MODULE B4- IT'S A GREEN WORLD

Population: All the organisms of one species in a habitat

Community: Different species in a habitat make this up.

ESTIMATE POPULATION SIZES BY SCALING UP FROM A SMALL SAMPLE AREA:

• A quadrat is a square frame enclosing a known area. You can study the smalle area within a quadrat and scale up your findings to make estimates for larger areas.
• Count up all the organisms in a 1 m^2 quadrat
• Multiply the number of organisms by the total area of the habitat

ESTIMATE POPULATION SIZES USING CAPTURE-RECAPTURE:

• Capture a smaple of the population and mark the animals in a harmless way
• Release them back and recapture another sample.
• Count how many of this sample are marked.
• Estimate using equation:     
  • population size = number in first sample x number in second sample / number in second sample previously marked.

1) The sample size affects the accuracy of the estimate:

2) When using the capture-recapture data you have to make these assumptions:

ECOSYSTEMS ARE SELF SUPPORTING:

• An ecosystem is all the organisms living in a particular area, as well as all the non-lving conditions.
• A habitat is just the place where an organism lives
• Ecosystems are SELF SUPPORTING- they contain everything they need to maintain themselves.
• Water, nutrients and essential elements like carbon all get recycled within the ecosystem.
• The ONLY THING that's needed from outside the ecosystem is an ENERGY SOURCE (SUN)

TRANSECTS ARE USED TO INVESTIGATE THE DISTRIBUTION OF ORGANISMS:

• DISTRIBUTION: Where organisms are found within a particular area.
• You can investigate distribution using lines called transects.
• To do a transect:
  • Mark out a line using a TAPE MEASURE.
  • Place quadrats next to each other all the way along the line
  • Count and record the organisms you find in the quadrats
• If it's difficult:
  • you can calculate the percentage cover, this means estimating the percentage area of the quadrat covered by a particular type of organism.
• You can plot the results of a transect in a kite diagram.

THE DISTRIBUTION OF ORGANISMS IS AFFECTED BY ABIOTIC FACTORS:

• Abiotic factors are all the non-living, physical factors in an environment- light, temperature, water, oxygen, salinity and soil quality.
• The distribution of organisms is affected by abiotic factors because:
  • Organisms are ADAPTED to live in certain PHYSICAL CONDITIONS. This means they're more likely to survive and reproduce in areas with these conditions.
  • Many organisms can only survive in the conditions they're adapted to.

CHANGES  IN ABIOTIC FACTORS CAN LEAD TO ZONATION:

• ZONATION: The gradual change in the distribution of species across a habitat.
• A gradual change in abiotic factors can lead to the zonation of organisms in a habitat

BIODIVERSITY IS A MEASURE OF THE VARIETY OF LIFE IN AN AREA- IT INCLUDES:

• The amount of variation between individuals of the same species in an area.
• The number of different species in an area.
• The number of different habitats in an area.

Biodiversity is important- ecosystems with a HIGH level of biodiversity are HEALTHIER than those without. This is because MORE DIVERSE ecosystems are better able to cope with CHANGES in the ENVIRONMENT.

NATURAL ECOSYSTEMS HAVE A HIGHER BIODIVERSITY THAN ARTIFICAL ONES:

• NATURAL ECOSYSTEMS: maintain themselves without any major interference from humans
• ARTIFICIAL ECOSYSTEMS: they are created and maintained by humans

NATIVE WOODLANDS Vs FORESTRY PLANTATIONS:

1) Variety of tree species-----One species of tree is planted for timber

2) Trees are different sizes and ages------Blocks of trees are planted at the same time

3) Variety of plant species------Fewer plant species because trees are densely planted

4) Variety of habitats-----Fewer habitats because there aren't enough plant species to create them.

5) Variety of animals species-----Fewer animal species because they aren't as many habitats.

LAKES Vs FISH FARMS:

1) Many different fish species-----One fish species is farmed for food.

2) Variety of plant species----Fewer plant species- fish food is added and the food waste can cause algal blooms- blooms blocks out sunlight, killing the plants.

3) Variety of animal species-----Fewer animal species- Predators are kept out and pests are killed. Less food and fewer habitats because of the lack of plants.

PHOTOSYNTHESIS IS A TWO STAGE PROCESS:

• Photosynthesis uses energy from the sun to change carbon dioxide and water into glucose and oxygen.
• It takes place in chloroplasts in plant cells- they contain pigments like chlorophyll that absorb light energy.
• 6CO2 + 6H2O ====  C6H1206 +6C02
• Photosynthesis actually happens in two main stages:
  • 1) Light energy is used to split water into oxygen gas and hydrogen ions.
  • 2) Carbon dioxide gas then combines with the hydrogen ions to make glucose and water.
• WATER ISN'T ONE OF THE OVERALL PRODUCTS OF PHOTOSYNTHESIS- it gets used up in the first stage than is made in the second stage.

GLUCOSE IS CONVERTED INTO OTHER SUBSTANCES:

1) FOR RESPIRATION:      Plants use some of the glucose for respiration. This releases energy so they can convert the rest of the glucose into various other useful substances.

2) MAKING CELL WALLS:    Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant.

3) STORED IN SEEDS:     Glucose is turned into LIPIDS for storing in seeds. E.g. sunflower seeds contains a lot of oil.

4) STORED AS STARCH:

• Glucose is turned into starch and stored in roots, stems and leaves- ready for use when photosynthesis is not taking place like at night.
• Starch is INSOLUBLE- makes it good for storing- it can't dissolve and it doesn't affect the water concentration inside cells.

5) MAKING PROTEINS:    Glucose is combined with nitrates to make amino acids, which are then made into proteins- used for growth and repair.

