SNAB biology topic 4 AS



species- a group of organisms with similar morphology, physiology, and behavior, which can interbreed to produce fertile offspring, and are reproductively isolated from other species.

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individual organisms do not adapt to their niche, natural selection fuels the evolution that allows adaptations to occur. 

Behavioral adaptations- changes in an organism's behaviour which aids its survival.

anatomical adaptations- changes in the observable or dissectable characteristics of an organism which helps it survive.

Physiological adaptations- changes in the features of the internal workings of an organism which aids its survival

co-adaptations- mutual adaptations of species, where they eventually tend to depend on one another.

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Evolution by natural selection

A population has naturally occurring genetic variation caused by random genetic mutations. 

A change in the environment causes a change in the strength of selection pressure acting on an organism

An allele with previously no advantage now becomes favorable.

Organisms with that allele are now more likely to survive and reproduce, passing on the advantageous allele to future generations.

There is a change in the allele frequency of that population, meaning the population has adapted.

Strength of selection pressure- the risk of immediate death acting on a group of organisms.

Gestation period- the time taken to produce offspring

Gene pool- all alleles in a population (larger= more variation= easier to adapt.)

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Allele Frequency

allele frequency is worked out by using the Hardy Weinberg principle.

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Biological diversity

Biodiversity- biological diversity as a result of the variety of life due to natural selection. Biodiversity can indicate the number of species, the genetic diversity within a species or the phenotype diversity within a species.

Taxonomy- the act of putting organisms into a group, such as the biological hierarchy system or the binomial nomenclature system

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The kingdoms

Anamalia- Multicellular heterotrophic organisms with eukaryotic cells.

Plantae- Multicellular autotrophic organisms with eukaryotic cells.

Fungi- unicellular or multicellular heterotrophic organisms with eukaryotic cells.

Protoctista- eukaryotic organisms who are uni or multicellular and who are hetero or autotrophic. 

.Prokaryotes - organisms with prokaryotic cells.

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Convergent evolution

dolphins and sharks may be believed to be from the same type of Animalia classification due to their similar features, but a shark is a fish and a dolphin is a mammal. They look similar due to the fact that they occupy the samniche, and have adapted through natural selection to the environments they are in, and in this instance, they are in very similar environments. This is called convergent evolution

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Phylogenetic tree of life

an alternate classification system was put forward, which shows the most recent common ancestor of different kingdoms and organisms. 

The order of the three domains are:

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Sub-species- two distinct populations, whose members can be separated from the rest of the species due to distinct anatomical and morphological features. Two subspecies can reproduce to produce fertile offspring. 

Genus- group of closely related species.

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Genetic variation

Genetic diversity- a unique combination of alleles caused by sexual reproduction and the mechanisms involved in variation. The more the variety the genotypes, the abler they are to adapt.

crossing over- where genetic information is shared between homologous chromosomes. 

independent assortment- variation resulting in the assortment of chromosomes before division.

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Sources of genetic variation

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Heterozygosity and diversity

Species with a large gene pool and a short gestation period and more heterozygotic genes, they are more genetically diverse.

species richness- the number of species in a defined area.

Species evenness - *** many of each species there are in a defined area.

Simpsons diversity index


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A species is endemic to an area if they naturally thrive in that area without the requirement of human modification. 

Biodiversity hotspots are measured by the level of vascular plant diversity due to them losing over 80% of their habitat and being endemic to specific regions internationally.

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plant cell

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Cellulose polymers are made of units of beta glucose monomers. each beta glucose monomer is vertically inverted to allow 1-4 glycosidic bonds to form between each monomer. Hydrogen bonds form between the chains of beta glucose, forming microfibrils, which cross-link with one another to form a mesh, which is strengthened by hemicellulose and pectins in the cell wall.

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The xylem is the part of the vascular bundle involved in water transport. It is made of autolysed cells with no complex organelles present, meaning the cell is dead.

The cell is lysed due to a breakdown of the tonoplast, leading to hydrolytic enzymes being released, which digest the cell contents. They usually digest the end cell walls or leave sieves. 

The xylem is lignified, meaning lignin integrates within the cell wall and wraps around the cell wall, strengthening the cell and waterproofing the cell.

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Water diffuses out of the stoma down a concentration gradient. 

Water evaporates out of the cells lining the sub stomal cavity.

The evaporated water is replaced by capillary action within the cell walls.

A continuous column of water is drawn up the xylem to the leaves.

This mechanism only works upwards from the roots to the leaf cells.

This is able to happen due to cohesion between water molecules and the adhesion of water molecules to the surface of the xylem.

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Phloem and translocation

The phloem translocates organic substances up and down the cell from source cells to sink cells.

source cells- leaves.

sink cells- flower, fruit, bulb cells.

 sieve tube element cells are alive as they contain cytoplasm

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Vascular bundle transport

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zoos are used for conservation, breeding, education, and protection. 

They can be seen as unethical due to the lack of space for the animals and the fact that the companies are for PROFIT.

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Captive breeding programmes

Captive breeding programmed aim to increase the number of individuals, maintain genetic diversity and to reintroduce organisms to the wild.

Genetic drift- when alleles are lost in sexual reproduction

inbreeding depression- reproduction between closely related species, which reduces the overall fitness of a population as recessive characteristics are more likely to be expressed.

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Millenium seed bank partnership

Millenium seed bank partnership aims to avoid potentially catastrophic effects on human wellbeing by maintaining plant diversity, food security, and habitat regeneration

the seeds are dried to prevent germination

the seeds are cleaned to obtain a pure sample

the seeds are x-rayed to check their health

they are stored airtight to ensure there is no moisture

the seeds are frozen at minus twenty Celsius to slow decay and enzymes

The seeds are constantly checked for verification and testing for the perfect growing temperature

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Clinical trials

Pre-clinical – testing on tissues and organs, to test the toxicity. Animal testing is carried out to test the effect on whole organisms and to assess possible side effects.

Phase 1 - using healthy volunteers to test the side effects of taking the drug without it being impacted by the disease. 

Phase 2- a small group of ill patients to test whether the drug actually works.

Phase 3- double-blind large-scale trial to test whether there is a significant statistical change in those who take the drug and to further test the side effects.

Phase 4/post-clinical – constantly monitoring the drug for possible side effects.

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Drug testing

75-80% of the world's population uses plant extracts to cure or relieve pain

Odema is treated with extracts from the foxglove plants, which are ‘poisonous’ a Victorian scientist William withering tested his drugs in different doses.

Why animal testing?

They usually are lab-bred, so there is reduced genetic variation to see the effects on similar organisms. 

It does not pose any harm to humans

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