Bio Paper 2

• In a community, each species depends on other species for things such as food, shelter, pollination and seed dispersal. This is called interdependence

  It means that any major change in the ecosystem can have far-reaching effects

  Stable communities are communities where all the species and environmental factors are in balance so the population sizes are roughly constant
• A change in the environment could be an increase or decrease in an abiotic factor. These changes affect the size of populations in a community, meaning they can also affect the population sizes of other organisms that depend on them

  A change in environment could be the introduction of a new biotic factor (eg. predator or pathogen). These changes affect the size of populations in a community, which can have a knock-on effect because of interdependence
• Structural Adaptations - features of an organism's body structure

  eg. artic animals have white fur so they're camouflaged against the snow, helping them avoid predators and sneak up on prey

  eg. animals that live in cold places have a thick layer of blubber and a low surface area to volume ratio to help them retain heat
• Behavioural Adaptations - ways the organisms behave.

  eg. many species migrate to warmer climates during the winter to avoid the problems of living in cold conditions
• Functional - things that go on inside an organism's body that can be related to reproduction and metabolism

  eg. desert animals conserve water by producing little sweat and small amounts of concentrated urine

  eg. brown bears hibernate over winter. They lower their metabolism which conserves energy, so they don't have to hunt when there's not much food about
• Extremophiles - an organism that lives in an extreme environment
• Food Chain:

  Producer -> Primary Consumer -> Secondary Consumer -> Tertiary Consumer
• Producers make their own food using energy from the sun. They make glucose by photosynthesis, some of which is used to make other biological molecules in the plant. These are the plant's biomass - which can be thought as energy stored in a plant.

  Energy is transferred through living organisms in an ecosystem when organisms eat other organisms
• Environmental changes cause the distribution of organisms to change.

  These environmental changes can be caused by seasonal factors, geographic factors or human interaction

  For example:

  • water availability
  • temperature
  • atmospheric gases composition
• The Water Cycle

  • energy from the sun makes water evaporate from land, sea and plants, turning it into water vapour
  • the water vapour is carried upwards as warm air rises
  • when it gets higher up it cools and condenses to form clouds
  • water falls from the clouds as precipitation onto land, where it provides fresh water for plants and animals
• Elements cycled back into the food chain

  • living things are made of materials they take from the world around them, these get passed up the food chain
  • these materials are returned to the environment in waste products, or when organisms die and decay
  • materials decay because they're broken down by microorganisms. This happens faster in warm, moist aerobic conditions, when microorganisms are more active
  • decay buts the stuff that plants need to grow back into the soil
  • in a stable community, the materials that are taken out of the soil and used by plants are balanced by those that are put back in
• The Carbon Cycle

  • CO2 is removed from the atmosphere by green plants and algae during photosynthesis
  • when plants and algae are eaten by animals, some carbon becomes part of the fats and proteins in their bodies. This carbon moves through the food chain
  • when the animals respire, some carbon is returned to the atmosphere as CO2
  • when plants and animals die, detritus feeders and microorganisms feed on their remains. When these organisms respire, CO2 is returned to the atmosphere
  • the burning of wood and fossil fuels releases CO2 back into the air
• Factors Affecting Decay

  Temperature - warmer temperatures increase decomposition as enzymes work faster

  Water Availability - faster in moist conditions because organisms involved need water to carry out biological processes

  Oxygen Availability - needed for organisms to respire and survive

  Number of Decay Organisms - the more microorganisms and detritus feeders, the faster decomposition
• Biogas is mainly made up of methane, which can be burned as a fuel

  Lots of different microorganisms produce biogas, they decay plant and animal organisms anaerobically. This type of decay produces methane gas

  Biogas is made in a fermenter called a digester or a generator, which need to be kept at a constant temperature to keep the microorganisms respiring
• Biogas Generators

  • Batch generators make biogas in small batches. They're manually loaded up with waste, which is left to digest, and the by-products are cleared away at the end of each session
  • Continuous generators make biogas all the time. Waste is continually fed in and biogas is produced at a steady rate. These are more suited to large-scale projects
• Biodiversity is the variety of different species of organisms within an ecosystem

  High biodiversity is important as different species depend on each other.

  For humans to survive, its important that a good level of biodiversity is maintained, however lots of human actions are reducing biodiversity
• • increasing population is putting more pressure on the environment as we're taking more resources
  • people are demanding a higher standard of living, so we use more raw materials and energy for the manufacturing process, meaning we're taking more resources from the environment quicker
  • many raw materials are being taken quicker than they can be replaced, meaning we'll run out
• We're producing more waste, which causes pollution. This reduces biodiversity

  • Water - sewage and toxic chemicals from industry can pollute lakes, rivers and oceans, affecting the plants and animals that rely on them for survival. The chemicals used on lands can also be washed into water
  • Land - we use toxic chemicals for farming, bury nuclear waste underground and dump household waste in landfills
  • Air - smoke and acidic gases released into the atmosphere can pollute the air
• The Greenhouse Effect

  • the temperature of the earth is a balance between the energy it gets form the sun and the energy it radiates back out into space
  • gases in the atmosphere naturally act as an insulating layer. They absorb most of the energy that would normally be radiated out into space, and re-radiate it in all directions, increasing the temperature of the earth
  • greenhouse gases help keep the energy in
  • an increase in greenhouse gases is causing the earth to gradually heat up
• Consequences Of Global Warming

  • the distribution of wild animals and plant species may change as temperature increases and amount of rainfall changes. Some may become more widely distributed and some less widely distributed
  • migration patterns may change
  • biodiversity could be reduced if some species are unable to survive a change in the climate, so become extinct
• Destroying Peat Bogs

