All the living (biotic) and nonliving (abiotic) things in an area and how they interact.

A living or once-living part of an ecosystem, such as plants, animals, fungi, or bacteria.

A nonliving part of an ecosystem, such as sunlight, temperature, water, soil, or air.

All the individuals of the same species living in a specific area.

All the different populations that live together in an area.

The specific place where an organism lives within an ecosystem.

All the different populations that live together in an area.

All the living (biotic) and nonliving (abiotic) things in an area and how they interact.

All the individuals of the same species living in a specific area.

Ecosystems and the Human Body: Systems, Balance, and Health — SHS Science Foundations: Integrated Chemistry, Biology, and Physics

Step 1: Systems Everywhere – From Forests To Your Body

What Is a System?

A system is a set of parts that interact and depend on each other. Forests, ponds, and your own body are all systems. When their parts work together in balance, the system stays healthy.

From Energy & DNA To Systems

Earlier, you learned how energy flows in food chains and how DNA stores information. Now we zoom out and look at how whole systems, not just single processes, stay in balance.

Two Kinds of Systems

We will compare ecosystems (forests, lakes, coral reefs) and body systems (circulatory, nervous, etc.). Both have inputs, outputs, feedback, and limits where conditions are safe.

Your Goals

You will learn to define ecosystems, describe water and carbon cycles, summarize major body systems, and connect lifestyle choices to how your body keeps its balance (homeostasis).

Step 2: Ecosystems, Habitats, and Biotic/Abiotic Factors

What Is an Ecosystem?

An ecosystem is all the living and nonliving things in an area and how they interact. It includes plants, animals, microbes, plus air, water, soil, and climate.

Biotic vs Abiotic

Biotic factors are living or once-living parts (plants, animals, fungi, bacteria). Abiotic factors are nonliving parts (sunlight, temperature, water, soil, air, rocks).

Habitats

A habitat is the specific place where an organism lives inside an ecosystem, like a woodpecker in tree trunks or mushrooms on a damp forest floor.

Levels of Organization

From smallest to largest: organism (one wolf), population (all wolves), community (wolves, deer, trees), ecosystem (community plus soil, air, water, climate).

Interactions Everywhere

Biotic and abiotic factors affect each other: plants need light and water; trees create shade and cooler soil; earthworms mix soil and change its nutrients.

Step 3: A Pond Ecosystem – Putting The Pieces Together

Pond Abiotic Factors

In a pond, abiotic factors include sunlight, water depth and temperature, and rocks or mud that provide surfaces and hiding places.

Pond Biotic Factors

Biotic parts include producers (algae, plants), consumers (insects, fish, frogs, birds), and decomposers (bacteria, fungi) that break down dead material.

Key Interactions

Plants make oxygen for animals. Fish eat insects and smaller fish. Decomposers recycle nutrients from dead matter back into the water and mud for plants.

When Balance Is Lost

Extra fertilizer can cause algal blooms. Too many algae block light and, when they die, decomposers use up oxygen. Fish can suffocate. The system loses balance.

Step 4: Cycles of Matter – Water and Carbon

Matter Cycles

Energy flows one way through food chains, but matter cycles. Atoms like carbon and water molecules are reused again and again in ecosystems and in your body.

Water Cycle Basics

Water evaporates from oceans and land, and plants add water vapor by transpiration. It condenses into clouds, falls as precipitation, and then runs off or soaks into the ground.

Water and You

The same water that falls as rain can later be in your blood, your cells, or your sweat. You are literally part of the water cycle.

Carbon Cycle Basics

In the carbon cycle, plants take in CO2 in photosynthesis. Animals eat plants. Respiration and decomposition return CO2 to the air and soil.

Human Impact on Carbon

Burning fossil fuels and cutting forests adds extra CO2 to the atmosphere. Since the late 1800s this has driven climate change, affecting ecosystems and human health.

Step 5: Trace a Molecule – Thought Exercise

Use this short thought exercise to connect cycles to your own body.

Pick one: water molecule or carbon atom.
In your mind (or on paper), list five places it might travel over 100 years.

Include at least two ecosystem locations (like ocean, soil, forest) and at least two locations in living things (like leaf, cow, your muscle cell).

For each step, ask:

What process moved it? (examples: evaporation, photosynthesis, respiration, drinking, eating)
Did energy move with it, or just matter?

Finally, answer in one sentence: How are you connected to ecosystems through this molecule?

If you want a challenge, try this pattern for a carbon atom: atmosphere → leaf → caterpillar → bird → soil microbe → atmosphere again.

Pause for 1–2 minutes and actually sketch or list your path before moving on.

Step 6: Human Body Systems – The Internal Ecosystem

Circulatory System

The circulatory system (heart, blood, vessels) transports oxygen, nutrients, hormones, and wastes. It is like the transport network or river system of your body.

Respiratory System

The respiratory system (nose, trachea, lungs, alveoli) brings oxygen in and removes carbon dioxide. Gas exchange happens in tiny air sacs called alveoli.

Digestive System

The digestive system (mouth, stomach, intestines, liver, pancreas) breaks food into small molecules, absorbs them into blood, and removes solid waste.

