Chapter 2: Change and Stability in Ecosystems
Lesson 2.1- Cycling of Matter in Ecosystems
Ecosystems are always changing even if they don’t appear to be. They remain the same overall by
changing constantly. This is called equilibrium (balance).
Sometimes equilibrium is lost. Often it is because of humans. Ex: clearcutting.
Ecosystems can recover, but it takes many years or centuries.
Organic substances- always contain atoms of carbon and hydrogen. Ex: proteins, sugars, fats.
Inorganic substances- do not contain a combination of carbon and hydrogen atoms. Ex: carbon
dioxide (CO2), water (H2O).
The materials on the earth that are used to make living things must be recycled. For example, every
carbon atom is recycled over and over again.
Food is organic, and digestion breaks down large molecules into smaller ones that cells use to build
new structures in the body.
Decay also works to recycle matter in dead bodies and feces.
Lesson 2.2- Pesticides
Pesticides- are chemical designed to kill pests
Pest is an organism that people consider harmful or inconvenient
Pesticides are usually used to protect species that are beneficial to humans, or kill species that are
harmful.
History of pesticides:
1. The first pesticides were natural elements that turned out to be harmful to humans too! Ex:
Lead, Mercury, arsenic.
2. The next pesticides were natural chemicals produced by plants.
3. Chemical pesticides were produced in laboratories. Some are very deadly and stick around a
long time in both the environment, and in organisms. Ex: DDT
4. Modern chemical pesticides are not stored in fat tissues (good), break down quickly in the
soil (good or bad), and can be dangerous to many different living things (bad).
Bioamplification - The process where toxins
keep building up in organisms as you go up
from one trophic level to the next; the
concentrations increase.
Chemical pesticides are not good forever.
Some pests are naturally resistant and survive
to make babies that are also resistant.
Eventually, these “superbugs” will take over.
Bioamplification
Lesson 2.5- The Carbon Cycle

Organic - substances that always contain atoms of carbon and hydrogen and often contain atoms of
oxygen and nitrogen. Ex. Proteins, sugars ect.

Inorganic - matter that doesn’t contain a combination of carbon and hydrogen. Ex. Water, carbon
dioxide etc.

Carbon is the key element for living things.

It is found in both the atmosphere and oceans as carbon dioxide (CO2).

During photosynthesis, plants use carbon dioxide with light and water to make sugar:
6CO2
+
Carbon dioxide +

6H2O
water
+
+
Light
light energy
→

C6H12O6
+
sugar (glucose) +
6O2
oxygen
Cellular respiration releases the carbon dioxide back to the atmosphere:
C6H12O6
glucose
+
+
6O2
oxygen
→

6CO2
carbon dioxide
+
+
6H2O
water

The carbon cycle refers to the cycling of carbon between the processes of photosynthesis and
cellular respiration.

Some carbon gets trapped in rocks and fossil fuels before being released to the atmosphere.

Humans are messing with the carbon cycle by releasing carbon stored in fossil fuels and by cutting
forests that take carbon from the atmosphere and store it. These 2 activities lead to global warming.
Lesson 2.6- The Nitrogen Cycle
Nitrogen is needed for DNA and for cells to make protein.
The movement of nitrogen through the ecosystem is called nitrogen cycle.
79% of earth’s atmosphere is nitrogen gas (N2), but organisms need it to be in the form of nitrate
(NO3-) to use it.
The process of changing nitrogen to nitrates is called nitrogen fixation. Lightning or soil bacteria
can cause nitrogen fixation to happen. Some of this bacteria is even attached to the roots of some
kinds of plants.
When decomposers break down dead plants and animals, nitrates are turned into ammonia (NH3)
and bacteria turn the ammonia into nitrates.
Some nitrates are broken down into nitrites and then back to nitrogen gas by bacteria in a process
called denitrification. Denitrification does NOT require oxygen.
Copy nitrogen cycle from p.66 of textbook!!
Lesson 2.7- Agriculture and Nutrient Cycles
When crops are harvested, valuable nutrients like nitrogen and phosphorus are removed from the
site. Fertilizers are materials used to replace the nutrients to the soil.
Too much fertilizer can be harmful, because high levels of nitrates can increase the acidity in the
soil to levels that are dangerous to organisms in the soil.
When fertilizers get into streams and lakes, they add to the nutrients in the water. If nutrient levels
get too high, they can create algal blooms. Algal blooms are large growths of algae. They cause the
levels of oxygen in the water to drop.
Lesson 3.3- Soil and It’s Formation
The quality and amount of soil determines the health of plants and affects the biodiversity of the
ecosystem.
Most soils are made up of the following layers from top to bottom:
Litter: - partly decomposed leaves and grass.
Topsoil:
- small pieces of rock mixed with humus (decaying plant and
animal matter)
- This layer is usually dark because of the humus, which is
black.
- There are usually a lot of nutrients in this layer because of
the humus.
Subsoil: - more larger stones, and less humus than the topsoil
Bedrock: - mostly solid rock. It marks the bottom of the soil.
Litter
Topsoil
Subsoil
Bedrock
Acid rain can increase the acidity of the soil, which causes nutrients to mix with water and drain out
of the soil.