Cambridge IGCSE0610

Characteristics of living organisms

Biology 0610 Chapter Notes

What this chapter covers

Characteristics of living organismsConcept and uses of classification systemsFeatures of organisms

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1. Movement

Movement is an action by an organism or part of an organism causing a change of position or place.

The whole organism does not have to move. A change of position by one part of it also counts.

Worked example 11 mark

A single-celled organism swims towards a source of light. Which characteristics of living things does this behaviour involve?

A growth and excretion · B growth and sensitivity · C movement and sensitivity · D movement and excretion

1
C: movement and sensitivity. [1]

2. Sensitivity

Sensitivity is the ability to detect and respond to changes in the internal or external environment.

Both parts count. The organism must detect the change and then respond to it.

Examiner insight

“Many candidates appreciated that the experiment on woodlice demonstrated sensitivity. Some candidates incorrectly opted for respiration.”

Worked example 11 mark

Earthworms come to the soil surface after heavy rain. Which characteristic of living organisms does this show?

A growth · B nutrition · C reproduction · D sensitivity

1
D: sensitivity. [1]

3. Respiration

Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

Respiration happens inside cells. It is not the same as breathing.

Examiner insight

“Many candidates appreciated that the release of energy from nutrient molecules is respiration. Some candidates incorrectly selected nutrition.”

Worked example 12 marks

State what is meant by respiration.

1
chemical reactions in cells [1]
2
that break down nutrient molecules and release energy for metabolism [1]

4. Growth

Growth is a permanent increase in size and dry mass.

Every part of the wording matters. The increase must be permanent, and it must be in both size and dry mass.

Worked example 11 mark

Which two characteristics of living organisms does phototropism demonstrate?

A growth and nutrition · B growth and sensitivity · C movement and nutrition · D nutrition and sensitivity

1
B: growth and sensitivity. [1]

5. Reproduction

Reproduction is the processes that make more of the same kind of organism.

It is a characteristic of all living organisms, animals and plants alike.

Examiner insight

“Many candidates appreciated that excretion, sensitivity, and reproduction are characteristics of all animals and all plants. Some candidates incorrectly believed that these are characteristics of animals only.”

Worked example 11 mark

State what is meant by reproduction.

1
the processes that make more of the same kind of organism [1]

6. Excretion

Excretion is the removal of the waste products of metabolism and substances in excess of requirements.

Undigested food is not a waste product of metabolism. Its removal is egestion.

Examiner insight

“A significant number of candidates incorrectly believed that undigested food is removed by excretion. Egestion is the process that removes undigested food.” “Candidates need to understand that egestion is not an example of excretion.”

Worked example 12 marks

Distinguish excretion from egestion.

1
excretion is the removal of the waste products of metabolism and substances in excess of requirements [1]
2
egestion is the removal of undigested food [1]

7. Nutrition

Nutrition is the taking in of materials for energy, growth and development.

For a plant, the materials include carbon dioxide, which is needed for photosynthesis.

Examiner insight

“Since the carbon dioxide is diffusing into the leaf, the correct response is nutrition as carbon dioxide is required for photosynthesis.” “The majority of candidates did not realise that the bubbles containing oxygen meant that this diagram is showing photosynthesis rather than respiration. They then need to link this to nutrition, as photosynthesis is not a characteristic of all living things, but it is needed for plant nutrition.”

Worked example 12 marks

State what is meant by nutrition.

1
the taking in of materials [1]
2
for energy, growth and development [1]

8. Several characteristics at once

One action often shows more than one characteristic. Match each part of the action to its own definition.

Name only the seven characteristics. Breathing and digestion are not among them. Respiration and nutrition are.

Examiner insight

“The experimental evidence led successful candidates to realise that the microorganisms were demonstrating movement, nutrition and sensitivity.” “The most frequent error was to list breathing and digestion as characteristics.”

Worked example 11 mark

A man moves from a sitting position and walks towards a closed door. He opens the door and takes a short walk. Which characteristics of living organisms are demonstrated by the man?

