TOP

OCR Categories Archives: Module 4: Biodiversity, Evolution and Disease

Classification and Evolution

4.3 Classification and Evolution

Biological Classification

Binomial system – a system that uses the genus name and the species name to avoid confusion when naming organism

Classification – the process of placing living things into groups

Reasons for classification:

  • For convenience
  • To make the study of living things easier
  • For easier identification
  • To show the relationships between species

Modern Classification Hierarchy

As you descend the taxonomic ranks from Domain à Species it becomes harder to distinguish and separate closely related organisms from each other and to place them accurately.

Reasons for the binomial naming system:

  • The same organism may have a completely different common name in different parts of a country
  • Different common names are used in different countries
  • Translation of languages and dialects may give different names
  • The same common name may be used for a different species in a different part of the world

Using observable features for classification

Species – a group of organisms that can freely interbreed to produce fertile offspring

This definition does not work for organisms that reproduce asexually and is very hard to apply to organisms known only from fossil records and the like.

Phylogenetic definition of species – a group of individual organisms that are very similar in appearance, anatomy, physiology, biochemistry and genetics

Early classification systems by Linnaeus and Aristotle were based solely on appearance and features which limited the classification to observable features only.

The Five Kingdoms

Evidence used in Classification

  • Biological Molecules

Some biological molecules, such as those for DNA replication and respiration are essential for life and therefore all living things have a variant that can be compared to show how closely related they are. If we assume that the earliest living common ancestors to living things had the same version of these molecules then any changes are a direct result of evolution.

  1. Cytochrome C

The protein cytochrome C is essential in respiration but is not identical in all species due to evolution. The sequences of amino acids in the protein can help draw conclusions about how closely related they are. If the sequences are the same then the two species must be closely related and if they are different they are not so closely related. The more differences found between the sequences, the less closely related the two species.

  1. RNA Polymerase

RNA Polymerase is also used as an indicator of evolution because of its essential role in protein synthesis

 

  • DNA
  1. Genome Sequencing

Advances in genome sequencing have meant that the entire base sequence of an organism’s DNA can be determined. The DNA sequence of one organism can then be compared to the DNA sequence of another organism. This will show you how closely related they are to each other.

  1. Comparing amino acid sequences

Proteins are made of amino acids. The sequence of amino acids in a protein is coded for by a base sequence in the DNA. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.

 3. Immunological Comparisons

Similar proteins will bind to the same antibodies. So, if antibodies to a human version of a protein were added to isolated samples from other species, then any protein similar to the human version will be recognised and bind to the antibody.

Artificial Classification – classification for convenience, e.g. in plant identification books, sorting by flower colour

Natural Classification – Biological classification involving a detailed study of the individuals in a species, it uses many characteristics, reflects evolutionary relationships and may change with advancing knowledge

Phylogeny– the study of the evolutionary relationships between organisms

Divergent evolution is where another species has evolved from the original common ancestor and the two species get progressively less similar.

Convergent evolution is where two species, who may share the same environment and therefore the same factors that affect survival, evolve similar characteristics.

Natural Selection

Natural Selection – the term used to explain how features of the environment apply a selective force on the reproduction of individual in a population

Charles Darwin did not invent the theory of evolution but he proposed natural selection as a mechanism towards the theory. It was controversial at the time as it countered the popular religious beliefs.

Darwin developed his ideas from the expedition he sailed with the HMS Beagle around the Galapagos Islands. Wallace was another naturalist who came to the same conclusion as Darwin.

  1. Offspring generally appear similar to their parents
  2. No two individuals are identical
  3. Organisms have the ability to produce large numbers of offspring
  4. Populations in nature tend to remain fairly stable in size
  5. There is a struggle to survive
  6. Better adapted individuals survive and pass on their characteristics
  7. Over time a number of changes may give rise to a new species

Fossil Evidence

In the past the world was inhabited by species that were different from those present today.

Old species have dies out and new species have arisen.

The new species that have appeared are often similar to the older ones found in the same place.

One of the most complete fossil records is that of the horse.

 

Variation

Variation – the presence of variety – the differences between individuals

Intraspecific variation – variation between members of the same species

Interspecific variation – the differences between species

Continuous variation – variation where there are two extremes and a full range of values in between

Discontinuous variation – variation where there are distinct categories and nothing in between

Causes of Variation

  1. Inherited or genetic variation

This includes the combination of alleles that is inherited from our parents which is completely unique to us (unless there is an identical twin).

