Diversity Of Organisms

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Variation Between Organisms

Variation refers to the differences that exist between organisms.
Variation can be seen in visual appearance, behaviour, and biochemistry.
Variation arises from a combination of genetic and environmental factors.
Genetic variation is generated by mutation and by the combination of alleles during sexual reproduction.
The environment can affect gene expression, e.g. temperature, nutrient availability, and oxygen concentration.
Variation exists both between species and within a species; no two individuals are identical when all characteristics are compared.
Variation can be discontinuous (distinct categories, e.g. blood type) or continuous (measured on a scale, e.g. height).

Species Classification and the Binomial System

Classification is the process of putting organisms into groups; the science of classification is taxonomy.
The smallest taxonomic group is the species.
Historically, species were classified by morphology (observable characteristics), known as the morphological species concept.
Carl Linnaeus developed the binomial system of naming species, giving each species a two-part Latin name.
The first part of the binomial name is the genus (capitalised), and the second is the species name (lower-case), e.g.×Canis lupus×.
Binomial names are written in italics when typed or underlined when handwritten.
After first use, the genus name can be abbreviated, e.g.×Triticum aestivum×becomes×T. aestivum×.
Classification based on morphology alone can be misleading because species with similar appearance are not always closely related.

The taxonomic hierarchy

Biological Species Concept

The biological species concept defines a species as a group of organisms that can interbreed to produce fertile offspring.
This concept has limitations: it cannot be applied to organisms that reproduce asexually, such as bacteria.
It is difficult to apply when fertile hybrids are produced, e.g. the 'wholphin' (a cross between a melon-headed whale and a bottlenose dolphin).
It cannot be used for extinct species because they cannot be bred to test fertility.
Other characteristics used to determine species include morphology, DNA sequences, biochemistry, ecology, and evolutionary lineage.
The characteristics used depend on the organism; e.g. bacteria may be classified by biochemistry or ecology, while extinct species may be classified by evolutionary lineage.

Speciation and Distinguishing Populations from Species

Speciation is the process by which one species gives rise to two or more new species.
Speciation can occur when populations become isolated (e.g. geographically), preventing gene flow between them.
Different environmental conditions can lead to different natural selection pressures, and genetic drift can also contribute to speciation.
Once speciation has occurred, the two species are reproductively isolated and can no longer interbreed to produce fertile offspring.
Speciation occurs gradually over long time periods, so it can be difficult to pinpoint when two populations become separate species.
Assigning separate species status can be subjective; e.g. killer whales show variation between populations and some scientists believe there may be more than one species.

Chromosome Number

A diploid cell contains two complete sets of chromosomes (2n); haploid cells contain one set (n).
In animals, haploid cells are gametes (egg and sperm).
During fertilisation, haploid gametes fuse to form a diploid zygote; both gametes must have the same number of chromosomes for the zygote to be viable.
Every body cell arising from the zygote has the same chromosome number, except red blood cells which have no nucleus.
Different species have different chromosome numbers; e.g. humans have 46 (23 pairs) and chimpanzees have 48 (24 pairs).
The diploid number is always even because it must be divisible by two to produce a whole haploid number.
Differences in chromosome number can prevent organisms from different species from breeding successfully.
Chromosome number is not linked to how 'advanced' a species is in evolutionary terms.

Karyograms: Skills

A karyogram is an image showing all chromosomes in a cell arranged by size, shape, and banding pattern, placed with their homologous pairs.
A karyotype is the appearance of a complete set of an individual's chromosomes, including number, size, shape, and banding.
To make a karyogram, cells are stained and viewed under a light microscope; photographs are taken during metaphase of cell division.
Chromosomes are arranged by size, shape, and banding pattern; this can be done with paper and scissors or on a computer.
Chromosomes with a central centromere are metacentric; those with a near-terminal centromere are acrocentric.
Chromosome pair 23 (sex chromosomes) often does not fit the size-order pattern because the X chromosome is very large.
Karyograms can provide evidence for chromosome fusion; e.g. chimpanzee chromosomes 12 and 13 may have fused to form human chromosome 2.
Evidence for this fusion includes matching banding patterns, centromere location, and the presence of satellite DNA and telomeric DNA in human chromosome 2.

