Cheat Sheet: Tissues In Action

1. Introduction

1.1 Definition & Hierarchy

1.2 Plant vs Animal Tissue Differences

• Movement - Plants: fixed in one place; Animals: capable of movement
• Cell wall - Plants: present, gives rigidity and strength; Animals: absent, allows shape change
• Nutrition - Plants: produce food by photosynthesis; Animals: obtain and digest food from various sources
• Growth - Plants: localized in meristems; Animals: distributed throughout the body
• Shape flexibility - Plants: limited due to rigid cell wall; Animals: high flexibility without cell wall

2. Plant Tissues

2.1 Meristematic Tissue

2.1.1 Apical meristem

• Located at tips of roots and shoots
• Actively dividing cells cause lengthwise growth
• Onion-bulb experiment: root growth occurs from tips

2.1.2 Lateral meristem

• Ring of dividing cells in stem producing inward and outward new cells
• Forms annual growth rings used to estimate tree age

2.1.3 Intercalary meristem

• Located at base of internode or just above node
• Enables regrowth after cutting (e.g., grass regrowth, hedge bushiness)

2.2 Meristematic Cell Characteristics

• Small size
• Thin cell walls
• Large, prominent nucleus
• Dense cytoplasm with many organelles
• Vacuoles absent
• Tightly packed cells with no intercellular spaces

2.3 Permanent Tissues

2.3.1 Simple permanent tissues

• Parenchyma
  • Structure: living cells with thin walls and intercellular spaces
  • Function: food storage and photosynthesis in green parts; forms air spaces in aquatic plants
  • Location: cortex, pith, mesophyll of leaves
• Collenchyma
  • Structure: living cells with unevenly thickened corners due to pectin
  • Function: support with flexibility
  • Location: stem periphery, leaf stalks
• Sclerenchyma
  • Structure: dead cells with thick lignified walls
  • Function: strength and rigidity; forms woody structure
  • Location: stems, leaf veins, seed coats

2.3.2 Protective tissue - Epidermis

• Single outer layer of flat, rectangular cells
• Cuticle: waxy layer on epidermis that reduces water loss
• Root hair: epidermal projections that increase absorption surface area
• Stomata: epidermal pores for gaseous exchange and transpiration
• Transpiration pull in xylem aids upward water movement

2.4 Conducting Tissues (Complex)

• Xylem components
  • Tracheids - tubular, thick-walled, dead cells
  • Vessels - tubular, thick-walled, dead cells
  • Xylem parenchyma - living cells
  • Xylem fibres - dead, sclerenchymatous cells
• Phloem components
  • Sieve tubes - long tubular cells with perforated end walls
  • Companion cells - specialised parenchyma regulating sieve tubes
  • Phloem parenchyma - stores resins, tannins, latex
  • Phloem fibres - sclerenchymatous cells providing strength

2.5 Tissue Systems in Plants

• Dermal tissue system - outer covering (epidermis); protects and reduces water loss
• Ground tissue system - main body between dermal and vascular tissues; includes parenchyma, collenchyma, sclerenchyma
• Vascular tissue system - conducting tissues xylem and phloem

3. Animal Tissues

3.1 Epithelial Tissue

• Composition: closely packed cells with little intercellular space
• Exchange - single layer of thin flat cells; location: lining of blood vessels and lungs
• Protection - many cell layers with outer flat cells; location: skin, mouth, oesophagus
• Secretion - cuboidal or columnar cells specialised for release; location: salivary glands, sweat glands, stomach lining
• Sensory - specialised receptor cells with cilia; location: nostrils, taste buds, inner ear
• Absorption - single layer of tall cells often with hair-like structures; location: lining of small intestine

