TOPIC 4

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  • Created by: moll99
  • Created on: 06-01-17 12:41

Species Concept

All species are given a unique scientific name in Latin to distinguish them from similar organisms.

In this binomial system, the first word is the genus name and the second word is the species name - for example, humans are known as homosapiens.

Giving organisms a scientific name enables scientists to communicate about organisms in a standard way that minimises confusion - all scientists, in all countries, will call a species by the same name.

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Breeding Programmes

Some zoos have captive breeding programmes to help endangered species.

Captive breeding programmes involve breeding animals in controlled environments.

Species that are endangered, or already extinct in the wild, can be bred together in zoos to help increase their numbers. Panda's are bred in captivity because their numbers are critically low in the wild.

There are some problems with breeding programmes though:

  • Animals can have problems breeding outside their natural habitat, which can be hard to recreate in a zoo. Pandas do not reproduce as successfully in captivity as they do in the wild.
  • Many people think it's cruel to keep animals in captivity, even if it's done to keep them from going extinct.
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Conservation of Biodiversity

The extinction of a species, or the loss of genetic diversity within a species, causes a reduction in global biodiversity.

Some species have already become extinct and there are lots of endangered species - species that are at risk of extinction because of a low population or a threatened habitat.

Conservations involves the protection and management of endangered species.

Zoos and seedbanks help to conserve endangered species and conserve gentic diversity.

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The Hardy-Weinberg Principle

The Hardy-Weinberg Principle predicts that frequencies of alleles in a population won't change from one generation to the next. But this is only true under certain conditions - it has to be a large population where there's no immigration, emigration, mutations or natural selection.

The Hardy-Weinberg equation can be used to predict allele frequency:

                                    p+q = 1                    where P = the frequency of the dominant allele

                                                                   where Q = the frequency of the recessive allele

Or to predict genotype and phenotype frequency:

                                   p^2+2pq+q^2=1         where p^2 = the frequency of homozygous                                                                                                          dominant allele

                                                            where 2pq = the frequency of the heterozygous                                                                                                           genotype

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Geographical Isolation

Geographical isolation occurs when a physical barrier divides a population of a species - floods, volcanic eruptions and earthquakes can all cause barriers that isolate some individuals from the main population.

Conditions on either side of the barrier will be slightly different and because the environment is different on each side, different characteristics will become more common due to natural selection.

Mutations will take place independently in each population, which would change the allele frequencies which then leads to changes in phenotype frequencies.

Eventually the populations will become genetically distinct, meaning they will have changed so much they are no longer able to breed with eachother. 

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Speciation

A species is a group of similar organisms that can reproduce to give fertile offspring.

Speciation is the development of a new species.

It occurs when populations of the same species become reproductively isolated - the changes in the alleles of the populations prevent them from successfully breeding together. These changes include: 

  • Seasonal changes - individuals from the same population develop different mating seasons, or become sexually active at different times of the year.
  • Mechanical changes - changes in genitalia prevent successful mating.
  • Behavioural changes - a group of individuals develop courtship rituals that aren't attractive to the main population.

A population could become reproductively isolated due to geographical isolation or random mutations which intoduce new alleles to the population.

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Five Kingdoms

Prokaryotae - Bacteria - Prokaryotes, unicellular, no nucleus.

Protoctista - Algae, protozoa - Eukaryotic cells, usually live in water, single-celled or simple multi-cellular organisms

Fungi - Moulds, yeasts, mushrooms - Eukaryotic, chitin cell wall, saprotrophic (absorbs substances from dead or decaying organisms)

Plantae - Mosses, ferns, flowering plants - Eukaryotic, multicellular, cell walls made from cellulose, can photosynthesise, contain chlorophyll, autotrophic (produce their own food)

Animalia - Nematodes, molluscs, insects, fish, reptiles, birds, mammals - Eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals)

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Classification

Taxonomy is the science of classifcation. It involves naming organisms and organising them into groups based on their similarities and differences. Ths makes it easier for scientists to identify and study them.

There are eight levels of groups used in classification.

Similar organisms are first sorted into one of the three very large groups called domains. Then they're sorted into kingdoms

Similar organisms from that kingdom are then grouped into a phylum. Similar organisms from each phylum are then grouped into a class and so on, down the eight levels of hierachy.

Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

As you move down the hierachy, there are more groups but there are fewer organisms in each group.

Species in the same genus can be very similar, with similar phenotypes and genotypes, but they're seperate species because they can't breed together.

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Reintroduction

The reintroduction of plants grown from seedbanks or animals bred in zoos can increase their numbers in the wild, helping to conserve their numbers or bring them back from the brink of extinction.

