MYP Integrated Sciences Transfer and Transformation of Energy Notes

How Does Energy Enter and Move Through Living Systems?

1. Every organism needs a constant supply of energy to survive.
2. Most usable biological energy comes from the sun.
3. Plants capture sunlight and convert it into chemical energy stored in glucose.
4. Because plants start the movement of energy into living systems, they are known as producers.
5. Without producers capturing this energy, ecosystems would not have a long-term energy supply.

How Do Plants Capture and Store Energy?

1. Plants absorb light through chlorophyll in their leaves.
2. They convert this light energy into chemical energy by making glucose.
3. The energy stored in glucose becomes the starting point for all energy transfer in ecosystems.
4. Plants use some of this energy for growth, reproduction, and repair.

Why Is Stored Chemical Energy Important?

1. Chemical energy in glucose is stable, meaning it does not disappear immediately like sunlight.
2. It is transportable, allowing plants to move energy to different parts of the organism.
3. Other organisms can access this energy when they eat plant material.
4. This makes plant biomass the main energy source that supports consumers.

How Does Energy Move Beyond Plants?

1. Energy transfers when one organism consumes another.
2. The chemical energy stored in plant biomass moves into the consumer.
3. The consumer uses some of this energy for movement, growth, repair, and maintaining body conditions.
4. Only a portion becomes stored in the consumer’s own biomass.
5. This partial transfer continues each time one organism feeds on another.

Example

• Energy enters a grass blade from sunlight.
• That energy becomes available to any organism that eats the grass.

Why Does Less Energy Become Available at Each Step?

1. Although the detailed structure of feeding relationships is covered later under "Food chains and webs:, the key idea here is simple:
   1. Organisms must use some energy to stay alive.
   2. Movement, temperature control, repair, and basic cell activity all require energy.
   3. Energy used this way does not remain stored in biomass.
   4. As a result, only part of the energy eaten by an organism becomes available to whatever eats it next.

Why Must Energy Continuously Enter Ecosystems?

1. Energy can't cycle in ecosystems.
2. Once energy is released as heat, living organisms can't use it again.
3. Ecosystems therefore require a constant input of new energy.
4. Sunlight provides this input and keeps the system functioning over time.

Energy Is A Useful "Currency" For Describing Change

In physics, energy is a way to keep track of what can cause change. If an object can do work (for example, lift a load, speed something up, heat something up), then it has energy.

The idea of work connects forces and energy transfer. When a force moves an object through a distance, energy is transferred. For a constant force in the same direction as the motion:

$$W = Fd$$

Energy is measured in joules (J), the same unit as work.

Energy Stores And Pathways Explain Where Energy "Is" And How It Moves

A good way to organize thinking is:

• Energy stores: where energy is held in a system.
• Energy transfers (pathways): how energy moves between stores.

Common Energy Stores At This Level

• Kinetic energy: energy of motion.
• Gravitational potential energy: energy due to position in a gravitational field (height).
• Thermal energy: energy associated with the random motion of particles (temperature).
• Elastic potential energy: energy stored when an object is stretched or compressed.
• Chemical potential energy: energy stored in chemical bonds (released or absorbed in reactions).
• Nuclear potential energy: energy stored in the nucleus due to nuclear forces (very large, harder to access).

Typical Transfer Pathways

• Mechanical work (forces doing work)
• Electrical work (charges moving through a potential difference)
• Heating (due to temperature difference)
• Radiation (energy carried by waves, including light and infrared)

Conservation Of Energy Is A Fundamental Law

The law of conservation of energy states:

• Energy can be transferred between objects and transformed from one form to another.
• Energy cannot be created or destroyed.
• Therefore, the total energy of a closed system remains constant.

This is one of the most fundamental ideas in physics. You use it whenever you track energy before and after a process.

Gravitational Potential Energy Often Transforms Into Kinetic Energy

When an object falls, its gravitational potential energy decreases and its kinetic energy increases. If we ignore air resistance, the decrease in gravitational potential energy equals the increase in kinetic energy.

Gravitational potential energy near Earth's surface is:

$$E_p = mgh$$

where $m$ is mass (kg), $g \approx 9.8\,\text{m s}^{-2}$, and $h$ is vertical height (m).

Kinetic energy is:

$$E_k = \frac{1}{2}mv^2$$

What Conservation Predicts For Falling Objects

If no energy is transferred to thermal stores (no significant air resistance), then:

$$mgh = \frac{1}{2}mv^2$$

The mass cancels, so the speed after falling through height $h$ does not depend on mass:

$$v = \sqrt{2gh}$$

Friction And Air Resistance Transfer Energy To Thermal Stores

In real situations, friction and air resistance do work that transfers energy out of the "useful" mechanical stores.

For example, a ball rolling down a slope:

• Gravitational potential energy decreases.
• Kinetic energy increases, but not as much as it would in an ideal case.
• Some energy is transferred to thermal energy of the ball, ramp, and air.
• A small amount may become sound.

This does not violate conservation of energy. It changes where the energy ends up.

Elastic, Chemical, And Nuclear Energy Are All "Stored By Work Against Forces"

A key unifying idea is that many energy stores arise because work was done against a force:

Elastic Potential Energy

Stretching an elastic band or compressing a spring requires work against a tension (restoring) force. That work becomes elastic potential energy, which can later be transferred to other stores (often kinetic energy).

Chemical Potential Energy

At the atomic level, energy can be stored in chemical bonds. During some reactions, bonds break and form, and energy may be released, often as thermal energy. Explosives are an extreme example: stored chemical energy is rapidly transferred into kinetic energy of fragments, work done breaking materials, and thermal energy, with a small fraction as sound.

Nuclear Potential Energy

Some nuclei are unstable and can decay. Energy stored by short-range nuclear forces is nuclear potential energy. It is difficult to access, but the quantities involved can be enormous.

Energy Transfer Chains Describe Devices And Living Systems

Many technologies can be described as an energy transfer chain (a sequence of transfers and transformations). Being able to identify these chains is a key skill.

Examples:

• Loudspeaker: electrical energy transferred to kinetic energy (vibration of the cone), then to sound energy in the air, with some thermal energy.
• Microphone: sound energy causes vibrations (kinetic), transformed into electrical energy.
• Light bulb: electrical energy transformed into light (radiation) and thermal energy (often most becomes thermal).
• Solar (photovoltaic) cell: radiation from the Sun transferred into electrical energy.
• Plant leaf (photosynthesis): light energy transferred into chemical potential energy stored in molecules.

Efficiency Explains Why Useful Output Is Less Than Input

In many systems, we care about how much of the input energy becomes the desired output.

Efficiency is less than 1 (or less than 100%) when energy is transferred to unwanted stores, usually thermal energy. Improvements in technology often aim to reduce these unwanted transfers, which is important for sustainability.

Energy Diagrams Help You Communicate Conservation Clearly

A clear energy explanation usually includes a diagram showing:

• the starting store(s)
• arrows showing transfers
• ending store(s), including "wasted" thermal energy

Laws And Theories, Why Conservation Matters

A scientific law describes something that always holds under specified conditions. Conservation of energy is treated as fundamental: in any correct description, total energy must balance.

A scientific theory aims to explain why laws and observations occur. Theories can be revised if new evidence contradicts them, whereas a law is a robust relationship that must be obeyed within its domain.