3.2 Connective Tissue

• Blood
  • Structure/matrix: fluid plasma containing RBCs, WBCs, platelets
  • Function: transport of nutrients, gases, hormones; immune defence; clotting
• Bone
  • Structure/matrix: rigid matrix containing calcium and phosphorus compounds
  • Function: strength, support, protection
• Cartilage
  • Structure/matrix: soft, jelly-like matrix
  • Function: flexibility and cushioning of bone ends
• Tendon
  • Structure: tough connective tissue
  • Function: connects muscle to bone
• Ligament
  • Structure: strong, flexible connective tissue
  • Function: connects bone to bone and provides stability

3.3 Muscular Tissue

• Skeletal / Striated muscle
  • Structure: long cylindrical, unbranched, multinucleate, striated
  • Control: voluntary
  • Location: attached to bones
  • Function: movement and locomotion
• Smooth / Unstriated muscle
  • Structure: spindle-shaped, single nucleus, no striations
  • Control: involuntary
  • Location: stomach, intestines, blood vessels
  • Function: digestion and peristalsis
• Cardiac muscle
  • Structure: cylindrical, branched, single nucleus, faint striations
  • Control: involuntary
  • Location: heart only
  • Function: pumps blood continuously without fatigue

3.4 Nervous Tissue

• Neurons (nerve cells)
• Cell body - contains nucleus and controls cell activities
• Dendrites - receive signals from other neurons
• Axon - long fibre carrying messages to axon terminals for transmission to other cells

4. Musculoskeletal & Skeletal System

4.1 Musculoskeletal System

• Components: bones, muscles, joints, cartilage, tendons, ligaments
• Muscles pull on bones to produce movement
• Tendons attach muscles to bones
• Adult human skeleton constitutes about 12-15% of body weight

4.2 Types of Joints

• Ball and socket joint
  • Description: rounded head of one bone fits into a hollow of another
  • Movement: forward, backward, sideways and circular
  • Example: shoulder joint, hip joint
• Hinge joint
  • Description: bones meet like a door hinge
  • Movement: bending and straightening in one direction
  • Example: elbow, knee
• Pivot joint
  • Description: one bone rotates around another
  • Movement: side-to-side rotation
  • Example: neck (skull connected to backbone)
• Fixed joint
  • Description: flat bones joined tightly together
  • Movement: no movement
  • Example: skull bones

4.3 Skeletal System

• Backbone (vertebral column) - series of vertebrae supporting the body
• Intervertebral cartilage discs - cushion between vertebrae allowing flexibility and protecting the spinal cord
• Rib cage - 12 pairs of ribs protecting heart and lungs
• Ribs join spine at back and sternum at front via flexible cartilage to allow expansion during breathing

5. Totipotency & Experiments

5.1 Totipotency

5.2 F. C. Steward's Experiment on Carrot Phloem (1958)

• Researcher and date - F. C. Steward, 1958
• Finding - phloem cells can dedifferentiate and regenerate entire plants under suitable conditions
• Experimental outcomes
  • Solid medium + nutrients - increase in fresh weight: reduced; conditions: light yes, air no
  • Liquid medium + nutrients - increase in fresh weight: 20% increase; conditions: light yes, air yes
  • Liquid medium + nutrients - increase in fresh weight: reduced; conditions: light no, air yes
• Conclusions from experiment
  • Highest biomass observed with liquid medium + nutrients (20% increase)
  • Lowest biomass observed with solid medium + nutrients (reduced growth)
  • Animal cells are unlikely to give identical results due to different growth requirements
• Commercial applications
  • Mass propagation of plants using totipotent cells
  • Genetic engineering of plants via totipotent cells

6. Scientists Spotlight

6.1 B. G. L. 29 Swamy

• Renowned Indian botanist
• Author of Hasuru Honnu describing Western Ghats plants
• Received Kendra Sahitya Akademi Award in 1978

6.2 Sipra Guha Mukherjee & S. C. Maheshwari

• Developed complete plant from anther culture using artificial nutrient medium under laboratory conditions
• Contributed to crop improvement via plant tissue culture