AS Edexcel SNAB Biology Revision - Topic 4

  • Created by: Katherine
  • Created on: 25-04-14 19:17

What is a Species?

A species is a group of organisms with similar morphology, physiology and behaviour, which can interbreed to produce fertile offspring, and which are reproductively isolated (in place, time or behaviour) from other species.

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Each habitat has a particular set of conditions which supports a distinctive combination of organisms. Within a habitat there may be may populations of organisms. Each population is a group of interbreeding individauls of the same species found in an area. The various populations in an area make up a community.

An organism's environment provides all its essential resources such as energy, raw materials, a place to live and a mate. Most resources needed for survival are in limited supply. In order to survive and reproduce, organisms must compete successfully for the resources they need, against other organisms of the same and different species.

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Different niches avoid competition:

Two species sharing the same habitat tend not to be in competition with each other. Each species occupies a particular niche. A niche chan be defined as the 'way an organism exploits (uses) its environemnt'. All the species sharing a habitat have different niches. 

If two species live in the same habitat and have exactly the same role within the habitat - the same food source, the same time of feeding, the same shelter size and so on, they occupy the same niche. 

Better adapted organisms will out-compete the other and exclude it from the habitat.

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Being adapted means being specialised to suit the environement in which the organism lives. Features which enable organisms to survive are called 'adaptations'. Adaptations can be classified as behavioural, physiological or anatomical, though these are not hard and fast categories - there is some over lap.


A process in which an organism becomes fitted to its environment

— —Depends on: strength of selection pressure, size of gene pool, reproductive rate of organism 

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Types of Adaptation:

— —Anatomical à (e.g. ears of African elephants larger than Asian elephant due to environment) —Behavioural à (e.g. sheep ignoring sounds which are not important to them) —Physiological à (e.g. formation of sun tan when skin is exposed to sunlight)

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Behavioural Adaptations:

Behavioural adaptations are any actions by organisms which help them to survive or reproduce. 

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Physiological Adaptations:

Physiological adaptations are features of the internal workings of organisms which help them to survive or reproduce.

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Anatomical Adaptations:

Anatomical adaptations are the structures we can see when we observe or dissect an organism.

Eg. the bodies of bumblebees show adaptations used to collect nectar and pollen. Each has a long tounge through which it can suk nectar from flowers.

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Co-adaptation, for example, is when the plant and its pollinator become dependent on each other and more and more closely adapted. 

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Natural Selection:

Natural selection is the mechanism, first proposed by Darwin and Wallace, by which organisms change over time as they adapt to their changing environmenrs. As a population increases in size, a greater proportion of individuals will die or fail to reproduce owing to competition for resources, such as food and space. Disease and extreme environmental conditions may also cause the deaths of some individuals .This string for survival is known as the struggle for existance.

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Survival of the fittest:

In this struggle for existance there will be winners and losers. Winners are those individuals which, by chance. possess some characteristic which gives them an advantage over others. This differential survival is called the "survival of the fittest". ( Here, "fit" means well adapted, rather than physically fit in an athletic sense.) 

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Evolution by natural selection:

Evolution is more precisely defined as "a change in allele frequently in a population over time (generations)".  For natural selection to lead evolution, there must be some genetic variation in the population. An allele can be selectively neutral (i.e. had no advantage or disadvantage) but suddenly becomes selectively very advantageous when the environment changes.

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Being Adaptable:

The ability og a population to adapt to new conditions will depend on:

  • The strength of the selection pressure
  • The size of the gene pol
  • The reproductive rate of the organism.

Insects, such a mosquitoes, have rapidly become resistant to insecticides such as DDT, becuase (i) the selection pressure is strong (DDT orignially killed mor than 99% of all mosquitoes) (ii) there are millions of mosquitoes with a very large gene pool and (iii) mosquitoes reproduce very quickly, so any survivng (resistant) ones can quickly build up numbers, passing on their resitance to their offspring. 

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Gene Pool:

A gene pool consists of all the alleles of the genes present in a population.

The concept of a gene pool in useful when thinking about the biodiversity and adaptability of any species. Populations with a bigger gene pool (more different alleles of each gene) are said to have greater genetic diversity. New alleles are produced all the time by mutation of existing alleles. but this is a slow and random process. When the population of a species declines too far, some alleles are lost, and the genetic diversity (biodiversity) of the species declines.