  1. Environmental variation

Many characteristics are brought out by environmental changes. For example, an overfed pet can become obese and a person’s skin tone may change due to exposure to the sun.

  1. Combined effects

Humans have become taller as the result of a better overall diet but however well your diet, you are unlikely to grow as tall as other people if your family is short.

Not all genes are active at any one time e.g. puberty is a time when many different genes are activating.

Changes in the environment can also directly affect which genes are active.

STATISTICS   D:

  1. Sample a population – this has to be random
  1. Mean – to show variation between samples

3. Standard Deviation – to show the spread of values about the mean

4. Spearman’s Rank Correlation Coefficient – to consider the relationship of the data

5. Student’s t-test – used to compare two means

Adaptation

Adaptation – a characteristic that enhances survival in the habitat

Anatomical adaptations – structural features

Behavioural adaptations – the ways that behaviour is modified for survival

Physiological adaptations – affect the way that processes work (also called biochemical)

Marram Grass (example)

Natural Selection

  1. Mutation creates an alternative version of a gene (alleles)
  2. This creates genetic variation between the individuals of a species (intraspecific variation)
  3. When resources are scarce, the environment will select those variations (characteristics) that give an advantage. There is a selection pressure.
  4. Individuals with an advantageous characteristic will survive and reproduce
  5. Therefore they pass on their advantageous characteristics (inheritance)
  6. The next generation will have a higher proportion of individuals with the successful characteristics. Over time, the group of organisms becomes well adapted to their environment.

Pesticide Resistance in insects

An insecticide applies a very strong selection pressure. If the individual insect is susceptible then it will die, but if it has resistance it will survive and reproduce, spreading the resistance through the entire population.

e.g. Mosquitos have developed and enzyme that can break down the pyrethroids used to treat mosquito nets.

e.g. Insect populations have become resistant to the insecticide DDT which binds to a receptor on the plasma membrane of certain cells in insects. This is due to mutations in the genes coding for cell surface receptors.

When insects become resistant it leads to pesticides accumulating in the food chain. When predators eat the insect they may get a large dose of the insecticide. This is why DDT is banned in many areas.

Micro-organisms

The use of antibiotics is a strong selection pressure on bacteria. MRSA is a very resistant bacteria that has cropped up because of over prescription of antibiotics. Medical researchers are struggling to develop new and effective drugs as the bacterial populations rapidly become resistant to them.

Continue Reading

Communicable Diseases

Communicable Diseases

Organisms that cause disease

Pathogen – a microorganism that causes disease

Transmission of Pathogens

Lifecycle of a pathogen:

  • Travel from one host to another (transmission)
  • Entering the hosts tissues
  • Reproducing
  • Leaving the hosts tissues

Direct Transmission

Overcrowding, poor ventilation, poor health, poor diets, homelessness and living and working with people who have migrated from areas where disease is more common, all may affect the likelihood of catching a disease.

Indirect Transmission

Some pathogens, like the protoctista plasmodium that causes malaria, use vectors for transmission.

Indirect transmission of plant pathogen occurs as a result of insect attack.

The fungus that causes Dutch elm disease is carried by the beetle Scolytus multistriatus

Plant Defences against pathogens

Passive Defences

  • Physical Defences
  1. Cellulose cell wall – this acts as a physical barrier but also contains many chemical defences that can be activated when a pathogen is detected
  2. Thickening of the cell wall with lignin – lignin is a phenolic compound and completely waterproof as well as largely indigestible
  3. Waxy cuticles – these prevent water collecting on the cell surfaces which removes the water that the pathogenic cells need to survive
  4. Bark – most back also contains a variety of chemical defences as well as being a physical barrier to disease
  5. Stomatal closure- stomata are possible points of entry for pathogens and so the guard cells can close them when pathogenic organisms are detected
  6. Callose – callose is a large polysaccharide that is deposited in the sieve tubes at the end of the growing season around the sieve plates and blocks the flow in the tube. This can prevent a pathogen spreading around the plant
  7. Tylose formation – tylose is a balloon like swelling or projection that fills the xylem vessel, when fully formed it can completely block off that part of the xylem vessel. It also contains a high concentration of chemicals such as terpenes that are toxic to pathogens
  • Chemical Defences
  1. Plant tissues contain a variety of chemicals that have anti-pathogenic properties including terpenoids, phenols, alkaloids and hydrolytic enzymes.
  2. Some of these chemicals such as the terpenes in tyloses and the tannins in bark are present before infection. However, because the production of chemicals requires a lot of energy, many chemicals are not produce until after an infection is discovered.

