Biology - Everything.

Question 1

Compare and contrast prokaryotic and eukaryotic cells

Answer 1

‘Pro’= Before, ‘Karyo’= Nucleus. First cells were simple, single celled organisms. Simple cells - one ‘room’ Genetic material not in a nucleus. Small - 0.1-5 micrometre. Important for life - cyanobacteria (2.3bya), helpful bacteria.
‘Euk’ = True, ‘Karyo’= nucleus. More complex cells. Evolved compartments. More efficient structure. Main compartments: nucleus, vacuoles, cell wall, membrane. Much larger - 10-100 micrometres. Can be further classified as plant or animal.

Question 2

Compare and contrast unicellular and multicellular cells

Answer 2

Unicellular cells are singular cells that are amoeba. They go around eating things and are eukaryotes.

Multicellular cells are many cells and have specific jobs. They have tissues and can be lung tissues that take in oxygen and release carbon dioxide.

Question 3

Compare and contrast plant and animal cells.

Answer 3

Plant cells have a cell wall, as well as a cell membrane. In plants, the cell wall surrounds the cell membrane. This gives the plant cell its unique rectangular shape. Animal cells have a cell membrane, but no cell wall.

Question 4

State the cell theory.

Answer 4

The cell theory underlies the study of any cell and is essential to biology and biologists understanding of cells.
It states that:
1. All living organisms are composed of cells. They may be unicellular or multicellular.
2. The cell is the basic unit of life.
3. Cells arise from pre-existing cells.
(They are not derived from spontaneous generation.)

Question 5

Describe the function of the main organelles Use scientific vocabulary and avoid comparisons – e.g. The nucleus contains genetic material and controls the activities of the cell (the “brain” of the cell is not an appropriate answer).

Answer 5

Organelles are the key to a eukaryotic cells survival. These compartments help cells carry out unique functions.
Nucleus: The nucleus controls and regulates the activities of the cell like the growth. It also carries genes.
Cell wall: The cell wall surrounds the plasma membrane of plant cells and provides tensile strength and protection.
Vacuoles: Membrane- bound cell organelles. Vacuoles in the animal and plant cells are very different. Animal cells’ vacuoles are usually small and help seize waste. Where as plant cell vacuoles help maintain water balance.

Question 6

Distinguish between mitosis and meiosis. Compare and contrast the processes (purpose of the process, type of cells involved (location in the body), number of cells produced, name and number of chromosomes in the parent cells, name and number of chromosomes in the daughter cells).

Answer 6

Mitosis had 4 stages in total plus an interphase. It happens in somatic cells and produces 2 diploid daughter cells. The chromosome number remains the same. However, the genetic variation doesn’t change.

Meiosis has 8 stages in total plus interphase. it happens in germ cells and its purpose is sexual reproduction. it produces4 haploid daughter cells but the chromosome number is halved in each daughter cell. And genetic variation is increased.

Same: They produce new cells. Have similar basic steps. Start with a single parent cell.

Question 7

Draw, label and describe the phases of mitosis. Use key words such as: centromere, spindle fibres, poles of the cell, centrioles, equator/metaphase plate, sister chromatids, chromatin, nuclear envelope and kinetochores.

Answer 7

Mitosis is where a single parent cell divides into 2 identical daughter cells. Mitosis is also the way in which old and damaged cells are replaced.

1. Before mitosis starts, the parent cell replicates its DNA.
2. Mitosis then starts with the DNA condensing into chromosomes.
3. The chromosomes align at the equator of the cell.
4. Sister chromatids are pulled apart to the poles of the cell.
5. Finally, the cell membrane pinches off, making two daughter cells.

Question 8

Explain why cell division needs to occur in both multicellular and unicellular organisms.

Answer 8

Unicellular organisms need cell division for reproduction whereas multicellular organisms need it for tissue growth and maintenance as well as to repair cells.

