B4 It's a green world

Ecology in the local environment

Distribution of organisms

> Take a garden for example: it is a habitat to the animals and plants living in it and they all make up the community. The number of there community is called population (a bit like human society) > A natural eco system has a large veriety of life living there - it had good biodiversity. For example a native woodland and lakes. However an artificial ecosystem (created by humans) will have a worse biodiversity. For example a forestry plantation or fish farms                                    > In an artificial ecosystem humans delibratly protect a certain species and remove any other species that would lower the yield                                                                                           > The distrubution of organisms can be mapped using a transect line (which can show zonation - changes in abiotic factors) - a long length of string is laid across an area and at regular intervals, the organisms in the 'quadrat' are counted.                                                                               > Food chains and webs show interdependents, with energy transfer. The exchange of gases in photosysthesis and respiration ensure an overall balance

Population size

> Population size is estimated by using data from samples (bigger samples are more accurate)     > Capture-recapture assumes: no deaths, identical sampling and markings not affect survival   

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Chemistry of photosynthesis

During photosynthesis, light splits oxygen gas and hydrogen ions and then carbon dioxide combines with hydrogen ions producing  glucose and water.

Simple sugars in photosynthesis: release energy; convert into cellulose to make cells; convert into proteins for growth and repair; and convert into starch, fats and oils for storage. Starch is used for storage because it is insoluable and doesn't move unlike glucose which affect water concentration and causes osmosis. 

History of photosynthesis

Greek scientists believe plants took minerals from soil but Van Helmont concluded the uptake depended on something else. Priestley showed plants produce oxygen by keeping a rat alive

The rate of photosynthesis

The rate of photosynthesis increases with carbon dioxide, light and a higher temperature. However, during the night the plant will respire so it is still getting energy.

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Leaf structure [picture]

Leaf structure


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Leaf structure [writing]

Leave structure

  • Outer epidermis is transparent for light to enter into the cells
  • Upper palisade contains most chloroplast because they recieve the most light
  • Spongy mesophyll cells are loosely spaced for osmosis to take place
  • Arrangement of mesophyll cells creates a large surface area for more gases to enter and exit

Leaf adaptions for photosynthesis

  • Broad - large surface area for as much light as possible
  • Thin - so gases can diffuse easily and light can get to all cells
  • Contain chlorophyll and other pigments to use light from all the spectrum
  • Network of vascular bundles (veins) for support and transport of chemicals
  • Specialised guard cells control the opening and closing of the stomata which will regulate the flow of carbon dioxide and oxygen.

By having many pigments, plants can maximise the use of the Sun's light energy because each pigment will absorb different wavelengths of light from the Sun

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Diffusion and osmosis


Definition: the net movement of particles in a gas or liquid from an area of high concentration to low concentration resulting in the random movement of the particles. This explains how water, carbon dioxide and oxygen can enter the leaves. The rate of osmosis can increase with:a shorter distance for molecules to travel; steeper concentration gradient; and greater surface area.


This is a type of diffusion depending on a partially-permeable membrane allowingthe passage of water molecules but not large glucose molecules. Osmosis is a consequence of random movement of water molecules which is not restricted by the partially permeable membrane. 

Water in cells

When water enters into plant cells, the turgor pressure increases which pushes on cell wall and making the cell ridgid (turgid). If too much water leaves the cell, it looses pressure and the cell wilts (flaccid). Animal cells also change pressure but because they lack supporting cells, when there is too much water, the cell bursts (lysis)

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Transport in plants

Xylem and phloem cells

They are made up of specialised plant cells and both tissues are continuous from the root through the stem into the leaf. They both form vascular bundles in broad leaved plants. Xylem cells carry water and minerals from roots to leaves. Phloem cells carry food substances such as sugars up and down stems (translocation)


This is the evaporation and diffusion of water from inside leaves - it helps create a continous flow of water from the roots to the leaves.

  • The rates is increases by: light intensity which opens the stomata; increasing temerature which increases evaporation; increasing air movement which increases evaporation; and deacreasing humidity which allows more water to evaporated into the atomsphere.
  • Structure of a leaf adapted to reduce water loss - guard cells change size depending on stomatal openings. They contain chloroplast so photosynthesis will produce sugars and increase the turgor pressure. Bceuase of the different thickness of walls, guard cells curve, opening the stomata
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Plants need minerals

Uses of minerals

  • Nitrates make proteins for cell growth, nitrogen produces amino acids. Lack of causes poor growth and yellow leaves
  • Phosphates are involved in respiration and growth, phosphorous makes DNA and membranes. Lack of causes poor root growth and discoloured leaves
  • Potassium is used in respiration and photosynthesis, it helps enzyme action. Lack of causes poor flower and root growth and discoloured leaves
  • Magnesium is involved in photosynthesis and is used to make chlorophyll. Lack of causes yellow leaves

Mineral uptake

Minerals are usually present in low soil concentrations therefore minerals are taken up by roots through active transport. Active transport enables minerals to enter high concentrations against the concentration gradient

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Detritivores feed on dead and decaying material (e.g. maggots) which increases the rate of decay because the surface area increases. The rate of decay can also increase with temperature, oxygen and water. Temperature and oxygen will increase the rate of respiration, and water will allow material to be digested and absorbed more efficiently.

Saprophyte is a fungus and it feeds on dead and decaying material. It will produce an enzyme to digest food outside their cells and reabsorb the simple soluble substance - extracellular digestion

Food preservation

These will reduce the rate of decay

  • Canning kills bacteria in a sealed vacuum
  • Cooling slows down growth and reproduction and freezing kills the bacteria 
  • Drying food takes away water so bacteria cannot feed and grow
  • Adding salt or sugar will kill bacteria because of the high osmotic concentration will remove water
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Pesticides vs Organic farming

Pestcides help get a better crop yield but... They can enter the food chain and cause harm to predators; they can harm other organisms in the habitat; and some take a long time to break down. Organic farming doesnt't use pesticides or artificial fertilisers... instead it uses animal manure and compost. It also uses crop rotation to avoid building up soil pests; nitrogen fixing crops; and varying seed planting times. 

Biological control

This used living organisms to control pests which avoids using pesticides. However many attempts have caused other problems like a rapid increase in their population and becoming a pest

Hydroponics and intensive farming 

This uses artificial pesticides and fertilisers and is very efficient for large crop yields but it raises concerns about animal cruelty. Plants can be grown without soil because it uses recycled water containing minerals ina glasshouse. This means it has a better control of mineral levels and disease. Efficiency is improved because of energy transfer in food chains removing competition

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