A excretion, respiration and sensitivity · B growth, excretion and respiration · C growth, nutrition and reproduction · D nutrition, respiration and sensitivity

1
A: excretion, respiration and sensitivity. The man does not grow, feed or reproduce here, which rules out B, C and D. [1]

Recap

Movement: a change of position or place by an organism or part of an organism.
Respiration: chemical reactions in cells that release energy from nutrient molecules.
Sensitivity: detecting and responding to changes in the internal or external environment.
Growth: a permanent increase in size and dry mass.
Reproduction: the processes that make more of the same kind of organism.
Excretion: removal of waste products of metabolism and substances in excess of requirements.
Nutrition: taking in materials for energy, growth and development.

9. Grouping organisms by shared features

Organisms can be classified into groups by the features that they share.

Vertebrates are identified by a backbone. The vertebrate groups include amphibians, reptiles, birds, mammals and fish. Birds have feathers. Mammals have fur or hair, external ears and mammary glands. Arachnids have four pairs of legs, a body divided into two main parts and an exoskeleton.

Examiner insight

“Common misconceptions were that amphibians had scales, that amphibians did not lay eggs and that only mammals could maintain their body temperature.” “Candidates are expected to know the characteristics used to classify the main groups of vertebrates.”

Worked example 13 marks

Table 1.1 shows some features of amphibians and reptiles.

Complete Table 1.1 by placing ticks in the boxes to show whether each feature is typical of amphibians or reptiles or both.

feature	amphibians	reptiles
scales
lungs
laying eggs

1
scales: reptiles only [1]
2
lungs: amphibians and reptiles [1]
3
laying eggs: amphibians and reptiles [1]

10. Species

A species is a group of organisms that can reproduce to produce fertile offspring.

The word applies to all organisms, not to animals only. A horse and a donkey belong to the same genus, but their offspring, the mule, is not fertile. So they are different species.

Examiner insight

“Relatively few appreciated that to be of the same species, the offspring had to be fertile.” “Several candidates described how members of the same species would be similar in terms of genetics or morphology, whilst true this is not the definition of a species.”

Worked example 12 marks

Describe what is meant by the term species.

1
a group of organisms [1]
2
that can reproduce to produce fertile offspring [1]

11. The binomial system

The binomial system is an internationally agreed system of naming species. The scientific name of an organism is made up of two parts, showing the genus and the species.

The genus comes first and starts with a capital letter, as in Bombina variegata. The species comes second and starts with a lower-case letter.

Examiner insight

“Some candidates incorrectly believed that it is the second name that represents the genus.” “This question was well-answered although a few did not appreciate that the first letter of the species part of the name is written in lower case.”

Worked example 11 mark

Which parts make up the scientific name of an organism?

A genus and species · B genus and kingdom · C kingdom and species · D kingdom, genus and species

1
A: genus and species. [1]

12. Dichotomous keys

A dichotomous key is a key that uses paired choices. Each choice is about an identifiable feature, for example whether a bird has webbed feet or a beak that curves upwards.

To use a key, start at question 1 and work through each stage. To construct one, pick a feature that splits the group in two. Repeat for each group until every organism is named.

Examiner insight

“It is important that candidates work through each stage of the dichotomous key in order to identify a specimen.”

Worked example 13 marks

The table is a key to four birds, E, F, G and H.

Use the key to identify a bird that has webbed feet and a pouch under its beak. Give the question numbers you followed.

question	feature	yes	no
1	webbed feet?	go to 2	go to 3
2	pouch under the beak?	bird E	bird F
3	beak curves upwards?	bird G	bird H

1
question 1: webbed feet, yes, so go to 2 [1]
2
question 2: pouch under the beak, yes [1]
3
the bird is E [1]

13. Classification, evolution and DNA

Classification systems aim to reflect evolutionary relationships between organisms.

The sequences of bases in DNA are used to classify organisms. Individuals of one species have very similar base sequences. Bacteria are hard to classify by appearance, so comparing their DNA is more accurate.