Question 9

Describe how genetic variation results from meiotic division

Answer 9

During meiosis, homologous chromosomes (1 from each parent) pair along their lengths. The chromosomes cross over at points called chiasma. At each chiasma, the chromosomes break and rejoin, trading some of their genes. This recombination results in genetic variation.

Question 10

Explain the difference between somatic & sex cells (gametes)

Answer 10

Somatic cells and gametes are two types of cells which are involved in asexual and sexual reproduction of organisms, respectively. Somatic cells can be found everywhere in the body whereas gametes are restricted to reproductive organs. Male gametes are called sperms while female gametes are called ova.

Question 11

Organise from largest to smallest: nucleotide, cell, nucleus, DNA, chromosome and gene.

Answer 11

Cell
Nucleus
Chromosome]
DNA
Nucleotide
Gene

Question 12

Describe the relationship between DNA, genes and chromosomes.

Answer 12

Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells that contain a person’s genes. Genes are contained in chromosomes, which are in the cell nucleus.

Question 13

What does a chromosome have?

Answer 13

Chromosome
Centromere
Sister chromatids
Homologous chromosomes

Question 14

Differentiate between sex chromosomes and autosomes.

Answer 14

Humans have 22 homologous pairs of autosomes and one pair of sex chromosomes. The main difference between autosomes and sex chromosomes is that autosomes are involved in determining the somatic characters of an individual and sex chromosomes are involved in determining the sex and the sex-related hormonal traits

Question 15

Describe a karyotype and explain its purpose. Analyse the karyotype to find out whether:
- it is from a female or male

Answer 15

The male karyotype refers to the appearance of the complete set of chromosomes in a somatic cell of a male while the female karyotype refers to the appearance of the complete set of chromosomes in a somatic cell of a female.

Question 16

Describe a karyotype and explain its purpose. Analyse the karyotype to find out whether:
- it has come from a sex cell or an autosome

Answer 16

A normal human karyotype consists of 22 pairs of autosomes and two sex chromosomes. Note the similar size and striped (banding) pattern between each of the pairs. The autosomal chromosome pairs are numbered and arranged from largest to smallest.

Question 17

Describe a karyotype and explain its purpose. Analyse the karyotype to find out whether:
- It is normal or abnormal

Answer 17

Under the light microscope. If a karyotype shows a usual number and structure of chromosome set, it is known as a normal karyotype. Abnormal karyotype shows an unusual number or structurally malformed chromosomes in the karyotype. This is the key difference between normal and abnormal karyotype.

Question 18

Describe and explain an abnormality (e.g. Trisomy – additional chromosome – how could it have occurred?)

Answer 18

A genetic disorder is a disease caused in whole or in part by a change in the DNA sequence away from the normal sequence. Genetic disorders can be caused by a mutation in one gene (monogenic disorder), by mutations in multiple genes (multifactorial inheritance disorder), by a combination of gene mutations and environmental factors, or by damage to chromosomes (changes in the number or structure of entire chromosomes, the structures that carry genes).

Question 19

Expand the acronym DNA (what does it stand for?)

Answer 19

DNA stands for Deoxyribonucleic Acid

Question 20

Define DNA (what is it?)

Answer 20

Your traits are determined by a special molecule called deoxyribonucleic acid, or DNA for short. DNA is arranged into a ladder-like structure called a Double Helix. (where two strands of DNA are twisted together). A molecule of DNA is made up of millions of tiny subunits called Nucleotides.

Question 21

Label the parts of a double helix

Answer 21

Phosphorus
Pentose sugar
Nitrogenous bases
Hydrogen bonds

Question 22

Compare DNA to a “twisted ladder”. (Using this comparison: What forms the “uprights” of the ladder and what forms the “rungs” of the ladder?)

Answer 22

A DNA molecule is made up of two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T).

Question 23

Label the parts of the nucleotides

Answer 23

Phosphate
Pentose sugar
Nitrogenous base

Question 24

Compare a nucleotide and a codon.

