Plant Structure and Functions of Plant Parts
OVERVIEW
INSTRUCTOR:
UNIT: Performance of Technical Skills Related to Plant and Soil Science and Technology
LESSON: Plant Structure and Functions of Plant Parts
IMS REFERENCE: IMS #8384
PLANT STRUCTURE AND FUNCTIONS OF PLANT PARTS
Topic Goal:
The student shall be provided the opportunity to describe the structure and functions of plant parts
as a means of performing technical skills related to plant and soil science and technology.
Topic Objectives:
After completing the topic, the student will be able to:
1. recognize the physiological similarities/differences between plant cells and animal cells;
2. describe the major structural parts of a plant cell;
3. identify types of plant tissue; and
4. explain structural parts and functions of plant roots, stems, leaves, and flowers.
STUDENT NOTES KEY
All living organisms consist of cells. Groups of cells with similar functions form tissues. Tissues
with similar functions form organs.
Plant organs and the specialized tasks they perform include:
Roots – provide support; absorb water & nutrients
Stems – connect the roots and leaves
Leaves – capture energy from sunlight and use it to make food for the plant
Flowers – attract pollinators and produce seeds and fruit
Roots, stems, and leaves are vegetative structures. Flowers are reproductive structures.
THE PLANT CELL
The cell is the basic structural and functional unit for all living organisms. Organelles within a
cell perform specialized functions.
Organelles with common functions in both plant and animal cells include:
Nucleus – synthesizes ribosomes and RNA and stores DNA
Endoplasmic Reticulum (ER) – prepares protein for export; synthesizes steroids; regulates
calcium levels; and breaks down toxins
Mitochondrion – converts energy from organic compounds to energy for cellular activities
Ribosomes – organize protein production
Microtubules – contribute to cell support and division
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Plant Structure and Functions of Plant Parts
Golgi Complex – processes and packages substances made by the cell
Cell membrane – semi-permeable structure that separates the cellular contents from the
outside
Lysosomes – digest old organelles and foreign substances
Three organelles that are found only in plant cells are plastids, vacuoles, and the cell wall.
Plastids contain DNA, store starches and fats, and contain pigments involved in photosynthesis.
Vacuoles store metabolic wastes and often occupy as much as 90% of a cell’s volume. The cell
wall is composed of cellulose fiber and gives plant cells a very defined shape.
PLANT TISSUE SYSTEMS
A plant tissue is an organized mass made up of similar types of cells. Three classifications of
tissues based on their origin, structure, and physiology are: dermal tissue, ground tissue, and
vascular tissue.
Dermal tissue forms the outer layer, or epidermis, of the plant. This type of tissue is responsible
for a plant’s environmental interactions including light passage and gas exchange. In some types
of plants, this tissue often has environmental adaptation features that regulate water loss from the
plant and the exchange of carbon dioxide and oxygen from within the plant.
Ground tissue consists of three types of cells that function in storage, metabolism, and support.
Parenchyma cells have thin, primary cell walls and highly functional cytoplasm. These types of
cells are the most common and abundant type of cells in plant tissues, making up the fleshy parts
of fruits, roots, and tubers.
Collenchyma cells are elongated cells with thick cell walls.
These types of cells contain
cellulose, which provides “flexible” support for plant stems and leaves. Sclerenchyma cells
develop extensive secondary cell walls that contain lignin, suberin, and/or cutin. The longevity of
these types of cells is short because the rigidity of their cell walls prevents them from exchanging
the necessary components needed for active metabolism.
Vascular tissues consist of xylem and phloem. Xylem consists of trachids and vessels, which
function to conduct and transport water and minerals from the soil up through the plant. Phloem
consists of sieve elements and companion cells, which function in the transport of sugars, amino
acids, and other small molecules from the leaves to other parts of the plant.
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Plant Structure and Functions of Plant Parts
PLANT ORGANS
Dermal, ground, and vascular tissues within a plant associate to form the plant’s organs, which
include the roots, stems, leaves, and flowers.
Roots are located mostly (above / below) the soil surface and represent about 50% of a plant’s
weight. Roots function to absorb water and nutrients from the soil, support the plant in an upright
position, and distribute food produced in the leaves to the growing areas of the roots. Based on
the relative sizes of primary and secondary roots, classifications of root systems include taproot,
fibrous, and adventitious.
Zones of root growth and differentiation include the:
Meristem – area of active cell division and growth (root tip)
Zone of elongation – nutrient and water absorption occurs causing cells to increase in size
Zone of differentiation/maturation – cells undergo changes to become specific tissues
(epidermis, cortex, and vascular tissue)
Root hairs located along the main root form as an outgrowth of the epidermal cells. Their
primary function is to absorb water and nutrients from the soil. The root cap, located at the
outermost tip of a root, covers and protects the root’s growing region. It also directs root growth
through the soil.
A plant’s stems serve as supportive structures for the plant’s leaves. They also function in the
transport of water and nutrients from the roots to the leaves and in the transport of food energy
created in the leaves to other plant parts.
The internal anatomy of a woody stem consists of:
Xylem and phloem – to conduct water, nutrients, and food reserves
Cambium – the site of cell division and active cell growth (meristematic tissue)
Pith – the parenchyma layer at the center of a stem
Structures making up the external anatomy of woody and herbaceous stems include:
Terminal buds – growing points located at the tips of stems
Axillary buds – growing points located in the leaf axils
Node – the point of leaf attachment to the stem
Internode – the area of the stem located between nodes
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Plant Structure and Functions of Plant Parts
Some plant stems have developed modifications for protection and to store additional food and
water. Examples of above-ground stem modifications include thorns, prickles, stolons, spurs,
pseudobulbs, and cladophylls. Rhizomes, tubers, corms, and bulbs are examples of below-ground
stem modifications.
The leaves on a plant function to capture sunlight for the plant processs of photosynthesis. Plant
leaves contain stomata that allow for gas exchange and transpiration.
The internal anatomy of a leaf consists of the:
Cuticle – a thin film covering the outer layer of the leaf to protect it from excessive
temperatures and water loss
Epidermis – cell layer on the upper and lower sides of a leaf that protects the inner cell
layers and contains the guard cells to regulate stomatal opening and closing
Mesophyll – innermost cell layers that contain the palisade parenchyma cells for
photosynthesis and the spongy parenchyma cells for gas exchange
The flat portion of a leaf is the leaf blade (or lamina). The petiole attaches it to the plant stem.
Stipules located in the leaf axils function as food manufacturing structures.
Flowers are the plant organs that function in plant reproduction. Flowers vary in size, structure,
and composition among plant species.
Parts of a complete flower include the:
Calyx – leaf-like structures that form an outer ring around the base of a flower and function to
enclose and protect the flower bud before it opens
Corolla – often colorful and/or scented to attract specific pollinators to the flower
Pistil – the female reproductive organs (stigma, style, ovary)
Stamen – the male reproductive organs (anther, filament)
Flower types based on the presence or absence of the four floral parts include:
Perfect complete – contains all four floral parts
Perfect incomplete – lacks only petals and/or sepals
Incomplete – lacks one of the four floral parts
Pistillate – has a pistil, but no stamens (imperfect incomplete flower)
Staminate – has stamens, but no pistil (imperfect incomplete flower)
Sterile – lacks both pistil and stamens
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Plant Structure and Functions of Plant Parts
A monoecious plant is one in which staminate and pistillate flowers exist on the same plant.
Dioecious plants are those in which the male (staminate) and female (pistillate) flowers exit on
completely separate plants.
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