Metabolism and Levels of Organization of Life

METABOLISM (CONTINUED) — CLEANED & EXPANDED NOTES

Metabolism refers to all the chemical reactions occurring in the body of a living organism.
These reactions enable organisms to grow, reproduce, repair tissues, generate energy, and maintain life.

Metabolism is divided into two main types:

1. Anabolism (Building Up Reactions)

These are reactions that build complex molecules from simpler ones.
They require energy.

Examples include:

• Photosynthesis – plants building glucose from carbon dioxide and water
• Protein synthesis – building proteins from amino acids
• Formation of glycogen from glucose

Anabolism = construction.

2. Catabolism (Breaking Down Reactions)

These are reactions that break down complex molecules into simpler ones.
They release energy that the body can use.

Examples include:

• Respiration – glucose is broken down to release energy
• Digestion – food molecules are broken into smaller absorbable units
• Breakdown of fat into fatty acids and glycerol

Catabolism = destruction / energy release.

Together, anabolism and catabolism form metabolism, the continuous chemical activity that keeps organisms alive.

LEVELS OF ORGANIZATION OF LIFE — CLEAN & FORMATTED NOTES

Living organisms are highly structured and organized.
Their organization follows a definite hierarchy from the simplest to the most complex level.

Below is the complete and correct biological hierarchy:

1. Atom

Atoms are the smallest and most fundamental units of matter.
Examples: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).

2. Molecule

Atoms combine to form molecules.
Examples:

• CO₂
• H₂O
• NH₃ (ammonia)

3. Biomolecules (Macromolecules)

Small molecules join to form large biological molecules (macromolecules).
Macromolecules are also called polymers, made from repeating units called monomers.

Examples of biomolecules:

• Proteins
• Carbohydrates
• Lipids
• Nucleic acids (DNA & RNA)

Example:

• Amino acids (monomers) → protein (polymer)
• Nucleotides (monomers) → DNA/RNA (polymer)

4. Organelles

Biomolecules combine to form organelles, which are specialized structures within a cell that perform specific functions.

Examples:

• Mitochondria
• Ribosomes
• Golgi apparatus
• Nucleus

Organelles = functional compartments inside cells.

5. Cell

Organelles together form a cell, which is the basic structural and functional unit of life.

Types of cells include:

• Prokaryotic cells
• Eukaryotic cells
• Somatic (body) cells
• Gametic (sex) cells

A single cell can be an entire organism (e.g., Amoeba).

6. Tissue

A tissue is a group of similar cells performing a specific function.

Examples:

• Muscle tissue
• Nervous tissue
• Epithelial tissue
• Parenchyma (in plants)

7. Organ

An organ is made up of different tissues working together.

Examples:

• Heart
• Liver
• Leaf
• Root

8. Organ System

Organ systems are groups of organs working together to perform complex functions.

Examples:

• Digestive system
• Respiratory system
• Circulatory system
• Root-shoot system (plants)

9. Organism

An organism is a complete living individual.

Examples:

• Human
• Dog
• Mango tree
• Bacteria

10. Population

A population is a group of organisms of the same species living in the same place at the same time.

Example:

• All humans in Lagos
• All mango trees in a forest

11. Community

A community is all the different populations (different species) living in the same environment and interacting.

Example:
In a pond:

• Fish
• Frogs
• Algae
• Insects
• Bacteria

All form a community.

12. Ecosystem

An ecosystem includes the community PLUS the non-living (abiotic) components.

Abiotic components include:

• Water
• Air
• Soil
• Light
• Minerals

Example:

• Pond ecosystem
• Desert ecosystem
• Forest ecosystem

13. Biosphere

The biosphere is the largest level of organization.
It includes all ecosystems on Earth where life exists.

COMPLETE HIERARCHY (WRITE THIS IN YOUR NOTES)

Atom → Molecule → Biomolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

 

ORGANIZATION OF LIFE (Simplified Notes)

Living things are organized from simple → complex levels.
Here is the correct order:

1. Atom → 2. Molecule → 3. Macromolecule → 4. Organelle → 5. Cell → 6. Tissue → 7. Organ → 8. Organ System → 9. Organism → 10. Population → 11. Community → 12. Ecosystem → 13. Biosphere

1. Atom

• The smallest unit of matter.

2. Molecule

• When two or more atoms combine.
  Example: Water (H₂O), Oxygen (O₂)

3. Macromolecule (Polymer)

• Large molecules such as proteins, DNA, starch.

