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User:OldakQuill/Revision/Biology

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10.1 - The cell is the basic unit of structure in prokaryotic and eukaryotic organisms

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10.2 - The electron microscope and the technique of cell fractionation may be used to study ultrastructure

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  • Arrangement of phospholipids, proteins and carbohydrates in the fluid-mosaic model of membrane structure.
    • The hydrophilic head of phospholips faces outward (and is in contact with water; tails are hydrophobic and face toward centre. Two layers of these - proteins float in membrane - carbohydrates poke out from certain proteins. Proteins can be intrinsic (right through) or extrinsic - hydrophilic amino acids on outside, hydrophobic face lipids. Carbohydrates (glycoproteins when attached to protein) are involved in cell recognition and protection.
  • Diffusion and factors which determin it's rate. Fick's law - diffusion rate [proportional to] (surface area X difference in concentration)/thickness of exchange surface
    • Only lipid soluble molecules can - in very small amounts. It requires no energy and is uncontrollable
  • Osmosis as the movement of water from a solution of less negative water potential to a solution of more negative water potential through a partially permeable membrane.
    • Pure water has a water potential of 0psi - all solutions containing water "prefer" this. Water always falls from high to low water potential. The lower the water potential, the greater the osmotic pressure
  • The role of protein molecules and energy in active transport and facilitated diffusion
    • Active transport is requires a protein to "pump". Proteins are specific to molecules and the process requires energy. Only transport mechanism which can go up gradient
    • Facilitated diffusion, or passive transport, uses protein also - no energy is required. Only down concentration gradient. Channel (full of water) or carrier (bonding) proteins.
  • Endocytosis: Transport into cell by vesicle. For large ammounts of substance. Pinocytosis (for small substances) or phagocytosis may then occur.
  • Exocytosis: Transport out of cell by vesicle. Both require energy.

10.4: Large molecules are important in the structure and functioning of cells:

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10.5 - Enzymes are proteins which control biochemical reactions in cells

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  • Protein nature of enzymes: most acts as scaffolding to active site, amino acids at active site hold substrate in position.
  • Enzymes as catalysts lowering activation energy through the formation of an enzyme-substrate complex - lower activation energy by stabilising transition state
  • Lock and key enzyme model: Substrate exactly fits into active site, the site then changes altering molecule - lowering activation energy. For example, may pull bond making easier to brake - or increase pH.
  • Induced fit enzyme model: active site distorts and fits around substrate inducing transition state - lowering activation energy.
  • Effects of the following on enzyme activity:
    • Temperature: optimum temperature - steadily rises to this, dramatically drops due to denatureing of enzymes.
    • pH: optimum pH also - but rate at other pHs evenly fall around this,
    • Substrate concentration: Large linear increase initially - gets shallower after saturation point (though still gradually rises)
    • Enzyme concentration: Linear increase until flatens out (limitted by enzyme concentration - reacting with as many substrates per unit time possible).
    • Competitive inhibitors: Same structure of activation site as enzyme. So decreases rate.
    • Non-competitive inhibitors: Binds to another part of enzyme, so that active sites no longer fuse with substrate.

10.6 - Tissues contain similar cells, and organs are structures made of different tissues

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  • Epithelial tissue: protective tissue for internal (and external) outer surface. A form of protection
  • Features of alveolar epithelium over which gas exchange takes place: Single cell thick, large surface area with blood vessels close by
  • Blood is specialised tissue containing a number of different cell types. Confined to recognition of:
  • Structure of RBCs in relation to their transport function: RBCs do not have nuclei to maximise storage volume. Their surface is shaped to maximise surface:volume ratio. Haemoglobin attaches to oxygen to transport to muscle, etc. Shape means they can go through small capillaries.
  • Relationship between size and surface area to volume ratio: Shape is such that gas exchange is maximised with surroundings.
  • Blood vessels are organs
  • Structure of the following in relation to their function:
    • Arteries: Thick elastic tissue which allows for high pressure - carries blood from heart, small lumen, no valves, typically carries oxigenated blood, 0.1-10mm
    • Arterioles: Allows excahnge between tissues, single cell thick wall, low pressure, no valves - 8 micrometres
    • Veins: carry blood back to heart, thiner collagen-filled wall, lower pressure, many valves.

10.7 - The blood system is a mass flow system which moves substances from one part of the body to another. It is linked with exchange surfaces.

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10.8 - The functioning of the heart plays a central role in the circulation of blood and relates to the level of activity of an individual

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14.1 - Continuity is maintained by the transmission of genetic information from generation to generation

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  • The process of meiosis emphasising the reduction in chromosome number (to 23) and the independent assortment of homologous chromosomes (pair of chromosomes seen during division, side-by-side), chiasma (a crossover) formation and the exchange of genetic material between homologous chromosomes.
Names of subdivisions of prophase I are not required.
  • Principles of Mendelian inheritance - solve problems involving any of the following four features presented as data derived from specific crosses or as pedigrees:
    1. monohybrid crosses (TTxTt etc. 3:1) and dihybrid crosses (RrYy x RrYy, etc become RY|Ry|rY|ry and RY|Ry|rY|ry. 9:3:3:1)
    2. multiple alleles - dominant and recessive in terms of phenotype
    3. sex linkage (all genes along a chromosome are linked by chromosome - normally 500 to 1000 genes long)
    4. codominance - where two alleles are expressed in phenotype - example is blood groups in humans
Autosomal linkage is not required.
  • Reasons why experimental results may be expected only to approximate Mendelian ratios: the allele is random - we can only predict ratio over large numbers. May be using too few samples.
  • Application of chi-squared test: X2 = [sumof](d2/x)

