BOT 102 Review

BOT 102: Introductory Botany – Comprehensive Study Summary (Weeks 1-11)

Week 1: General Classification of Plants

1.1 Introduction to Plant Classification

• Plant classification (plant taxonomy): Systematic arrangement of plants into hierarchical groups based on shared characteristics (morphology, anatomy, reproductive structures, biochemistry, molecular/genetic data).
• Taxonomy: Science of classifying organisms.
• Systematics: Study of diversity and evolutionary relationships of organisms.
• Purposes of Classification: Reflects phylogeny, provides orderly identification/naming, allows prediction of characteristics, offers universal reference (binomial nomenclature).

1.2 The Taxonomic Hierarchy

Plants are classified using a nested hierarchy of ranks, from broadest to most specific:

Kingdom > Division/Phylum > Class > Order > Family > Genus > Species

Examples:

• Maize: Plantae > Magnoliophyta (Angiospermae) > Liliopsida (Monocotyledonae) > Poales > Poaceae > Zea > Zea mays
• Hibiscus: Plantae > Magnoliophyta (Angiospermae) > Magnoliopsida (Dicotyledonae) > Malvales > Malvaceae > Hibiscus > Hibiscus rosa-sinensis

1.3 Binomial Nomenclature

Each species has a scientific name with two parts, formalized by Carl Linnaeus:

• Genus name: Always capitalized.
• Specific epithet: Always in lowercase.
• Both names are italicized (or underlined when handwritten), e.g., Mangifera indica.
• May be followed by the abbreviation of the authority (e.g., L. for Linnaeus).

1.4 Basis of Classification

• (a) Artificial classification: Based on easily observable characters (e.g., habit, color, size); does not reflect natural relationships.
• (b) Natural classification: Based on sum total of morphological, anatomical, and reproductive similarities; groups naturally related plants.
• (c) Phylogenetic classification: Based on evolutionary descent and ancestry, supported by molecular data (DNA/RNA); basis of modern systematics (e.g., APG system).

1.5 Major Groups within Kingdom Plantae

Divided based on vascular tissue presence/absence, and seed production/protection:

1. Non-vascular plants (Bryophytes): Mosses, liverworts, hornworts. Lack true xylem/phloem, roots/stems/leaves. Require water for fertilization.
2. Vascular plants (Tracheophytes): Possess xylem and phloem.
   • a) Seedless vascular plants (Pteridophytes): Ferns, club mosses. Reproduce by spores. Require water for fertilization.
   • b) Seed-bearing vascular plants (Spermatophytes):
     • Gymnosperms: "Naked-seeded"; seeds not enclosed in an ovary/fruit (e.g., Pinus, Cycas).
     • Angiosperms: Flowering plants; seeds enclosed within an ovary (develops into fruit). Most diverse. Subdivided into Monocotyledons and Dicotyledons.

1.7 Key Terms

• Taxonomy: Science of classification of organisms.
• Systematics: Study of diversity and evolutionary relationships of organisms.
• Taxon (pl. Taxa): A named group of organisms at any rank.
• Phylogeny: Evolutionary history/relationship of a group of organisms.
• Nomenclature: The system of naming organisms.

Week 2: Distinguishing Features of Monocotyledons and Dicotyledons

2.1 Introduction

Angiosperms are divided into two classes based on the number of cotyledons (seed leaves) in the embryo:

• Monocotyledonae (monocots): One cotyledon.
• Dicotyledonae (dicots): Two cotyledons.

This embryological difference correlates with consistent anatomical and morphological differences.

2.2 Comparative Features (Summary)

• Cotyledon number: Monocots: One; Dicots: Two.
• Root system: Monocots: Fibrous (adventitious roots); Dicots: Taproot (main root with lateral branches).
• Leaf venation: Monocots: Parallel; Dicots: Reticulate (net-like).
• Stem vascular bundles: Monocots: Scattered, closed (no cambium); Dicots: Arranged in a ring, open (cambium present).
• Secondary growth: Monocots: Generally absent; Dicots: Generally present (vascular cambium produces wood/bark).
• Floral parts: Monocots: Multiples of 3 (trimerous); Dicots: Multiples of 4 or 5 (tetramerous/pentamerous).
• Pollen grain structure: Monocots: Monocolpate (single furrow/pore); Dicots: Tricolpate (three furrows/pores).
• Examples: Monocots: Maize, rice, wheat, banana, palms; Dicots: Beans, hibiscus, mango, sunflower, roses.

2.3 Root System in Detail

• Monocot roots: Primary root short-lived, replaced by fibrous adventitious roots. Spreads widely but shallowly.
• Dicot roots: Radicle persists, forms dominant taproot with lateral branches. Often deep-penetrating, modified for storage (e.g., carrot).

