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Classifying different types of organisms

A huge variety of organisms live on our planet. Scientists have categorized organisms to make them easier to identify. This is called classification.

Organisms can be classified into different species. A species contains individuals with the same physical characteristics and common ancestors.

So far, scientists have identified around 290,000 species of plants, 1,250,000 species of animals and 5 million species of bacteria living on our planet.


Classifying animals

Animals can be divided into two groups.

Vertebrates have a backbone. They have a firm body because of the muscles that connect to their skeleton.

Invertebrates do not have a backbone. They have soft inner bodies that are held in shape either by a flexible covering of outer cells or by a hard covering called an exoskeleton.

animals

vertebrates invertebrates


Animal classification


Vertebrate classification


More about mammals

Mammals are classified into three subgroups:

monotremes – They lay eggs but suckle their young, e.g. platypus.

marsupials – They give birth to tiny underdeveloped young that develop in a pouch outside the mother's body, e.g. kangaroo.

placentals – The young are attached to a placenta inside the womb. Newborns are already developed, e.g. bear.

What type of mammal are humans?


Invertebrate classification


More about arthropods

Arthropods are divided into four subgroups:

myriapods – They have many feet and long bodies of many segments, e.g. millipedes, centipedes.

arachnids – They have eight legs, no wings and their bodies are in two segments, e.g. spider, mite.

insects – They have six legs, and many have two pairs of wings, e.g. dragonfly, moth, ladybird, wasp.

crustacea – They have gills, more than six legs and two pairs of antennae, e.g. crab, barnacle, lobster, shrimp.


Which type of invertebrate?


Classifying plants

Plants can be classified according to the structure of the vascular tissue (‘veins’) in their leaves.

Monocotyledons are plants that have leaves with parallel veins. Maize plants are monocotyledons.

Dicotyledons are plants that have wide leaves with branched veins. Horse chestnut trees are dicotyledons.

Plants can also be classified according to whether they reproduce via seeds (like flowering plants) or spores (like mosses and liverworts).


Classifying plants



Variation within a species

Organisms of the same species are similar but not identical.

Even though people are all from the same species, there are many ways in which they are different from each other.

The differences that occur both between different species and within the same species are called variation.


Family resemblance


Inherited characteristics

The members of this family tree are related and so they share certain similar characteristics, such as hair colour and eye colour.

Shared family characteristics are inherited from parents.

So why don’t all family members look exactly alike?

Why are identical twins more similar than brothers and sisters?


What is variation?

Children inherit characteristics from their parents. Each child inherits a different combination of characteristics. This is called inherited variation.

Variation can come about for two reasons. What are they?

Other characteristics are affected by a person’s surroundings. This called environmental variation.


Which type of variation?


Inherited or environmental?

Deciding if a characteristic is inherited or caused by environmental factors can cause a lot of discussion.

Scientists have now decided that only four features are truly inherited and not affected by the environment at all.

What are the four truly inherited characteristics?

natural eye colour

natural hair colour

blood group

certain inherited diseases.


Nose shape is inherited, but over time it may be affected by the environment.

For instance, someone might have a nose that looks just like their mother’s. But if they were in an accident, they might break their nose and put a kink in it.

Inherited or environmental?

Most features are caused by a mixture of inheritance and environmental factors.


Continuous and discontinuous variation

Characteristics can be classified in different ways. How would you categorize variation in eye colour? Could height be categorized in the same way?

A feature that can be measured and given a value from a range of values shows continuous variation.

A feature that cannot be measured but is one of a few distinct options shows discontinuous variation.

Which type of variation are eye colour and height?


Continuous or discontinuous?



Where is the inherited information?

An organism’s features can be inherited or caused by environmental factors.

Inherited features are those that have been passed from the parents to their offspring.

In all living things, inherited features are passed on in genetic material.

Where is the genetic material found?


Where is the inheritance information?


How are characteristics inherited?


