B2 Model Answers

Why are scientists unsure about how life started on Earth?

1. there is a lack of valid/reliable evidence

2. because early organisms were soft bodied or because some remains destroyed by geological activity

How do fossils provide evidence that species alive today have evolved from simpler organisms?

1. (define fossils) fossils are remains of organisms from many years ago

2. fossils show changes over time - evolution

3. fossils have similar features to present day species

Suggest an explanation for the development of 4 species originating from 1?

1. isolation of species, the species have become separated

2. by a physical barrier, which is.....

3. genetic variation within both isolated species - contain different alleles

4. because of different environmental conditions  natural selection takes place-alleles coded for successful characteristics survive and get passsed on to the next generation via sexual reproduction

5. eventually species become so different/evolved/changed they can no longer successfully breed together to produce fertile offspring- speciation

Compare issues involved in use of embryo screening for cystic fibrosis and polydactyly.

Screening for cystic fibrosis:

1. allows decision (eg. termination)

2. reduces the number of people in the population who sufferer

3. reduce health care costs

Screening for polydactyly:

1. there are alternative cures for 'disfigurement'

2. life condition but its not life threatening

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