Brief Revision Notes

Bullet pointed notes for Unit 2 and 3 GCSE Biology.

Grouped according to CGP Complete Revision and Practice Guide (not Units)

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Edward Saunders 2012 ©
Cells and Cell Functions
Cell Features
· Cytoplasm contains enzymes; where reactions occur
· Nucleus contains genetic info in the chromosomes
· Membrane controls what goes in and out
· Ribosomes where proteins are made
· Mitochondria where reactions for aerobic respiration occurs
· Rigid cell wall supports and strengthens cell (cellulose)
· Chloroplasts contain chlorophyll for photosynthesis
· Permanent vacuole contains cell sap: a weak solution of sugar and salts
Specialised plant cells
· Pailsade Cells
· Lots of chloroplasts
· Tall = large surface area for absorbing CO2 from air in the leaf
· Thin = enables lots of cells to be at the top of the leaf where the light intensity is greatest
· Guard Cells
· Plenty of water = turgid = stomata open (so gases can be exchanged for photosynthesis)
· Short of water = flaccid = stomata close (so water loss is reduced)
· Thin outer walls/thick inner walls (assist opening and closing)
· Light sensitive (close at night to reduce water loss without losing out on photosynthesis)
· Deoxyriose Nucleic Acid
· Found in the nucleus à chromosomes
· "double helix of paired bases"
· 2 strands
· Each strand: many small groups of nucleotides
· Each nucleotide contains a base
1. DNA splits ("unzips")
2. Bases on free floating nucleotides in the nucleus match up
3. Cross links form between bases and the original DNA & the nucleotides are
joined together
Protein Synthesis
"A gene is a section of DNA that codes for a particular protein"
· Chains of amino acids
· Differentiated by no. and order of amino acids
Order of bases determine order of amino acids in the chain

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20 different amino acids (in cytoplasm of cells)
Each acid is coded for by a sequence of 3 bases
Amino acids come from diet (+ transamination in the liver, when excess amino acids are converted in ones that are
Ribosomes (organelle)
Where proteins are made
RNA: likea messenger between DNA and ribosome
1. DNA splits
2. Bases on free floating nucleotides match up with one strand (but don't form links) = RNA
3. RNA passes out of the nucleus
4.…read more

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o Random movement in both directions but there is a net change
E.g.…read more

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o Emulsifies fats (increases S.A for lipase action)
o Plasma
"pale yellow liquid which carries:"
Red/white blood cells
Digested food products (glucose/amino acids)
o Red Blood Cells
Transports oxygen
Biconcave (large S.…read more

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3. Adjustment of water content in the blood
1. Urea
o A poisonous waste product from the liver
Amino acids are converted into fats and carbohydrates (as proteins can't be stored)
2. Adjustment of ion content
o Ions (such as sodium) are absorbed from food into the blood
If the ion content is wrong the water concentration is reduced/increased meaning
that too much water is drawn out/into cells
o Excess ions are
Filtered out by the kidneys
Lost in sweat
3.…read more

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Growth "an increase in size or weight"
1. Size height width length circumference
2. Wet Weight incl. all water (varies a lot day to day: drinking/sweating)
3. Dry Weight excl.…read more

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Worked in monastery gardens and noticed the variation between different pea plants in the 1850s
Identified predictable patterns and that some characteristics were dominant over others
Ideas not initially accepted as they had no knowledge of genes/DNA
o Mendel had nothing to support his observations/ lacked credibility
o Only accepted at the turn of the 20th century
Plants and Energy Flow
Carbon Dioxide + Water Glucose + Oxygen
4 requirements
Light (energy) Chlorophyll (pigment that absorbs energy & uses…read more

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o For cell growth
Stunted growth
Yellow leaves
Produce chlorophyll
o For photosynthesis
Yellow leaves
o For DNA and Cell Membranes
Poor root growth
Purple leaves
For enzymes (that control respiration & photosynthesis)
Discoloured leaves
Poor flower and fruit growth
Pyramids of Number
show no.…read more

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Disadvantages Lots of animals in a small space Animals vulnerable to weather
Calves leave their mothers at just 8 Eggs can't be collected easily
Cowsheds need cleaning Feedstuff is expensive
Heating/lighting costs More land needed
Disease spreads quickly Calves take longer to gain weight
Animals unable to behave naturally Fewer eggs laid in winter when it's
cold outside
Animals' legs may break due to
excessive weight
Fish Farms e.g.…read more

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Carbon Cycle
Only one arrow down: PHOTOSYNTHESIS
o Green plants use carbon from CO2 to make carbohydrates, fats and proteins
Respiration (plants and animals) releases CO2 back in to the air
Dead matter can:
o Be eaten
o Decompose
o Be turned into useful human products
o Become a fossil fuel
Released back
o Respiration
o Decomposition
o Combustion
o Photosynthesis
Organs and Systems 2
Molecular Transport
o "passive movement of molecules from an area of high…read more


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