biology unit 1b

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 and 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.The theory of evolution states that evolution happens by natural selection.

• 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.

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

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.