4.1.5

Nutrient Cycles

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Saprobionts

Saprobionts are microorganisms (e.g. bacteria and fungi) that feed on dead or decaying organic matter. Saprobionts play an important role in decomposition and in recycling nutrients.

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Importance of nutrient recycling

  • Nutrient recycling is an important process in ecosystems because it allows the nutrients to be continuously reused.
  • Nutrients are recycled in the nitrogen cycle by saprobionts.
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Saprobiont nutrition

  • Saprobionts secrete enzymes onto the dead organic matter. This is called extracellular digestion.
    • The enzymes break down large, insoluble molecules into smaller, soluble molecules.
    • These smaller molecules can then be absorbed by the saprobiont.
    • The saprobiont will then either store the molecules or use them in respiration.
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Role in nitrogen cycle

  • Saprobionts are important in the ammonification stage of the nitrogen cycle.
    • Through extracellular digestion, saprobionts break down organic matter that contains nitrogen (e.g. urea, proteins, nucleic acids).
    • Ammonium ions are released as a result of extracellular digestion.
  • These ions then move onto the next stage of the nitrogen cycle: nitrification.

Nitrogen Cycle

The nitrogen cycle shows how nitrogen is transferred between organisms and their ecosystem. There are four steps in the nitrogen cycle, each of which involves bacteria:

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1) Nitrogen fixation

  • Atmospheric nitrogen (N2) is converted to ammonia (NH3) by nitrogen-fixing bacteria in the soil.
  • Bacteria (e.g. Rhizobia) form a mutualistic relationship with leguminous plants by inhabiting their root nodules.
    • Leguminous plants (e.g. alfalfa, peas, beans) are a family of plants.
  • The bacteria provide a source of ammonium ions for the plants and the plant provides sugars.
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2) Ammonification

  • When an organism dies or produces waste (e.g. faeces), it is decomposed by saprobionts.
  • This releases the nutrients contained inside.
  • Saprobionts decompose the organisms' biomass by extracellular digestion and inorganic ammonium ions are released into the soil.
  • Ammonification is a by-product of saprobiont nutrition.
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3) Nitrification

  • Ammonium ions that are released from ammonification are converted into nitrates by bacteria in the soil.
    • Nitrifying bacteria (e.g. Nitrosomonas) firstly convert NH4+ ions to nitrites.
    • Another bacteria (e.g. Nitrobacter) then convert nitrites to nitrates.
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4) Denitrification

  • Denitrifying bacteria convert nitrates in the soil back into atmospheric nitrogen (N2).
  • This takes place in anaerobic conditions (e.g waterlogged soils).

