sbn revision notes

SECTION A (SHORT ANSWER QUESTIONS, 40 MARKS)

1) Describe the methods used for preparing herbarium specimens. (6 marks)

Collection of Specimens: The first step in preparing herbarium specimens is to collect plant samples from the field. This involves selecting healthy plants and avoiding obscured or damaged specimens. The specimen should include flowers, fruits, leaves, and sometimes roots to provide a complete representation of the plant.
Pressing: After collection, specimens are pressed using a herbarium press. This involves placing the plant material between sheets of blotting paper or newspaper and applying even pressure. The pressing should occur promptly to prevent drying out or deterioration.
Drying: Specimens should be thoroughly dried to prevent mold growth and ensure preservation. Traditionally, air-drying is used, but modern methods utilize dehydrators or ovens set at low temperatures to hasten the process.
Labeling: Each specimen is labeled with crucial data, including the scientific name, date of collection, location, habitat, and collector's name. This label is often glued to the bottom of the herbarium sheet.
Mounting: Once dried and labeled, specimens are mounted onto herbarium sheets, usually made of acid-free paper to prevent degradation over time.
Storage: Finally, the mounted specimens are stored in herbarium cabinets under controlled environmental conditions to enhance longevity.

2) Describe how to store herbarium specimens. (5 marks)

Environmental Conditions: Herbarium specimens should be stored in a temperature-controlled environment, ideally between 18-24 degrees Celsius (64-75 degrees Fahrenheit), with humidity levels maintained at 40-50% to avoid mold and insect infestations.
Storage Cabinets: Specimens are kept in herbarium cabinets that shield them from light, which can cause fading of colors and degradation of plant tissues. Cabinets should be made of non-reactive materials.
Arrangement: Specimens are organized systematically, usually by family and then genera, to facilitate retrieval. Proper cataloging is crucial for easy access.
Protection from Pests: Regular monitoring for pests is necessary. Specimens may be treated with insecticides or stored with silica gel packets to reduce moisture.
Digitization: Many modern herbariums digitize their collections to ensure backup and enable remote access, allowing researchers to study specimens without physical handling.

3) List characteristics of Coniferophyta.

Vascular Plants: Coniferophyta are vascular plants characterized by xylem and phloem.
Cones: Reproductive structures typically in the form of cones rather than flowers.
Needle-like Leaves: Leaves are often needle-like or scale-like, adapted to conserve water and withstand cold conditions.
Pollination: Mostly wind-pollinated.
Seed Formation: Seeds are usually exposed on the scales of cones, a trait known as gymnospermy.
Wood Formation: They have a thick layer of wood due to secondary growth, contributing to their structure and longevity.

4) Explain why the 18 S rRNA gene is employed in the identification of plants. (4 marks)

Molecular Marker: The 18 S rRNA gene is a part of the ribosomal RNA sequence, commonly used as a molecular marker due to its presence in all eukaryotic organisms.
Conserved Sequence: It exhibits highly conserved regions that allow for universal primer design, making it applicable across a wide range of plant species.
Phylogenetic Studies: Variability in the 18 S rRNA gene helps in constructing phylogenetic relationships and determining evolutionary lineage, providing insight into plant taxonomy and biodiversity.
Easy Amplification: The gene can be easily amplified and sequenced using standard laboratory techniques, facilitating rapid identification and classification of plant species.

5) Outline the contributions of Carl Linnaeus to modern plant taxonomy. (6 marks)

Binomial Nomenclature: Developed the system of binomial nomenclature, where each species is assigned a unique, two-part Latin name, consisting of the genus name and the specific epithet (e.g., Homo sapiens).
Classification System: Established a hierarchical classification system that arranged plants into categories (kingdom, class, order, genus, species) based on shared characteristics.
Systema Naturae: His work, Systema Naturae, laid the foundational principles for biological classification, influencing future taxonomy systems.
Type Specimens: Introduced the concept of type specimens, which serve as a reference point for the identity of species and accurate classification.
Promotion of Botanical Study: Encouraged systematic botanical studies and documentation, promoting the exploration and understanding of biodiversity.
Standardized Terminology: Created standardized terminology that allowed for improved communication among botanists and clearer descriptions of plant species.

6) Describe adaptive radiation using relevant examples. (6 marks)

Definition of Adaptive Radiation: Adaptive radiation refers to the rapid evolution of diversely adapted species from a common ancestor in response to varying environmental pressures and ecological niches.
Example - Darwin's Finches: A classic example of adaptive radiation is Darwin's finches found in the Galápagos Islands. They evolved from a common ancestor into multiple species with different beak sizes and shapes adapted to specific food sources (e.g., large beaks for cracking seeds, slender beaks for probing flowers).
Example - Cichlid Fish: Another example is the adaptive radiation of cichlid fish in African Great Lakes. Various species evolved specialized feeding methods, body sizes, and reproductive strategies in response to the diverse aquatic environments and niches within these lakes.
Significance: Adaptive radiation illustrates the principles of natural selection and the impact of ecological diversity on species evolution, demonstrating how organisms can rapidly adapt to exploit available ecological opportunities.

7) Outline the characteristics of the typological species concept. (5 marks)

Definition: The typological species concept defines species based on a specific type specimen that embodies the defining characteristics of that species.
Morphological Focus: Emphasizes morphological traits, often focusing on physical features such as shape, size, and color.
Single Type Specimen: Relies on a single specimen as the primary reference point for the species, known as the type specimen.
Limited Variation Consideration: This concept tends to overlook variations within populations, as it does not account for the genetic and ecological diversity among individuals.
Historical Context: Predominant in early taxonomy, it has been largely replaced by more modern concepts that acknowledge evolutionary relationships and genetic diversity, yet it still provides a foundational understanding of species identification.

8) Discuss authorship as a rule of botanical nomenclature. (4 marks)

Definition of Authorship: Authorship in botanical nomenclature refers to the individual or group who first validly publishes a scientific name, thus establishing it within the scientific community.
Citation of Authors: When naming a species, the author’s name is included alongside the scientific name (e.g., Quercus rubra L. indicates Linnaeus as the author).
Principle of Priority: The principle of priority states that the first validly published name of a species takes precedence over later names, promoting stability in nomenclature.
Role in Taxonomy: Proper attribution to authors is critical for historical acknowledgment and for tracing the development of botanical knowledge, ensuring clarity and continuity in scientific communication.