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What is biodiversity?

Biodiversity means the variety of life, and in particular the wealth of different species that exists as a result of evolution by natural selection. In biological terms, it refers to the variety of species that belong to every different group of organisms, animals, plants, fungi, bacteria and other microorganisms, living in all the habitats on the plantet. Biodiversity also refers to the diversity within species.

Biologists want to be able to quantify biodiversity. Once biodiversity has been assessed, the data can be mapped on both a local and global scale to reveal patterns in diversity. This can help to focus conversation efforts on vulnerable habitats or species. But to do this and to understand the Earth's biodiverstiy, biologists need to define what is meant by biodiversity and be able to measure it. This is only possible if they can identify and classify the species observed. 

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Sorting & Grouping

A hierarchical system:

Placing animals into groups based on shared features, known as classification or taxonomy, results in a manageable number of categories and has been the principal aim of all classification systems.

A taxonomic hierarchy is created. This is a series of nested groups or taxa (singular taxon), in which the members all share one or more common features or homologies.

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Taxonomic Hierarchy:

—The science of classification: —Kingdom —Phylum —Class —Order —Family —Genus —Species —  Remember : King Peter Called Out For Genuine Scientists 

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Kingdoms: Animalia

There are 5 kingdoms: Animalia, Plantae, Fungi, Protoctista & Prokaryotae:

Animalia Kingdom: 

Multicellular eukaryotes that are heterotrophs, organisms that obtain energy as "ready made" organic molecules by ingesting material from other organisms.

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Kingdoms: Plantae

There are 5 kingdoms: Animalia, Plantae, Fungi, Protoctista & Prokaryotae:

Plantae Kingdom:

Multicellular eukaryotes that are autotrophs, organisms the make their own organic molecules by photosynthesis (except for a few parasites).

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Kingdoms: Fungi

There are 5 kingdoms: Animalia, Plantae, Fungi, Protoctista & Prokaryotae:

Fungi Kingdom:

Multicellular eukaryotes that are heterotro[s, which absorb nutrients from decaying matter after external digestion.

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Kingdoms: Protoctista

There are 5 kingdoms: Animalia, Plantae, Fungi, Protoctista & Prokaryotae:

Protoctista Kingdom:

Eukaryotes that photosynthesise or feed on organic matter from other sources but are not included in the other kingdoms, included single-celled protozoa, such as Amoeba and Paramecium, and algae.

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Kingdoms: Prokaryotae

There are 5 kingdoms: Animalia, Plantae, Fungi, Protoctista & Prokaryotae:

Prokaryotae Kingdom:

Prokaryotae organisms, includes bacteria and blue- green bacteria (cyanobacteria).

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Evidence Supports 3 Domains:

Woese proposed a new system of classificaiton, a universal phylogentic tree cased on 3 domains, the Archaea, the Bacteria and the Eucarya. The organisms in each of the three domains contain RNA squences that are unique to their domain.

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Genetic Diversity:

— —The number of different alleles in a population —Allele frequency

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Species Richness

—The total number of different species within a given area or community .Calculated using Simpson Diversity Index: Diversity = N(N-1)


Where N = total no. of organisms of all species found & n = no. of individuals of each species.

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Species Evenness:

Species evenness refers to how close in numbers each species in an environment are. 

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How are plant cells different to animal cells?

There are two fundamental differences:

  • The plant cells has a rigid cell wall
  • The plant cell contain chloroplasts

Chloroplasts are the site of photosynthesis, where energy from the sun is used to make storage molecules. Starch is found in storage vacuoles in the cytoplasm called amyloplasts. In addition to the cell wall and chloroplasts in plant cells, there is often a large central vacuole surrounded by a vacuolar membrane (tonoplast).

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Labelled Plant Cell:


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Cell Walls - The secret of their strength

Cellulose -

A plants strength comes in part from the thin cellulose walls of plant cells and the "glue" that holds them together.

Cellulose is a polysaccharide. It is a polymer of glucose, but the glucose it is made from is slightly different from that which forms starch. The OH (hydroxyl) groups on the first carbon atoms are on opposite sides.

