GCSE Edexcel Biology Topic 1

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  • Created on: 02-07-18 12:15

Types of Cells

Eukaryotic cells have a nucleus enclosed in the membrane (i.e. plant and animal cells)

Cell contains cytoplasm, cell membrane & genetic material in nucleus

Prokaryotic cells don't have a nucleus enclosed in the membrane and their DNA is free in the cytoplasm (i.e. bacterial cells)

Cell contains cytoplasm, cell wall, plasmid DNA, chromosomal DNA, flagellum and ribosomes

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Animal Cell

Typical size of animal cell: 10-30µm

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Plant Cell

Typical size of plant cell: 10-100µm

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Bacterial Cell

Typical size of bacterial cell: 2µm

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Specialised animal cells

Red blood cells carry oxygen around the body (contains no nucleus and has large surface area)

Egg cells carries the female’s DNA and nourishes the developing embryo in the early stages (Contains a haploid nucleus, cell membrane, cytoplasm and mitochondria)

Ciliated epithelial cells move substances (contains cilia, cell membrane nucleus and cytoplasm)

Sperm cells transport the male’s DNA to the female’s egg (contains a tail, mitochondria, nucleus and acrosome)

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Light microscopes were invented in the 1590s. It works by passing light through the specimen.

Electron microscopes were invented in the 1930s. It works by using electrons to see much smaller things in detail.

Microscopes magnify images and increase the resolution of an image.

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Formulae of magnification

Total magnification = eyepiece lens magnification × objective lens magnification

Magnification = image size ÷ real size

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Unit and standard form


Standard Form









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Enzymes are biological catalysts that help the reactions in the body by speeding up the rate of the reaction.

Enzymes are a large protein molecule made up of amino acids folded to create a certain shape.

The enzyme’s shape helps another molecule “fit” into it (‘lock and key’ mechanism)

This shape can be destroyed (denatured) by high temperatures or the wrong pH.

Enzymes work best at the optimum temperature/pH.

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'Lock and Key' Mechanism


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Formula for rate of reaction/enzyme activity

Rate is a measure of how much of something changes overtime

Rate = Amount of reactant/product formed ÷ time

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Types of enzymes

Breakdown of starch into glucose in presence of amalyse enzymes (produced in the mouth, pancreas and small intestine)

Breakdown of proteins into amino acids in presence of the presence of protease enzymes (produced in the stomach, pancreas and small intestine)

Breakdown of lipids into glycerol and fatty acids in presence of lipase enzymes (produced in the pancreas and small intestine)

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Testing for biological molecules

Starch is tested for with iodine - Just add iodine solution to the sample, if starch is present, the sample will change from browny-orange to blue-black. If it isn’t, it will stay browny-orange.

Use the emulsion test for lipids – Shake the substance with ethanol and add water. If there are any lipids, they will precipitate out of the liquid and show up as a milky emulsion.

The biuret test is used for proteins – Add a few drops of potassium hydroxide and then copper (II) sulfate. If there’s no protein, the solution will stay blue. If there is protein present, it’ll turn purple.

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Diffusion is when particles spread from an area of high concentration to an area of low concentration. The particles move along a ‘concentration gradient’. Diffusion can be accelerated by increasing the temperature of the particles, which makes them move faster, or by making the surface area of the membrane bigger.

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Osmosis is when water diffuses from a concentrated area (lower solute concentration) to a less concentrated area (higher solute concentration) through a partially permeable membrane (only tiny molecules can pass through).

The water acts like it’s trying to ‘even up’ the concentration on both sides of the membrane.

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Osmosis in Potatoes

When the water concentration in the sucrose solution is higher than the water concentration in the potato cylinder, the mass of the cylinder increases due to osmosis.

When the water concentration are isotonic (same water concentration), there is no change in mass.

When the water concentration in the sucrose solution is lower than the cylinder, the mass of the cylinder decreases.

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Active transport

Active transport is the movement of particles across a membrane. It is against a concentration gradient (from an area of lower concentration to an area of higher concentration) using energy transferred during respiration.

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