Answer 24

The nucleotide triplet that encodes an amino acid is called a codon. Each group of three nucleotides encodes one amino acid.

Question 25

List the nitrogenous bases

Answer 25

Adenine, Guanine, Cytosine and Thymine.

Question 26

State the complementary base pairing rule.

Answer 26

Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

Question 27

Define the term ‘mutation’.

Answer 27

These are alterations to genes. One small change in the DNA can result in a different protein being made. Some mutations are harmful, even fatal (e.g. cancer), while some can even be beneficial (e.g insects resisting pesticides). Mutations can be random…but they can also be caused by exposure to radiation, certain chemicals, or even too much UV from sunlight!

Question 28

Suggest how a mutation can affect the production of proteins.

Answer 28

Sometimes, mutations prevent one or more proteins from working properly. By changing a gene’s instructions for making a protein, a variant can cause a protein to malfunction or to not be produced at all.

Question 29

Explain how mutations can be both detrimental to the organism and beneficial. Provide examples.

Answer 29

The majority of mutations are neutral in their effects on the organisms in which they occur. Beneficial mutations may become more common through natural selection. Harmful mutations may cause genetic disorders or cancer.

Question 30

Explain the effect of environmental factors on an organism’s phenotype. Provide an example.

Answer 30

Genes play an important part in influencing phenotype, but genes are not the only influence. Environmental factors such as diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens can all impact which of an animal’s genes are expressed, which ultimately affects the animal’s phenotype. The shape of a person’s nose is inherited from their parents. However if a nose is broken causing the shape to change, this is an environmental change. Apart from eye colour, natural hair colour, blood group and some inherited diseases, all other features are caused by a mixture of inheritance and environmental factors.

Question 31

Compare and contrast:

- haploid and diploid

Answer 31

Haploid cells contain only one set of chromosomes (n). Diploid, as the name indicates, contains 2 sets of chromosomes (2n). Haploid cells are formed by the process of meiosis. Diploid cells undergo mitosis.

Question 32

Compare and contrast:

- homozygous and heterozygous

Answer 32

When both genes of a pair are the same letter they are called homozygous. e.g. TT – homozygous dominant. tt – homozygous recessive

Question 33

Compare and contrast:

- hybrid and purebred

Answer 33

Purebreds are the offspring that result from mating between genetically similar parents while hybrids are the offspring that are the result of mating between two genetically dissimilar parents.

Question 34

Compare and contrast:

- dominant and recessive

Answer 34

Dominant - Masks the other trait; the trait that shows if present. Represented by a capital letter
Recessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are present. Represented by a lowercase letter

Question 35

Compare and contrast:

- genotype and phenotype

Answer 35

Genotype – The genetic makeup of an organism; The gene (or allele) combination an organism has. Example: Tt, ss, GG, Ww
Phenotype – The physical characteristics of an organism; The way an organism looks Example: Curly hair, straight hair, blue eyes, tall, green .

Question 36

Examine a pedigree to determine whether a trait is: - Dominant or recessive

Answer 36

If the trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous.

Question 37

Define the three types of diversity

Answer 37

Species Diversity / Genetic Diversity / Ecosystem Diversity

Question 38

Discuss how variation occurs in sexually reproducing organisms (independent assortment, recombination and mutations).

Answer 38

Genetic diversity: the most important in terms of evolution. If there is genetic diversity or a large number of variations of the same gene (alleles), there will be a large variety of phenotypes (physical characteristics). Certain phenotypes might be advantageous for a particular environment, giving the individual an increased chance of survival. If an individual has a greater chance of survival, it will be more likely to go on to reproduce. The offspring will be more likely to inherit the advantageous gene, giving them an increased chance of survival too. As the gene becomes more common in the population, the whole species becomes more successful. Genetic diversity can also arise between individuals. This can happen when chromosomes get shuffled and crossed over during meiosis, and through the independent assortment of chromosomes into gametes.

