Living organisms are made up of cells, but cells rarely work alone. Groups of similar cells join together to perform specific functions. Such organized groups of cells are known as tissues.
Tissues help organisms carry out specialized activities efficiently. In multicellular organisms, different tissues perform different functions, allowing the body to function as a coordinated system.
The term tissue was coined by Marie François Xavier Bichat.
Table of Contents
What Is Tissue?
A tissue is a group of structurally similar cells that work together to perform a particular function.
Examples Of Tissues
- Blood
- Phloem
- Muscle tissue
The branch of biology that studies tissues is known as Histology.
Classification Of Tissues
Tissues are broadly divided into:
- Plant tissues
- Animal tissues
Plant Tissues
Plants are stationary organisms and require strong supporting structures.
Unlike animals, many plant tissues are dead at maturity. This provides mechanical strength while reducing maintenance requirements.
Plant tissues are classified into:
- Meristematic tissue
- Permanent tissue
Meristematic Tissue
Meristematic tissue consists of actively dividing cells.
These cells continuously divide and contribute to plant growth throughout life.
Meristematic tissues are responsible for producing new cells that later differentiate into permanent tissues.
Characteristics Of Meristematic Tissue
- Cells are generally isodiametric in shape.
- Cells are tightly packed.
- Intercellular spaces are absent.
- Dense protoplasm is present.
- Large nucleus is present.
- Cell wall is thin and made of cellulose.
- Vacuoles are absent.
- Plastids occur as proplastids.
Functions Of Meristematic Tissue
- Increase in plant length.
- Increase in plant girth or thickness.
- Formation of new tissues.
- Repair and regeneration.
Types Of Meristematic Tissue
Meristems are classified according to their position in the plant.
Apical Meristem
Apical meristems are present at the growing tips of roots and shoots.
Functions
- Responsible for primary growth.
- Increases plant length.
Example
Growth of stem tips and root tips.
Intercalary Meristem
Intercalary meristems occur at the base of leaves or internodes.
They are commonly found in grasses.
Functions
- Promote longitudinal growth.
- Help rapid regrowth after grazing or cutting.
Example
Growth of grass after mowing.
Lateral Meristem (Cambium)
Lateral meristems are located along the sides of stems and roots.
Functions
- Responsible for secondary growth.
- Increase stem and root diameter.
Example
Growth in thickness of tree trunks.
Permanent Tissue
Permanent tissues are formed from meristematic tissues.
These tissues consist of mature cells that have lost the ability to divide.
The process by which cells acquire permanent shape, size, and function is called differentiation.
Permanent tissues are classified into:
- Simple permanent tissue
- Complex permanent tissue
- Protective tissue
Simple Permanent Tissue
Simple permanent tissue consists of only one type of cell.
Three main types are:
- Parenchyma
- Collenchyma
- Sclerenchyma
Parenchyma
Parenchyma is the simplest and most unspecialized permanent tissue.
It consists of living cells that are loosely packed with large intercellular spaces.
It is often called the packing tissue of plants.
Characteristics Of Parenchyma
- Living cells
- Thin cellulose walls
- Large intercellular spaces
- Soft tissue
Functions Of Parenchyma
- Food storage
- Water storage
- Healing and repair
- Photosynthesis in some cases
Chlorenchyma
When parenchyma contains chloroplasts and performs photosynthesis, it is called chlorenchyma.
Aerenchyma
When parenchyma contains large air spaces, especially in aquatic plants, it is called aerenchyma.
Aerenchyma helps aquatic plants float.
Collenchyma
Collenchyma consists of elongated living cells.
The cell walls are unevenly thickened at the corners due to cellulose and pectin.
Characteristics Of Collenchyma
- Living cells
- No intercellular spaces
- Uneven wall thickening
- Flexible tissue
Functions Of Collenchyma
- Provides support
- Provides elasticity
- Allows bending without breaking
Example
Young stems and leaf stalks (petioles).
Sclerenchyma
Sclerenchyma is a rigid tissue composed of dead cells.
The cell walls are heavily thickened due to lignin deposition.
Characteristics Of Sclerenchyma
- Dead cells
- Thick lignified walls
- High mechanical strength
- Little or no internal space
Functions Of Sclerenchyma
- Provides rigidity
- Provides support
- Protects plant parts
Examples
- Coconut husk
- Hard shell of nuts
Comparison Of Simple Permanent Tissues
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Nature | Living | Living | Dead |
| Cell Wall | Thin | Unevenly thickened | Thick lignified |
| Intercellular Space | Present | Absent | Absent |
| Main Function | Storage | Support and flexibility | Strength and rigidity |
Complex Permanent Tissue
Complex tissues contain more than one type of cell working together.
The two major complex tissues are:
- Xylem
- Phloem
Xylem
Xylem is the chief conducting tissue for water and minerals.
It transports water from roots to aerial parts of the plant.
Movement in xylem is generally unidirectional.
Components Of Xylem
Tracheids
- Dead cells
- Water conduction
Vessels
- Dead cells
- Efficient water transport
Xylem Parenchyma
- Living cells
- Food storage
Xylem Fibres
- Dead cells
- Mechanical support
Functions Of Xylem
- Transport water
- Transport minerals
- Provide support
Phloem
Phloem transports food manufactured by plants.