Genomes and Genome Size

The genome is all of the genetic information in an organism, including coding and non-coding DNA, mitochondrial DNA, chloroplast DNA, and plasmid DNA (in prokaryotes).
DNA sequencing determines the base sequence of DNA; genome-wide comparisons can be made between individuals and species.
There is a high level of genome similarity within and between species; humans share about 99.9% of their DNA with other humans and about 99% with chimpanzees.
Differences between individuals are due to different alleles; single base changes are called single nucleotide polymorphisms (SNPs).
Genome size varies widely: viruses and bacteria have small genomes, prokaryotes generally have smaller genomes than eukaryotes, and plant genomes vary greatly.
Genome size is measured in million base pairs or C-value (haploid nuclear DNA content); 1 pg = 978 Mb.
Genome size does not always correlate with organism complexity; e.g. humans have 3,100 Mb, hagfish 4,200 Mb, and common wheat 17,000 Mb.
Factors to consider include non-coding DNA, polyploidy in plants, and that 'complexity' can be defined in different ways.

Uses of Genome Sequencing

Genome sequencing allows the base sequence of an organism's genome to be identified; methods are becoming faster and cheaper, with next-generation sequencing (NGS) techniques.
Sequence data can be used to determine evolutionary relationships (phylogenetics), personalised medicine, and more.
Phylogenetics classifies species based on evolutionary origins and shared common ancestry.
DNA, mRNA, and amino acid sequences can be compared; the more similar the sequences, the more closely related the species are.
Species separated for longer have accumulated more mutations, so their sequences differ more.
Cytochrome c is often used for comparison because it is present in many organisms and shows sufficient variation.
Sequence data can be used to create phylogenetic trees showing evolutionary relationships.
Genome sequencing can be used in personalised medicine: identifying disease risks, developing targeted drugs, and selecting treatments based on an individual's genotype.

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1.Which is the correct definition for a species according to the biological species concept?
Easy
- AA group of organisms which can interbreed to produce fertile offspring.
- BA group of organisms which look similar.
- CA group of organisms with similar characteristics.
- DA group of living things.
2.Which of the following statements about genomes is not correct?
Easy
- AHumans have the most genes of any organism.
- BHumans have around 20 000 genes.
- CSpecies vary in the number of genes they have.
- DThe number of genes of an organism is not proportional to genome size.
3.The image shows a karyogram. Which of the statements about the karyogram is correct?
Medium
- AThe source of DNA for the karyogram was a human cell.
- BThe source of DNA for the karyogram was a haploid cell.
- CAll 23 pairs of chromosomes are arranged in descending order of size.
- DChromosome banding is visible.
4.What is an appropriate unit for comparing the length of genomes?
Medium
- AMillion base pairs
- BMicrometers
- CNanometers
- DPicometer
5.What is the most efficient way to compare the genome sizes of different species?
Medium
- AExtract information from an online database.
- BRead scientific articles and extract relevant information.
- CCompare the chromosome number of the different species.
- DCompare the proteome size of the different species.
6.Which of the following statements about genome sequencing are correct? (select all that apply)
Medium
- AScientists can now look for correlations between changes in a gene and particular human traits.
- BThe genomes of many species have now been sequenced.
- CAdvancing computer technology means that the rate at which a genome can be sequenced continues to increase.
- DScientists now know the location and role of every human gene.
- EGenome sequencing technology is now so advanced that further developments are not expected.
7.The two karyotypes belong to a donkey (Q) and a horse (R). Breeding these two individuals resulted in the production of a sterile mule (S). Why would S be sterile?
Hard
- AThe process of meiosis will not be possible in S as homologous pairs cannot form.
- BThe sex of the mule (S) will be undetermined at birth due to the unnatural combination of chromosomes.
- CDifferent combinations of alleles formed as a result of crossbreeding Q and R which leads to disadvantageous characteristics in S.
- DThere are different numbers of chromosomes in the gametes of Q and R so S would not live long enough to breed.
8.What is the smallest taxonomic group?
Easy
- ASpecies
- BGenus
- CFamily
- DKingdom

