IB Biology HL

All topics, made from Kognity

What are the eight functions of life carried out by all living organisms?

The eight functions of life are metabolism, response to stimuli, homeostasis, growth, reproduction, respiration/movement, excretion, and nutrition. These processes are essential for maintaining life and ensuring the survival of organisms.

Why are viruses not considered living organisms?

They cannot independently carry out all functions of life.

What is the difference between prokaryotic and eukaryotic cells?

Prokaryotic cells lack a nucleus and membrane-bound organelles; eukaryotic cells have both.

What are the components common to all cells?

DNA, cytoplasm, and a plasma membrane.

What is the function of ribosomes and how do prokaryotic and eukaryotic ribosomes differ?

Ribosomes synthesize proteins; prokaryotic ribosomes are 70S, eukaryotic ribosomes are 80S.

What evidence supports the theory of endosymbiosis?

Mitochondria and chloroplasts have double membranes, circular DNA, 70S ribosomes, and replicate via binary fission.

What is cell differentiation and why is it important?

It’s the process where cells become specialized; it enables multicellularity.

What is a nucleosome?

A segment of DNA wrapped around a core of histone proteins, helping regulate gene expression.

What is the difference between naked and histone-bound DNA?

Prokaryotic DNA is naked; eukaryotic DNA is bound to histones. Naked DNA exists in a free form without proteins, while histone-bound DNA is complexed with histone proteins, providing structure and regulation in eukaryotic cells.

What experiment provided evidence that DNA is the genetic material?

Hershey and Chase’s bacteriophage experiment.

What is the role of the plasma membrane?

Controls the entry and exit of substances in and out of the cell.

What is the function of the mitochondria?

Produces ATP through cellular respiration.

How does the surface area-to-volume ratio affect cell size?

As cells grow, the ratio decreases, limiting efficient exchange of materials.

What are atypical eukaryotic cells and give examples?

Cells that deviate from the standard structure (red blood cells have no nucleus, skeletal muscle is multinucleate.

What are the components of a light microscope and their functions?

Lenses magnify specimens using visible light; used for viewing live or stained cells.

What is the function of the rough and smooth ER?

Rough ER synthesizes and processes proteins; smooth ER synthesizes lipids and detoxifies.

What does the Golgi apparatus do?

Modifies, sorts, and packages proteins and lipids for storage or transport.

What is the function of lysosomes?

Contain digestive enzymes to breakdown waste.

What is the cytoskeleton’s role in the cell?

Maintain cell shape and assists with transport and division.

What is the function of vesicles in cells?

Transport substances within the cell.

What elements are most commonly found in living organisms?

Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

What property of water makes it an excellent solvent in biological systems?

Its polarity, which allows it to form hydrogen bonds with other polar molecules.

What causes water molecules to be cohesive and adhesive?

Hydrogen bonding between molecules.

What are condensation and hydrolysis reactions?

Condensation links monomers by removing water; hydrolysis breaks polymers by adding water.

What is the structure of a nucleotide?

A phosphate group, a pentose sugar, and a nitrogenous base.

What is the difference between DNA and RNA?

DNA contains deoxyribose sugar and thymine, RNA contains ribose sugar and uracil.

What type of bond links nucleotides together in DNA and RNA?

phosphodiester bonds

What is complementary base pairing?

Adenine pairs with thymine (or uracil in RNA), cytosine pairs with guanine.

Why is DNA replication described as semi-conservative?

Each new DNA molecule consists of one original strand and one newly synthesized strand.

What enzymes are involved in DNA replication and what are their roles?

Helicase (unwinds DNA), DNA polymerase III (adds nucleotides), primase (adds primers), ligase (joins Okazaki fragments).

What direction does DNA replication and transcription occur in?

5’ to 3’ direction.

What are introns and exons?

Introns are non-coding regions removed from mRNA; exons are coding regions that are expressed.

What is alternative splicing?

The process by which different combinations of exons are joined to produce multiple proteins from one gene.

What is the function of tRNA in translation?

tRNA brings amino acids to the ribosome and pairs its anticodon with the mRNA codon.

What is the role of ribosomes in translation?

They facilitate the binding of tRNA to mRNA and catalyze peptide bond formation.

What is the genetic code and why is it called degenerate and universal?

It’s the set of rules by which mRNA codons are translated into amino acids. Degenerate means multiple codons code for one amino acid; universal means the same code is used by almost all organisms.

What is the role of ATP in cells?

It provides energy for cellular processes by releasing energy when its phosphate bond is broken.

What is glycolysis and what are its products?

The first step in cell respiration; breaks glucose into 2 pyruvate, 2 ATP, and 2 NADH.

What are the products of the Krebs cycle for one molecule of glucose?

6 NADH, 2FADH2, 2ATP, and 4 CO2

What is chemiosmosis in cellular respiration?

The movement of protons across the inner mitochondrial membrane through ATP synthase the generate ATP.

What is the role of oxygen in aerobic respiration?

It acts as the final electron acceptor in the electron transport chain to form water.

What is the function of photosystem II in photosynthesis?

It captures light energy and splits water molecules (photolysis) to release electrons, protons, and oxygen.

What is the Calvin cycle and where does it occur?

The light-independent reactions of photosynthesis; it occurs in the stroma of chloroplasts and synthesizes glucose.

What is the role of Rubisco in photosynthesis?

It catalyzes the fixation of CO2 with RuBP to start the Calvin cycle.

What are the limiting factors of photosynthesis?

Light intensity, carbon dioxide concentration, and temperature.

