Biology Notes

Biology Past Questions and Answers (2023)

Question 1a: Explanation of Terms

Taxonomy

• Definition: Taxonomy is the branch of Biology concerned with the classification, naming, and identification of living organisms based on their shared characteristics.

• Purpose: It organizes life into a hierarchy to illustrate evolutionary relationships.

• Hierarchical Structure: (Ranked from Broadest to Most Specific)

  • Kingdom (e.g., Animalia)

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

Binomial Nomenclature

• Definition: A formal system of naming organisms, introduced by Carl Linnaeus, using two parts (both in Latin) ensuring that scientists globally use the same name for the same organism.

• Components:

  • Genus: The first name; always begins with a capital letter.

  • Species: The second name; always begins with a lowercase letter.

• WASSCE Writing Rules:

  • If written by hand, both words must be underlined separately.

  • If typed, names must be in italics.

• Examples:

  • Human: Homo sapiens (or Homo sapiens)

  • Maize: Zea mays (or Zea mays)

  • Lion: Panthera leo (or Panthera leo)

Question 1b: Characteristics of Classes of Organizations

1. Class: Hepaticae (Liverworts)

• Thalloid Body: The plant body consists of a simple, flattened thallus that is not differentiated into true roots, stems, or leaves.

• Dorsiventral Symmetry: They grow flat on the ground with distinct upper (dorsal) and lower (ventral) surfaces.

• Unicellular Rhizoids: Possess simple, unbranched, hair-like structures for anchorage and water absorption.

• Gemma Cups: Many species have these specialized structures for asexual reproduction.

• Simple Sporophyte: The sporophyte is very small, often lacks a seta (stalk), and is entirely dependent on the gametophyte for nutrition.

2. Class: Musci (Mosses)

• Leafy Appearance: The plant body is differentiated into "stem-like" and "leaf-like" structures, although they lack true vascular tissue.

• Radial Symmetry: The tiny "leaves" are generally arranged in a spiral or radial pattern around a central "axis."

• Multicellular Rhizoids: Unlike liverworts, mosses have branched, multicellular rhizoids for stronger anchorage.

• Complex Capsule: The sporophyte consists of a foot, a long seta, and a complex capsule with a lid (operculum) for regulated spore dispersal.

• Protonema Stage: The life cycle includes a filamentous, branched stage called a protonema that develops from a germinating spore.

Key Difference Between Hepaticae and Musci

• Hepaticae are prostrate (lying flat), while Musci are usually erect (standing up).

Summary Comparison of Hepaticae and Musci

Question 1c: Five Elements Supplied to Plants by Fertilizers

• Fertilizers are important for providing necessary nutrients to plants to ensure healthy crop yields.

• The five common elements supplied are:

  • Nitrogen (N): Essential for rapid leaf and stem growth, commonly found in Urea or NPK fertilizers.

  • Phosphorus (P): Critical for root development and flower/fruit formation.

  • Potassium (K): Aids in disease resistance and overall plant resilience.

  • Magnesium (Mg): Central atom in chlorophyll, necessary for photosynthesis.

  • Calcium (Ca): Important for cell wall structure and maintaining soil pH balance.

• WASSCE Tip: Be familiar with NPK 15-15-15, a common fertilizer, where the numbers represent the percentage of Nitrogen, Phosphorus, and Potassium in that order.

Question 2a: Importance of Water to Plants

• Water is often described as the most critical solvent for life and plays various vital roles in plants. Here are five precise ways it is important to plants:

  • Photosynthesis: Acts as a raw material; in the presence of sunlight and chlorophyll, it combines with carbon dioxide to produce glucose (food).

  • Turgidity (Support): Fills plant cells, creating turgor pressure which keeps cells firm and prevents wilting.

  • Transport Solvent: Serves as a medium that carries dissolved mineral salts from roots to leaves (via xylem) and food from leaves to other parts (via phloem).

  • Transpiration (Cooling): Evaporation from leaves helps to lower the plant's temperature, preventing overheating in high sunlight.

  • Germination: Softens the seed coat and activates enzymes that start the growth of the embryo.

• WASSCE Practical Tip: Be ready to describe an experiment showing the ascent of sap, often demonstrated by placing a Balsam plant in a beaker of colored water (eosin solution).

Summary List of Water's Importance to Plants

1. Water is a raw material for photosynthesis.

2. It maintains turgidity, keeping the plant upright.

3. It acts as a transport medium for minerals from roots.

4. Evaporation through transpiration cools the plant.

5. Water is essential for softening the seed coat to initiate germination.

Question 2a: High Concentration of Salts and Its Impact on Transpiration

• In WASSCE Biology, the reason for reduced transpiration in plants due to high salt concentration in the soil is explained through osmosis. Here’s a breakdown:

  • Lower Water Potential: High salt concentration in soil creates a stronger (more concentrated) soil water solution compared to the sap in root cells.

  • Exosmosis: Water is drawn out of the plant into the soil by osmosis instead of entering the roots.

  • Loss of Turgidity: Plant cells lose water and become flaccid (soft), which causes wilting.

  • Stomatal Closure: To conserve remaining water, plants close their stomata (tiny pores on leaves).

  • Reduced Transpiration: As a result of closed stomata, water vapor cannot escape, significantly slowing or stopping transpiration.

Summary of Water Potential Concepts

• Understanding "High" vs. "Low" Water Potential can be critical, where high water potential means lower solute concentration within cells and promotes water uptake, in contrast to low water potential, which can lead to loss of water and turgidity.