StemUp: OCR A A level Biology 4.2.2 Classification and evolution

What is classification in biology? (2)

- The act of arranging organisms into groups

- Based on their similarities and differences

What is taxonomy? (1)

The study of classification

What are the eight levels of taxonomic hierarchy? (8)

1. Domain

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genus

8. Species

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What happens as you move down the taxonomic hierarchy? (2)

- There are more groups at each level

- But fewer organisms in each group

What is a species? (1)

A group that contains only one type of organism (e.g., humans, dogs)

What is the binomial system of naming species? (3)

- Genus (capitalised)

- species (lowercase)

- E.g., Homo sapiens.

Why is the binomial system advantageous over common names? (1)

Universal and recognised worldwide

How does the binomial system help avoid confusion? (2)

- It avoids confusion

- Caused by different common names for the same organism

What is an example and features of the Prokaryotae kingdom? (2)

- Example: Bacteria

- Features: Prokaryotic, unicellular, no nucleus (DNA is free), smaller ribosomes, less than 5μm

What is an example and features of the Protictista kingdom? (2)

- Example: Algae, Protozoa

- Features: Eukaryotic, usually live in water, unicellular or simple multicellular organisms

What is an example and features of the Fungi kingdom? (2)

- Example: Moulds, Yeast, Mushrooms

- Features: Eukaryotic, chitin cell wall, saprotrophic (absorb substances from dead/decaying organisms), single-celled or multicellular organisms

What is an example and features of the Plantae kingdom? (2)

- Example: Mosses, Ferns, Flowering plants

- Features: Eukaryotic, multicellular, cellulose cell walls, photosynthetic, contain chlorophyll, autotrophic/photoautotrophic (produce own food using light).

What is an example and feature of the Animalia kingdom? (2)

- Example: Nematodes, Molluscs, Insects, Fish, Reptiles, Mammals, Birds

- Features: Eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals)

What were early classification systems based on, and what was their limitation? (2)

- Early classification systems used observable features

- But they might not accurately show how related organisms are

What do modern classification systems use alongside observable features? (4)

- Molecular evidence (DNA and proteins)

- Embryological evidence (development stages)

- Anatomical evidence (body structure and function)

- Behavioural evidence (behaviour and social organisation)

How is molecular evidence used in classification? (3)

- By comparing DNA base sequences and amino acid sequences in proteins (e.g. cytochrome C)

- Which shows the degree of relatedness between organisms

- The more similar the sequences, the more closely related the species are

What is embryological evidence in classification? (2)

- It involves comparing the similarities in the early stages of an organism's development

- To determine how closely related organisms are

What is anatomical evidence in classification? (2)

- It compares the structure and function of body parts in different organisms

- To assess their relatedness

What is behavioural evidence in classification? (2)

- It involves comparing the similarities in behaviour and social organisation among organisms

- To help classify them

What system has replaced the five-kingdom classification system? (1)

Three-domain system

How did the old five-kingdom system classify organisms? (2)

- Into five groups

- Plant, Animal, Fungi, Protista, and Prokaryotae (Monera)

What are the three domains in the modern classification system? (3)

- Eukarya

- Archaea

- Bacteria

Which organisms are placed in the Eukarya domain? (2)

- Organisms that contain a nucleus

- Including four of the five kingdoms (Plant, Animal, Fungi, and Protists)

Why were organisms in the kingdom Prokaryotae separated into two domains in the new system? (2)

- Because new evidence showed that Archaea and Bacteria evolved separately

- Archaea are more closely related to Eukarya than Bacteria

What molecular evidence supports the three-domain system? (2)

- RNA polymerase is different in Bacteria and Archaea

- Archaea (but not Bacteria) have similar histones to Eukarya

What cell membrane evidence supports the three-domain system? (2)

- The bonds in lipids in the cell membranes of Bacteria and Eukarya are different

- The development and composition of flagellae differ between the domains

What is phylogeny? (1)

The study of the evolutionary history of groups of organisms

What does a phylogenetic tree represent? (2)

- It demonstrates how all organisms

- Have evolved from shared common ancestors

According to phylogenetics, what defines a species? (1)

A species is the smallest group that shares a common ancestor

How does phylogeny relate to classification systems? (2)

- Classification systems now take phylogeny into account when arranging organisms into groups

- System = cladistics

What were Darwin's four key observations that led to his theory of evolution? (4)

- Organisms produce more offspring than survive

- There is variation in the characteristics of members of the same species

- Some characteristics can be passed on from one generation to the next

- Individuals best adapted to their environment are more likely to survive.

