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TNPSC BIOLOGY (ENGLISH) 

WHAT IS THE ORGANISATION OF THE LIVING BODY?

In unicellular organisms, the single cell performs all life functions. It functions independently. However, multicellular organisms have various levels of organization within them. Multicellular organisms have the following five levels of organization ranging from simplest to most complex.

           1. Cells: Are the bsic unit of structure and function in living things. It may serve a specific function within the organism. Eg., blood cells, neve cells, bone cells etc.

           2. Tissues: Made up of cells that are similar in structure and function and which work together to perform a specific activity. Eg., blood, nerve, bone etc. Humans have four basic tissues: Connective, Epithelial, Muscle and Nerve.

           3. Organs: Made up of tissues that work together to perform a specific gravity. Eg., heart, brain, skin, etc.,

           4. Organ System: Groups of two or more tissues that work together to perform a specific function for the organism. Eg., Circulatory system, nervous system, skeletal system etc.,

The human body has 11 organ systems: circulatory, digestive, endocrine, excretory (Urinary), immune (Lymphatic), integumentary, muscular, nervous, reproductive, respiratory and skeletal.

          5. Organisms: Entire living things that can carry out all basic life processes. Meaning they can take take in materials, release energy from food, release wastes, grow, respond to the environment and reproduce.

Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protist. Eg., bacteria, amoeba, mushroom, sunflower, human.

 

Organization in plants:

Internal Organisation of Plants

Levels of organization in plant anatomy are Tissues – Tissue Systems – Organs – Plant body. Study of tissues and tissue systems of plant body is called Histology.

 

Plant Tissues 

A group of similar or dissimilar cells that have a common origin and function is called tissue. Tissues are formed as a response to division of labour. Tissues are of two types namely,

            (a) Merismatic Tissue

            (b) Permanent Tissue

 

Meristematic tissues

A group of undifferentiated cells having the power of cell division is called Meristematic tissue or Formative tissue. The term ‘Meristem’ was coined by K.Nageli. Characteristic of Meristematic tissue,

             (i) cells are small in size and isodiametric, cubical or polyhedral in shape.

             (ii) Cells are arranged compactly without intercellular spaces.

            (iii) Cells are young and immature.

            (iv) Cell wall is thin and formed of cellulose.

            (v) Dense Cytoplasm and abundant with numerous smaller vacuoles.

           (vi) Proplastids are present.

           (vii) Ergastic substances present.

          (viii) Prominent big nucleus is present.

           (ix) Cells divide continuously and show active metabolism.

 

Types of Meristems:

Meristems which originate from embryonic tissues and continue to remain active in mature parts of the plant is called Primary meristems.

Meristems derived from permanent cells by dedifferentiation is called secondary meristem.

Based on the position, meristems are classified into 3 types,

(i) Apical, (ii) Intercalary and  (iii) Lateral Meristems.

 

Apical meristems

 Apical meristem is present at the growing tips of stems and inceases the length of the plant body.

 

Intercalary meristems

Occupy base of the leaves and the base of the intermodal regions in plantssuch as grasses (mostly in monocotyledonous plants). These help in elongation of the intermodes.

 

Lateral meristems

Occupying the lateral regions of the stems and roots which bring about increase in the width of the plant body. It helps in secondary growth and produces secondary xylem and secondary phloem.

 

Permanent Tissues

 A group of differentiated cells with definite shape and specific function is called permanent tissue.

 

The permanent tissues are classified as

      1. Simple tissues

      2. Complex tissues

      3.  Special Tissues

 

Simple tissues

 A tissue with the cells of similar structure (one type of cells) and function is called simple tissue.

      a. Parenchyma

      b. Collenchyma

      c. Sclerenchyma

 

Parenchyma

✦ The cells of the parenchyma are generally thin walled with intercellular spaces. They are living cells.

✦ They are generally present in all organs of a plant.

✦ Serve to store and conduct food materials, water and minerals.

 

Collenchyma

✦ Have unevenly thickened walls. These thickenings are due to the deposition of more cellulose, hemi-cellulose and pectin. The thickening is confined to the corners of the cells.

✦ They generally occur in the dicot stem in two or more layers below the epidermis.

✦ It is absent in the roots. It also occurs in petiole and pedicel.

✦ Like Parenchyma, Collenchyma is also a living tissue

✦ The main function of Collenchyrna is to provide strength and flexibility to the growing organs. Hence the plant parts bend but not break.

✦ Majumdar identified three types of Collenchyma: Angular Collenchyma; Lacunar Collenchyma; and Lamellar Colllenchyma.

 

Sclerenchyma

✦ Widely distributed and important mechanical tissue. It is a dead tissue. The cells are thick with lignified walls. They give mechanical support to the organs. This has two types of cells- Sclereids and Fibres.

 

Sclereids

✦ Short sclerenchyma cells are called sclereids. They are found in fleshy fruits, seeds, roots and leaves. Sclereids are stone cells which are commonly found in shells of the nut, pulp of certain fruits such as pear and Sapota.

 

Fibres

✦ The fibres are elongated strands with simple pits throughout its length. It provides mechanical support and rigidity to the plant parts. Fibers extracted from different [plant parts are useful in textile and jute industries.

 

Complex permanent tissues

Xylem and Phloem are the complex tissues. These are component parts of vascular bundles.

 

Xylem

✦ Xylem is mainly concerned with the transport of nutrients, water and minerals upwards in the plant body. It forms a continuous tube through the roots, stems, leaves, flowers and fruits by the fusion of elongated cells.

✦ It is composed of different kinds of cells namely.

