National 4 / 5 Biology

Life on Earth

Use the following table as a checklist for your revision.

Remember to ask your teacher for help with anything you don’t understand.

Learning Outcomes/ Mandatory Course Key Content / Learned notes / Completed Practice Questions / Got help from my teacher
1. Biodiversity and the distribution of life.
a. Biotic, abiotic and human influences are all factors that affect biodiversity in an ecosystem.
b. Grazing and predation are biotic factors; pH and temperature are abiotic factors.
c. Biomes are the various regions of our planet as distinguished by their similar climate, fauna and flora.
Global distribution of biomes can be influenced by temperature and rainfall.
d. An ecosystem consists of all the organisms living in a particular area and the non-living components with which the organisms interact.
e. A niche is the role that an organism plays within a community. It includes the use it makes of the resources in its ecosystem and its interactions with other organisms in the community including competition, parasitism, predation, light, temperature and nutrient avavilability
2. Energy in ecosystems
a. At each level in a food chain 90% of energy is lost as heat, movement or undigested materials.
b. Definitions and comparisons of pyramids of biomass, enrgy and numbers.
c. Nitrogen in ecosystems. Animal and plant proteins are produced from nitrates. The roles of nitrifying, denitrifying, root nodule and free-fixing soil bacteria.
Decomposers convert proteins and nitrogenous wastes to ammonium and nitrate.
d. Competition in ecosystems. Interspecific competition is when individuals of different species compete for the same resource in an ecosystem. Intraspecific competition is when individuals of the same species compete for exactly the same resources.
3. Sampling techniques and measurement of abiotic and biotic factors.
a. Sampling plants and animals using quantatitive techniques including quadrats and pitfall traps.
b. Evaluation of limitations and sources of error in pitfall traps and quadrats.
c. Measuring abiotic factors
Learning Outcomes/ Mandatory Course Key Content / Learned notes / Completed Past Paper Quests / Got help from my teacher
4. Adaptation, natural selection and the evolution of species.
a. A mutation is a random change to genetic material. Mutations may be neutral, confer an advantage or a disadvantage. Mutations are spontaneous and are the only source of new alleles.
Environmental factors such as radiation and chemicals can increase rate of mutation.
b. Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.
c. Natural selection/survival of the fittest occurs when more offspring are produced than the environment can sustain. Only the best adapted individuals survive to reproduce, passing on the genes that confer the selective advantage.
d. Speciation occurs after a population becomes isolated and natural selection follows a different path due to different conditions/selection pressures.
5. Human impact on the environment
a. Increasing human populationrequires an increased food yield.
b. Fertilisers can leach into fresh water causing algal blooms. This leads to reduction in oxygen levels.
c. Pesticides sprayed onto crops can accumulate in the bodies of organisms over time. As they are passed along food chains, toxicity increases and can reach fatal levels.
d. Indicator species are species that by their presence or absence indicate environmental quality/levels of pollution.
e. Biological control and GM crops may be alternatives to mitigate the effects of intensive farming on the environment.

Biodiversity and the Distribution of Life

Plants and animals interact with each other and with their environment. You will study the feeding relationships between organisms, how the energy flows through food chains and how nutrients are cycled. This knowledge will help you predict how the environment might change over time, and how we as humans can manage those changes, and how we can conserve and protect plants and animals.

You need to be able to understand and apply the following terms and definitions:

Biomes – large areas of the Earth which have similar climatic conditions, particularly in terms of temperature and rainfall, and because of this have similar communities of flora (plants) and fauna (animals).

Biomes can be grouped into 5 main types: aquatic, deserts, forests, grasslands and tundra.

Ecosystem – a natural biological unit made up of living organisms and the non-living surroundings with which the organisms interact.

Examples of ecosystems include heather moorland, Caledonian forest, coral reefs, etc.

AbioticFactors – non-living factors that affect ecosystems. Examples include rainfall, temperature, soil pH, light intensity, etc.

Biotic Factors – living factors that affect ecosystems. Examples include food availability, grazing, predation, competition and disease.

Niche– the role that an organism plays within its community. It includes the use it makes of the resourcesavailable including light, temperature and nutrient availability, and its interactions with other organisms including competition, parasitism and predation.

Energy in Ecosystems

Energy Loss in Food Chains

In this food chain when the grass seeds are eaten by the vole, energy is transferred from the grass seeds to the vole. When the vole is eaten by the Barn owl energy is again transferred.

