3B2 Cycling of Matter and Energy

Question 1

What is the primary source of energy for most ecosystems?

Answer 1

The Sun

Solar energy is captured by producers through photosynthesis, converting light energy into chemical energy stored in organic molecules.

Question 2

Define:

energy transfer in an ecosystem

Answer 2

The movement of energy through producers, consumers, and decomposers.

Energy flows one way in ecosystems, starting from the sun to producers, then passing through trophic levels, and finally reaching decomposers that break down organic matter.

Question 3

Describe how energy flows in a food chain.

Answer 3

Sun → Producers → Consumers → Decomposers.

Each step represents a trophic level, with energy decreasing as it moves up the chain.

Question 4

True or False:

Energy cycles in an ecosystem just like matter.

Answer 4

False

Energy flows in one direction and is eventually lost as heat, while matter is continuously recycled through biogeochemical cycles.

Question 5

List the three main trophic levels in an ecosystem.

Answer 5

1. Producers (Autotrophs)
2. Consumers (Heterotrophs)
3. Decomposers

These trophic levels structure the energy flow in ecosystems, ensuring that nutrients cycle efficiently.

Question 6

Fill in the blank:

A/an ________ is an organism that makes its own food using sunlight.

Answer 6

producer

Producers (plants, algae) use photosynthesis to create energy-rich molecules.

Question 7

Why do energy transfers between trophic levels lose efficiency?

Answer 7

Energy is lost as heat through metabolism, respiration, and movement.

The 10% Rule states that only ~10% of energy is transferred to the next trophic level, while 90% is lost as heat and waste.

Question 8

Define:

primary consumers

Answer 8

Herbivores that feed directly on producers.

Examples include deer, rabbits, and grasshoppers, which eat plants to obtain energy.

Question 9

List three examples of primary consumers.

Answer 9

1. Deer
2. Caterpillars
3. Rabbits

These herbivores rely directly on plants for sustenance.

Question 10

What do you call organisms that eat primary consumers?

Answer 10

Secondary consumers

Secondary consumers can be carnivores (meat-eaters) or omnivores (eat both plants and animals), such as snakes and foxes.

Question 11

Define:

tertiary consumers

Answer 11

Predators that consume secondary consumers.

Examples include hawks, sharks, and large carnivores that are at higher trophic levels.

Question 12

What is an apex predator?

Answer 12

A top predator with no natural predators.

Examples include lions, orcas, and bald eagles, which regulate populations of lower trophic levels.

Question 13

Fill in the blank:

The process by which decomposers break down organic material is ________.

Answer 13

decomposition

Decomposition is essential for nutrient cycling and ecosystem health.

Question 14

What organisms break down dead matter and recycle nutrients?

Answer 14

Decomposers

Fungi, bacteria, and detritivores (e.g., worms, vultures) decompose organic material, returning nutrients to the soil.

Question 15

True or False:

Energy flows from decomposers to consumers in an ecosystem.

Answer 15

False

Energy flows from producers to consumers, and decomposers break down waste but do not transfer energy upward.

Question 16

What term describes interconnected food chains in an ecosystem?

Answer 16

Food web

A food web provides a more realistic representation of feeding relationships compared to a single food chain.

Question 17

Why do food webs provide a better model than food chains?

Answer 17

It shows multiple feeding relationships.

Most organisms eat more than one type of food, making food webs more accurate than linear food chains.

Question 18

Why do ecosystems need both producers and decomposers?

Answer 18

Producers create energy, while decomposers recycle nutrients.

Producers convert sunlight into energy, forming the base of the food chain, while decomposers break down dead organisms, returning essential nutrients to the soil.

Question 19

What process allows producers to capture solar energy?

Answer 19

Photosynthesis

Photosynthesis enables plants, algae, and cyanobacteria to convert sunlight into chemical energy, which fuels growth and supports the entire food chain.

Question 20

True or False:

Matter cycles between the Earth, atmosphere, and living things.

Answer 20

True

Matter is recycled through biogeochemical cycles like the water, carbon, and nitrogen cycles. In contrast, energy flows in one direction through the food chain and is eventually lost as heat.

Question 21

Define:

biogeochemical cycle

Answer 21

The transfer of elements between biotic and abiotic components.

