Biology 1B Revision

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Organisms survive in many different environments because they have adapted to them. Desert animals save water and keep cool. A large surface area compared to volume lets them lose more body heat. They lose less water by producing small amounts of concentrated urine. Little sweat. Very thin layers of body fat/thin coat to help lose body heat. The sandy colour gives them a good camouflage to have avoid predators and sneak up on prey.

Arctic animals have a rounded shape to keep their surface area to a minimum- reduces heat loss. Thick layer of blubber for insulation and an energy store when food is scarce. They have thick, hairy coats. White fur to camouflage. Desert plants- small surface area. Lose water vapour from the surface area of their leaves. Water storage tissues too. Extensive roots to absorb water quickly over a large area/ deep roots to access underground water. To protect themselves, plants and animals have special features such as:

  • Armour (thorns, sharp spines, shells)
  • Poisons (like bees and poison ivy)
  • Amazing warning colours to scare off predators

So microorganisms known as extremophiles have adpated to live in extreme conditions like super hot volcanic vents and very salty lakes.

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Competition and Environmental Change

Organisms need things from their environment and from other organisms in order to survive and reproduce. Plants need light, space, water and minerals (nutrients) from the soil. Animals need space (territory), food, water and mates. Organisms compete with each other from their own and other species for the same resources. The population of red squirrels is decreasing as grey squirrels are competing against them. The environment in which plants and animals live changes all the time. The changes are caused by living factors/non-living such as:

Living Factors

  • A change in the occurance of infectious diseases
  • A change in the number of predators
  • A change in the number of prey or the availibility of food sources
  • A change in the number or types of competitors

Non-Living Factors

  • A change in average temperature
  • A change in average rainfall
  • A change in the level of air or water pollution
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Competition and Environmental Change: Part 2

Environmental changes can effect animals and plants in three different ways:

  • Population size increases: More prey=more food for predators. Predators survive and reproduce
  • Population size decreases: eg. number bees in UK ae falling rapidly. Experts think that this could be because, pestisides may be having a negative effect on bees, there is less food available, or there is more disease
  • Population distribution changes: This means a change in where the organism distribution of birds in Germany is changing because of the rise in average temperature
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Measuring Environmental Change

It is difficult to measure exactly how the environment is changing. They can be measured using living indicators and non- living indicators.

Living Indicators

  • Some organisms are very sensitive to changes in their environment, and can be studied to see the effect on human activities. These organisms are known as indicator species.
  • For example, air pollution can be monitored by looking at certain types of lichen that are sensitive to the amount of sulpher dioxide in the atmosphere. The number and type of litchen can indicate how clean the air is. Raw sewage released into a river can indicate the dissolved oxyen in water as the bacterial population of the water increases and uses up the oxygen. Invertebrate species have aapted to live in polluted conditions, such as maggots.

Non- Living Indicators

  • Scientists collect information on this. They use satellites to mesaure the temperature of the sea surface and the amount of snow and ice cover. Atmospheric temperature can be told by using automatic weather stations. They measure rainfall using rain gauges to calculate the average rainfall and dissolved oxygen meatures to measure water pollution. All these methods are very accurate and modern to give us accurate results.
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Pyramids Of Biomass

Tropic level = feeding level. There is less energy and less biomass everytime you move up a stage (trophice level) in the food chain. There are usually fewer organisms every time you move up one level too. This isn't always true though. A better way to think at the food chain is to think about biomass instead of number of organisms. You can use the information to construct a pyramid.

Each bar of biomass shows the mass of living material at that stage of the food chain (like how much they would all weigh if you put them together). So one fox would have a big biomass and hundreds of fleas would have little biomass. They are usually always pyramid shaped. All the information for the pyramid is given, you just need to construct it.

The bar along the bottom is always the producer (i.e plant). The next bar will be the primary consumer (the animal that eats the plant), then the secondary consumer (the animal that eats the primary consumer) and so on.

You also need to look at pyramids of biomass and explain what they show about the food chain. Just keep in mind how much each thing weighs in compariosn with eachother and you will probably have a good idea what the number of the object is. Biomass and energy are decreasing as you go up the levels, it's just that one tree can have a big biomass, and can fix a lot of the sun's energy using it's leaves.

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Energy Transfer and Decay

This is about why there is less energy and biomass each time you move up a trophic level. Energy from the sun is the source of energy for nearly all life on earth. Green plants and algae use a small percentage of the light energy from the sun to make food during photosynthesis. This energy is stored in the substances which make up cells of plants and algae, then works it's way through the food chain as animals eat them and each other.

Respiration supplies the energy for all life's processes including movement. Most of the energy is eventually lost to the surroundings as heat (especially for birds and mammals who need to maintain a constant temperature). Some of the material which makes up plants and animals is inedible (eg bone), so it doesn;t pass to the next stage of the food chain. Material and energy are also lost from the food chain in waste material. This expains why you have biomass pyramids. Most of the biomass is lost and so does not become biomass in the next level up. it also explains why you hardly ever get food chains with more than about five trophic levels. So much energy is lost at each stage that there is not enough left to support more organisms after 4 or 5 stages.

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Energy Transfer and Decay: Part 2

Living things are made out of materials they take from the world around them. Plants take in elements such as carbon, oxygen, hydrogen and nitrogen from the air and soil and these turn into complex compounds such as carbs, proteins that make up living organisms and then pass through the food chain. The elements are returned to the environment in waste products produced by organisms, or when the organisms die. These materials decay because they are broken down (digested) from microorganisms - that is how the elements are put back in the soil.

