Biology GCSE Revision


Topic 1

Key Concepts in  Biology

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Magnification= image size/real size                    

  • Milli (mm) = *10^-3
  • Micro (um) = *10^-6
  • Nano (nm) = *10^-9
  • Pico (pm) = *10^-12

Magnification: The no. of times larger an image is than the object that produced it.

Resolution: The smallest change that can be meaasured. how clear an image is.

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Cells -Animal and Plant

  • Eukaryotic - Complex 
  • Prokaryotic - Unicellular organisms

Eukaryotic:A cell with a nucleus that is eukaryotic.   

Prokaryotic: A cell with no nucleus or chromosomes that is unicellular.

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Specialised Cells

Specialised Cells: A cell that is adapted for a certain specific function.

Small Intestinal Cells 

  • Microvilli - Increase surface area of the cell

Egg Cell

  • Cell Membrane - Cell membrane hardens after one sperm has entered
  • Cytoplasm - Packed with nutrients for growth  and development of embryo
  • Haploid Nucleus - Fertilisation

Sperm Cell

  • Acrosome - Enzymes break down substances in jelly coat of egg cell
  • Large no. of Mitochondria - Release lots of energy for the tail to swim
  • Tail - Allows sperm to move
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Specialised Cells 2

Ciliated Epithelial Cells

  • These cells move substances along the surface of the tissue
  • Found in the linings of the airway and the fallopian tube
  • They help move mucus up the throat so it can be swallowed and doesn't reach the lungs.
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Inside Bacteria

Bacteria are prokaryotes because they do not have nuclei or chromosomes.

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Inside Bacteria 2


  • Membrane-bound Nucleus present
  • More than one
  • Usually multicellular
  • Animals and Plants
  • Mitochondria present
  • Large ribsomes
  • Chloroplasts present in plants
  • Cell wall in plants and fungi
  • Vacuole present
  • 10-100 um
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Inside Bacteria 3


  • No nucleus
  • Plasmid chromosomes
  • Unicellular
  • Bacteria & Archaea
  • No mitochondria
  • Small Ribosomes
  • Vacuole present
  • 1-10 um
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Enzymes and Nutrition

Protein => Amino Acids                    Starch=> Glucose                      Lipid => Fatty Acids + Glycerol

Synthesis: To build a large molecule from smaller subunits.

  • Complex Carbs and proteins are both polymers
  • Enzymes catalase the synthesis and breakdown of substances by speeding up the rate of reaction.

Process in Animals

Molecules are too big to pass through walls of  digestive system so enzymes break them down into smaller, soluble molecules => easily pass through walls, bloostream and cells.

Process in Plants

Plants store energy in the form of starch which is broken down by enzymes into sugars => respired to transfer energy for cells.

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Enzymes and Nutrition 2

Amylase (Carbohydrase)

  • Saliva and Small Intestine and Pancreas - Breaking down starch to small sugars


  • Most Cells (especially liver) - Breaking down hydrogen peroxide made in many cell reactions to water and oxygen.

Statis Synthase

  • Plant - Synthesis of starch from glucose

DNA Polymerase

  • Nucleus - Synthesis of DNA from monomers

Glycogen Synthase

  • Muscles or Liver - synthesis of glycogen from glucose
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Enzymes and Nutrition 3


  • Produced in the stomach, small intestine and pancreas.
  • Proteins => Amino Acids.
  • pH 1-2

Enzyme: A protein produced by living organisms, which is a biological catalyst that speeds up the rate of reaction.

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Testing foods


  • Benedict's Reagent
  • Add and place in 75oC water bath
  • Form coloured precipitate


  • Iodine Solution
  • Starch present: 


  • Emulsion Test
  • Shake with ethanol for 1 min until it dissolves
  • Pour into water => milky emulsion (precipitate)


  • Biuret Test
  • Add potassium hydroxide => alkaline & add copper(II) sulfate (blue) => if present:
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Testing foods 2

  • We can measure the amount of energy in a food by burning it in a calorimeter.

