B4 Revision

Darwin observed that many vertebrates shared what type of limb?

Who influenced and was involved in the development of Darwin's Theory?

Darwin observed that many [blank_start]vertebrates[blank_end] shared the [blank_start]pentadactyl[blank_end] limb. He suggested that this may be because the vertebrates had all [blank_start]evolved[blank_end] from one, original species.

Biological controls have no limitations and are completely risk free.

Biological control involves the introduction of [blank_start]living[blank_end] organisms into an area affected by [blank_start]pests[blank_end]. The biological controls [blank_start]attack and eat[blank_end] the pests, eradicating the issue from the area. However, if too successful, these controls can [blank_start]eliminate[blank_end] the food supplies of native species. They may also attack the native species. If proper research is not carried out prior to their introduction, they may prove to be [blank_start]ineffective[blank_end] or a [blank_start]pest[blank_end] themselves.

Tissue culture samples are often grown on...

Living cell cultures are required to study viruses.

[blank_start]Selective breeding[blank_end] is a process which is commonly used to extract and reproduce desirable characteristics in livestock and crops. This is useful as it can improve the organisms being farmed, often resulting in [blank_start]better[blank_end] yield, better [blank_start]quality[blank_end] produce and more [blank_start]profit[blank_end] for the farmer. However, selective breeding also has risks. [blank_start]Alleles[blank_end] are responsible for these characteristics, and by reducing the [blank_start]variety[blank_end] of these alleles, the opportunities for varied breeding in the future are minimised. Furthermore, by making many organisms [blank_start]genetically identical[blank_end], the farmer is allowing their produce to become more liable to wipeout in [blank_start]environmental changes[blank_end] or the introduction of a [blank_start]virus[blank_end] or disease. More [blank_start]genetic variation[blank_end] would reduce the potential coverage of these kinds of changes.

Methods which can be used to control problems in farming include:

GM insulin has some issues. The most prominent problem is:

Herbicides and fertilisers have advantages and disadvantages. Herbicides can kill weeds, but can also kill crops. The fact that herbicides can kill crops is a [blank_start]disadvantage[blank_end]. Fertilisers increase plant growth, but can cause water pollution. The fact that fertilisers increase plant growth is an [blank_start]advantage[blank_end]. The fact that fertilisers can cause water pollution is a [blank_start]disadvantage[blank_end].

Chemicals used to control insects on crops are called herbicides.