Charles Darwin was an English naturalist.
He studied variation in plants and animals during a five-year voyage around the world in the 19th century.
Darwin’s ideas caused a lot of controversy, and this continues to this day, because the ideas can be seen as conflicting with religious views about the creation of the world and creatures in it.
Darwin’s theory of evolution explains how species of living things have changed over geological time.
The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria.
The basic idea behind the theory of evolution is that all the different species have evolved from simple life forms.
These simple life forms first developed more than three billion years ago - the Earth is about 4.5 billion years old.
The theory of evolution states that evolution happens by natural selection. Here are the key points:
- Individuals in a species show a wide range of variation.
- This variation is because of differences in genes Individuals with characteristics most suited to the environment are more likely to survive and reproduce.
- The genes that allowed the individuals to be successful are passed to the offspring in the next generation.
Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve.
The world’s human population has passed 6 billion and continues to increase.
The growth in the human population and the increase in the standard of living are putting strains on the global environment.
Some of the ways in which this is happening:
- non-renewable energy resources, such as coal, oil and natural gas, are being used up rapidly
- raw materials are being used up rapidly
- more waste is being produced
- more pollution is being caused
Most rubbish is buried in landfill sites and not all of it comprises safe materials. Even common household items can contain toxic chemicals such as poisonous metals. Industrial waste is also discharged onto the land. Many farmers apply pesticides to improve their crops, but these can damage living things. Toxic chemicals can be washed from the land into rivers, lakes and seas.
Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas.
Many aquatic invertebrate animals cannot survive in polluted water, so their presence or absence indicates the extent to which a body of water is polluted.
Most rubbish is buried in landfill sites and not all of it comprises safe materials.
Even common household items can contain toxic chemicals such as poisonous metals. Industrial waste is also discharged onto the land.
Many farmers apply pesticides to improve their crops, but these can damage living things.
Toxic chemicals can be washed from the land into rivers, lakes and seas.
Lichens are plants that grow in exposed places such as rocks or tree bark.
They need to be very good at absorbing water and nutrients to grow there, and rainwater contains just enough nutrients to keep them alive.
Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens, and prevent them from growing.
This makes lichens natural indicators of air pollution. For example:
- bushy lichens need really clean air
- leafy lichens can survive a small amount of air pollution
- crusty lichens can survive in more polluted air
Deforestation. It has some important consequences:
- forest habitats are destroyed
- soil erosion increases, which causes barren land, flooding and land slides
- atmospheric pollution is caused when forests are cleared by burning trees
The term biodiversity refers not only to the number of different species, but also to all the variations within and between species, and all the differences between the habitats and ecosystems that make up the Earth’s biosphere.
The loss of forests reduces biodiversity and we run the risk of losing organisms that might have been useful in the future - for example as sources of new medicines. There is also a moral responsibility to look after the planet and its resources.
Methane and carbon dioxide are greenhouse gases.
They absorb heat energy and prevent it escaping into space.
This keeps the Earth warmer than it would be without these gases.
Carbon dioxide is produced by burning fossil fuels.
Urbanisation means the growth of cities. These are some of the effects of urbanisation:
- increased pollution
- increased energy consumption
- land no longer used for food production
- loss of natural habitats
- decline of rural towns and villages as people leave them to live in cities
Sustainable development means improving our quality of life without damaging the quality of life of future generations.
It is important to all of us, not just the other inhabitants of the planet, that sustainable development is achieved.
This involves each of us as individuals, and careful planning at local, regional and global levels.
wordmeaning environment all the conditions that surround a living organism habitat the place where an organism lives population all the members of a single species that live in a habitat community all the populations of different organisms that live together in a habitat ecosystem a community and its habitat
Polar bears are well adapted for survival in the Arctic. They have:
- a white appearance as camouflage from prey on the snow and ice
- thick layers of fat and fur for insulation against the cold
- a small surface area to volume ratio, to minimise heat loss
- a greasy coat that sheds water after swimming
- large furry feet to distribute their load and increase grip on the ice
- a large surface area to volume ratio to maximise heat loss
The genetic information passed from parent to offspring is contained in genes carried by chromosomes in the nucleus.