2.4 Leaf Venation in Detail

• Monocot leaves: Main veins run parallel, connected by fine cross-veins.
• Dicot leaves: Prominent midribs with branching lateral veins forming a net-like (reticulate) pattern.

2.5 Stem Anatomy in Detail

• Monocot stem: Vascular bundles scattered, no distinct cortex/pith, bundles closed (no cambium, no secondary tissue).
• Dicot stem: Vascular bundles arranged in a ring, distinct cortex/pith, bundles open (cambium present, allows secondary thickening).

2.6 Floral Structure in Detail

• Monocot flowers: Parts in threes or multiples of three (trimerous). Sepals/petals often similar (tepals).
• Dicot flowers: Parts in fours or fives (tetramerous or pentamerous). Sepals/petals usually distinct.

2.7 Germination Pattern

• Monocot seeds: Single cotyledon remains below/at soil surface (e.g., maize).
• Dicot seeds: Often epigeal (cotyledons raised above soil, e.g., bean) or hypogeal (cotyledons remain below soil, e.g., pea).

2.8 Economic and Ecological Significance

• Monocots: Cereal crops (staple food), palms, bananas, sugarcane, lilies, orchids.
• Dicots: Most vegetables, legumes, fruit trees, timber trees (due to secondary growth), majority of ornamental flowering plants.

Week 3: Features of Vascular Plants, Morphology of Non-Vascular Plants

3.1 Vascular Plants (Tracheophytes)

Plants with specialized conducting tissues (xylem and phloem) for water, minerals, and food transport.

3.1.1 Key Features of Vascular Plants

• Presence of xylem (water/mineral transport, mechanical support) and phloem (food transport).
• True roots, stems, and leaves, differentiated into distinct tissue systems.
• Well-developed cuticle on aerial surfaces to reduce water loss.
• Stomata for regulated gas exchange.
• Dominant sporophyte generation in life cycle.
• Lignified cell walls (especially in xylem) for structural rigidity and upright growth.

3.1.2 Classification of Vascular Plants

1. Pteridophytes (seedless vascular plants): Ferns, club mosses, horsetails. Reproduce via spores.
2. Gymnosperms: Vascular seed plants with naked seeds (e.g., Pinus, Cycas).
3. Angiosperms: Vascular seed plants with seeds enclosed in a fruit.

3.1.3 Functional Significance

Efficient long-distance transport allows larger body sizes and occupation of diverse terrestrial habitats.

3.2 Non-Vascular Plants (Bryophytes) — Morphology

Simple, small land plants lacking true vascular tissue. Restricted to moist habitats. Includes Mosses, Liverworts, and Hornworts.

3.2.1 General Morphological Features of Bryophytes

• Body is a thallus (undifferentiated) or differentiated into stem-like/leaf-like structures (not true stems/leaves).
• Anchored by rhizoids (thread-like filaments), not true roots.
• No true vascular tissue; water/mineral movement by diffusion, capillarity, osmosis.
• Gametophyte-dominant life cycle (the green plant body seen is the haploid gametophyte).
• Sporophyte is smaller, non-photosynthetic, dependent on gametophyte.
• Reproduction requires external water film for flagellated male gametes (antherozoids) to swim to egg.
• Lack well-developed cuticle and stomata (on gametophyte).

3.2.2 Morphology of a Typical Moss (e.g., Funaria)

Gametophyte: leafy gametophore with stem-like axis, leaf-like phyllids, and multicellular rhizoids. Sporophyte: stalk (seta) with terminal capsule (sporangium) containing spores.

3.2.3 Morphology of a Typical Liverwort (e.g., Marchantia)

Flattened, dichotomously-branching, ribbon-like thallus with unicellular rhizoids. Dorsal surface has air pores to photosynthetic cells.

3.2.4 Morphology of Hornworts (e.g., Anthoceros)

Simple, flat, lobed thallus. Distinguished by a long, horn-shaped sporophyte growing continuously from a basal meristem, typically with one large chloroplast per cell.

3.3 Comparative Summary: Vascular vs Non-Vascular Plants

• Xylem & Phloem: Vascular: Present; Non-Vascular: Absent.
• Roots/Stems/Leaves: Vascular: True, well-differentiated organs; Non-Vascular: Not true organs (rhizoids, thallus/phyllids).
• Dominant Generation: Vascular: Sporophyte; Non-Vascular: Gametophyte.
• Maximum Size: Vascular: Very large (trees); Non-Vascular: Generally small, low-growing.
• Habitat: Vascular: Wide range, including dry areas; Non-Vascular: Restricted to moist/shaded habitats.
• Fertilisation: Vascular: May be independent of external water (seed plants); Non-Vascular: Requires external water film.

