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KEY CONCEPTS
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animal cells: eukaryotic
nucleus: contains genetic material – arranged into chromosomes, controls activity of cell
cell membrane: holds cell together, controls things entering/leaving
mitochondria: aerobic respiration reactions – transfers energy cell needs to work
ribosomes: involved in genetic material translation & protein synthesis
b
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bacteria: prokaryotic – single-celled
chromosomal DNA: controls cell’s activities/replication, floats free in cytoplasm
plasmid DNA: extra DNA not part of chromosome, can be passed between bacteria
cell membrane
ribosomes
flagellum/flagella: rotates to make bacterium move towards/away form toxins/nutrients
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sperm cell: transports male DNA to egg
acrosome: stores enzymes needed to break through egg’s membrane
haploid nucleus: to produce full nucleus (duploid zygote) when combined with egg
mitochondria: provides energy to swim distance
tail: to swim to egg
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Ciliated epithelial: moves material
cilia beat to move substances in one direction along tissue surface
Lines surface of organs – airways to remove mucus
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number/size/scale – estimations + when to use them
cm x 10 = mm
mm x 1000 = μm
image = actual x magnification
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Put into equation
Estimate by rounding numbers to check answer is right

μm x 1000 = nm
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relationship between quantitative units in relation to cells:
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micro 10-6
c
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pico 10-12
e
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Core Practical: Investigate biological specimens using microscopes – magnification calculations
& labelled scientific drawings from observations
Light microscope
Thin slice – allows light to pass through it
Clean slide & use pipette to put drop of water on it – secures specimen in place (use tweezers)
If specimen transparent: add drop of stain – makes it easier to see
Place cover slip – press down gently so there’s no air bubbles
Clip slide onto stage
Select lowest-powered objective lens
Focus: Coarse adjustment knob – move stage up so slide is just beneath objective lens
Look through eyepiece, move stage downwards until nearly in focus
Fine adjustment knob – until clear image
Calculate field of view: position clear ruler on stage, measure diameter of circular area visible
For greater magnification – swap to higher-powered objective lens, refocus & recalculate field of view
Scientific drawing
Sharp pencil – outlines of main features (no colouring/shading)
Keep in proportion
Label important features – straight lines that don’t cross
Include magnification used and scale
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Enzymes denature
Too hot / extreme pH: bonds holding enzyme together break – active site changes shape – substrate won’t fit
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Core Practical: Investigate effect of pH on enzyme activity
Amylase (enzyme) catalyses breakdown of starch to maltose
If starch present: iodine solution turns from browny-orange to blue-black
Drop of iodine solution into spotting tile
Bunsen burner/heatproof mat/tripod/gauze/thermometer – heat beaker of water until 35˚C – try keep constant
Syringe into boiling tube (into beaker of water): 3cm3 amylase solution + 1cm3 buffer solution (pH 5) – & wait
5 minutes
Add 3cm3 starch solution in boiling tube
Mix & start timer
Continuous sampling to record how long it takes for amylase to break down all starch
Pipette to take sample from boiling tube into spotting tile well – every 10 seconds
When iodine solution remains browny-orange – starch no longer present
Repeat experiment with different pH buffer solutions: see how pH affects time for amylase to break starch
down
Control: concentration/volume of amylase solution
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Enzymes: biological catalysts in synthesis
Breaking down
Digestive enzymes
Large insoluble food molecules (too big to pass through digestive system walls): broken down → smaller
soluble molecules – so bloodstream can absorb them by diffusion
Plants
Plants store energy as starch (carbohydrate) – when needed: broken down → sugars (smaller molecules) – can
be respired to transfer energy for use in cells
Carbohydrates – Carbohydrase: carbohydrate → glucose
Protein – Protease: protein → amino acids
Lipids – Lipase: lipids → fatty acids + glycerol
Synthesis: enzymes used to synthesise carbohydrates/proteins/lipids from their smaller compounds
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Calorimetry – measuring energy contained in food by burning it
Dry food / water / flame
Weigh food
Set volume of water in boiling tube & measure temperature
Set fire to food using Bunsen burner
Hold food under boiling tube until flame goes out – relight & repeat until food no longer sets alight
Measure temperature of water again
Temperature change of water shows energy given off – food gives off heat when burnt
Energy transferred J =
mass of water g
x
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Transport of substances in/out of cells
Active transport
against concentration gradient: area of low → high
Requires energy from proteins – mitochondria
In cell membrane: carries certain molecules across membrane

Respiration
Minerals get into root hair cell
Diffusion
Movement of particles from area of high → low concentration – until equilibrium
Passive process: doesn’t require energy
Only very small molecules can diffuse through cell membranes (not starch/protein)
Happens in fluids – move about randomly
Faster diffusion
larger surface area: folded membranes – more particles can get through a smaller length
Large surface area : volume ratio
steeper concentration gradient: rapid diffusion
higher temperature: more kinetic energy for particle collisions
Osmosis
Diffusion of water across partially permeable membrane: from area of high → low water concentration
Passive process – doesn’t require energy
Animal
Reactions in cytoplasm produce / use up water
Osmosis to keep water levels balanced
Water needs to osmote to keep our solute level balanced – so cells stay healthy
Plant
Keeps cells turgid
Cell wall prevents from bursting
Lost water from osmosis makes plants flaccid
Too much water – membrane will peel away and cells become plasmoloysed
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Calculate percentage gain/loss of mass in osmosis
Change of mass x 100
Initial mass



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