Cellulose is made up of B-Glucose units. A condensation reaction between the -OH group on the first carbon of one glucose and the -OH on the fourth carbon of the adjacent glucose links the two glucose molecules. A 1,4 glycosidic bond forms. In cellulose, all the glycosidic bonds are 1,4; there are non of the 1,6 glycosidic bonds that occur in starch. Because of this, cellulose is a long unbranched molecule.

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Microfibrils are bundles of cellulose molecules:

Each cellulose chain typically contains between 1000 and 10000 glucose units. Unlike an amylose molecule that winds into a spiral, the cellulose molecules remain as straight chains, forming bundles called microfibrils. Individually, the hydrogen bonds are relatively weak compared with the glycosidic bonds, but together the larger number of hydrogen bonds in the microfibril produces a strong structure.

If you look more closely at a plant cell wall, you can see that it is formed of microfibrils. These microfibrils are bundles of about 60-70 cellulose molecules. The microfibrils are wound in a helical arrangement around the cell and stuck together with a polysaccharide glue.

The glue that holds together the microfibrils is composed of short, branched polysaccharides known as hemicelluloses and pectins. These short polysaccharides bind both to the surface of the cellulose and to each other, and hold the cellulose microfibrils together.

Pectins are alos an important component of the middle lamella - the region found between the cell walls of adjacent. The pectins act s cement and hold the cells together.

The arrangement of the cellulose microfibrils within a matrix of hemicelluloses and pectins makes the cell wall very strong - rather like steel reinforced rubber tyres. In this analogy, the hemicellulose matrix is the rubber, and the cellulose microfibrils are the reinforcing steel cables. This makes a strong by pliable structure. The microfibrils are laid down at different angles, which makes the wall strong and flexible. 

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  • —Straight chain of single glucose units
  • —β-1,4- glycosidic linkages formed by condensation reactions
  • —Held together by hydrogen bonds between –OH groups (micro fibrils)
  • —Alternate glucose units rotated by 180°
  • —Insoluble, tough, slightly elastic
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Crossing the cell wall:

Cell walls do not separate plant cells completly. Narrow fluid-filled channels, called plasmodesmata, cross the cell walls, making the cytoplasm of one cell continuous with the cytoplasm of the next. Cell walls are also fully permeable to water and solutes.

At some places the cell wall is thin because only the first layer of cellulose is desposited. The result is a pit in the cell wall. Plasmodesmata are often located in these pits, aiding the movement of substances between cells. 

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  • —Microscopic channels that link adjacent cells, enabling for transport and communication to occur between them
  • —Cytoplasm continuous between the cells
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Tubes for transport and strength:

To build a tall plant such as a tree, some of the cells within the stem must be stiffened to provide mechanical support. At the same time, some cells must allow water and mineral (inorganic ions) to pass from the roots to the leaves.

There are two specialised types of cell particular importance in fulfilling these functions. These are:

  • xylem vessels - these form tubes for transport, and their stiffened cells walls help support the plant.
  • sclerenchyma fibre - columns of these cells with their stiffened cell walls also provide support.
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Where in the stem are these specialised cells?

There are three basic types of tissue found within plants. The three types of tissue are: dermal tissue (epidermis), vascular tisue and ground tissue. 

The vascular tissue is within a cross-section of a stem from a dicotyledon. Each vascular bundle xylem vessels and phloem sieve tubes. On the outside of the bundles are sclerenchyma fibres. In a young dicotyledon, the vascular tissue is in bundles towards the outside of the stem. In trees and shrubs these separate bundles merge to form a continous ring as the plant ages. The xylem vessels carry water and inorganic ions up through the stem. The phloem transport sugars made by photosynthesis in the leaves up and down the plant.

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Xylem vessels for transport:

The xylem vessels are made up of large cells with thick cell walls. They form a column of cells acting as tubes for the transport of water and mineral ions. In order to transport water, the cell walls have to be waterproofed. The plant does this by producing another polymer - lignin. This polymer impregnates the cellulose cell wall and, as the cells become lignified, the entry of water and solutes into them is restricted. At about the same time, the tonoplast breaks down, and there is autolysis of the cell contents. During autolysis, the cell organelles, cytoplasm and cell surface membrane are broken down by the action of enzymes and are lose, leaving an empty tube. 

The ends walls between the cells of the columns are lost or become highly perforated. Long tubes form as a result of this process, and they are continuous from the roots of the plant to the leaves. The cellulose microfibrils and lignin in the cell walls of the xylem vessels give the tubes great strength. 