3.4 Ecological and Economic Importance of Bryophytes

• Pioneer species in ecological succession.
• Peat mosses (Sphagnum) form peat bogs (carbon sinks), used as soil conditioner, fuel.
• Bioindicators of air/water pollution.
• Help retain soil moisture and reduce erosion.

Week 4: Duration of Life of Plants

4.1 Introduction

Plants are classified by life span into annuals, biennials, and perennials, based on how long they live and complete their reproductive cycle.

4.2 Annuals

• Complete entire life cycle (germination to death) within one growing season (less than one year).
• Fast growth, substantial resources to seed production.
• Usually herbaceous, monocarpic (flower/fruit once then die).
• Examples: Maize, rice, beans, tomato, sunflower.
• Summer annuals (spring germinate, die autumn/winter); Winter annuals (autumn germinate, overwinter, die spring/summer).

4.3 Biennials

• Complete life cycle over two growing seasons (roughly two years).
• First year: Vegetative growth, produces rosette of leaves, stores food (e.g., fleshy root, corm).
• Undergoes vernalization (cold exposure) to trigger reproductive growth.
• Second year: Uses stored reserves to produce flowering stalk, flowers, fruits, seeds, then dies.
• Monocarpic.
• Examples: Carrot, cabbage, onion, celery, sugar beet.

4.4 Perennials

• Live for more than two years.
• Typically polycarpic (flower and produce seed repeatedly over many seasons/years).

Types of Perennials

• Herbaceous perennials: Above-ground parts die back seasonally, but underground storage organs (rhizomes, bulbs, tubers) survive and regrow. Examples: Ginger, banana, turmeric.
• Woody perennials: Retain persistent woody stems, increase in girth via secondary growth.
  • Trees: Single main woody trunk, tall (e.g., mango, oil palm).
  • Shrubs: Multiple woody stems from near ground level, shorter than trees (e.g., hibiscus, rose).
  • Lianas/woody climbers: Woody stems that climb using supports (e.g., some Bauhinia).
• Creepers/Prostrate plants: Weak stems trail along the ground, sometimes rooting at nodes (e.g., sweet potato).

4.5 Comparative Summary (Key Differences)

• Life span: Annuals: <1 year; Biennials: ~2 years; Perennials: >2 years.
• Flowering: Annuals: Once (monocarpic); Biennials: Once (monocarpic) in 2nd year; Perennials: Repeatedly (polycarpic).
• Growth habit: Annuals: Herbaceous; Biennials: Herbaceous (rosette in year 1); Perennials: Herbaceous or woody.
• Food storage: Annuals: Minimal (to seeds); Biennials: In roots/bulbs in year 1; Perennials: In perennating organs or woody tissue.

4.6 Ecological and Agronomic Significance

Understanding plant life duration is crucial for agriculture: annuals allow rapid rotation but require repeated planting; perennials require initial investment but provide continuous yields, reduce soil disturbance, and protect against erosion.

Week 5: Plant Life Cycles

5.1 Introduction: Alternation of Generations

All land plants (embryophytes) exhibit alternation of generations: alternating between a haploid (n) gametophyte generation (produces gametes by mitosis) and a diploid (2n) sporophyte generation (produces haploid spores by meiosis).

General Cycle: Spore (n) → Gametophyte (n) → Gametes (n) → Fertilization → Zygote (2n) → Sporophyte (2n) → Spores (n).

5.2 Life Cycle in Bryophytes (Gametophyte-Dominant)

• Gametophyte (e.g., moss plant) is large, long-lived, photosynthetic, free-living, dominant.
• Antheridia (male) produce flagellated antherozoids; archegonia (female) produce egg.
• Requires external water for antherozoids to swim and fertilize egg, forming diploid zygote.
• Zygote develops into a sporophyte (foot, seta, capsule/sporangium) attached to and dependent on the gametophyte.
• Meiosis in capsule produces haploid spores, which germinate into new gametophyte (via protonema in mosses).

5.3 Life Cycle in Pteridophytes (Sporophyte-Dominant, e.g., Ferns)

• Sporophyte (e.g., fern plant) is large, dominant, long-lived, with true roots, stems (rhizomes), and leaves (fronds).
• Sori (clusters of sporangia) on fronds produce haploid spores by meiosis.
• Spores germinate into a small, short-lived, independent, photosynthetic gametophyte (prothallus).
• Prothallus bears antheridia and archegonia.
• Requires external water for motile antherozoids to swim for fertilization.
• Zygote develops into new sporophyte, initially dependent on prothallus, then independent.