Active Defences

  • Cell walls become thickened and strengthened with additional cellulose
  • Deposition of callose between the plant cell wall and cell membrane near the pathogen. Callose deposits impeded cellular penetration at site of infection, strengthen the cell wall and block of plasmodesmata.
  • Oxidative bursts that produce highly reactive oxygen molecules capable of damaging the cells of invading pathogens
  • An increase in the production of chemicals
  • Necrosis – deliberate cell suicide
  • Canker – a sunken necrotic lesion in the woody tissue such as the main stem or branch that causes the death of the cambium tissue in the bark.

Primary Defences against Disease

Primary defences are the defences in place that prevent pathogenic material from entering the body.

The Skin

The skin is the main primary defence. The outer layer of skin is called the epidermis and consists of layers of keratinocytes. The keratinocytes are produces at the base of the epidermis and migrate out to the surface of the skin, slowly drying out and their cytoplasm in replaced by the protein keratin in the process of keratinisation. By the time the cells reach the surface they are dead. The layer of dead keratinised cells act as effective layer of disease prevention.

Blood Clotting and skin repair

  1. Abrasions or lacerations damage the skin and open the body to infection
  2. The body prevents excess blood loss by forming a clot and making a temporary seal to prevent infection
  3. Calcium ions and 12 clotting factors are released from the platelets and damaged tissue
  4. Damage to blood vessel exposes collagen
  5. Platelets bind to collagen fibres and release clotting factors, a temporary plug is formed
  6. Inactive thrombokinase in blood (factor X) is turned into active thrombokinase (an enzyme)
  7. Prothrombin in blood and thrombonkinase and Ca2+ ions make active thrombin
  8. Active thrombin turns the soluble fibrinogen in the plasma into insoluble fibrin which attach to the platelets in the plug and clot, trapping more red blood cells and platelets.
  9. As the skin grows and the scab shrinks the edges of the laceration are pulled together.

 

Mucous Membranes

The epithelial layer contains mucus-secreting cells called goblet cells and also mucus secreting glands under the epithelium.

The mucus traps any pathogens that may be in the air

The epithelium is also ciliated

Cilia are tiny hair-like organelles that can move in a coordinated fashion to waft the mucus along.

Coughing and sneezing – areas that are prone to microorganism attack are sensitive and respond to irritations by coughing sneezing and vomiting in the hope that the expulsion of air will propel the pathogen from the body.

Inflamation – the tissue may be hot and painful as the presence of harmful microorganisms has been detected by mast cells which release a cell signalling substance called histamine which causes vasodilation to make the capillary walls more permeable to white blood cells and proteins. The increased production of tissue fluid causes the swelling (oedema)

Eyes are protected by antibodies and enzymes in tear fluid

The ear canal is lined with wax

The female reproductive system is protected by a mucus plug in the cervix and by maintaining relatively acidic conditions in the vagina.

Specific Immune Response

Antibodies – specific proteins released by plasma cells that can attach to pathogenic antigens

Clonal expansion – an increase in the number of cells by mitotic cell division

Interleukins – signalling molecules that are used to communicate

Specific immune response involves B lymphocytes (B cells) and T lymphocytes (T cells) which are white blood cells with specialised receptors on their cell surface membranes. Antibodies are produced by B lymphocytes, and these neutralise foreign antigens. Long term disease protection is provided. An immunological memory is produced as B memory cells are released and circulate in the body for a number of years.

 

 

 

  1. Pathogen enters the body
  2. The antigens on the pathogen are presented on the pathogens cell membrane as it travels in the body fluids, on infected cells, and on the plasma membrane of macrophages that have engulfed the pathogens during the secondary non-specific response.
  3. T cells (from thymus) and B cells (from bone marrow) must detect the antigen from one of these three sources
  4. The detection of the pathogenic antibodies triggers clonal expansion in both T and B cells.
  5. T helper cells release cytokines that further stimulate the development of B cells
  6. Proliferation occurs once the correct lymphocytes have been activated.
  7. Cells differentiate and T & B memory cells are produced to remain in the blood should the body ever come under attack from the same pathogen again.
  8. T killer cells attack infected host cells and plasma cells make antibodies (the differentiation for this is triggered by cytokines from the macrophages
  9. Finally T regulator cells end the immune response to prevent the attack of the body’s own cells.

