What are the main differences between prokaryotic and eukaryotic organisms?

Prokaryotic organisms, such as bacteria, lack a nucleus and membrane-bound organelles, while eukaryotic organisms, including plants and animals, have a defined nucleus and organelles. This distinction is fundamental in the study of organisms in the IB MYP Science curriculum, as it helps students understand the complexity and diversity of life forms.

How do organisms adapt to their environments?

Organisms adapt to their environments through evolutionary processes that enhance their survival and reproduction. These adaptations can be structural, such as the thick fur of polar bears for insulation, behavioral, like birds migrating to warmer areas during winter, or physiological, such as the ability of some desert plants to store water. Understanding these adaptations is crucial in the IB MYP Science curriculum to appreciate the diversity of life on Earth.

What role do organisms play in ecosystems?

Organisms play various roles in ecosystems, including producers, consumers, and decomposers. Producers, like plants, convert sunlight into energy through photosynthesis. Consumers, such as animals, feed on other organisms, and decomposers, like fungi and bacteria, break down dead matter, recycling nutrients back into the ecosystem. This interconnectedness is a key concept in the IB MYP Science curriculum, highlighting the balance and sustainability of ecosystems.

Why is biodiversity important in ecosystems?

Biodiversity is crucial because it ensures ecosystem resilience, providing stability and the ability to recover from disturbances. High biodiversity increases the variety of resources and habitats, supporting a wide range of organisms. In the IB MYP Science curriculum, students learn that biodiversity contributes to ecosystem services, such as pollination, water purification, and climate regulation, which are vital for human survival.

How do human activities impact organisms and their habitats?

Human activities, such as deforestation, pollution, and climate change, significantly impact organisms and their habitats by altering natural environments and reducing biodiversity. These changes can lead to habitat loss, species extinction, and ecosystem imbalance. The IB MYP Science curriculum emphasizes the importance of understanding these impacts to promote conservation efforts and sustainable practices that protect organisms and their ecosystems.

Why is "Saying whales/dolphins are fish." a common mistake in Organisms II?

Why it happens: They live in water. How to avoid it: They produce MILK and give LIVE BIRTH → mammals. Habitat is not what defines a class — body covering and reproduction do.

Why is "Saying bats are birds." a common mistake in Organisms II?

Why it happens: They fly. How to avoid it: Bats have FUR and produce MILK → mammals. Birds are defined by FEATHERS.

Why is "Writing binomial as 'Homo Sapiens' or 'homo sapiens'." a common mistake in Organisms II?

Why it happens: Forgetting capitalisation rule. How to avoid it: ALWAYS: Capital G in genus, lowercase species, italics. Example: *Homo sapiens*.

Organisms II – Study Notes & Past Paper Style Questions | IB MYP Sciences (Years 1-5)

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Organisms II — IB MYP Sciences: vertebrate groups and invertebrate basics

Year-3 spiral on classification within the Animal kingdom. This MYP Sciences note covers the five vertebrate classes, key invertebrate groups, and the binomial naming system.

At a glance

Animals split into VERTEBRATES (have a backbone) and INVERTEBRATES (no backbone).
Five vertebrate classes: FISH, AMPHIBIANS, REPTILES, BIRDS, MAMMALS.
Each class has signature features (e.g. mammals have hair + produce milk).
Invertebrates include arthropods (insects, spiders), molluscs, worms, cnidarians.
BINOMIAL nomenclature: every species has a 2-part Latin name (e.g. Homo sapiens).
First word = GENUS (capital). Second word = species (lowercase). Whole name italicised.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — List the five vertebrate classes and one feature of each.
MYP Sciences A — Distinguish vertebrate from invertebrate.
MYP Sciences A — Apply binomial naming convention correctly.
MYP Sciences C — Classify a new organism using its features.

The five vertebrate classes

Fish, amphibians, reptiles, birds, mammals.

Within the Animal kingdom, animals with a BACKBONE (vertebrae running down the spine) are called vertebrates. There are five main classes.

