surgery. Potential applications of cloned animals
Reproductive cloning may allow copies of animals to be made for benefits in agriculture and
medicine. Sheep such as Dolly have been cloned to overproduce a high quantity of a protein
important for blood clotting in humans. It may soon be possible to clone extinct species of
animals.Drawbacks of cloning animals may include the fact that most cloned species are unable
to develop into healthy animals. Dolly for example was only one of 277 cloned embryos.
There have been significant health effects of cloning including increase in birth size and a
variety of defects in vital organs such as the liver, brain and heart.Ethical biotechnology- In medicine modern biotechnology finds promising applications in such areas as: drug
production, pharmacogenomics (how a person’s genes affects their response to drugs),
and genetic testing (or genetic screening): techniques in molecular biology detect ge-
netic diseases. - To test the developing foetus for Down syndrome, amniocentesis and chorionic villus
sampling can be used.
5.6 The leaf as an organ
You have learnt about individual tissues found in plants and animals. We will now look at
how tissues join together to form organs. An organ is a collection of tissues joined together
as a structural unit in order to perform a common function. In later chapters we will look
at the various organs found in animals. In this section, we will discuss how a plant leaf
is an example of an organ. We will present its structure with respect to its functions in
photosynthesis, gaseous exchange and transport.Leaves are typically found in vascular plants, which have lignified tissues allowing them to
conduct water. Leaves are usually flat and thin to allow for maximum gaseous exchange
and capture of light. The organisation of the leaf has evolved to allow maximum exposure
of chloroplasts to light, and to absorb carbon dioxide. Leaves have stomata, pores found
in the leaf epidermis, which allow the plant to regulate the exchange of carbon dioxide,
oxygen and water vapour with the atmosphere. The shape and structure of leaves varies
considerably from one plant to another. This depends on the climate, available light intensity,
presence of grazing animals, nutrients and competition from other plants. Leaves are either
dorsiventralorisobilateral. Dorsiventral leaves have both surfaces differing from each other
in appearance and structure. Isobilateral leaves have both surfaces looking the same. Leaves
can also store food and water and are modified to perform these functions.Leaf structure DUMMY
The leaf is a collection of tissues which include:- Theepidermiswhich covers the upper and lower surfaces.
- Themesophyllinside the leaf which is rich in chloroplasts.
- Thevascular tissuecontains the veins (where xylem and phloem are present).
150 5.6. The leaf as an organ