Biology Revision Bites

Short bursts of information for B2, which I found helpful so thought you might too. They are based on what I was struggling with, but if there is a particular B2 topic you want me to create a card in this set for, then just comment and I'll do one ASAP :)

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Embryo screening

This involves checking IVF embryos for genetic abnormalities. A cell is taken and analysed for conditions. It could be used to select an embryo matching tissues of ill siblings. The embryo would be implanted and at birth, stem cells would be taken from the umbilical cord to treat the sick child.

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Advantages of stem cells

Stem cells will dramatically change treatment of diseases, and theraoy already exists to treat leukaemia. There is variation in its potential uses and this includes long-term illnesses. People can opt-in to the bone-marrow register and the sperm and eggs used to create embryos are specific for this; they are not taken from fertility treatments. This means less pressure on the NHS.

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Stem Cells

They can come from bone marrow; they differentiate and are already used to treat leukaemia. They can also be taken from embryos, which are destroyed after extraction.

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When gametes join, a single body cell with new chromosomes forms. A new individual develops as the cell divides by mitosis.

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Disadvantages of Embryo Screening

Embryo screening is not perfect, and there is no 100% guarantee. It can cause misdiagnosis of a disorder. IVF is painful and expensive, and the process could be used to create designer babies.

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Old + New Species

We have evidence of life from fossils, the remains of organisms. These can be parts that don't decay, like bones, parts replaced by minerals, or preserved traces, like footprints. We can learn from fossils how organisms have changed. However, most early life was soft-bodied, so their fossils were destroyed by geological activity.

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The parent cell copies genes from 2 gametes. It then divides into 4, and similar chromosomes join up. When divided, each gamete has 1 set of chromosomes.

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New Species

These can arise as a result of one of the following: Isolation, when 2 populations of a species separate; Genetic Variation, when each population has a range of alleles; Natural Selection, when alleles controlling characteristics are selected from a population; or Speciation, when populations are so different that successful interbreeding is impossible.

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Disadvantages of stem cells

Extracting bone marrow is painful and transplants are risky. Scientists could be working on fertility treatment instead, and there are less donors available for this. IVF is expensive to the tax payer and embryos are destroyed after use. The process could lead to human cloning.

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Two chemicals are produced: insulin breaks down glucose into glycogen when blood sugar level is high, and glucagon turns glycogen into glucose when blood sugar level is low.

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Most animal cells differentiate at an early stage. Many plant cells have the ability to differentiate throughout their life span. In mature animals, cell division is restricted to repair and replacement.

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