krit.club logo

Classification and Biodiversity - Evolution and Natural Selection

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Evolution occurs when heritable characteristics of a species change over time. This process is driven primarily by Natural Selection, which acts on the variation within a population.

•

Sources of variation in a population include: 1. Mutation (change in the DNA sequence), 2. Meiosis (crossing over and independent assortment), and 3. Sexual reproduction (random fertilization).

•

Adaptations are characteristics that make an individual suited to its environment and way of life. These are developed over generations, not within a single lifetime.

•

Evidence for evolution includes the fossil record, selective breeding of domesticated animals, and homologous structures. The pentadactyl limb (five-fingered limb) found in mammals, birds, amphibians, and reptiles is a prime example of adaptive radiation from a common ancestor.

•

Classification involves grouping organisms into a hierarchy of taxa: Domain →\rightarrow Kingdom →\rightarrow Phylum →\rightarrow Class →\rightarrow Order →\rightarrow Family →\rightarrow Genus →\rightarrow Species.

•

Binomial nomenclature is the formal system of naming species using two parts: the Genus (capitalized) and the species (lower case), both written in italics (e.g., HomoHomo sapienssapiens).

•

The three domains of life are ArchaeaArchaea, EubacteriaEubacteria, and EukaryotaEukaryota. Viruses are not classified in this system as they are not considered living organisms.

•

Natural Selection follows the acronym VISTA: Variation, Inheritance, Selection (survival of the fittest), Time, and Adaptation/Change in Allele Frequency.

📐Formulae

p+q=1p + q = 1

p2+2pq+q2=1p^2 + 2pq + q^2 = 1

D=N(N−1)∑n(n−1)D = \frac{N(N-1)}{\sum n(n-1)}

💡Examples

Problem 1:

Explain how the evolution of antibiotic resistance in bacteria like StaphylococcusStaphylococcus aureusaureus (MRSA) provides evidence for natural selection.

Solution:

  1. Variation: Some bacteria develop a mutation that provides resistance to an antibiotic. 2. Selection Pressure: When the antibiotic is applied, non-resistant bacteria die. 3. Reproduction: The resistant bacteria survive and reproduce. 4. Inheritance: The resistance gene is passed to the next generation via binary fission or horizontal gene transfer (plasmids).

Explanation:

Over time, the frequency of the resistant allele increases in the population, making the antibiotic ineffective. This shows evolution happening in a short, observable timeframe.

Problem 2:

A population of plants has two alleles for flower color: RR (dominant, red) and rr (recessive, white). If the frequency of the recessive phenotype (rrrr) is 0.090.09, calculate the frequency of the dominant allele (pp).

Solution:

Given q2=0.09q^2 = 0.09. Therefore, q=0.09=0.3q = \sqrt{0.09} = 0.3. Since p+q=1p + q = 1, then p=1−0.3=0.7p = 1 - 0.3 = 0.7.

Explanation:

The frequency of the dominant allele RR (pp) is 0.70.7 or 70%70\%. This is based on the Hardy-Weinberg principle for populations in genetic equilibrium.

Problem 3:

Identify the Phylum for a plant that has roots, leaves, and woody stems, produces seeds in cones, and lacks fruit.

Solution:

ConiferophytaConiferophyta

Explanation:

Plants in ConiferophytaConiferophyta are characterized by having vascular tissue, producing seeds in cones (gymnosperms), and typically having needle-like leaves.