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1Cell Biology

1.1Introduction to Cells

1.1.1Introduction to Cells

1.1.2Cell Size & Surface Area

1.1.3Surface Area to Volume Ratio

1.1.4Eukaryotic vs Prokaryotic Cells

1.1.5Stem Cells

1.1.6Stem Cells in Disease

1.2Ultrastructure of Cells

1.2.1Eukaryotic Cells & Organelles

1.2.2Golgi, Lysosomes & Ribosomes

1.2.3Cell Walls & Vacuole

1.2.4Prokaryotes

1.2.5Binary Fission

1.2.6Subcellular Components & Organelles

1.3Membrane Structure

1.3.1Cell Membrane Structure & Permeability

1.4Membrane Transport

1.4.1Passive Movement Across Membranes

1.4.2Active Movement Across Membranes

1.4.3Endocytosis & Exocystosis

1.5The Origin of Cells

1.5.1Origins - Endosymbiosis

1.6Cell Division

1.6.1The Cell Cycle

1.6.2Mitosis

1.6.3Regulation of the Cell Cycle

1.6.4End of Topic Quiz - The Cell Cycle

1.6.5IB Multiple Choice - The Cell Cycle

1.6.6Extended Response - Mitosis

2Molecular Biology

2.1Water

2.1.1Water & Hydrogen Bonding

2.1.2IB Multiple Choice - Water & Hydrogen Bonding

2.1.3Extended Response - Water

2.2Carbohydrates & Lipids

2.2.1Monosaccharides

2.2.2Disaccharides & Polysaccharides

2.2.3Triglycerides & Phospholipids

2.2.4Cellulose

2.2.5Starch & Glycogen

2.3Proteins

2.3.1Structure & Functions of Proteins

2.4Enzymes

2.4.1Enzymes

2.4.2Factors Affecting Enzyme Activity

2.4.3Enzyme-Controlled Reactions

2.4.4End of Topic Test - Enzymes

2.5Structure of DNA & RNA

2.5.1DNA & RNA

2.6DNA Replication, Transcription & Translation

2.6.1Protein Synthesis

2.6.2Transcription & Translation

2.6.3End of Topic Test - DNA, Genes & Protein Synthesis

2.6.4Exam-Style Question - Protein Synthesis

2.6.5End of Topic Test - Coronavirus Translation

2.6.6IB Multiple Choice - Transcription

2.6.7IB Multiple Choice - Translation

2.7Cell Respiration

2.7.1Overview of Respiration

2.7.2Anaerobic Respiration

2.7.3End of Topic Test - Anaerobic Respiration

2.7.4Respiration Experiments

2.7.5End of Topic Test - Respiration

2.7.6IB Multiple Choice - Respiration

2.8Photosynthesis

2.8.1Overview of Photosynthesis

3Genetics

3.1Genes

3.1.1Genes

3.1.2Mutations

3.2Chromosomes

3.2.1Chromosomal Theory of Inheritance

3.2.2Chromosomal Basis of Inherited Disorders

3.2.3IB Multiple Choice - Chromosomal Inheritance

3.3Meiosis

3.3.1Meiosis

3.3.2Mitosis vs Meiosis

3.3.3Meiosis & Genetic Diversity

3.3.4End of Topic Quiz - Meiosis

3.3.5IB Multiple Choice - Meiosis

3.4Inheritance

3.4.1Key Terms

3.4.2Mendelian Genetics & Common Ancestry

3.4.3Mendelian Laws

3.4.4Monohybrid Crosses & Law of Segregation

3.4.5Introduction to Non-Mendelian Inheritance

3.4.6Codominance

3.4.7Multiple Alleles

3.5Genetic Modification & Biotechnology

3.5.1DNA Technology

3.5.2PCR & Gel Electrophoresis

3.5.3Genetic Modification

3.5.4Cloning

4Ecology

4.1Species, Communities & Ecosytems

4.1.1Population Dynamics

4.1.2Communities & Measuring Diversity

4.1.3Relationships Between Populations

4.1.4Overview of Ecosystems

4.1.5Nutrient Cycles

4.1.6Fertilisers

4.1.7Eutrophication

4.1.8Chi-Squared Test

4.2Energy Flow

4.2.1Energy

4.2.2Energy Flow

4.2.3Biomass & Food Chains

4.2.4Heterotrophs & Autotrophs

4.3Carbon Cycle

4.3.1Carbon Cycle

4.4Climate Change

4.4.1Carbon Dioxide

4.4.2The Greenhouse Effect

4.4.3Global Warming

4.4.4Maintaining Biodiversity

5Evolution & Biodiversity

5.1Evidence for Evolution

5.1.1Evidence for Evolution - Fossils & DNA

5.1.2Evidence for Evolution - Anatomy & Geography

5.1.3IB Multiple Choice - Evidence for Evolution

5.1.4Extended Response - DNA & Evolution

5.2Natural Selection

5.2.1Introduction

5.2.2Evolutionary Fitness

5.2.3Natural Selection & Variation

5.2.4End of Topic Quiz - Natural Selection

5.2.5IB Multiple Choice - Natural Selection

5.2.6Speciation

