AQA Biology Unit F211 Revision

All of my revision notes for F211, I hope they are useful!

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Revision Cells, Exchange and Transport
Module 1: Cells
1.1.1. Cell Structure
a) Using a light microscope, magnification of 1500X is possible, with a resolution of around 200nm.
With a transmission electron microscope, magnifications of 2,000,000X are possible, with a resolution of
around o.o5nm. With a scanning electron microscope, magnifications of 250,000X are possible, with a
resolution of around 0.4-1.6nm.
b) Magnification: The degree by which the image is enlarged.
Resolution: The ability to separate the images of small objects that are close together.
c) Staining ­ Coloured stains are chemicals that bind to chemicals on or in the specimen. This allows the
specimen to be seen. Some stains bind to specific cell structures. For example, acetic orcein stains DNA
dark red. Gentian violet stains bacterial cell walls.
d) Linear Magnification = Image size ÷ Actual Size
Image Size = Magnification x Actual µm nm = ÷ 1000 µm mm = x 1000
Actual size = Image Size ÷ Magnification
E.g. Actual Size = Image ÷ Magnification = 55 ÷ 6000X = 9.2µm
Labeled Diagram of a eukaryotic cell, including nucleus, nucleolus, nuclear envelope, rough and smooth
endoplasmic reticulum, Golgi apparatus, ribosomes, mitochondria, lysosomes, chloroplasts, plasma (cell
surface) membrane, centrioles, flagella, cilia and microtubules.

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Nucleus ­ Contains nucleoplasm, which contains chromosomes. Chromosomes are made from DNA,
attached to proteins. These form chromatin. The nucleus controls cellular activity by regulating chemical
reactions. It is also involved in the synthesis of proteins and enzymes. When replicating, the nucleolus
makes rRNA and assembles ribosomes.
Nucleolus ­ Essentially a knot of chromatin, it produces ribosomes and has no membranes.
Nuclear Envelope ­ Double membrane: Outer membrane is continuous with membranes of endoplasmic
reticulum, which contain ribosomes.…read more

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The Golgi apparatus also plays a role in the intercellular transport of lipids. Lysosomes are formed here too.
These organelles are surrounded by a membrane containing digestive enzymes which are used to break
down old organelles in the cell.
Ribosomes are small structures (200nm in diameter) that are made from RNA and proteins. They play a
central role in allowing the formation of proteins using the mRNA from transcription. They construct the
proteins form individual amino acids, following the sequence of bases on the mRNA.…read more

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Glycoproteins are found in the outer layer, with carbohydrate portions contributing to the glycocalyx.
Glycolipids which have carbohydrates attached to them (glycocalyx) extend into the intercellular space.
Cholesterol is sometimes found in the bilayer with polar groups near phospholipid polar groups.
Microtubules are straight, unbranched, hollow structures of diameter 20-25nm. They comprise part of the
cytoskeleton in the cytoplasm. The walls are made from tubulin (protein). The length of the microtubule
can be altered by the addition or subtraction of tubulin.…read more

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RER ­ Synthesis of ribosomes; transport of proteins.
SER ­ Transport of proteins and lipids, lipid synthesis: makes vesicles.
Golgi apparatus ­ Makes vesicles, adds carbohydrates to proteins (modification).
Ribosomes ­ Makes proteins by joining amino acids.
Mitochondria ­ Release energy for the cell (ATP) as respiration is carried out.
Lysosomes ­ Enzymes to break down damaged or old organelles.
Chloroplasts ­ Site of photosynthesis.
Plasma membrane ­ Controls movement of materials in and out of the cell.…read more

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The cell wall is rigid and composed of murein (polysaccharide chains linked by peptides forming a strong, complex 3D
network). Slime capsule or layer outside the cell wall in some cases.
Pilli or fimbriae are flamentous structures attached to the cell wall or slime capsule.
Flagella can be found as a single structure or distributed across the outside of the cell. A single fibril is 20nm thick and
several µm in length, depending on the cell.
No mitochondrion, chloroplasts, ER, Golgi apparatus or cytoskeleton.…read more

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Cell Membranes
The cell surface membrane is not simply a `sack' created to hold all of the cytoplasm and organelles. It is a very
important structure which functions to allow certain substances to enter or leave the cell. It can `pump' other
substances into the cell against the concentration gradient or `pump' other waste substances out of the cell.
Some of the transport processes happen `passively' without the cell needing to expend any energy to make them
happen. These processes are called `passive transport processes'.…read more

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The plasma membranes of the cells in a growing shoot contain receptors that allow them to detect the molecules
that regulate growth.
Muscle cell membranes contain a large number of the channels that allow the rapid uptake of glucose to provide
energy for muscle contraction.
The internal membranes of chloroplasts contain chlorophyll and other molecules needed for photosynthesis.
The plasma membranes of white blood cells contain proteins that enable the cells to recognize foreign cells and
particles.…read more

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Some (extrinsic) proteins partially embedded in the bilayer on the inside or the outside face; other (intrinsic)
proteins completely spanning the bilayer.
Glycoproteins and glycolipids
Some of the phospholipid molecules making up the bilayer, and some of the proteins found in the membrane, and
also have a small carbohydrate part attached. They are called glycolipids. Where protein molecules have a
carbohydrate part attached, they are called glycoproteins.
Cholesterol gives the membranes of some eukaryotic cells mechanical stability.…read more

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Membrane receptor proteins serve as connection between the cell's internal and external environments.
Transport proteins play an important role in the maintenance of concentrations of ions. These transport proteins
come in two forms: carrier proteins and channel proteins.
Membranes and Temperature
Increasing temperature gives molecules more kinetic energy, so they move faster. This increased movement of
phospholipids and other components makes membranes leaky, which allows substances that would normally not do
so to enter or leave the cell.…read more


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