Variation & Evolution (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

1. Variation exists in a population due to mutation.

2. Individuals with advantageous characteristics are more likely to survive.

3. Survivors are more likely to reproduce and pass on their alleles.

4. Over time, advantageous alleles become more common in the population.

True.

Darwin's theory of natural selection holds that all living things evolved from simple life forms that first developed more than three billion years ago.

Individuals in a species show a wide range of variation caused by differences in genes. Those most suited to the environment have a higher chance of survival and pass their alleles to offspring.

Alfred Wallace did pioneering work on speciation, and more evidence gathered over time has built on his work to produce our current understanding of how new species form.

Speciation is the process by which two populations of the same species become so different that they can no longer interbreed to produce fertile offspring, forming two new species.

True.

A physical barrier (such as a new river or mountain range) can isolate two populations. Different selection pressures then cause them to evolve differently, potentially leading to speciation.

The environment differs on each side of the barrier, creating different selection pressures. Natural selection favours different characteristics in each population, so over many generations they become increasingly distinct.

False.

Evolution refers to changes in species over time, while natural selection is the mechanism by which that change takes place. Evolution is the outcome; natural selection is the process.

A fossil is the preserved remains of an organism from millions of years ago, found in rocks. Fossils provide evidence for evolution by showing how organisms have changed over time.

An evolutionary tree is a diagram that shows the relationships between species over evolutionary time. Each new branch represents speciation — the point at which a new species evolved.

True.

The more similar the DNA base sequences of two species, the more closely related they are and the more recent their common ancestor.

Antibiotic-resistant strains of bacteria develop because a chance mutation may cause some bacteria to survive antibiotic treatment. These bacteria reproduce, passing on the genes for resistance.

Bacteria reproduce very rapidly (roughly every 20 minutes), so evolution occurs over a much shorter time span compared to larger organisms, making it possible to observe the process directly.

Antibiotic resistance is the ability of bacteria to survive and reproduce despite exposure to an antibiotic, arising through natural selection when a chance mutation confers resistance.

False.

After antibiotic treatment, non-resistant bacteria are killed. Only the resistant bacteria survive, reproduce, and pass on resistance genes, so resistant bacteria come to dominate the population.

Fossils show how much or how little different organisms have changed over time. By comparing fossils from different geological periods, scientists can track the gradual development of species.

Because DNA base sequences code for amino acid sequences in proteins, the similarity in amino acid sequences between species can also be used to determine how closely related they are.

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

The binomial system gives each organism a two-part scientific name: the genus (capitalised) followed by the species (lowercase). For example, Homo sapiens. Names are always written in italics.

True.

The genus always starts with a capital letter and the species name starts with a lower case letter, e.g. Homo sapiens. Binomial names are written in italics.

The sequence of classification from broadest to most specific is: Kingdom, Phylum, Class, Order, Family, Genus, Species.

DNA sequencing allows scientists to compare the base sequences of different species. The more similar the sequences, the more closely related the species. This gives a more scientific and accurate classification than studying physical features alone.

Morphology is the study of the overall form and shape of an organism. It was one of the original methods used to classify living things before microscopy and DNA analysis became available.

True.

As microscopes improved and understanding of biochemical processes advanced, scientists proposed new classification models, eventually leading to the use of DNA sequences to determine how closely related species are.

Organisms in the same species share features because they descend from a common ancestor and therefore share similar DNA sequences. The more closely related two species are, the more features they share.

False.

Linnaeus originally classified organisms using physical structure and characteristics. DNA analysis only became possible much later, when new technology allowed scientists to compare base sequences.

Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic traits by choosing parents with desirable characteristics and breeding them together over many generations.

Not all offspring will show the desired characteristics. Only those that do are selected and bred together. This must be repeated over many successive generations before all offspring reliably show the selected traits.

True.

Humans have used selective breeding for thousands of years to increase the yield and quality of crops (such as rice and maize) and animal products (such as meat and milk).

Selective breeding can lead to inbreeding, which reduces the gene pool. This increases the chance of organisms inheriting harmful genetic defects or being vulnerable to new diseases.

Any two from:

1. High milk yield

2. High quality meat

3. Good quality wool (sheep)

Inbreeding occurs in selective breeding when closely related individuals are repeatedly bred together, reducing the gene pool and increasing the risk of harmful genetic defects and disease vulnerability.

False.

Reducing the gene pool through inbreeding decreases the variety of alleles in the population, so there is less chance of resistant alleles being present. This makes the population more vulnerable to new diseases.

Any two from:

1. Disease resistance

2. Increased crop yield

3. Hardiness to weather conditions (e.g. drought tolerance)

True.

All breeds of domestic dog are descended from wolves. Humans have used selective breeding over thousands of years to produce breeds with many different characteristics.

Genetic engineering is the process of changing the genetic material of an organism by removing, altering, or inserting genes from another organism, which may or may not belong to the same species.

A vector is used to insert the selected gene into the target organism. One example is a bacterial plasmid (a piece of circular DNA); a virus can also be used as a vector.

True.

Because genes can be transferred directly between organisms, genetic engineering is much faster than selective breeding, which requires many generations to establish a desired trait.

In genetic engineering, enzymes are used to isolate the required gene. This gene is then inserted into a vector which carries it into the target cells.

Recombinant DNA is the DNA of an organism that now contains DNA from another organism as well. This is produced during genetic engineering when a gene is inserted into a host organism.

A transgenic organism (genetically modified organism) is one that has received genetic material from another organism through genetic engineering and now expresses the desired characteristics.

False.

In genetic engineering, selected genes can be transferred between organisms that may or may not belong to the same species. This is a key difference from selective breeding.

Genes are introduced at an early stage of development so that the organism develops with the desired characteristics — all cells in the organism will contain the new gene as it divides and grows.

False.

An ethical argument concerns the rights and wrongs of a technology (e.g. whether it is morally acceptable). A practical argument concerns whether the technique is safe or feasible to carry out.