Question 39

Discuss how environmental conditions produce different phenotypes

Answer 39

Environmental factors such as diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens can all impact which of an animal’s genes are expressed, which ultimately affects the animal’s phenotype.

Question 40

Explain the processes involved in natural selection and the formation of a new species

Answer 40

Several processes are involved in natural selection: 
• variation,
• isolation and competition, and
• selection.
Natural selection requires these processes, and given enough time, can result in speciation or the formation of a new species.
Populations must have existing variation for natural selection to occur.
 Variation: when a population has a range of different phenotypes, due to large genetic diversity, or range of genes available. This is so phenotypes that aid survival are available to be selected for, if the environment changes.
Mutations, gene flow, and genetic drift all act to change the allele frequency within a population, and also the variation of phenotypes.
Genetic diversity (and variation of phenotypes) is necessary to avoid extinction when selection pressures change.
If the advantageous gene already exists in the gene pool, organisms with this gene can survive and reproduce, and make the advantageous allele more common.
To be called a species, members must be able to reproduce with one another and produce offspring that are also able to reproduce (i.e. offspring that are viable). As long as members of populations of a species are able to interact and reproduce, they can pass genes between their gene pools. Therefore they will remain the same species.
For example, although different breeds of dogs look very different, they are still able to reproduce viable offspring, so are the same species.
 Donkeys and horses however, can produce offspring, but these offspring (mules) cannot reproduce themselves (are not viable). Therefore, horses and donkeys are classed as two different species.
 The population on which natural selection is acting must be isolated from other populations of the species, often geographically. If the two populations are not isolated, then genes will pass between the two populations via interbreeding and gene flow, and the two populations will not become two different species. Competition between organisms can occur for food, mates and habitats. Weaker organisms are likely to be outcompeted, and will often die before being able to pass on their genes. This is necessary because it means only organisms with phenotypes advantageous to survival, will live to reproduce and pass on their genes.
The final requirement for natural selection is selection.
Selection: a force that favours organisms with advantageous genes (and therefore phenotypes) over those without them. This causes the allele frequency of a population to change, with the advantageous variation of a gene becoming more frequent.
 For example: a cold climate is a selection pressure from nature for thick fur.A hot and dry climate is a selection pressure for needing to drink very little water, as with camels.

Question 41

Distinguish between biotic and abiotic selection agents. Provide examples.

Answer 41

Bio= living
Survival of a species can be affected by living things such as predator, competition with same or different species over food and diseases.
Abio = without life
Survival of species is affected by non-living things such as wind, heat, weather, cold, water availability, soil, pH, space and oxygen

Question 42

Define gene pool and list the factors that can cause changes in the gene pool.

Answer 42

A gene pool refers to the combination of all the genes (including alleles) present in a reproducing population or species. A large gene pool has extensive genomic diversity and is better able to withstand environmental challenges. There are four processes that can encourage evolutionary change: • Natural Selection • Mutations • Gene Flow • Genetic Drift.

Question 43

Compare & contrast theories of Evolution – Lamarck compared to Darwin

Answer 43

Origin of Species – Charles Darwin. Charles Darwin suggested that natural selection was the process in which species change over time and develop into new Their theories are different because Lamarck thought that organisms changed out of need and after a change in the environment and Darwin thought organisms changed by chance when they were born and before there was a change in the environment.

Question 44

Interpret the evidence for evolution – biogeography, homologous structures, embryonic development, fossils, DNA-amino acid analysis

Answer 44

Fossils:
Remains of organisms preserved in the earth.Sometimes these fossils are similar to present day animals and a large amount of fossils which indicate that there has been a change in evolution.

However:
Very few organisms are fossilised. Large chunks of the evolutionary record are missing. This is because fossilisation requires specific conditions.
- No oxygen is present (no decay)
- Temperature is low
- Hidden from scavengers

DNA:
By comparing the genes or DNA, amino acid sequence, and even cellular structure, we can infer evolutionary relationships. If two organisms have molecular structures that are similar, it makes sense that they are closely related. On the other hand, if two organisms have molecular structures that are very different, we assume they separated from each other evolutionarily a much longer time ago. By comparing DNA scientists can see evolutionary relationships/species ancestry. It compares the types of Amino Acids formed from a species DNA. The more similar the DNA strand and types of amino acids produced, the more closely the two organisms are related.

