Biology by Bradford
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The subtopic in the middle and eleven tasks round it: label three diagrams, complete three tables, put a process in order and fill 60 gaps. Every standard level statement has a box; the three boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Evaporation from the leaves the forest, and the water vapour is carried inland to fall again. Clear too much forest and this could fail, pushing the ecosystem past a ; how much forest is enough is still . A forest cut from 2000 km² to 1700 km² has changed by %.
| In primary succession | Early | Late |
|---|---|---|
| Size of plants | small and low-growing | |
| Primary production | high | |
| Species diversity | low | |
| Food webs | complex | |
| Nutrient cycling | slow, in thin soil |
Succession can be set off by a change in the environment or in biotic factors. The first colonists of bare ground, such as lichens, are .
1234Some ecosystems, such as the Namib Desert, have kept much the same character for tens of millions of years: natural ecosystems tend to be . Staying that way takes a steady supply of , the of nutrients, enough for populations to adapt, and a climate that stays within the of the species living there.
Number the steps in order.
Nutrient enrichment like this is . As the decomposers multiply, the water's rises.
| Pollutant | Why it lasts or builds up | Harm to wildlife |
|---|---|---|
| DDT | fat-soluble, so it is stored in fatty tissue rather than | thin eggshells in birds of prey |
| Mercury | taken in faster than it is lost, so levels are highest in top | damage to the nervous system |
| Macroplastic | , so it lasts for decades or longer | animals become or swallow it |
| Microplastic | fragments smaller than mm | eaten by plankton and filter feeders, passing up food chains |
A toxin reaching a higher concentration at each step up a food chain is .
In given conditions, succession tends to lead to one particular final community: the . People can stop it short, which is : by farm livestock stops grassland turning into woodland, and draining prevents their natural development. In some ecosystems there is no single end point, and communities replace one another in a repeating cycle, , as when old heather plants die back and the gap is colonised again.
A is a small model ecosystem for testing how one variable affects its stability. A sealed glass vessel is better than an open tank: still passes through the glass, but no can enter or leave. Aquatic and systems tend to work better than terrestrial ones.
Sea otters eat the sea urchins that would otherwise graze a kelp forest bare, so the otter is a : its effect on the community is far bigger than its numbers. Remove such a species and the ecosystem may . Rewilding restores natural processes by bringing back , as wolves were returned to Yellowstone, by reconnecting habitats over large areas, and by keeping human low, as at Hinewai Reserve in New Zealand, where native forest is regrowing through introduced .
Harvesting from a wild population can go on indefinitely only if the rate of harvesting is than the rate of . A fish stock such as North Sea cod is assessed from survey catches, the ages of the fish landed and the catch per unit , and scientists advise catch . Where Brazil nuts are gathered, counting the shows whether enough new trees are growing up to replace the old ones.
| Factor | Why it threatens sustainability |
|---|---|
| Soil erosion | bare, ploughed is lost to wind and rain faster than it forms |
| Leaching | rain washes soluble below the roots and into rivers |
| Fertilizers and other inputs | phosphate rock is , and nitrogen fertilizer takes a lot of energy to make |
| Agrochemicals | kill species they were not aimed at and pollute water |
| Carbon footprint | machinery, fertilizer making and transport release |
Some ecosystems, such as the Namib Desert, have kept much the same character for tens of millions of years: natural ecosystems tend to be stable. Staying that way takes a steady supply of energy, the recycling of nutrients, enough genetic diversity for populations to adapt, and a climate that stays within the tolerance of the species living there.
Evaporation from the leaves cools the forest, and the water vapour is carried inland to fall again. Clear too much forest and this could fail, pushing the ecosystem past a tipping point; how much forest is enough is still uncertain. A forest cut from 2000 km² to 1700 km² has changed by −15 %.
A mesocosm is a small model ecosystem for testing how one variable affects its stability. A sealed glass vessel is better than an open tank: energy still passes through the glass, but no matter can enter or leave. Aquatic and microbial systems tend to work better than terrestrial ones.
Sea otters eat the sea urchins that would otherwise graze a kelp forest bare, so the otter is a keystone species: its effect on the community is far bigger than its numbers. Remove such a species and the ecosystem may collapse. Rewilding restores natural processes by bringing back apex predators, as wolves were returned to Yellowstone, by reconnecting habitats over large areas, and by keeping human impact low, as at Hinewai Reserve in New Zealand, where native forest is regrowing through introduced gorse.
Harvesting from a wild population can go on indefinitely only if the rate of harvesting is lower than the rate of replacement. A fish stock such as North Sea cod is assessed from survey catches, the ages of the fish landed and the catch per unit effort, and scientists advise catch quotas. Where Brazil nuts are gathered, counting the seedlings shows whether enough new trees are growing up to replace the old ones.
| Factor | Why it threatens sustainability |
|---|---|
| Soil erosion | bare, ploughed topsoil is lost to wind and rain faster than it forms |
| Leaching | rain washes soluble nutrients below the roots and into rivers |
| Fertilizers and other inputs | phosphate rock is finite, and nitrogen fertilizer takes a lot of energy to make |
| Agrochemicals | pesticides kill species they were not aimed at and pollute water |
| Carbon footprint | machinery, fertilizer making and transport release greenhouse gases |
Nutrient enrichment like this is eutrophication. As the decomposers multiply, the water's biochemical oxygen demand rises.
| Pollutant | Why it lasts or builds up | Harm to wildlife |
|---|---|---|
| DDT | fat-soluble, so it is stored in fatty tissue rather than excreted | thin eggshells in birds of prey |
| Mercury | taken in faster than it is lost, so levels are highest in top predators | damage to the nervous system |
| Macroplastic | non-biodegradable, so it lasts for decades or longer | animals become entangled or swallow it |
| Microplastic | fragments smaller than 5 mm | eaten by plankton and filter feeders, passing up food chains |
A toxin reaching a higher concentration at each step up a food chain is biomagnification.
| In primary succession | Early | Late |
|---|---|---|
| Size of plants | small and low-growing | large |
| Primary production | low | high |
| Species diversity | low | high |
| Food webs | simple | complex |
| Nutrient cycling | slow, in thin soil | fast |
Succession can be set off by a change in the abiotic environment or in biotic factors. The first colonists of bare ground, such as lichens, are pioneer species.
In given conditions, succession tends to lead to one particular final community: the climax community. People can stop it short, which is arrested succession: grazing by farm livestock stops grassland turning into woodland, and draining wetlands prevents their natural development. In some ecosystems there is no single end point, and communities replace one another in a repeating cycle, cyclical succession, as when old heather plants die back and the gap is colonised again.