  • Bogs are areas of land that are acidic and waterlogged. Plants that live in bogs don't fully decay when they die because there's not enough oxygen.
  • The partly-rotted plants gradually build up to form peat.
  • The carbon in the plants is stored in the peat instead of being released into the atmosphere
  • peat bogs are often drained so that the area can be used as farmland, or the peat is cut up and dried to use as fuel, or used as compost
  • carbon dioxide is released when its burnt as fuel
  • destroying peat bogs destroys habitats so reduces biodiversity
• Programmes To Protect Ecosystems And Biodiversity

  • Breeding programmes prevent endangered species from becoming extinct. Animals are bred in captivity to make sure the species survives if it dies out in the wild. Individuals can sometimes be released into the wild to boost or re-establish a population
  • Programmes to reintroduce hedgerows and field margins around fields on farms where only a single crop grows. Field margins are areas of land around the edges of fields where wildflowers and grasses are left to grow. Hedgerows and field margins provide a habitat for a wider variety of organisms
• Programmes To Protect Ecosystems And Biodiversity

  • Programmes to protect and regenerate rare habitats help to protect the species that live there. This preserves the ecosystem and biodiversity in the area
  • people are encouraged to recycle to reduce the amount of waste that gets dumped in landfill. This could reduce the amount of land taken over for landfill, leaving ecosystems in place
  • some governments have introduced regulations to reduce the level of deforestation taking place and the amount of carbon dioxide being released into the atmosphere by businesses
• Conflicting Pressures Affecting How Biodiversity Is Maintained

  • costs money, which may be prioritised for other things
  • may result in a loss of jobs which could affect the local economy if people move away with their family to find work
  • conflict between protecting biodiversity and food security, as farmers see certain organisms as pests, therefore kill them to protect crops and livestock, which results in biodiversity being affected
  • sometimes land with high biodiversity has to be used for development
• Trophic Levels

  • different stages of a food chain
  • consists of one or more organisms that perform a specific role in the food chain
  • named after their location in the food chain using numbers
• Trophic Level 1: Producers

  Trophic Level 2: Primary Consumers

  Trophic Level 3: Secondary Consumers

  Trophic Level 4: Tertiary Consumers
• Decomposers

  decompose any dead plant/animal material left in an environment by secreting enzymes that break down the dead stuff into small soluble food molecules. These then diffuse into the microorganisms
• Adrenaline

  brain detects fear or stress and sends nervous impulses to the adrenal glands, which responds by secreting adrenaline. It gets the body ready for flight or fight by triggering mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles. For example, adrenaline increases heart rate
• Thyroxine - regulates metabolism

  • basal metabolism rate - the speed at which chemical reactions in the body occur while the body is at rest
  • important for processes in the body, such as stimulating protein synthesis for growth and development
  • thyroxine is released in response to thyroid stimulating hormone (TSH), which is released from the pituitary gland
• Thyroxine - Negative Feedback

  a negative feedback system keeps the amount of thyroxine in the blood at the right level:

  • brain detects level of thyroxine in the blood is higher than normal
  • the secretion of TSH from the pituitary gland is inhibited
  • the amount of thyroxine released from the thyroid gland is reduced
  • level in the blood falls back to normal
• Auxin

  • plant hormone controlling the growth near the tips of shoots and roots
  • controls the growth of a plant in response to light (phototropism) and gravity (gravitropism/geotropism)
  • produced in the tips and moves backwards to stimulate the cell elongation process, which occurs in the cells just behind the tips
  • if the tip of a shoot is removed, no auxin is available and the shoot may stop growing
  • extra auxin promotes growth in the shoot but inhibits growth in the root
• Shoots grow towards light

  • when a shoot tip is exposed to light, more auxin accumulates on the side that's in the shade than the side that's in the light
  • this makes the cells grow faster on the shaded side, making the shoot grow towards the light
• Shoots grow away from gravity

  • when a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
  • this causes the lower side to grow faster, bending the shoot upwards
• Roots grow towards gravity

  • a root growing sideways will also have more auxin on it's lower side
  • in a root the extra auxin inhibits growth
  • this means the cells on top grow faster, and the root bends downwards
• Use Of Auxins - Killing Weeds

  • most weeds growing in fields of crops/on a lawn are broad-leaved, in contrast to grasses and cereals which have very narrow leaves
  • selective weedkillers have been developed using auxins, which only affect the broad-leaved plants
  • the weedkillers disrupt normal growth patterns, which soon kills them, but leave grass and crops untouched
• Use Of Auxins - Growing From Cuttings

  • normally, if you stick cuttings in the soil they won't grow
  • if you add rooting powder (which contains auxins), they will produce roots rapidly and start growing as new plants
  • this enables growers to produce lots of clones of a plant very quickly
• Use Of Auxins - Growing Cells In Tissue Culture

  • tissue culture can be used to grow clones of a plant from a few of it's cells
  • hormones such as auxins need to be added to the growth medium (along with nutrients) to stimulate cells to divide to form both roots and shoots
• Gibberellin (plant growth hormone) - stimulates seed germination, stem growth and flowering

  Ethene (gas produced by aging parts of a plant) - influences the growth of the plant by controlling cell division. Also stimulates enzymes that cause fruit to ripen
• Use Of Gibberellin - Controlling Dormancy

  • lots of seeds won't germinate until they've been through certain conditions. This is called dormancy
  • seeds can be treated with gibberellin to alter dormancy and make them germinate at times of the year that they wouldn't normally
  • also helps to make sure all the seeds in a batch germinate at the same time
• Use Of Gibberellin - Growling Larger Fruit

  • seedless varieties of fruit often do not grow as large as seeded fruit
  • if gibberellin is added to these fruits, they will grow larger to match the normal types