As energy flows through the food chain there is a loss of energy because:

  • Some parts of the body such as the cellulose in the cell walls of the grass seeds, and the bone and hair in the vole, have little nutritional value so may be left uneaten or are expelled as undigested materials from the body
  • The energy is used for moving about.
  • In the case of warm blooded animals, energy is used for keeping warm. As a result much of the energy is lost as heat.

In total about 90% of the energy taken in by an organism is used for heat, movement and indigestible materials and so is lost. This leaves only 10% to be built up into body parts that can be used by the next organism in the food chain.

Ecological Pyramids

A food chain can be represented quantitatively (with numbers) in the form of a pyramid of numbers, below is one for the previous food chain. From this graph we can see there are fewer Barn owls than voles; which makes sense because a Barn owl must eat several voles to get enough energy in order to survive.

The Barn owl food chain is a typical food chain with a large number of producers but decreasing numbers of consumers. However, if the producer was a tree for example, followed by insects, then the bottom bar would appear small as many organisms feed on one tree. In this instance apyramid of biomass is more useful as the tree is much larger. A pyramid of biomass shows the total dry mass of the organisms at each link in the food chain.

In some food chains both the pyramid of numbers and biomass show a smaller producer bar. This is because some producers can reproduce very quickly. In this case, a measurement of the total energy produced at each link in the food chain will be more accurate. When we represent this information in a pyramid of energy we alwaysget a true pyramid shape.

The following diagram compares the pyramids of number, biomass and energy for two different food chains. Note that it is only the pyramid of energy that is truly pyramid shaped in both examples

Competition

Habitats have limited amounts of the resources needed by living organisms. Organisms must compete with others in order to get enough of these resources to survive. If they are unsuccessful and cannot move to another habitat, they will die.

Animals

Some of the resources that animals compete for:

  • food
  • water
  • space
  • mates

Plants

Plants make their own food using photosynthesis, so they do not need to compete for food but they may compete for:

  • light
  • water
  • space
  • minerals

There are two types of competition:

Intraspecific Competition: This is when plants or animals of the same species compete for exactly the same resources, eg Barn owls living in the same area will compete for voles, or wheat plants growing together in a field compete for space.

Interspecific Competition: This is when plants or animals of different species compete for the same resources, eg red and grey squirrels compete for food, or oak trees and hazel trees growing in the same wood will compete for light.

The Nitrogen Cycle

Nitrogen is essential for the formation of many chemicals in nature including amino acids in proteins. The nitrogen cycle explains how nitrogen is recycled in the environment.

Approximately 78% of the air is nitrogen gas. Because nitrogen is so un-reactive, it cannot be used directly by plants to make protein. Only nitrates are useful to plants, so plants are dependent on other processes to convert nitrogen and other nitrogen containing compounds into nitrates in the soil.

Plants absorb nitrates from the soil and use these to build up proteins. The plant may be eaten by an animal, and it in turn is used to produce animal protein.

Urea and other waste material such as the dead bodies of plants and animals is broken down by decomposers. This results in nitrogen being returned to the soil as ammonia.

Ammonia is converted to nitrites and then to nitrates by nitrifying bacteria in the soil.

Nitrogen gas can also be converted to nitrate compounds by nitrogen-fixing bacteria. These bacteria can be found free-living in soil or in the root nodules of leguminous plants such as peas, beans and clover. The plant can use the nitrate to make protein.

In some conditions denitrifying bacteria in the soil break down nitrates and return nitrogen to the air. This is usually in waterlogged soil.

Sampling Techniques and Measurement of Abiotic and Biotic Factors

Sampling Techniques

If you are studying plants and animals in an ecosystem you may need to find ways of capturing and counting them in order to estimate the population size.. There are many different ways to do this depending on the animal or plant you are studying. These are known as sampling techniques.

A pitfall trap is used to collect animals that live on the soil surface and amongst leaf litter.

lid

pot

alcohol

Avoiding Errors When Using a Pitfall Trap

  • Several pitfall traps should be set up to give reliable results.
  • The opening of the trap should be disguised by a lid, eg leaves or bark so that trapped animals are not seen and eaten by predators.
  • A preservative liquid, eg alcohol is put in the bottom of the trap to humanely kill and preserve the animals.

