AQA AS Biology Unit 1 3.1.3 Cells and Movement In and Out of them

Notes on topic 3.1.3 from the AQA AS Biology specification.

I made these using my class notes the AQA AS Biology textbook and the specification.

If you have any corrections or queries please leave them in the comments and I'll try and help.

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Preview of AQA AS Biology Unit 1 3.1.3 Cells and Movement In and Out of them

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Revision: Unit 1 Biology and Disease 3.1.3 Cells and Movement In and Out of them
Light microscope:
Maximum magnification is x1500.
Maximum resolution is 0.2µm (200nm).
Focusing method is eyepiece lens and objective lens.
Specimen preparation is
o Wet mount on slide
o Stained
o Can be living or dead
Image is viewed through the eyepiece at the actual specimen.
Advantages
o Can view specimens which are alive
o Can view plant and animal cells, bacteria and some large organelles.
Disadvantages
o Can't view objects which are closer than 0.2µm apart.
Transmission Electron Microscope (TEM)
Maximum Magnification is x500, 000.
Maximum resolution is 0.001µm (1nm).
Focusing method is electromagnetic lenses
Specimen preparation
o Killed, dehydrated and fixed
o Coated in heavy metal stains
o Must be dead
Image is viewed on a fluorescent screen and then that image is fed onto a computer screen.
Advantages
o Can view very small specimens
o Specimens can be viewed at a higher magnification and resolution so sub-cellular
images can be seen.
Disadvantages
o Artefacts
Features that are caused by the harsh preparation and do not really exist in
the living cell.
o Specimens must be dead.
o A vacuum is needed.
Scanning Electron Microscope (SEM)
Maximum magnification is x500, 000 / x200, 000.
Maximum resolution is 0.001µm (1nm).
Focusing method is electromagnetic lenses.
Specimen preparation
o Killed, dehydrated and fixed.
o Coated in a thin layer of gold.
o Must be dead.

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Image is viewed on a fluorescent screen and then that image is fed onto a computer screen.
Advantages
o 3D images can be viewed.
o Specimens can be viewed at a higher magnification and resolution so sub-cellular
images can be seen.
Disadvantages
o Artefacts
Features that are caused by the harsh preparation and do not really exist in
the living cell.
o Specimens must be dead.
o A vacuum is needed.…read more

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Site of respiration.
Do have ribosomes.
o Site of protein synthesis.
o They are smaller than those found in eukaryotic cells.
Eukaryotic Cells
Have a "true" membrane-bound nucleus and membrane bound organelles.
o Animal, plant and fungal cells are Eukaryotic.
Animal Cell
The Nucleus
Relatively large (10-20µm).
Surrounded by a double membrane layer.
There is darker region within the nucleus called the nucleolus which is responsible for
producing ribosomal RNA and Ribosomes.…read more

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µm
Surrounded by a double layer of membrane.
Inner layer is folded into a series of cristae which provide a large surface area.
Central area is filled with fluid called the matrix.
o Matrix contains DNA and Ribosomes.
Ribosomes
The site of Protein Synthesis.
Can be found free in the cytoplasm or attached to the ER.
Consists of two subunits which are made from ribosomal RNA and protein.
They are not membrane-bound.…read more

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Watery liquid containing dissolved materials.
Cytoskeleton
System of protein microtubules and microfilaments which give the cell some support.
Centrioles
A pair of short cylinders. Each made of nine fibres.
Form a spindle-shaped structure of protein fibres on which the chromosomes move during
nuclear division.
Additional features found in plant cells
Cellulose Cell Wall
Consists of cellulose microfibrils and other polysaccharides.
Provides mechanical support and protection.
Prevents cell from bursting.
Chloroplast
Surrounded by two membranes.…read more

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Cells are suspended in an ice cold, isotonic fluid.
Ice cold to reduce enzyme activity.
Isotonic to prevent osmotic damage to the organelles.
2. Cells are then broken open in a homogeniser.
Disrupts the cell membrane but leaves the organelles intact.
Any whole cells or debris is filtered off leaving a homogenate.
o Contains the cell organelles.
Since organelles differ in density, they will separate out at different speeds.…read more

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Shake the sample with ethanol in a boiling tube. Pour the liquid into another boiling
tube full of water.
A milky white precipitate forms if lipids are present.
Contain the elements carbon C, hydrogen H, and oxygen O.
o The large numbers of C-C and C-H bonds mean that fats and oils and other major
types of lipid are important as energy stores in plants and animals.
They are large molecules and are insoluble in water.…read more

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Carrier proteins
o Channel proteins
o Cell surface antigens
o Components in energy transfer reactions such as respiration and photosynthesis
Proteins and lipids have short branching carbohydrate components, glycoproteins and
lipoproteins.
Membranes also contain cholesterol. They fit neatly into the bilayer between the
phospholipid molecules.
Movement in and out of Cells
Diffusion
Diffusion is the movement of particles from a region of high concentration to a region
of low concentration.
Diffusion is a passive process.…read more

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The surface area between the two regions
The larger the surface area, the faster the rate of diffusion.
o The temperature
At higher temperatures molecules have more kinetic energy and diffuse
more quickly.
Facilitated Diffusion
Diffusion sped up by specific membrane proteins. Occurs down a diffusion gradient and
therefore does not require energy from the cell.
o It is a passive process.
Intrinsic proteins help larger or polar molecules to pass across the membrane of a cell.
Channel proteins transport charged ions and polar molecules.…read more

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Osmosis in Animal Cells
In hypotonic solutions, water will move by osmosis into the cells which will swell until they
eventually burst.
In hypertonic solutions, water will move by osmosis out of the cells which will then shrink.
To prevent this from happening, animals need to osmoregulate.
o Control the water potential of body fluids.
Osmosis in Plant Cells
In hypotonic solutions, water will move by osmosis into the cells
causing a high turgor pressure, making the cell turgid.…read more

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