Chapter 1 Reading Guide and Notes
Science 10
1.1 Capturing Energy from the Sun
Define the following terms:
Ecosystem :organisms (all living things) and the environment with which they interact (non-living)
Producers: green plants and some bacteria that can produce food (chemical energy) from sunlight. They make up the first trophic level in ecosystems.
primary consumers :organisms that directly consume producers. They make up the second trophic level in ecosystems. (herbivores)
secondary consumers: organisms that directly consume primary consumers. They make up the third trophic level in ecosystems. (carnivores and omnivores)
What is the source of energy for an ecosystem?
Sunlight or solar energy
How does solar energy become part of an ecosystem?
It gets converted to chemical (food) energy by producers.
Explain why understanding energy flow in an ecosystem is important.
No living thing can survive without a source of energy.
Explain why more energy is found in the producers of an ecosystem than the consumers.
Plants are getting the most direct energy input. At each trophic level, a large amount of energy is lost through growth and metabolism, especially as heat.
1.2 Feeding Levels
What is a trophic level?
A trophic level can be thought of as a feeding level.
What percentage of energy that enters a trophic level remains stored and becomes available food for the next level?__10%____
Examine Figure 1.5. What percentage of energy at each trophic level is lost as thermal energy? ____30%__
What percentage goes to decomposers?___ 60%____
Define these terms:
Detritivores: organisms that consume dead organisms and their waste.
Decomposers: the smallest detritivores (bacteria and fungi) which break down and consume the last remaining energy from a food chain
Explain what information is shown in a pyramid of numbers.
It’s a graph that shows the number (count) of organisms at each trophic level of an ecosystem. It usually has the appearance of a pyramid.
How does size of organisms generally change as you move up through the trophic levels shown in a pyramid of numbers?
Although numbers go from high to low, the size of the organisms increase, because consumers generally have to be larger than their food.
What is a reversed pyramid of numbers and why does it occur?
It is a pyramid showing a small first tropic level. It occurs when the producers are very large organisms that produce a lot of food, such as trees.
Define biomass:
It is the dry mass of living things (ignores the water, which has no food value) For example, think of an Egyptian mummy, which is ahuman reduced to only biomass.
How is a pyramid of biomass different from a pyramid of numbers?
It only shows mass, so you cannot determine how many organisms are at each level.
Explain why the first two trophic levels in an ocean ecosystem create an inverted pyramid of biomass.
The green plankton (producers) grow so quickly that they can double their numbers in a few days, so less biomass is present at any one time. The zooplankton (consumers) grow more slowly and live longer, so there are more of them present.
Explain what information is shown in a pyramid of energy flow.
It’s a graph that shows ONLY the energy flowing from one level to the next.
Explain why an inverted pyramid of energy flow cannot occur?
There must be less energy at each level, because energy is lost from all living things in their life processes (moving, growing, reproducing, metabolism)
Why do food chains rarely have more than four links?
By the time you reach a fourth trophic level, there is very little food energy left.
1.3 Populations
Using Figure 1.15, give an example of a population size being decreased when the food supply is decreased.
Sea lions and seal populations will decrease if there are fewer fish.
Using Figure 1.15, give an example of a population size being increased when fewer consumers are present to eat it.
Sea urchin populations will increase when the sea otter population decreases.
Define carrying capacity.
It is the largest population of a particular species that an ecosystem can support.
Summarize the four factors that determine carrying capacity:
Materials and energy: there is a limited amount of matter (nutrients) and energy (all energy comes from the available sunlight) available in an ecosystem
Food chains: the food supply available to a population depends on the biomass available to its trophic level
Competition: organisms compete for their needs, such as food and mates
Density: all species are limited by the number of organisms that can share a space
Define:
intraspecific competition: competition within the same species (wolves compete and fight over territory)
interspecific competition: competition between two different species (deer and rabbits eat the same types of plants)
Define the two types of factors that control population growth and give examples of each.
density dependent factors: (due to overcrowding) diseases, aggression, stress, neglect of offspring
density independent factors: (regardless of numbers) these are due to drastic changes in the ecosystem, such as drought, flood, forest fire
1.4 Feeding People
Define productivity: the average amount of new plant biomass each year
What is needed for plants to grow? (list as many factors as you can)
water
carbon dioxide
sunlight
nutrients (nitrogen, phosphorus and potassium are the main three)
temperature
How is it sometimes possible to turn deserts into productive farmland?
Irrigation (adding water to the soil) and fertilization (adding nutrients) make it possible for crops to grow.
Why is it not always possible to turn tropical forests into productive farmland? (List as many problems as you can)
Non-native crops don’t always grow well in warm, wet environments. Pests and diseases from the surrounding forest can affect them.
Changes to the native forest changes the ecosystem, which affects the soil and water.
What other problems may result from turning tropical forests into productive farmland? (List as many problems as you can)
The forest litter (detritus) protects the soil and decomposers recycle the nutrients, so when the dead material is removed, the soil is less fertile.
The detritus and trees prevent rains from washing away the soil and its nutrients, so the soil becomes less fertile or erodes when exposed.
How is the average Canadian’s food intake different from many people around the world?
We eat more food energy (calories or joules) and a higher proportion of our food is meat.
What is the most likely result of the dietary difference on the amount of farmland needed to produce our food supply?
Meat eaters need more farmland to produce the same food energy. (Trophic levels – animals lose a lot of the food energy to their life processes.)
Define monoculture.
It is agriculture that produces a single variety of crop, such as a cornfield.
Explain the difference in food chains of natural ecosystems compared to agricultural systems.
Natural ecosystems are far more complex.
How does nature keep insect pests under control?
The populations of plants that they eat are spread out, so the insects cannot grow quickly in a small area and have to make more effort to find food.
What are pesticides?
They are chemicals that kill insects and other pests.
What factors have reduced the death rate and allowed the human population to grow?
Improved health care (medical)
Increased food supply (agriculture)
Sanitation (sewer systems) prevent disease by removing waste)
What human demands, other than food, take up some of Earth’s biological productivity?
Consumer products – cotton for clothing, wood for building, minerals for metals
List other human activities that reduce plant biomass in natural ecosystems.
Burn forests
Drain wetlands
pave areas for roads
build golf courses
dam rivers