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Xylem vessels cut open to show their structure:


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How is water transported through Xylem Vessels?

Xylem vessels are effectively fluid filled tubes through which water moves upwards from the roots to the shoots. Water evaporates from all surfaces of the plant, mostly from the large surface area of the leaves. The majority of the evaporation occurs from the surfaces of the cells that line the substomatal cavities in the leaves. Water diffuses out through the stomata down a diffusion gradient. Water evaporating from the plant in this way is known as transpiration. The water that leaves a plant leaf by transpiration is replaced by water absorbed through the roots. In the tallest trees, water may move up to 100m though the plant. 

It is evaporation of water from cells in the substomatal cavities of the leaves that provides the force needed to draw water up a plant. The small channels between the cellulose microfibrils in the cells walls act as tiny capillaries. Capillaries have the ability to draw water up them by capillary action, which is caused by surface tension. As water evaporates from the surface ofs of the cells walls within the leaf, it is replaced by means of capillary action within the cell walls. This draws more water to the cell surfaces. The thousands of minute capillaries in the cell walls indside the leaves produce a massive pull on the water behind them. This pull is sufficient to draw water up the xylem vessels. Water moves up the xylem vessels and through the cell walls within the leaf in a continuous stream. This stream of water passing through the plant is known as the transpiration stream.  The energy to do this all comes from the sun. 

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How is water transported through Xylem Vessels? Si

1.) Water vapour diffuses out through the stoma down a diffusion gradient.

2.) Water evaporates from the surfaces of cells lining the substomatal cavity.

3.) Water replaced by means of capillary action within the cell walls.

4.) Water is drawn out of the Xylem.

5.) A continuous column of water is drawn up through the xylem. 

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The importance of Water to plants - Cohesion/ tens


Hydrogen bonding between water molecules results in strong cohesive forces between water molecules that keep the water together as a continuous column in xylem vessels.

Surface tension:

 Surface tension at water surfaces is also partly caused by these cohesive forces between water molecules, which cause the surface layer of water to contract. This is useful for some small aquatic organisms, such as duckweed and pond skatersm which can be supported on this surface film.

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The importance of Water to plants - Solvent Proper

Solvent Properties:

The solvent properties of water described in Topic 1 mean that dissolved substances can be transported around plants through the xylem and phloem. Once in cells, dissolved chemicals move freely around in an aqueous envrionment and can react, often with water itself being involved in the reactions, for example in hydrolysis and condensation reactions. The synthesis of sugars from water and carbon dioxide in photosynthesis is important to plants, and to all organisms which depend of plants for their food supply.

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The importance of Water to plants - Thermal Proper

Thermal Properties:

A large imput of water causes only a small increase in temperature, so water warms up and cools down slowly. This is extremely usedul for organisms, helping them to avoid rapid changes in their nternal temperatures, and enabling many of them to maitain a fairly steady temperature even when the temperature of their surroundings varies considerably.

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The importance of Water to plants - Density/ Freez

Density & Freezing Properties:

Unlike most liquids, water expands as it freezes. As liquid water cools, the molecules slow down, enabling the maximum number of hydrogen bonds to form between the water molecules. These hydrogen bonds hold the water molecules further apart than in liquid water, making ice less dense than liquid water. So ice floats, enabling organisms to survive in liquid water under the ice in frozen oceans, ponds and lakes. 

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What else do Xylem Vessels transport?

The movement of water through the xylem provides a mass flow systemfor the transport of inorganic ions. These are absorbed into the roots and are required throughout the plant.

Nitrate ions are needed by plants in order to make amino acids. Amino acids contain one or more nitrogen atoms. Unlike us, plants make all their own amino acids from scratch using inorganic materials. By a sequence of enzyme controlled reactions, the nitrogen from nitrate ions (transported in the xylems) is combined with organic molecules from photosynthesis to make all 20 amino acids. Plants cannot grow without nitrate ions; like all organisms, their cell cytoplasm is made largely up of proteins, built by joining amino acids together. Some other important biological molecules found in plants also contain nitrogen atoms, notably chlorophyll, nucleic acids, ATP and some plant growth sbstances.