5.4 Life Cycle in Gymnosperms (e.g., Pinus)

• Greater sporophyte dominance and marked reduction of gametophyte.
• Independence from external water for fertilization (key adaptation to dry environments).
• Pine tree is the sporophyte, bearing male (pollen) and female (seed) cones.
• Male cones produce microspores → pollen grains (reduced male gametophyte).
• Female cones bear ovules, each containing a megaspore → reduced female gametophyte with archegonia.
• Pollination (wind) transfers pollen to ovule; pollen tube delivers non-motile male gametes directly to egg.
• After fertilization, ovule develops into a seed containing new diploid embryo (next sporophyte generation), which is 'naked' (not enclosed in a fruit).

5.5 Life Cycle in Angiosperms (Flowering Plants)

• Most extreme reduction of gametophyte generation.
• Unique feature: double fertilization.
• Flowering plant is the sporophyte; flowers are reproductive structures.

5.5.1 Formation of Gametophytes

• Microsporogenesis (in anther): Microspore mother cells → haploid microspores → pollen grain (mature male gametophyte, with tube cell and generative cell).
• Megasporogenesis (in ovule): Megaspore mother cell → four megaspores (one survives) → embryo sac (mature female gametophyte, with 8 nuclei in 7 cells, including egg cell and central cell with two polar nuclei).

5.5.2 Pollination and Double Fertilisation

• Pollination: Pollen transferred to stigma (by wind, water, animals).
• Pollen tube grows down style, delivering two sperm cells to embryo sac.
• Double Fertilization:
  1. First sperm cell + egg cell → diploid (2n) zygote (develops into embryo).
  2. Second sperm cell + two polar nuclei of central cell → triploid (3n) endosperm (nutritive tissue).
• Ovule develops into seed (embryo + endosperm + seed coat).
• Ovary wall develops into fruit (pericarp), enclosing and protecting seeds (defining feature of angiosperms).

5.6 Comparative Trend Across Groups

• Bryophytes: Gametophyte dominant, large/independent; Requires water for fertilization.
• Pteridophytes: Sporophyte dominant, small/independent gametophyte (prothallus); Requires water for fertilization.
• Gymnosperms: Sporophyte dominant, very reduced/dependent gametophyte; No external water (pollen tube).
• Angiosperms: Sporophyte dominant, extremely reduced/dependent gametophyte; No external water (pollen tube), double fertilization.

Evolutionary trend: Progressive reduction of gametophyte, increasing sporophyte dominance, and independence from external water for fertilization.

Week 6: Growth and Forms of Plants

6.1 Plant Growth: Definitions and Characteristics

Growth: Irreversible, permanent increase in size, mass, and/or cell number, usually localized to specific regions called meristems.

6.1.1 Meristems

Regions of continuously dividing, undifferentiated cells responsible for growth.

• Apical meristems: At tips of roots and shoots; responsible for primary growth (increase in length).
• Lateral meristems: Parallel to sides of roots/stems (vascular cambium, cork cambium); responsible for secondary growth (increase in girth/thickness).
• Intercalary meristems: Between mature tissue (e.g., base of internodes/leaves in grasses); allow renewed elongation after damage.

6.1.2 Primary and Secondary Growth

• Primary growth: From apical meristems; produces primary plant body (increase in length of roots/shoots), forms primary tissues (epidermis, ground, primary vascular tissue).
• Secondary growth: From lateral meristems (vascular cambium → secondary xylem/phloem; cork cambium → periderm/bark); results in increased girth. Characteristic of gymnosperms and most dicots.

6.1.3 Phases of Growth

Typically follows a sigmoid (S-shaped) growth curve:

1. Lag phase: Slow initial growth as cells adjust.
2. Log (exponential) phase: Rapid growth (maximal cell division and elongation).
3. Stationary phase: Growth rate slows, eventually plateaus as maturity is reached.

6.2 Plant Forms (Habits)

General form, size, and structure of a mature plant, determined by stem nature (herbaceous vs woody) and growth pattern.

• 6.2.1 Herbs: Soft, green, non-woody stems; usually die back seasonally. Examples: tomato, spinach.
• 6.2.2 Shrubs: Woody perennial plants, smaller than trees; multiple woody stems from ground level, no single dominant trunk. Examples: hibiscus, rose.
• 6.2.3 Trees: Large, woody perennial plants with single, main woody trunk (persists), branching crown well above ground. Undergo extensive secondary growth. Examples: mango, oil palm.
• 6.2.4 Climbers (Lianas/Vines): Weak stems, climb using adaptations.
  • Twiners: Stem coils around support (e.g., yam).
  • Tendril climbers: Modified leaves/stems form tendrils (e.g., passion fruit).
  • Root climbers: Adventitious roots attach stem to support (e.g., ivy).
  • Scramblers: Use hooks/thorns (e.g., bougainvillea).
• 6.2.5 Creepers/Prostrate plants: Weak stems trail along ground, sometimes rooting at nodes. Examples: sweet potato.

