Adaption in animals
- Animals in cold climates (e.g. in the Arctic) have thick fur and fat under the skin (blubber) to conserve heat.
- Some animals in the Arctic are white in the winter and brown in the summer. This means that they are camouflaged so they are not easily seen.
- Bigger animals have smaller surface areas compared to their volume, this means that they can conserve heat more easily but it is also more difficult to lose heat.
- In dry conditions (desert) animals are adapted to conserve water and to stop them getting too hot. Animals in the desert may hunt or feed at night so that they remain cool during the day.
Adaption in plants
- Plants compete for light, water and nutrients.
- In dry conditions, e.g. deserts, plants have become very well adapted to conserve water, e.g. cacti.
- Plants are eaten by animals. Some plants have developed thorns, poisonous chemicals and warning colours to put animals off.
Competition in animals
- Animals compete with eachother for water, food, space, mates and breeding sites.
- An animal's territory will be large enough to find water, food and have space for breeding.
- Predators compete with their prey, as they want to eat them.
- Predators and prey may be camouflaged, so that they are less easy to see.
- Prey animals compete with each other to escape from the predators and to find food for themselves.
- Some animals, e.g. caterpillars, may be poisonous and have warning colours so that they are not eaten.
Competition in plants
- All plants compete for water, nutrients and light. For example, in woodland some smaller plants (e.g. snowdrops) flower before the trees are in leaf, so that they have enough light, water and nutrients.
- Some plants spread their seeds over a wide area so that they do not compete with themselves.
- The cell contains chromosomes.
- Chromosomes are made up of genes.
- The male and female sex cells (gametes) contain the genes so the genetic information is passed on to the offspring.
- Genes control the development of the characteristics of the offspring.
Types of reproduction
- Sexual reproduction involves the fusion of sex cells (gametes). There is a mixing of genetic information so the offspring show variation.
- Asexual reproduction does not involve the fusion of sex cells. All of the genetic information comes from one parent. All of the offspring are identical to the parent.
- These identical individuals are known as clones.
Clones are identical to the parent. Cloning is used to produce new individuals that you want.
- In plants the process is cheap and effective. Plants can be cloned by taking cuttings and growing them, or taking groups of cells and growing them under special conditions (tissue culture).
- With animals it is much more difficult to clone. Embryo transplants are used to clone animals. In this process, embryos are split into smaller groups of cells then each group is allowed to develop in a host animal.
New ways of cloning animals
- Fusion cell and adult cell cloning are also used to clone animals.
- In adult cell cloning, the nucleus of the animal you want is placed in an empty egg cell. This cell is then developed in a different animal.
Genetic engineering involves changing the genetic make-up of an organism.
Genes are "cut out" of the chromosomes of an organism using an enzyme. The genes are then placed in the chromosome of another organism.
The genes may be placed in an organism of the same species so that it has "desired" characteristics or in a different species. For example, the gene to produce insulin in humans can be placed in bacteria so that they produce insulin.
Many people argue about whether or not genetic engineering is "right". Will it create new organisms that we know nothing about? Is it going against nature?
The origins of life on earth
It is believed that the Earth is about 4500 million years old and that life began about 3500 million years ago.
There is some debate as to whether the first life developed due to the conditions on Earth, or whether simple life-forms arrived from another planet.
We can date rocks. Fossils are found in rocks, so we can date when different organisms existed.
Theories of evolution
Lamarck's theory stated that acquired characteristics can be passed on to the next generation. People found this difficult to believe. For example, if two parents were to build up their muscles in the gym, Lamarck's theory would predict that this characteristic would be passed on to their offspring!
Darwin's theory stated that small changes took place over time. All organisms vary and therefore some are more likely to survive (natural selection). Those that are best adapted breed and pass on their characteristics.
It took a long time for Darwin's theory to be accepted. Many people wanted to believe that God was responsible for the creation of new species.
Due to sexual reproduction, there is variation between members of a species. For example, all antelope are different to each other. Those members of a species with the "best" characteristics survive to breed.
Weaker members of the species may die from:
- lack of food (or being caught by predators)
- variation in the climate (a very wet or very cold/hot period of weather)
The survival of organisms with the "best" characteristics is known as "survival of the fittest".
The fact that the best adapted animals and plants survive is known as "natural selection".
"Extinction" means that a species that once existed has been completely wiped out.
Extinction can be caused by a number of factors, but always involves a change in circumstances:
- A new disease may kill all members of a species.
- Climate change may make it too cold or hot, or wet or dry, for a species and reduce its food supply.
- A new predator may evolve or be introduced to an area that effectively kills and eats all of the species.
- A new competitor may evolve or be introduced into an area. The original species may be left with too little to eat.
- The habitat the species lives in may be destroyed.
The effects of the population explosion
There are increasing numbers of people on our planet.
Many people want and demand a better standard of living.
We are using up raw materials and those that sre non reknewable cannot be replaced.
We are producing more waste and the pollution that goes with it.
We are also using land that animals and plants need to live on. It's being used for building, quarrying, farming and dumping waste.
- the water with sewage, fertiliser and toxic chemicals
- the air with gases such as sulfur dioxide and with smoke
- the land with pesticides and herbicides and these can then be washed into the water
- Burning fuels can produce sulfur dioxide (and nitrogen oxides).
- These dissolve in water in the air, forming acidic solutions.
- The solutions then fall as acid rain - sometimes a long way from where the gases were produced.
- Acid rain kills organisms. Enzymes, which control reactions, are very sensitive to pH (acidity or alkalinity).
- Burning fuels (combustion) releases carbon dioxide.
- Cows and rice fields release methane gas.
- Both of these gases are "greenhouse gases". As these gases increase in the atmosphere, it retains more heat from the Sun. The Earth is therefore warming up.
- This warming may cause a number of changes in the Earth's climate and cause sea levels to rise.
- We are cutting down forests (deforestation). This is making the problem worse because trees take up carbon dioxide (during photosynthesis). When the trees die, they release this carbon dioxide back to the atmosphere.
As our population rises, we use up more of the Earth's resources. There are many examples, e.g. land, fossil fuels and minerals.
"Sustainable development" means finding ways of reducing this need for more resources.
This may mean finding alternatives to some resources. For example:
- fuels for cars
- recycling what we already have, e.g. plastics, aliminium in cans
- using land that has already been used previously, e.g. for building new homes.
Planning for the future
- Lichens indicate the level of air pollution. The more species of lichen growing, the cleaner the air. Freshwater invertebrates indicate the level of water pollution in the same way. The wider the range of these invertebrates the cleaner the water in the steams, river or pond. Some freshwater invertebrates will only live in polluted water.
- The world population is growing and needs suitable housing. It is important not to use up green areas of the countryside too much but to use areas that have already been built upon (called brown field sites). Many countries put aside areas of land which are important for wildlife and will not allow any development on them.