GCSE Biology Unit 2 - Homeostasis & genetics.

Fairly comprehensive notes on;

  • homeostasis
  • genetic inheritance
  • cell division
  • ethical debates surrounding genetics.

 Be aware that the gaps in the notes where diagrams would fit are designed to be hand-written diagrams, furthering your own knowledge and familiarity with the processes.

Created for the 2011 AQA Unit 2 exam. Any changes to the specification since then are not included.

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  • Created by: Sarah
  • Created on: 03-01-12 18:21

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For your body to function properly, the conditions must stay as constant as
possible. This is done through homeostasis keeping internal conditions constant
within a very narrow range.

Waste Products

The cells of your body are constantly creating waste products due to chemical
reactions ­ there are two main…

Page 2

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Temperature Control

Temperature receptors in the skin detect changes in temperature, whereas the
blood temperature is assessed by the thermoregulatory centre in the
hypothalamus of the brain.

When the body is too cold ...
o Vasoconstriction occurs so less heat can radiate from the skin's surface.
o Muscles contract to…

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The Diabetes Debate

Two scientists named Banting and Best discovered in the 1920s how animal
insulin could be used to treat human diabetes. Ever since diabetes sufferers have
used either genetically engineered insulin or insulin from cows, pigs and dogs to carry
on life as normal. But Banting and Best's…

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The `father of genetics' was a monk, Gregor Mendel, in the 1800s who saw the
patterns in breeding green and yellow peas and deduced the concept of dominant and
recessive characteristics. However, his work was not recognised as it was too
complex for scientists of the day to understand,…

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Mitosis divides cells to make copies identical to the original, with the same
number of chromosomes. It's used in growth and repair, or to replace damaged cells.
Mitosis is used primarily in asexual reproduction for some plants' reproduction, like the
strawberry plant. The offspring are clones of the parent,…

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During sexual reproduction, two gametes containing half sets of
chromosomes fuse to form an embryo with a full set of genetic information. To make
these gametes, cells must divide by meiosis to ensure that the new cells have only half
the original number of chromosomes. In humans it only…

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X and Y Chromosomes

The 23rd pair of chromosomes is the X and Y chromosomes, and dictates
gender. All men have an XY pair ­ the Y causes male characteristics. All women have
an XX pair ­ the XX combination causes female characteristics.

When making sperm, the X and Y…

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Genetic Diagram

Alleles are different versions of the same gene aka. alleles for blue eyes and
alleles for brown eyes. Generally you receive two, one from mother and one from father,
but only one expresses itself.
Bb : this is a dominant brown eyes allele paired with a recessive blue…

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o Aa denotes mild form of `sickle cell trait' which ironically protects against
malaria, so in malarial areas the allele is passed onto children ­ in nonmalarial
areas it does not persist.

Genetic Screening

Embryos can be screened for a certain genetic disorder the egg is fertilized
through IVF and…

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Many people suffer and die because parts of their body do not work properly. In
1998, two scientists managed to culture human embryonic stem cells, which we
now hope can be encouraged to grow into new differentiated cells we could
potentially use them to grow new organs for transplant surgery…


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