Transport in phloem is generally bidirectional.
Components Of Phloem
Sieve Tubes
- Living cells
- Main conducting elements
Companion Cells
- Living cells
- Assist sieve tubes
Phloem Parenchyma
- Living cells
- Food storage
Phloem Fibres
- Dead cells
- Mechanical support
Phloem fibres are also called bast fibres.
Functions Of Phloem
- Transport food
- Distribution of organic nutrients
- Storage
Xylem Vs Phloem
| Feature | Xylem | Phloem |
|---|---|---|
| Function | Water transport | Food transport |
| Direction | Unidirectional | Bidirectional |
| Major Cells | Mostly dead | Mostly living |
| Support | Strong support | Limited support |
Protective Tissue
Protective tissues form the outer covering of plants.
They protect internal tissues from injury and environmental damage.
Protective tissue includes:
- Epidermis
- Cork
Epidermis
The epidermis is the outermost protective layer covering leaves, stems, and roots.
Functions Of Epidermis
- Protection from pathogens
- Protection from mechanical injury
- Prevention of water loss
- Regulation of gas exchange
Cutin
In desert plants, the epidermis is covered with a waxy layer called cutin.
Cutin reduces water loss.
Cork (Phellem)
Cork is the protective outer layer of woody plants.
It is composed of dead cells.
Its walls contain suberin.
Functions Of Cork
- Prevents water loss
- Protects against pathogens
- Protects against injury
- Produced by cork cambium
Animal Tissues
Animal tissues originate from embryonic germ layers:
- Ectoderm
- Mesoderm
- Endoderm
Animal tissues are classified into four major groups:
- Epithelial tissue
- Connective tissue
- Muscular tissue
- Nervous tissue
Epithelial Tissue
Epithelial tissue forms the covering of the body and lines internal organs and cavities.
The cells are tightly packed and rest on a basement membrane.
Functions Of Epithelial Tissue
- Protection
- Absorption
- Secretion
- Excretion
- Filtration
Example
Skin acts as a protective epithelial tissue.
Types Of Epithelial Tissue
Simple Squamous Epithelium
Cells are thin and flat.
Location
- Lung alveoli
- Blood vessels
- Bowman’s capsule
Function
- Diffusion
- Filtration
Cuboidal Epithelium
Cells are cube-shaped.
Location
- Kidney tubules
- Gland ducts
Function
- Secretion
- Absorption
Columnar Epithelium
Cells are tall and pillar-like.
Location
- Intestinal lining
Function
- Absorption
- Secretion
Ciliated Epithelium
Contains hair-like cilia.
Location
- Respiratory tract
- Oviduct
Function
- Movement of substances
Glandular Epithelium
Specialized for secretion.
Function
- Produces hormones
- Produces enzymes
- Produces mucus
Connective Tissue
Connective tissue connects, supports, and protects body organs.
Functions
- Binding
- Support
- Storage
- Transport
Examples
- Blood
- Bone
- Cartilage
- Tendons
- Ligaments
Muscular Tissue
Muscular tissue is responsible for movement.
Muscle cells contain contractile proteins.
Types Of Muscular Tissue
Skeletal Muscle
- Voluntary
- Striated
- Attached to bones
Smooth Muscle
- Involuntary
- Non-striated
- Found in internal organs
Cardiac Muscle
- Involuntary
- Striated
- Found only in the heart
Nervous Tissue
Nervous tissue consists of neurons and supporting cells.
It forms the brain, spinal cord, and nerves.
Functions
- Receives stimuli
- Conducts nerve impulses
- Controls body activities
Neuron
The neuron is the structural and functional unit of the nervous system.
FAQs On Tissue
What is tissue?
Tissue is a group of similar cells that work together to perform a specific function.
Who coined the term tissue?
The term tissue was coined by Marie François Xavier Bichat.
What is histology?
Histology is the branch of biology that studies tissues.
What are the two major categories of plant tissues?
Meristematic tissue and permanent tissue.
What is the function of apical meristem?
Apical meristem increases the length of roots and shoots.
What is chlorenchyma?
Chlorenchyma is parenchyma containing chloroplasts and performing photosynthesis.
Why is sclerenchyma called a supporting tissue?
Because it provides maximum strength, rigidity, and support to plant parts.
What is the difference between xylem and phloem?
Xylem transports water and minerals, whereas phloem transports food.
Which tissue forms the outer covering of plants?
Epidermis forms the outer protective covering.
What are the four major animal tissues?
Epithelial, connective, muscular, and nervous tissues.
Last Moment Exam Cheat Sheet – Tissue
- Tissues are groups of similar cells performing specific functions.
- Plant tissues are classified into meristematic and permanent tissues.
- Meristematic tissue is responsible for plant growth.
- Permanent tissues perform specialized functions.
- Xylem transports water and minerals.
- Phloem transports food.
- Epidermis and cork provide protection.
- Animal tissues include epithelial, connective, muscular and nervous tissues.
- Epithelial tissue covers and protects body surfaces.
- Muscular tissue enables movement.
- Nervous tissue controls body functions.