6.3 Growth Habits Summary (Key Differences)

• Herb: Soft, non-woody stem; No support needed; e.g., tomato.
• Shrub: Woody, multi-stemmed; No support needed; e.g., hibiscus.
• Tree: Woody, single trunk; No support needed; e.g., mango.
• Climber: Weak, woody or non-woody; Yes (external support); e.g., yam.
• Creeper: Weak, trailing; No (grows along ground); e.g., sweet potato.

6.4 Factors Affecting Plant Growth and Form

• Genetic factors: Inherent species-specific patterns.
• Light: Intensity, quality, duration (photoperiod) affect elongation, branching, flowering.
• Water availability: Affects turgor-driven cell elongation and growth rate.
• Temperature: Affects metabolic/enzymatic reactions.
• Mineral nutrients: Required for cellular material synthesis.
• Plant hormones: Auxins, gibberellins, cytokinins, ethylene, abscisic acid regulate growth.

Week 7: Cell Structure and Function — Part I

7.1 The Plant Cell: Overview

Eukaryotic cells with membrane-bound nucleus and organelles. Distinct from animal cells by rigid cell wall, large central vacuole, and plastids (e.g., chloroplasts).

7.2 The Cell Wall

Rigid, non-living structure external to plasma membrane, providing shape, mechanical support, protection against osmotic bursting.

Layers of the cell wall

• Middle lamella: Outermost layer, shared between adjacent cells, composed of calcium and magnesium pectates; cements cells together.
• Primary wall: Thin, flexible layer in young, growing cells; cellulose microfibrils in hemicellulose/pectin matrix; allows cell expansion.
• Secondary wall: Thick, rigid layer internal to primary wall after growth stops; in cells needing strength (e.g., xylem, sclerenchyma); often lignified (rigidity, waterproofing).

Functions of the cell wall

• Mechanical strength and support.
• Determines cell shape.
• Prevents excessive water uptake and bursting (counteracts turgor pressure).
• Permits water/solute movement (via plasmodesmata and pits).
• Barrier against pathogens.

7.3 The Plasma Membrane (Plasmalemma)

Selectively permeable membrane, phospholipid bilayer with proteins (fluid mosaic model). Regulates substance movement (diffusion, osmosis, facilitated diffusion, active transport).

7.4 The Nucleus

Largest, most conspicuous organelle; control centre.

• Nuclear envelope: Double membrane with nuclear pores.
• Nucleoplasm: Semi-fluid matrix.
• Chromatin: Diffuse network of DNA and associated proteins (histones); condenses into chromosomes.
• Nucleolus: Dense region for ribosomal RNA synthesis and ribosome assembly.

Function: Houses genetic material (DNA), controls cellular activities by regulating gene expression.

7.5 The Cytoplasm and Cytosol

• Cytoplasm: All living contents between plasma membrane and nucleus.
• Cytosol: Fluid matrix of cytoplasm; site of metabolic reactions (e.g., glycolysis).

7.6 Plastids

Double-membrane-bound organelles unique to plant cells, involved in photosynthesis, storage, pigmentation.

• 7.6.1 Chloroplasts: Site of photosynthesis; contain chlorophyll (in grana/thylakoids, stroma). Possess own circular DNA and ribosomes (endosymbiotic theory).
• 7.6.2 Chromoplasts: Contain non-chlorophyll pigments (carotenoids) responsible for yellow, orange, red colors of fruits/flowers/roots.
• 7.6.3 Leucoplasts: Colorless plastids specialized for storage (e.g., amyloplasts for starch, elaioplasts for lipid, proteinoplasts for protein).

7.7 The Vacuole

Mature plant cells have a single, large central vacuole (up to 90% cell volume), bounded by tonoplast.

• Functions: Storage (water, ions, sugars, pigments, waste products).
• Maintenance of turgor pressure (pressure against cell wall), essential for rigidity in non-woody tissues.
• Contains hydrolytic enzymes (lysosome-like function).

7.8 Mitochondria

Double-membrane-bound organelles, site of aerobic cellular respiration, producing ATP. Inner membrane folded into cristae (electron transport chain); interior matrix has Krebs cycle enzymes. Possess own DNA and ribosomes.

7.9 Summary Table (Key Organelles)

• Cell wall: Rigid, layered; Support, shape, protection.
• Plasma membrane: Phospholipid bilayer; Selective permeability, transport.
• Nucleus: Double membrane, chromatin, nucleolus; Genetic control centre.
• Chloroplast: Double membrane, grana/thylakoids, stroma; Photosynthesis.
• Vacuole: Single membrane (tonoplast), fluid-filled; Turgor, storage, waste.
• Mitochondrion: Double membrane, cristae, matrix; Aerobic respiration/ATP production.

Week 8: Cell Structure and Functions Part II

8.1 Introduction

Covers remaining organelles, cytoskeleton, cell-to-cell communication, and plant/animal cell comparison.