What is the basic premise of Darwin's theory of evolution by natural selection? (2)

- Individuals with advantageous adaptations are more likely to survive, reproduce, and pass on their traits

- Leading to evolution over time

What is a selection pressure? (2)

- Environmental factors that affect an organism's chances of survival

- Such as predation, disease, or competition

How do genes contribute to evolution according to modern understanding? (3)

- Genes determine many of an organism's characteristics

- Advantageous alleles can be passed on to offspring

- Leading to evolution over generations

How does the fossil record provide evidence for evolution? (3)

- By arranging fossils in chronological order

- Gradual changes in organisms can be observed

- Showing the process of evolution over time

How does DNA provide evidence for evolution? (2)

- Evolution causes gradual changes in an organism's DNA

- Organisms that diverged more recently have more similar DNA sequences

What is variation? (2)

- refers to the differences that exist between individuals

- Within a species (intraspecific) or between different species (interspecific)

What is an example of intraspecific variation? (1)

Different beak sizes in birds

What is an example of interspecific variation? (1)

Size differences between bird species

What is continuous variation? (2)

- Occurs when individuals within a population vary within a range

- With no distinct categories (e.g., height in humans, milk yield in animals)

What is discontinuous variation? (2)

- Occurs when there are distinct categories

- Each individual falls into one category (e.g., blood group in humans, seed shape in plants)

How do genetic factors cause variation? (3)

- Arises from different genes and alleles

- Leading to differences in genotype

- Which in turn results in variation in phenotype (e.g., blood group, antibiotic resistance)

How do environmental factors cause variation? (2)

- Environmental factors like climate, lifestyle, or diet

- Can influence characteristics (e.g., accent, height based on nutrition)

How do both genetic and environmental factors contribute to variation? (2)

- Genetics determine the potential for certain traits (e.g., height)

- Environmental factors (e.g., diet) influence how those traits develop

What does standard deviation indicate in a sample? (3)

- Measures the spread of values around the mean

- A large SD indicates high variability

- While a small SD means the values are closely grouped around the mean

What are adaptations? (2)

- Features that increase an organism's chances of survival and reproduction

- Improve the chances of its offspring reproducing successfully

What are behavioural adaptations? (2)

- Ways that an organism acts to increase its chance of survival

- E.g., playing dead to avoid predators or engaging in courtship behaviour to increase the chances of successful mating

What are physiological adaptations? (2)

- Processes inside an organism's body that help it survive

- E.g., hibernation to conserve energy in winter or bacteria producing antibiotics to reduce competition for resources

What are anatomical adaptations? (2)

- Structural features of an organism's body that enhance its survival

- e.g., streamlined body shape for faster swimming or thick blubber for warmth in cold environments

What is an ecological niche? (2)

The role of an organism within its habitat

- Including what it eats, when it eats, and where it feeds

Why do unrelated organisms sometimes have similar adaptations? (2)

- They can develop similar adaptations when they evolve in similar environments or to fill similar ecological niches

- Convergent evolution

What are the three different groups of mammals? (3)

- Placental mammals (e.g., humans)

- Marsupials (e.g., kangaroos)

- Egg-laying monotremes (e.g., duck-billed platypus)

What are the characteristics of marsupial mammals? (2)

- Have a short gestation period, do not develop a full placenta, and are born early in development

- The young continue to develop in the mother's pouch, where they attach to a teat and receive milk

What are the characteristics of placental mammals? (3)

- Placental mammals have a longer gestation period and develop a placenta during pregnancy

- Which allows for nutrient and waste exchange between the fetus and mother

- The young are born more fully developed

How does the evolution of pesticide resistance occur in insects? (3)

- Genetic mutations create alleles that confer pesticide resistance

- Insects with this resistance allele survive exposure to pesticides and pass the allele to the next generation

- Leading to a population with more resistant individuals

What are the implications of pesticide resistance in insects for human populations? (3)

- Crop infestations become harder to control

- Requiring broader pesticides that may harm beneficial insects

- It could also lead to the spread of diseases like malaria if disease-carrying insects become pesticide-resistant