Thêm câu hỏi

9.The biological species concept can be applied to bacteria.
Easy
True or false?
10.Which of the following are causes of genetic variation within a species? (select all that apply)
Medium
- AMutation
- BCombining alleles in different ways during sexual reproduction
- CEnvironmental temperature
- DNutrient availability
- EGenetic drift
11.Match each type of variation with the correct example.
Medium
- Discontinuous variation
- Continuous variation
- Human blood type
- Human height
12.Order the taxonomic groups from smallest to largest.
Medium
- Species
- Genus
- Family
- Order
- Class
13.Which of the following is a limitation of the biological species concept?
Medium
- AIt cannot be applied to organisms that reproduce asexually.
- BIt cannot be applied to organisms that reproduce sexually.
- CIt can only be applied to extinct species.
- DIt requires knowledge of an organism's DNA sequence.
14.A mule is the sterile offspring of a horse and a donkey. Why is a mule sterile?
Hard
- AThe sex of the mule is undetermined at birth due to the unnatural combination of chromosomes.
- BDifferent combinations of alleles formed as a result of crossbreeding lead to disadvantageous characteristics.
- CThere are different numbers of chromosomes in the gametes of the horse and donkey so the mule would not live long enough to breed.
- DMeiosis cannot occur in the mule because homologous pairs cannot form.
15.Which of the following statements about the human genome are correct? (select all that apply)
Medium
- AHumans share around 99.9% of their DNA with other humans.
- BHumans have around 20,000 genes.
- CThe number of genes of an organism is proportional to genome size.
- DHumans have the most genes of any organism.
- EHumans share around 99% of their DNA with chimpanzees.
16.Which of the following is the best method to compile a table of genome sizes for several plant species?
Medium
- ACarry out a breeding experiment.
- BUse an online genome size database.
- CCount the chromosomes under a microscope.
- DMeasure the physical size of the plants.
17.Cells in metaphase of mitosis were used to construct the karyogram. Explain the reason for this.
Medium
- AChromosomes are at their most condensed and most visible during metaphase
- BChromosomes have already separated to opposite poles during metaphase
- CChromosomes are invisible during metaphase as they are uncoiled
- DHomologous chromosomes are pairing up during metaphase
18.List two characteristics of the chromosomes that are used to arrange them in a karyogram. (select all that apply)
Medium
- ASize
- BShape
- CBanding pattern
- DNumber of genes
- EBase sequence
19.Apart from sex determination, state one other use of studying the karyotype of an individual.
Medium
- ATo identify chromosomal abnormalities such as an extra chromosome
- BTo determine the exact base sequence of every gene
- CTo measure the genome size in megabases
- DTo identify the species of the individual
20.State the best method that can be used to compile the information found in the table.
Easy
- ASearch an online genome size database
- BCount the chromosomes of each species under a microscope
- CMeasure the mass of each plant
- DCompare the number of genes in each species
21.A student wants to compare the DNA base sequences of a gene from four closely related plant species. Which method would give the most reliable comparison of their evolutionary relationships?
Medium
- ACompare the base sequence of several different genes from each species
- BCompare the base sequence of a single gene from each species
- CCompare the total genome size of each species
- DCompare the number of chromosomes in each species
22.Cytochrome c is often used when comparing the amino acid sequences of different species to investigate evolutionary relationships. Which property makes it suitable for this purpose?
Hard
- AIt is present in a wide range of organisms and shows variation between species
- BIt is only found in mammals, so it shows recent evolutionary changes
- CIt is a small molecule that mutates very rapidly
- DIt is found only in plants, allowing plant relationships to be studied
