B5 Core Questions
Core Questions for Topic 5: Inheritance, Variation and Evolution
QUESTION
ANSWER
1
Describe the cells produced by meiosis.
4 cells, genetically different.
2
Describe the cells produced by mitosis.
2 cells, genetically identical (clones).
3
What are gametes?
Sex cells.
4
Name the gametes in animals.
Sperm and egg.
5
Name the gametes in plants.
Pollen and egg.
6
Complete the sentence: "Sexual reproduction leads to ... in the offspring."
Variety.
7
State two differences between asexual and sexual reproduction (max 5).
1. Asexual reproduction involves only one parent.
2. No fusion of gametes.
3. No mixing of genetic information.
4. Genetically identical offspring.
5. Only mitosis used.
8
What effect does meiosis have on the number of chromosomes in a cell?
Halves it.
9
By what process is the number of chromosomes restored?
Fertilisation.
10
In animals, where are the gametes formed?
Ovaries and testes.
11
State the three key steps in meiosis.
1. Copies of the DNA are made.
2. The cell divides twice to form 4 gametes, each with a single set of chromosomes.
3. All 4 cells are genetically different from each other.
12
When a new cell is formed through fertilisation, how does it divide?
Mitosis.
13
What is the name of the process by which cells develop into specific cell types?
Specialisation / differentiation
14
State 3 advantages of sexual reproduction.
1. Produces variation in the offspring.
2. If the environment changes, variation gives a survival advantage by natural selection.
3. Natural selection can be sped up by humans in selective breeding to increase food production.
15
State 4 advantages of asexual reproduction.
1. Only one parent needed
2. More time and energy efficient as do not need to find a mate
3. Faster than sexual reproduction
4. Many identical offspring can be produced when conditions are favourable
16
Describe how malarial parasites use both forms of reproduction.
Reproduce asexually in the human host, but sexually in the mosquito.
17
Describe how fungi use both forms of reproduction.
Reproduce asexually by spores but also reproduce sexually to give variation.
18
Describe how plants use both forms of reproduction.
Runners such as strawberry plants, or bulb division such as daffodils.
19
The genetic material in the nucleus of a cell is….
DNA
20
Describe the structure of DNA.
A polymer made up of two strands forming a double helix.
21
Name the structure within which DNA is contained.
Chromosomes.
22
What is a gene?
A small section of DNA on a chromosome.
23
What is the function of a gene?
To code for a particular sequence of amino acids in order to make a specific protein.
24
What is a genome?
The entire genetic material of an organism.
25
State 3 ways in which understanding of the human genome will be important.
1. To search for genes linked to different types of disease
2. To understand and treat inherited disorders
3. To trace early human migration patterns
26
Name the three parts of a DNA molecule.
A phosphate group, a sugar molecule and a nucleotide base
27
Name the four nucleotides found in DNA.
Adenine, thymine, guanine and cytosine
28
How many bases code for a particular amino acid?
3
29
What is a set of three nucleotide bases called?
A codon
30
Which cell organelle synthesises proteins?
Ribosomes.
31
How is the protein sequence correctly assembled?
Using a template molecule from the DNA.
32
What brings specific amino acids to the ribosomes?
Carrier molecules.
33
When the protein chain is complete, what process aids it to form its unique shape?
Folding.
34
Name three uses of proteins in the body.
1. Enzymes
2. Hormones
3. Structural proteins e.g. collagen
35
What is a change in the DNA sequence called?
A mutation.
36
Name three potential consequences for a protein of a mutation.
1. No change or a slight change so no effect on the protein
2. Altered protein, so an enzyme may stop working
3. Mutation within a non-coding region nearby to a gene may affect the expression (production) of a protein
37
What is a gamete?
A sex cell (egg or sperm; egg or pollen).
38
What is a chromosome?
A thread-like structure which contains coiled up DNA and proteins.
39
What is a gene?
A sequence of DNA nucleotide bases that codes for a specific protein.
40
What is an allele?
A different version of a gene.
41
What does the term "dominant" mean?
The individual only needs one copy of this allele for its phenotype to be seen.
42
What does the term "recessive" mean?
The individual needs two copies of this allele for its phenotype to be seen.
43
What does the term "homozygous" mean?
The individual has two identical alleles for this gene.
44
What does the term "heterozygous" mean?
The individual has two different alleles for this gene.
45
What is a genotype?
The genetic makeup of an organism for a particular gene (e.g. RR).
46
What is a phenotype?
The physical characteristics of an organism (e.g. red flowers).
47
What is polydactyly?
A condition that causes the individual to have extra fingers or toes.
48
Is it a dominant or recessive condition?
