IB Biology Topic C4.2.2 Sunlight Revision Notes (SL/HL)

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

Sunlight is the principal energy source for most ecosystems on Earth.
Plants, algae, and cyanobacteria capture sunlight through photosynthesis, converting light energy into chemical energy stored in carbon compounds such as glucose.
This chemical energy then moves through the ecosystem as organisms feed on producers and on one another.

Note

Sunlight powers most ecosystems, but a minority run on chemical energy instead.

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some ecosystems thrive in complete darkness, powered by chemical energy rather than light.

Deep-sea hydrothermal vents: these ocean-floor vents release hot, mineral-rich water.
1. Bacteria there use chemosynthesis, drawing chemical energy from reactions such as the oxidation of hydrogen sulfide to build organic compounds.

Definition

Chemosynthesis

The process by which certain organisms (like sulfur bacteria) use energy from inorganic molecules (such as hydrogen sulfide) to produce food in the absence of sunlight.

Example

In the Pacific Ocean, vent communities of giant tube worms, clams, and shrimp all depend on chemosynthetic bacteria.

Some Caves Are Also Powered by Chemosynthesis

Many caves depend on organic matter carried in from outside, such as fallen leaves or animal droppings.
In rare cases such as Movile Cave in Romania, chemosynthetic bacteria form the base of the food web with no input of sunlight.

Common Mistake

It is a common misconception that all life depends on sunlight.
Chemosynthetic ecosystems are fully independent of solar energy.

Sunlight as an Energy Source Is a Generalisation With Real Exceptions

Theory of Knowledge

The claim that sunlight sustains most ecosystems is a scientific generalisation, a broad pattern drawn from observation rather than a rule without exceptions.
How does the discovery of chemosynthetic ecosystems reshape our idea of what life needs to survive?
Could these exceptions guide the search for life on other planets?

Active recall

What is the principal energy source for most ecosystems?
How do producers convert sunlight into a form of energy other organisms can use?
Name one type of ecosystem that runs on chemical energy instead of sunlight.
What process do chemosynthetic bacteria use to make organic compounds?

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

Sunlight is the principal energy source for most ecosystems on Earth.
Plants, algae, and cyanobacteria capture sunlight through photosynthesis, converting light energy into chemical energy stored in carbon compounds such as glucose.
This chemical energy then moves through the ecosystem as organisms feed on producers and on one another.

Note

Sunlight powers most ecosystems, but a minority run on chemical energy instead.

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some ecosystems thrive in complete darkness, powered by chemical energy rather than light.

Deep-sea hydrothermal vents: these ocean-floor vents release hot, mineral-rich water.
1. Bacteria there use chemosynthesis, drawing chemical energy from reactions such as the oxidation of hydrogen sulfide to build organic compounds.

Definition

Chemosynthesis

The process by which certain organisms (like sulfur bacteria) use energy from inorganic molecules (such as hydrogen sulfide) to produce food in the absence of sunlight.

Example

In the Pacific Ocean, vent communities of giant tube worms, clams, and shrimp all depend on chemosynthetic bacteria.

Some Caves Are Also Powered by Chemosynthesis

Many caves depend on organic matter carried in from outside, such as fallen leaves or animal droppings.
In rare cases such as Movile Cave in Romania, chemosynthetic bacteria form the base of the food web with no input of sunlight.

Common Mistake

It is a common misconception that all life depends on sunlight.
Chemosynthetic ecosystems are fully independent of solar energy.

Sunlight as an Energy Source Is a Generalisation With Real Exceptions

Theory of Knowledge

The claim that sunlight sustains most ecosystems is a scientific generalisation, a broad pattern drawn from observation rather than a rule without exceptions.
How does the discovery of chemosynthetic ecosystems reshape our idea of what life needs to survive?
Could these exceptions guide the search for life on other planets?

Active recall

What is the principal energy source for most ecosystems?
How do producers convert sunlight into a form of energy other organisms can use?
Name one type of ecosystem that runs on chemical energy instead of sunlight.
What process do chemosynthetic bacteria use to make organic compounds?

IB Biology Topic C4.2.2: Sunlight Notes

IB Biology Topic C4.2.2: Sunlight Notes

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some Caves Are Also Powered by Chemosynthesis

Sunlight as an Energy Source Is a Generalisation With Real Exceptions

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some Caves Are Also Powered by Chemosynthesis

Sunlight as an Energy Source Is a Generalisation With Real Exceptions

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

IB Biology Topic C4.2.2: Sunlight Notes

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

IB Biology Topic C4.2.2: Sunlight Notes

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some Caves Are Also Powered by Chemosynthesis

Sunlight as an Energy Source Is a Generalisation With Real Exceptions

Sunlight Is the Principal Energy Source That Sustains Most Ecosystems

A Minority of Ecosystems Run on Chemical Energy, Not Sunlight

Some Caves Are Also Powered by Chemosynthesis

Sunlight as an Energy Source Is a Generalisation With Real Exceptions