Groups of Angiosperms

  Monocots

  • one cotyledon
  • parallel veins
  • Vascular tissue scattered in a complex arrangement
  • Floral parts are usually in multiples of 3
  • fibrous root system
• Major Groups of Angiosperms

  Eudicots

  • 2 cotyledons
  • branched veins
  • Vascular tissue arranged in rings
  • Floral parts usually in multiples of 4 or 5
  • Taproot usually present
• Typical Plant Organs

  A root anchors a plant in the soil, absorbs and transports water and minerals, and stores carbohydrates. Together, all the roots of a plant make up the root system. Near the tips of the root are tiny finger-like projections called root hairs that increase the surface area, allowing more efficient absorption of water and minerals.
• Typical Plant Organs

  The shoot system of a plant is made up of stems, leaves, and structures for reproduction, which in angiosperms are flowers.
• Typical Plant Organs

  The stems bear the leaves and buds. A stem has nodes, points at which leaves are attached, and internodes, portions of the stem between nodes. The leaves are the main photosynthetic organs in most plants, as green stems can also perform photosynthesis. Most leaves consist of a flattened blade and a stalk, or petiole, which joins the leaf to a node of the stem.
• Typical Plant Organs

  The buds of a plant are undeveloped shoots. When a plant stem is growing in length, the terminal bud (or apical bud) at the tip of the stem has developing leaves and a compact series of nodes and internodes. The axillary buds, one in each of the crooks formed by a leaf and the stem, are usually dormant. In many plants, the terminal bud produces hormones that inhibit the growth of the axillary buds, a phenomenon called apical dominance: allows plants to grow taller, increasing the exposure to light. .
• Modified Plant Organs

  Modified stems include that of a strawberry, which has a horizontal stem called a stolon or runner that grows along the ground. Ginger is another type of modified stem, which looks like a root-like structure called a rhizome, horizontal stems that grow below the soil surface
• Modified Plant Organs

  A potato has rhizomes that end in enlarged structures specialized for storage called tubers (which are the ones we eat). Potato “eyes” are axillary buds on the tubers that can grow, so you may try planting them.
• Modified Plant Organs

  Plant bulbs, meanwhile, are underground shoots containing swollen leaves that store food (for example, an onion). Other modified plant leaves include tendrils, which help vines cling to solid structures, while some grasses and monocots have long leaves without petioles. Other eudicots have enormous petioles--the stalk we eat, as in celery. The spines of cactuses are actually modified leaves that protect them from being eaten; in turn, the large green stem acts for photosynthesis and water storage
• 3 types of plant tissue system

  • Dermal
  • Vascular
  • Ground
• A tissue system is made of one or more tissues organized into a functional unit within a plant. Each plant organ is made up of three tissue systems--dermal, vascular, and ground--which are arranged differently in leaves, stems, and roots.
• The dermal tissue system is the plant’s outer protective covering, like an animal’s skin. In nonwoody plants, the dermal tissue is made of a single layer of tightly packed cells called the epidermis. On leaves and most stems, the dermal cells secrete a waxy coating called the cuticle which helps prevent water loss
• The vascular tissue system is made up of the xylem and phloem tissues which provide support and long-distance transport between the root and shoot systems.
• Tissues that are neither dermal nor vascular make up the ground tissue system. The ground tissue system makes up most of the bulk of a young plant, filling the spaces between the epidermis and vascular tissue system. Ground tissue internal to the vascular tissue is called pith, while those external to the vascular tissue are called the cortex. The ground tissue system has many functions such as photosynthesis, storage, and support
• Roots

  Water and minerals absorbed from the soil must enter through the epidermis. In the center of the root, the vascular tissue systems form a vascular cylinder, with xylem cells radiating from the center like spokes of a wheel and phloem cells filling in the wedges between the spokes. The ground tissue system of the root, between the vascular cylinder and epidermis, is made up entirely of the cortex. Cortex cells store food and take up minerals that enter the root. The innermost layer of the cortex is the endodermis, a cylinder one cell thick.
• Roots