If inorganic ions are not absorbed in sufficient amounts, the plant will show deficiency symptoms. For example, if the plant lacks magnesium it is unable to make chlorophyll and the older leaves become yellow (yellow leaves may also be a sign of nitrogen deficiency). A lack of calcium causes stunted growth due to the role of calcium ions in the structure of the cell wall and in the permeability of the cell membrane.

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Properties of Xylem

—Water transport: —Lumen -> enables vertical movement         of water —Waterproof   -> prevents water loss —Pores -> enables sideways movement of         water —Support: —Lignin  -> strength —Rings/spirals  -> strength and flexibility

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Properties of Phloem

Translocation -> movement of sugars up and down the plant, requires energy —Sieve tube elements -> living, tubular cells, connected end to end, cytoplasm is present but in small amounts,  lacks a nucleus and most organelles for more space for solutes to move, cell walls made of cellulose so solutes can move laterally a well as vertically —Sieve plates -> formed by perforations in cell walls

Companion cells -> controls the movement of solutes and provides ATP for active transport in the sieve

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Xylem and Sclerenchyma for support:

Lignin not only waterproofs the cell walls, it also makes them much stiffer and gives the plant much greater tensile strength. Instead of forming a uniform layer on the inside of the xylem cell walls, lignin is often laid down in spiral or in rings.

Xylem vessels are not the only cells that become impregnated with lignin. The sclerenchyma fibres associated with vascular bundles in the stem and leaves also have lignin deposited in their cell walls. As with xylem vessels, the sclerenchyma fibres die once lignified, leaving hollow fibres. The strength of these fibres varies in different plant species depending on the length of the fibres and the degree of lignificaiton.

The taller a plant needs to grow, the greater the proportion of its stem that become lignified. In a tree, this is the majority of the trunk: the living parts are towards the surface (under the bark) and grow new layers each year. These layers are the annual rings. In annual plants the lignification is confined to the vascular bundles. The plant stem relies on tightly packed, fully trgid parenchyma cells to maintain its shape and keep it erect. A turgid cll is one that is completely full, with its cell contents pressing out on the cell wall. Turgor supports the leaves of all plants including those of trees. If a cell loses water, turgor is lost. If a high proportion of a plant's cells lose their turgidity, the plant wilts.

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What is Lignin?

  • —Polymer produced by plant cells to strengthen the cell wall
  • —Lignin impregnates cell wall, cells become lignified
  • —Entry of water and solutes into them become restricted
  • —Tonoplast breaks down, autolysis of cell contents (cell contents broken down by enzymes and are lost)
  • —Leaves an empty tube
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Properties of Starch:

  • —Branched chain of single glucose units
  • —1,6 and 1,4 α glucose linkages formed by condensation reactions
  • —Composed of more than one type of molecule (amylopectin and amylose)
  • —All monomers have the same orientation
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Structure & Function of Starch:

  • —Consists of many glucose monomers à glucose is the respiratory substrate
  • —Large -> unreactive, in soluble, no osmotic effect
  • —Compact -> can be stored
  • —Branched -> increased mobilisation of glucose units
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Useful Plant Fibres:

Humans use plants in many ways. Plant fibres can be used to freely because they are:

  • Long and thin
  • Flexible
  • Strong

How do we extract fibres from plants?

To obtain fibres we must take the plant apart. This can be done mechanically by pulling out the fibres or by digesting the surrounding tissue. Cellulose, and particularly cellulose combined with lignin, is very resistant to chemical and enzymic degradation, whilst the polysaccharides that hold the fibres together can be dissolved away.

The more lignin there is present, the harder it is to separate fibres. To produce fibre pulp from trees, caustic alkali is required. For flax, and other suitable plants, a milder treatment is used, and in some traditional processes, the stems are piled in heaps, allowing bacteria and fungi to do the work. This process, and its more modern chemical and enzymic equivalents is celled "retting".

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Chemical defences against attack:

Many plants have adaptations that provide chemical defences to repel and even kill animals that feed on them. One strategy is to produce a chemical that is distasteful or even toxic. If the animal takes a bite and the taste is offensive, the animal is deterred from feeding further. If its chemicals kill the predator, the plant will avoid future attacks. 

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Natural Antibacterials:

Plants sometimes store toxic compounds in hairs on the surfaces of their leaves. These chemicals are toxic to microbes and some insects, but attractive to us as flavouring in foods or tea. 

