Example 1: using a key
Use Figure 1 to identify an animal with no legs and no shell.
- Has legs? No.
- Has a shell? No.
- It is an earthworm.
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IB DemystifiedMYP Sciences
Characteristics and classification of living things
Scientists have named about two million species, and there are millions more still to discover. To make sense of this huge variety, biologists sort living things into groups using the features they share.
Recommended for MYP 1 · About 3 lessons · Criteria A, B, C and D
On this page
- Learning objectives
- Before you start
- Key vocabulary
- Understanding the ideas
- Vertebrate groups
- Classification in the real world
- Worked examples
- Assessment tips
- Check your understanding
- Practice questions
- Investigation
- Criterion-linked questions
- Challenge questions
- Topic check
- Review your mistakes
- Your progress
Learning objectives
By the end of this topic you should be able to:
- describe the seven characteristics of living things
- classify organisms into kingdoms and vertebrate and invertebrate groups
- use and write identification keys
- explain what a species is and why scientific names are used
- estimate populations using quadrats
- discuss how people affect other species
Before you start
You will use these skills. If any feel shaky, review them first.
- plant and animal cells (see Cells and microscopy)
- reading tables
- means (averages)
Key vocabulary
- Organism
- Any living thing.
- Species
- A group of organisms that can breed together to produce fertile offspring.
- Vertebrate
- An animal with a backbone.
- Invertebrate
- An animal without a backbone.
- Kingdom
- One of the largest groups of living things, such as animals, plants or fungi.
- Key
- A series of questions used to identify an organism.
Understanding the ideas
-
What is it?
All living things carry out seven life processes, remembered as MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.
-
Why does it happen?
Scientists classify organisms by shared features. The largest groups are kingdoms, such as animals, plants, fungi and bacteria. Animals are divided into vertebrates (fish, amphibians, reptiles, birds and mammals) and invertebrates (such as insects, spiders, worms and snails).
-
How do we know?
Biologists identify organisms using keys and give each species a two-part scientific name, such as Homo sapiens, a system created by Carl Linnaeus in the 1700s. Quadrats and surveys help them count how many of each species live in an area.
-
Why does it matter?
Knowing which species live in an area helps us protect them. Many species are threatened by habitat loss, pollution and illegal trade.
-
What does it connect to?
Classification links to cells, ecosystems, evolution and genetics in biology, and to sorting and organising data in mathematics.
Vertebrate groups
- Fish: scales, fins and gills; lay eggs in water.
- Amphibians: moist skin; lay eggs in water; live on land and in water (frogs, toads).
- Reptiles: dry scaly skin; lay leathery eggs on land (lizards, snakes, turtles).
- Birds: feathers, beaks and wings; lay hard-shelled eggs.
- Mammals: fur or hair; most give birth to live young and all feed them milk.
Classification in the real world
Scientists in Pakistan survey birds at wetlands such as Haleji Lake to track migrating species. New species of insects, plants and fungi are still discovered every year, including in the Himalayas and Karakoram.
Worked examples
Example 2: estimating a population
Three 1 m² quadrats held 3, 5 and 4 dandelions. The lawn is 50 m². Estimate the number of dandelions.
- Mean = (3 + 5 + 4) ÷ 3 = 4 per m².
- Estimate = 4 × 50 = 200 dandelions.
Assessment tips
Classification questions often use keys, pictures and survey data. Expect to:
- Use keys to identify organisms, and write simple keys.
- Classify organisms using their features.
- Process quadrat and survey data, including means.
- Discuss how people can protect species.
Common mistakes: calling spiders insects; saying whales are fish; writing key questions that are opinions, such as "Is it big?"; and forgetting to leave out anomalous quadrats.
Check your understanding
Quick questions on the ideas above. Try each one before using a hint.
Practice questions
Investigation: sorting and keying leaves
Partially guided investigation · about 40 minutes · groups
- Research question
- Can you build a key that correctly identifies six different leaves collected from the school grounds?
- Scientific background
- Leaves differ in shape, edge, arrangement and vein pattern. Good key questions use features that anyone can see clearly.
- Hypothesis
- Write your own prediction, with a scientific justification.
- Variables
- Identify your independent, dependent and control variables, and explain how you will control them.
- Apparatus
- Six different leaves (collected fallen leaves, or photos), hand lens, ruler, paper and pencil.
- Method
- Look closely at each leaf and list its features (shape, edge, size, simple or compound).
- Choose a question that splits the leaves into two groups.
- Keep asking yes/no questions until every leaf has its own name.
- Swap keys with another group and test whether theirs works on your leaves.
Safety. Collect only fallen leaves or ask permission, wash hands afterwards, and avoid plants that can irritate skin.
Then evaluate: which of your questions worked best, and did any give different answers for different people?
Criterion-linked questions
Criterion B: inquiring and designing
Criterion C: processing and evaluating
Criterion D: reflecting on the impacts of science
Challenge questions
Harder problems in unfamiliar contexts. Plan before you calculate.
Topic check
Five questions picked at random from the whole topic. Take a new set whenever you like.
Review your mistakes
Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.
Your progress
Tracked separately for each skill, on this device only.
| Skill | Correct | Status |
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