This could also help organisms that rely on these plants or animals for food or as part of their habitat.

The reintroduction of plants and animals also contributes to restoring habitats that have been lost.

This can cause problems such as:

  • Reintroduced organisms could bring new diseases to habitats, harming other organisms living there.
  • Reintroduced animals may not behave as they would if they'd been raised in the wild. They may have problems finding food or communicating with valid members of their species.
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Advantages and Disadvantages

Advantages:

  • It's cheaper to store seeds than to store fully grown plants.
  • Larger numbers of seeds can be stored as they need less space.
  • Less labour is required to look after seeds than plants.
  • Seeds can be stored anywhere, as long as it is cool and dry.
  • Seeds are less likely to be damaged by disease, natural disaster or vandalism.

Disadvantages:

  • Testing seeds for viability can be expensive and time-consuming.
  • It would be too expensive to sotre all types of seed and regularly test them for viability.
  • It may be difficult to collect seeds from some plants as they may grow in remote locations.
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Genetic Diversity

Diversity within a species is the variety shown by the individuals of that species, or within a population of that species.

Individuals of the same species vary because they have different alleles.

Genetic diversity is the variety of alleles in the gene pool of a species or population.

The gene pool is a the complete set of alleles in a species or population.

The greater the variety of alleles, the greater the genetic diversity. 

You can investigate the changes in the genetic diversity of a population over time, or how two populations of the same species show different diversity.

To measure genetic diversity you can look at genotype and phenotype.

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Evolution

Mutations can introduce new alleles into a population, which means they show a variation in phenotypes. Some of these alleles determine characteristics that can make the individual more likely to survive.

Selection pressures such as predation, disease and competition create a struggle for survival.

Individuals without the advantegous alleles don't survive, which means there is less of them. Individuals with better adaptations are more likely to survive and pass on their alleles to their offspring.

Overtime, the number of individuals with the advantegous alleles increases. 

Over generations, this leads to evolution as the frequency of the advantageous alleles in the population increase and the favourable adaptations become more common.

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Sampling

1) Choose an area to sample - a small area within the habitat being studied. To avoid bias, this should be randomly selected.

2) Count the number of individuals of each species in the sample area, and how you do this depends on what you're counting: 

  • For plants you'd use a quadrat (a frame which is placed on the ground).
  • For flying insects you'd use a sweepnet (a net on a pole).
  • For ground insects you'd use a pitfall trap (a small put that insects can't get out of).
  • For aquatic animals you'd use a net.

3) Repeat the process - take as many samples as possible which gives a better indication of the whole habitat.

4) Use the results to estimate the total number of individuals or the total number of different species (the species richness) in the habitat being studied.

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Measuring Species Diversity

A habitat is the place where an organism lives. It's important to measure species diversity so you can compare different habitats, or study how a habitat has changed over time. You can measure species diversity in different ways:

  • Count the number of different species in an area. The number of different species in the area is called species richness. The higher the number of species, the greater the species richness. However, this gives no indication of the abundance of each species.
  • Count the number of different species and the number of individuals in each species. Then use an index of diversity to calculate species diversity.

This can be very time consuming so a sample population is taken. Estimates about the whole habitat are based on the sample.

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Heterozygosity Index

You can measure genetic diversity within a species using the heterozygosity index.

Heterozygotes have two different alleles at a particular locus. A higher proportion of heterozygotes in a population means that the population has greater genetic diversity,

The heterozygosity index can be calculated using the following formula:

                                       H = number of heterozygotes

                                   number of individuals in a population

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Index of Diversity

An index of diversity is a way of measuring species diversity. It's calculated using an equation that takes both the number of species (species richness) and the abundance of each species (population sizes) into account. You can calculate the index of diversity using this equation:

                                               D = N(N-1)

                                                     Σn(n-1)

N = Total number of organisms of all species.

n = Total number of organisms of one species.

Σ = 'sum of' (added together)

The higher the number, the more diverse the area is. If all the individuals are of the same species, the index is 1.

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Biodiversity and Endemism

Biodiversity is the variety of living organisms in an area which includes:

  • Species Diversity: the number of different species and the abundance of each species in an area.
  • Genetic Diversity: the variation of alleles within a species, or a population of species.

Endemism is when a species is unique to a single place - isn't naturally found anywehre else in the world.

Natural selection, leading to adaptation and evolution has increased biodiversity on Earth over time. But human activites, such as farming are reducing speces diversity - causing biodiversity to fall.