23.Which of the following are limitations of the biological species concept? (select all that apply)
Medium
- AIt cannot be applied to organisms that reproduce asexually
- BIt cannot be applied to extinct species
- CIt can be difficult to apply when different species produce fertile hybrids
- DIt cannot be applied to organisms that reproduce sexually
- EIt requires knowledge of an organism's DNA sequence
24.A genome includes both coding DNA and non-coding DNA.
Easy
True or false?
25.The number of genes an organism has is always proportional to its genome size.
Easy
True or false?
26.Match each term with its correct definition.
Medium
- Genome
- Karyotype
- C-value
- Single nucleotide polymorphism
- All of the genetic information in an organism
- The appearance of a complete set of an individual's chromosomes
- The haploid nuclear DNA content of an organism
- A difference in a single nucleotide between DNA sequences
27.Place the steps of making a karyogram in the correct order.
Medium
- Cells are stained and viewed under a light microscope
- Photographs are taken of the chromosomes during metaphase
- Photographs of the chromosomes are cut up
- Chromosomes are arranged by size, shape and banding pattern
28.What name is given to the science of classification?
Easy
- ATaxonomy
- BGenetics
- CEcology
- DPhylogeny
29.Which term describes a group of organisms that can interbreed to produce fertile offspring?
Easy
- ASpecies
- BGenus
- CPopulation
- DCommunity
30.Which of the following is the smallest taxonomic group?
Easy
- ASpecies
- BGenus
- CFamily
- DOrder
31.In the binomial name Canis lupus, which part is the genus?
Easy
- ACanis
- Blupus
- CCanis lupus
- DNeither part
32.What is the diploid chromosome number of a human?
Easy
- A46
- B23
- C48
- D24
33.What is the haploid chromosome number of a chimpanzee?
Easy
- A24
- B48
- C23
- D46
34.Which of the following describes a haploid cell?
Medium
- AA cell containing one complete set of chromosomes
- BA cell containing two complete sets of chromosomes
- CA cell containing no chromosomes
- DA cell containing four complete sets of chromosomes
35.What is a karyogram?
Medium
- AAn image showing all of the chromosomes in a cell arranged by size, shape and banding pattern
- BA graph showing the number of chromosomes in a cell over time
- CA diagram showing the stages of mitosis
- DA table listing the genes found on each chromosome
36.Which of the following is the correct definition of a genome?
Medium
- AAll of the genetic information in an organism
- BAll of the genes that code for proteins in an organism
- CThe total number of chromosomes in a cell
- DThe sequence of bases in a single gene
37.Which unit is used in genome size databases to express genome size in number of bases?
Easy
- AMegabase (Mb)
- BPicogram (pg)
- CMicrometer (µm)
- DNanometer (nm)
38.What is a single nucleotide polymorphism (SNP)?
Medium
- AA difference in a single nucleotide between DNA sequences
- BA chromosome that has lost a single gene
- CA protein that differs by one amino acid between species
- DA mutation that adds an extra chromosome
39.Which of the following statements about the Human Genome Project is correct?
Medium
- AIt involved sequencing the entire human genome.
- BIt proved that humans have the most genes of any organism.
- CIt showed that all human genes have a known function.
- DIt was completed before any other genome was sequenced.
40.Which of the following is a use of genome sequencing in medicine?
Medium
- AIdentifying individuals at high risk of developing certain diseases
- BDetermining the number of chromosomes in a cell
- CMeasuring the rate of photosynthesis in a plant
- DClassifying organisms using morphological characteristics
41.What is the term for the process by which one species gives rise to two or more new species?
Easy
42.Calculate how many times bigger the genome of Paris japonica (149 890 million base pairs) is than that of Genlisea margaretae (63 million base pairs). Give your answer to the nearest whole number.
Medium
43.Complete the sentence about the binomial naming system.
Medium
The first part of a binomial name is the ____ and the second part is the ____.