5.3Classification of Biodiversity

5.3.1Introduction to Biodiversity

5.3.2Keystone Species

5.3.3Courtship & Ancestry

5.3.4Classification

5.4Cladistics

5.4.1Evolutionary Relationships

5.4.2IB Multiple Choice - Species & Taxonomy

6Human Physiology

6.1Digestion & Absorption

6.1.1Overview of Digestion

6.1.2Digestion in Mammals

6.1.3Absorption

6.1.4End of Topic Test - Substance Exchange & Digestion

6.1.5End of Topic Test - Substance Ex & Digestion

6.2The Blood System

6.2.1The Circulatory System

6.2.2The Heart

6.2.3Blood Vessels

6.2.4Cardiovascular Disease

6.3Defence Against Infectious Disease

6.3.1Immune System

6.3.2The Immune Response

6.3.3Antibodies

6.3.4Primary & Secondary Response

6.3.5Vaccines

6.3.6HIV

6.3.7End of Topic Test - Immune System

6.3.8Exam-Style Question - Immune System

6.3.9End of Topic Test - Immune System

6.4Gas Exchange

6.4.1Lung Structure & Alveoli

6.4.2Ventilation

6.4.3Lung Disease

6.4.4Lung Disease Data

6.5Neurons & Synapses

6.5.1Neuron Structure

6.5.2Transmission of an Impulse

6.5.3Speed of Transmission

6.5.4End of Topic Test - Neurones & Action Potentials

6.5.5Synapses

6.5.6Types of Synapse

6.5.7Medical Application

6.5.8End of Topic Test - Synapses

6.5.9End of Topic Test - Nervous Comm&Coord

6.6Hormones, HomeoStasis & Reproduction

6.6.1Overview of Homeostasis

6.6.2Blood Glucose Concentration

6.6.3Controlling Blood Glucose Concentration

6.6.4End of Topic Test - Blood Glucose

6.6.5Type I & Type II Diabetes

6.6.6Human Reproductive Systems

6.6.7Hormonal Control of the Menstrual Cycle

7AHL: Nucleic Acids

7.1DNA Structure & Replication

7.1.1DNA

7.1.2RNA

7.1.3DNA Replication

7.1.4DNA Replication - Summary

7.1.5IB Multiple Choice - DNA Replication

7.2Transcription & Gene Expression

7.2.1Introduction to Transcription & Protein Synthesis

7.2.2Types of RNA

7.2.3Transcription

7.2.4RNA Processing in Eukaryotes

7.2.5IB Multiple Choice - Transcription

7.3Translation

7.3.1Translation

7.3.2Retroviruses

7.3.3Scientific Practices: Coronavirus

7.3.4IB Multiple Choice - Translation

8AHL: Metabolism, Cell Respiration & Photosynthesis

8.1Metabolism

8.1.1Molecules to Metabolism

8.2Cell Respiration

8.2.1Glycolysis

8.2.2Aerobic Respiration

8.3Photosynthesis

8.3.1Light-Dependent Reaction

8.3.2Light-Independent Reaction

8.3.3End of Topic Test - Photosynthesis Reactions

8.3.4Limiting Factors

8.3.5Photosynthesis Experiments

8.3.6End of Topic Test - Photosynthesis

8.3.7End of Topic Test - Photosynthesis

9AHL: Plant Biology

9.1Transport in the Xylem of Plants

9.1.1Structure

9.1.2Cohesion-Tension Theory

9.1.3Investigating Transpiration Rate

9.2Transport in the Phloem of Plants

9.2.1Structure

9.2.2Translocation

9.3Growth in Plants

9.3.1Plant Tropisms

10AHL: Genetics & Evolution

10.1Meiosis

10.1.1Stages of Meiosis

10.2Inheritance

10.2.1Linked Genes

10.2.2Sex-Linked Genes

10.2.3Non-Nuclear Inheritance

10.2.4Chi-Squared Test

10.2.5End of Topic Quiz - Inheritance

10.2.6IB Multiple Choice - Non-Mendelian Genetics

10.2.7Introduction to Non-Mendelian Inheritance

10.2.8Extended Response - Inheritance

10.2.9Grade 4-5 (Scientific Practices) - Inheritance

10.3Gene Pools & Speciation

10.3.1Populations

10.3.2Mutations, Genetic Drift, & Gene Flow

10.3.3Speciation

10.3.4Rate of Speciation

10.3.5Allopatric & Sympatric Speciation

11AHL: Animal Physiology

11.1Antibody Production & Vaccination

11.1.1Immune System

11.1.2The Immune Response

11.1.3Antibodies

11.1.4Primary & Secondary Response

11.1.5Vaccines

11.2Movement

11.2.1Skeletal Muscle

11.2.2Sliding Filament Theory

11.2.3Contraction

11.3The Kidney & Osmoregulation

11.3.1Kidneys & Osmoregulation

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Overview of Ecosystems

Fertilisers