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Lesson Objectives:
Lesson Objectives:
God willing, at the end of this lesson you will have learnt how to:
understand the importance of learning about vegetative organs and their functions.
identify the different parts of a plant.
identify the functions of the various parts of the plant.
LESSON SIGNIFICANCE
LESSON SIGNIFICANCE
Why learn about the different parts of a plant and their functions?
How could that help you in farming or even in life in general?
Plants are very important to life on earth providing many essential ecological services such as purifying water, maintaining ideal oxygen and carbon dioxide levels in the atmosphere as well as regulating climate and soil development, among other things. Plants provide foods, timber and a whole host of other products useful to man.
Understanding the different parts of plants and their functions and how plants have adapted to their environment is important to understanding how to better cultivate those plants that are useful. An understanding of roots, he different types, how they grow and their functions e.g. have allowed farmers to make the steps necessary to prepare the soil to enhance root growth. An understanding of flowers and their functions have allowed farmers to identify ways of promoting flowering and hence improving fruit production or delaying flowering and enhancing leaf production.
Understanding plants parts, their structure and their functions has also helped in understanding principles that can be further applied in other fields of study such as biology, engineering (producing stronger materials), architecture (producing more durable buildings), etc.
All in all, understanding the parts of plants and their functions is very important not only to crop productions and soil management but also to other fields.
Plant Vegetative ORgans
Plant Vegetative ORgans
Together, the organs of a plant allow it to carry out the seven processes of life.
Movement - all living things move, even plants
Respiration - getting energy from food
Sensitivity - detecting changes in the surroundings
Growth - all living things grow
Reproduction - making more living things of the same type
Excretion - getting rid of waste
Nutrition - taking in and using food
The phrase MRS GREN is one way to remember them:
Vascular plants have two distinct organ systems:
a shoot system: generally grows above ground, where it absorbs the light needed for photosynthesis.
a root system: supports the plants and absorbs water and minerals, is usually underground.
Review
Review
Answer the following from memory.
Why is understanding the vegetative organs of plants important to farmers?
What are the seven life processes carried out collectively by these organs?
List the two organ systems of vascular plants.
If you can't remember any then reread the content until you do before moving on!
The Shoot System
The Shoot System
The shoot system consists of two portions:
the vegetative (non-reproductive) parts of the plant, such as the leaves and the stems, and
the reproductive parts of the plant, which include flowers and fruits.
Vegetative Plant Parts
Vegetative Plant Parts
STEMS
Stems are usually above ground, although the stems of some plants, such as the potato, also grow underground.
Stems may be herbaceous (soft) or woody in nature. They may be classified as:
Shoot: A young stem (1 year old or less) with leaves.
Twig: A young stem (1 year old or less) that is in the dormant winter stage (has no leaves).
Branch: A stem that is more than 1 year old, typically with lateral (side) stems radiating from it.
Trunk: A woody plant's main stem.
A stem may be unbranched, like that of a palm tree, or it may be highly branched, like that of a magnolia tree.
Their main function is to provide support to the plant, holding leaves, flowers and buds; in some cases, stems also store food for the plant.
The stem of the plant connects the roots to the leaves, helping to transport absorbed water and minerals to different parts of the plant. It also helps to transport the products of photosynthesis, namely sugars, from the leaves to the rest of the plant.
There are two important tissues responsible for this:
Xylem tissue transports water and nutrients from the roots to different parts of the plant. Phloem tissue, which transports organic compounds from the site of photosynthesis to other parts of the plant.
Unlike xylem conducting cells, phloem conducting cells are alive at maturity.
The xylem and phloem always lie adjacent to each other. In stems, the xylem and the phloem form a structure called a vascular bundle;
Growth in plants occurs as the stems (and roots) lengthen. This is referred to as primary growth resulting from the mitosis of special cells called apical meristems.
Secondary growth is characterized by an increase in thickness or girth of the plant, and is caused by cell division in the lateral meristem. This type of growth is more common in woody plants and some dicotyledons, but rarely occurs in monocotyledons.
Stems can continue to grow throughout a plant’s life: a phenomenon called indeterminate growth.
Some of the cells in the stem contain lignin, which provides hardiness and strength.