 

T lymphocytes

Come from the bone marrow and develop in the thymus

T helper cells (Th) – release cell signalling molecules (cytokines) that stimulate the immune response of B cells to develop and stimulate phagocytosis by phagocytes

T killer cells (Tk) – attack and kill host-body cells that display the foreign antigen as well as infected body cells

T memory cells (Tm) – provide long term immunity by staying in the blood for a long time

T regulator cells (Tr) – inhibit and end the immune response, preventing autoimmunity

They are involved in cell-mediated response (combat microorganisms)

They are a complementary shape to the antigen of pathogens and once the T cell has found a complementary antigen clonal expansion takes place produced by mitosis

 

B lymphocytes

Grow completely in the bond marrow

Plasma cells – derived from the B lymphocytes, these cells manufacture antibodies

B memory cells – cells that remain in the blood for a long time, providing long-term immunity

They are involved in the humoral response (producing antibodies)

 

Cell signalling

Macrophages release monokines which attract neutrophils (by chemotaxis – the movement of cells towards a particular chemical) and stimulate differentiation of B cells (and the release of antibodies)

T cells and macrophages release interleukins which stimulate clonal expansion (proliferation) and the differentiation of B & T cells

Many cells release interferon which inhibits virus replication and stimulates T killer cells

 

Autoimmune diseases

A disease that occurs when the immune system attacks a part of the body

Arthritis – a painful inflammation of a joint that starts with antibodies attacking the membranes around the joint

Lupus – swelling and pain in any part of the body, antibodies attack certain proteins in the nucleus of cells and affected tissue

Antibodies

Antigens are molecules that stimulate an immune response, usually proteins/glycoproteins in the pathogen’s plasma membrane, and when detected the production of antibodies is commenced.

Antibodies are specific to the antigen as antigens are specific to the organism. Our own antigens are recognised as ‘self’ by the immune system and do not provoke a response

Antibodies are immunoglobins (complex proteins produces by the plasma cells) and are released in response to an infection, they have a region with a specific shape to the antigen, antibodies attach to antigens and render them harmless

4x polypeptide chain, 2x light chains & 2x heavy chains

The tips of the y are the variable region but is the same for every type of antibody

 

A group of antibodies that bind to pathogen antigens and then act as binding sites for phagocytic cells

Some are non-specific

Some are produced as part of a specific immune response and bind to specific antigens

Antibodies flag up a pathogen for the phagocyte/attach to antigen which has a use to the pathogen, disabling it.

They also prevent the pathogen to enter the host cell.

Neutralise pathogens that use their antigens to bind to host cells etc.

By attaching onto the pathogen they make them easier to identify and easier for the phagocytes to bind to them/engluf them.

Antibodies that cause the pathogens to stick together (agglutinate) by making crosslinks between their antigens

This makes the pathogen non-effective and easily phagocytosed

 

Anti-toxins

Some antibodies bind to molecules that are release by pathogenic cells. These molecules may be toxic and the action of anti-toxins render them harmless.

Primary and Secondary Responses

Primary immune response – initial response caused by a first infection
Secondary immune response – more rapid and vigorous response caused by a second or subsequent infection by the same pathogen

  1. infection by pathogen
  2. lag phase
  3. antibodies produced
  4. antibody level rises to combat infections
  5. pathogen dealt with
  6. antibody level declines – short lived
  7. secondary immune response is much faster

 

Vaccination

Vaccination – a way of stimulating an immune response so that immunity is achieved, provides immunity to specific disease by deliberate exposure to a weakened/dead strain of antigenic material

Antigenic material takes many forms:

  • Whole live microorganisms (usually not very harmful g. smallpox which prevents cowpox virus, a much nastier disease)
  • Harmless attenuated version of the pathogenic organism e.g. measles & TB
  • Dead pathogen e.g. typhoid
  • Antigen preparations only, no actual pathogen e.g. hep B
  • Toxoids – harmless version of a toxin e.g. tetanus

 

 

