Biology

Ecology: Definitions Ecology: The scientific study of the interactions between organisms and their environment that determines the distribution and abundance of organisms Ecology is a science Environmentalism is a cause Conservation Biology is the integration of these two: using science to support a political cause Population ecology: experimental field approach: natural populations manipulated to test specific predictions arising from controversial ecological theory Organismal ecology: studies how an organism?s structure, physiology, and (for animals) behaviour meet environmental challenges Population: all the individuals of the same species within an ecosystem Population ecology focuses on factors affecting how many individuals of a species live in an area

Cell Cycle Regulation Cell cycle control systems The frequency of cell division varies with the type of cell Caused by the difference in regulation at the molecular level The stages of the cell cycle are regulated by a distinct cell cycle control system (similar to a clock) The cell cycle control system is regulated by both internal and external controls The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received Cell cycle control systems: interphase and mitosis Interphase Makes up about 90% of the cell cycle: can be divided into subphases: G1 phase (?first gap?) S phase (?synthesis?) G2 phase (?second gap?) The cell grows during all three phases Chromosomes are only duplicated during the S phase

The Cytoskeleton The cytoskeleton extends throughout the cytoplasm It organises cell structure and activities, anchoring many organelles in place It provides mechanical support, maintaining the cells shape: it?s domed in shape and stabilised by opposing forces It is also very dynamic, and can be dismantled and reassembled quickly, to change the shape of the cell Form The cytoskeleton is a network of fibres, the molecular structures include: Microtubules: the thickest of the fibres at 25nm (15nm lumen) Microfilaments: the thinnest of the fibres at 7nm Intermediate filaments: range in diameter from 8?12nm, larger than microfilaments but smaller than microtubules Roles

Chromatin: Types of chromatin Chromatin In non-dividing cells, the DNA exists as chromatin and appears uncoiled and randomly dispersed After DNA replication (S phase) the chromatin begins to condense in preparation for mitosis Chromatin consists of 50% DNA, 50% proteins, mainly histones Chromatin is the structure that the eukaryotic genome is packaged into It allows long molecules of DNA to fit into the small volume of the nucleus The basic structural unit of chromatin is the nucleosome Further folding and compaction of chromatin produces visible metaphase chromosomes during cell division Heterochromatin vs Euchromatin Euchromation Active Chromatin The majority of chromatin is this form Less condensed, lightly packed in the nucleus (basic ?beads on a string? form ?check)

The last ice age produced many different species mainly because of vicariance events; the glaciers physically separated populations from each other. Sympatry: populations that live close enough to interbreed Gene flow prevents speciation in sympatric populations A mating between a tetraploid individual and a diploid individual produces: triploid individuals: which likely produce nonviable gametes with an uneven number of chromosomes All polyploid individuals contain more than two haploid sets of chromosomes
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