8.2 Biodiversity
Biodiversity refers to the diverse variety of life forms existing on Earth. It encompasses life at multiple levels, ranging from variations in genes among individuals of the same species to the wide array of distinct species and diverse ecosystems. By studying evolutionary relationships through phylogeny and understanding both in situ and ex situ conservation methods, humans can appreciate and protect the biological wealth that sustains ecological balance and human survival.
Learning Objectives
- Define biodiversity and explain its three levels: genetic diversity, species diversity, and ecosystem diversity.
- Describe phylogeny and explain the use of phylogenetic trees and homologous structures in biological classification.
- Outline the evolutionary lineage of land plants from green algae to angiosperms.
- Explain the importance of biodiversity to the environment and humans.
- Differentiate between in situ conservation and ex situ conservation, citing relevant examples.
Levels of Biodiversity & Evolutionary Branching of Land Plants
Biodiversity exists at three levels, while land plants share a branching evolutionary history from green algae to angiosperms.
Genetic Diversity
Gene variations within a population and between different populations of the same species.
Species Diversity
Variation and variability of organisms on Earth, comprising species richness and species evenness.
Ecosystem Diversity
Biotic communities and ecological processes in terrestrial, marine and aquatic environments.
Short Explanation
Definition
Biodiversity — the diverse variety of life forms existing on Earth. It is divided into three distinct types: genetic diversity, species diversity, and ecosystem diversity.
Genetic diversity
Refers to the gene variations of an individual within a population and gene variations between different populations of the same species. Differences in genes arise due to individual isolation and adaptation to differing environments. No two individuals of the exact same species are identical. For example, the huge variety in gene combinations provides genetic variation in cultivated rice (paddy), yielding many varieties worldwide.
Species diversity
Refers to the variation and variability of organisms on Earth. It encompasses two components: species richness and species evenness. Tropical rainforests possess huge species diversities, containing 5 to 10 million insect species and over two million species of flowering plants.
Ecosystem diversity
Refers to the biotic community and ecological processes occurring in ecosystems on land, in the sea, and across other aquatic environments. Diverse ecosystems rich in biodiversity include oceans, deserts, and swamps.
Phylogeny and phylogenetic tree
Phylogeny is the evolutionary history of a species or a group of organisms that are genetically linked. A phylogenetic tree is a branching diagram that represents hypotheses on evolutionary relationships among a group of organisms. Branches indicate how groups diverge from a common ancestor.
Homologous structures
Homologous structures are body parts or anatomical structures observed across multiple organisms that share a common ancestor, even though the functions of these structures may differ. The forelimbs of humans, cats, whales, and bats share the identical skeletal framework: humerus, radius, ulna, carpal, metacarpal, and phalanx. They differ in size, length, and specific function, proving they originated and diverged from one common ancestor.
Evolutionary lineage of land plants
Evidence suggests land plants evolved from a common ancestor: green algae. The evolutionary sequence is: non-vascular plants (mosses) → seedless vascular plants (ferns) → seed plants, which split into gymnosperms (non-flowering vascular plants with seeds, e.g., conifers) and angiosperms (flowering vascular plants with seeds enclosed inside fruits). Angiosperms are considered the most successful plants because their seeds are enclosed inside fruits to ensure species survival.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What are the two main components that define species diversity in a biological community?
Why are the forelimbs of humans, cats, whales, and bats considered homologous structures?
What is the main difference between in situ conservation and ex situ conservation?
Common Mistakes
- Confusing species richness with species evenness: Richness refers strictly to the total count of different species, whereas evenness refers to how evenly individuals are distributed among those species.
- Assuming homologous structures must perform the same function: Homologous structures share a common ancestral skeletal design but often perform completely different functions (e.g., swimming in whales vs flying in bats).
- Misclassifying gymnosperms as flowering plants: Gymnosperms produce seeds but are non-flowering; only angiosperms produce flowers and enclose their seeds within fruits.
- Classifying wildlife rehabilitation centres or national parks as ex situ: Because organisms remain in their natural environment, these are in situ conservation efforts.
Concept Misunderstandings
Genetic diversity means differences between entirely different species.
Genetic diversity refers to variations in genes among individuals of the same species (both within one population and between different populations).
Angiosperms are primitive land plants because they rely on fruit.
Angiosperms are the most advanced and successful land plants because their enclosed seeds inside fruits protect the embryo and maximise survival.
Ex situ conservation means abandoning animals in damaged forests.
Ex situ conservation refers to deliberate human-managed care outside their native natural habitats, such as in botanical gardens, seed banks, or accredited zoos.
Summary
- Biodiversity exists at three levels: genetic diversity, species diversity, and ecosystem diversity.
- Phylogeny tracks the evolutionary history of genetically linked organisms using branching phylogenetic trees.
- Homologous structures (e.g., human arm, cat limb, whale flipper, bat wing) indicate descent from a common ancestor despite functional differences.
- Land plants evolved from green algae along the sequence: non-vascular mosses → seedless vascular ferns → gymnosperms → angiosperms.
- Biodiversity preserves ecological balance, food supplies, and medicine.
- Protection is achieved via in situ conservation (within natural habitat) and ex situ conservation (outside natural habitat).
Short Activity
Objective: test your understanding of biodiversity, phylogeny, plant evolution and conservation.
A. Objective Quiz
Which group of land plants is considered the most successful because their seeds are enclosed inside fruits to ensure species survival?
What term describes anatomical body parts across different organisms that originate from a common ancestor but perform different functions?
B. Fill in the Blanks
Species diversity includes the total number of species in a community, known as species richness, and the relative species distribution in a community, known as species .
Conserving wildlife within their natural habitat, such as in national parks and permanent forest reserves, is called conservation.
C. Matching / Drag and Drop
Match each conservation method or evolutionary plant group to its correct textbook description. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Category or Concept to Its Description
Write the correct category or concept next to each description.
| Characteristic or Example | Category / Concept |
|---|---|
| 1. Conserving species in their natural habitat such as Sepilok Orangutan Rehabilitation Centre | |
| 2. Conserving species outside their natural habitats such as in zoos and botanical gardens | |
| 3. First land plants evolved from green algae, represented by mosses | |
| 4. Non-flowering vascular plants that bear seeds, such as conifers |
Answer choices: In situ conservation • Ex situ conservation • Non-vascular plants • Gymnosperms
