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Plant Science

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Land Plant Characteristics
•They provide protection for their embryos which has increased over time
•They have multicellular haploid and diploid phases
•They can be compared by the presence or absence of conductive tissue
Three Major Groups Of Land Plants
•Non-vascular
•Seedless vascular
•Seeded vascular
Non-Vascular Land Plants
•No conducting tissue
•Often grouped together as bryophytes
•Usually small and grow close to the ground
•Include mosses, liverworts, and hornworts
Seedless Vascular Land Plants
•Well-developed vascular tissue
•Do not produce seeds
•Include horsetails, ferns, club mosses, and whisk ferns
Seeded Vascular Land Plants
•Most living plant species are in this group
•Seeds contain an embryo, a supply of nutrients, and a protective outer coat
•Have extensive vascular tissue and include some of the world's largest organisms
Seeded Vascular Land Plants Are Divided Into
Gymnosperms and angiosperms
Gymnosperms
Have seeds that do not develop within an enclosed structure
Angiosperms
Have seeds that develop within a protective structure
Tissues of angiosperms
•Dermal tissue
•Ground tissue
•Vascular tissue
Dermal Tissue
This outer protective covering protects against physical agents and pathogenic organisms; it prevents water loss and may have specialized structures for various purposes
Ground Tissue
Consists mostly of thin-walled cells that function in storage, photosynthesis, support, and secretion
Vascular Tissue
Xylem and phloem carry out long-distance conduction of water, minerals, and nutrients within the plant and provide support
Root Tissues
•Absorb mineral ions and water from the soil
•Anchor the plant
•Have an epidermis that provides a protective outer layer
Root Cortex
•Involved in conducting water from the soil to the interior vascular tissue
•May also be modified to carry out storage functions
Root Endodermis
•Surrounds the vascular tissue
Stem Tissues
The plant region where leaves are attatched
Stem Node
The area of where a leaf joins the stem
Stem Internode
Area between two nodes
Stem Vascular Bundle
Consists of phloem, cambium, and xylem
Stem Epidermis
•Involved in protection
•Has pores called lenticels that allow gas exchange
Transporting Tissues Of The Stem
Xylem and phloem
Stem xylem
Mainly carries water and dissolved minerals from the roots to the leaves
Stem phloem
Transports organic nutrients throughout the plant
Stem cambium
An area of rapidly diving cells that differentiate into xylem and phloem
Stem cortex
It supports and may have storage functions
Stem Central Pith Region
A storage and support area
Leaf Tissues
•Involved in photosynthesis
•Have vascular tissue which includes xylem and phloem
•Xylem and phloem occur together in veins or vascular bundles
Leaf Cuticle
•A layer of wax as an outermost layer
•Protects against water loss and insect invasion
•If not present, the outermost layer is the epidermis which protects
Leaf xylem
Brings water to the leaves
Leaf phloem
Carries the products of photosynthesis to the rest of the plant
Palisade Mesophyll
•A densely packed region of cylindrical cells in the upper portion of the leaf
•Cells contain large numbers of chloroplasts to carry out photosynthesis
•Located in the upper portion of the leaf where light is most available
•Cells here allow maximum photosynthesis
Spongy Mesophyll
•Bottom portion of the leaf
•Consists of loosely packed cells with few chloroplasts
•Many air spaces in this area providing gas exchange surfaces
•Located just superior to the stomata allowing continuous channels for gas exchange
Stomata Or Stomatal Pores
•Occur on the bottom surface of leaves and they allow oxygen and carbon dioxide exchange
•This area receives less light with a resulting lower temperature
•Lower temperature minimizes water loss from the pores and the plant, thus the lower epidermis usually has a thinner cuticle than the upper epidermis
•The positioning of the epidermis is such that the remaining structures of the leaf are protected and supported
Guard Cells
Control the opening and closing of the stomata
Leaf Veins
•Are distributed throughout the leaf so as to transport raw materials and products of photosynthesis
•Occur roughly in the middle of the leaf so as to be near all cells
Two Classes Of Angiosperms
Monocots and dicots
Monocots
•Parallel venation in leaves
•3 flower parts or multiples of 3
•Seeds contain only one cotyledon (seed leaf)
•Vascular bundles arranged throughout the stem
•Root system mainly fibrous
•Pollen grain with one opening
Dicots
•Netlike venation pattern in leaves
•4 or 5 flower parts or multiples of 4 or 5
•Seeds contain two cotyledons (seed leaves)
•Vascular bundles arranged as a ring in the stem
•Root system involves a taproot (main root)
•Pollen grain with three openings
Monocot Characteristics
•Veins usually parallel
•Floral organs usually in multiples of three
•One cotyledon
•Vascular tissue scattered
•Root system usually fibrous (no main root)
•Pollen grain with one opening
Dicot Characteristics
•Veins usually netlike
•Floral organs usually in multiples of four or five
•Two cotyledons
•Vascular tissue usually arranged in a ring
•Taproot (main root) usually present
•Pollen grain with three openings
Two Types Of Root System
Taproot and fibrous
Prop Roots
Thick adventitious roots that grow from the lower part of stem and brace the plant ex. corn
Storage Roots
Specialized cells within the root store large quantities of carbohydrates and water ex. carrots and beets
Pneumatophores
Produced by plants that live in wet places, these roots extend above the soil or water surface and facilitate oxygen uptake ex. mangroves and cypress trees
Buttress Roots
Large roots that develop near the bottom of trees to provide stability ex. fig tree
