كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

A3.1Theme A — Unity and diversity

Diversity of organisms — IB Biology SL Revision Notes & Topical Questions

10 min read 13 parts Lesson 9 of 11 2 quizzes

📚 IB Biology SL Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

0%read

Lesson summary

A3.1 Diversity of organisms — IB BIOLOGY SL notes: Describe variation, species concepts, chromosome number, karyograms and genomes, and the uses of genome sequencing.Variation = differences between organisms in appearance, behaviour or biochemistryAppearance includes fur colour o…

Genetic causes
Environmental causes
Identical twins
Continuous variation
Binomial name
Same genus

Section 1 of 13Variation and its causes

Variation

Variation differences between organisms in appearance, behaviour or biochemistry

Appearance includes fur colour or body length.
Behaviour includes courtship rituals and aggression.
Biochemistry includes antibiotic resistance and metabolic products.

Genetic causes

Genetic causes different alleles, produced by mutation and by the combination of alleles in sexual reproduction

Environmental causes

Environmental causes temperature, nutrients, oxygen, diet and light affect gene expression, but the effects are not inherited

Identical twins

Identical twins they have the same alleles but differ slightly because of the environment

No two individuals are identical, except clones

Continuous variation

Continuous variation measured on a scale with no clear groups, such as height
It is usually polygenic and influenced by the environment.

Discontinuous variation

Discontinuous variation falls into distinct categories, such as black or brown fur or ABO blood group

Section 2 of 13Classification and the binomial system

Classification and the binomial system

Taxonomy

Taxonomy the science of classifying and naming organisms into groups called taxa

The species is the smallest taxonomic group.

Linnaeus

Linnaeus an 18th-century Swedish botanist, the father of taxonomy
Before him names were long descriptions, such as the tomato's Solanum caule inermi herbaceo and so on.
He introduced two-part Latin names, so the tomato became Solanum lycopersicum.

Binomial name

Binomial name genus first, then species, in Latin
The genus starts with a capital and the species with a lower-case letter, as in Apis mellifera.
Type it in italics or underline it by hand.
After the first full use the genus can be abbreviated, as in T. aestivum.

Same genus

Same genus species in one genus share similar traits, such as Canis lupus, Canis latrans and Canis familiaris

Universal names

Universal names scientists worldwide use the same name, avoiding confusion over local names

Limitation

Limitation morphology alone misleads, as lookalikes may be distant relatives, so many Linnaean species were reclassified

Section 3 of 13Species concepts

Species concepts

Morphological species concept

Morphological species concept a species is a group of organisms that are morphologically unique

It is quick but mimicry and variation can mislead.

Biological species concept

Biological species concept a species is a group of organisms that can interbreed to produce fertile offspring

Limitations of the biological concept

Asexual organisms such as bacteria cannot be classified by interbreeding.
Rare fertile hybrids, such as the wholphin, blur the line.
Extinct species such as the woolly mammoth cannot be tested for interbreeding.
Geographically isolated populations cannot meet, so interbreeding cannot be tested.

Other criteria

DNA sequence similarity.
Biochemistry, such as whether bacteria produce carbon dioxide or methane.
Ecological niche.
Evolutionary lineage from fossils.

Use together

Use together scientists may use several concepts at once, and fossils need morphology or lineage

Section 4 of 13Populations and speciation

Speciation

Speciation the process by which one species gives rise to two or more new species

Isolation stops gene flow between populations.
Different selection pressures or genetic drift make the populations diverge.
Reproductive isolation completes the split.

Gradual change

Gradual change differences build up slowly, so no single moment marks a new species
Deciding when two populations are separate species is partly subjective.

Orca example

Orca example killer whales form several ecotypes, and experts disagree about whether there are several species

Congo River example

Congo River example bonobos and chimpanzees were separated by the river

Section 5 of 13Chromosome number

Diploid cell

Diploid cell a cell with two complete sets of chromosomes (2n), usually body cells

Haploid cell

Haploid cell a cell with one set (n), usually the gametes

Fertilisation

Fertilisation n + n gives a diploid zygote, so both gametes must have the same chromosome number

Rules for chromosome numbers

Each individual of a species has the same number of chromosomes.
The diploid number is always even.
The number is not linked to how advanced a species is.
Different numbers help prevent successful breeding between species.
State whether the figure is for chromosomes, pairs or the haploid set.

Organism	Diploid number	Gamete number	Note
Human	46	23	One pair fewer than the great apes
Chimpanzee	48	24	Two chromosomes fused in humans
Dog	78	39	Many small chromosomes
Rice	24	12	Crop plant
Fruit fly	8	4	Model organism
Horse threadworm	4	2	Very few chromosomes

Must know
- humans 46 and chimpanzees 48

Section 6 of 13Karyograms

Karyograms

Chromosome

Chromosome a strand of DNA containing genes, which are seen as an X after replication
The two arms are joined at the centromere.
Metacentric chromosomes have the centromere near the middle and equal arms.
Acrocentric chromosomes have it near one end and unequal arms.