Microorganisms work best in warm, moist conditions, and break down faster when there is plenty of oxygen available. Compost bins are ideal conditions for this. All the important elements are recycled, returned to the soil, ready to be used by new plants and put into the food chain again. There is a constant cycle happening in a stable community as the materials taken out of the soil and used are balanced by those put back in.

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The Carbon Cycle

(see diagram)

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Different species look different, but even organisms of the same species will usually look a least slightly different. These differances are called the variation within a species. There are two dfferent types of variation: genetic variation and envirnomental variation.

All plants and animals have characteristics that are in some ways similar to their parents. This is because the characteristics are determined by the genes inherited from their parents. These genes are passed on in sex cells (gametes) which offspring develop from. Most animals and quite a lot of plants get some genes from the mother and some from the father. This combining of genes from two parents cause genetic variation- no two of the species are genetically identical (other than identical twins). Some characteristics are determined only by genes, such as eye colour, blood group and inherited disorders (eg haemophilia).

The environment that the organisms live and grow in also cause differences between members of the same species. This is called environmental variation. This covers a wide range of differences such as getting a suntan, getting yellow leaves, etc. Any difference that has been caused by the conditions something lives in.

Most characteristics (eg body weight, height, etc) are determined by a mixture of genetic and environmental variation factors. For example, the maximum height than an animal or plant grows can be determined by genes but whether it actually grows depends on it's environment.

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Genes, Chromosomes and DNA

  • Most cells in your body have a nucleus.
  • The nucleus contains your genetic material in the form of chromosomes.
  • The human cell nucleus contains 23 pairs of chromosomes. There are two no. 19 chromosomes, two no. 12s, two 3s etc.
  • Chromosomes carry genes. Different genes control the development of different characteristics, e.g hair colour.
  • A gene is a short length of the chromosome, which is quite a long length of DNA. There can be different versions of the same gene, which give different versions of a characteristic, like blue or brown eyes. The different versions of the same gene are called alleles instead of genes.
  • The DNA is coiled up to form the arms of a chromosome
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Sexual reproduction is where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent. In sexual reproduction, the mother and father produce gametes (eg sperm and egg cells in animals). In humans, each gamate contains 23 chromosones-half the chromosomes in a normal cell (instead of having two of each chromosomes, a gamete has just one of each). The egg and sperm cell then fuse together (fertilisation) to form a cell with the full number of chromosomes half from mum, half from dad. This is why the offspring inherits features from both parents.

Sexual reproduction involves the fusion of male and female gametes. Because there are 2 parents, the offsrping contain a mixture of their aprents' genes.

Asexual Reproduction produces genetically identical cells. An ordinary cell can make a new cell by dividing into two. The new cell has exactly the same genetic information (ie genes) as the parent cell- this is known as asexual reproduction. X shaped chromosomes have two identical halves, so the chromosone splits down the middle to form two identical ets of half chromosomes. A membrane forms around each set and the DNA replicates itself to form two identical cells with compete sets of x-shaped chromosomes. This is how all animals grow. Some organisms produce offspring using this method. In this method there is only one parent. There is no fusion of gametes, no mixing of chromosomes, and no genetic variation between parent and offspring. The offspring are genetically identical to the parent. They're clones.

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Theory of evolution: More than 3 billion years ago, life on earth began as simple organisms from which all the more complex organisms evolved.

Looking at the similarities and differences between organisms allows us to classify them into groups. Studying these helps us to understand how all living things are related (evolutionary relationships) and how they interact with each other (ecological relationships). Plants make their own food using photosynthesis and are fixed to the ground. Animals move about the place and can't make their own food. Microorganisms are different as bacteria is single celled.

Evolutionary Relationships

  • Species with similar characteristics often have similar genes because they share a recent common ancestor, so they are closely related. They often look alike and tend to live in a similar habitat. Genetically different species may look alike too such as dolphins and sharks. They have both adapted to living in the same environment, but they are from different ancestors. Evolutionary trees show common ancestors between organisms. The more recent the common ancestor, the more closely related the two species.
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Evolution: Part 2

Ecological Relationships

  • If we see organisms in the same environment with different characteristics, it suggests they may be competition. Differences between them in the same environmetn (eg dolphines swim in small groups, herrings swim in large groups) can show predator-prey relationships. (dolphins hunt herring).

Charles Darwin came up wih idea of natural selection. Individuals within a species show variation because of the differences in their genes. Individuals with certainc characteristics that make them better adapted to the environment have a better chance of survival and are more likely to brred successfully. So, the genes that are responsible for the useful characteristics are more likely to be passed on to the next generation.

Evolution can occur due to mutations. A mutation is a chance in an organism's DNA. Most of the time they have no effect, but sometimes they can be beneficial by producing a useful characteristic. This characteristic may give the organism a btter chance of surviving and reproducing. If so, it is more likely to be passed on to future generations by natural selection. Over time, it will accumulate in a population.

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Evolution: Part 3

Darwin's idea was very controversional at the time. First of all, it went against common religious beliefs about how life on Earth developed-it was the first explanation for our own exsistance without the need for God. Darwin couldn't give a good explanation for why these new, characteristics appeared or exactly how individual organisms passed on their beneficial characteristics to their offspring. But he didn't know anything about genes and mutations. There wasn't enough evidence to convince many scientists, as not many studies had been done at this time.

There were different scientific hypotheses about evolution around his time, such as Lamarck's. He argued that if a characteristics were used a lot by an organism then it would become more developed during it's lifetime. He believed that these characteristics would be passed on to the next generation.

Scientists can develop different hypotheses from similar observations. They do many experiments and find out the beliefs and influentional reasons towards each one then if there is enough evidence, like Darwin's theory, then the theory becomes an accepted hypothesis.

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