Conservation is needed to help maintain biodiversity. It is also really important for endemic species because they're particularly vulnerable to extinction. They're only found in one place, so if their habitat is threatened they can't migrate and their numbers decline.

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Seedbank Stores

A seedbank is a store of lots of seeds from lots of different species of plant.

They help to conserve biodiversity by storing the seeds of endangered plants. If the plants become extinct in the wild, the stored seeds can be used to grow new plants.

Seedbanks also help to conserve genetic diversity. For some species they store a range of seeds from plants with different characteristics.

The work of seedbanks involves:

  • Creating the cool, dry conditions needed for storage. This means seeds can be stored for a long time.
  • Testning seeds for viability (the ability to grow into a plant). Seeds are planted, grown and new seeds are harvested to put back into storage.
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Classification of Organisms

The classification of organisms is based on their phenotypes, genotypes and how related they are.

Early classification systems only used observable phenotypes to place organisms into groups such as whether they lay eggs or could fly. But scientists don't always agree on the relative importance for different features and groups based solely on physical features may not show how related organisms are. For example, sharks and whales look quite similar and they both live in the sea. But they are not closely related. 

New technologies that have enabled organisms' genotypes to be determined have resulted in new discoveries being made and the relationships between organisms being clarified. For example, skunks were classified in the family mustelidae (weasels and badgers) until their DNA sequence was found to be significantly different to other members of that family. They were reclassified into the family mephitidae.

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Adapting to a Niche

Organisms can be adapted to their niche in three ways. Adaptations are features that increase an organism's chance of survival and reproduction.

They can be behavioural, physiological or anatomical adaptations.

  • Behavioural: Ways an organism acts that increase its chance of survival - possums play dead if they are being threatened by a predator.
  • Physiological: Processes inside an organism's body that increase its chance of survival - brown bears hibernate by lowering their metabolic rate over winter which conserves energy.
  • Anatomical: Structural features of an organism's body that increase its chance of survival - otters have a streamlined shape which makes it easier for them to glide through the water.
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Niches

A niche is a role a species has within its habitat. This includes:

  • Its interactions with other living organisms - such as the organisms it eats and those it's eaten by.
  • Its interactions with the non-living environment - the oxygen an organism breathes in, and the carbon dioxide it breathes out.

Every species has its own unique niche and a niche can only be occupied by one species.

It may look like two species are filling the same niche but there will be slight differences

If two species try to occupy the same niche, they will compete with each other until there is only one of the species left. 

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New Taxonomic Groupings

New data about a species can influence the way it is classified. New data has to be evaluated by other scientists to check that experiments or studies were designed properly and that the conclusions are fair.

Scientists can share their new discoveries in meetings and scientific journals. If scientists generally agree with the new data, it can lead to an organism being reclassified or lead to changes in the classification system structure.

A new, three domain classification system has been proposed based on new data. 

In the older, five kingdom system of classification, all organisms are placed into one of the five kingdoms. In the new, three domain system, all organisms are placed into one of the three domains - large superkingdoms that are above the kingdoms in the taxonomic hierachy.

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Plant Cell Organelles

Cell wall: rigid structure that surrounds plant cells, made mainly of cellulose. Supports the plant cells.

Middle lamella: outermost layer of the cell, acts as an adhesive, sticking plant cells together. Gives the plant stability.

Plasmodesmata: channels in the cell walls that link cells together, allows transport of substances and communication between cells.

Pits: regions of the cell wall where it is very thin, arranged in pairs. Allows transport of substances between cells.

Chloroplast: small structure surrounded by a double membrane, has membranes inside called thylakoid membranes. Membranes are stacked in some parts to form grana. Grana are lined by lamellae. Photosynthesis occurs here - some happens in grana, some in stroma.

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Plant Cell Organelles Cont'd

Amyloplast: small organelle enclosed by a membrane, contain starch granules. Store the starch grains and convert starch back to glucose if the plant needs it.

Vacuole and Tonoplast: vacuole is a compartment surrounded by a membrane called the tonoplast, contains cell sap. Keep the cells turgid and are involved in the breakdown and isolation of unwanted chemicals in the cell. Tonoplast controls what enters and leaves the vacuole.

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Xylem Vessels

The function of the xylem vessels is to transport water and mineral ions up the plant, and provide support.

They're very long tube-like structures formed from dead cells. The tubes are found together in bundles.

The cells are longer than they are wide, they have a hollow lumen (they contain no cytoplasm) and have no end walls.

This makes an uninterrupted tube, allowing water and mineral ions to pass up through the middle easily.

Their walls are thickened with the woody substance lignin, which helps to support the plant.