  The monocot root also shares similarities with eudicots in an outer layer of the epidermis which surrounds a large cortex, with a vascular cylinder at the center. The difference is that the monocot vascular tissue is made of a central core of cells surrounded by a ring of xylem and phloem
• Stems

  The stems of eudicots look quite different from monocots. Both stems have vascular tissue systems arranged in vascular bundles but in a monocot, the bundles are scattered whereas in a eudicot they are arranged in a ring that separates the ground tissue into cortex and pith regions. The cortex fills the space between the vascular ring and epidermis while the pith fills the center of the stem and is often important in food storage. A monocot stem’s ground tissue is not separated into these regions due to the vascular bundles not forming a ring
• Leaf

  A typical eudicot leaf’s epidermis is interrupted by tiny pores called stomata (singular, stoma) which allow gas exchange (CO2 and O2 ) between the plant and the surrounding air. Also, most of the water vapor lost by a plant passes through the stomata. Each stoma is flanked by two guard cells which are specialized epidermal cells that regulate the opening and closing of the stoma.
• Leaf

  The ground tissue of the leaf is called the mesophyll, found between the upper and lower epidermis. The mesophyll contains mainly cells specialized for photosynthesis. In a typical eudicot leaf, the cells in the lower area of a mesophyll are loosely arranged, with a labyrinth of air spaces through which CO2 and O2 circulate. The air spaces near the stoma become larger to facilitate gas exchange with the outside environment. In many monocots’ and other eudicots' leaves, the mesophyll is arranged in distinct upper and lower areas
• Veins

  The vascular tissue system of both monocots' and eudicots' leaves is made up of a network of veins, which is a vascular bundle composed of xylem and phloem tissues surrounded by a protective sheath of cells. The veins’ xylem and phloem are in close contact with the leaf’s photosynthetic tissues and ensure those tissues are supplied with water and mineral nutrients from the soil and that sugars made in the leaves can be transported throughout the plant. The vascular structure also acts as a support for the shape of the leaf
• Types of Plant Cell

  • Parenchyma cell
  • Collenchyma cell
  • Sclerenchyma cell
• Parenchyma cells are the most abundant cell type in most plants. They usually have only primary cell walls that are thin and flexible. Parenchyma cells perform most metabolic functions of the plant. They can also divide into other types of plant cells under certain conditions.
• Collenchyma cells resemble parenchyma cells in lacking secondary walls, but they have unevenly thickened primary cell walls. The cells provide flexible support in actively growing parts of the plant with young stems and petioles often having collenchyma cells just below their surface. These living cells elongate as stems and leaves grow.
• Sclerenchyma cells have thickened secondary walls usually strengthened with lignin, an important chemical component of wood. Mature sclerenchyma cells cannot elongate and thus are found in regions of the plant that have stopped growing in length. As such, when they mature, most sclerenchyma cells die and their remaining cell walls support the plant the way steel beams do for a building’s interior
• Sclerenchyma cells can be fiber, long and slender cells usually arranged in strands. These fiber cells are found in commercially important plants such as hemp fibers, used for making rope and clothing, and flax fibers which are woven into linen. Sclereids are shorter than fiber cells but have thick, irregular, and very hard cell walls. Sclereids impart the hardness to nutshells and seed coats and the gritty texture we feel when touching a pear
• Xylem and Phloem Tissues

  The xylem tissue of angiosperms includes two types of tubular water-conducting cells: tracheids, which are long, thin cells with tapered ends; and vessel elements which are wider, shorter, and less tapered. Chains of tracheids or vessel elements aligned end-to-end to form a system of tubes that convey water from the roots to the stems and leaves. When mature, the xylem tissues die and leave behind their cell walls which allows water transport.
• Xylem and Phloem Tissues

