The diversity of living organisms (AS Level) flashcards

Topic 1: The diversity of living organisms

The taxonomic hierarchy, from largest to smallest group

Domain, kingdom, phylum, class, order, family, genus, species. Each group sits inside the one above, with no overlap between groups.

Species

A group of organisms with similar characteristics that can interbreed to produce fertile offspring. A mule (infertile offspring of a horse and a donkey) shows why 'fertile' is essential.

How is a binomial name written?

Genus then species. The genus has a capital letter, the species is lower case, and both are in italics (or underlined when handwritten).

Phylogenetic classification, and the evidence used for it

Grouping by evolutionary relationships and common ancestry. Evidence: DNA base sequences, mRNA sequences and amino acid sequences of proteins; the more similar, the more recent the common ancestor.

Species richness and species diversity

Species richness: the number of different species present. Species diversity: the number of species and the number of individuals in each.

A community has 3 species with 10, 4 and 1 individuals. Calculate the index of diversity, d = N(N − 1) ÷ Σn(n − 1).

N = 15, so N(N − 1) = 210. Σn(n − 1) = 90 + 12 + 0 = 102. d = 210 ÷ 102 = 2.06

How can genetic diversity be measured (3.1.11.1)?

By comparing the base sequence of DNA or of mRNA, the frequency of specific base sequences or alleles in populations, or the amino acid sequence of the proteins they code for.

Three causes of genetic diversity

Mutation; meiosis (crossing over and independent assortment); and random fertilisation.

Why are quadrats placed at random coordinates, and why does sample size matter?

Random coordinates remove bias from the person sampling, so the sample represents the area. The sample must be large enough for a reliable mean; a small one may miss species by chance.

Condensation and hydrolysis

Condensation joins two molecules by a chemical bond, releasing a water molecule. Hydrolysis breaks the bond using a water molecule.

Facilitated diffusion compared with active transport

Facilitated diffusion: passive movement down a concentration gradient through channel or carrier proteins; no ATP. Active transport: movement against a concentration gradient by carrier proteins, using ATP.

Properties of the genetic code

A triplet of bases codes for each amino acid. It is universal (same in all organisms), non-overlapping and degenerate (most amino acids have more than one triplet).

Starch compared with cellulose

Starch: α-glucose; amylose (unbranched, coiled) and amylopectin (branched); insoluble, compact energy store in plants. Cellulose: β-glucose; straight, unbranched chains joined by hydrogen bonds into microfibrils, giving the cell wall high tensile strength.

Test for a non-reducing sugar

After a negative Benedict's test, boil a fresh sample with dilute hydrochloric acid, neutralise with sodium hydrogencarbonate, then heat with Benedict's reagent. A coloured precipitate shows a non-reducing sugar (the acid hydrolysed it).

Triglyceride compared with phospholipid

Triglyceride: one glycerol and three fatty acids joined by ester bonds in condensation reactions. Phospholipid: one fatty acid is replaced by a phosphate-containing group, giving a hydrophilic head and hydrophobic tails.

Competitive compared with non-competitive inhibitors

Competitive: similar shape to the substrate, binds the active site; its effect is reduced by adding more substrate. Non-competitive: binds away from the active site and changes its shape; adding more substrate does not overcome it.

Transcription in prokaryotes compared with eukaryotes

In both, RNA polymerase joins mRNA nucleotides. In prokaryotes transcription produces mRNA directly. In eukaryotes it produces pre-mRNA, which is spliced (introns removed) to form mRNA.

Nuclear DNA of a eukaryote compared with DNA of a prokaryote

Eukaryotic nucleus: long, linear, associated with proteins such as histones that package it into chromosomes. Prokaryotes (and mitochondria and chloroplasts): shorter, circular, not associated with proteins.