Biogeography:
Biogeography is the study of the geographical distribution of living things. This can lead to one species evolving into two or more different species. Closely related species usually live in areas that are geographically close to each other.

Embryology:
The study of organisms as an embryo. Embryos are often analysed to determine the similarities among species. It is suggested that genes that control early growth of vertebrates may be similar to ancestors and it can be linked. By comparing and contrasting embryo’s we are able to see similar embryonic features on closely related organisms.

Homologous Structures:
Similarities in structures between species suggest they descended from a common ancestor.

Analogous Structures:
Have different anatomies but similar function.
These are seen on organisms that are not necessarily closely related, but live in similar environments and have similar. For example, the wings of a fly, a moth, and a bird are analogous because they developed independently as adaptations to a common function—flying.

Question 45

Produce a hypothesis (IF-THEN statement – a prediction that can be tested)

Answer 45

“If i do not study then i will fail the exam.”

Question 46

Identify the variables in the scientific method

Answer 46

independent (IV); Dependent (DV); controlled (CV; extraneous (EV)

Question 47

Decide whether an experiment is a “fair” test.

Answer 47

A Fair Test is based on just one difference or change (the Independent variable). In most experimental inquiries, we want to figure out if the change we make is actually causing the effect we see. In a fair test, it is important to only change one variable at a time.

Question 48

Describe what a pathogen is & list the main groups

Answer 48

Pathogens are microbes - organisms too small to be visible to the naked eye - that cause infectious diseases.

There are five main groups of pathogens:

• Bacteria: prokaryotes, which are single-celled organisms with a simple internal structure that lacks a nucleus.
• Viruses: much smaller than a bacterium and typically consisting of a nucleic acid molecule in a protein coat, can multiply only within the living cells of a host.
• Prions: an abnormal form of a normally harmless protein found in the brain.
• Fungi: eukaryotic, though most pathogenic fungi are unicellular and affect the host’s skin.
• Protists: eukaryotic and includes protozoans which have elaborate life cycles.

Question 49

Describe ways that contagious diseases can be spread (transmitted) throughout the community

Answer 49

Some infections are spread when body fluids such as blood, saliva, urine (wees), faeces (poos) or semen come into direct contact with an uninfected person through kissing, sexual contact or through a needlestick injury. Examples of diseases spread through body fluids: hepatitis B.

Question 50

State the main role of the immune system

Answer 50

It is a network of cells, tissues and organs which all have a variety of different functions and work together to protect our bodies from bacteria, viruses, parasites, and fungi—these all have the potential to make us sick.

Question 51

Distinguish between innate and acquired immunity

Answer 51

Acquired immunity is when a vaccine contains either dead pathogens, harmless pathogens or a harmless pathogen toxin. When you are vaccinated your B lymphocytes (B cells) makes antibodies just as if regal pathogens had got into your body. We call this active immunity. In some situations (both natural and artificial), a person can be given ready - made immunity. This situation is called passive immunity.
Natural passive immunity is important in protecting the new - born baby against disease; The baby receives ready - made antibodies from its mother both across the placenta and in breast milk. These antibodies help the baby fight off disease in the first few months of life. Artificial passive immunity is provided when ready - made antibodies are injected directly into the blood of a person in immediate danger from a disease. Passive immunity provides immediate protection (there is no delay while antibodies are formed by the body).
The immunity, however does not last and there is no memory, as the foreign antibodies in the injection have not stimulated the immune system. Performed tetanus antitoxin, containing antibodies made by horses against tetanus, may sometimes be given to a patient who has not previously been vaccinated and is suspended of having contracted the disease tetanus.