44.Calculate how many times bigger the genome of Paris japonica (149,890 million base pairs) is than that of Genlisea margaretae (63 million base pairs). Give your answer to the nearest whole number.
Medium
45.Mistletoe is a diploid plant with 10 pairs of homologous chromosomes and a genome size of 90,000 million base pairs. Calculate the average size of one chromosome in million base pairs.
Medium
46.Complete the sentence about the biological species concept.
Easy
According to the biological species concept, a species is a group of organisms that can interbreed to produce ____ offspring.
47.Mistletoe (Viscum album) is a diploid plant with 10 pairs of homologous chromosomes and a genome size of 90,000 million base pairs. Calculate the average size of one chromosome in million base pairs.
Medium
48.The diploid chromosome number of a chimpanzee is 48. State the haploid chromosome number of a chimpanzee.
Medium
49.The genome of the Japanese canopy plant (Paris japonica) is 150,000 million base pairs. Express this genome size in megabases (Mb).
Medium
50.The genome of Paris japonica is 150,000 million base pairs. The genome of Genlisea margaretae is 63 million base pairs. Calculate how many times bigger the genome of Paris japonica is than that of Genlisea margaretae. Give your answer to 1 decimal place.
Medium
51.Complete the sentence about chromosome number.
Easy
A cell with two complete sets of chromosomes is described as ____ and has the symbol ____, while a gamete with one complete set is described as ____ and has the symbol ____.
52.What is the term for the method of naming species that gives each species a two-part Latin name?
Medium
53.Explain why cells in metaphase of mitosis are used to construct a karyogram.
Hard
54.Explain why it can be difficult for scientists to determine whether two populations are still the same species.
Hard
55.The prickly pear cactus has been cultivated to have no spines. These cultivars are kept separate from wild prickly pear populations. Explain why it can be difficult for scientists to determine whether these two groups are still the same species.
Hard
56.Identify the sex of this individual.
Easy
57.Explain how genome sequencing can be used to determine the evolutionary relationships between species.
Hard
58.Calculate how many times bigger the genome of Paris japonica (149 890 million base pairs) is than that of Genlisea margaretae (63 million base pairs). Give your answer to the nearest whole number.
Medium
- A2141 times
- B2617 times
- C2379 times
- D2855 times
59.Calculate how many times bigger the genome of Paris japonica (149,890 million base pairs) is than that of Genlisea margaretae (63 million base pairs). Give your answer to the nearest whole number.
Medium
- A2141 times
- B2617 times
- C2855 times
- D2379 times
60.Mistletoe is a diploid plant with 10 pairs of homologous chromosomes and a genome size of 90,000 million base pairs. Calculate the average size of one chromosome in million base pairs.
Medium
- A4050 million base pairs
- B4500 million base pairs
- C4950 million base pairs
- D5400 million base pairs
61.Mistletoe (Viscum album) is a diploid plant with 10 pairs of homologous chromosomes and a genome size of 90,000 million base pairs. Calculate the average size of one chromosome in million base pairs.
Medium
- A4950 million base pairs
- B5400 million base pairs
- C4050 million base pairs
- D4500 million base pairs
62.The diploid chromosome number of a chimpanzee is 48. State the haploid chromosome number of a chimpanzee.
Medium
- A26 chromosomes
- B24 chromosomes
- C28 chromosomes
- D22 chromosomes
63.The genome of the Japanese canopy plant (Paris japonica) is 150,000 million base pairs. Express this genome size in megabases (Mb).
Medium
- A165000 Mb
- B150000 Mb
- C180000 Mb
- D135000 Mb
64.The genome of Paris japonica is 150,000 million base pairs. The genome of Genlisea margaretae is 63 million base pairs. Calculate how many times bigger the genome of Paris japonica is than that of Genlisea margaretae. Give your answer to 1 decimal place.
Medium
- A2619 times
- B2857 times
- C2143 times
- D2381 times

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