Biology Key Principles

Summary of all the AS key principles for the exams

  • Created by: gemma-t96
  • Created on: 03-05-14 14:19

Properties of water that make ideal for transport

Polar molecule. 2 H molecules slightly + oxygen - as electrons are more concentrated here. 

H bonding holds molecules together. 

Solvent properties: Ionic & polar molecules dissolve easily in water.

Hydrophilic -  like water

Hydrophobic - don't dissolve in water 

Thermal Properties: Large input of energy = small increase in temperature - steady temp maintained.

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Large biological molecules are often built from su

Polymers, proteins & nucleic acids are made by linking identical or similar subunits, known as monomers together to form either staight or branched chains

Lipids also made in the same way but are not polymers as they do not have chains of monomers.

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The effect of increase in the size on surface area

Unicellular organisms have the whole cell surface membrane as the exchange surface

Substances that diffuse in/out of a cell move down a concentration gradient which is maintained by the cell constantly using absorbed  substances & producing waste. 

Larger multicellular orgainsms have problems absorbing substances because of the size of the organism's SA compared to it's volume. Known as SA:V ration. Calculated by dividing the organisms total SA by it's volume

Organisms that get larger, the surface area of volume gets less. 

Larger organisms have organs that increase the surface area to volume ratio. 

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Protein structure is the key to protein function

All amino acids contain anime, carboxylic acid & hydrogen attached to a central c atom. Each type of amino acid has a different size chain called the R group.

Primary structure: 2 AA join by condensation to form dipeptide with peptide forming between the 2 subunits. Repeated = polypeptide chains. Sequence of AA in chain = P

Secondary: Chain of AA twists to form a helix. H bonds between C=O of carboxylic and -NH of amine group stablise the shape. Several chains link together H bonds hold parallel chains.  
1 protein molecule there may be some alpha and some beta pleated sheets.

Tertiary & quaternary: Polypeptide chain bends and folds to produce 3D shape. Bonds and hydrophobic interactions between R groups maintain final tertiary structure
 R group is polar and attracts other polar molecules = hydrophilic. Non polar groups = hydrophobic. Non polar R groups arranged so they face inside of the protein. Only proteins with several polypeptide chains have Q structure, single chain = tertiary

Globular: chain is spherical, soluble e.g. transport proteins & haemoglobin. Precise shapes for enzymes
 Fibrous: remain as long chains, crosslinked for additional strength. Insoluble e.g. keratin 

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Enzyme function depends on protein 3D structure

Lock & key theory: Substrate form temp bonds with AA of active site = enzyme - substrate complex. Reaction complete enzyme remains unchanged. Enzyme = lock, substrate = key
Induced fit: Active site is flexible, enzyme changes shape slightly, fitting closer together
Activation Energy: Bonds change within/between molecules. Energy needed for this = activation energy. Heat provides energy without  enzyme, atoms agitated, become unstable & reaction proceeds.

How do enzymes reduce activation energy: Random movement causes enzyme & substrate to collide & substrate enters active site. Complex forms, charged groups attract, distorting substrate & aiding bond breaking/formation. Products released from active site leaving enzyme unchanged ready to accept another substrate molecule

Finding rates of enzyme controlled reactions: measured by determining quantity of substrate used OR quantity of product formed in time. Fixed quanitity of enzyme & substrate it would proceed quickly at first, when substrate used up = slower reaction & stops.

How do enzyme & substrate concentrations affect rate of reaction: Initial rate directly proportional to enzyme conc, increase in linear fashion 

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Are all cells basically the same?

Prokaryotic cells

Bacteria & cyanobacteria. Cells don't have a nucleus or other membrane bound organelles. Most are extremely small. DNA lies freely in cytoplasm. Cell wall always present 

Eukaryotic cells: 

Contain membrane bound organelles e.g. mitochondria, larger than prokaryotes, don't always have a cell wall. 

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Why is Mitosis so important?

Ensures genetic consitency which is important on growth & repair & asexual reproduction 

Growth and Repair
develops from single cell into mulitcellular organism, all cells have same genetic info. Some can regenerate lost/damaged parts. It also allows old and damaged cels to be replaced by new identical copies

Asexual Reproduction
Reproduce without using gametes Bacteria undergo binary fission, cell grows and divides into 2 new cells.  

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Polygenic inheritance

Number of genes involved in inheritance of a characteristic e.g. heigth/skin colour
Conditions that use several genetic & 1 + environmental factors = multifactorial

How it works:
Eye colour is an example of polygenic interitance , slleles at several different loci control eye colour. The pigment absorbs light so brown eyes appear dark. Blue eyes have little pigment so light reflects off the iris. 

The greater the number of loci involved, the greater the number of possible strands. 

Height & weight: each allele has a small effect on characteristic & effects of several alleles combine to produce phenotype of an individual. 

Use of homozygous and heterozygous alleles help determine the characteristics displayed.

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What is a species?

Group of organisms with similar morphology, physiology & behaviour, which can interbreed to produce fertile offspring and which are reproductively isolated from other species

Hybrids produced when 2 species interbreed.

Two species can be reclassified as a single species.

Use of DNA analysis to identify species along with observing living populations to see if they can breed fertile offspring.  

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How are plant cells different from animal cells?

Plant cells have rigid cell wall & contain cholorplasts

Chloroplasts are the site of photosyntheis, starch is found in storage vaculoes called amyloplasts & there is often large central vacuole surrounded by vacuolar membrane called a tonoplast.

Parenchyma - type of plant tissue found throughout the plant. Cells fill spaces between more specialsed tissues and may have specialised functions e.g. roots have role in storage & leaves contain cholorplasts & form photosynthetic tissue

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The importance of water to plants

Cohesion & surface tension

H bonding between water molecules results in cohesive forces between water molecules that keep water together as continuous column in xylem vessels
Surface tension at water surfaces is partly caused by cohesive forces between water to contract.

Solvent properties

Dissolved substances can be transported around plants through xylem & phloem. Once in cells, dissolved chemicals move freely around in an aqueous environmen and can react, often with water itself being involed.

Thermal Properties

Large energy input = small increase in temp, avoids rapid changes

Density & freezing properties

Liqiud water cools = molecules slow down, max no of H bonds to form between water molecules. Hold molecules further apart making ice less dense & can float. 

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Key to survival in a changing environment

Genetic uniformity - individuals within population have similar genotypes, advantage in stable environments. If it changes a genetically diverse population will have the advantage

Natural selection results in adaptiation & accumulation of genotypes favoured by the environment.

Essential for long-term survival that populations should be able to evolve as a result of NS

Evolution is unlikely unless there is genetic variation to enable evolution to happen or there is a high mutation rate.

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