Examiner insight

“Some candidates referred to base pairs instead of base sequences.”

Worked example 13 marks

Two strains of bacteria look identical under a microscope. Explain why scientists use DNA to classify them.

1
bacteria are hard to classify by appearance [1]
2
so comparing the sequences of bases in their DNA is more accurate [1]
3
individuals of the same species have very similar base sequences [1]

14. Reading an evolutionary tree

Organisms that share a more recent ancestor are more closely related. Their DNA base sequences are more similar than those of organisms that share only a distant ancestor.

The two species whose branches split last share the most recent common ancestor.

Examiner insight

“Many candidates described the lion and leopard as sharing a common ancestor and not identifying that this ancestor was the most recent common ancestor.”

Worked example 12 marks

Figure 1.2 shows the evolutionary relationships between several species of cat based on their DNA sequences. The diagram should be interpreted from left to right. Each branch shows the point at which a new species was formed.

Use Figure 1.2 to determine which two species are most closely related. Explain your answer.

1
lion and leopard [1]
2
they share the most recent common ancestor (their branches split most recently) [1]

Recap

Organisms are classified into groups by the features that they share.
A species is a group of organisms that can reproduce to produce fertile offspring.
Scientific name: two parts, genus first (capital letter), species second (lower case).
A dichotomous key uses paired choices about identifiable features. Work through every stage.
Extended: classification systems aim to reflect evolutionary relationships.
Extended: the sequences of bases in DNA are used to classify organisms.
Extended: a more recent common ancestor means more similar base sequences.

15. The animal and plant kingdoms

Organisms are placed in a kingdom by their features. Birds and arachnids are both groups in the animal kingdom. The plant kingdom is another kingdom.

Plants have a cell wall. A feature used to place an organism in the animal kingdom must be shared by all animals. Having lungs or being a vertebrate is not a feature of all animals.

When a question asks for a kingdom, name a kingdom. Mammals, insects and crustaceans are groups inside the animal kingdom. They are not kingdoms.

Examiner insight

“Many candidates correctly stated plants or fungi but many incorrectly stated mammals or other animal groups.” “Some candidates identified additional statements, including that all animals have lungs and are vertebrates.”

Worked example 11 mark

Birds are one group in the animal kingdom. State the name of one other kingdom.

1
plant [1]

16. The groups of vertebrates

The five main groups of vertebrates are mammals, birds, reptiles, amphibians and fish.

All birds have feathers, and feathers are only found in birds. All mammals have hair and produce milk. Mammals also have vertebrae, but that does not separate them from other vertebrates.

Reptiles have dry, scaly skin and lay eggs with leathery shells. Fish also have scales, so scales alone do not identify a reptile. Fish have gills. Amphibians lay eggs and do not have scales. Four limbs, claws and laying eggs are shared by several groups, so none of them identifies a bird or a mammal.

Examiner insight

“While many candidates opted correctly, identifying feathers as the visible feature that can be used to classify a bird, some candidates incorrectly opted for wings.” “While most candidates optioned correctly, quite a large number believed that having four limbs is a characteristic of mammals.”

Worked example 11 mark

A student finds a vertebrate that has the features listed.

1 claws · 2 feathers · 3 four limbs · 4 lays eggs

Which of these features mean that this vertebrate must be a bird?

A 1 and 3 · B 1 and 4 · C 2 and 3 · D 2 only

1
D: feathers only (feature 2) [1]

17. The groups of arthropods

All arthropods have jointed legs, a segmented body and an exoskeleton. Not all arthropods have antennae.

The four main groups are insects, arachnids, crustaceans and myriapods. Insects have three pairs of jointed legs. Arachnids have four pairs (8 legs) and a body divided into two main parts. Crustaceans have two pairs of antennae and five or more pairs of legs. Myriapods have many segments and many legs. Some myriapods have two pairs of legs on each segment.

Write the group name, not a common name such as spider or lobster.

