Lesson overview
Living things and keys: How can you name a living thing you have never seen before?
Put six mystery leaves behind a hand lens and name each one with a dichotomous key, one pair of statements at a time. Find out what a shared first part of a scientific name means, build a key of your own for four leaves you know, and (Supplement) compare short DNA strips to see which trees are most closely related.
Suggested sequence
- Lesson 1 · Is it alive? The seven characteristics of living organisms, and how to test whether something is alive. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 2 · Naming with a key. Dichotomous keys: naming organisms by features you can see, and building a key of your own. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Species and scientific names. Species, two-part scientific names and, in the Supplement, what DNA shows about relationships. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 7 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 10 questions, 15 min, lesson closed.
Learning goals
Part 1: Is it alive?
- Describe the seven characteristics of living organisms: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition (1.1.1)
- Use all seven characteristics to decide whether something is alive (1.1.1)
- Tell respiration from breathing, growth from swelling, and excretion from egestion (1.1.1)
Part 2: Naming with a key
- Use a dichotomous key to identify organisms (1.2.4)
- Choose identifiable features and write them as pairs of opposite statements (1.2.4)
- Construct and test a dichotomous key (1.2.4)
Part 3: Species and scientific names
- State that organisms can be classified into groups by the features that they share (1.2.1)
- Describe a species as a group of organisms that can reproduce to produce fertile offspring (1.2.2)
- Describe the binomial system: an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species (1.2.3)
- Supplement: explain that classification systems aim to reflect evolutionary relationships, and that sequences of bases in DNA are used as a means of classification (S1.2.5, S1.2.6)
- Supplement: explain that groups of organisms which share a more recent ancestor have base sequences in DNA that are more similar than those that share only a distant ancestor (S1.2.7)
Misconceptions to listen for
- “Respiration is breathing.” — Match respiration to the reactions in cells: breathing only moves air in and out of the lungs.
- “Growth is any increase in size.” — Match growth to the description with permanent and dry mass: swelling with water is not growth.
- “The flytrap snapping shut is movement, not sensitivity.” — It does move, but the point of the example is that it detects the touch and responds: match it to sensitivity.
- “Urine is egestion.” — Urea is made by reactions in cells, so removing it is excretion; egestion is passing out undigested food as faeces.
- “The flame is alive because it uses oxygen and grows.” — A flame shows a few of the characteristics, and none by reactions in cells; living organisms show all seven, and they are made of cells.
- “The crystal grows, so it must be alive.” — The crystal gets bigger as salt comes out of the solution onto it; it takes nothing in and is not an organism.
- “Faeces are excretion.” — Faeces were never part of the cells' reactions: passing them out is egestion, not excretion.
- “Breathing is one of the seven.” — The characteristic is respiration, the reactions in cells; breathing is only how some animals get oxygen in.
- “Anything that releases carbon dioxide must be alive.” — A flame releases carbon dioxide too. One characteristic cannot decide whether something is alive.
- “The seeds are dead, because they show no characteristics.” — A dry seed can be alive, respiring very slowly. Give it water, air and warmth: if it germinates, the other characteristics appear.
Scope
The seven characteristics of living organisms (1.1.1) in the reading and practice; classifying organisms by the features they share (1.2.1), species (1.2.2) and the binomial system (1.2.3) in the reading, the practice and the genus step of the experiment; using and constructing dichotomous keys based on identifiable features (1.2.4) through the leaf-key experiment; classification and evolutionary relationships (Supplement 1.2.5), DNA base sequences in classification (Supplement 1.2.6) and more similar sequences for a more recent common ancestor (Supplement 1.2.7) through the DNA step. The DNA strips in the experiment are illustrative.