Tissues

The One Thing

A tissue is a group of similar, specialised cells that work together to perform a particular function. The structure and arrangement of cells within a tissue are closely adapted to the function the tissue performs.

Reactions, Processes and Experiments

Key Terms

• Tissue: A group of similar cells organised to perform a specific function.
• Meristematic tissue: Plant tissue made of actively dividing cells that produces new growth.
• Apical meristem: Meristem at the tips of roots and shoots that increases plant length.
• Intercalary meristem: Meristem near nodes or the bases of leaves that supports internode growth and regrowth after cutting or grazing.
• Lateral meristem: Meristem along the sides of stems and roots that increases girth.
• Permanent tissue: Plant tissue formed from meristematic cells that have stopped dividing and become specialised.
• Simple permanent tissue: Permanent tissue made of one type of similar cell, including parenchyma, collenchyma and sclerenchyma.
• Parenchyma: Living, usually thin-walled cells that store food, fill spaces and may perform photosynthesis.
• Chlorenchyma: Parenchyma containing chlorophyll and specialised for photosynthesis.
• Aerenchyma: Parenchyma with large air spaces that helps aquatic plants float and exchange gases.
• Collenchyma: Living cells with unevenly thickened corners that provide flexible support.
• Sclerenchyma: Dead cells with thick, lignified walls that provide strength and rigidity.
• Protective tissue: Tissue that covers and protects plant parts, including epidermis and cork.
• Epidermis: The outermost plant layer that reduces water loss and protects against injury and infection.
• Stomata: Tiny epidermal pores that allow gas exchange and regulate water loss through transpiration.
• Cork: Protective tissue made of dead cells containing suberin, making it resistant to water and gases.
• Complex permanent tissue: Plant tissue made of different cell types working together, mainly xylem and phloem.
• Xylem: Vascular tissue that transports water and minerals from roots and provides support.
• Xylem components: Tracheids, vessels, xylem parenchyma and xylem fibres; most are dead except xylem parenchyma.
• Phloem: Vascular tissue that transports food made in leaves to other parts of the plant.
• Phloem components: Sieve tubes, companion cells, phloem parenchyma and phloem fibres; phloem fibres are generally dead while the others are living.
• Epithelial tissue: Animal tissue forming coverings and linings that protects, absorbs, secretes or permits exchange.
• Squamous epithelium: Thin, flat-cell epithelium suited to diffusion and filtration.
• Cuboidal epithelium: Cube-shaped epithelium involved in secretion and absorption.
• Columnar epithelium: Tall-cell epithelium specialised for absorption and secretion.
• Ciliated epithelium: Epithelium with hair-like cilia that move substances.
• Glandular epithelium: Epithelium specialised for secretion of enzymes, mucus or hormones.
• Connective tissue: Tissue that connects, supports, binds, transports or protects body parts.
• Areolar tissue: Loose connective tissue that fills spaces, supports organs and assists repair.
• Adipose tissue: Fat-storing connective tissue providing insulation, energy storage and protection.
• Tendon: Strong connective tissue joining muscle to bone.
• Ligament: Elastic connective tissue joining bone to bone at joints.
• Cartilage: Flexible supporting tissue found in the nose, ear and trachea.
• Bone: Hard connective tissue supporting the body, protecting organs and providing muscle attachment.
• Blood: Fluid connective tissue transporting gases, nutrients, wastes, hormones and heat.
• Muscular tissue: Tissue composed of contractile cells that produces movement.
• Striated muscle: Voluntary, cylindrical muscle with visible stripes, attached mainly to bones.
• Unstriated muscle: Involuntary, spindle-shaped muscle without stripes, found in internal organs.
• Cardiac muscle: Involuntary, branched and rhythmic muscle found only in the heart.
• Nervous tissue: Tissue that receives stimuli and transmits electrical impulses for coordination and control.
• Neuron: The structural and functional unit of nervous tissue, consisting of a cell body, dendrites and an axon.
• Extracellular matrix: Material surrounding connective-tissue cells, which may be fluid, soft, flexible or hard.
• Division of labour: The organisation of specialised cells and tissues so that particular tasks are performed efficiently.
• Organ: A structure made of multiple tissues working together.

Easily Confused

• Meristematic tissue and permanent tissue: Meristematic cells actively divide and produce growth, whereas permanent cells have generally stopped dividing and perform specialised functions.
• Apical, intercalary and lateral meristems: Apical meristem increases length at root and shoot tips; intercalary meristem supports internode growth near nodes or leaf bases; lateral meristem increases thickness along stems and roots.
• Parenchyma, chlorenchyma and aerenchyma: Parenchyma mainly stores food and fills spaces; chlorenchyma performs photosynthesis; aerenchyma contains large air spaces and supports buoyancy and gas exchange.
• Collenchyma and sclerenchyma: Collenchyma provides flexible support through living cells with unevenly thickened corners; sclerenchyma provides rigid strength through dead, lignified cells.
• Xylem and phloem: Xylem transports water and minerals, generally upward from roots; phloem transports food from sources such as leaves and may move it in different directions.
• Tendon and ligament: A tendon joins muscle to bone and is strong but less flexible; a ligament joins bone to bone and is more elastic.
• Striated, unstriated and cardiac muscle: Striated muscle is usually voluntary and striped; unstriated muscle is involuntary and lacks stripes; cardiac muscle is involuntary, branched and rhythmic.
• Tissue and organ: A tissue is a group of similar cells performing a particular function; an organ contains multiple tissues working together.
• Dendrites and axon: Dendrites receive signals, whereas the axon carries impulses away from the cell body.

What Gets Asked

• Classify plant tissues into meristematic and permanent tissues, then identify apical, intercalary or lateral meristem from its location and function. The common error is confusing growth in length with growth in girth.
• Compare parenchyma, chlorenchyma, aerenchyma, collenchyma and sclerenchyma by structure and function. Marks are lost by assigning rigid support to collenchyma or flexible support to sclerenchyma.
• Describe xylem and phloem, including their components and transport functions. The specific slips are stating that phloem transport is only upward or that every xylem component is dead.
• Identify epithelial tissues from their cell shape, location and function. Thin squamous cells should be linked with diffusion and filtration, whereas cuboidal and columnar cells should be linked with secretion or absorption.
• Distinguish connective tissues by their functions and properties. In particular, tendons join muscle to bone, while ligaments join bone to bone and are more elastic.
• Compare striated, unstriated and cardiac muscle, or explain the structure and direction of impulse transmission in a neuron. The relevant distinctions are voluntary versus involuntary control, visible stripes, rhythmic contraction, and the different roles of dendrites, the cell body and the axon.