Are Plants And Animals Made Of Same Types Of Tissues?

Plants and animals differ significantly in their structure, function, and growth patterns, reflecting their distinct lifestyles. These differences are evident in the types and organisation of their tissues.

Key Differences:

1. Movement/Locomotion: Plants are typically stationary or fixed, whereas animals move around in search of resources.
2. Supportive Tissue: Since plants need to stand upright, they have a large proportion of supportive tissues. These supportive tissues often contain dead cells, which provide mechanical strength without requiring high energy maintenance. Animals, being mobile, have less need for extensive rigid supportive tissue throughout their body; their supportive tissues (like bone) are generally living.
3. Energy Consumption: Animals consume more energy due to locomotion and other active functions compared to sedentary plants. Consequently, most animal tissues are living and metabolically active, requiring more energy.
4. Growth Pattern: Growth in plants is often limited to specific regions containing actively dividing cells (meristematic tissues). Some plant tissues divide throughout their life. Animal growth is generally more uniform, without distinct regions of continuously dividing tissue in mature organisms (though cell division for replacement and repair occurs).
5. Structural Organisation: The organisation of organs and organ systems is more complex and localised in animals than in plants. This is linked to animals' need for rapid movement, complex responses, and diverse feeding mechanisms, contrasting with plants' sedentary mode of life based on photosynthesis.

These fundamental differences necessitate different types of tissues and different arrangements of tissues in plants and animals.

Plant Tissues

Plant tissues can be broadly classified based on their ability to divide:

1. Meristematic Tissue: Dividing tissue, responsible for growth.
2. Permanent Tissue: Non-dividing tissue, formed from meristematic tissue after differentiation.

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Meristematic Tissue

Plant growth occurs only in specific areas because the actively dividing tissue, the meristematic tissue (or meristem), is located in these regions.

Characteristics of Meristematic Tissue Cells:

• Cells are very active.
• They have dense cytoplasm.
• They have thin cellulose cell walls.
• They possess prominent nuclei.
• They typically lack vacuoles (or have very small ones), as they are primarily involved in division and not storage of large amounts of material or waste.

Location and Types of Meristematic Tissue:

• Apical Meristem: Found at the tips of roots and stems. Responsible for increasing the length of the plant (primary growth).
• Lateral Meristem (Cambium): Found along the sides of stems and roots. Responsible for increasing the girth or diameter of the stem and root (secondary growth).
• Intercalary Meristem: Found near the nodes of stems or at the base of leaves (especially in grasses). Responsible for growth in length in those specific regions, allowing recovery after grazing.

Cells produced by meristematic tissue initially resemble meristem cells but undergo changes as they mature, specialising into components of permanent tissues. This process is called differentiation.

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Permanent Tissue

Cells produced by meristematic tissue that take on a specific role and lose their ability to divide form permanent tissue.

The process by which meristematic cells develop into permanent tissue with a specific shape, size, and function is called differentiation.

Permanent tissues are classified into two main types:

1. Simple Permanent Tissue
2. Complex Permanent Tissue

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Simple Permanent Tissue

Simple permanent tissues are made up of only one type of cells that are structurally and functionally similar.

There are three main types of simple permanent tissue:

1. Parenchyma:
   • The most common simple permanent tissue.
   • Consists of relatively unspecialised, living cells with thin cell walls.
   • Cells are often loosely arranged, resulting in large intercellular spaces.
   • Primary function: Storage of food.
   • Specialised parenchyma:
     • Chlorenchyma: Contains chloroplasts for photosynthesis (found in leaves and green stems).
     • Aerenchyma: Found in aquatic plants, with large air cavities to help the plants float.
2. Collenchyma:
   • Provides flexibility and mechanical support to plant parts (like leaf stalks and stems of climbers), allowing them to bend without breaking.
   • Cells are living, elongated, and irregularly thickened at the corners.
   • Has very little intercellular space.
3. Sclerenchyma:
   • Makes plant parts hard and stiff (e.g., husk of coconut, seed coats, veins of leaves).
   • Cells are dead at maturity.
   • Cells are long and narrow, with cell walls significantly thickened due to the deposition of lignin (a hard, waterproof substance). This thickening is often so extensive that there is no internal space (lumen) left in the cell.
   • Provides strength and rigidity to plant parts.

