AS Biology Theme 1

Theme 1: Classification of Living Organisms

Topic 1.1 Classification

Objectives

• Learners will know how the hierarchical classification systems are used.

Learning Outcomes

• Learners should be able to:

  • Use and describe the binomial system of naming organisms.

  • Describe the use of a hierarchical classification system for living organisms.

  • Explain the concept of natural classification, based on homologous features and evolutionary relationships.

  • Construct dichotomous keys for the identification of locally occurring organisms.

  • Discuss the meaning of the term species, limited to the biological, morphological, ecological, and behavioral concepts.

Binomial System

Definition

• The binomial system refers to giving organisms a scientific name composed of two name parts:

  • Genus: The first part, starting with a capital letter.

  • Species: The second part, starting with a lower case letter.

• The binomial name is written in italics when typed and underlined when handwritten.

Examples of Binomial Names

• Tiger: Panthera tigris

• Honey bee: Apis mellifera

• Cheetah: Acinonyx jubatus

• Leopard: Panthera pardus

• Welwitschia: Welwitschia mirabilis

• Donkey: Equus asinus

• Cattle: Bos taurus

• Kudu: Tragelaphus strepsiceros

• Papaya: Carica papaya

• Lemon: Citrus limon

Hierarchical Classification System

Overview

• Living organisms are divided into several groups based on shared features and genetic relationships.

Structure

• The classification starts from the broadest category, Kingdom, which is the largest group. There are five kingdoms:

  • Prokaryotes (including bacteria)

  • Protista

  • Fungi

  • Plantae

  • Animalia

Levels of Classification

• Kingdom -> Phylum (plural: phyla) -> Class -> Order -> Family -> Genus -> Species.

6 Kingdoms of Organisms

From Domains

The classification expands from domains: Archaea, Bacteria, and Eukarya to the six kingdoms:

Natural Classification

Definition

• Based on the ideas of homologous structures and evolutionary relationships.

Homologous Structures

• Features of organisms that are similar in structure, position and development but adapted for different purposes.

Example of Homologous Structures

• Examples include the flipper of a whale, the human arm, the front leg of a cat, and the wings of a bat. All these structures have similar bones but serve different functions.

Characteristics of Homologous Structures

• Similar in structure.

• Similar in position and development.

• Share common ancestry.

• May not have similar functions and can appear very different.

Artificial Classification

Analogous Structures

• Features that perform similar functions but differ in structure.

• No evolutionary relationship implied between organisms with analogous structures.

$Class Work$

1. Outline the Hierarchical system in descending order. (3)

2. Prokaryotic and eukaryotic organisms can be classified depending on their cellular structure:

   • Describe three structural differences between prokaryotic and eukaryotic cells. (3)

3. In the field of taxonomy, organisms are identified by using their species and genus names:

   • What is the term used for this method of naming organisms?

4. Use the name of a sheep (Ovis aries) to describe the term mentioned in 3. (a)

5. Complete the table by filling in the blank spaces with the correct terms related to the European water vole, Arvicola amphibius.

6. Explain how homologous structures provide evidence for the theory of evolution by common descent, using an example. (6)

7. Identify another method for defining species and one limitation.

Concepts of Species

Definition

• A group of organisms capable of interbreeding and producing fertile offspring

• The term species can be defined through several concepts:

  1. Biological species concept

  2. Morphological species concept

  3. Ecological species concept

  4. Behavioral species concept

1. Biological Species Concept

• Defined as a group of closely related species that have the potential to interbreed and produce viable, fertile offspring.

• Central Idea: Interbreeding ability is crucial.

• Limitations: Applies poorly to extinct species and asexual reproduction species.

2. Morphological Species Concept

• Group of organisms that are similar in appearance both internal and external structures. Based on body size, shape, and other structural features.

• Advantage: Useful for extinct species without DNA.

• Limitation: May be misleading due to convergent evolution.

3. Behavioral Species Concept

• Defines species based on unique behaviors, particularly mating behaviors, that distinguish one group from another.

• Courtship signals enable individuals to recognize their species and find mates.

• Limitation: Hard to observe behaviors; not applicable to asexual organisms.

4. Ecological Species Concept

• Members of a species possess unique adaptations to specific environmental conditions, competing for the same resources. Focuses on ecological niche (role within an ecosystem).

• Limitations: Organisms of the same lineage occupying the same niche may be indistinguishable, such as bats and birds.

Dichotomous Keys

Construction

• When constructing a dichotomous key:

  • Avoid using colors or vague size descriptors.

