The Kingdom Plantae 2
8. The Plant Kingdom (Plantae) - 2
Morphology
A plant has two organ systems: 1) the shoot system, and 2) the root system. The shoot system is above ground and includes the organs such as leaves, buds, stems, flowers. The root system includes those parts of the plant below ground, such as the roots, tubers, and rhizomes.
A plant has two organ systems: 1) the shoot system, and 2) the root system. The shoot system is above ground and includes the organs such as leaves, buds, stems, flowers. The root system includes those parts of the plant below ground, such as the roots, tubers, and rhizomes.
Root
The major functions of roots are hold a plant in the ground, to absorb water and minerals from the soil, in some cases store food and in rare cases produce a new plant. There are two main types of root. In one type, the taproot system, a single large root grows straight down.
In the other type, the fibrous root system, there are several main roots with many smaller branching roots of almost equal diameter.
The major functions of roots are hold a plant in the ground, to absorb water and minerals from the soil, in some cases store food and in rare cases produce a new plant. There are two main types of root. In one type, the taproot system, a single large root grows straight down.
In the other type, the fibrous root system, there are several main roots with many smaller branching roots of almost equal diameter.
Primary root
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The first toot to develop, thickest and grows downwards ( primary root)
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Secondary Root
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All roots arises from primary root and grow sidewise
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Apical meristem
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tip of the root and stems is capable of rapidly dividing cells responsible for primary growth
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Root hair
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hair-like outgrowth of some surface cells of plant roots that greatly increases the area available for the absorption of water & minerals.
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adventitious roots
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roots that arise from stems or leaves. If formed high up on a stem are termed aerial or prop roots (seen in banayan and certain orchids.)
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Stem
It is the portion of vascular plants that commonly bears leaves and buds. It is usually is aerial, upright and elongate, but may be highly modified in structure. Stems that grow above ground are called aerial stems and below the ground are called Subterranean stems. There are two classes of aerial stems – herbaceous and woody. Herbaceous stems are slender, greenish and comparatively soft. The plants with herbaceous stems are called herbs. Woody stems are thicker, taller and harder than herbaceous stems. These may be either trees or shrubs. A tree has a thick main stems called the trunk, which branch abundantly. In shrub there are a number of comparatively slender main stems which branch abundantly.
Types of stems
It is the portion of vascular plants that commonly bears leaves and buds. It is usually is aerial, upright and elongate, but may be highly modified in structure. Stems that grow above ground are called aerial stems and below the ground are called Subterranean stems. There are two classes of aerial stems – herbaceous and woody. Herbaceous stems are slender, greenish and comparatively soft. The plants with herbaceous stems are called herbs. Woody stems are thicker, taller and harder than herbaceous stems. These may be either trees or shrubs. A tree has a thick main stems called the trunk, which branch abundantly. In shrub there are a number of comparatively slender main stems which branch abundantly.
Types of stems
stolons or runners
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stems that grow horizontally above the surface e.g. strawberry
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rhizomes
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underground stems looks like roots e.g. ginger, turmeric, arrowroot
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Tubers
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thickened underground stems. e.g. potato
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bulb
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short underground stem that bears a cluster of thick, overlapping leaves and stores food. e.g. Onions, tulips ,lilies
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tendrils
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climbing organs called are some times modified stems
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twiner
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stem that spirals around a solid support.
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cladodes (Phylloclades)
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These are leaf like stems. They appear because the real leaves are very small, therefore non functional. e.g. butchers broom and the prickly pear.
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Succulent stems
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They become very fat because of water accumulation. They use it as a reservoir for the long dry periods they have to stand. e.g. cacti
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Leaf
It is part of plant that serves primarily as the plant’s food making organ and takes part in transpiration and respiration. It may store food and water and provide structural support. A leaf is an extension of a plants stem. Some plants whose leaves change colour and lose their leaves in the autumn called deciduous. Those plants such as laurels and pines, the leaves do not change colour and do not fall off in autumn and are called evergreens.
Leaf consists of a flattened portion, called the blade, that is attached to the plant by a structure called the petiole.
The outer surface of the leaf has a thin waxy covering called the cuticle (A), this layer's primary function is to prevent water loss within the leaf. (Plants that leave entirely within water do not have a cuticle). Directly underneath the cuticle is a layer of cells called the epidermis (B). The vascular tissue, xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells called bundle sheath cells (C), and they create a circle around the xylem and the phloem. One the picture, xylem is the upper layer of cells (D) and is shaded a little lighter than the lower layer of cells - phloem (E). Recall that xylem transports water and phloem transports sugar (food).