Energy in Food (J) = Mass of water (g) * Temp. change in water (oC) * 4.2

Energy/g in food (J/g) = Energy in Food (J) /Mass of food (g)

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Enzyme Action

  • Active site is where the substrate fits in the enzyme and starts the action.
  • Enzymes only work with specific substrates that fit in the active site.
  • Change in pH or temperature can affect the shape of the active site => enzyme has been denatured.
  • Catalysis is important for life proceses because reaction happen much faster.
  • Enzymes have a particular shape as a result of the sequence of amino acids in the chain.

Enzyme specificity:Is the ability to choose the specific substrate that fits in the active site.

Lock-&-Key Hypothesis

  • When the key fits into lock=> represents fusing of enzyme-substrate complex =>shapes match.
  • This is like the one substrate fitting in the active site of an enzyme. 
  • Substrate broken down into products.
  • Enzymes used to speed up reactions without using high temps.
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Enzyme Activity

The Effect of Temperature

  • Changing the temperature changes the rate of enzyme-catalysed reaction.
  • If it gets too hot, some bonds holding enzyme together break and changes shape of active site=>substrate won't fit.
  • Optimum temp. is where enzyme is most active.
  • As temp. rises, KE increases
  • After optimum temp, less successful collisions
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Enzyme Activity 2

Substrate Concentration

  • Affects the rate of reaction
  • Higher concentration, faster reaction=>more likely enzyme will meet and react with substrate.
  • Extra left if all active sites full.
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Enzyme Activity 3

Effect of pH

  • If too high or too low, interferes with bonds holding enzymes together=> changes shape of active site and denatures enzyme.
  • Optimum pH is usually 7.
  • Pepsin in the stomach works best at pH 2.
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Transporting Substances

Active Transport

Active Transport: Is the movement of particles across membrane against a concentration gradient (low to high concentration) using energy transferred during respiration.

Digestive System

  • When high con. of nutrients in blood=> nutrients diffuse naturally into blood.
  • When low con.=>active transport allows nutrients to be taken into blood=>essential against starvation. 
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Transporting Substances 2 - Active Transport 2

The Process

  • Active Transport involves specialised proteins on cell membrane
  • When proteins are given energy => specfic molecule will be transported from one side to the other.
  • Used to acquire minerals in short supply => for healthy growth in plants:

      =>Nitrates - DNA/ protein

      =>Phospates - DNA

      =>Sulphates - Amino Acids

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Transporting Substances 3


Diffusion:Is the net movement of particles down a concentration gradient (from an area of hight concentration to low).

  • Happens in both liquids and gases=>particles move around freely.
  • Only very small molecules can diffuse through cell membranes like glucose, amino acids, water and oxygen.
  • Bigger the difference between concentrations => steeper concentration gradient =>faster rate of diffusion.
  • Rapid in gases
  • Slower in liquids
  • Slowest in solids.
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Transporting Substances 4


Osmosis: Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of higher water concentration to a region of lower water concentration

  • Water molecules can pass both ways => water molecules move about randomly 
  • Steady net movement of water into region with fewer water molecules
  • => solute gets more dilute.
  • Eventually stop when both sides are in equilibrium. 
  • Passive process
  • Water will move from high water and low solute to low water and high solute
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Transporting Substances 5 - Osmosis 2

Effect on Cells and Tissues -Tonicity


More solute outside cell => water leaves cell to dilute it

=> Plasmolysed: When contents of plant cells pull away from the cell wall after water leaves it.

=> Turgid: When plant cell is full and its contents are pressed against the cell wall.


Dilute outside cell (no solute) => water enters cells to make solution more concentrated.

=> Crenated: When an animal cells are shrivelled up (result of water loss)

=> Lysis: When plants cells burst or break

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Transporting Substances 5 - Osmosis 3 Core Practic

Osmosis Practical


1) Put different sucrose concentration                                                                                                      in different boiling tubes

2) Cut similar sized potatoes 

3) Blot each piece dry, measure and                                                                                                       record mass and put one in each tube

4) After 15 mins, remove and blot dry

5) Measure and record mass

  • Concentration in cell sap => water in both become isotonic and net movement stops

Final - Initial Mass / Initial Mass * 100%

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