Examiner insight

“Few candidates knew that the features that are characteristic of all arthropods are jointed legs and a segmented body.” “Candidates incorrectly gave common names of arthropods instead of the scientific group names.”

Worked example 12 marks

Arachnids are also in the animal kingdom. State two features of arachnids that are absent in birds.

1
8 legs / 4 pairs of legs [1]
2
body divided into two main parts [1]

18. Classifying with a key

To classify an organism, compare its features with the features of each group. A key that uses paired choices is a dichotomous key. Each step has two options, and each option sends you to a name or to the next step.

Work through every step in order. Count carefully: legs come in pairs, and the number of pairs helps to decide the arthropod group.

Examiner insight

“It is important that candidates work through each stage of the dichotomous key in order to identify a specimen.”

Worked example 11 mark

The bar chart shows the number of arthropods and the types of arthropod in 1 m² area of a field.

How many of these arthropods have more than three pairs of jointed legs?

A 27 · B 31 · C 33 · D 38

1
read the bars: arachnids 10, crustaceans 12, insects 16, myriapods 5
2
insects have exactly three pairs, so leave them out
3
10 + 12 + 5 = 27, so A [1]

19. The five kingdoms

All organisms are placed in one of five kingdoms: animal, plant, fungus, prokaryote and protoctist.

Prokaryotes do not possess a nucleus. All prokaryotes have a cell wall, a cell membrane and circular DNA. Flagella, plasmids and capsules are found in some prokaryotes but not in all, so they are not features of the kingdom.

Bacteria are a group within the prokaryote kingdom, not a kingdom. Plants and prokaryotes have a cell wall, but not all protoctists do.

Examiner insight

“A common error was to give bacteria which is a group within the prokaryote kingdom. Protist or protoctista was a common answer; however, not all organisms belonging to this kingdom have cell walls.” “A few candidates did not read that the feature should be of all prokaryotes, and listed plasmids and capsules among their answers.”

Worked example 13 marks

A cell does not have a nucleus. Name the kingdom it belongs to and state two features that all members of this kingdom have.

1
prokaryote [1]
2
cell wall [1]
3
circular DNA (or cell membrane) [1]

20. Ferns and flowering plants

The plant kingdom includes ferns and flowering plants. Ferns have spores. Flowering plants have seeds.

Flowering plants are dicotyledons or monocotyledons. A monocotyledon has narrow, strap-like leaves with parallel veins, flower parts in multiples of three and one seed leaf (cotyledon). A dicotyledon has broad leaves with branched veins.

Producing fruit does not identify a dicotyledon. One seed leaf does not mean one seed.

Examiner insight

“Dicotyledons have broad leaves and branched veins, not parallel.” “Some candidates could give a reason why orange trees are classified as dicotyledonous plants although many candidates incorrectly stated that it is because the trees produce fruit.”

Worked example 12 marks

A flowering plant has narrow strap-like leaves. Its flower parts are in multiples of three. Name the group of flowering plants it belongs to and state one more feature of this group.

1
monocotyledon [1]
2
parallel veins (or one seed leaf) [1]

21. Viruses

A virus has two features: a protein coat and genetic material.

The protein coat is not a cell wall or a cell membrane. Viruses do not have a cell wall. Virus is not the name of a kingdom.

Examiner insight

“A common error was to identify the protein coat as the cell wall or membrane.”

Worked example 12 marks

State the two features of a virus.

1
protein coat [1]
2
genetic material [1]

Recap

Name a kingdom when asked for one: animal and plant are kingdoms, mammals and insects are not.
Vertebrate groups: mammals, birds, reptiles, amphibians, fish.
Birds: feathers. Mammals: hair and milk. Four limbs and eggs do not identify a group.
All arthropods: jointed legs, segmented body, exoskeleton.
Insects 3 pairs of legs, arachnids 4 pairs, crustaceans 2 pairs of antennae, myriapods many legs.
Dichotomous key: work through every step in order.
Extended: five kingdoms are animal, plant, fungus, prokaryote, protoctist.
Extended: all prokaryotes have a cell wall, cell membrane and circular DNA, and no nucleus.
Extended: ferns have spores, flowering plants have seeds. Monocotyledons have parallel veins, dicotyledons branched veins.
Extended: a virus has a protein coat and genetic material.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