Protective Tissues - Epidermis and Cork:

The outermost layer of cells covering the entire plant surface is the epidermis. It is a simple permanent tissue, usually a single layer of cells, but thicker in dry habitats for protection against water loss.

• Function: Primarily protective. It prevents water loss, mechanical injury, and invasion by pathogens.
• Epidermal cells are typically flattened and form a continuous layer with no intercellular spaces.
• On aerial parts, the epidermis often secretes a waxy, water-resistant layer called the cuticle. Desert plants may have a thick waxy coating of cutin for extreme water conservation.
• Stomata: Small pores present in the epidermis of leaves (and some stems), typically surrounded by two kidney-shaped guard cells. Stomata regulate gas exchange (CO₂ uptake for photosynthesis, O₂ release) and transpiration (loss of water vapour).
• Epidermal cells of roots have root hairs, which increase the surface area for water absorption.

As plants grow older, especially in stems and roots, the outer protective layer changes. A strip of secondary meristem in the cortex produces layers of cells that form the cork (also called bark). Cork cells are dead and compactly arranged without intercellular spaces. Their walls contain suberin, making the cork layer impervious to gases and water. Cork provides protection against mechanical injury, desiccation, and infection.

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Complex Permanent Tissue

Complex permanent tissues are made up of more than one type of cells. These different cell types work together to perform a common, coordinated function.

The main complex tissues in plants are xylem and phloem, which are the primary components of the vascular bundle, responsible for transport throughout the plant.

1. Xylem:
   • Responsible for the transport of water and minerals from the roots to other parts of the plant.
   • Provides mechanical support to the plant.
   • Composed of four types of elements: tracheids, vessels, xylem parenchyma, and xylem fibres.
   • Tracheids and vessels are tubular structures with thick walls. Many of the conducting cells (tracheids and vessels) are dead at maturity.
   • Xylem parenchyma is living and stores food. Xylem fibres are primarily supportive.
   • Xylem is a crucial adaptation for terrestrial plants.
2. Phloem:
   • Responsible for the transport of food (sugars produced during photosynthesis) from the leaves to other parts of the plant (translocation).
   • Composed of five types of cells: sieve cells, sieve tubes, companion cells, phloem fibres, and phloem parenchyma.
   • Sieve tubes are the main conducting cells, which are tubular with perforated walls (sieve plates).
   • Except for phloem fibres, all other phloem cells are living.

Animal Tissues

Animals possess different types of tissues compared to plants, reflecting their active lifestyles and complex organ systems. Animal tissues are broadly classified into four main types based on their structure and function:

1. Epithelial Tissue
2. Connective Tissue
3. Muscular Tissue
4. Nervous Tissue

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Epithelial Tissue

Epithelial tissue (also called epithelium) forms the covering or protective layers in the animal body. It covers most organs and cavities and forms barriers that separate different body systems.

Locations: Skin, lining of the mouth, lining of blood vessels, lung alveoli, kidney tubules, etc.

Characteristics:

• Cells are tightly packed and form continuous sheets.
• There is very little cementing material and almost no intercellular spaces between cells.
• Any substance entering or leaving the body must cross an epithelial layer. The permeability of epithelial cells regulates the exchange of materials.
• Epithelial tissue is usually separated from the underlying connective tissue by a non-cellular basement membrane.

Types of Epithelial Tissue (based on shape and function):

• Simple Squamous Epithelium: Consists of extremely thin and flat, irregularly shaped cells forming a delicate lining. Found where diffusion or filtration occurs (e.g., lining of blood vessels, lung alveoli, lining of oesophagus and mouth).
• Stratified Squamous Epithelium: Squamous cells arranged in multiple layers. Provides protection against wear and tear. Found in the skin.
• Cuboidal Epithelium: Consists of cube-shaped cells. Provides mechanical support. Found in the lining of kidney tubules and ducts of salivary glands. Can also form glandular epithelium when folded inwards to form glands.
• Columnar Epithelium: Consists of tall, pillar-like cells. Found where absorption and secretion occur (e.g., inner lining of the intestine). Facilitates movement across the epithelial barrier.
• Ciliated Columnar Epithelium: Columnar epithelial cells with hair-like projections called cilia on their surface. Ciliary movement pushes substances along. Found in the respiratory tract, where cilia move mucus to clear the airways.
• Glandular Epithelium: Epithelial tissue that specialises to secrete substances. Can be formed by inward folding of epithelial tissue.