Water and mineral ions move into and out of the vessels through pits in the walls where there's no lignin.

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Sclerenchyma Fibres

The function of sclerenchyma is to provide support - they are not involved in transport.

Like xylem vessels - they are also made of bundles of dead cells that run vertically up the stem.

The cells are longer than they are wide, and have a hollow lumen, but they have end walls.

Their walls are also thickened with lignin, but they don't contain pits. They have more cellulose than other plant cells.

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Phloem Tissue

The function of phloem tissue is to transport organic solutes (mainly sugars) from where they're made in the plant to where they are needed. This is known as translocation. Phloems are purely transport tissue.

Phloem tissue contains different types of cells including sieve tube elements and companion cells. Sieve tube elements are living cells that are joined to form sieve tubes.

The sieve parts are the end walls which allow solutes to pass through.

Sieve tube elements have no nucleus, a very thin layer of cytoplasm and a few organelles. The cytoplasm of adjacent cells is connected through the holes in the sieve plates.

Sieve tube elements cannot survive on their own so there is a companion cell for every sieve tube element.

Companion cells carry out the living functions for both themselves and their sieve cells. For example, they provide the energy for active transport of solutes.

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Vascular Bundles

In the stem, xylem vessels group together with phloem tissue to form vascular bundles. Sclerenchyma fibres are usually associated with vascular bundles.

They form two types of cross-sections:

  • Transverse cross-section: this means the sections cut through each structure at a right angle to it's length.
  • Longitudinal cross-section: this means the cross-sections are taken along the length of a structure.
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Starch in Plants

Starch is the main energy storage material in plants.

Cells get energy from glucose. Plants store excess glucose as starch and when a plant needs more energy, it breaks down the stored starch to release glucose.

Starch is a mixture of two polysaccharides of alpha-glucose, amylose and amylopectin:

  • Amylose: a long unbranched chain. The angles of the glycosidic bonds means it has a coiled structure. This structure makes it compact which makes it ideal for storage as you can fit more in a small space.
  • Amylopectin: a long branched chain. It's side branches make it easier for enzymes to reach the glycosidic bonds which means that glucose can be released quickly.

Starch is insoluble in water, so water cannot enter the cells by osmosis. This makes it good for storage.

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Plant Fibres

Plant fibres are made up of long tubes of plant cells. They're strong meaning they are useful for things such as ropes or fabrics.

Plant fibres are strong for a number of reasons but there are two main ones:

  • The arrangement of microfibrils in the cell wall. The cell wall contains microfibrils in a net-like arrangement, the strength of the microfibrils and their arrangement gives plant fibres strength.
  • The secondary thickening of cell walls. When some structural plant cells finish growing they produce a secondary cell wall between the normal cell wall and the cell membrane. The secondary cell wall is thicker than the normal cell wall and usually has more of a woody substance called lignin - this makes plant fibres even stronger.
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Trial and Error Drug Testing

Before new drugs become available to the general public they need to be tested to make sure they work and don't have any side effects. In the past, drug testing was a lot less scientific than modern clinical trials.

William Withering

  • William Withering discovered that an extract of foxgloves could be used to treat dropsy (swelling brought about by heart failure). This extract contained the drug digitalis.
  • Withering made a chance observation - a patient suffering from dropsy made a good recovery after being treated with a traditional remedy. Foxgloves are poisonous, so Withering started testing different versions of the remedy with different concentrations of digitalis. This became known as digitalis soup.
  • Too much digitalis poisoned his patients, while too little had no effect.
  • It was through trial and error that he discovered the right amount to give to a patient.
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Modern Drug Testing

Drug testing protocols are much more controlled now. Before the drug is testing on a living thing, computers are used to model the potential effects. Tests are also carried out on human tissues in a lab, then are tested on live animals before clinical trials are carried out on humans. During clinical trials, drugs undergo three phases of testing:

  • Phase One: test the new drug on a small group of healthy individuals. It's done to find out things like safe dosage, if there are any side effects and how the body reacts to the drug.
  • Phase Two: if a drug passes phase one it will then be tested on a larger group of people (patients) to see how well the drug actually works.
  • Phase Three: the new drug is compared to existing treatments, and the drug is tested on hundreds or even thousands of patients. The group will be split in two and one group recieves the old treatment and one recieves the new so they can compare them.

Placebo: In phase 2, the group is split in two and one group is given a placebo - an inactive substance that looks exactly like the drug. This shows if the drug actuall works.

Double Blind: In phase 2 and 3, clinical trials are usually double blind so neither the patients nor the doctors know who has which drug.

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