Classification and genetic engineering | Pearson Edexcel GCSE Biology Notes

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The key idea

Classification reflects similarities and evolutionary relationships.Genetic engineering transfers a useful gene into another organism.

Classification and genetic engineeringClassification nests groups; engineering transfers a chosen gene.

Revision notes

The bit that matters

Learn the process in clean chunks. If a sentence explains a cause, make sure you can say the effect too.

Classification systems

Carl Linnaeus classified living things into a hierarchy of kingdom, phylum, class, order, family, genus and species, based on their structure and characteristics.Organisms are named using the binomial system with two parts, the genus and the species.As microscopes and understanding of biochemistry improved, the classification system was developed further.

The three domains

Due to evidence from chemical analysis Carl Woese proposed the three domain system, dividing life into archaea, bacteria and eukaryota.Archaea are primitive bacteria often living in extreme environments.Bacteria are true bacteria, and eukaryota includes protists, fungi, plants and animals.Evolutionary trees use current and fossil data to show how closely related different species are.

Genetic engineering

Genetic engineering involves modifying the genome of an organism by transferring a gene from one organism to another so that the organism produces a desired characteristic.Enzymes are used to cut out the required gene, which is inserted into a vector such as a plasmid or virus, and the vector inserts the gene into the cells of the target organism.If transferred at an early stage all the cells of the organism will have the new gene.

Uses and concerns of genetic engineering

Bacteria have been genetically engineered to produce human insulin for treating diabetes.Genetically modified crops, or GM crops, can be made resistant to insects or herbicides, giving higher yields, and crops can be enriched with nutrients such as golden rice with extra vitamin A.Concerns include possible effects on wild populations and uncertainty about long term effects on human health.

Key terms

Definitions to learn

Classification

The grouping of living organisms according to their characteristics.

Binomial system

Naming organisms using two parts, the genus and the species.

Three domain system

Dividing life into archaea, bacteria and eukaryota.

Genetic engineering

Modifying the genome by transferring a gene from one organism to another.

Vector

Something such as a plasmid or virus used to carry a gene into a cell.

GM crop

A genetically modified crop with a transferred gene giving a useful feature.

Worked example

Outline how bacteria can be engineered to produce human insulin.

Identify the human insulin gene.

Cut the gene and a bacterial plasmid using enzymes.

Insert the gene into the plasmid.

Place the recombinant plasmid into bacteria and culture them.

Final answer

Modified bacteria express the human insulin gene.

Exam habit

Distinguish selective breeding (choosing parents over generations) from genetic engineering (directly inserting a gene).For genetic engineering answers, name each enzyme used and its role.

Watch out

Selective breeding chooses parents; genetic engineering directly changes DNA.

Examiner tips

How to score full marks

1Learn the order of classification groups and the two parts of a binomial name, genus then species.
2Name Linnaeus for the original hierarchy and Woese for the three domain system.
3When evaluating genetic engineering, give specific benefits and specific concerns rather than vague statements.

Practice questions

Try these yourself

Open each answer only after you have explained the full biological process.

1What is binomial naming?

Mark scheme

1.Give both parts of the scientific name.

A two-part scientific name using genus and species.

2Give one possible benefit of genetic engineering in crops.

Mark scheme

1.Think yield, nutrients or resistance.

Examples include improved yield, disease resistance or increased nutritional value.

3Why can classification systems change?

Mark scheme

1.Link new evidence to relationships.

New genetic evidence can reveal different evolutionary relationships.

4Name the two parts of an organism's binomial name.[1 mark]

Mark scheme

1.Recall the levels used to name a species.

Genus and species (1)

5Name the three domains proposed by Carl Woese.[1 mark]

Mark scheme

1.Recall the highest classification groups.

Archaea, bacteria and eukaryota (1)

6Explain why the classification of organisms has changed over time.[3 marks]

Mark scheme

1.Link to improvements in technology and knowledge.

Improvements in microscopes allowed internal structures to be seen (1); developments in biochemistry and chemical analysis gave new evidence (1); this led to systems such as the three domain system (1)

7Describe how bacteria can be genetically engineered to produce human insulin.[4 marks]

Mark scheme

1.Mention enzymes, the gene and a vector.

Enzymes are used to cut the human insulin gene out of the human DNA (1); the gene is inserted into a vector such as a plasmid (1); the plasmid is transferred into the bacterium (1); the bacterium then produces human insulin (1)

8Genetically modified crops can increase food production but some people oppose them. Evaluate the use of GM crops, giving benefits and concerns.[4 marks]

Mark scheme

1.Give specific benefits.
2.Give specific concerns and a conclusion.

GM crops can give higher yields because they are resistant to insect pests or herbicides (1); they can be enriched with nutrients such as extra vitamin A in golden rice (1); however there are concerns about effects on populations of wild flowers and insects or biodiversity (1); and uncertainty about the long term effects on human health (1)

9State the correct order of the seven levels in the Linnaean classification hierarchy, from largest group to smallest.[1 mark]

Mark scheme

1.Recall the hierarchy from kingdom down to species.

Kingdom, phylum, class, order, family, genus, species (1) (all seven in correct order).

10Explain why organisms in the same genus are more closely related to each other than organisms that share only the same family.[3 marks]

Mark scheme

1.Link shared classification level to shared characteristics and common ancestors.

Organisms sharing the same genus share more characteristics (1) and have a more recent common ancestor (1) than those that only share the same family; the closer the classification group shared, the more recently the evolutionary lineages diverged (1).

11Describe the role of restriction enzymes and ligase enzymes in genetic engineering.[3 marks]

Mark scheme

1.Give the function of each enzyme type.

Restriction enzymes cut DNA at specific sequences, cutting out the desired gene from the donor organism's DNA (1); they cut the vector (plasmid) at the same sequence to open it up (1); ligase enzyme joins the gene into the opened plasmid, sealing the DNA strands (1).

12Suggest two ethical arguments for and two arguments against the genetic engineering of farm animals to produce useful human proteins in their milk.[4 marks]

Mark scheme

1.Consider welfare, medical benefit, ownership and long-term effects.

For: it could produce valuable medicines such as therapeutic proteins cheaply and in large quantities (1); it could save lives of patients who depend on proteins currently difficult to produce (1). Against: it raises animal welfare concerns as the process can cause suffering during creation of GM animals (1); there are concerns about unpredictable effects on the animal's health and the long-term consequences of releasing GM organisms into the environment (1).

13An evolutionary tree shows that lions (Panthera leo) and tigers (Panthera tigris) diverged more recently from a common ancestor than lions and leopards (Panthera pardus). What does this suggest about the similarities between these species?[4 marks]

Mark scheme

1.Interpret the tree in terms of shared ancestry and time.
2.Link to shared characteristics.

Lions and tigers diverged more recently, meaning they share a more recent common ancestor (1); this suggests they are more genetically similar to each other than lions and leopards are (1); they are likely to share more structural and biochemical characteristics (1); however all three are in the same genus, Panthera, meaning they share a relatively recent common ancestor compared to organisms in different genera (1).

Official exam-board sources

Specification Past papers

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