AQA Biology Unit 2 Revision Notes

Notes are in simple note form and are my adapted notes from the notes I found on this website:

All topics from Unit 2 AQA Biology.  

There may be spelling mistakes and it also isn't in proper sentences. 

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  • Created by: Amy
  • Created on: 13-06-16 14:41
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Biology Unit 2
Cells & Cell Structures
All living things made up cells. Structure different type's cells relates function. Get in/out cells
dissolved substances cross cell membrane. Cell smallest unit life.
Human & Plant Cells:
Nucleus ­ controls activity cell
Cytoplasm ­ most chemical reactions take place
Cell membrane ­ controls passage substances in/out cell
Mitochondria ­ most energy released in respiration
Ribosomes ­ Protein synthesis occurs
Plants also have:
Cell wall ­ made cellulose & strengths plant cell
Chloroplasts ­ absorb light energy to make food plant cell
Permanent vacuole ­ filled cell sap in plant cell
Singlecelled organism
Cell's nucleus, cytoplasm & membrane surrounded cell wall
Singlecelled organism
Cell consists cytoplasm & membrane surrounded cell wall
Genes not in nucleus
Cells may specialised carry out particular function:
Root hair cell ­ large surface area absorb water & minerals easily
Palisade cell ­ lots chloroplasts for photosynthesis
White blood cell ­ change shape to engulf microbe
Sperm cell ­ tail to swim
Nerve cell ­ long nerve fibre carry messages other cells
Movement in/out cells
Get in/out cell dissolved substances cross cell membrane
Solutes ­ particles solution e.g. glucose, sodium ions, chloride ions can move in/out by
Solvent ­ liquid particles dissolved e.g. water
Solutes & solvents ­ molecules move round randomly
Spreading particles gas/substance in solution resulting net movement area high concentration
to area low
Oxygen required respiration pass through cell membrane by diffusion

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Greater difference concentration faster rate diffusion
Tissues, Organs & Organ Systems
Cells multicellular organisms differentiate & adapt specific functions. Tissues lots similar cells.
Organs lots tissues doing specific functions. Organs organised in organ system work together form
organism.…read more

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Light energy absorbed green substances ­ chlorophyll in chloroplasts
Energy used converting CO (from air) & water (from soil) to sugar (glucose)
Oxygen release byproduct
Carbon dioxide + water glucose + oxygen
Where it happens:
Leaves ­ main site
Mesophyll cells ­ place occurs
Cells contain lots chloroplasts
Chloroplasts contain chlorophyll
Factors limit rate:
Temperature ­ lower temp.…read more

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Affect rate organism's metabolism
Organisms can't maintain constant high body temperature
Can't tolerate extreme temperatures
Organisms maintain constant high body temperature also struggle survive extreme
Availability nutrients
E.g.…read more

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Change distribution population organisms 2 neighbouring habitat
Choose start ­ end position of transect
Determine direction & length transect
Lay down tape/string mark out transect
Sample organisms along line
Take recording factors could influence distribution along line
Types transects:
Record organisms touching line suitable regular intervals
Place quadrat start position record content
If long put quadrat suitable regular intervals along transect
Proteins functions inside/outside cells living organisms.…read more

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Enzymes structure & function:
Enzymes biological catalysts increase rate chemical reaction
Enzymes ­ protein molecules made long chain amino acids
Long chains folded produce special shape enable molecules fit in enzyme
Shape vital enzymes function
Only 1 type enzyme (substrate) fit in enzyme
Active site part enzyme substrate fit in
Activation Energy
Order chemical reaction take place energy required activation energy
Enzymes reduce activation energy of reaction
Effect temperature on Enzymes
Rate enzymes controlled reactions increase as temp.…read more

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Wall stomach muscular & churns food
Food remains stomach few hours
Food leaves stomach small squirts to small intestines
Digestive & absorption small intestines
2 mains jobs:
Complete digestion food
Absorb soluble products digestion in blood
Digestion small intestines
3 juices released:
Produced liver
Stored gall bladder
Released in smaller intestines
2 maim substances in bile:
· Alkali ­ neutralise stomach acid
· Bile salts ­ convert large fat droplets small fat droplets ­ for large surface area
enzymes act on
· No enzymes…read more

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Supplying heat expensive ­ enzymes used industry processes cheaper
Enzymes sensitive temp. & pH change
Temp. & pH need carefully monitored expensive
Respiration cells take place aerobically/anaerobically energy released used variety ways. Human
body needs react increased demand energy during exercise.…read more

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All changes increase blood flow to muscles & increase supply sugar & oxygen & increase rate
removal CO
Glucose stored glycogen in muscles increase amount glucose can respired
Anaerobic respiration
During exercise insufficient oxygen reaching muscles use anaerobic respiration to get energy
It is incomplete breakdown glucose producing lactic acid
Breakdown glucose incomplete less energy released than during aerobic respiration
Glucose lactic acid + small amounts energy released
Lactic acid ­ poisonous ­ only tolerate small amount in body
Muscle subject long periods vigour…read more

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Cell divide 2 form 2 genetically identical cells
Cells undergo cell division again & again
Cells carry out function the die
Asexual reproduction
Cells offspring produced mitosis from parent cells
Contain same genes as parents ­ genetically identical
Cell differentiation
Differentiation results some genes turned on some turned off
Once cells specialised carry out role
Most types animal cells differentiate early stage
Lots plants ability did it throughout life
Mature animal cells division mainly restricted to repair & replace
Stem cells
Made differentiate in different…read more


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