Biology by Bradford
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The subtopic in the middle and 13 tasks round it: label three diagrams, complete two tables, put a process in order and fill 65 gaps. Every box is standard level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
A population is a group of organisms of one living in the same area that normally . Separate populations are told apart by : members of one do not normally breed with members of another. All the interacting populations in an area, plants, animals, fungi and bacteria alike, make up a .
At first are plentiful and there are few predators or diseases, so numbers double again and again at a steady rate. Plotted on a scale against time, this early growth gives a . The S-shaped curve is an idealized : test it by counting yeast cells or duckweed fronds as they multiply.
The is the largest population an environment can support for a long time, set by limited resources such as food, water, nest sites or, for plants, light. As a population grows denser, competition for these, the risk of and the spread of pathogens all increase. These factors push numbers back towards the limit: . A flood or a hard frost kills a share whatever the density: a factor.
Number the steps in order.
Quadrats will not do for animals. Population size = M × N ÷ R (the Lincoln index): if 30 are marked and 6 of the 40 caught later carry a mark, the estimate is . It assumes no births, deaths or between the samples, and no lost marks.
Members of one species need the same resources, so when these run short they compete: competition. Robins defend feeding , and crowded seedlings shade each other out. Yet many cooperate: wolves hunt in packs to bring down prey bigger than themselves, emperor penguins through the Antarctic winter to save heat, and meerkats take turns as .
Counting every individual is rarely practical, so population size is estimated from samples, chosen so that every part of the area has an equal chance of being picked. The estimate always differs a little from the true size: the . For organisms, such as barnacles or buttercups, place quadrats at coordinates, count the individuals in each and scale the mean up to the whole area. The of the mean count shows how much counts vary between quadrats, and so how evenly the population is spread.
| Relationship | Example |
|---|---|
| a caterpillar eating oak leaves | |
| an owl catching and eating a vole | |
| a tick living on its deer , feeding on its blood | |
| the cholera bacterium invading the human gut and causing disease | |
| lions and hyenas hunting the same scarce prey |
In each pair both species gain: . The legume gets fixed ; the orchid gets and, as a seedling, sugars; the coral gets sugars made by . In return each partner gets sugars, shelter or CO₂.
Grey squirrels, brought to Britain from North America in the 1870s, digest acorns better than red squirrels, which had lived there since the end of the last Ice Age. In oak woods the greys gather more of the autumn food, so the reds lose out. This in gaining is what makes an introduced species : it spreads at the expense of the species.
| B present | B absent | Total | |
|---|---|---|---|
| A present | 4 (expected ) | 16 (expected ) | 20 |
| A absent | 21 (expected ) | 9 (expected ) | 30 |
| Total | 25 | 25 | 50 |
Two plant species, A and B, in 50 random quadrats. Expected = row total × column total ÷ 50. χ² = , with degree of freedom; that is above the critical value of 3.84 (p = 0.05), so the two occur together less often than chance predicts. Field like these suggest competition but cannot prove it; a laboratory experiment, or a field that takes one species away, can test it.
Black walnut trees release juglone into the soil, which stops many other plants germinating or growing nearby: this is . The soil fungus Penicillium secretes penicillin, an that kills nearby . In both, a chemical released into the environment deters .
Fur-trading records from Canada show snowshoe hares and lynx rising and falling in a cycle about years long. Lynx numbers peak a little the hares: more prey feeds more predators, which then cut the prey back. Control by predators from the level above is control; a limit set by food from the level below is control. Both act, but one is usually dominant.
1234A population is a group of organisms of one species living in the same area that normally interbreed. Separate populations are told apart by reproductive isolation: members of one do not normally breed with members of another. All the interacting populations in an area, plants, animals, fungi and bacteria alike, make up a community.
Counting every individual is rarely practical, so population size is estimated from samples, chosen so that every part of the area has an equal chance of being picked. The estimate always differs a little from the true size: the sampling error. For sessile organisms, such as barnacles or buttercups, place quadrats at random coordinates, count the individuals in each and scale the mean up to the whole area. The standard deviation of the mean count shows how much counts vary between quadrats, and so how evenly the population is spread.
Quadrats will not do for motile animals. Population size = M × N ÷ R (the Lincoln index): if 30 are marked and 6 of the 40 caught later carry a mark, the estimate is 200. It assumes no births, deaths or migration between the samples, and no lost marks.
At first resources are plentiful and there are few predators or diseases, so numbers double again and again at a steady rate. Plotted on a logarithmic scale against time, this early growth gives a straight line. The S-shaped curve is an idealized model: test it by counting yeast cells or duckweed fronds as they multiply.
The carrying capacity is the largest population an environment can support for a long time, set by limited resources such as food, water, nest sites or, for plants, light. As a population grows denser, competition for these, the risk of predation and the spread of pathogens all increase. These density-dependent factors push numbers back towards the limit: negative feedback. A flood or a hard frost kills a share whatever the density: a density-independent factor.
Members of one species need the same resources, so when these run short they compete: intraspecific competition. Robins defend feeding territories, and crowded seedlings shade each other out. Yet many cooperate: wolves hunt in packs to bring down prey bigger than themselves, emperor penguins huddle through the Antarctic winter to save heat, and meerkats take turns as sentries.
| Relationship | Example |
|---|---|
| Herbivory | a caterpillar eating oak leaves |
| Predation | an owl catching and eating a vole |
| Parasitism | a tick living on its deer host, feeding on its blood |
| Pathogenicity | the cholera bacterium invading the human gut and causing disease |
| Interspecific competition | lions and hyenas hunting the same scarce prey |
In each pair both species gain: mutualism. The legume gets fixed nitrogen; the orchid gets minerals and, as a seedling, sugars; the coral gets sugars made by photosynthesis. In return each partner gets sugars, shelter or CO₂.
Grey squirrels, brought to Britain from North America in the 1870s, digest acorns better than red squirrels, which had lived there since the end of the last Ice Age. In oak woods the greys gather more of the autumn food, so the reds lose out. This competitive advantage in gaining resources is what makes an introduced species invasive: it spreads at the expense of the endemic species.
| B present | B absent | Total | |
|---|---|---|---|
| A present | 4 (expected 10) | 16 (expected 10) | 20 |
| A absent | 21 (expected 15) | 9 (expected 15) | 30 |
| Total | 25 | 25 | 50 |
Two plant species, A and B, in 50 random quadrats. Expected = row total × column total ÷ 50. χ² = 12, with 1 degree of freedom; that is above the critical value of 3.84 (p = 0.05), so the two occur together less often than chance predicts. Field observations like these suggest competition but cannot prove it; a laboratory experiment, or a field manipulation that takes one species away, can test it.
Fur-trading records from Canada show snowshoe hares and lynx rising and falling in a cycle about 10 years long. Lynx numbers peak a little after the hares: more prey feeds more predators, which then cut the prey back. Control by predators from the level above is top-down control; a limit set by food from the level below is bottom-up control. Both act, but one is usually dominant.
Black walnut trees release juglone into the soil, which stops many other plants germinating or growing nearby: this is allelopathy. The soil fungus Penicillium secretes penicillin, an antibiotic that kills nearby bacteria. In both, a chemical released into the environment deters competitors.