Sexual reproduction produces offspring that resemble their parents, but are not identical to them.
Asexual reproduction produces offspring - clones - which are genetically identical to their parents.
Plants can be cloned artificially using cuttings or tissue culture.
Animals can be cloned using embryo transplants or fusion cell cloning.
Genetic information from one species can be transferred to another species using genetic engineering.
A gene is a section of DNA that carries the code for a particular protein.
Different genes control the development of different characteristics of an organism.
Many genes are needed to carry all the genetic information for a whole organism.
Chromosomes, found in the cell nucleus, contain many genes.
Sexual reproduction happens when a male gamete and a female gamete join.
This fusion of gametes is called fertilisation.
Sexual reproduction allows some of the genetic information from each parent to mix, producing offspring that resemble their parents, but are not identical to them. In this way, sexual reproduction leads to variety in the offspring.
Animals and plants can reproduce using sexual reproduction.
Asexual reproduction only needs one parent, unlike sexual reproduction, which needs two parents.
Since there is only one parent, there is no fusion of gametes and no mixing of genetic information.
As a result, the offspring are genetically identical to the parent and to each other.They are clones.
Asexual reproduction in plants can take a number of forms.
Many plants develop underground food storage organs that later develop into the following year’s plants.
Potato plants and daffodil plants are examples that do this.
Some plants produce side branches with plantlets on them.Other plants, such as strawberries, produce runners with plantlets on them.
The simplest way to clone a plant involves taking a cutting.
A branch from the parent plant is cut off, its lower leaves removed and the stem planted in damp compost. Plant hormones are often used to encourage new roots to develop.
The cutting is usually covered in a clear plastic bag at this stage to keep it moist and warm.
After a few weeks, new roots develop and a new plant is produced.
The method is easy enough for most gardeners to do successfully.
Another way of cloning plants is by tissue culture, which works not with cuttings but with tiny pieces from the parent plant.
Sterile agar jelly with plant hormones and lots of nutrients is needed.
This makes tissue culture more expensive and difficult to do than taking cuttings.
A developing embryo is removed from a pregnant animal at an early stage, before the embryo’s cells have had time to become specialised.
The cells are separated, grown for a while in a laboratory and then transplanted into host mothers.
When the offspring are born, they are identical to each other and genetically related to the original pregnant animal.
They are not related to their host mothers because they contain different genetic information.
Fusion cell cloning involves replacing the nucleus of an unfertilised egg with the nucleus from a different cell.
The replacement nucleus can come from an embryo, but if it comes from an adult cell, it is called adult cell cloning.
- An egg cell was removed from the ovary of an adult female sheep, and its nucleus removed.
- The nucleus from an udder cell of a donor sheep was inserted into the empty egg cell.
- The fused cell then began to develop normally, using genetic information from the donated DNA.
- Before the dividing cells became specialised, the embryo was implanted into the uterus of a foster mother sheep.
Genetic engineering is also called genetic modification or GM.
It is not the same as cloning.
Although cloning techniques are used in genetic engineering, the two things should not be confused.
cloninggenetic engineering produces exact copies produces a unique set of genes genes copied within the same species genes can be swapped across species
Certain enzymes can cut pieces of DNA from one organism, and join them into a gap in the DNA of another organism.
This means that the new organism with the inserted genes has the genetic information for one or more new characteristics.
For example, the organism might produce a useful substance, or be able to carry out a new function. We say that the organism has been genetically modified.
The animation shows how the method can be used to produce bacteriathat produce insulin. This is a human hormoneand valuable to people with diabetes.
Bacteria reproduce quickly, so a lot of insulin can be made quickly.