⋆ Tracheids

 Xylem vessels

 Xylem fibres

 Xylem parenchyma

 

a.Tracheids

✦ Tracheids are elongated, tapering cells with blunt ends. They have lignified secondary wall

✦ They are the chief water conducting elements in Pteridophytes and Gymnosperms

 

b. Xylem vessels

✦ Xylem vessels have perforations at the end and the placed one above the other like a long pipe

✦ They are seen in the xylem of angiosperms .They conduct water mineral nutrients and also provide mechanical strength to the plant body

 

c. Xylem Fibres

✦ The fibres of Sclerenchyma associated with the xylem are known as xylem fibres. They give additional mechanical strength to the plant. They are also called wood fibres.

 

d. Xylem Parenchyma

✦ The parenchyma cells associated with xylem are known as xylem parenchyma. It is the only living tissue amongst xylem cells.

✦ They store food reserves in the form of starch and fat. They also help in conduction of water.

 

Phloem

✦ Phloem conducts food materials from leaves to the other parts of the plant. It is also called leptome or blast. It is made up of four types of cells.

Sieve elements

 Companion cells

 Phloem fibres

 Phloem parenchyma

 

Sieve elements

✦ Sieve elements are the conducting elements of the phloem, Sieve elements are of two types - sieve cells and sieve tubes.

✦ Sieve cells are cells with unspecialized sieve areas. Contains vacuolated protoplast without nucleus. These  are present in Pteridophytes and Gymnosperms. Sieve tubes are living cells with more specialized sieve areas. These are present in Angiosperms.

 

Companion cells

✦ They are associated with sieve elements. They have a prominent nucleus and cytoplasm.

✦ They help the sieve tube in conduction of food materials in angiosperms.

 

Phloem Fibres 

✦ They are called as bast-fibres. They give mechanical support to the plant.

✦ Among the four types of phloem cells, phloem fibres are the only dead tissues.

 

Phloem Parenchyma      

The parenchyma cells associated with phloem are called phloem parenchyma. They store starch and fats.

 

Special Tissues:

These are located in different parts of the plant body and widely distributed in different plant genera. It is also called ssecretory tissue or glandular tissue.

 

Morphology of the plant

The study of various external features of the organism is known as morphology.

Adaptation: Any alteration in the structure or function of an organism or any of its part that results from natural selection and by which the organism becomes better fitted to survive and multiply in its environment.

Root: The root is underground part of the plant and develops from elongation of radicle of the embryo.

 

Types of root system:

(i) Tap Root System: Originates from Radicle. Dicotyledonous plants, e.g., Gram, pea, mango.

(ii) Fibrous Root System: Originates from base of the stem, Monocotyledonous plants, e.g., wheat, paddy, grasses.

(iii) Adventitious Root System: Originates from part of the plant other than radical – Banyan tree (Prop roots), Maize (Stilt roots), Rhizophora (Respiratory roots)

Root Cap: The root is covered at the apex by thumble like structure which protects the tender apical part.

Modifications of Root: Roots are modified for support, storage of food, respiration.

For Support: Prop roots in Banyan tree, stilt roots in maize and sugarcane.

For Respiration: Pneumatophores in Rhizophora (Mangrove).

For Storage of Food: Fusiform (Radish), Napiform (Turnip), Conical (Carrot).

 

The Stem:

Stem is the aerial part of the plant and develops from plumule of the embryo. It bears nodes and internodes.

Modifications of Stem: In some plants the atems are modified to perform the function of storage of food, support, protection and vegetative propagation.

For food storage: Rhizome (Ginger), Tuber (Potato), Bulb (Onion), Corm (Colocasia).

For Support: Stem tendrils of watermelon, grapewine, cucumber.

For Protection: Auxillary buds of stem of citrus, Bougainvillea get modified into pointed thorns. They protect the plants from animals.

For Vegetative Propagation: Underground stems of grass, strawberry, lateral branches of mint and jasmine.

For Assimilation of Food: Flattened stems of Opuntia contain chlorophyll and perform photosynthesis.

 

The Leaf:

Develop from shoot apical meristem, flattened, green structure, manufacture the food by photosynthesis. It has bud in axil. A typical leaf has leaf base, petiole and lamina.

 

Types of leaf:

          1. Simple (Single leaf blade) e.g., Mango, Peepa

          2. Compound (Leaf has number of leaflets)

          3. Pinnately Compound (Neem, Rose)

          4. Palmately Compound (Silk Cotton)

Venation: The arrangement of veins and veinlets in the lamina of leaf.

 

Types of Venation:

1. Reticulate: Veinlets form a network as in leaves of dicotyledonous plants (China Rose, Peepul);

2. Parallel: Veins are parallel to each other as in leaves of monocotyledonous plants (grass, maize and sugarcane).

 

The Flower:

A flower is modified shoot. It is a reproductive unit in angiosperms. Flowers may be unisexual or bisexual, bracteates or abracteate.

 

Parts of flower:

      1. Calyx: Sepals, Green in colour, leaf like whorl.

      2. Corolla: Petals, usually brightly colored to attract insects for poliination.

      3. Androecium: Stamens are male organs and produce pollen grains. Stamens may be epipetalous (attach to petals). Ex: Brinjal, Datura or ephiphyllus (attach to perianth).

      4. Gynoecium: Made up of one or more carpels, female reproductive part consists of stigma, style and ovary; ovary bears one or more ovules.

Aestivation: The mode of arrangement of sepals or petals in floral bud

 

The Fruit:

The matured ripened ovary develops into fruit. The parthenocarpic fruits are formed from ovary without fertilization.

 

The Seed:

The ovules after fertilization develop into the seeds. A seed is made up of seed coat and an embryo. An embryo is made up of an embryonic axis having plumule and radicle with one or two cotyledons.

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