State what is meant by movement.1 mark
Name the characteristic of living organisms described as the release of energy from nutrient molecules in cells.1 mark
A student writes that breathing is a characteristic of all living things. Name the characteristic the student should have written and state what it is.2 marks
A seedling is watered and its mass rises for an hour. A week later its size and dry mass have both increased. State which change is growth and why.2 marks
An organism removes salts that are in excess of its requirements. Name the characteristic of living organisms that this shows.1 mark
A person eats a meal. Undigested food leaves the body as faeces. State whether this is excretion and name the process.2 marks
A student says that excretion, sensitivity and reproduction are characteristics of animals only. State whether the student is correct and give a reason.2 marks
A student lists the characteristics of a mouse as: movement, breathing, digestion and reproduction. (a) Identify the two entries that are not characteristics of living organisms. (b) Name the characteristic that each should be replaced by.4 marks
Pondweed is placed in water in bright light. Carbon dioxide diffuses from the water into its leaves. Bubbles containing oxygen leave the leaves. A student writes: ‘Gases are moving in and out, so this is respiration.’ (a) Name the process that the bubbles containing oxygen indicate. (b) Name the characteristic of living organisms that the pondweed demonstrates by taking in carbon dioxide. Give a reason. (c) State what respiration is, to show why the student is wrong.4 marks
A student watches a small sea animal that lives fixed to a rock and never leaves it. The student records five observations. 1. When its tentacles are touched, they pull in towards its mouth. 2. It takes a shrimp into its body. 3. Undigested pieces of shrimp later leave its body. 4. It takes in water and becomes larger for an hour, then returns to its original size. 5. A small part breaks off and becomes a new animal of the same kind. (a) Observation 1 demonstrates two characteristics of living organisms. Name each one and give the evidence for it. (b) The student writes that observation 3 is excretion. Explain why the student is wrong. (c) The student writes that observation 4 is growth. Explain why the student is wrong. (d) Name the characteristic demonstrated by observation 2 and the characteristic demonstrated by observation 5.7 marks
State one feature that is found only in birds.1 mark
State two features of an arachnid that a bird does not have.2 marks
A horse and a donkey breed to produce a mule. The mule is not fertile. Explain why a horse and a donkey are different species.2 marks
The scientific name of a goat is Capra hircus. State the genus and the species.2 marks
A student writes the scientific name of a goat as ‘capra Hircus’. Describe the two mistakes.2 marks
Beetle P has wings and spots. Beetle Q has wings and no spots. Beetle R has no wings. Construct a dichotomous key that identifies each beetle.4 marks
Use this key to identify an animal with no backbone and eight legs. Show your route. 1. Backbone? Yes: go to 2. No: go to 3. 2. Feathers? Yes: animal V. No: animal W. 3. Eight legs? Yes: animal X. No: animal Y.3 marks
Scientists classify a new species of frog. State which is more accurate: comparing its anatomy with that of other frogs, or comparing its DNA. State what is compared in the DNA.2 marks
The diagram shows the evolutionary relationships between five species of lizard, J, K, L, M and N, based on their DNA sequences. It is read from left to right. (a) State which two species are most closely related. Explain your answer. (b) A student says J and K are just as closely related. Explain why the diagram disproves this. (c) State the two species with base sequences least similar to that of M. Explain your answer.6 marks
Scientists find a bacterium, X. They compare the same short stretch of its DNA with that of three known species of bacteria, P, Q and R. The sequences of bases are: ``` X A T G C C A T G G A P A T G C C A A G G A Q A T G T C A A G C A R T T C C G A T C G T ``` (a) Count the number of positions at which X differs from P, from Q and from R. (b) List P, Q and R in order, most closely related to X first. Explain your answer. (c) Individuals of species P differ at up to 2 positions. Suggest the species of X, with a reason.7 marks