Karyotype

Karyotype the appearance of a complete set of chromosomes, including number, size, shape and banding

Karyogram

Karyogram an image of the karyotype with chromosomes arranged in homologous pairs

Pair 23 is often out of size order because it holds the sex chromosomes and X is large.
Humans have XX for female and XY for male.

Uses

Uses detecting trisomy, such as Down syndrome, and determining sex

Collect dividing cells.

Stop division at metaphase.

Stain the chromosomes and photograph them under the light microscope.

Cut out the photographs or use a computer to pair homologous chromosomes.

Arrange the pairs by decreasing size, shape and banding pattern.

Section 7 of 13Human chromosome 2 and testable hypotheses

Hypothesis

Hypothesis chromosomes 12 and 13 of a common ancestor fused to form human chromosome 2
Losing a whole pair would be harmful, so fusion is more likely.

Supporting evidence

The combined length of chimp 12 and 13 matches human chromosome 2.
The banding matches, and the chimp 12 centromere position matches.
Satellite DNA marks the position of a lost second centromere.
Telomeric DNA sits in the middle of the chromosome.

Evidence against

The lengths overlap slightly rather than matching perfectly.
The centromere position of chimp 13 does not match.

Wording

Wording say humans and chimps share a common ancestor and never that humans came from chimps

Testable hypothesis

Testable hypothesis a statement that can be accepted or rejected using available evidence

It is not testable if there is no evidence, such as the ancestor liking singing.
Avoid vague words such as may or could, and do not phrase it as a prediction or a causal conclusion.

Section 8 of 13Genomes and sequence similarity

1Genome

Genome all of the genetic information of an organism

It includes coding and non-coding DNA, mitochondrial and chloroplast DNA, and plasmids in prokaryotes.

2Similarity

Similarity humans share about 99.9% of their DNA with each other and about 99% with chimpanzees
Closely related individuals have more similar genomes.

3SNP

SNP a single nucleotide polymorphism, a one-base difference arising by mutation

Most SNPs do not change the protein.
They are used to trace ancestry and disease risk.

4Databases

GenBank and NCBI hold DNA, RNA and protein sequences that can be compared between species

Section 9 of 13Genome size

Organism	Type	Genome (million base pairs)	Comment
T2 phage	Virus of E. coli	0.17	Tiny viral genome
E. coli	Bacterium	5	Prokaryotes are small
Fruit fly	Insect	140	Compact animal genome
Human	Mammal	About 3100	Smaller than hagfish (4200)
Common wheat	Polyploid crop	About 17 000	Wild einkorn only about 5000
Paris japonica	Flowering plant	About 150 000	Among the largest known

C-value

C-value the haploid nuclear DNA content, in picograms or megabases

1 pg = 10^-12 g, which is about 978 Mb, and 1 Mb = 10⁶ bases.

Size and complexity

Size and complexity they are not linked
The genome includes non-coding DNA.
Polyploidy inflates plant genomes.
Our view of complexity may be wrong.

Section 10 of 13Uses of genome sequencing

Methods

Methods automated next-generation sequencing, becoming faster and cheaper each year

Phylogenetics

Phylogenetics classifying species by evolutionary origin
More similar DNA, mRNA or amino acid sequences mean a more recent common ancestor.
Cytochrome c is often compared, and using several genes improves accuracy.
Ancient DNA lets extinct species join phylogenetic trees.

Personalised medicine

Human Genome Project data are used to design drugs that target specific proteins
Targeted drugs can cause fewer side effects.
Screening can find risk mutations, such as for breast cancer, allowing preventive surgery or lifestyle change.
A genotype can predict how well a person responds to treatment.

Identification tools

A dichotomous key uses yes or no choices about observable features.
DNA barcoding compares a short gene sequence with a database.
eDNA from water or soil detects rare or hidden species.

Section 11 of 13More from the specification

Section 12 of 13Key terms

Term	Meaning
Variation	Differences in characteristics between individuals caused by genes, environment or both.
Biological species concept	A species is a group of organisms that can interbreed to produce fertile offspring.
Binomial nomenclature	The two-part Latin naming system of genus plus species devised by Linnaeus.
Karyogram	An image of an individual's chromosomes arranged in pairs by size, shape and banding.
Genome	All the genetic information of an organism.
SNP	A single nucleotide polymorphism, a one-base difference in DNA between individuals.
C-value	The haploid nuclear DNA content of an organism.
DNA barcoding	Identifying a species from a short standard DNA sequence.

Section 13 of 13Exam technique

Saying morphology is enough to define a species — lookalike species may be distantly related

Saying humans evolved from chimpanzees — they share a common ancestor

Giving the haploid number as the diploid number — the diploid number is twice the haploid number and always even

Thinking a bigger genome means a more complex organism — genome size does not match complexity

Last updated: 18 October 2026