What is non-cyclic photophosphorylation?

The light-dependent pathway where electrons move from water to NADP+, generating both ATP and NADPH

What is photolysis?

The splitting of water using light energy, producing electrons, protons, and oxygen.

What are the products of the light-dependent reactions of photosynthesis?

ATP and NADPH

What is a gene?

A heritable factor that consists of a length of DNA and influences a specific characteristic.

What is an allele?

A specific form of a gene, differing from other alleles by one or a few DNA bases.

What is a genome?

The complete set of genetic material in an organism, including all of its genes and non-coding sequences.

What is a gene mutation?

A change in the base sequence of a gene.

What is sickle cell anemia caused by?

A base substitution mutation in the gene coding for the beta chain of hemoglobin.

What is a karyogram?

A diagram that displays the complete set of chromosomes in an individual, arranged in pairs and organized by size, shape, and number.

What is a diploid cell?

A cell that contains two complete sets of chromosomes, one from each parent.

What are homologous chromosomes?

Chromosome pairs of the same length and centromere position that carry genes for the same traits.

What is meiosis and what does it produce?

A type of cell division (sexual) that reduces the chromosome number by half, producing four genetically distinct haploid gametes.

What are the two key processes during meiosis that increase genetic variation?

Crossing over in prophase I and independent assortment in metaphase I.

What is nondisjunction?

Failure of chromosomes to separate properly during meiosis, leading to gametes with abnormal chromosome numbers.

What is a genotype?

The genetic makeup of an organism (the alleles it possesses).

What is a phenotype?

The observable characteristics of an organism resulting from its genotype and environment.

What is codominance?

A condition in which both alleles are expressed equally in the phenotype.

What are sex-linked genes?

Genes located on sex chromosomes, often referring to genes on the X chromosome (because X chromosome is guaranteed from women)

Why are X-linked recessive traits more common in males?

Males only have one X-chromosome, so one recessive allele will result in the trait.

What is a dihybrid cross?

A genetic cross involving two different traits.

What is a polygenic inheritance?

Inheritance of a characteristic controlled by two or more genes.

What are SNPs (Single Nucleotide Polymorphisms)?

Variations at a single base position in DNA among individuals.

What is a pedigree chart?

A diagram that shows the occurrence of phenotypes of a particular gene in a family across generations.

What is gene linkage?

The tendency of genes located close together on a chromosome to be inherited together during meiosis.

What is a recombination frequency?

The percentage of recombinants in offspring; used to map gene loci on chromosomes.

What statistical test is used to analyze genetic crosses?

The chi-squared test.

What are the expected ratios for a dihybrid cross of heterozygotes?

9:3:3:1 for dominant-dominant, dominant-recessive, recessive-dominant, recessive-recessive phenotypes.

What is the purpose of the Human Genome Project?

To determine the complete sequence of the human genome and identify all human genes.

How is DNA used in gene sequencing?

DNA is cut into fragments, sequenced, and reassembled to determine the order of bases.

What is DNA barcoding used for?

Identifying species from environmental samples by analyzing specific DNA markers.

What is a species?

A group of organisms that can interbreed and produce fertile offspring.

What is a population?

A group of individuals of the same species that live in the same area at the same time.

What is a community?

A group of populations living and interacting with each other in an area.

What is an ecosystem?

A community and its abiotic environment.

What is a trophic level?

A position an organism occupies in a food chain.

What are autotrophs?

Organisms that produce their own food from inorganic substances (e.g. via photosynthesis)

What are heterotrophs?

Organisms that obtain organic molecules from other organisms.

What are the types of heterotrophs?

Consumers, detritivores, and saprotrophs.

What is a food chain?

A sequence of organisms, each of which is eaten by the next in the chain.

What is a food web?

A network of interconnected food chains in a community.

Why is energy transfer between trophic levels inefficient?

Energy transfer between trophic levels is inefficient due to energy loss in the form of heat, metabolic processes, and waste, resulting in only about 10% of energy being passed on to the next level.

What limits the number of trophic levels in a food chain?

Energy loss at each trophic level.

What is the role of decomposers?

They break down dead organisms and recycle nutrients back into the ecosystem.

What is a carbon sink?

A natural reservoir that stores carbon e.g., forests or oceans. The ocean is considered the largest carbon sink.

What is the greenhouse effect?

Warming of Earth’s surface due to greenhouse gases trapping infrared radiation.

What are the main greenhouse gases?

Carbon dioxide, methane, nitrous oxide, and water vapor

How does deforestation affect the carbon cycle?

Reduces carbon sequestration (the removal of carbon dioxide from the atmosphere and storage in biomass or underground), increases CO2 in the atmosphere

What is climate change linked to in terms of biology?

Species distribution, migration patterns, extinction rates, and biodiversity loss

What is a mesocosm?

A small, self-sustaining ecosystem used to study ecological interactions under controlled conditions.

What is the role of methane in the carbon cycle?

Methane is produced by methanogenic archaea in anaerobic environments and oxidized to CO2 in the atmosphere.

What is peat and how does it form?

Peat is partially decomposed organic matter that accumulates in acidic, anaerobic conditions.

What is bioaccumulation?

The buildup of toxins in an organism’s tissues over time

What is biomagnification?

Biomagnification is the process by which the concentration of toxins increases at each successive trophic level in a food chain, leading to higher exposure in top predators.

What is the precautionary principle?

If an action may cause harm to the environment or health, precautionary measures should be taken even without full scientific certainty.

What is the chi-squared test used for in ecology?

To determine whether there is a significant association between two species.