GREEK SCIENTISTS CONCLUDED THAT PLANTS GAIN MASS FROM SOIL MINERALS:

• Around 350BC Greek scientists studied plant growth. The observed that the only thing touching plants was soil.
• They said plants must grow and gain mass by taking in minerals from the soil.

VAN HELMONT DECIDED THAT PLANTS GAIN MASS BY TAKING IN WATER:

• In 1648 Helmont dried some soil, weighed it, and put it in a pot.
• He planted a willow tree weighing 2.2kg in the soil. He added rain water to the pot.
• 5 years later he removed the tree from the pot and it weighed 76.7kg- it gained a mass of 74.5kg.
• He dried the soil and weighed it- the mass had changed very little
• He concluded that because the weight of the soil changed so little, the tree must have gained mass from another source. He only added water to it must've gained weight through the water.

PRIESTLY'S EXPERIMENTS SHOWED THAT PLANTS PRODUCE OXYGEN:

• He placed a burning candle in a sealed container and observed that the flame went out after a short time
• He then placed a burning candle and a living plant in the container-the flame went out after a short time but after a few weeks the candle could be re-lit
• He decided that the burning candle used up something in the container. He decided that the living plant 'restored the air' so that candle could burn again.

ANOTHER EXPERIMENT THAT HE DID:

• He filled a sealed container with exhaled air, he put a mouse in the container and observed that it only survived for a few seconds.
• He filled another sealed container with exhaled air- he put a living plant and waited a few days. He put a mouse and it survived for a few minutes.
• He decided that the living plant restored the air
• He concluded that plants restore something to the air that burning and breathing take out.

THE OXYGEN PRODUCED IN PHOTOSYNTHESIS COMES FROM WATER:

• To find out where the oxygen came from they supplied plants with water containing an isotope of oxygen called oxygen 18.
• It was found that when the plants photosynthesised, they released oxygen 18
• This shows that oxygen came from the water that was supplied to the, not the CO2

THERE ARE 3 LIMITING FACTORS THAT CONTROL THE RATE OF PHOTOSYNTHESIS:

1) Not enough light slows down the ROP- If the light level is raised, ROP will increase but only up to a certain point. Beyond that, it won't make a difference because either temp. or co2 will be the limiting factor.

2) Too little carbon dioxide also slows down ROP- the amount of co2 will incease the ROP but after that light and temp becomes the limiting factor.

3) The temp has to be just right- as the temp increases so does ROP but if the temp is too high, the plants enzymes will be denatured and it will rapidly decrease.

DIFFUSION IS THE NET MOVEMENT OF PARTICLES FROM AN AREA OF HIGHER CONCENTRATION TO AN AREA OF LOWER CONCENTRATION

• They happen in liquids and gases- the indivudal particles in these substances are free to move about randomly.

CELL MEMBRANES:

• They hold the cell together but they let stuff in and out- only small molecules can diffuse through cell membranes (simple sugars, water or ions)
• Particles flow through the cell membrane from where there's a higher concentration to where there's a lower concentration.
• If there is a lot more particles on one side of the membrane then there's an overall movement from that side.
• THE RATE OF DIFFUSION DEPENDS ON:
  • Distance- substances diffuse more quickly when they haven't got far to move.
  • Concentration gradient- substances diffuse faster if there's a big difference in concentration.
  • Surface area- the more surface there is available for molecules to move across, the faster they can get from one side to the other.

LEAF STRUCTURE:

PLANTS CARRY OUT BOTH PHOTOSYNTHESIS AND RESPIRATION:

• Photosynthesis: carbon dioxide + water = glucose +oxygen (requires energy)
• Respiration: glucose + oxygen = carbon dioxide + water (energy released)
• Photosynthesis only happens during the day, but plants must respire all the time
• During the day, plants make more oxygen by photosynthesis than they use in respiration. So, in the daylight they release oxygen and take in CO2.
• At night, plants only respire- no light for photosynthesis.

PLANTS EXCHANGE GASES BY DIFFUSION

Photosynthesis: It uses up lots of carbon dioxide. This makes more carbon dioxide move into the leaf by diffusion. At the same time lots of oxygen is being made as a waste product. Some is used in respiration but the rest diffuses out of the leaf.

Respiration: There's no photosynthesis going on because of no light. Lots of CO2 is made in respiration and lots of oxygen is used up. Lots of CO2 in the leaf but not much O2. Now it's mainly CO2 diffusing out and oxygen diffusing in.

LEAVES ARE ADAPTED FOR EFFICIENT PHOTOSYNTHESIS:

• Leaves are broad, there's a large SA for gases to diffuse.
• Their thin- CO2 and water vapour diffuse a short distance to reach photosynthesising cells
• There are holes, stomata, lets in CO2 but releases O2. They allow water to escape (transpiration)
• Leaves have guard cells surrounding each stoma- controls when the stoma opens/closes- allows the guard cells to control gas exchange
• Air spaces in the spongy mesophyll layer- CO2 AND O2 moves betweeen the stomata and the photosynthesising cells. There's a large SA area for gas exchange.

LEAVES HAVE A NETWORK OF VASCULAR BUNDLES:

• They are the transported vessels, xylem and phloem.
• They deliver water and other nutrients to every part of the leaf, they take away the glucose produced by photosynthesis.
• They support the leaf structure.

LEAVES ARE ADAPTED TO ABSORB LIGHT:

• They are broad- the large SA are exposed to light
• Leaves contain chloroplasts which contains chlorophyll and other photosynthetic pigments to absorb light energy.
• Different pigments absorb different wavelengths of light.
• The cells that contain the most chloroplasts are arranged in the palisade layer (top of the leaf) to get the most light.
• The upper epidermis is transparent so that light can pass through it to the palisade layer.