  Food-conducting cells known as sieve-tube elements are also arranged end-to-end and are part of the phloem tissue. But unlike water-conducting cells, sieve tube elements remain alive at maturity but lose most of their organelles. This reduction in cell content allows them to facilitate the transport of nutrients.
• Xylem and Phloem Tissues

  The end walls between sieve-tube elements are called sieve plates and have pores that allow fluid to flow from cell to cell along the sieve tube. Alongside each sieve-tube element is a companion cell, which produces and helps transport proteins to their connected sieve-tube element.The end walls between sieve-tube elements are called sieve plates and have pores that allow fluid to flow from cell to cell along the sieve tube. Alongside each sieve-tube element is a companion cell, which produces and helps transport proteins to their connected sieve-tube element.
• Although plants are stationary, they still respond to the environment by altering their growth. Whereas animals are characterized by a determinate growth, where they cease to grow after reaching a certain size, most plants can continue to grow so long as they live, a condition called indeterminate growth. Indeterminate growth, however, does not mean plants are immortal.
• Flowering plants can be characterized based on their life cycles. Annual plants emerge from seeds, grow, and die in a single year or in a growing season. Biennials complete their life cycle in two years, with flowering and seed production occurring in the second year. Perennials are plants that live and reproduce for many years.
• Types of Plant Growth

  • Primary
  • Secondary
• Primary Growth

  Plants can keep growing because of tissues called meristems, which contain unspecialized cells that divide when conditions permit. Meristems at the tips of roots and buds of shoots are called apical meristems that enable a plant to lengthen in a process called primary growth.
• Primary Growth

  Primary growth in plants can be seen when viewing a slide of an onion root under a microscope. The tip of the root is covered by a root cap that protects the actively dividing cells of the apical meristem. Growth in length occurs just behind the root tip where three zones of primary growth can be observed. These are the zones of cell division, elongation, and differentiation. These zones can overlap with no sharp boundaries between them.
• Primary Growth

  The zone of cell division includes the apical meristem and the cells derived from it, which also include the cells of the root cap. In the zone of elongation, cells grow longer and this allows the root to dig deeper into the soil. The three tissue systems, which we discussed earlier, complete their development in the zone of differentiation.
• Primary Growth

  The same elongation process also pushes the shoot of a plant upward. When viewing the tip of a young, growing shoot under a microscope, you will be able to observe the apical meristem as a dome-shaped mass of dividing cells at the tip of the terminal bud. Elongation occurs below this meristem which causes the shoot to lengthen upwards. As the apical meristem advances upward, some of its cells remain behind, becoming axillary bud meristems at the base of the leaves
• Secondary Growth

  Woody plants grow in diameter in addition to length, thickening in regions where primary growth has ceased. This increase in thickness of stems and roots is called secondary growth and is due to the activity of dividing cells in the lateral meristems. The dividing cells are arranged into two cylinders, the vascular cambium, and the cork cambium
• Secondary Growth

  The vascular cambium is a thin cylinder of meristem cells between the primary xylem and primary phloem. It is wholly responsible for the production of secondary growth. Secondary growth involves adding layers of vascular tissue on either side of the vascular cambium.
• Secondary Growth

  Tissues produced by secondary growth are called secondary tissues with the vascular cambium giving rise to two new tissues: the secondary xylem to its interior and secondary phloem to its exterior. The secondary xylem makes up the wood of a tree and the annual layering of the secondary xylem results in tree rings.
• Secondary Growth

  When secondary growth begins, the epidermis is shed and replaced by a new outer layer called cork. Mature cork cells are dead and have thick, waxy walls that protect underlying tissues from water loss, physical damage, and pathogens. Cork is produced by the cork cambium, which first forms from parenchyma cells in the cortex.
• Secondary Growth

  Everything external to the vascular cambium is called bark. Its main components are the secondary phloem, the cork cambium, and the cork. The youngest secondary phloem acts for sugar transport, while the older secondary phloem dies along with the cork cambium