4. Organelle

• Tiny specialized structures inside a cell.
  Examples:
  • Mitochondria → produces energy
  • Ribosomes → make proteins
  • Nucleus → controls activities of cell

👉 If you see a cell as a human, organelles are like your organs—eyes, legs, heart.

5. Cell — The Fundamental Unit of Life

• Basic structural, functional and genetic unit of life.
• All living things are made of cells.

There are two types:

A. Prokaryotic Cells

• No membrane-bound nucleus
• No membrane-bound organelles
• DNA is scattered in cytoplasm
• Usually unicellular
  Examples: bacteria, blue-green algae (cyanobacteria)

B. Eukaryotic Cells

• Have true, membrane-bound nucleus
• Organelles are membrane-bound
• Can be unicellular or multicellular
  Examples: plants, animals, fungi, protists

👉 “Eu” means true → true nucleus.

6. Tissue

• Group of similar cells performing a specific function.
  Examples:
• Muscle tissue
• Nerve tissue
• Xylem & phloem in plants

7. Organ

• Formed when different tissues work together.
  Examples:
• Heart
• Lungs
• Kidney
• Leaf
• Root

8. Organ System

• Group of organs working together to perform a major function.
  Examples:
• Digestive system
• Reproductive system
• Nervous system
• Skeletal system

9. Organism

• A single, complete living being.
  Examples:
• Human
• Goat
• Cockroach
• Mango tree

10. Population

A population is:

“All organisms of the same species living in a particular place at a particular time and capable of interbreeding.”

Key words you must mention:
✔ Same species
✔ Interbreeding
✔ Same place
✔ Same time

Examples:

• Population of humans in Lagos in 2025
• Population of goats in Shomolu
• Population of cows in Kara market

👉 You cannot mix species. Humans + goats ≠ population.

11. Community

A community is:

“Different populations of organisms living together in the same place.”

Examples:
In your living room:

• Humans
• Ants
• Cockroaches
• Spiders

In a classroom:

• Students
• Mosquitoes
• Houseflies
• Bacteria

👉 Community = all living things only.

12. Ecosystem

An ecosystem consists of:

Biotic (living) components

Humans, goats, plants, bacteria, insects

Abiotic (non-living) components

Water, air, sunlight, soil, temperature

Ecosystem = Biotic + Abiotic in an environment

Examples:

• Forest ecosystem
• Pond ecosystem
• Marine ecosystem
• Desert ecosystem

13. Biosphere

• The part of Earth where life exists.
• Largest level of organization.

 

✅ BIOTIC AND ABIOTIC FACTORS

1. Biotic Factors

These are the living components of the environment.
Examples:

• Plants
• Animals
• Humans
• Fungi
• Bacteria
• Protists

2. Abiotic Factors

These are the non-living components of the environment.
Examples:

• Temperature
• Sunlight
• Wind
• Pressure
• Water
• Soil
• Humidity
• pH
• Minerals

👉 The abiotic factors determine which organisms can survive in an environment, while the biotic factors interact with each other (food chains, competition, predation).

✅ INTERACTIONS BETWEEN LIVING AND NON-LIVING THINGS

Biotic and abiotic factors influence one another.

✔ How abiotic factors affect living things:

• Sunlight → allows plants to carry out photosynthesis.
• Temperature → affects the distribution of animals (e.g., reptiles need warmth).
• Water → necessary for hydration and metabolism.
• Soil nutrients → determine the type of plants that can grow.

✔ How living things affect the environment:

Humans:

• Polluting the environment
• Littering plastics
• Blocking drainage → causes mosquito breeding
• Deforestation → leads to erosion

Animals:

• Earthworms improve soil fertility
• Termites build mounds that change soil structure

Plants:

• Add oxygen to the atmosphere
• Improve soil fertility

👉 Conclusion:
Biotic and abiotic components are interdependent. Changes in one can affect the other.

✅ THE BIOSPHERE

The biosphere is the part of the Earth that supports life.

It includes:

• Lithosphere (land)
• Hydrosphere (water bodies)
• Atmosphere (air)

If you were not taught this in secondary school, your teacher indeed owes you refund! 😄

✅ FULL ORGANIZATION OF LIFE (From largest to smallest)

1. Biosphere
2. Ecosystem (biotic + abiotic)
3. Community (different populations)
4. Population (organisms of same species)
5. Organism
6. Organ system
7. Organ
8. Tissue
9. Cell
10. Organelle
11. Macromolecule
12. Molecule
13. Atom