  • Use distinct, visible, recognizable features to divide organisms into two groups.

  • Be precise in descriptions and do not combine more than one feature at a time.

  • Format should start with numbered questions or statements (e.g., 1(a) and 1(b)).

Example of Dichotomous Key for Animals

1. a) Wings present… go to 2 b) Wings absent… go to 3

   2. a) One pair of wings… housefly
      b) Two pairs of wings… butterfly

   3. a) Legs present… centipede
      b) Legs absent… earthworm

Example of Dichotomous Key for Plants

1. a) Leaves needle-like… Red pine (Pinus resinosa) b) Leaves broad and flat… go to 2

   2. a) Leaf margin deeply lobed… White oak (Quercus alba)
      b) Leaf margin not lobed… go to 3

   3. a) Leaf heart-shaped… Eastern redbud (Cercis canadensis)
      b) Leaf oval… Quaking aspen (Populus tremuloides)

Topic 1.2 Biodiversity

Objectives

• Know three levels of biodiversity, the importance of random sampling, and assess their distribution and abundance of organisms in their locality.

Learning Outcomes

• Learners should be able to:

  • Define ecosystem and niche.

  • Explain biodiversity at different levels (species, ecosystem, genetic).

  • Use Simpson’s Index of Diversity (D) to calculate biodiversity.

  • Describe and use methods to assess the distribution and abundance of organisms.

Defining Terms

• Ecosystem: A unit made of both biotic (living) and abiotic (non-living) components that interact and function together.

• Niche: The functional role of an organism within an ecosystem, including what it eats, where it lives, its behavior, and its interactions with others.

Levels of Biodiversity

1. Species Diversity: The number of species and their relative abundance (species richness & species evenness).

2. Ecosystem Diversity: The number and range of different ecosystems and habitats.

3. Genetic Diversity: The genetic variation within each species.

Importance of Biodiversity

• Prevent extinction of species.

• Enable organisms to adapt to changes in ecosystems.

• Provide a range of materials and food necessary for survival.

Assessing Biodiversity

• Habitat diversity (sand dunes, ponds).

• Species richness and their relative abundance.

• Genetic variation within species.

Random Sampling Importance

• Minimizes bias, ensuring equal opportunity for organisms to be included in samples.

• Enhances the reliability of biodiversity estimates.

Simpson’s Index of Diversity (D)

• Measures diversity, accounting for species present and their relative abundance.

• Formula: $D = 1 - rac{ ext{Σ}(n/N)^2}$

  • where:

  • $n$ = total number of organisms of a particular species.

  • $N$ = total number of organisms of all species.

  • $D$ ranges from 0 (no diversity) to 1 (highest diversity).

Methods to Assess Distribution and Abundance

1. Frame Quadrats:

   • Square frames used for sampling vegetation and slow-moving animals.

   • Estimate frequency and density of species.

   • Formula for % cover: $rac{ ext{number of squares covered}}{ ext{total squares}} imes 100$.

2. Mark-Release-Recapture:

   • Method for mobile organisms, involving capturing, marking, and recapturing.

3. Line Transects:

   • Continuous or interrupted sampling along a long measuring tape.

4. Belt Transects:

   • Strip sampling (e.g., 1m wide) over a defined distance either continuously or at intervals.

Importance of Maintaining Biodiversity

• Moral and Ethical: Responsibility to protect other species.

• Ecological: Increases ecosystem stability.

• Economic: Provides resources for medicine and tourism.

• Aesthetic: Enjoyment of natural beauty.

• Agricultural: Genetic diversity helps crops survive.

Bioaccumulation, Biomagnification and Eutrophication

• Bioaccumulation: Increase in concentration of a pollutant in an organism

• Biomagnification: Increase in concentration in a food chain

• Eutrophication: Excessive nutrient enrichment of water, lead to algal blooms, depleting oxygen and harming aquatic life.

Conservation Efforts

1. Zoos: Captive breeding, research, healthcare, education.

2. Frozen Zoos: Store genetic material for endangered species.

3. Conserved Areas: Protect ecosystems from human interference.

4. Seed Banks: Preserve plant genetic diversity.

5. Controlling Alien Species: Mitigate harmful impacts on native ecosystems.

6. Restoration of Degraded Habitats: Through erosion control, reforestation, and local species reintroduction

$Class Work$

1. Investigate the negative impact of rhino and elephant poaching on tourism in Namibia, South Africa, and Botswana.

2. Develop solutions required at local, national, and global levels to combat poaching.