State the feature that shows a vertebrate must be a bird.1 mark
A student is asked to name one kingdom other than the animal kingdom. The student writes mammals. Explain why this is wrong and give a correct answer.2 marks
State two features found in all mammals but not in all vertebrates.2 marks
State two features of all arthropods. Explain why antennae is not a correct answer.3 marks
Use the key to identify an animal that has six jointed legs and antennae shorter than its body. Name the arthropod group it belongs to. | step | feature | go to | | --- | --- | --- | | 1 | six jointed legs | step 2 | | | eight jointed legs | step 3 | | 2 | antennae longer than body | P | | | antennae shorter than body | Q | | 3 | stripes on legs | R | | | no stripes on legs | S |2 marks
A collection holds 5 insects and 3 arachnids. A student calculates the total number of jointed legs as 5 × 3 + 3 × 4 = 27. State the student's mistake and calculate the correct total.4 marks
A student labels the outer layer of a virus as its cell wall. Give the correct name of this layer and state the other feature of a virus.2 marks
A student writes: bacteria, plants and protoctists are three kingdoms, and all their members have a cell wall. Identify the two mistakes. Then state one feature, other than a cell wall, that all prokaryotes have.3 marks
A student examines four samples, P, Q, R and S, from a hot spring and records their features in the table. (a) The student says P and S belong to different kingdoms because only P has a flagellum and plasmids. Explain why the student is wrong. (b) The student says R is a prokaryote because it has no nucleus and its coat is a cell wall. State what R is and explain why it is not a prokaryote. (c) One student says Q cannot be a protoctist because it has no cell wall. Another says Q is a prokaryote because it is a single cell. Explain why each student is wrong. | sample | nucleus | cell wall | other features recorded | | --- | --- | --- | --- | | P | no | yes | circular DNA, flagellum, plasmids | | Q | yes | no | single cell | | R | no | no | a protein coat and genetic material only | | S | no | yes | circular DNA, no flagellum, no plasmids |6 marks
A student records 40 plants in a woodland clearing. The table shows the four types found. The student writes: K and L are the dicotyledons because they produce fruit. (a) Classify J, K, L and M as precisely as the features allow. (b) Calculate the percentage of the flowering plants that are dicotyledons. Give your answer to the nearest whole number. (c) Explain, using K and M, why the student's reason is wrong. (d) Write one step for a dichotomous key that separates K from L and M. | type | number | has | leaves | veins | flower parts in threes | fruit seen | | --- | --- | --- | --- | --- | --- | --- | | J | 12 | spores | | | no flowers | no | | K | 9 | seeds | narrow, strap-like | parallel | yes | yes | | L | 14 | seeds | broad | branched | no | yes | | M | 5 | seeds | broad | branched | no | no |8 marks

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Read the notes

1. Movement#

2. Sensitivity#

3. Respiration#

4. Growth#

5. Reproduction#

6. Excretion#

7. Nutrition#

8. Several characteristics at once#

9. Grouping organisms by shared features#

10. Species#

11. The binomial system#

12. Dichotomous keys#

13. Classification, evolution and DNA#

14. Reading an evolutionary tree#

15. The animal and plant kingdoms#

16. The groups of vertebrates#

17. The groups of arthropods#

18. Classifying with a key#

19. The five kingdoms#

20. Ferns and flowering plants#

21. Viruses#

End-of-chapter exercise

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Chapter at a Glance

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Related chapters

1. Movement

2. Sensitivity

3. Respiration

4. Growth

5. Reproduction

6. Excretion

7. Nutrition

8. Several characteristics at once

9. Grouping organisms by shared features

10. Species

11. The binomial system

12. Dichotomous keys

13. Classification, evolution and DNA

14. Reading an evolutionary tree

15. The animal and plant kingdoms

16. The groups of vertebrates

17. The groups of arthropods

18. Classifying with a key

19. The five kingdoms

20. Ferns and flowering plants

21. Viruses