Garlic extracts have been found to destroy bacteria such as Campylobacter and Helicobacter which cause intestinal infections. This is potentially important as some strains of the bacteria are now resistant to widely used antibiotics such as penicillin. The active ingredient in garlic is allicin; this is known to interfere with lipid synthesis and RNA production. Allicin is only produced when the plant is cut or damaged. Its inactive precursor, Alliin, is converted into the active from by the enzyme alliinase. 

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Drug testing today:

Today a potential new drug must pass a series of tests if it is to be developed into a new product. It has to be proven to be effective, safe and capable of making a profit. 

A series of trials of the compond begin, There are 5 stages in all. The first is preclinical testing, followed by 3 stages of clinical trials and finally after licensing trials.

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Pre-Clinical Trials

Animal studies and labatory studies on isolated cells and tissue cultures assess safety and determine whether the compound is effective against the target disease. These tests can take several years to completel. Thousands of chemicals go through pre-clinical testing, but only a handful are ever approved for clinical trials on humans. Animal trials form the basis of applications for the clinical trials on humans, which are authorised by the Medicines and Healthcare products Regulatory Agency (MHRA), an independant body of scientists, doctors and members of the public.

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Clinical Trials - Phase I:

A small group of volunteers are told about the drug and given different doses. These volunteers are normally healthy, but there are circumstances where drugs are first tested on sick patients. The trial confirms whether or not the compound is being absorbed, distributed, metabolised and excreted by the body in the way predicted by the labatory tests. The effects of different doses are monitored. In the UK a review of the data collected is made by the UK MHRA.

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Clinical Trials - Phase II:

Small groups of volunteer patients (100-300) people with the disease) are treated to look at the drug's effectiveness. If the results are promising, phase III trials are set up.

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Clinical Trials - Phase III:

A large group of patients (1000-3000 people) is selected and divided randomly into two groups. One group is given the compound being investigated. The second is given an inactive "dummy" compound known as a placebo. If there is an existing treatment for the disease, the standard treatment is given rather than a placebo. It is important that neither of the patiets nor the doctors know who is having the compound under investigation and who is having the placebo or standard treatment. This is known as a double blind trial randomised control trial, and is considered the gold standard of valid testing.

If the compound being invested is effective, then the results will show a statistically significant improvement in the patients recieving the treatment compared with patients given the placebo or standard treatment. The tests also look for any adverse reaction in the patients. The way is now open to license the compound as a drug, after which can be marketed.

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After Testing:

Trials continue to collect data on the effectiveness and safety of a new drug after the drug has been licensed.

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Clinical Trial Summary:

— —Animal testing (e.g. rats) legal requirement, to look for toxicity, well known metabolism, no harm to humans —Phase 1 Small dose of drug tested on a small no. of healthy individuals, check for side-effects —Phase 2 àTested on small no. of patients to measurement effectiveness of drug —Phase 3 Double blind trial, testing on larger group of patients

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Seeds for survival:

Seeds are vital to the survival of a plant. They are adapted to ensure they:

  • Protect the embryo
  • Aid dispersal
  • Provide nutrients for the new plant
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What's in a seed:

The outer layers of the ovule become lignified forming a tough seed coat which protects the embryo within the seed. The surrounding ovary develops into the fruit which often has an important role in seed dispersal.

In some species the stored food in the seed remains outside the embryo in storage tissue called endosperm. This is common in monocotyledons, for example cereals. Seeds of this type are called endospermic. In many dicotyledons the embryo absorbs the stored nutrients from the endosperm and the food is stored in the seed leaves (cotyledons) which swell to fill the seed. In some seeds there are no apparent coyledons and the food is stored in the hypocotyls, the developing stalk.

When conditions are suitable and any dormancy has been broken, the seed takes in water through a small pore in the seed coat. Absorbing water triggers metabolic changes in the see. Production of plant growth substances is switched on and these cause the secretion of enzymes that mobilise the stored food reserves. Maltase and amylase break the starch down into glucose which is converted to sucrose for transport to the radicals and plumule. Proteases break down the proteins in the food store to give amino acids and lipases break down the stored lipids to give glycerol and fatty acids.

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What can we do with starch from seeds?

