Types of Biological Tissues
Plant Tissues
Meristematic Tissues
Allow for growth. Their cells are small with thin cell walls, a large nucleus, and no intercellular spaces.
- Primary Meristems: Responsible for growth in length (apical meristems) and formation of primary phloem and xylem. Apical meristems are the most important.
- Secondary Meristems: Responsible for growth in girth (diameter). Examples include:
- Cambium: Forms secondary xylem and phloem internally.
- Phellogen: Originates cork tissue externally and inner cortical parenchyma.
Adult Plant Tissues
Parenchyma Tissue
Performs different functions:
- Chlorophyll Parenchyma: Located inside stems and leaves, performs photosynthesis.
- Storage Parenchyma: Stores reserve substances (e.g., starch).
- Aquifer Parenchyma: Stores water.
- Aerenchyma: Stores air, promotes gas exchange.
- Vascular Parenchyma: Accompanies vascular tissues.
Protective Tissues
- Epidermis: A single, flattened layer of living cells found in leaves, stems, and roots. Regulates water and gas exchange.
- Endodermis: Located in the interior of the root. A single layer of living cells with an impermeable layer (Casparian Strip). Regulates the entry of water and ions.
- Cork (Suber): Layers of dead cells filled with air, forming the outer bark.
Support Tissues
Provide resistance and support in plants.
- Collenchyma: Found in young, growing parts of woody plants and herbaceous plants. Provides flexible support. Types include angular, lamellar, and lacunar.
- Sclerenchyma: Composed of dead cells with lignified walls. Provides rigid support and strength.
Vascular Tissues
Highly specialized cells that transport sap. These tissues form the veins:
- Xylem: Woody tissue that transports crude sap (water and minerals) from roots to shoots.
- Primary xylem originates from the apical meristem during primary growth.
- Secondary xylem originates from the cambium during secondary growth.
- Cell types include vessel elements and tracheids.
- Phloem: Tissue that transports phloem sap (sugars).
- Primary phloem is produced from the apical meristem during primary growth.
- Secondary phloem is produced from the cambium during secondary growth.
- Cell types include sieve elements and companion cells.
Specific cell descriptions (related to Xylem):
- Vessel Elements: Form cylindrical vessels arranged in rows. Their transverse partitions are perforated.
- Tracheids: Long and slender with pointed ends, connected by pits (areas with thin walls).
Secretory Tissues
Produce or accumulate waste or useful substances. They can be external or internal:
- External: Nectaries, Hydathodes, and stinging hairs.
- Internal: Laticifers (accumulate latex) and resin ducts.
Animal Tissues
Epithelial Tissue
Forms a continuous sheet covering the body surface and lining the cavities of hollow organs. It rests on connective tissue via a basement membrane. Functions include protection and absorption.
Covering Epithelium
Can be classified by cell layers and shape:
- Simple: A single layer of cells.
- Squamous: Found in blood vessels, alveoli.
- Cuboidal: Found in the wall of ovaries, kidney tubules.
- Columnar: Found in the small intestine.
- Stratified: Multiple layers of cells.
- Squamous: Found in the epidermis.
- Cuboidal: Found in mammary gland ducts.
- Pseudostratified: Appears multilayered but is a simple columnar epithelium with nuclei at different levels.
Glandular Epithelium
Specialized cells in the secretion of substances. They form glands. There are three types:
- Exocrine: Secrete substances onto an external surface or into a duct.
- Endocrine: Secrete hormones directly into the bloodstream.
- Mixed: Contain both exocrine and endocrine components (e.g., pancreas).
Connective Tissues
Connect and support other tissues. Generally highly vascular (except cartilage). Cell types include fibroblasts, histiocytes (macrophages), mast cells, adipocytes, and blood cells (which circulate within blood, a type of connective tissue).
Loose Connective Tissue
Connects and relates to other tissues. Contains various cell types and fibers in a loose matrix.
Adipose Tissue
Stores fat, found under the skin and around organs.
Cartilage Tissue
Provides support for soft tissues and lines joints (articular cartilage). Composed of a cartilage matrix and cells (chondrocytes) housed in lacunae. Surrounded by the perichondrium (except articular cartilage).
- Hyaline: Found in costal cartilage, trachea, bronchi, and nose.
- Elastic: Found in the external ear and epiglottis.
- Fibrous: Found in intervertebral discs and menisci.
Bone Tissue
Forms bones. Provides internal support, protects vital organs, contains bone marrow (generates blood cells), and is involved in calcium and phosphorus metabolism. Composed of a mineralized bone matrix, forming lamellae.
- Inorganic Component: Calcium phosphate and calcium carbonate.
- Organic Component: Collagen and amorphous ground substance, provides elasticity.
Bone cells include osteoblasts, osteocytes, and osteoclasts.
Blood Tissue
Considered a specialized connective tissue. Composed of plasma (containing ionized minerals) and blood cells (red blood cells, white blood cells, platelets).
Muscle Tissue
Composed of highly specialized cells that contract. Muscle cells do not typically divide.
- Skeletal Muscle: Inserts into bones, responsible for voluntary movement. Cells are striated, multinucleated, and arranged in bundles surrounded by connective tissue sheaths (endomysium, perimysium, epimysium). Controlled by the central nervous system.
- Cardiac Muscle: Found in the heart walls, responsible for pumping blood. Cells are striated, branched, typically have one or two central nuclei, and are connected by intercalated discs. Controlled by the autonomic nervous system.
- Smooth Muscle: Found in the walls of digestive and respiratory tracts, blood vessels, etc. Responsible for involuntary movements. Cells are spindle-shaped, non-striated, and have a single central nucleus. Contraction is slow and involuntary.