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Biology Unit 2 Notes
Variation
The differences that exist between individuals, there are two types:
o Interspecific ­ variation that exists between different species
o Intraspecific ­ differences that occur within a species, caused by genetic and
environmental factors.
Individuals of the same species may seem similar but no two…

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factors. Experiments were carried out to see if environmental conditions affected
antioxidant levels found that the environmental conditions caused a great deal of variation.
Scientists now believe that antioxidant levels in berries are due to both genetic and
environmental factors.


Genetics
DNA is a polynucleotide ­ made up of lots…

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Contain linear DNA molecules ­ chromosomes ­ thread like structures each
made up of one long molecule of DNA, so long it has to be wound up around
proteins (histones) to fit into the nucleus.

Histones also help to support the DNA.

DNA + protein are then coiled up v.…

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Mutations are changes in the base sequence of an organism's DNA. Thus mutations can produce
new alleles of genes. A gene codes for a particular protein so if the sequence of bases in a gene
changes, a non-functional or different protein could be produced. All enzymes are proteins, if
there's…

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Type of cell division where the cells are diploid to start with, but from meiosis haploid cells
are formed ­ the chromosome number has halved.

The DNA unravels + replicates so there are 2 copies of each chromosome called chromatids.
The DNA condenses to form double-armed chromosomes made from 2…

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the gene pool thus reduces genetic diversity. The survivors reproduce + a larger population
is created from a few individuals.

E.g. Northern Elephant Seals ­ hunted by humans in the late 1800s, original population was
reduced to around 50 seals ­ reproduced to give a new population of around 100'000…

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Variation in Biochemistry + Cell Structure
Haemoglobin

RBCs contain haemoglobin (Hb) ­ large protein with a quaternary structure ­ 4 polypeptide
chains which each have a haem group that contains iron.

Hb has a high affinity for oxygen ­ each molecule can carry four oxygen molecules, in the
lungs, oxygen…

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saturated, it gets harder for more oxygen molecules to join, thus the curve has a steep bit in
the middle where it's v. easy for oxygen molecules to join, and shallow bits at each end
where it's harder.

When the curve is steep, a small change in pO2 causes a…

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Main energy storage material in plants

Cells get energy form glucose, the plants store the excess glucose as starch and when the
plant needs more energy it breaks down the starch to release the glucose.

Mixture of two polysaccharides of alpha-glucose ­ amylose and amylopectin

o Amylose ­ long, unbranched…

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pieces of thylakoid membrane). Some parts of photosynthesis happen in the grana and
others happen in the stroma (a thick fluid found in the chloroplasts).


Cell Cycle + DNA Replication
The cell cycle is the process that all body cells from
multicellular organisms use to grow and divide:

It starts…

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