Biology Notes: Key Concepts in Taxonomy, Plant Anatomy and Metabolism
1. Binomial Nomenclature – Rules
Binomial nomenclature is the scientific naming system using two words: Genus + species. The genus begins with a capital letter and the species with a small letter. Scientific names are written in italics or underlined separately when handwritten. Names are generally Latin or Latinised. Example: Mangifera indica.
2. Artificial and Natural Classification – Difference
Artificial: based on a few selected characters, mainly superficial features; does not show true relationships.
Natural: based on many characters such as morphology, anatomy and reproduction; shows overall similarities and natural relationships among organisms.
3. Biosystematics and Taxonomy
Biosystematics: study of organisms, their variation and evolutionary relationships.
Taxonomy: science of identification, nomenclature and classification of organisms. Taxonomy mainly organises organisms into groups, while biosystematics also considers their evolutionary relationships.
4. Herbarium, Lichen and Viroid
Herbarium: collection of dried, pressed and properly labelled plant specimens.
Lichen: symbiotic association between an alga or cyanobacterium and a fungus.
Viroid: very small infectious agent consisting of naked RNA without a protein coat.
5. Merits and Demerits of Five-Kingdom Classification
Merits: separates prokaryotes from eukaryotes; separates unicellular and multicellular organisms; considers mode of nutrition; places fungi separately.
Demerits: some organisms are difficult to place; boundaries between kingdoms can be unclear; evolutionary relationships are not completely represented.
6. General Characters of Pteridophytes
Pteridophytes are vascular cryptogams. They possess true roots, stems and leaves with xylem and phloem. They do not produce flowers or seeds and reproduce by spores. The sporophyte is dominant and independent. They generally grow in moist and shady places. Examples: Pteris, Selaginella, Equisetum.
7. Seed Habit of Pteridophytes
Seed habit means the development of features leading toward seed formation. Some pteridophytes show heterospory, producing microspores and megaspores. The megaspore may be retained and the female gametophyte develops within it. These features are considered important steps toward the evolution of seeds.
8. Seed Habit in Pteridophytes – Features
Important features are heterospory, formation of microspores and megaspores, reduction in number of megaspores, retention of megaspore, and development of female gametophyte within the megaspore. These features resemble some stages in seed evolution.
9. Monocots and Dicots – Difference
Monocots: one cotyledon, fibrous root, parallel venation, vascular bundles scattered, floral parts usually in threes.
Dicots: two cotyledons, tap root, reticulate venation, vascular bundles usually in a ring, floral parts usually in fours or fives.
10. Inflorescence, Floral Formula and Floral Diagram
Inflorescence: arrangement of flowers on the floral axis. It may be racemose or cymose.
Floral formula: symbolic representation of different floral parts.
Floral diagram: graphical representation showing number, arrangement and relationship of floral parts.
11. Solanaceae Family
Solanaceae includes herbs, shrubs and sometimes small trees. Leaves are generally alternate and simple. Flowers are bisexual, actinomorphic and pentamerous. The calyx has 5 fused sepals; the corolla has 5 fused petals; stamens are 5 and epipetalous. The ovary is superior and bicarpellary. Fruit is usually a berry or capsule. Examples: Solanum, Datura, Petunia, Nicotiana.
12. Tissue System in Plants
There are three tissue systems:
- Epidermal tissue system – protects the plant and includes epidermis, stomata and trichomes.
- Ground tissue system – includes cortex, pith and related tissues; performs storage and photosynthesis.
- Vascular tissue system – consists of xylem and phloem and conducts water, minerals and food.
13. Anatomy of Monocot and Dicot Stem and Leaf
Dicot stem: vascular bundles arranged in a ring, usually open with cambium; distinct cortex and pith.
Monocot stem: vascular bundles scattered and usually closed; ground tissue is not clearly differentiated.
Dicot leaf: generally dorsiventral with distinct palisade and spongy tissues.
Monocot leaf: generally isobilateral with similar upper and lower surfaces.
14. Glycolysis
Glycolysis is the breakdown of one glucose molecule into two pyruvate molecules. It occurs in the cytoplasm and does not directly require oxygen. It involves a series of enzymatic reactions that produce ATP and NADH. It is the first major stage of cellular respiration.
15. Krebs Cycle
The Krebs cycle occurs mainly in the mitochondrial matrix. Acetyl-CoA combines with oxaloacetate and undergoes a series of reactions. During the cycle, carbon dioxide is released and NADH, FADH₂ and ATP/GTP are produced. These reduced coenzymes supply electrons to the electron transport system.
16. Electron Transport System (ETS)
The ETS occurs on the inner mitochondrial membrane. Electrons from NADH and FADH₂ pass through a series of electron carriers. The energy released is used to pump H⁺ ions across the membrane, creating a proton gradient. H⁺ returns through ATP synthase and drives ATP formation. Oxygen acts as the final electron acceptor.
17. Chemiosmotic Hypothesis
The chemiosmotic hypothesis explains ATP formation through a proton gradient. Electron transport pumps H⁺ ions across the inner mitochondrial membrane, creating an electrochemical gradient. H⁺ ions flow back through ATP synthase, and the energy released is used to form ATP from ADP and Pi.
18. C3 and C4 Plants – Difference
C3 plants: first stable product is a 3-carbon compound; Calvin cycle occurs in mesophyll cells; Kranz anatomy absent; photorespiration is relatively higher.
C4 plants: first stable product is a 4-carbon compound; have Kranz anatomy; initial CO₂ fixation occurs in mesophyll cells; photorespiration is very low; better adapted to high light and temperature.
19. Factors Affecting Photosynthesis
Major factors are light, carbon dioxide, temperature, water, chlorophyll and mineral nutrients. Increasing light intensity increases photosynthesis up to a limit. Higher CO₂ generally increases the rate up to a saturation point. Temperature affects enzyme activity. Water shortage closes stomata and reduces CO₂ entry.
20. Photorespiration
Photorespiration is a light-dependent process associated mainly with C3 plants. When RuBisCO acts as an oxygenase, it combines RuBP with O₂ instead of CO₂. This leads to loss of fixed carbon and energy and produces no useful sugar. It occurs through chloroplasts, peroxisomes and mitochondria.
21. Differentiation and Dedifferentiation
Differentiation: process by which unspecialised cells become specialised in structure and function.
Dedifferentiation: process in which mature differentiated cells regain the ability to divide. Example: formation of cambium from mature cells. Dedifferentiated cells may later undergo redifferentiation.
22. Physiological Effects of Auxin, Cytokinin and ABA
Auxin: promotes cell elongation, root initiation, apical dominance and fruit growth.
Cytokinin: promotes cell division, shoot formation and delays leaf ageing.
ABA: promotes seed dormancy, inhibits growth and causes stomatal closure during water stress.
23. Respiratory Quotient of Carbohydrates and Fats
Respiratory quotient (RQ) = CO₂ released / O₂ consumed.
For carbohydrates: RQ = 1.0.
For fats: RQ ≈ 0.7.
Thus, the RQ differs according to the respiratory substrate being oxidised.
24. Photosynthesis
Photosynthesis is the process by which green plants prepare food using CO₂ and water in the presence of light and chlorophyll, releasing oxygen. It mainly occurs in chloroplasts. The overall equation is:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll).
25. Well-Labelled Flower Diagram
Draw a neat longitudinal section of a flower and label: sepal, petal, anther, filament, stigma, style, ovary, ovule, thalamus and pedicel. Show the four main whorls: calyx, corolla, androecium and gynoecium.