Class	Body covering	Eggs	Body temp	Examples
Fish	Scales	Soft eggs, in water	Cold-blooded (ectotherm)	Salmon, shark
Amphibians	Moist, smooth skin	Soft eggs, in water	Cold-blooded	Frog, salamander
Reptiles	Dry scales	Leathery eggs, on land	Cold-blooded	Snake, lizard, turtle
Birds	Feathers	Hard-shelled eggs	WARM-blooded (endotherm)	Eagle, sparrow
Mammals	Hair / fur	Live young (most); produce MILK	WARM-blooded	Human, dog, whale

Invertebrates

97% of animal species have no backbone.

Most animal species — about 97% — are INVERTEBRATES. The main groups at MYP level:

Arthropods (by far the biggest group). Jointed legs, exoskeleton (chitin). Includes:
- Insects (6 legs, 3 body parts — head/thorax/abdomen)
- Arachnids (8 legs — spiders, scorpions)
- Crustaceans (often 10 legs — crabs, lobsters)
- Myriapods (lots of legs — centipedes, millipedes)
Molluscs: soft body, often with a shell. Snails, slugs, octopuses (no shell), clams.
Annelids (segmented worms): earthworm, leech.
Cnidarians (stinging cells): jellyfish, coral, sea anemone.
Echinoderms (spiny-skinned): starfish, sea urchin.

The arthropod group is so successful because the EXOSKELETON gives protection, supports the body on land, and prevents drying out.

Arthropods = jointed legs + exoskeleton (insects, spiders, crabs).
Insects: 6 legs, 3 body parts.
Molluscs (soft body), Annelids (segmented worms), Cnidarians (stinging), Echinoderms (spiny).

Binomial naming

Every species has a 2-part Latin name.

Common names are unreliable — a 'robin' in the UK is a different species from a 'robin' in the US. Scientists use a Latin two-part name that is the same worldwide. This is binomial nomenclature (introduced by Linnaeus in 1758).

Rules:

First word = GENUS. Capital letter (e.g. Homo).
Second word = species. Lowercase (e.g. sapiens).
Italicise the whole name (or underline if writing by hand).
After first use, abbreviate the genus to the first letter — H. sapiens.

Examples:

Homo sapiens — modern humans.
Panthera leo — lion. Panthera tigris — tiger. Same genus.
Canis lupus — wolf. Canis familiaris (or C. lupus familiaris) — domestic dog.
Quercus robur — English oak.

The genus tells you the close relative; the species name uniquely identifies the organism. Species in the same genus often share more features (and DNA) than species in different genera.

Two words: Genus (capital) + species (lowercase).
Italicise the whole name.
Same name worldwide — avoids common-name confusion.

Quick recap

Vertebrate = has backbone; invertebrate = doesn't.
5 vertebrate classes: fish, amphibians, reptiles, birds, mammals.
Only birds and mammals are warm-blooded.
Arthropods are the biggest invertebrate group.
Binomial name = Genus + species, italicised, Latin.

Memorise this

Verbatim phrases and definitions MYP criterion-A markschemes credit.

5 vertebrate classes: F-A-R-B-M (Fish, Amphibian, Reptile, Bird, Mammal)
Birds + Mammals = warm-blooded
Insects: 6 legs, 3 body parts. Spiders: 8 legs, 2 body parts
Binomial: Homo sapiens — capital G, italics

How it’s examined

Criterion A: name vertebrate classes / write binomial correctly. Criterion C: classify a new organism using features given.

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

Organisms II – Study Notes & Past Paper Style Questions | IB MYP Sciences (Years 1-5) | Tutopiya

Organisms II

Detailed Study Notes

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Organisms II — frequently asked questions

Organisms II — IB MYP Sciences: vertebrate groups and invertebrate basics

At a glance

What you’ll learn

The five vertebrate classes

Invertebrates

Binomial naming

Quick recap

Memorise this

How it’s examined

Step-by-step worked examples — Organisms II

1Place the organism in a vertebrate class

2Write the binomial name correctly

3Insect or spider?

Key Definitions and Keywords — Organisms II

Vertebrate

Invertebrate

Ectotherm (cold-blooded)

Endotherm (warm-blooded)

Binomial nomenclature

Common Mistakes and Misconceptions — Organisms II

✕Saying whales/dolphins are fish.

✕Saying bats are birds.

✕Writing binomial as 'Homo Sapiens' or 'homo sapiens'.