The bark protects the plant against physical damage and helps reduce water loss. In some plants, the stem has many openings, known as lenticels, which allow the interior cells to exchange gases with the outside atmosphere.
Microscopic view of the cross section of a vascular plant stem
Review
Review
Answer the following from memory.
Name the two portions of the shoot system and list the organs in each portion.
Are all stems aboveground?
Define each of the four classes of stems.
List four functions of the stem.
What are the xylem and phloem and what do they do?
What are two differences between primary and secondary growth?
What is indeterminate growth?
What is the difference between lignin and bark?
What are lenticels?
If you can't remember any then reread the content until you do before moving on!
Stem Modifications
Some plant species have modified stems that are especially suited to a particular habitat and environment.
A rhizome is a modified stem that grows horizontally underground and has nodes and internodes. Vertical shoots may arise from the buds on the rhizome of some plants, such as ginger and ferns.
Corms are similar to rhizomes, except they are more rounded and fleshy (such as in gladiolus). Corms contain stored food that enables some plants to survive the winter.
Stolons are stems that run almost parallel to the ground, or just below the surface, and can give rise to new plants at the nodes. Runners are a type of stolon that runs above the ground and produces new clone plants at nodes at varying intervals: strawberries are an example.
Tubers are modified stems that may store starch, as seen in the potato (Solanum sp.). Tubers arise as swollen ends of stolons, and contain many adventitious or unusual buds (familiar to us as the “eyes” on potatoes).
A bulb, which functions as an underground storage unit, is a modification of a stem that has the appearance of enlarged fleshy leaves emerging from the stem or surrounding the base of the stem, as seen in the iris.
Practical Activity:
Practical Activity:
Draw diagrams of each of the modifications of a stem on a page and include in your portfolio.
Aerial modifications of stems are tendrils and thorns.
Tendrils are slender, twining strands that enable a plant (like a vine or pumpkin) to seek support by climbing on other surfaces.
Thorns are modified branches appearing as sharp outgrowths that protect the plant; a common example includes the roses.
Review
Review
Answer the following from memory.
List eight different ways that stems may be modified by plants to suit their particular habitat and environment.
If you can't remember any then reread the content until you do before moving on!
Quiz
Quiz
Complete the following quiz in your portfolio.
NODES AND INTERNODES
Nodes are points of attachment for leaves, aerial roots, and flowers. The stem region between two nodes is called an internode.
Primary Growth occurs through the extension of the internode by the reproduction of cells at the node.
TERMINAL AND AXILLARY BUDS
An axillary bud is usually found in the axil—the area between the base of a leaf and the stem—where it can give rise to a branch or a flower.
The apical bud is found at the apex (tip) of the shoot and contains the apical meristem.
The growth of the apical bud diminishes the growth of axillary buds that form along the sides of branches and stems, a phenomenon called apical dominance. If the apical bud is removed, then the axillary buds will start forming lateral branches.
Gardeners make use of this fact when they prune plants by cutting off the tops of branches, thus encouraging the axillary buds to grow out, giving the plant a bushy shape. Likewise removing axillary buds promotes the growth of the apical bud.
LEAVES
A leaf is lateral photosynthetic organ of shoot with restricted growth. Its functions are photosynthesis, respiration, transpiration, and synthesis of secondary chemicals .
Most leaves are usually green, due to the presence of chlorophyll in the leaf cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll. The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat.
Each leaf typically has a leaf blade called the lamina, which is also the widest part of the leaf. Some leaves are attached to the plant stem by a petiole. Leaves that do not have a petiole and are directly attached to the plant stem are called sessile leaves. Small green appendages usually found at the base of the petiole are known as stipules. Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue. The edge of the leaf is called the margin.
Leaf veins are vascular bundles coming to the leaf from stem. Frequently, there is a main vein and lateral veins.
Leaves exhibit determinate growth, which ceases when a plant part reaches a particular size.
From left to right: sheath, stipules and ocrea.
Leaf Structure and Function
The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. The epidermis helps in the regulation of gas exchange. It contains stomata: openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing.
The epidermis is usually one cell layer thick; however, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. A waxy layer known as the cuticle covers the leaves of all plant species. The cuticle reduces the rate of water loss from the leaf surface. Other leaves may have small hairs (trichomes) on the leaf surface.