  • Herd vaccination – providing the vaccine to all or almost all of the population so that the pathogen cannot spread, it is necessary to vaccinate 80 – 95% of the population to completely immunise the population
  • In the UK young children are immunised against the following diseases: diphtheria, tetanus, whooping cough, polio, meningitis, measles, mumps and rubella.
  • Ring vaccination – used when a new disease case is reported, vaccinated all people in the immediate vicinity of the case, also used to control livestock disease
  • Epidemic – a rapid spread of disease through a high proportion of the population
  • Influenza – a killer disease caused by a virus, people aged 65+ are most at risk as well as people with respiratory tract problems, the swine flu pandemic is an example of this virus

 

Types of immunity

Active immunity – immune system activated and own antibodies manufactured

Artificial immunity – immunity achieved as a result of medical intervention

Natural immunity – immunity achieved through normal life processes
Passive immunity – immunity achieved when antibodies are passed to the individual through breast feeding or injection

Development of Drugs

Antibiotic – a chemical which prevents the growth of microorganisms, can be antibacterial or antifungal

Personalised medicine – development of designer medicines for individuals

Synthetic biology – re-engineering of biology, from the production of new molecules that mimic a natural process to the use of natural molecules to produce new biological systems that do not exist in nature

The antibiotic penicillin was discovered by Alexander Fleming accidentally.

 

Traditional remedies

Morphine originated in the use of sap from unripe poppy seed heads in Neolithic times, in the 12th century the opium from poppies was used as an anaesthetic and by the 19th century morphine and opium were used to reduce nervous action in the central nervous system

Willow bark is used to relieve pain and fever. Its active ingredient was found to reduce the side effect of stomach bleeding by adding an acetyl group which lead to the development of aspirin and ibuprofen

Wildlife remedies

Monkeys, bears and other animals rub citrus oils on their coats as insecticides and antiseptics to prevent insect bites and infection. Birds line their nests with medicinal leaves to protect young from blood sucking mites. Chimps swallow leaves folded in a particular way to remove parasites from the digestive tract

Further plant research

Scientists use the traditional plant medicines as a starting point for new medicines and then try to isolate their active ingredient.

Pharmaceutical companies also research the way that microorganisms cause disease so that they can model ideal proteins and glycoproteins to act as medicines on these drugs. E.g. the HIV virus binds to the CD4 and CCR5 receptors on T helper cells. In order to cure this scientists are experimenting with blocking this binding with other similarly shaped proteins generated in computer models.

Overuse and misuse of antibiotics have enabled microorganisms to develop resistance which limits the effectiveness of current medicines.

Phagocytes

 

 

 

 

Continue Reading

Maintaining Biodiversity

Maintaining Biodiversity

(a) outline the reasons for the conservation of animal and plant species, with reference to economic, ecological, ethical and aesthetic reasons

How are humans reducing biodiversity?

  • Disruption of food chains – over-harvesting
  • Killing to remove competitors for our food – using pesticides to kill insects, fungi and other pests
  • Pollution – especially industrial pollution causing climate change
  • Habitat destruction – e.g. deforestation for agriculture
  • Inadvertent introduction of new predators and competition to areas
  • Killing for protection – attempting to kill insects that are vectors of disease (e.g. Anopheles mosquitoes) or to remove the threat of a predator
  • Agriculture – only harvesting one species (monoculture) creates a low species diversity

 

 

(b) discuss the consequences of global climate change on the biodiversity of plants and animals, with reference to changing patterns of agriculture and spread of disease

Climate change has a major impact on the biodiversity of plants and animals. As the climate changes, species that have lost their genetic variation and are unable to evolve, will be unable to adapt to the changes in temperature and rainfall in the area where they live. The only alternative for them is to migrate. However, there will be obstructions to this migration:

  • major human developments
  • agricultural land
  • large bodies of water
  • humans

For example, the golden toad of the Costa Rican cloud forest moves uphill as the climate warms up to stay in the most suitable habitat. However when it reaches the top of the hill it has nowhere to go. Therefore this species is becoming extinct as the climate changes.

(c) explain the benefits for agriculture of maintaining the biodiversity of animals and plant species

Allowing biodiversity to increase means that genetic diversity also increases. Wild animals and plants may hold the answer to problems caused by climate change as they have adapted to overcome the problems presented by the environment over many years as well as pests and disease. By careful selection and breeding from wild species, we may be able to breed new crop varieties that can cope with the new conditions created by climate change. Genetic engineering to produce transgenic species can be used.