8.2 The Endoplasmic Reticulum (ER)

Extensive network of interconnected membranous tubules and flattened sacs (cisternae), continuous with nuclear envelope.

• Rough ER (RER): Studded with ribosomes; synthesizes proteins for secretion, plasma membrane, or other organelles; involved in protein folding.
• Smooth ER (SER): Lacks ribosomes; synthesizes lipids/steroids, detoxifies compounds.

8.3 The Golgi Apparatus (Golgi Body/Dictyosome)

Stack of flattened, membrane-bound sacs (cisternae). Receives proteins/lipids from ER, modifies (e.g., glycosylation), sorts, and packages them into vesicles. In plant cells, crucial for synthesizing and secreting polysaccharides for cell wall construction.

8.4 Ribosomes

Small, non-membrane-bound structures of rRNA and proteins. Site of protein synthesis (translation). Found free in cytosol, bound to RER, and within mitochondria/chloroplasts.

8.5 Peroxisomes and Glyoxysomes

Small, single-membrane-bound organelles with oxidative enzymes.

• Peroxisomes: In leaf cells, role in photorespiration (with chloroplasts and mitochondria).
• Glyoxysomes: Specialized peroxisomes in fat-storing seeds; contain enzymes of glyoxylate cycle, converting stored fats to sugars during germination.

8.6 The Cytoskeleton

Dynamic network of protein filaments throughout cytoplasm, providing structural support, cell shape maintenance, intracellular movement.

• Microtubules: Hollow tubes of tubulin; involved in cell division (spindle fiber formation), guiding cellulose deposition, intracellular transport.
• Microfilaments: Solid filaments of actin; involved in cytoplasmic streaming, cell shape changes.

8.7 Plasmodesmata

Minute channels traversing the cell wall, connecting cytoplasm of adjacent plant cells (lined by plasma membrane continuum). Allow direct communication and transport of water, nutrients, signaling molecules, functionally linking plant cytoplasm into symplast.

8.8 Comparing Plant and Animal Cells (Key Differences)

• Cell wall: Plant: Present (cellulose); Animal: Absent.
• Plastids (chloroplasts): Plant: Present; Animal: Absent.
• Vacuole: Plant: Large, single, central; Animal: Small, if present, numerous.
• Shape: Plant: Fixed, rectangular/polygonal; Animal: Variable, usually rounded.
• Centrioles: Plant: Generally absent; Animal: Present.
• Storage carbohydrate: Plant: Starch; Animal: Glycogen.
• Plasmodesmata: Plant: Present; Animal: Absent (have gap junctions).

8.9 Cell Division: A Brief Overview

Plant growth involves cell division (mitosis) followed by cytokinesis (cytoplasm division). Plant cytokinesis involves formation of a cell plate (from Golgi-derived vesicles) from center outwards, forming a new cell wall between daughter cells (unlike animal cells that divide by pinching).

Week 9: Morphology of Flowering Plants

9.1 Introduction

Morphology: Study of external form and structure. Flowering plant (angiosperm) body is organized into a root system and a shoot system (stem, leaves, flowers, fruits).

9.2 The Root System

Underground portion, from radicle, lacks nodes/internodes/chlorophyll.

Functions of roots

• Anchorage.
• Absorption of water and mineral nutrients (via root hairs).
• Storage of food reserves (e.g., taproots).
• Conduction of water/minerals upward, photosynthates downward.
• Synthesis of hormones (e.g., cytokinins).

Types of root systems

• Taproot system: Single dominant primary root with smaller lateral roots (typical of dicots).
• Fibrous root system: Numerous adventitious roots of similar size, replacing short-lived primary root (typical of monocots).

Root modifications

• Storage roots: Swollen for food storage (e.g., cassava, carrot, sweet potato).
• Prop/stilt roots: Adventitious roots for extra support (e.g., maize, mangrove).
• Pneumatophores: Specialized roots growing upward for gas exchange in waterlogged soils (e.g., mangrove).
• Aerial roots: Growing above ground, absorb atmospheric moisture (e.g., orchids).

9.3 The Stem

Aerial, ascending axis, bearing nodes (leaf/bud attachment) and internodes (regions between nodes), with apical and axillary buds.

Functions of the stem

• Support and elevation of leaves, flowers, fruits.
• Conduction of water/minerals (xylem) and food (phloem).
• Storage of food and water.
• Vegetative propagation.

Stem modifications

• Rhizome: Underground horizontal stem (e.g., ginger).
• Tuber: Swollen underground stem for storage, with "eyes" (nodes with buds) (e.g., potato).
• Corm: Short, vertical, swollen underground stem (e.g., cocoyam).
• Bulb: Short stem surrounded by fleshy storage leaves (e.g., onion).
• Stolon/runner: Horizontal above-ground stem that roots at nodes (e.g., strawberry).
• Thorns (stem thorns): Hardened, pointed stem modification for defence (e.g., Bougainvillea, Citrus).

