Plant Evolution Plants originated from green algae that lived in ponds that occasionally dried out.
Angiosperms Angiosperms have dominated the land for over 100 million years. Known as “flowering plants” There are about 250,000 known species of flowering plants living today. Most of our food comes from flowering plants Roots, such as beets and carrots Fruits of trees and vines, such as apples, nuts, berries, and squashes Fruits and seeds of legumes, such as peas and beans; Grains, such as rice, wheat, and corn
Angiosperms Divided into two groups: Names refer to the first leaves that appear on the plant embryo. Embryonic leaves are called seed leaves, or cotyledons: Monocots (embryo has one seed leaf) Dicots (embryo has two seed leaves)
Angiosperms Monocots: Orchids, bamboos, palms, and lilies, as well as grains and other grasses Leaves have parallel veins Stems have vascular tissues arranged in a complex array of bundles. Flowers have petals and other parts in multiples of three. Roots form a fibrous system (a mat of threads) that spread out below the soil surface. Make excellent ground cover that reduces erosion.
Dicots: True dicots include most shrubs and trees (except for conifers), as well as many food crops. Leaves have a multibranched network of veins Stems have vascular bundles arranged in a ring. Flower usually has petals and other parts in multiples of four or five. Large, vertical root (called a taproot) goes deep into the soil You can see this if you try to pull up a dandelion
Plant Body Composed of organs with various tissues reflective of their evolutionary history as land-dwelling organisms. Must draw resources from two environments: Water and minerals from soil CO 2 and light from air
Plant Body Plant body is divided up to two main parts: Subterranean part root Aerial part shoot
Plant Body Root system: Anchors in the soil, absorbs and transports minerals and water, and stores food. Monocots Fibrous root system consists of a mat of generally thin roots spread out shallowly in the soil Dicots have one main vertical taproot with many small secondary lateral roots growing outward. Both Monocots and Dicots have tiny projectsions called root hairs: Enormously increase the root surface area for absorption of water and minerals.
Plant Body Shoot system: Made up of stems, leaves, and adaptations for reproduction (flowers) Stems are parts of the plant that are generally above ground and support the leaves and flowers. Composed of: Nodes Points at which leaves are attached Internodes Portions of the stem between nodes Leaves are the main photosynthetic organs in most plants (green stems also perform photosynthesis) Consist of a flattened blade and a stalk, or petiole, which joins the leaf to a node of the stem.
Plant Body Shoot system (continued): Two types of buds that are undeveloped shoots: Terminal bud Found at the apex (tip) of the stem, has developing leaves and a compact series of nodes and internodes Axillary bud one of each of the angles formed by a leaf and the stem, are usually dormant.
Plant Body Apical dominance Results from the terminal bud producing hormones that inhibit growth of the axillary buds. By concentrating resources on growing taller, apical dominance is an evolutionary adaptation that increases the plant’s exposure to light Important where vegetation is dense. Removing the terminal buds usually stimulates growth of the axillary buds. Branching is important for increasing exposure the environment
Modified Roots, Stems, and Leaves Modified roots: Some plants have unusually large taproots that store food in carbohydrates such as startch: Carrots, turnips, sugar beets, and sweet potatoes Sugar Beet
Modified Roots, Stems, and Leaves Modified Stems: Stolon “runner”; has a horizontal stem that grows along the ground surface Plantlets form at nodes along their length, enabling a plant to grow asexually Example: strawberry Rhizomes Look like large, brownish, rootlike structures Horizontal stems that grown just below or along the soil surface Store food, and having buds, can also spread and form new plants Potato plant has enlarged structures specialized for storage called tubers (the potatoes we eat)
Modified Roots, Stems, and Leaves Modified stems (continued) Bulbs Modified stems that are also used for underground food storage (onions)
Modified Roots, Stems, and Leaves Modified Leaves: Tendrils Tips coil around a stem, help plants climb Examples: grapevines, peas Tendril- Pea Plant
Plant Tissues in Stems and Leaves Each plant organ- root, stem, or leaf- is made up of three tissue systems: Dermal Vascular Ground tissues
Plant Tissues in Stems and Leaves Dermal Tissue Forms an outer protective covering. Acts as first line of defense against physical damage and infectious organisms. Consists of a single layer of tightly packed cells called the epidermis: Epidermis of leaves and most stems is covered with a waxy layer called cuticle, which helps prevent water loss. Typical dicot leaf also has pores on its epidermis called stomata which allow CO2 exchange between the surrounding air and the photosynthetic cells inside the leaf. Surrounded by guard cells: Regulate the size of the stoma
Plant Tissues in Stems and Leaves Vascular Tissue: Made up of: Xylem type of vascular tissue that is made up of cells that transport water and dissolved ions from the roots to the leaves Phloem type of vascular tissue that is made up of cells that transport sugars from leaves or storage tissues to other parts of the plant
Plant Tissues in Stems and Leaves Vascular Tissue (continued): In the stem.. Vascular tissue forms vascular bundles Dicots arranged in a circle
Plant Tissues in Stems and Leaves Vascular Tissue (continued): In the leaf… Vascular tissue form network of veins In the veins, the xylem and phloem are continuous with the vascular bundles of the stem. Allows them to be in close contact with photosynthetic tissues, ensuring water and mineral nutrients from the soil are supplied, and that sugars made in the leaves are transported throughout the plant
Plant Tissues in Stems and Leaves Ground Tissue (continued): Accounts for the bulk of a young plant, by filling in spaces between the epidermis and vascular tissue. Functions include photosynthesis, storage, and support. Ground tissue inside vascular tissue is called pith Ground tissue external to vascular tissue is called cortex Dicot Stem
Plant Tissue in Stems and Leaves Ground Tissue (continued): Ground tissue of dicot stems… consists of both a cortex region and pith region Ground tissue of the leaf… Is called Mesophyll : Sandwiched between the upper and lower epidermis Consists mainly of photosynthesis cells Loosely arranged to provide air spaces which CO 2 and O 2 can circulate Main location of photosynthesis
Plant Growth Growth in plants is made possible by tissues called meristems. A meristem consists of cells that divide frequently, generating additional cells. Some products of this division remain in the meristem and produce still more cells, while others differentiate and are incorporated into tissues and organs of the growing plant.
Plant Growth Apical Meristems Meristems at the tips of roots and in the buds of shoots Cell division in the apical meristems produces the new cells that enable a plant cell to grow in length primary growth Enables roots to push through the soil and allows shoots to increase exposure to light and CO2. Growth occurs behind the root tip in three zones of primary growth: Zone of cell division, zone of elongation, and zone of maturation Zone of maturation brings about the three tissue systems (dermal, ground, and vascular)
Plant Growth Lateral meristems Associated with the increase in thickness of stems and roots secondary growth Caused by the activity of two cylinders of dividing cells that extend along the length of roots and stems: Vascular cambium Secondary growth adds layers of vascular tissue on both sides of the vascular cambium wood Cork cambium Outer cambium that forms the secondary growth of the epidermis cork