The number of potential new medicines and the range of possible vaccines that could be developed from wild plants and microorganisms is unknown. It’s important to maintain genetic diversity of wild plants and animals because of the potential that exists in the wide range of species currently alive.

(d) describe the conservation of endangered plant and animals species, both in situ and ex situ, with references to the advantages and disadvantages of these two approaches

(e) discuss the role of botanic gardens in the ex situ conservation of rare plant species or plant species extinct in the wild, with reference to seed banks

(f) discuss the importance of international co-operation in species conservation with reference to The Convention in International Trade in Endangered Species (CITES) and the Rio Convention on Biodiversity

(g) discuss the significance of environmental impact assessments (including biodiversity estimates) for local authority planning decisions

 

Continue Reading

Biodiversity

Biodiversity

(b) explain how biodiversity may be considered at different levels; habitat, species and genetic.

  • Habitat – The range of habitats in which different species live. Each habitat will be occupied by a range of organisms.
  • Species – The differences between species. This could be structural differences (between a tree and an ant) or functional differences (between bacteria that cause decay and those that help to digest food).
  • Genetic – Genetic variation between individuals belonging to the same species, ensures that they do not all look alike.

(c) explain the importance of sampling in measuring the biodiversity of a habitat

In order to measure the biodiversity of a habitat, you need to observe all the species present. However, observing the whole habitat is time-consuming and difficult. Sampling involves taking a small portion of the habitat and studying the area carefully. You can then multiply up the numbers of individuals of each species found, on order to estimate the number in the whole habitat.

Sampling is a balance of ease and accuracy. To improve the accuracy of the estimation, repeated samples are taken and also the sample size must be large.

(d) describe how random samples can be taken when measuring biodiversity

Where do you sample?:

  1. Random Sampling– A basic way to do this is to stand within the area, and just throw the quadrat, however, it is not truly random. A better way is to use a calculator to generate random numbers, to get coordinates of where you will place your quadrat. The first number is the x coordinate and the second number is the y coordinate.
  2. Systematic Sampling– In some situations, you may want to sample more systematically. In this case, you could sample along a transect. A transect is a line taken across a habitat. You stretch a tape measure across the habitat and take samples along the line. You can use a:
  • Line Transect – recording each organism which is touching the line at suitable, regular intervals.
  • Belt Transect – placing a quadrat against the line, recording its contents, then placing the next quadrat immediately touching the first one, repeating this along the transect.
  • Interrupted Belt Transect – placing quadrats at regular intervals along the transect.

Sampling Plants:

Quadrats are square frames used to define the size of the ample area. It’s important to choose the right size of the quadrat (normally 50cm or 1m quadrats are used) depending on the size of the area. The quadrat is placed randomly and the abundance is measures. You could:

  • Habitat – The range of habitats in which different species live. Each habitat will be occupied by a range of organisms.
  • Species – The differences between species. This could be structural differences (between a tree and an ant) or functional differences (between bacteria that cause decay and those that help to digest food).
  • Genetic – Genetic variation between individuals belonging to the same species, ensures that they do not all look alike.

(c) explain the importance of sampling in measuring the biodiversity of a habitat

In order to measure the biodiversity of a habitat, you need to observe all the species present. However, observing the whole habitat is time-consuming and difficult. Sampling involves taking a small portion of the habitat and studying the area carefully. You can then multiply up the numbers of individuals of each species found, on order to estimate the number in the whole habitat.

Sampling is a balance of ease and accuracy. To improve the accuracy of the estimation, repeated samples are taken and also the sample size must be large.

(d) describe how random samples can be taken when measuring biodiversity

Where do you sample?:

  1. Random Sampling– A basic way to do this is to stand within the area, and just throw the quadrat, however, it is not truly random. A better way is to use a calculator to generate random numbers, to get coordinates of where you will place your quadrat. The first number is the x coordinate and the second number is the y coordinate.
  2. Systematic Sampling– In some situations, you may want to sample more systematically. In this case, you could sample along a transect. A transect is a line taken across a habitat. You stretch a tape measure across the habitat and take samples along the line. You can use a:
  • Line Transect – recording each organism which is touching the line at suitable, regular intervals.
  • Belt Transect – placing a quadrat against the line, recording its contents, then placing the next quadrat immediately touching the first one, repeating this along the transect.
  • Interrupted Belt Transect – placing quadrats at regular intervals along the transect.