9.4 The Leaf

Lateral appendage of stem, typically flattened and thin. Primary site of photosynthesis and transpiration.

Parts of a typical leaf

• Leaf base: Point of attachment; may bear stipules.
• Petiole: Stalk connecting leaf blade to stem (sessile leaves lack petiole).
• Lamina (leaf blade): Expanded, flattened portion; contains midrib and veins.

Leaf types

• Simple leaf: Single, undivided lamina (e.g., mango).
• Compound leaf: Lamina divided into distinct leaflets attached to a common rachis; pinnately compound (leaflets along central axis, e.g., neem) or palmately compound (leaflets radiating from single point, e.g., silk cotton).

Leaf arrangement (phyllotaxy)

• Alternate: One leaf per node, arranged alternately.
• Opposite: Two leaves per node, positioned opposite.
• Whorled: Three or more leaves per node, arranged in a circle.

Leaf modifications

• Tendrils: For climbing (e.g., pea).
• Spines: For defence and water conservation (e.g., cactus).
• Storage leaves: Fleshy, water-storing (e.g., Aloe vera, onion bulb scales).

9.5 The Flower

Specialized reproductive structure of angiosperms, borne on a pedicel, expanding into a receptacle, upon which floral parts are arranged in four whorls:

1. Calyx: Outermost whorl, composed of sepals (usually green); protect flower bud.
2. Corolla: Composed of petals (usually brightly colored); attract pollinators.
3. Androecium: Male reproductive whorl, composed of stamens (each with a filament and an anther producing pollen).
4. Gynoecium (pistil): Female reproductive whorl, composed of one or more carpels (each differentiated into an ovary (containing ovules), a style, and a stigma (receives pollen)).

Notes:

• Perianth = calyx + corolla.
• Tepals: When sepals and petals are not differentiated.
• Complete flower: Possesses all four whorls.
• Bisexual (perfect/hermaphrodite) flower: Has both androecium and gynoecium.
• Unisexual (imperfect) flower: Has either staminate (male) or pistillate (female) parts only.

Week 10: Types of Fruits and Seeds

10.1 The Fruit: Definition and Formation

A fruit is the matured, ripened ovary of a flower (sometimes with associated floral parts); protects developing seeds and aids dispersal. Parthenocarpy: Fruit development without fertilization, producing seedless fruits (e.g., some banana varieties).

The fruit wall, the pericarp, develops from the ovary wall and has three layers:

• Epicarp (exocarp): Outermost skin.
• Mesocarp: Middle layer, often fleshy or fibrous.
• Endocarp: Innermost layer, in contact with seeds; may be hard and stony (e.g., mango "stone").

10.2 Classification of Fruits

Based on (i) number of flowers/ovaries and (ii) texture of pericarp.

10.2.1 Simple Fruits

Develop from a single ovary of a single flower.

• (a) Simple fleshy fruits (pericarp fleshy/succulent at maturity):
  • Berry: Entirely fleshy pericarp, 1+ seeds embedded (e.g., tomato, banana).
  • Drupe: Fleshy mesocarp, hard/stony endocarp forming a "stone" around single seed (e.g., mango, coconut).
  • Pome: False fruit; fleshy edible part from receptacle/floral tube surrounding true ovary (core) (e.g., apple, pear).
  • Pepo: Berry-like with hard, thick rind (cucurbit family) (e.g., watermelon).
  • Hesperidium: Berry with leathery, oil-glandular rind and segmented flesh (citrus) (e.g., orange, lemon).
• (b) Simple dry fruits (pericarp dry, hard, or papery at maturity):
  • Dehiscent (split open):
    • Legume/pod: Splits along two sutures (e.g., beans, groundnut pod).
    • Capsule: Splits various ways to release many seeds (e.g., cotton, okra).
  • Indehiscent (do not split open):
    • Achene: Small, single-seeded, seed not fused to pericarp (e.g., sunflower "seed").
    • Caryopsis (grain): Single-seeded, seed coat fused to pericarp (grasses) (e.g., maize, rice).
    • Nut: Single-seeded, hard, woody pericarp (e.g., cashew nut, groundnut kernel).

10.2.2 Aggregate Fruits

Develop from numerous separate carpels (ovaries) of a single flower, which fuse into one structure (e.g., custard apple, soursop, raspberry, strawberry).

10.2.3 Multiple (Composite) Fruits

Develop from ovaries of many separate flowers clustered on a single inflorescence, fusing into what appears to be a single fruit (e.g., pineapple, jackfruit, fig).