Question 52

Identify the three lines of defence and summarise their overall functions and key features.

Answer 52

1st:
Physical and chemical barriers form the first line of defence. The skin provides a physical barrier to the entry of pathogens and is rarely penetrated by microorganisms. The skin produces chemical secretions that inhibit the growth of bacteria and fungi. Tears, mucus, and saliva help to wash microbes away.
2nd:
The inflammatory response (Innate Immunity): This is non-specific and will attack everything in your body the same way. Example: Phagocytes, a white blood cell (WBC) will seek and engulf whatever is foreign to your body. Inflammation. Fever- a prolonged increase in core body temperature above the normal range of 36.5–37.5°C.
3rd: The lymphatic system is a series of vessels and capillaries that carry fluid from around your cells back to your heart. In areas to the lymphatic system there are swellings or nodes (lymph nodes) that trap pathogens consumed by white blood cells. The lymphatic system carries lymphocytes and macrophages that destroy foreign proteins from the lymph fluid.
B lymphocytes: produce antibodies which help destroy pathogens
T lymphocytes: kill pathogens and infected cells of the body. The immune response (adaptive immunity): This does target specific pathogens, using specialised cells and chemical substances called antibodies. Using these resources the body can learn to identify particular types of pathogen, remembering them and mounting strong defences if they ever show up again. It has two main roles:identify and destroy specific pathogens and build long-lasting immunity against the pathogens in case they infect the body again.

Question 53

What are white blood cells?

Answer 53

They help the body fight infection and other diseases.

Question 54

What are phagocytes?

Answer 54

A type of immune cell that can surround and kill microorganisms, ingest foreign material, and remove dead cells.

Question 55

What are T cells?

Answer 55

Kill infected cells of the body and pathogens that have invaded the body.

Question 56

What are B cells?

Answer 56

Divide into plasma cells which produce antibodies. Each antibody is specific to particular antigens (markers found on pathogens). Antibodies help phagocytes destroy pathogens.

Question 57

What are memory cells?

Answer 57

Memory B and T cells are produced during an immune response. This means that next time, the response is faster and stronger.

Question 58

What are antibodies?

Answer 58

Each different type of antigen causes a different type of antibody to be produced. An antibody can only bind to the antigen that caused it to be produced.

Question 59

What are vaccinations?

Answer 59

Vaccination or immunization is a procedure that provides artificially acquired active immunity for the person receiving it. Vaccines that are effective against bacteria and viruses have been produced, but to date there are no useful vaccines for humans against protozoa, roundworms, flatworms, or fungi.

Question 60

What is immunity?

Answer 60

We have natural resistance to certain illnesses. Immunity involves a specific defence
response by the host to invasion by foreign organisms or substances.

Question 61

What is acquired, act passive immunity?

Answer 61

Each different type of antigen causes a different type of antibody to be produced. An antibody can only bind to the antigen that caused it to be produced.

Question 62

What is evolution?

Answer 62

is the process of genetic change in a species over many generations through genetic inheritance, sometimes resulting in the formation of a new species.

Question 63

What is generation?

Answer 63

time between the birth of one organism, and the point in time when that organism produces its own offspring.
The process of evolution normally occurs slowly, most often in response to changes in a species’ environment. The changes in the environment exerts a pressure - we call this natural selection.

Question 64

What is natural selection?

Answer 64

The increase or decrease in the frequency of certain alleles within a population due to pressures and acts on traits that help species survive and reproduce in a particular environment.

Question 65

What are pressures affect to environmental results?

Answer 65

Biotic and abiotic pressures

Question 66

What are biotic and abiotic pressures?

Answer 66

Biotic (from living organisms) or Abiotic (from the non-living environment).
Organisms better-suited to their environment are more likely to survive, reproduce and pass their genes on. After many generations, natural selection may alter the genetic makeup of entire populations!
It can take much longer for a new species to evolve from a population.

