IB MYP Integrated Science- Biology - Nutrient cycle-Study Notes - New Syllabus

Nutrient Cycles

🌱 Introduction

Nutrients like carbon, nitrogen, phosphorus, sulfur, and water constantly circulate between:

• Living organisms
• Soil
• Water
• Atmosphere

These cycles ensure that essential elements are reused instead of being lost.
Without nutrient cycles, life would run out of raw materials for growth, repair, and energy.

🔄 Why Nutrient Cycles Matter

• Maintain ecosystem balance
• Recycle essential elements
• Support plant growth (primary productivity)
• Link abiotic and biotic components
• Allow nutrients to flow from non-living → living → non-living

🌿 Major Nutrient Cycles

Carbon Cycle

Movement of Carbon

Carbon flows as:

• CO₂ in the air and dissolved in water
• Glucose, proteins, fats in living organisms
• Fossil fuels
• Carbonates in rocks

Main Steps

• Photosynthesis: CO₂ → glucose (plants)
• Respiration: glucose → CO₂ (all organisms)
• Combustion: burning fuels releases CO₂
• Decomposition: carbon in dead organisms → CO₂
• Ocean exchange: CO₂ dissolves into oceans
• Formation of fossil fuels: dead organisms under pressure

Carbon cycle is tightly linked to climate change.

Nitrogen Cycle

Needed for: Proteins, DNA, ATP, chlorophyll.

Main Steps

• Nitrogen fixation (N₂ → NH₃/NH₄⁺)
• Ammonification
• Nitrification
• Assimilation
• Denitrification (NO₃⁻ → N₂)

Ensures plants get nitrates, the most usable nitrogen form.

Phosphorus Cycle

Why Important? Essential for DNA, RNA, ATP (energy currency), and Cell membranes (phospholipids).

Key Features

• No atmospheric phase
• Starts from rock weathering
• Phosphate ions (PO₄³⁻) enter soil/water
• Plants absorb phosphates
• Animals obtain phosphates by feeding
• Decomposers return phosphates to the soil
• Sedimentation → rocks → uplift

Slow cycle often limits plant growth.

Water Cycle (Hydrologic Cycle)

Movement of Water

Involves:

• Evaporation
• Transpiration (plants lose water vapor)
• Condensation
• Precipitation
• Runoff
• Groundwater flow

Powers energy flow and nutrient distribution.

Sulfur Cycle

Importance: Sulfur forms some amino acids (cysteine, methionine) and important proteins and enzymes.

Key Steps

• Weathering of rocks releases sulfate (SO₄²⁻)
• Plants absorb sulfate
• Animals ingest sulfur through food
• Decomposition releases sulfur into soil
• Bacteria convert sulfur compounds → H₂S, SO₂
• Volcanic eruptions emit sulfur gases

Influences acid rain formation.

Oxygen Cycle

Key Processes

• Photosynthesis: releases O₂
• Respiration: uses O₂
• Decomposition: uses O₂
• Combustion: uses O₂

Oxygen also stored in oceans and rocks.
Linked closely with the carbon cycle.

🌾 How Nutrient Cycles Link Biotic and Abiotic Worlds

• Plants (Producers): Take in carbon (CO₂), nitrogen (nitrates), phosphorus, sulfur, water and convert them into biomass.
• Animals (Consumers): Get nutrients by eating plants/animals and return nutrients through waste.
• Decomposers (Fungi, Bacteria): Break down dead organisms and release nutrients back into soil/water. Essential for nutrient recycling; without decomposers → cycles stop.

🌊 Human Impacts on Nutrient Cycles

• Carbon Cycle: Burning fossil fuels → excess CO₂; Deforestation reduces CO₂ absorption.
• Nitrogen & Phosphorus Cycles: Overuse of fertilizers → eutrophication; Sewage and livestock waste add excess nutrients.
• Sulfur Cycle: Industrial emissions → acid rain.

Human activity speeds some cycles and disrupts others.

📋 Summary Table – Major Nutrient Cycles

📦 Quick Recap 
Nutrient cycles recycle essential elements through living and non-living parts of ecosystems.
✔ Carbon → energy flow, climate
✔ Nitrogen → proteins, DNA
✔ Phosphorus → ATP, DNA
✔ Water → movement of substances
✔ Sulfur → proteins
✔ Oxygen → respiration, photosynthesis