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Connective Tissue

Connective tissue serves the function of connecting various tissues and organs, providing support and packing them together. It is the most abundant tissue in the body.

Characteristics:

• Cells are typically loosely spaced and embedded in an intercellular matrix.
• The nature of the matrix varies greatly among different types of connective tissues, determining their specific function. The matrix can be jelly-like, fluid, dense, or rigid.

Types of Connective Tissue:

• Blood:
  • Considered a fluid connective tissue.
  • Consists of a liquid matrix called plasma.
  • Cells like Red Blood Corpuscles (RBCs), White Blood Corpuscles (WBCs), and platelets are suspended in the plasma.
  • Plasma contains proteins, salts, and hormones.
  • Function: Transports gases (oxygen, carbon dioxide), digested food, hormones, and waste materials throughout the body.
• Bone:
  • A strong, rigid, and nonflexible connective tissue.
  • Forms the skeleton that supports the body, anchors muscles, and protects vital organs.
  • Bone cells are embedded in a hard matrix of calcium and phosphorus compounds.
• Ligament:
  • Connective tissue that connects two bones together.
  • Very elastic with considerable strength.
  • Contains very little matrix.
• Tendon:
  • Connective tissue that connects muscles to bones.
  • Fibrous tissue with great strength but limited flexibility.
• Cartilage:
  • Connective tissue with widely spaced cells embedded in a solid matrix of proteins and sugars.
  • Provides flexibility and support.
  • Smoothens bone surfaces at joints. Also found in the nose, ear, trachea, and larynx. (Allows folding of the ear cartilage, unlike rigid bone).
• Areolar Tissue:
  • Loose connective tissue found between the skin and muscles, around blood vessels, nerves, and in bone marrow.
  • Fills spaces inside organs, supports internal organs, and helps in tissue repair.
• Adipose Tissue:
  • Fat-storing connective tissue located below the skin and between internal organs.
  • Cells (adipocytes) are filled with fat globules.
  • Functions: Stores fat, acts as an insulator against heat loss, and cushions organs.

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Muscular Tissue

Muscular tissue is composed of elongated cells called muscle fibres. This tissue is responsible for movement in our body through the contraction and relaxation of muscle fibres.

Muscle cells contain special proteins called contractile proteins that enable contraction and relaxation.

Types of Muscular Tissue:

1. Striated Muscle (Skeletal Muscle or Voluntary Muscle):
   • Attached mainly to bones and responsible for voluntary body movements (movements we can consciously control, like moving limbs).
   • Cells are long, cylindrical, unbranched, and multinucleate (contain many nuclei).
   • Appear striated (show alternate light and dark bands) under a microscope due to the arrangement of contractile proteins.
2. Smooth Muscle (Involuntary Muscle or Unstriated Muscle):
   • Controls involuntary movements (movements we cannot consciously control, like the movement of food in the digestive tract, contraction/relaxation of blood vessels).
   • Found in the iris of the eye, ureters, and bronchi of the lungs.
   • Cells are long with pointed ends (spindle-shaped) and uninucleate (contain a single nucleus).
   • Do not show striations under a microscope.
3. Cardiac Muscle (Involuntary Muscle):
   • Specialised muscle tissue found only in the heart.
   • Responsible for the rhythmic contraction and relaxation of the heart throughout life.
   • Cells are cylindrical, branched, and uninucleate.
   • Show faint striations.
   • Move involuntarily.

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Nervous Tissue

All cells can respond to stimuli to some extent, but cells of the nervous tissue are highly specialised for receiving stimuli and transmitting information rapidly from one part of the body to another.

Locations: Brain, spinal cord, and nerves.

Structure of Nervous Tissue:

The functional unit of nervous tissue is the nerve cell or neuron.

A typical neuron consists of:

• A cell body (soma) containing the nucleus and cytoplasm.
• Short, branched projections called dendrites, which receive signals from other neurons.
• A single, long projection called the axon, which transmits signals away from the cell body to other neurons, muscles, or glands.
• The axon ends in nerve endings.

Individual nerve cells can be very long, up to a metre. Many nerve fibres bundled together by connective tissue form a nerve.

The signal transmitted along a nerve fibre is called a nerve impulse. Nerve impulses enable rapid communication within the body, allowing responses to stimuli and coordinating movements.

The interaction between nervous tissue (transmitting impulses) and muscular tissue (responding by contracting) is fundamental for rapid, coordinated movements in animals.

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