Question 67

What is Darwin’s theory of evolution

Answer 67

Darwin theorised that all species evolved from a common ancestor, and that they became new species through the process of natural selection.

Question 68

What is evolutionary change?

Answer 68

Can be encouraged by any process which alters the allele frequency in a population’s gene pool.

Question 69

What are the four processes that can encourage evolutionary change?

Answer 69

Natural selection
Mutations
Gene flow
Genetic Drift

Question 70

What is the allele frequency?

Answer 70

Unless there are any evolutionary processes acting on a population, the allele frequency in the population’s gene pool should remain the same from generation to generation. Although the proportions of phenotypes in the population may change, the proportions of alleles in the gene pool should not. Organisms with beneficial phenotypes will be better equipped to survive, reproduce, and, therefore, pass their advantageous genes on. Over time, advantageous genes become more common in the gene pool.

Question 71

What is natural selection?

Answer 71

Natural selection was first proposed by Charles Darwin. Darwin’s idea was that populations typically produce more offspring than the surrounding environment can support. As a result, there is competition for survival.
Organisms with beneficial phenotypes will be better equipped to survive, reproduce, and, therefore, pass their advantageous genes on.
Over time, advantageous genes become more common in the gene pool.
Natural selection can appear random, due to having no specific end goal aside from making organisms best suited to their environment. It is a process in which an organism adapts (becomes better-suited to their environment), through nature selecting for genes that code for advantageous phenotypes.

Question 72

What is a mutation?

Answer 72

a change in an organism’s genetic code, or DNA. Sometimes, mutations can cause the protein they code for to change, leading to a change in the organism’s phenotype. Mutations that occur in gametes (sex cells) are the sole source of new alleles.
In much the same way as other alleles, mutations that are beneficial will be selected for. Organisms that have them will be more likely to survive, reproduce and pass these mutations on to the next generation.
Mutations may also be harmful. These will be selected against, as the organism is more likely to die before it gets a chance to reproduce.

Question 73

What is genetic diversity?

Answer 73

the random change in the allele frequency of a population. This can occur simply through the random pattern of mating or after a catastrophic event.
For example: a giant foot kills a proportion of purple beetles, reducing the frequency of the purple allele in the gene pool.
The gene pool has now changed.
Before the foot rudely stomped on the beetles, there were more purple alleles in the population. The change in allele frequency means that evolution has occurred!

Question 74

What is gene flow?

Answer 74

The addition or removal of alleles from a gene pool through immigration and emigration.
Immigration is when new organisms join a population and emigration is when members of a population leave.

Question 75

What is genetic drift?

Answer 75

The addition or removal of alleles from a gene pool through immigration and emigration.
Immigration is when new organisms join a population and emigration is when members of a population leave.
Genetic drift: the random change in the allele frequency of a population. This can occur simply through the random pattern of mating or after a catastrophic event.
For example a giant foot kills a proportion of purple beetles, reducing the frequency of the purple allele in the gene pool.
The gene pool has now changed.
Before the foot rudely stomped on the beetles, there were more purple alleles in the population. The change in allele frequency means that evolution has occurred!

Question 76

What are the several processes that are involved in natural selection?

Answer 76

Variation
isolation/ competition
Selection

Natural selection requires these processes, and given enough time, can result in speciation or the formation of a new species.
Populations must have existing variation for natural selection to occur.

Question 77

What is variation in natural selection?

Answer 77

When a population has a range of different phenotypes, due to large genetic diversity, or the range of genes available. This is so phenotypes that aid survival is available to be selected for if the environment changes.

Question 78

What is isolation/ competition in natural selection?