Starch is easy to extract from plants because it is in granules which do not dissolve in water, but can be washed out.

Thickening: When starch granules are heated in water they suddenly swell, absorb water, and thicken the liquid. This is "gelatinisation", and this thickening process is the basis of both custard and wallpaper.

Stiffening Fabrics: The stiffening of cloth of paper by starch is known as "sizing",and enormous amounts of starch are used in paper. A starch mixture appliced to the surface is gelatinised and then cooled, allowing bonds to form between the starch molecules. The addition of water reverses the stiffening. This reversal is celled "plasticisation" (the material becomes flexible again) and water is the plasticiser.

Super Absorbents: If starch is chemically cross linked before it is gelatinised then particles are formed which can be dried. When rehydrated these particles can take up large amounts of water.

Starch Foam: The temperature at which starch gelatinises depends on the amount of water present. At water contents of less than 10% the gelatinisation occurs at much higher temperatures, above the boiling point of water.

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What can we do with vegetable oils?

Seeds are a rich source of oils which we regularly use in cooking and for other industrial uses:

Fuels: Vegetable oils can be used as a fuel instead of petroleum based products. Biodiesel produced today can be used in unmodified diesel engines alternating with petroleum diesel. It produces less sulphur dioxide than diesel, and less carbon dioxide when you take into account the carbon dioxide used by the plants grown to produce it.

Across the UK there is a growing market for biodiesel. It is possible to buy biodiesel made from waste vegetable cooking oil, or from oil crops such as **** seed.  It is avaliable either as 100% biodiesel, or as a blend with fossil fuel diesel, for use in standard diesel engines.

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The use of oil based plastics and fuels is not sustainable for several reasons:

Buring oil-based fossil fuesl releases carbon dioxide into the atmosphere contributing to global warming.

Oil reserves will enentually run out.

Plastics generate non-biodegradable waste, creating major waste disposal problems.

The use of plant-based products should help to reduce these problems. Although burning fuel made from vegetable oils also produces carbon dioxide, this carbon dioxide has been removed from the atmosphere relatively recently when the crop that produced the oil was grown. The carbon dioxide released will be about the same quantity as the amound fixed, so there is no net change in carbon dioxide in the atmosphere, unlike when burning fossil fuels, which release carbon stores built up over long periods of time.

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The role of zoos:

In having over 1000 registered collections, Zoos aim to have significant impact in conservation, research and education.

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Centres for scientific research:

Zoos can play a vital role as research centres, enabling us to understand how to conserve particular species. e.g. The Mountain Chicken.

13 of the Mountain Chicken were taken in 1999 to Jersey Zoo, allowing keeper scientists to find out more about their elusive lifestyle. Breeding trial were set up to establish a captive breeding programme.  This was done as, if the frog was to be saved from extinction, more information was needed about its needs.

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Captive breeding programmes:

Today an important role of zoos is the successful breeding of the animals in their care. The aims of a captive breeding programme include:

  • Increasing the number of individuals of the species if numbers are very low.
  • Maintaining genetic diversity within the captive population.
  • Reintroducing animals into the wild if possible.
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How genetic variation is lost:

Genetic drift:

In a small population, some of the alleles may not get passed on to offspring purely by chance. This change in the allele frequencies over time is known as genetic drift, and leads to a reduction in genetic variation.


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Variation - the key to survival

Genetic uniformity, where individuals within a population have similar genotypes, can be an advantage in a stable environment. But if the envrionment changes, a new disease emerges or a population moves, a genetically diverse population will be at an advantage.

Scientists interested in the preservation of species can hope that there is sufficient genetic diversity in the population to ensure that some of the individuals can cope with any new conditions, allowing the population to survive. This is natural selection and it results in adaptation, the accumulation of genotypes favoured by the envrionemnt. No natural envrionment remains unchanged forever. It is therefore essential for long term survival that populations should be able to evolce as a result of natural selection. Such evolution is unlikely unless there is genetic variation to enable evolution to happen, or the mutation rate is very high.

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Inbreeding Depression:

In a small population, the likelihood of closely related individuals mating increases. This inbreeding causes the frequency of homozygous genotypes to rise, with the loss of heterozygous. Inbreeding results in individuals inheriting recessive alleles from both parents, and the accumulation of the homozygous recessive genotypes in the offspring. Many recessive alleles have harmful effects so inbreeding depression results. The offspring are less fit, may be smaller, may live shorter lives and the females may produce fewer eggs.