Identical twins


Non-identical twins


Inheritance quiz



Masses of beefsteak tomatoes

78.5

102.3

113.2

83.2

118.1

110.8

99.6

84.8

98.4

100.4

108.3

87.4

100.2

106.4

105.6

105.2

109.4

91.9

97.5

98.6

111.3

97.3

95.7

102.1

112.7

112.6

99.8

97.1

109.0

103.7

102.1

119.3

109.7

99.8

103.8

93.8

109.4

91.7

92.1

109.3

94.4

96.1

113.5

102.4

89.2

88.9

108.8

111.8

92.2

104.6

The mass of 50 beefsteak tomatoes was measured (in grams) and the results recorded in the following table:


Masses of beefsteak tomatoes

The masses of the beefsteak tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 78 g and 82 g, 82 g and 86 g and so on.

What does this graph show?

freq

uenc

y

mass of beefsteak tomatoes (grams)


Masses of plum tomatoes

40.0

57.2

74.4

59.0

60.5

56.3

59.4

49.7

58.6

43.1

62.2

63.1

61.3

63.9

71.1

55.7

68.3

71.9

60.6

58.2

65.3

48.5

71.0

64.4

62.0

50.2

61.8

71.2

63.7

60.1

58.1

64.5

48.1

44.9

64.4

55.6

54.7

46.5

64.5

68.3

73.0

47.7

71.6

59.8

65.7

52.3

59.4

42.0

59.6

72.5

The mass of 50 plum tomatoes was also measured (in grams) and the results recorded in the following table:


Masses of plum tomatoes

The masses of the plum tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 40 g and 44 g, 44 g and 48 g and so on.

What does this graph show?

freq

uenc

y

mass of plum tomatoes (grams)


Comparing tomatoes

Compare the frequency graphs for the masses of the tomatoes.Are there any differences between the two sets of results?

Distribution of mass of beefsteak tomatoes.

Distribution of mass of plum tomatoes.

freq

uen

cyfr

equ

ency

mass (g)

mass (g)


Comparing tomatoes

Other questions to consider when comparing the frequency graphs for the masses of the beefsteak and plum tomatoes:

1. What can you say about the variation of mass within each species of tomato and the variation between the two sets of results?

2. Are there any other measurements of the tomatoes that can be easily recorded and would show a similar set of results to the measurements of mass?

3. Some quantities cannot be measured immediately but are important to those who grow and those who buy a crop of tomatoes, e.g. disease resistance and time taken to ripen. Can you think of any more quantities like this?



Selecting desirable characteristics

Genetic engineering – this involves changing an organism’s genetic material to produce useful characteristics.

Farmers, horticulturalists and scientists may want to produce plants or animals with useful characteristics.

There are several ways of doing this:

Selective breeding – this involves breeding individuals with desirable characteristics over generations to produce organisms with certain qualities.


Selective breeding

Selective breeding is a process humans use to produce animals or plants that have useful characteristics.

Milk farmers choose cows with the highest milk yield to breed with a suitable bull. Continuing to do this over several generations can produce a whole herd of cows with a very high milk yield.

Apple growers want to produce a type of apple that is tasty and resistant to disease. This can be done over several generations by crossing a variety of apple known for its taste with another variety that shows strong resistance to disease.


Selective breeding of cows


Selective breeding


Genetic engineering

Genetic engineering involves changing an organism’s genetic material. This can result in a change in the organism’s characteristics.

Genetic engineering is used to produce genetically-modified (GM) organisms that have useful characteristics.

How are GM crops useful to humans?

For example, microbes can be genetically engineered to produce vaccines for human diseases.


Why use genetic engineering?

Some crops plants can be genetically engineered to be disease, herbicide or frost-resistant. These crops could produce larger crop yields.

Crops, such as golden rice, have been engineered to contain extra vitamins. These could be useful in countries where malnutrition is a problem.

Why do some people think that GM crops are unsafe?


Disadvantages of genetic engineering

Also, GM crops could cause people to have unknown or unforeseen allergic reactions.

GM organisms have characteristics that do not occur naturally, so it’s very hard to predict the effect they may have on the environment and wildlife.

It is possible that GM crops could cross-pollinate with naturally-occurring plants. For example, this could result in weeds with herbicide resistance, that would be very hard to get rid of.


Do you agree with genetic engineering?



Glossary


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Multiple-choice quiz

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