Sampling Plants:

Quadrats are square frames used to define the size of the ample area. It’s important to choose the right size of the quadrat (normally 50cm or 1m quadrats are used) depending on the size of the area. The quadrat is placed randomly and the abundance is measures. You could:

  • Count the number of individuals of each species.
  • Estimate the percentage cover of each species – this is the proportion of the area within the quadrat which it occupies.
  • Use an abundance scale, such as the ACFOR scale, by estimating which one of these best describes the abundance of each species within the quadrat.
  • A point quadrat may be used. This is a frame holding a number of long needles or pointers. You lower the frame into the quadrat and record any plant touching the needles. It can also be useful for measuring the height of plants.
    Sampling Animals:

(f) use Simpson’s Index of Diversity (D) to calculate the biodiversity of a habitat, using the formula

D = 1-[Σ(n/N)2]


Simpson’s index of diversity is a measure of the diversity of a habitat. It takes into account both species richness and species eveness. It is calculated by the formula:

(g) outline the significance of both high and low values of Simpson’s Index of Diversity

A high value of Simpson’s Index indicates a diverse habitat, which provides a place for many different species and many organisms to live in. Small changes to the environment would only affect one species. If the species is only a small part of the habitat, the total number of individual affected is a small proportion of the total number present. Therefore the effect on the whole habitat is small. The habitat tends to be stable and able to withstand changes.

A low value of Simpson’s Index indicates a less diverse habitat, which provides a habitat for only a few different species. A small change to the environment that affects one of those species could damage or destroy the whole habitat. Such a small change could be a disease or predator, or even something that humans have done nearby.

(h) discuss current estimates of global diversity

Estimates of global diversity varies across the world. One estimate includes:

  • 4,000 bacteria, 70,000 fungi, 80,000 protocista, 300,000 plants, 130,000 invertebrates and 40,000 vertebrates
  • 2 million species in the world – 100,000 in the UK

These figures are estimates because

  • We cannot be sure we have found all the species.
  • New species are being found all the time.
  • Evolution and speciation are continuing
  • Many species are becoming endangered or extinct.

 

Continue Reading

Classification

Classification

(b)explain the relationship between classification and phylogeny

By grouping things into their evolutionary relationships in natural classification phylogeny, which studies the relationship, we can see what organisms are closely related to each other with common ancestors and determine using genetics which organisms belong where and help identify organisms which should be classified in certain areas.

(e)outline the binomial system of nomenclature and the use of scientific (Latin) names for species

The binomial system uses two names to identify each species: the genus name and the species name. Latin was a universal language, which means that species are given a universal name. For example, Homo sapiens is the binomial name given to humans. Homo refers to the genus to which humans belong. The genus name is always given a capital first letter. The species name is sapiens. Thus humans are Homo sapiens, which can be abbreviated to H. sapiens. In printed text it is in italics, in handwritten text it is underlined.

(f)use a dichotomous key to identify a group of at least six plants, animals or organisms

A dichotomous key uses a series of questions with two alternative answers to help you identify an organism. Each question have two answers – yes or no – and will lead you to another question. Eventually the answers will lead you to the name of the specimen. A good dichotomous key will have one question fewer than the number of species it can identify.

(g)discuss the fact that classification systems were based originally on observable features but more recent approaches draw on a wider range of evidence to clarify relationships between organisms, including molecular evidence

Using Biochemistry in Classification:

Evidence from biochemistry can help to determine how closely related one species is to another. Certain large biochemical molecules are fund in all living things. But they may not be identical in all living things. The differences reflect the evolutionary relationships.

(h)compare and contrast the five kingdom and three domain classification systems

In 1990, Carl Woese suggested a new classification system of domains, basing his ideas on detailed study of RNA. In the three domain system, organisms with cells that contain a nucleus are placed in the domain Eurkarya. Organisms that were in the kingdom Prokaryotae (unicellular organisms with no nucleus) were separated into two domains: Bacteria (Eubacteria) and the Archaea (Archaebacteria).