Below the epidermis of dicot leaves are layers of cells known as the mesophyll, or “middle leaf.” The mesophyll of most leaves typically contains two arrangements of parenchyma cells: the palisade parenchyma and spongy parenchyma.
The palisade parenchyma (also called the palisade mesophyll) has column-shaped, tightly packed cells, and may be present in one, two, or three layers.
Below the palisade parenchyma are loosely arranged cells of an irregular shape. These are the cells of the spongy parenchyma (or spongy mesophyll). The air space found between the spongy parenchyma cells allows gaseous exchange between the leaf and the outside atmosphere through the stomata.
Both layers of the mesophyll contain many chloroplasts. Guard cells are the only epidermal cells to contain chloroplasts.
Like the stem, the leaf contains vascular bundles composed of xylem and phloem.
a) view of lower epidermis showing stoma, b) view of guard cells; c) cross section of stoma.
Leaf Adaptations
Leaf Adaptations
Coniferous plant species that thrive in cold environments, like spruce, fir, and pine, have leaves that are reduced in size and needle-like in appearance. These needle-like leaves have sunken stomata and a smaller surface area: two attributes that aid in reducing water loss. In hot climates, plants such as cacti have leaves that are reduced to spines, which in combination with their succulent stems, help to conserve water. Many aquatic plants have leaves with wide lamina that can float on the surface of the water, and a thick waxy cuticle on the leaf surface that repels water.
Review
Review
Answer the following from memory.
What is the difference between a node and an internode?
What is the difference between the axillary and apical buds?
What is known as apical dominance?
How can farmers use this to their advantage?
What are the functions of the leaf?
What is responsible for the green colour in leaves and how are they important?
Draw a diagram of the leaf and label its main parts.
What are the internal parts of the leaf?
What is the function of each of the internal parts of the leaf?
State two adaptations of the leaf.
If you can't remember any then reread the content until you do before moving on!
References
References
Grade 9 SCCP Curriculum Guide
Biology. Libre Texts Website. <https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(OpenStax)>
BBC. What are the Organs of a Plant. BiteSize Biology website. <https://www.bbc.co.uk/bitesize/topics/znyycdm/articles/zjchsrd>
OSU Extension Service. Vegetative Plant Parts. Organ State University. <https://extension.oregonstate.edu/gardening/techniques/vegetative-plant-parts>
Image of Plant Organs <https://biology-forums.com/gallery/18099_27_04_12_6_27_57.jpeg>
Image of Cross Section of Vascular Bundle <https://bio.libretexts.org/@api/deki/files/1731/Figure_30_01_02f.jpg?revision=1>
Image of Vascular Bundles of Monocots and Dicots <https://bio.libretexts.org/@api/deki/files/1737/Figure_30_02_06.jpg?revision=1>
Image of Modified Stems <https://extension.oregonstate.edu/sites/default/files/styles/full/public/images/2019-01/fig8.png?itok=2vSRMtgF>
Image of Apical and Axillary buds <https://www.cactus-art.biz/note-book/Dictionary/aaa_Dictionary_pictures/Apical_and_axillary_bud.jpg>
Image of Apical dominance <https://ib.bioninja.com.au/_Media/apical-dominance_med.jpeg>
IMage of Sheaths, Ocrea and Stipules <https://bio.libretexts.org/@api/deki/files/14251/Screen_Shot_2019-01-04_at_2.20.20_PM.png?revision=1&size=bestfit&width=531&height=198>
Image of Leaf blade <https://bio.libretexts.org/@api/deki/files/1751/Figure_30_04_01.jpg?revision=1>
IMage of cross sexction of leafe <https://bio.libretexts.org/@api/deki/files/14258/Screen_Shot_2019-01-04_at_2.39.56_PM.png?revision=1&size=bestfit&width=624&height=412>
The Root. Introduction to Botany. LibreTexts. <https://bio.libretexts.org/Bookshelves/Botany/Book%3A_Introduction_to_Botany_(Shipunov)/05%3A_Tissues_and_Organs_-_How_the_Plant_is_Built/5.05%3A_The_Root>
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