Summary Everything you need to get a 9 for Biology GCSE
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Course
Biology
Institution
GCSE
Book
Grade 9-1 GCSE Biology for Edexcel
Using these notes only, I got a 9 for Biology GCSE! Full revision notes on all 9 topics are clearly divided into subsections with bullet points and highlighted keywords for easy reading. Colour customising is optional.
TOPIC 1: Key Concepts in
Biology
CELLS & MICROSCOPY:
Cells either can be eukaryotic (complex & multicellular, e.g. animal/ plant
cells) or prokaryotic (simple & single-celled, e.g. bacteria).
Both contain various subcellular structures, known as organelles.
ANIMAL CELLS: nucleus (genetic material in chromosomes & controls
activity), cytoplasm (gel-like substance where chemical reactions occur
using enzymes), cell membrane (hold cell together & controls what enters/
leaves), mitochondria (where aerobic respiration occurs to fix energy) &
ribosomes (involved in protein synthesis).
PLANT CELLS: cell wall (rigid structure of cellulose to strengthen &
support cell), large vacuole (contain cell sap- which is a weak solution of
sugars & salt- to maintain internal pressure to support cell) & chloroplast
(where photosynthesis occurs to make food by a green pigment, called
chlorophyll, absorbing sunlight) + all the animal organelles
BACTERIAL CELLS: chromosome (large loop of DNA that controls cell’s
activity & replication), plasmid (small loops of DNA) & flagellum (long hair-
like structure that rotates for movement away from harmful substances &
towards nutrients) + cytoplasm, ribosomes, cell wall & cell membranes.
Most cells in an organism are specialised, thus their structure helps them
carry out a specific function. This causes them to look very different.
HOW CELLS HAVE SPECIALISED/ DIFFERENTIATED:
1. Palisade cell to produce food for plant (chloroplast with chlorophyll to
absorb sunlight for photosynthesis).
2. Root hair cells to absorb water & minerals from the soil (large surface
area to increase water & mineral intake).
3. Goblet cell to produce mucus to trap microorganisms (ribosomes to
produce mucus protein).
4. Nerve cells to sends messages by electric impulses (longer than typical
cells for cover more area).
5. Red blood cells to carry oxygen & carbon dioxide round the body
(smooth for travelling in blood, no nucleus to increase space for oxygen
& biconcave to increase surface area).
6. Ciliated epithelial cells to move particles away in one direction (little
hairs called cilia on the top).
7. Sperm cells to transport male DNA to female egg cell (long tail to swim,
mitochondria to provide energy for long distance & acrosome at the front
with enzyme to digest egg cell’s membrane).
8. Egg cells to carry female DNA as well as nourish embryo (contains
nutrients in embryo & membrane changes structure right after
fertilisation).
, Gametes (sex cells) have haploid nuclei – this means they have half the
number of chromosomes in normal body cell. Therefore, when they combine
at fertilisation, the resulting cell has the correct number of cells
(23+23=46).
Microscopes can either use light or electrons; they are used to view
individual cells or subcellular structure that cannot be seen with the naked
eye. Stains are often used to make it easier to see or to highlight
organelles.
LIGHT MICROSCOPES (est. 1590s): use light & lenses to form an image &
magnify, can be used on living or dead cells, used to see individual cells or
large subcellular structures (e.g. nuclei & chloroplast), cheap, easy,
magnification of up to x2,000 & resolution down to 200nm.
ELECTRON MICROSCOPES (est. 1930s): uses electron beam &
electromagnetic lenses, only can be used on dead or abiotic cells
(dehydrated), expensive, type called Scanning Electron Microscope (SEM)
for 3D imaging, used to see organelles (e.g. internal structure of
mitochondria or chloroplasts), magnification of up to x2,000,000 &
resolution down to 0.2nm.
HOW TO PREPARE A SLIDE:
1. Add a drop of water to a clean slide for securing the specimen.
2. Cut an onion, separate into layers & use tweezers to remove epidermal
tissue from the bottom.
3. Using tweezers, place epidermal tissue on water on slide.
4. Add a drop of iodine solution as a stain (e.g. methylene blue for DNA or
eosin for cytoplasm).
5. Place a cover slip over the upright next to the water, then carefully lower
using a mounted needle (avoid air bubbles).
Magnification is the degree to which the size of an image is increased;
whereas, resolution is the degree to which an image is made clearer.
OBSERVING A SPECIMEN:
1. Clip slide onto stage.
2. Select lowest-powered objective lens.
3. Use coarse adjustment knob to move stage just below objective lens.
4. Looking down eyepiece, use coarse adjustment knob to move stage
downwards until in focus.
5. Adjust focus further using fine adjustment knob.
6. If you need greater magnification, swap to higher-powered objective
lens.
