AQA Biology Unit 1 Notes

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  • Created on: 19-03-14 13:50
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Unit 1
Cells and transport
Cells and their function:
Nucleus- largest organelle which is surrounded by a nuclear envelope (double membrane)
which contains pores. The pores are used for exchange of substances i.e. mRNA. The outer
layer of the membrane contains ribosomes and is continuous with the endoplasmic reticulum.
In eukaryotes it contains chromosomes (DNA wrapped around proteins called histones). The
chromosomes become visible before the cell divides, otherwise they appear as chromatin.
Red blood cells do not contain a nucleus.
Mitochondria- Contain a double membrane- the outer layer
controls the passage of materials in and out of the organelle.
The inner layer folds to form the cristae. Most of the
enzymes that control energy transfer reaction in later stages
of respiration are attached to the cristae. The matrix is the
inside of the organelle, and contains enzymes which are
involved in respiration, as well as protein, lipids and nucleic
acid. The intermembane space is the fluid filled areas of the
mitochondrion. The mitochondria are the site of aerobic respiration; it produces energy from
ATP and large numbers of mitochondria are found in cells with high activity e.g. the small
Lysosomes- A round organelle which is surrounded by a membrane with no internal structure.
It contains digestive enzymes which are secreted outside of the cell and can be used to digest
invading cells by enclosing them, or break down or destroy worn out components of the cell.
Rough Endoplasmic Reticulum- Consists of sheets of phospholipid membrane where
ribosomes are attached to. The R.E.R processes and transport
proteins that have been made by the ribosomes. It is surrounded
by the cytosol which is a solution containing enzymes, food
storage compounds and waste products.
Smooth Endoplasmic Reticulum- Membrane does not contain
ribosomes. It secretes steroids and it synthesises and processes
Ribosomes- A small organelle which is free-floating in the
cytoplasm or is attached to the R.E.R. They are found in prokaryotes and Eukaryotes, and are
involved in assembling protein from amino acids (translation). The ribosomes are made in the
nucleolus in the nucleus.
Golgi Body- Fluid-filled flattened sacs each surrounded by a membrane. There are vesicles
which are continually pinched off from the ends of these sacs. The function is to pack and
process new lipids and proteins, and produce lysosomes. It also adds carbohydrates which
make glycoprotein; this makes the organelle dense.
Microvilli- Folds in the plasma membrane which increase surface area; therefore there is an
increased rate of absorption for example.

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Prokaryotes (bacterium) Eukaryotes (mammals, green plants, fungi)
No nucleus, instead free-floating DNA which is long Contains a nucleus
and coiled up as a strand or DNA which is in a
plasmid (small loops of DNA which contains genes
for antibiotic resistance, for example)
Contains a cell wall but without cellulose Cell walls are present in plants and fungi
Cells are extremely small Larger cells
Smaller ribosomes Contains larger ribosomes which make protein
Simple or no flagella (hair-like structure which Contains cilia or flagella
enables the…read more

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TEMS's are good as
they give high resolution, so details can be seen within the cell, however they have to be used
on thin specimens which are dead, and the image is black and white.
Scanning electron microscopes- SEMs scan a beam of electrons across the specimen. This
knocks off electrons from the specimen, which creates a 3D image of the surface of the
specimen. SEM's are good as they can be used on thick specimens, but they give lower
resolution images than TEMS.…read more

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Fatty acids can be either saturated (don't have any double bonds between their carbon
atoms) or unsaturated (have double bonds between the carbon atoms).
The fluid mosaic model:
The Fluid mosaic model describes the arrangement of the phospholipid molecules in the
A phospholipid consists of a glycerol, two fatty acids and a phosphate group attached to the
glycerol. The phosphate is hydrophilic (attracts water) whilst the fatty acid tails are
Hydrophobic (repel water).…read more

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Diffusion is the net movement of particles (molecules or ions) from an area of a higher
concentration to an area of lower concentration, down a concentration gradient.
The process is passive, therefore ATP is not required. However, energy needed for the
process comes from the kinetic energy of the particles diffusing.
Particles will only diffuse through a membrane if they can move freely thorough it i.e. oxygen
molecules are small enough to pass easily through the spaces between the phospholipid
membrane.…read more

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The higher the concentration of water molecules, the higher the water potential. Pure water
has the highest water potential at 0; all solutions have a lower water potential than pure
Active transport
Active transport happens when molecules move from low to high against a concentration
gradient, requiring energy from ATP to do so.…read more

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The cholera bacterium produces a toxin called choleragen.
The toxin binds to the epithelial cells lining the small intestine; this causes chloride ion protein
channels in the plasma membrane to open, so more Cl- ions move into the small intestine
lumen. This build up lowers the water potential of the lumen, so water moves out of the blood
and tissues into the lumen by osmosis.
The increase in water into the lumen leads to diarrhoea, which causes the body to become
dehydrated.…read more

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Peristalsis of the stomach turns food into chime (acidic
The small intestine is made up of the duodenum and ileum.
The chime is moved along the small intestine by peristalsis in
the duodenum, bile (alkaline) and pancreatic juice neutralise
the acidity of the chyme, breaking it down into smaller
molecules. In the ileum, small soluble molecules (glucose and
amino acids) are absorbed through the villi that line the gut
wall, and are then absorbed by diffusion, facilitated
diffusion and active transport.…read more

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Starch is made from two polysaccharides, 20% is amylose
and 80%amylopectin. Amylose is in a helix, amylopectin is
branched. They are both long chains of a-glucose linked
together by glycosidic bonds, formed in condensation
reaction and are both compact so can be stored in large
amounts for release of energy.
When starch is digested it is broken down into maltose
by amylase, then into a-glucose by maltase.
Glycogen is made up of 1, 6 glycosidic bonds
between a-glucose.…read more



great notes, thank you! :)

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