B1B Revision Cards

An adaptation is a particular feature that enables an organism to survive in its environment

The polar bear

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

The Camel

Camels are well adapted for survival in the desert. They have:

• large, flat feet to spread their weight on the sand
• A large surface area to volume ratio to maximise heat loss
• The ability to tolerate body temperatures up to 42ºC

Desert Plants

Cacti are well adapted for survival in the desert. They have:

• stems that can store water
• widespread root systems that can collect water from a large area

In addition, cacti have spines instead of leaves. These minimise the surface area and so reduce water loss by transpiration. The spines also protect the cacti from animals that might eat them.

Arctic Plants

The Arctic is cold and windy with very little rainfall. Plants in the Arctic often grow very close to the ground and have small leaves. This helps to conserve water and to avoid damage by the wind.

Animals and plants compete for resources to help them survive.

Animals compete for:

• Food
• Water
• Space
• Mates

Plants compete for:

• Light
• Water
• Space
• Mineral salts

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. He explained his ideas about evolution in a book called On the Origin of Species, which was published in 1859.

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 finches

Darwin studied the wildlife on the Galápagos Islands - a group of islands on the equator almost 1,000 kilometres west of Ecuador. He noticed that the finches - songbirds - on the different islands there were fundamentally similar to each other, but showed wide variations in their size, beaks and claws from island to island. For example, their beaks were different depending on the local food source. Darwin concluded that, because the islands are so distant from the mainland, the finches that had arrived there in the past had changed over time.

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.

Natural selection

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.

Evidence for evolution came from fossils.

Exctinction is when a particular species are no longer there.

Here are some of the factors that can cause a species to become extinct:

• changes to the environment, such as a change in climate
• new diseases
• new predators
• new competitors

The fossil record shows that many species have become extinct since life on Earth began. Extinction is still happening and a lot of it occurs because of human activities. We compete with other living things for space, food and water, and we are very successful predators.

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.

The number of genes and chromosomes varies from species to species. For example, cells in human beings have 46 chromosomes that carry about 30,000 genes in each cell; and cells in fruit flies have eight chromosomes that carry about 13,600 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.

In human beings, each gamete contains 23 chromosomes, half the number found in the other cells of the body. When the male and female gamete fuse, the new embryo contains the full 46 chromosomes – half from the father and half from the mother.

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.

Plants

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. Busy Lizzy does this. Other plants, such as strawberries, produce runners with plantlets on them.

Animals

Asexual reproduction in animals is less common than sexual reproduction. It happens in sea anemones and starfish, for example.

Cuttings

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. After a few weeks, new roots develop and a new plant is produced.

Tissue Culture

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. Tissue culture involves the following steps:

1. Small amounts of parent tissue or a number of cells are taken
2. The plant material is transferred to plates containing sterile nutrient agar jelly
3. Plant hormones are added to stimulate the cells to divide
4. Cells grow rapidly into small masses of tissue
5. More growth hormones are added to stimulate the growth of roots and stems
6. The tiny plantlets are transferred into potting trays where they develop into plants

Embryo Transplants

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 (a bit like what happens in twins), 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

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.

'Dolly the sheep' was the first mammal to be cloned using adult cell cloning. She was born in the UK in 1996 and died in 2003. Here’s how she was produced:

1. An egg cell was removed from the ovary of an adult female sheep, and its nucleus removed.
2. The nucleus from an udder cell of a donor sheep was inserted into the empty egg cell.
3. The fused cell then began to develop normally, using genetic information from the donated DNA.
4. Before the dividing cells became specialised, the embryo was implanted into the uterus of a foster mother sheep. The result was Dolly, genetically identical to the donor sheep.

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.

Some people are excited by the almost limitless possibilities of cloning and genetic engineering, while some people believe the process is unethical and should be banned. Others are concerned about what might happen in the future.

The development of agriculture led to a population explosion that has accelerated enormously during the past 500 years. Unlike other species, humans can adapt to and survive in almost all habitats and climates

Impact of humans

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. Here are 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

Pollution is the addition of substances to the environment that may be harmful to living organisms. Population growth and increases in the standard of living cause more waste to be produced. If this waste is not handled correctly, it leads to pollution. The most obvious form of pollution is often simply just litter on the ground, but pollution can affect the air and water too.

Land Pollution

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. Many smoke alarms contain radioactive americium. 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

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.

The most common source of air pollution is the combustion of fossil fuels. This usually happens in vehicle engines and power stations.

Indicators of air pollution

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

In places where no lichens are growing, it's often a sign that the air is heavily polluted with sulfur dioxide.

The atmosphere has gases in it that help keep some of the heat in, these gases are methane and Carbon Dioxide. The greenhouse effect is a 'good' effect as it warms up the earth to a livable temperature.

The problems is more of these green house gases are being produced making the layer thick and making the Earth warmer. Extra methane

Rice paddy fields produce methane gas, and so do cattle. As the numbers of rice fields and cattle have increased, so has the amount of methane in the atmosphere.

Extra carbon dioxide

Carbon dioxide is produced by burning fossil fuels and this has increased with industrialiastion and cars. Deforestation has meant that less of this Carbon Dioxide produced is taken in and used up.

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.