Dominant.
49
State the genotype(s) that would result in polydactyly.
PP or Pp (homozygous dominant or heterozygous for this gene).
50
What is cystic fibrosis?
A condition which causes sticky mucus to build up in the lungs.
51
Is it a dominant or recessive condition?
Recessive.
52
State the genotype(s) that would result in cystic fibrosis.
cc (homozygous recessive).
53
How many pairs of chromosomes does an ordinary human body cell have?
23
54
How many pairs of chromosomes determine the sex of the individual?
1
55
What is the genotype of a female?
XX
56
What is the genotype of a male?
XY
57
Genes determine the phenotype of an organism – true or false?
False – the environment also plays a role.
58
What is variation within a population?
Differences in the characteristics of individuals in a population.
59
State three causes of variation in a population.
1. Genes
2. The environment
3. A combination of both
60
Within a population, there is normally very little genetic variation – true or false?
False – just look around you at humans!
61
What causes variation within a population?
Mutations.
62
How often does a mutation result in a new phenotype?
Very rarely.
63
What is evolution?
A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
64
True or false – does the theory of evolution by natural selection state that all living things evolved from simple life forms more than three billion years ago?
True.
65
Would the best organism within a species to survive and reproduce be:
a) the strongest?
b) the one which reproduces the fastest?
c) the best adapted to the environment?
c)
66
What is the definition of a species?
Organisms that can interbreed to produce fertile offspring.
67
What is selective breeding?
The process by which humans breed plants and animals for particular genetic characteristics.
68
Name two historic examples of selective breeding.
1. Breeding food crops from wild plants
2. Domesticating animals
69
How many generations of selective breeding does it take to obtain an organism with a desired characteristic?
Many!
70
State four modern examples of selective breeding.
1. Disease resistance in food crops
2. Animals which produce more meat or milk
3. Domestic dogs with a gentle nature
4. Large or unusual flowers
71
State a drawback to selective breeding.
Inbreeding – some breeds are prone to disease or inherited defects (e.g. some pugs have breathing problems).
72
What is genetic engineering?
The process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
73
State three ways plants might be genetically engineered.
1. Resistant to insect attack
2. Resistant to herbicides
3. Increased yields
74
Give one example of how bacterial cells have been genetically engineered.
To produce useful substances such as human insulin to treat diabetes.
75
How is a gene "cut out" from the genome of one species and inserted the genome of another?
Using enzymes.
76
Into what is the gene inserted?
A vector
77
Give two examples of vectors used in genetic engineering
A bacterial plasmid, a virus
78
When should a gene be transferred to another organism by genetic engineering?
At an early stage in their development
79
Why should a gene be transferred between organisms at an early stage of development?
So that they develop with desired characteristics.
80
State three concerns around genetically engineering plants.
1. Unknown effects on populations of wild flowers
2. Unknown effects on populations of insects
3. Some people feel the effects of eating GM crops on human health have not been fully explored
81
What is plant tissue culture?
Using small groups of cells from part of a plant to grow identical new plants.
82
What are "plant cuttings"?
An older, but simple, method used by gardeners to produce many identical new plants from a parent plant.
83
Where might these techniques be useful?
Horticulture and agriculture.
84
Describe the two steps involved in embryo transplanting.
Splitting apart cells from a developing animal embryo before they become specialised transplanting the identical embryos into host mothers.
85
Describe the steps involved in adult cell cloning or SCNT (somatic cell nuclear transfer) (5 steps)
1. The nucleus is removed from an unfertilised egg cell
2. The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
3. An electric shock stimulates the egg cell to divide to form an embryo
4. These embryo cells contain the same genetic information as the adult skin cell
5. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development
86
State a disadvantage to cloning plants and animals.
Reduces genetic variation, so makes populations more susceptible to disease.
87
Who is credited with the theory of natural selection?
Charles Darwin.
88
How did he come to develop his theory?
The result of observations on a round the world expedition, backed by years of experimentation and discussion and linked to developing knowledge of geology and fossils.
89
Who contributed to the theory of evolution but is often forgotten?
Alfred Russel Wallace.
90
State the three steps in the theory of evolution by natural selection.
1. Individual organisms within a particular species show a wide range of variation for a characteristic
2. Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
3. The characteristics that have enabled these individuals to survive are then passed on to the next generation
91
How was Darwin's theory published and when?
In a book, "On the Origin of Species", published in 1859.
92
State three reasons why Darwin's ideas were only slowly accepted.
1. The theory challenged the idea that God made all the animals and plants that live on Earth
2. There was insufficient evidence at the time the theory was published to convince many scientists
3. The mechanism of inheritance and variation was not known until 50 years after the theory was published
93
What theory did Jean-Baptiste Lamarck propose?