The three domain system was proposed because of new molecular evidence. This evidence showed that Bacteria was fundamentally different from Archaea and Eukarya:

  • Different cell membrane
  • Flagella with a different internal structure
  • Different enzymes (RNA polymerase) for building RNA
  • No proteins bound to their genetic material
  • Different mechanisms for DNA replication and for building RNA

Evidence also showed that Archaea was similar to Eurkaryotes:

  • Similar enzymes (RNA polymerase) for building RNA
  • Similar mechanisms for DNA replication and building RNA
  • Production of some proteins that bind to their DNA

Most scientists now agree that Archaea and Bacteria evolved separately and that Archaea are more closely related to Eurkarya than Bacteria.

 

Continue Reading

Evolution

Evolution

(a) define the term variation

Variation is the presence of differences between individuals. This can be within a species or between species.

(b) discuss the fact that variation occurs within as well as between species

The variation that occurs between species is usually obvious as there are obvious characteristics which separate one species from another. Within species, variation also occurs. For example, humans all have different characteristics (e.g. eye colour, hair colour, skin colour, nose shape) between members of the population, showing variation between different people. There are two forms of variation within a species – continuous and discontinuous.

(c) describe the differences between continuous and discontinuous variation, using examples of a range of characteristics found in plants, animals and microorganisms

There are two types of variation within a species.

(d) explain both genetic and environmental causes of variation

There are two general causes of variation.

Genetic variation and environmental variation are linked. In the past century, humans have become taller as a result of a better diet. But however good a diet you have, you are unlikely to grow very tall if all the rest of your family are short. This is because the height you can reach is limited by your genes.

(e) outline the behavioural, physiological and anatomical (structural) adaptations of organisms to their environments

Adaptation is a characteristic that enhances survival and long-term reproductive success.

Behavioural adaptation is an aspect of the behaviour of an organism that helps it to survive the conditions it lives in.

Physiological adaptation is one that ensures the correct functioning of cell processes.

Anatomical adaptation is one that is structural.

(f) explain the consequences of the four observations made by Darwin in proposing his theory of natural selection

Darwin proposed the idea of natural selection.

Darwin made 4 particular observations:

  • offspring generally appear similar to their parents
  • no two individuals are identical
  • organisms have the ability to produce large numbers of offspring
  • populations in nature tend to remain fairly stable in size

As all of the offspring are different, some may be better adapted than others. The better adapted individuals obtain enough food and survive long enough to reproduce, passing  on their characteristics to the next generation. The less well adapted individuals are likely to die before they reproduce, therefore the population does not grow indefinitely. Over a long period of time, a number of small variations may arise. Eventually, the species will accumulate many small variations and one group of organisms belonging to one species could give rise to another species. It may become so different that it  is unable to interbreed with the rest of the species.

(g) define the term speciation

Speciation is the formation of a new species from a pre-existing one. This is normally a long, slow process that generally takes many generations.

How does speciation occur?

  1. There is a reproductive barrier, meaning that some organisms are unable to breed with others in the group. A reproductive barrier is any factor that prevents effective reproduction between members of the species.
  • Allopatric speciation – geographical separation e.g. different groups of the same species living on different islands – the Galapagos Islands
  • Sympatric speciation – may be due to a biochemical change that prevents fertilisation, a behavioural change (e.g. a courtship dance that is not recognised) or a physical change (e.g. sexual organs of two groups of individuals are no longer compatible and they cannot mate)
  1. Variation that provides a benefit spread down the generations in a population through reproduction.
  2. If changes occur in only part of the group, but cannot spread to the whole group, then only part of the group will benefit, meaning only some members become different from the others. They may become so different they can no longer interbreed.

(h) discuss the evidence supporting the theory of evolution, with reference to fossil, DNA and molecular evidence

(i) outline how variation, adaptation and selection are major components of evolution

(j) discuss why the evolution of pesticide resistance in insects and drug resistance in microorganisms has implications for humans

  1. There is genetic variation is a population of bacteria/plants as mutation has occurred spontaneously meaning some bacteria/plants are naturally resistant to antibiotics/pesticides.
  2. The selective pressure for the population of bacteria/plants is the antibiotic/pesticide.
  3. The bacteria/plants with resistance will survive.
  4. The resistance allele will be passed on to the next generation.
  5. Resistance becomes more frequent within the population over many generations.

Problems with pesticide and drug resistance:

 

 

 

 

Continue Reading