Year 11 Geographers first week back...

On to Battle for the biosphere- looking at ecosystems one of my favourite topics to teach at any level-

Got to watch I do not go on too much.....

So we started by defining key terms-
Biosphere, biodiversity, biome, ecosystem, latitude, etc. into their books with the terms having matched them up, a job well done with most students applying their key stage 3 learning on deserts, rainforests and the cold climates to their definitions, along with nice cross curricular links to biology too.

Then we looked at the world's major BIOMES (large scale ecosystems)



Then we looked at the factors affecting biome location-
First the 2 global ones-
Precipitation and temperature .
Temperature at a global scale is dictated by the LATITUDE of a place

The students were able to describe the general pattern and give valid reasons for the pattern.  The higher the latitude (distance from the equator) the lower the temperature will be because at the equator (lowest latitudes) the sun's rays and therefore insolation (heat) are concentrated over smaller area so are more intense creating warmer temperatures, as you increase the latitude (move further from the equator) the sun's rays dissipate and the same amount of rays are spread over a wider area, meaning places at high latitudes are colder.

Furthermore the low latitudes have the same exposure to the insolation from the sun through the year, whereas the poles (higher latitudes) have periods where, due to the Earth's tilt, they face away from the sun and therefore receive no insolation at all.

Then we looked at precipitation and how globally it is controlled by AIR PRESSURE patterns like so




Students noted that High pressure means no clouds are able to form, thus there is little rain and thus little vegetation, leading to hot and cold deserts at areas where High pressure dominates; horse latitudes (apx. 30 degrees north and south of the equator) and poles.  The opposite occurs at low pressure areas, as low pressure allows clouds to form and thus rain is common, meaning more vegetation is able to grow, areas like these are found at the equator (doldrums) and mid latitudes (UK).

We then looked at factors that affect biome location at a local scale-

Altitude-



Students determined that as altitude increased vegetation and temperature decreased as above, as you increase height by 100 metres the temperature drops by 1 degree.

This is why you get snow on the equator at the summit of mount Kenya, because it is higher in latitude than surrounding forests, which are expected at the equator due to the intense heat and high rainfall, due to low latitude and low pressure creating increased potential for photosynthesis.

Prevailing (dominant) wind-
We then looked at wind and ocean currents, establishing that wind coming across an expanse of water like an ocean, would increase the precipitation of a region and thus mean it would have increased vegetation- thus explaining the pattern in South America

The wind north of the equator comes into South America from the east (Atlantic ocean) full of moisture, creating the Amazon rainforest in the north east of the continent, by the time the wind has reached the Atacama desert in Chile it has run out of moisture meaning parts of the Atacama have had no rain for 400 years.  The Andes mountains cause any remaining moisture to be lost as the air loses moisture as it rises over the high mountains.

If wind comes across land it will be dry (carry little moisture) meaning deserts are likely to form, e.g. the Sahara desert exists as the wind reaching it has had to travel across the vast expanse of the Eurasian continental landmass.

Albedo-

We looked at the role the colour of land plays, white land reflects heat, meaning the ice worlds of the poles are further cooled by their colour, we discussed the change in land colour if that ice melts and that it would end up brown, which being darker would absorb more heat, creating warmer conditions.

Meanwhile the rainforests at the equator are dark green, already warm due to their location and their colour helps retain heat too.

This week we are going to become climate detectives and look at rainforests in a bit more detail.