14.2 - Genetic and environmental factors influence variation between individuals

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  • Need for random sampling and importance of chance in contributing to differences between samples: avoids bias towards pariticular traits, chance hopes to reflect actual numbers - all tries to reflect and be representative
  • Collection and display of data by means of appropriate graphical techniques: abiotic and biotic factors, standard deviation and index of diversity
  • Concept of normal distribution about the mean. Understanding of mean (average) and standard deviation (indication of spread of results) as a measure of variation in a sample
  • Calculation and interpretation of standard error (Standard errors provide simple measures of uncertainty in a value). Candidates will not be required to calculate standard deviation or standard error in answer to questions of written papers.
  • Variation exists between members of a species (due to random gene mutation)
  • Significance of meiosis in generating genetic variation (new combinations of genes)
  • Gene mutation. Restricted to substitution of base (triplet is replaced), addition of base (triplet is added) and deletion of base (triplet is removed).
  • Interaction of genetic and environmental factors resulting in the phenotype (produce continuous variation - a less well nourished individual will be shorter, for example)
  • Polygenic inheritance: (determined by a great number of genes, all interacting with each other)

14.3 - Selection can influence the frequency of alleles in a population

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14.4 - Evolution has resulted in different species of organisms. They are classified into five kingdoms.

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  • Difiniton of a species in terms of variation and potential for breeding: a related group of organisms which can interbreed to produce fertile offspring.
  • Recognition of kingdom, phylum, class, order, family, genus and species division
  • Five kingdom system, distinguishing features of each:
    • Prokaryotae: unicellular, auto- or heterotrophic, motile or non-motile
    • Protoctista: unicellular, eukaryote, ancestors of other eukaryotes - algae, mould, etc.
    • Fungi: heterotrophic, non-motile, external digestion
    • Plantae: autotrophic, non-motile
    • Animalia: heterotrophic, motile
  • Hierarchy should be illustrated with reference to the classification of familiar organisms. Candidates will not have to recall individual organisms

14.5 - The concept of the ecosystem

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  • An understanding of the following:
    • ecosystem: community of organisms together with environment, functioning as a unit
    • community: group of interacting organisms living together in one place
    • population: group of organisms of one species occupying defined area and usually isolated from similar groups
    • environment: the abiotic factors in a specific area
    • habitat: describes the particular environment of a articular organism, population, community or ecosystem
    • niche: combines spatial habitat with functional relationships of an organism
  • An understanding of diversity in the context of ecological stability: the more diverse the more stable the ecology
  • Calculation of the index of diversity using d = (N(N-1))/([sum of]n(n-1)) - where N = total number of organisms of all species; and n = total number of organisms in each species.
  • In extreme environments the diversity of organisms is usually low. THis may result in the unstable ecosystem in which populations are usually dominated by abiotic factors .
  • In less hostile environments the diversity of organisms is usually high. This may result in a stable ecosystem in which populations are usually dominated by biotic factors

14.6 - Photosynthesis uses energy from sunlight to synthesise organic molecules from inorganic sources

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14.7 - Energy is transferred through food chains and webs in a community

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  • Ecological pyramids (trophic pyramids) by number (usually a successive decrease in no., easy to collect; producers can be massive - tree is same as grass, range of numbers so great hard to draw pyramid to scale, trophic level of organism may be difficult to ascertain), biomass (harder to obtain, standing crop biomass may remain the same, small organisms may have small standing crop biomass while productivity is same as large, weight for weight one species can have higher energy) and energy (hardest to collect, takes into account rate of production, each bar represents the amount of energy per unit area or volume flowing through a trophic level in time period, compare ecosystems, inverted pyramids not obtained, input of solar energy may be added) - final is best representation (more true)
  • Trophic levels of a producer, primary consumer, secondary consumer and decomposer
  • A quantitative consideration of the transfer of energy between trophic levels and its relative efficiency.

14.8 - Respiration produces ATP which is the immediate form of energy for many cell activities

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  • The use of different respiratory substrates (>1 anaerobic; 1 carboydrate; 0.9 protein; 0.7 fat) and the determination, calculation and interpretation of RQ (RQ = vol CO2/vol of O2)
  • RQ should be considered with reference to lipid, protein and carbohydrate.
  • The release of energy from carbohydrate by aerobic respiration. The production of ethanol or lactate and the regeneration of NAD in anaerobic respiration.

Thes prcoess should only be considered in so much detail to show that:

14.9 - Decomposition and recycling maintain the balance of nutrients in an ecosystem

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  • The importance of respiration and photosynthesis in giving rise ot short-term fluctuations and in the long-term global balance of oxygen and carbon dioxide.
  • The passage of nutrients through various trophic levels and the role of microorganisms in converting organic molecules to inorganic substances which are made available to plants. Illustrated with reference to the carbon cycle and nitrogen cycle.

14.10 - Human activity can impose far reaching effects on an ecosystem. THere is a potential conflict of interest between production and conservation

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  • Deforestation leading to the increase in land for agriculture. The influence of deforestation on diversity and on carbon and nitrogen cycling.
  • Conservation of forests allowing sustainable provision of resources
  • Specific knowledge will be required of this example only, although candidates may be required to interpret other material illustrating the general theme of this section.

Also, removing hedges means there is less for primary consumers to eat hence causing primary consumers numbers to deteriorate and hence less primary consumers can have widespread effects on the rest of the ecosytm.

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