Nervous System

The nervous system (brain, spinal cord, nerves) receives information, processes it, and sends signals. It is your body's control and communication network.

Systems Working Together

Digestive provides nutrients, respiratory provides oxygen, circulatory delivers both, and nervous adjusts heart rate, breathing, and digestion to keep balance.

Step 7: Homeostasis – Keeping Internal Balance

What Is Homeostasis?

Homeostasis is your body's ability to keep internal conditions stable, like temperature and blood sugar, even when the outside environment changes.

What Must Stay Stable?

Your body tightly controls temperature, blood sugar, water and salt balance, and blood pH and oxygen. These must stay in a safe range for cells to work.

Negative Feedback: Temperature

When you overheat, sensors signal your brain. You sweat and blood vessels widen. Heat is lost and temperature returns toward normal. This is negative feedback.

Ecosystem Analogy

Like homeostasis, ecosystems can self-correct: if a population grows too large, limited food and space reduce its size, moving it back toward balance.

When Balance Fails

If homeostasis is disturbed for a long time, disease can result, such as diabetes from long-term high blood sugar or heart disease from constant high blood pressure.

Step 8: Lifestyle Choices as "Abiotic Factors" For Your Body

Your Lifestyle as Environment

Imagine your body as an ecosystem and your lifestyle as its environment. Food, movement, sleep, and stress are like abiotic factors shaping how your systems function.

Nutrition

Balanced meals support digestion and circulation. Diets high in added sugars and ultra-processed foods can raise blood sugar and blood fats, stressing homeostasis.

Physical Activity

Regular movement strengthens heart and lungs and helps control blood sugar. Very low activity weakens muscles and circulation and raises risk of obesity and type 2 diabetes.

Sleep

Enough regular sleep supports nervous and hormone systems, mood, and immunity. Chronic sleep loss makes it harder to control blood sugar, blood pressure, and stress hormones.

Stress and Mental Health

Short stress is normal, but long-term stress keeps heart rate and blood pressure high and can disturb digestion and sleep. Healthy coping skills help your systems rebalance.

Step 9: Quick Check – Systems and Balance

Answer this question to check your understanding.

Which scenario best shows a negative feedback loop helping maintain homeostasis, similar to population control in an ecosystem?

Your body temperature rises, you start to sweat, and your temperature moves back toward normal.
You eat a large sugary snack every day and your average blood sugar level slowly increases over many months.
Extra fertilizer causes an algal bloom in a lake, and fish die from lack of oxygen.
A forest fire destroys most plants in an area and the soil erodes away.

Show Answer

Answer: A) Your body temperature rises, you start to sweat, and your temperature moves back toward normal.

Option A describes negative feedback: a change (higher temperature) triggers a response (sweating) that reverses the change and brings the system back toward its set point. The other options show longer-term imbalances or damage, not stabilizing feedback.

Step 10: Key Term Review

Flip these cards (mentally or with a partner) to review important terms.

Ecosystem: All the living (biotic) and nonliving (abiotic) things in an area and how they interact.
Biotic factor: A living or once-living part of an ecosystem, such as plants, animals, fungi, or bacteria.
Abiotic factor: A nonliving part of an ecosystem, such as sunlight, temperature, water, soil, or air.
Population: All the individuals of the same species living in a specific area.
Community: All the different populations that live together in an area.
Homeostasis: The process by which an organism maintains a stable internal environment despite external changes.
Negative feedback: A control process where a change triggers responses that work to reverse the change and restore balance.
Water cycle: The continuous movement of water between Earth's surface and the atmosphere through evaporation, condensation, precipitation, and runoff.
Carbon cycle: The cycling of carbon among the atmosphere, living things, oceans, soil, and fossil fuels through processes like photosynthesis and respiration.
Organ system: A group of organs that work together to perform a major function in the body, such as circulation or digestion.

Key Terms

Habitat: The specific place where an organism lives within an ecosystem.
Community: All the different populations that live together in an area.
Ecosystem: All the living (biotic) and nonliving (abiotic) things in an area and how they interact.
Population: All the individuals of the same species living in a specific area.
Homeostasis: The ability of an organism to maintain a stable internal environment despite changes in the external environment.
Water cycle: The continuous movement of water between Earth's surface and the atmosphere through processes such as evaporation, condensation, precipitation, and runoff.
Carbon cycle: The cycling of carbon among the atmosphere, living things, oceans, soil, and fossil fuels through processes like photosynthesis, feeding, respiration, decomposition, and combustion.
Organ system: A group of organs that work together to perform a major function in the body.
Biotic factor: A living or once-living part of an ecosystem, such as plants, animals, fungi, or bacteria.
Abiotic factor: A nonliving part of an ecosystem, such as sunlight, temperature, water, soil, or air.
Nervous system: The body system (brain, spinal cord, nerves) that receives information, processes it, and coordinates the body's responses.
Digestive system: The body system that breaks down food, absorbs nutrients, and eliminates solid waste.
Negative feedback: A control process in which a change in a condition triggers responses that work to reverse the change and restore balance.
Circulatory system: The body system (heart, blood, blood vessels) that transports substances like oxygen, nutrients, and wastes.
Respiratory system: The body system (lungs and airways) that brings oxygen into the body and removes carbon dioxide.