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Conserving Genetic Diversity:

Conservation to maintain the size of the wild populations is the best way to prevent genetic drift and inbreeding depression.

In Situ (in site) conservation:

Keeping Studbooks:

The studbook for an individual species shows the histroy and loaction of all of the captive animals of that species in the places which are co-operating in an overall breeding plan. London Zoo, for example, keeps studbooks for many species including the slow loris, the Sumatran tiger and the ocelot, and contributes to the studbook data for other species too.

Studbooks provide the raw data upon which all the breeding plans were based - the scientists understanding of genetics shapes the breeding plans themselves. The conservation scientists must ensure that genes from all the founder members of the population (  the original group of individuals, usually wild caught, on which the current population is based), or at least all the remaning breeding adults, are retained and are "equally" represented in the subsequent generations. This requires that individuals who breed poorly in captivity must be encouraged to breed, whilst those that are particularly good breeders must be limited in their breeding success.

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Introducing animals into the wild:

One role that zoos have in species conservation is captive breeding fro reintroduction. This involves breeding animals in captivitty that are then returned to their native habitats. Clearly this can only work if the habitat remains intact.  This is a complicated process, particularly when species need to learn new skills before they have the ability to survive in the wild.

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The Millennium Seed Band (MSB)

Plants are threatened worldwide by habitat destruction, climate change and over harvesting. Protecting and managing habitats conserves plants in situ, but they remain at risk from man made and natural disasters so there is also a role for ex situ, conservation, using a variety of methods including seed banks and botanic gardens. The aim of the Millennium Seed Bank Project is to conserve seed samples from threatened species of plants, with 10000 species already banked. Seeds are collected around the world. Some are kepy in the countries of origin, and some are sent to the Millennium Seed Bank in the UK.

Most plants produce large numbers of seeds, so collecting small samples is unlikely to damage a wild population. Most seeds are small and easy to store, and can survive in a desiccated state for many years.

The technology of seed preservation is improving all the time as more research is carried out. Seeds surive longer is kept dry and cool.

The seed collections are also used for research, habitat restoration and species reintroductions.

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Seed Bank Summary:

  • —Only seeds with a living embryo are taken, detected using X-ray
  • —Seeds are cleaned, dried
  • —Stored at low temperatures
  • —Viability regularly tested
  • —If viability decreases, collect fresh seed for storage
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  • —5mm of root tip cut, transferred to watch glass
  • —Add 30 drops of aceto-orecin stain, 3 drops HCL
  • —Heated 3-5 minutes (steam bath/Bunsen burner)
  • —Tissues transferred onto microscope slide, root tip gently pulled apart (mounted needles)
  • —More stain added, cover slip, tissue firmly squashed by thumb pressure
  • —Examined under high power microscope
  • —Safety precautions: Cut away from oneself, wear a lab coat
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CORE PRACTICAL - Mineral Deficiencies

  • —9 petri dishes (complete culture solution, minus phosphorus, minus magnesium, minus nitrogen, minus potassium, minus iron, minus sulphur, minus calcium, distilled water)
  • —15cm3 of water in each
  • —5 healthy Lemna plants into each, add lids and incubate together for several weeks, examining twice a week
  • —Record no. of live plants, green leaves, dead leaves, length of longest root
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CORE PRACTICAL: Plant Antimicrobials

  • —Crush extract (e.g. garlic or mint) in pestle with mortar, 10cm3 ethanol
  • —Filter off ethanol
  • —Add bacteria stain
  • —Bacteria need to be evenly distributed on sterile agar plate
  • —Incubate to encourage bacteria growth
  • —Measure diameter
  • —Safety: Don’t incubate at 37°C (pathogens will grow), aseptic technique (prevent contamination of pathogens)
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CORE PRACTICAL: Tensile Strenght of Plant Fibre

  • —Soak stem (with no leaves or flowers)
  • —Extract bundles of fibres from stem and dry them
  • —Add same masses each time until fibre breaks, recording the mass required
  • —Repeat experiment, using same length, diameter and fibre from same source
  • —Safety precaution: Wear goggles in case fibre snaps, be careful that the masses do not land on feet
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