Answer 78

Genetic diversity (and variation of phenotypes) is necessary to avoid extinction when selection pressures change.
If the advantageous gene already exists in the gene pool, organisms with this gene can survive and reproduce, and make the advantageous allele more common.
To be called a species, members must be able to reproduce with one another and produce offspring that are also able to reproduce (i.e. offspring that are viable). As long as members of populations of a species are able to interact and reproduce, they can pass genes between their gene pools. Therefore they will remain the same species.
For example, although different breeds of dogs look very different, they are still able to reproduce viable offspring, so are the same species.
 Donkeys and horses however, can produce offspring, but these offspring (mules) cannot reproduce themselves (are not viable). Therefore, horses and donkeys are classed as two different species.
 The population on which natural selection is acting must be isolated from other populations of the species, often geographically. If the two populations are not isolated, then genes will pass between the two populations via interbreeding and gene flow, and the two populations will not become two different species. Competition between organisms can occur for food, mates and habitats. Weaker organisms are likely to be outcompeted, and will often die before being able to pass on their genes. This is necessary because it means only organisms with phenotypes advantageous to survival, will live to reproduce and pass on their genes.

Question 79

What is selection in natural selection?

Answer 79

a force that favours organisms with advantageous genes (and therefore phenotypes) over those without them. This causes the allele frequency of a population to change, with the advantageous variation of a gene becoming more frequent.
For example: a cold climate is a selection pressure from nature for thick fur.A hot and dry climate is a selection pressure for needing to drink very little water, as with camels.

Question 80

What is speciation?

Answer 80

The process by which one species splits into two or more separate species. If enough natural selection of desirable phenotypes occurs, the end result can be speciation.
As in the case of Darwin’s finches, the finches were geographically isolated and each population had a large variation of genes coding for beak size and shape.
Different genes, on different islands, were selected for, depending on the food source available.Advantageous genes were passed on, and weaker organisms without these genes could not compete for food or mates. More died out without reproducing, eventually changing the populations enough to produce new species.
If speciation has occurred, the isolated population will no longer be able to interbreed with the original population and produce fertile offspring. Speciation has contributed to increased biodiversity on Earth.

Question 81

What is artificial selection?

Answer 81

Humans have been domesticating animals and growing crops for a long time. During this time, humans have learned to selectively breed plants and animals with the traits they find most desirable. When humans intentionally breed plants or animals with certain desirable characteristics, this is known as artificial selection (or selective breeding).
In artificial selection, organisms with undesirable traits are not allowed to breed.
Genetic diversity is decreased because only a small number of individuals with certain, desirable genes are selected to breed. Because of this, undesirable genes disappear from the gene pool. Unlike natural selection, artificial selection is directed by humans. This means it has a goal and is not affected by environmental factors, like predators. Inbreeding, or the mating of closely-related individuals, occurs often in organisms that are selectively bred.
This is a problem because it limits the gene pool even further, and increases the frequency of undesirable alleles that cause unhealthy traits.
In many cases, artificial selection has produced a product perfectly matching human desires, such as large green leafy lettuces or grapes without seeds.
However, artificial selection can reduce genetic diversity of a species so much that were a disease to strike, most would die out due to the lack of variation in phenotypes.
Inbreeding, or the mating of closely-related individuals, occurs often in organisms that are selectively bred.

This is a problem because it limits the gene pool even further, and increases the frequency of undesirable alleles that cause unhealthy traits. When a species with little variation in phenotypes, due to a lack of genetic diversity, is faced with disease or new environmental conditions, it is likely that the species will go extinct.
This is because the organisms are all very similar genetically.
It is likely none will possess a gene that may make them immune to the disease, so none will be able to survive to reproduce and pass on their genes. As this strong, mutually beneficial bond continued to develop, wolves’ bodies changed in shape and size, and their temperaments mellowed. They also learned to read the complex spread of human emotions and facial expressions.This change from wild wolf to docile dog is known as domestication. The process of domestication led to the beginning of a beautiful friendship between humans and modern day dogs. For as long as dogs have been an integral part of society, people have believed that dogs are trying to communicate with us. When humans communicate with each other, we don’t just rely on spoken words. We also rely on the recognition and understanding of facial expressions. These facial expressions can tell us a lot about the emotional state of a person, and provide us with cues on how to react in any given situation.