It is part of plant that serves primarily as the plant’s food making organ and takes part in transpiration and respiration. It may store food and water and provide structural support. A leaf is an extension of a plants stem. Some plants whose leaves change colour and lose their leaves in the autumn called deciduous. Those plants such as laurels and pines, the leaves do not change colour and do not fall off in autumn and are called evergreens.
Leaf consists of a flattened portion, called the blade, that is attached to the plant by a structure called the petiole.
The outer surface of the leaf has a thin waxy covering called the cuticle (A), this layer's primary function is to prevent water loss within the leaf. (Plants that leave entirely within water do not have a cuticle). Directly underneath the cuticle is a layer of cells called the epidermis (B). The vascular tissue, xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells called bundle sheath cells (C), and they create a circle around the xylem and the phloem. One the picture, xylem is the upper layer of cells (D) and is shaded a little lighter than the lower layer of cells - phloem (E). Recall that xylem transports water and phloem transports sugar (food).
Within the leaf, there is a layer of cells called the mesophyll. The word mesophyll is greek and means "middle" (meso) "leaf" (phyllon). Mesophyll can then be divided into two layers, the palisade layer (F) and the spongy layer (G). Palisade cells are more column-like, and lie just under the epidermis, the spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis. The air spaces between the spongy cells allow for gas exchange. Mesophyll cells (both palisade and spongy) are packed with chloroplasts, and this is where photosynethesis actually occurs.
Epidermis also lines the lower area of the leaf (as does the cuticle). The leaf also has tiny holes within the epidermis called stomata (H). Specialized cells, called guard cells (I) surround the stomata and are shaped like two cupped hands. Changes within water pressure cause the stoma (singular of stomata) to open or close. If the guard cells are full of water, they swell up and bend away from each other which open the stoma. During dry times, the guard cells close.
Plant tissues
Plant cell types rise by mitosis from a meristem. A meristem may be defined as a region of localized mitosis. Meristems may be at the tip of the shoot or root (a type known as the apical meristem) or lateral, occurring in cylinders extending nearly the length of the plant. A cambium is a lateral meristem that produces (usually) secondary growth. Secondary growth produces both wood and cork (although from separate secondary meristems).
Plant cell types rise by mitosis from a meristem. A meristem may be defined as a region of localized mitosis. Meristems may be at the tip of the shoot or root (a type known as the apical meristem) or lateral, occurring in cylinders extending nearly the length of the plant. A cambium is a lateral meristem that produces (usually) secondary growth. Secondary growth produces both wood and cork (although from separate secondary meristems).
1) Dermal - It covers the outer surface of herbaceous plants and prevent water loss. e.g guard cells.
2) Ground - It comprises the bulk of the primary plant body. e.g. Parenchyma, collenchyma, and sclerenchyma cells.
3) Vascular - It transports food, water, hormones and minerals within the plant. xylem, phloem, parenchyma, and cambium cells.
Parenchyma: A generalized plant cell type, parenchyma cells are alive at maturity. They function in storage, photosynthesis, and as the bulk of ground and vascular tissues.
Collenchyma: These cells support the plant. It consists of living cells that are characterized by thickening of cells particularly at corners.
Sclerenchyma: These cells support the plant but they are dead at maturity. They often occur as bundle cap fibers. Sclerenchyma cells are characterized by thickenings in their secondary walls. The fibers from jute and coconut are best examples of these cells.
Xylem: These cells conduct water and minerals from roots to leaves. The common name of Xylem is wood. Tracheids and vessels are major cells types both of which are dead at maturity.
Phloem: It transports food from the leaves to rest of the plant. They are alive at maturity. The two most common cells in the phloem are the companion cells and sieve cells. Companion cells retain their nucleus and control the adjacent sieve cells. Dissolved food, as sucrose, flows through the sieve cells.
Cambium: It is layer of actively dividing cells lying between xylem and phloem; forms additional xylem and phloem layers during secondary thickening. The layers formed in each year forms a distinctive series of concentric rings called annual rings. By counting the annual rings, we can find out the age of the tree.
Cork: It is the out layer of bark. These increases in girth as new layers of xylem and phloem are formed. It develops abundantly in certain trees. Commercial cork is taken from oak tree.
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