Cambridge International A Level Biology Revision Guide

Chapter 18: Biodiversity, classification and conservation
Botanic gardens
Botanic gardens play similar roles to zoos for endangered
plants. Seeds or cuttings are collected from species
in the wild and then used to build up a population
of plants from which, one day, some plants may be
reintroduced to their natural habitats. It is also possible
to take small samples of cells and grow them on agar
in sterile conditions. The cells divide by mitosis to give
a mass of cells that can be cloned by subdividing them.
When the cells are transferred to a medium containing an
appropriate mixture of plant hormones, they grow stems
and roots and can then be transferred to grow in soil.
These techniques of tissue culture and cloning are used
to produce large numbers of plants from a few original
specimens.
The roles of botanic gardens are to:
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protect endangered plant species; the world’s botanic
gardens already cultivate around one-third of the
world’s known plant species, many of which are
increasingly threatened in the wild by environmental
degradation and climate change
research methods of reproduction and growth so that
species cultivated in botanic gardens can be grown in
appropriate conditions and be propagated
research conservation methods so plants can be
introduced to new habitats if their original habitat has
been destroyed
reintroduce species to habitats where they have become
very rare or extinct
educate the public in the many roles of plants in
ecosystems and their economic value.
It often takes a long time to reintroduce a plant species
and ensure its survival. This is especially true with
slow-growing plants, such as Sargent’s cherry palm,
Pseudophoenix sargentii. Specimens of this species were
grown at the Fairchild Tropical Botanical Gardens in
Miami before being reintroduced to its natural habitat in
the Florida Keys.
As well as cultivating plants, botanic gardens may
store seeds in a seed bank. The Royal Botanic Gardens
at Kew, UK, runs a hugely ambitious project called the
Millennium Seed Bank, which began in 2000 (Figures
18.33 and 18.34). The bank’s ambition is to collect and
store seeds from at least 25% of the world’s plants by
2025, so that even if the plants become extinct in the wild
there will still be seeds from which they can be grown.
If possible, seeds of the same species are collected from
different sites, so that the stored samples contain a good
proportion of the total gene pool for that species.
Figure 18.33 The Millennium Seed Bank, Wakehurst Place,
UK. Seeds arriving at the seed bank are checked for pests
and diseases, assessed for viability, dried, and then stored in
airtight jars (Figure 18.34) and kept in the seed-storage vault
at − 20 °C.
Figure 18.34 A botanist with one of the seed collections in a
cold vault at the Millennium Seed Bank.
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