The idea that changes that occur in an organism during its lifetime can be inherited.
94
Are his ideas now accepted in the scientific community?
Only in very rare cases do scientists believe this is the case.
95
Whose studies lent most evidence to the idea of speciation (the formation of a new species from a common ancestor)?
Alfred Russel Wallace.
96
What is a species?
A group of organisms that have similar physical, biochemical and behavioural features, can breed to create fertile offspring and do not usually breed with individuals of another species.
97
Give the six steps in the process of speciation.
1. Geographical isolation (e.g. a flood divides an island in two)
2. Different selection pressures/conditions in the new environments
3. Genetic variation (due to mutations) within the groups
4. Best adapted individuals to the new conditions survive, reproduce and pass on these alleles
5. No interbreeding over time, groups become more different to each other
6. After a large amount of time, unable to interbreed successfully. They are now separate species.
98
Who is considered the "father" of modern genetics?
Gregor Mendel.
99
In which century did Mendel perform his famous breeding experiments on plants?
The mid-19th century.
100
What did Mendel theorise was transferred from parents to offspring?
"Heritable units"
101
In the late-19th century, scientists observed large structures in the nucleus for the first time. What were these?
Chromosomes.
102
What do we now know Mendel's "heritable units" are?
Genes.
103
In which century was the structure of DNA determined?
Mid-20th century.
104
What are fossils?
The remains of organisms from millions of years ago, found in rocks.
105
What are the three ways fossils may be formed?
1. From parts of organisms that have not decayed as one (or more) of the conditions needed for decay is absent.
2. Parts of the organisms have been replaced with minerals as they decay.
3. Preserved traces of organisms such as footprints, burrows and rootlet traces.
106
Why are few fossils of early life found?
Most early life were soft-bodied and so left little trace behind.
107
What does the lack of fossils of early life on Earth mean about the theories scientists have on the beginning of life on Earth?
We can't be certain about them as there is little evidence.
108
Why are fossils useful?
Can be used to determine how much or how little organisms have changed as life developed on Earth.
109
In evolutionary diagrams, what do junctions between the lines represent?
A common ancestor of two species
110
What is extinction?
When there are no remaining individuals of a species still alive.
111
State 3 of the 6 ways extinction can occur.
Changes to the environment over geological time; lack of food/prey; new predators; new diseases; new, more successful competitors; a single catastrophic event / natural disaster.
112
Why do bacteria evolve so rapidly?
They have a very fast reproduction rate.
113
New strains of bacteria are caused by…..
Mutation of their DNA.
114
State the 4 steps leading to the development of antibiotic resistance in a population of bacteria.
1. The population is exposed to an antibiotic, some of the population are resistant to the antibiotic.
2. The resistant bacteria are not killed, so survive the treatment.
3. These resistant bacteria reproduce and pass on the resistance genes to the next generation.
4. The new resistant strain spreads quickly as hosts are not immune to it and there is not effective treatment.
115
What is MRSA?
Methicillin-resistant Staphylococcus aureus (a bacterial species).
116
State three ways we can reduce the rate of antibiotic resistance development.
1. Stop prescribing antibiotics inappropriately, such as for viral infections.
2. Patients should complete their course of antibiotics so all bacteria are killed.
3. Use of antibiotics in agriculture should be restricted or banned.
117
Why aren't many new antibiotics being developed?
The development of new antibiotics is very costly and very slow.
118
Which is quicker, the development of new antibiotics or the development of antibiotic resistance in bacteria?
The development of antibiotic resistance in bacteria (currently).
119
Traditionally, how have we classified living things into groups?
Based on their physical chacracteristics and cell structure.
120
Who developed the first true classification system of living organisms?
Carl Linnaeus.
121
What are the titles of each classification level?
Kingdom, Phylus, Class, Order, Family, Genus, Species
122
Escherichia coli and homo sapiens are examples of the naming of organisms by the binomial system. Which two classification groups are used in these names?
Genus (Escherichia and homo) and species (coli and sapiens)
123
Name two developments which led to new classification systems being invented.
Developments in microscopes and development in the understanding of biochemical processes in cells.
124
Carl Woese proposed the "three-domain system" for living organisms. What are these three domains?
Archaea, Bacteria and Eukaryota
125
What are "Archaea"?
Primitive (old) bacteria often living in extreme environments.
126
Give an example of a type of cell in the Bacteria domain.
E. coli, S. Typhimurium, S. aureus
127
Give an example of a type of cell in the Eukaryota domain.
Protists, fungi, plants and/or animals