10.4 The Seed

Develops from a fertilized ovule; dispersal and propagation unit of gymnosperms and angiosperms. Comprises an embryo, stored food reserves, and a protective seed coat.

10.4.1 Structure of a Typical Seed

• Seed coat (testa): Protective outer covering (from integument). Bears hilum (attachment scar) and sometimes a micropyle (pollen tube entry, water uptake).
• Embryo: Young plant, comprising plumule (embryonic shoot), radicle (embryonic root), and cotyledon(s) (seed leaves).
• Endosperm: Nutritive tissue; abundant in many monocots (e.g., maize), but often absorbed by cotyledons in dicots (e.g., bean).

10.4.2 Seeds as Dispersal and Storage Units

Seeds allow survival during unfavorable periods (dormancy) and dispersal. Adaptations include wings, hooks, buoyant husks, edible flesh.

10.5 Seed Dispersal Mechanisms

• Wind (anemochory): Light seeds, wings, plumes/hairs (e.g., Terminalia, cotton).
• Water (hydrochory): Buoyant, waterproof coat (e.g., coconut, mangrove).
• Animals (zoochory): Fleshy/edible fruit, or hooks/spines (e.g., mango eaten, Desmodium hooks).
• Self-dispersal (autochory): Explosive/dehiscent pods (e.g., beans, balsam).

Week 11: Botanical Drawings and Use of the Microscope

11.1 Principles of Botanical Drawing

Accurate biological/botanical drawing is essential for recording observations. Prioritizes scientific accuracy over aesthetic effect.

11.1.1 General Rules for Biological Drawing

• Use sharp HB pencil on plain white paper; no pen initially.
• Draw only what is observed; no imagined detail.
• Use clean, single, continuous lines; avoid sketchy/hairy lines.
• Never shade; use stippling for densities if necessary.
• Drawings must be large enough to show detail (typically half a page).
• Maintain accurate proportions.
• Label lines drawn with a ruler, not crossing, touching exact structure.
• Labels written horizontally, to one side or around drawing.
• Include a title (e.g., "T.S. of dicot stem") and magnification (e.g., ×100) or scale bar.

11.2 Types of Botanical Drawings

• Low-power (plan) diagrams: Show outline and distribution of main tissues (e.g., vascular bundles, cortex, epidermis) without cellular detail.
• High-power (detail) drawings: Show a small part of specimen in cellular detail, illustrating individual cell structure, shape, arrangement, from a representative sector.

11.3 The Compound Light Microscope

Standard tool for examining small plant cells and tissues, using lenses for high magnification.

11.3.1 Parts of the Compound Microscope and their Functions

• Eyepiece (ocular lens): Magnifies x10, closest to eye.
• Objective lenses: Mounted on nosepiece (e.g., x4, x10, x40, x100); primary magnification.
• Nosepiece: Rotating turret holding objective lenses; switches magnifications.
• Stage: Flat platform for slide; may have clips or mechanical stage.
• Diaphragm/Iris: Regulates light passing through specimen.
• Condenser: Lens system beneath stage, focuses light onto specimen.
• Light source: Illuminates specimen from below (mirror or built-in lamp).
• Coarse adjustment knob: Rapid, large focusing movements (stage/tube).
• Fine adjustment knob: Small, precise focusing adjustments (stage/tube).
• Body tube: Connects eyepiece to objective lenses, maintains optical distance.
• Base: Supports microscope.
• Arm: Connects base to body tube; used for carrying.

11.3.2 Calculating Total Magnification

Total magnification = Eyepiece magnification × Objective lens magnification (e.g., x10 eyepiece × x40 objective = x400).

11.3.3 Proper Use and Care of the Microscope

1. Carry with both hands (base and arm).
2. Begin observation with lowest-power objective lens.
3. Place and secure slide on stage.
4. Use coarse adjustment knob (looking from side) to bring objective close to slide.
5. Looking through eyepiece, slowly move objective away with coarse adjustment until rough focus.
6. Use fine adjustment knob to sharpen focus.
7. Adjust diaphragm/light intensity for optimal contrast.
8. To increase magnification, rotate nosepiece to higher-power objective; refine focus with fine adjustment only (higher powers are close to slide, avoid contact).
9. After use, return to lowest power, remove slide, clean lenses with lens paper, store covered.

11.3.4 Preparing a Temporary (Wet Mount) Slide

1. Place a drop of water (or stain) in center of clean glass slide.
2. Place thin section or peel of specimen into the liquid.
3. Lower a coverslip at an angle with a mounted needle to avoid air bubbles.
4. Remove excess liquid with blotting paper.

11.4 Care of the Microscope

• Clean lenses only with special lens tissue; no cloth/paper towels or fingers.
• Do not force focusing knobs.
• Keep microscope covered, stored in dry, dust-free cabinet.
• Carry upright at all times.