Biogeochemical cycles, like the carbon and nitrogen cycles, recycle nutrients essential for sustaining life in ecosystems.

Question 22

Why are biogeochemical cycles important?

Answer 22

They recycle essential elements needed for life.

Without these cycles, nutrients would become depleted, making ecosystems unable to sustain life.

Question 23

True or False:

Energy is recycled in an ecosystem just like matter.

Answer 23

False

Unlike matter, which cycles through the environment, energy flows in one direction and is eventually lost as heat.

Question 24

Define:

carbon cycle

Answer 24

The movement of carbon through the environment.

Carbon cycles continuously between the atmosphere, organisms, and Earth through processes like photosynthesis, respiration, decomposition, and fossil fuel combustion.

Question 25

List **three ways** carbon is released into the atmosphere.

Answer 25

1. **Respiration** (by plants and animals) 2. **Decomposition** (of dead organisms) 3. **Combustion** (burning fossil fuels) ## Footnote Human activities *increase* CO₂ levels, contributing to climate change.

Question 26

What process **removes carbon dioxide** (CO₂) from the atmosphere?

Answer 26

Photosynthesis ## Footnote Plants and algae *absorb CO₂* and convert it into organic molecules, storing energy from sunlight.

Question 27

Why is carbon **important** for living organisms?

Answer 27

It forms **essential** organic molecules. ## Footnote Carbon is the foundation of *carbohydrates*, *proteins*, and *DNA*, making it crucial for structure, energy, and biological functions in all life forms.

Question 28

# Fill in the blank: The process that **releases CO₂** into the atmosphere is called \_\_\_\_\_\_\_\_.

Answer 28

respiration ## Footnote *Cellular respiration* converts glucose into energy, releasing CO₂ as a byproduct.

Question 29

# True or False: Carbon in fossil fuels was **originally** part of living organisms.

Answer 29

True ## Footnote *Fossil fuels*, such as coal, oil, and natural gas, originate from the remains of prehistoric plants and microorganisms that lived millions of years ago.

Question 30

What is the **role** of the ocean in the carbon cycle?

Answer 30

It **absorbs**, **stores**, and **cycles** carbon between water and marine life. ## Footnote **Phytoplankton** absorb CO₂, while shell-forming organisms use carbon to build calcium carbonate shells.

Question 31

# Define: nitrogen cycle

Answer 31

The **movement** of nitrogen in an ecosystem. ## Footnote Nitrogen moves between the *atmosphere*, *soil*, and *organisms*. It is essential for DNA and proteins but must be converted into usable forms for absorption.

Question 32

List **three** key nitrogen cycle processes.

Answer 32

1. **Nitrogen** fixation (N₂ → ammonia) 2. **Nitrification** (ammonia → nitrates) 3. **Denitrification** (nitrates → N₂ gas)

Question 33

What is the **main reservoir** of nitrogen on Earth?

Answer 33

The atmosphere ## Footnote About *78% of Earth's atmosphere* is nitrogen gas (N₂), but most organisms cannot use it in this form.

Question 34

Why do living organisms **need** nitrogen?

Answer 34

It is a key component of **amino acids**, **proteins**, and **DNA**. ## Footnote Nitrogen is *vital for growth*, especially in plants, which depend on nitrogen compounds in the soil.

Question 35

# Fill in the blank: The process that **converts** nitrogen gas into ammonia is called \_\_\_\_\_\_\_ \_\_\_\_\_\_\_.

Answer 35

nitrogen fixation ## Footnote *Nitrogen-fixing bacteria* in the soil and plant roots transform N₂ into ammonia, making it usable by plants.

Question 36

What **type of organisms** perform nitrogen fixation?

Answer 36

Certain bacteria, such as **Rhizobium**. ## Footnote These bacteria *live in root nodules of legumes* (e.g., beans, peas), converting nitrogen into a form plants can use.

Question 37

# True or False: Denitrification **increases** nitrogen availability in soil.

Answer 37

False ## Footnote *Denitrification* **returns** nitrogen to the atmosphere, removing it from the soil.

Question 38

What human activity is the **leading cause** of nitrogen pollution?

Answer 38

Excessive fertilizer use. ## Footnote *Agricultural runoff* introduces too much nitrogen into water systems, disrupting ecosystems.