It is unlikely that you would be able to count all of the plants and animals in an ecosystem because this would take too long. Instead, small samples which represent the whole ecosystem are taken

Plants are often sampled in this way using a quadrat. This is a square of a known area which is randomly placed on the site being studied. The plants inside the quadrat are identified and counted. From this information the estimate of the number of a certain plant can be calculated.

quadrat

sample site

plant

Avoiding errors when using a quadrat

  • Make the results more reliable by using a bigger number of quadrats.
  • Place the quadrats at random over the area being studied, don’t choose where to place it.
  • Make a rule to decide what to do with plants that fall partly in or out of the quadrat, eg more than half the plant in the quadrat counts, more than half out the quadrat doesn’t.

out

in

out in

in

out
Measurement of Abiotic Factors

It is useful to measure abiotic factors and various pieces of equipment can be used to do this. To make sure that your measurements are reliable the equipment must be used properly.

Abiotic
Factor / Equipment
Used / Sources
of
Error / Ways in Which Error is Minimised
Light Intensity / Light Meter / - standing in the way of the light and casting a shadow on the light meter
- light intensity may change throughout the day. / - don’t stand in front of the sensor.
- take readings at the same time of day and take several readings for reliability.
Soil Moisture / Moisture Meter / - probe not left long enough to monitor the moisture level.
- moisture left on probe from a previous measurement / - leave the probe in the soil for a few seconds before taking the reading.
- wipe the probe between each reading.
Temperature / Thermometer
(or temperature probe) / - thermometer not left in position long enough to monitor the temperature.
- temperature may change throughout the day. / - allow the thermometer to settle before taking the reading
- take readings at the same time of day and take several readings for reliability.
pH
(of soil or water) / pH probe
(or chemical test using indicator solution) / - probe not left long enough to monitor the moisture level.
- moisture left on probe from a previous measurement / - leave the probe in the sample for a few seconds before taking the reading.
- clean the probe between each reading.

Adaptation, Natural Selection and the Evolution of Species

Mutation

Changes to the genetic material are called mutations. Mutationsmay be a source of new alleles, (if you can’t remember the meaning of the term allele look back at yourVariation and Inheritancenotes in theMulticellular Organisms unit, or look it up in the glossary on the Biology web pages).

Mutations can be spontaneous (they just happen). They can also happen because of environmental factors such as:

  • Radiation, such as ultra-violet (UV) radiation in sunlight.
  • Chemicals, such as tar from cigarette smoke.

Mutations may be:

  • Neutral, ie have no effect. For example, the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene.
  • Disadvantageous, ie be harmful.For example, haemophilia is an inherited disorder that stops blood from clotting properly. It is caused by a mutated gene
  • Advantageous, ie be useful. For example, some rats have become resistant to warfarin (a rat poison). This is an advantage to the rat since it is no longer killed by warfarin. It is caused by a mutated gene.

Variation

Although all members of a species are similar to one another, eg a population of mice all have mice-like features, they are not identical to each other. This is because variation occurs within a species.

This variation makes it possible for a population to evolve over time in response to changing environmental conditions. Natural selectionis the process by which evolution occurs. Natural Selection

Imagine a breeding pair of mice arriving in a habitat where no other mice exist. In perfect conditions the pair could produce six offspring every two months. The offspring of mice become mature after only six weeks and so could go on to produce offspring of their own at the same rate. If all the mice survived and continued to breed the habitat would become overrun with mice. This does not happen because there is a struggle to survive and only a few mice will survive to reproduce.

Some mice will be:

  • poorly camouflaged or have slow reactions and be eaten by predators
  • poor at competing for food and so die of starvation
  • poor at competing for shelter or have thinner coats and so die of cold
  • killed by disease

Only the mice with the best characteristics for the habitat will survive to breed.This is known as survival of the fittest.

Mice are not genetically identical. They are produced by sexual reproduction which ensures they possess different combinations of genes from their parents. Important characteristics such as coat colour and thickness, speed and reactions, food finding ability, resistance to disease and aggressiveness will vary from mouse to mouse.

Only those mice with the best combinations of genes for the habitat will survive. This means that their gene combinations will be passed on to offspring. Mice with less useful combinations of genes will dies and so these genes are not passed on.

(The above example uses mice, but the same ideas can be applied to all species of plants and animals)

This process is known as natural selection and if it operates over millions of years it is thought that it can give rise to new species of plants and animals.

Speciation

A species is a group of organisms able to interbreed and produce fertile offspring.

As long as a population has the opportunity to interbreed and exchange genes, they remain one species. A population of one species can only evolve into more than one species if groups within the population become isolated from each other by barriers that prevent the two groups from inter breeding.

The diagram illustrates what could happen to populations of animals, which become separated. Once two groups are separated different mutations occur in each group. If the environments differ, different adaptations are favoured by natural selection. This leads to different characteristics evolving in each group as time passes. Eventually the groups become so different that if they come together again they are unable to interbreed and are now separate species.