Plant Structure and Growth
Plant Anatomy
Plants have tissues, organs, and organ systems just like any other multicellular organism.
Plants generally have 3 major organs
-Roots - Used for water and mineral absorption underground
-Stems - Involves growth, holds leaves, and holds flowers
-Leaves - Performs photosynthesis
The Roots make up an organ system known as the Root system
-Roots:
-Anchor the plant to the ground
-Absorb water and minerals
-And stores carbohydrates
-Large plants (Like trees) have a taproot
-A taproot is a long, strong, vertical root that penetrates deep into the soil
-The rest of the root system grows out from the sides of the taproot
-The roots growing out of the taproot are known as lateral roots
-Having a taproot allows a plant to grow taller
-Being taller not only helps with photosynthesis but it can also help with pollen distribution
-Taproots also help prevent a plant from getting uprooted
-Other plants have fibrous roots
-Most monocots have a fibrous root system
-Plants with a fibrous roots system cannot grow as tall as plants with taproots but they have the ability to repair roots and grow in many unusual ways
-Each root grows its own lateral roots and those lateral roots grow their own lateral roots
-Plants that have fibrous roots can grow roots out of their stem and sometimes out of their leaves.
-These plants, like grass, help hold soil together in large areas and prevent soil erosion
Root nutrition
-Roots do most of their absorption from their tips
-The tips of roots are surrounded by root hairs that increase their surface area for osmosis
There are many adaptations of roots
-Storage roots store food for the plant
-Pnumatophore roots reach for oxygen
-Areal roots or "strangling" roots start in the air and reach for the ground
-Like the strangler fig
-Stems
-The main job of a stem is to elongate and orient a plant in a way that maximizes photosynthesis
-Another function of a stem is to elevate reproductive parts
-Stems consist of:
-Nodes, the part where a leaf grows out of
-And internodes, the space between the nodes
-The tip of a stem is where most of a plants growth takes place. The tip is called the apical bud
-There are also axillary buds on the sides that can grow depending on light and other needs
-Leaves
-The main purpose of leaves is photosynthesis, heat dissipation, and gas exchange
-Leaves are made of 3 parts
-The blade, the bulk of the leaf
-The stalk, the part that attaches the leaf to the stem
-The petiole, the part where the stalk enters the node
-There are many leaf adaptations that have evolved
-Some leaves have evolved to be spins like in a cactus
-Some leaves are for food storage like an onion
-Some leaves are tendrils used to cling and climb like in a vine
Plant Tissues
-All plant organs are basically made up of 3 types of tissue
-Dermal
-Vascular
-Ground tissue
-Dermal tissue is the plants outer protective layer, the plants skin
-In non-woody plants there is usually only one layer of dermal tissue called the epidermis
-Sometimes there is a waxy protective layer over the epidermis called a cuticle
-In woody plants there is a periderm that replaces the older epidermis
-Vascular tissue is for transport of nutrients and water and consists of Phloem and Xylem
-There are vascular bundles that hold these veins
-Phloem transports food and Xylem transports water
-The vascular tissue of a root is known as stele
-Ground Tissue Systems
-Ground tissue is any tissue that is not dermal or vascular
-It is not simply filler tissue, it has a purpose
-Usually for helps with photosynthesis, storage, short distance transport, and support
-Ground tissue that is internal to the vascular tissue is known as pith
-Ground tissue that is external to the vascular tissue is known as cortex
-Major types of Plant Cells
-Parenchyma Cells
-Collenchyma Cells
-Sclerenchyma Cells
-Water conducting cells of the xylem
-Sugar conducting cells of the phloem
Group Work:
The class is going to split up into 5 groups.
-Choose a type of plant cell
-Create a group presentation in order to teach the class about your cell type
-Simple 3 minute presentation with at least one visual
-10 points
Plant growth
Plants are different than animals in that they have an indeterminate growth.
-Indeterminate growth means that a plant continues to grow throughout it's life
-An animal is limited to a embryonic or juvenile growth period
-A plant is capable of indeterminate growth because it has perpetually undifferentiated tissue called meristems
-Meristem tissue divides and grows when conditions are good
-At any given time a plant can have embryonic, developing organs and mature organs
-Some organs like leaves, thorns, and flowers undergo determinate growth where they stop once they reach a certain size
There are two types of meristems
-Apical meristems
-Lateral meristems
-Apical meristems are located at the tips of roots and shoots and in axillary buds of the shoots
-Apical meristem growth is known as primary growth. This is how roots get longer and spread out. It is also how plants get taller.
-Most herbaceous plants only go through primary growth
-Woody plants can also grow in thickness. This type of growth is known as secondary growth
-Secondary growth is caused by lateral meristem
-There are two types of lateral meristem
-Vascular cambium - adds layers of vascular tissue known as secondary phloem and secondary xylem
-Cork cambium that replaces the epidermis with a thicker and tougher periderm