Bulbs
Vertical, underground stems consisting of enlarged bases of leaves that store food ex. onions
Tubers
Horizontally growing stems below ground that are modified as carbohydrate-storage structures ex. potatoes
Rhizomes
Horizontal stems that grow just below the surface to allow plant spreading ex. ginger plant
Stolons
Horizontal stems growing above ground that allow a plant to reproduce asexually ex. strawberry plants
Tendrils
Structures that coil around objects to aid in support and climbing ex. pea plants produce tendrils from leaves
Reproductive Leaves
Produce tiny plants along the leaf margins that fall to the ground and take root in the soil ex. kalanchoe plants
Bracts Or Floral Leaves
Coloured modified leaves that surround flowers and attract insects for pollination ex. poinsettia
Spines
Reduce water loss, may be associated with modified stems that carry out photosynthesis ex. cacti
Merisptems
Two types of this tissue in dicots: Apical meristems and lateral meristems
Apical Meristems
•Sometimes referred to as primary meristems, occurs at the tips of roots and stems
•Produces primary tissues and causes primary growth
•Primary growth allows the root to extend throughout the soil
•Allows the stem to grow longer and so increases exposure to light and carbon dioxide
•Type of growth results in herbaceous, non-woody stems and roots
Lateral Meristems
•Allow growth in thickness of plants
•Secondary growth
•Two types of lateral meristem: vascular cambium and cork cambium
Vascular Cambium (Lateral Meristem)
•Produces secondary vascular tissue
•Lies between the xylem and the phloem in the vascular bundles - on the inside it produces secondary xylem which is a major component of wood, on the outisde it produces secondary phloem
Cork Cambium (Lateral Meristem)
Occurs within the bark of a plant and produces the cork cells of the outer bark
Tropisms
•Growth or movement responses to directional external stimuli
•May be positive (towards the stimulus) or negative (away from the stimulus)
•Common stimuli for plant tropisms include chemicals, gravity, touch, and light
•Generally plants have positive phototropism in stems and negative phototropism in roots
Auxins
•Are plant hormones that cause the positive phototropism of plant shoots and seedlings
•Found in the embryos of seeds, the meristems of apical buds and young leaves
•These hormones only work on plant cells that have auxin receptors
•Increase the flexibility of plant cell walls in young developing shoots
Root Cap
Important in protecting the apical meristem during primary growth of the root through the soil
Three Root Zones
Zone of cell division, zone of elongation, and zone of maturation
Zone Of Cell Division
New undifferentiated cells are forming, M phase of the cell cycle
Zone Of Elongation
Cells are enlarging in size, corresponds to G, of the cell cycle
Zone Of Maturation
Cells are becoming functional to the plant
Water Must Pass Through Several Regions Of The Root Before It Enters The Vascular Cylindar
Epidermis to cortex to vascular cylinder
Water And Root Hairs
•Water moves into the root hairs because they have a higher solute concentration and a lower water concentration than the surrounding soil. Therefore the water moves through the plasma membranes into the root hair cells
•Enters by osmosis
Two Routes Of Water Movement To The Vascular Cylinder
•If water moves from cell to cell, it is said to move by the symplastic route
•If the water is moves through the cell walls and the extracellular spaces, it is said to move by the apoplastic route
Mineral Ions From Soil To Root
•Diffusion of mineral ions and mass flow of water in the soil carrying these ions
•Aid provided by fungal hyphae
•Active transport
•When there is a higher concentration of mineral outside the root than inside, the mineral moves to the root
•These minerals are dissolved in and move via water
Fungal Hyphae
Fungal hyphae form a cover over the surface of young roots
Ions
•Often there is a higher concentration of various mineral ions inside the plant than outside
•Ions cannot cross the lipid bilayer
Proton Pump
•Most important active transport protein in the plasma membranes of plant cells
•The proton pump uses energy from ATP to pump hydrogen ions out of the cell
•This results in a higher hydrogen ion concentration outside the cell than inside. This creates a negative charge inside the cell
•This gradient results in the diffusion of hydrogen ions back into the cell
•The voltage difference is called a membrane potential
•The hydrogen ion gradient and the membrane potential represent forms of potential energy that can be used to absorb mineral ions
Terrestrial Plants
•Attain enormous sizes, three species of tree that are among Earth's largest living things:
•The redwood sequoia
•The giant eucalyptus
•The Douglas fir
Support In Terrestrial Plants
Thickened cellulose, cell turgor pressure, and lignified xylem
Light (Transpiration)
Speeds up transpiration by warming the leaf and opening stomata
Humidity (Transpiration)
Decreasing humidity increases transpiration because of the greater difference in water concentration
Wind (Transpiration)
Increases the rate of transpiration because humid air near the stomata is carried away
Temperature (Transpiration)
Increasing temperature causes greater transpiration because more water evaporates
Soil Water (Transpiration)
If the intake of water at the roots does not keep up with transpiration, turgor loss occurs and the stomata close this decreases transpiration
Carbon Dioxide (Transpiration)
High carbon dioxide levels in the air around the plant usually cause the guard cells to lose turgor and the stomata to close
Xerophytes
Plants adapted to arid climates
Stomata
Open and close because of changes in the turgor pressure of the guard cells that surround them