IB DP Biology Theme A: Unity and Diversity Review

Comprehensive practice flashcards for IB DP Biology Theme A (Unity and Diversity), covering Water & Nucleic Acids, Cells, Classification & Diversity, and Interactions & Ecosystems.

Which property of water is a direct result of hydrogen bonding between water molecules?

Its unusually high specific heat capacity.

In a molecule of DNA, adenine on one strand always pairs with which base on the complementary strand?

Thymine.

What is the monomer or building block of a protein?

An amino acid.

Which type of bond forms between two amino acids during protein synthesis with the release of a water molecule?

A peptide bond.

Which statement is part of the cell theory?

All cells arise from pre-existing cells.

Which feature is typically found in a prokaryotic cell but not in a eukaryotic cell?

Circular DNA not enclosed in a nuclear envelope.

As a spherical cell increases in radius, what happens to its surface area to volume ratio?

It decreases.

How does the fluid mosaic model describe the structure of the cell-surface membrane?

As a phospholipid bilayer with proteins embedded and able to move within it.

What two parts make up the scientific name of an organism in the binomial naming system?

The genus and the species epithet.

Which taxonomic rank contains the greatest number of different organisms?

Kingdom.

Under what condition are two organisms generally considered to belong to the same species?

When they can interbreed to produce fertile offspring.

What are primary consumers in a food chain?

Organisms that feed directly on producers.

Approximately what percentage of energy is typically transferred from one trophic level to the next?

$$10\%$$

What is a close, long-term interaction between two different species that benefits both of them called?

Mutualism.

In a classic predator-prey population cycle, what typically follows an increase in the prey population?

An increase in the predator population, after a time lag.

Why does water have an unexpectedly high boiling point compared to other Group 16 hydrides such as $H_2S$, $H_2Se$, and $H_2Te$?

Water molecules form hydrogen bonds with each other, which require significantly more energy to break than the weaker van der Waals' forces present between other Group 16 hydride molecules.

How are cohesion and adhesion defined as properties of water?

Cohesion is the attraction between like water molecules, whereas adhesion is the attraction between water molecules and other polar or charged surfaces/molecules.

Why is the high specific heat capacity of water biologically important?

It provides thermal stability for aquatic environments and inside organisms by buffering against rapid temperature changes.

Why is water described as a good solvent for polar and ionic substances?

Water molecules are polar and form hydration shells around charged ions and polar molecules, allowing them to dissolve easily.

What relationship between nitrogenous bases in DNA is stated by Chargaff's rule?

The percentage of adenine equals the percentage of thymine ($\%A = \%T$), and the percentage of guanine equals the percentage of cytosine ($\%G = \%C$).

What are two structural features that distinguish prokaryotic cells from eukaryotic cells?

Prokaryotic cells contain circular DNA not enclosed in a nuclear envelope and lack membrane-bound organelles, whereas eukaryotic cells have linear DNA enclosed in a nucleus and contain membrane-bound organelles.

Why are viruses generally not considered to satisfy the cell theory?

Viruses are acellular entities lacking cellular structures such as membranes and metabolic machinery, and they cannot reproduce independently without a host cell.

What is the mathematical relationship between the side length $L$ of a cube-shaped cell and its surface area to volume ratio?

The surface area to volume ratio is given by $SA:V = \frac{6}{L}$, meaning that as side length $L$ increases, the ratio decreases.

What is the surface area to volume ratio for a cube-shaped cell with a side length of $4\,mm$?

$1.5\,mm^{-1}$ (calculated as $\frac{6}{4\,mm} = 1.5\,mm^{-1}$).

Why is a large surface area to volume ratio advantageous for a cell, and why does it set an upper limit on cell size?

A large ratio enables efficient exchange of materials across the cell membrane relative to metabolic needs; as cell size increases, the ratio decreases until diffusion alone cannot meet metabolic demands.

In the fluid mosaic model, what does the term 'fluid' signify?

It signifies that phospholipids and embedded proteins within the membrane bilayer are able to move laterally.

What are two biological functions carried out by proteins embedded in the cell-surface membrane?

Transport of specific substances across the membrane (channel or carrier proteins) and serving as receptors for cell signaling.

How does species richness differ from species diversity?

Species richness is the total count of different species in an area, whereas species diversity accounts for both species richness and the relative abundance of each species.

What are the taxonomic ranks listed in order from broadest to narrowest among species, phylum, kingdom, and genus?

Kingdom, phylum, genus, species.

What is interspecific competition?

Competition between individuals of different species for the same limited environmental resources.

Why is energy transfer between trophic levels never $100\%$ efficient?

Energy is lost as metabolic heat during cellular respiration, through unconsumed organism parts, and via undigested waste and excretion.

Why do food chains rarely extend beyond four or five trophic levels?

Because approximately $90\%$ of energy is lost at each step, leaving insufficient energy to support viable populations at higher trophic levels.

Why do predator population changes lag behind prey population changes in predator-prey cycles?

Changes in prey population size directly impact food availability for predators, but time is required for predator reproduction, growth, or starvation to affect predator numbers.