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Biology (Characteristics of Life/Life Processes (Reproduction (Most…
Biology
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Osmosis
It is the net movement of water molecules across a partially-permeable membrane down a
water potential gradient.
Osmosis, like diffusion, is a passive process, and relies only on the kinetic energy of the water molecules.
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The higher the water potential, the higher concentration of water molecules there are
Osmosis in Animal Cells
If a cell is placed in a solution of higher water potential than that of the cytoplasm then water will enter and the cell will swell up. Likewise, a cell may shrink in volume if placed in a solution of lower (more negative) water potential.
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Osmosis in Plant Cells
Plant cells generally have a water potential that is markedly lower (more negative) than their surroundings, to absorb water.
As water flows into the cell, the pressure inside the cell increases, which pushes the cell contents against the cell wall; this is known as turgor pressure.
When turgor pressure is at its maximum, the cell is said to be turgid.
If the cell surface is pulled away from the cell membrane as a result of water loss, the cell is said to be plasmolysed.
The 5 Kingdoms of Life
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Fungi
Heterotrophic nutrition - fungi must synthesise organic molecules from pre-existing organic molecules obtained from their diet.
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Extracellular digestion - they secrete digestive enzymes onto their food and absorb the smaller molecules that are released such as glucose and amino acids.
Are usually saprotrophic (digesting dead organisms or material, thus helping the process of decomposition) but some are parasitic and will live in or on living plants or animals.
Grow a network (a mycelium) of fine, branching hair like structures called hyphae which can extend over many square miles.
Periodically send up fruiting bodies which produce reproductive spores which may have been produced sexually or asexually.
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Yeasts
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Can reproduce asexually by budding, in which a new small cell grows out of the side of an existing one.
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Protoctista
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Eukaryotes that cannot be classed as a plant, fungus or animal
Animals
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Heterotrophic nutrition - animals must synthesise organic molecules from pre-existing organic molecules obtained from their diet.
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Movement and nervous system - most animals can move their bodies. This movement is often coordinated through a well-developed nervous system.
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The number of cell layers in the embryo (two or three distinct layers form very early on which develop into specific organs and organ systems). Sponges do not have well-defined tissue types, however.
The very first branches of animals are the sponges. Although they have some specialised cells, they don't have distinct cell layers in the embryo or true organs. At one time sponges were classified as plants since they are sessile and lack any body symmetry.
Symmetry - e.g. bilateral symmetry as in humans, radial symmetry as in star fish, no symmetry as in sponges.
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Plants
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Possession of vascular tissue – specialised xylem and phloem which conducts water, mineral ions or sugars and amino acids throughout the plant.
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Possession of flowers and fruits – the majority of plant species are flowering plants in which the seeds are held in an enclosed structure.
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Diffusion
It is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.
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When equilibrium has been reached, there is still movement of particles, there is just no net movement.
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Viruses
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Reproduce by hijacking a host cell and using the virus genetic material to instruct the host cell to manufacture new viral proteins.
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Can infect plant, animal, and bacterial cells
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Classification
The Linnaean System
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Organised into groups
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Species Definition: A group of organisms with many characteristics in common which can interbreed and produce fertile offspring.
Binomial System
Binomial Nomenclature is when you put the Genus and the Species together, e.g. canis lupus
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Genus is in capitals, whereas Species is in lower case
Cells
Cell Structure
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All cells have cytoplasm
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In eukaryotic cells, the cytoplasm includes all of the material inside the cell and outside of the nucleus.
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All cells have ribosomes
A minute particle consisting of RNA and associated proteins found in large numbers in the cytoplasm of living cells.
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Mitochondria
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Since bacteria do not possess mitochondria, all of the reactions of respiration (and photosynthesis for those bacteria that are autotrophic) must take place in the cytoplasm.
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Chloroplast
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Chloroplasts absorb light energy to make food in the form of sugars such as glucose in the process of photosynthesis.
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2 main types of cells
Prokaryotic
Prokaryotic cells only include bacteria, and contain fewer components. In particular, prokaryotes lack a membrane-bound nucleus, in which the DNA is packaged into chromosomes.
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