CALCULATING MAGNIFICATION:
total magnification = eyepiece lens magnification x objective lens
magnification
magnification = image size / real size
, BIOLOGICAL MOLECULES &
TRANSPORT IN CELLS:
Living things produce enzymes to act as a biological catalyst for the
reactions inside a human body; they reduce the need for high temperatures
& only speed up useful reactions. Enzymes are large proteins, so they are
made up of chains of amino acids.
Catalysts are substances that increases the rate of reaction, without being
changed or used up.
Each enzyme has an active site with a unique shape – thus, they are specific
to one reaction because the substrate must fit properly for the reaction to
be catalysed.
Enzymes are said to have high specificity for their substrate, as shown by
the ‘lock & key model’.
If the enzyme’s amino acid bonds break, it denatures – this changes the
shape of the active site.
Enzymes need the right (optimum) conditions to work best, including:
temperature (if it gets too hot, the enzyme’s bonds break, it denatures &
the active site changes shape; however, if it’s too low, not enough heat
energy is convert to kinetic energy for the enzyme & substrate to collide),
substrate concentration (rate of reaction increases to point until it flattens
because the active sites are full & it become saturated), pH (if too high or
low, the bonds between the amino acids is broken down & the enzyme is
denatured) & inhibitor molecules (block the active site & change its
shape).
Most enzyme have an optimum temperature of 37oC (& denatures at 45oC)
& pH of neutral 7.
HOW TO INVESTIGATE THE EFFECT OF pH ON AMYLASE: this enzyme
catalyses the breakdown of starch in maltose. Starch is detected by iodine
solution (brown orange to blue-black).
1. Put a drop of iodine solution in every well of a spotting tile.
2. Using a Bunsen burner or electric water bath, heat water to amylase’s
optimum temperature.
3. Using a syringe, add 3cm3 of amylase solution & 1cm3 of buffer solution
with pH 5 (measured using pH meter) into a boiling tube & place in
water using test tube holder. Wait 5 minutes.
4. Using a different syringe, add 3cm3 of starch solution.
5. Immediately mix contents & start stop clock.
6. Use continuous sampling to record how long it takes to break down the
starch by dropping some in the spotting tile every 30 seconds with a
pipette, until no changes of colour.
7. Repeat with buffer solutions at different pHs.
8. Remember to control variables to make it a fair test.
CALCULATING RATE OF REACTION:
rate of reaction = 1/time OR change/time
, Enzymes are used to break down big biological molecules: carbohydrases
(carbohydrates/ polysaccharides to simple sugars e.g. maltose & glucose),
proteases (protein/ polypeptides to amino acids) & lipases (for fats/ lipids to
fatty acid & glycerol).
Enzymes are also used in synthesis reactions (opposite of breakdown
reactions).
When you prepare a solid food sample, you must: use a pestle & mortar,
transfer to beaker & add distilled water, mix with a glass rod, allow to
settle, & pipette out some liquid.
HOW TO TEST FOR REDUCING SUGARS (e.g. glucose):
1. Transfer 5cm3 of food sample to a test tube.
2. Prepare a water bath to 75oC.
3. Add 10 drops of Benedict’s reagent using a pipette.
4. Place test tube in water bath for 5 minutes.
5. During this time, if a reducing sugar is present, a coloured precipitate
will form. The further the colour change, the higher the concentration of
reducing sugar (blue to green to yellow to red).
HOW TO TEST FOR STARCH:
1. Transfer 5cm3 of food sample to a test tube.
2. Add a few drops of iodine solution (iodine dissolved in potassium iodide)
& gently shake.
3. If starch is present, colour will change from brown orange to blue-black.
HOW TO TEST FOR PROTEIN (Biuret test):
1. Transfer 2cm3 of food sample to a test tube.
2. Add 2cm3 of potassium hydroxide solution to make it alkaline
3. Add a few drops of copper (II) sulfate solution (blue).
4. If protein is present, colour will change from blue to purple.
HOW TO TEST FROM LIPIDS (emulsion test):
1. Transfer some food sample into a test tube.
2. Add 2cm3 of ethanol to a test tube.
3. Shake well until substance dissolves.
4. Pour into test tube of 2cm3 of distilled water
5. If lipids are present, they will precipitate out of the liquid as a milky
emulsion (more lipids, more noticeable).
Another test for lipids is a using filter paper; it becomes see-through.
Calorimetry can be used to see how much energy is contain in food by
burning it & measuring heat energy transferred. The results would be lower
as some energy is transferred to the surroundings instead.
HOW TO DO CALORIMETRY:
1. Weigh small amount of dry food, then skewer on mounted needle.
2. Add a set volume of water to a boiling tube (held with a clamp).
3. Measure temperature of water before using thermometer. Set food on
fire with Bunsen burner.
4. Immediately hold under water & keep relighting until the food will not
catch fire again.
5. Measure temperature of water again & record temperature change.
CALCULATING ENERGY CONTAINED IN FOOD:
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