JAMB Biology Notes-Living Organisms

Topic

Living Organisms

Sub-Topics

1. Characteristics of Living Organisms
2. Cell Structure and Functions of Cell Components
3. Levels of Organization in Living Organisms (Cell → Tissue → Organ → System → Organism)

Table of Contents

• Topic
• Sub-Topics
• 1. Characteristics of Living Organisms
  • Distinguishing Living from Non-living Things
• 2. Cell Structure and Functions of Cell Components
  • Definition of a Cell
  • Types of Cells
  • Basic Cell Components (Common to Plant & Animal Cells)
  • Additional Organelles Unique to Plant Cells
  • Comparing Plant and Animal Cells
• 3. Levels of Organization in Living Organisms
  • Logical Sequence
• SUMMARY/REINFORCEMENT
• ASSIGNMENT

1. Characteristics of Living Organisms

1. Nutrition: The process by which organisms obtain and utilize food for growth, energy, and maintenance.
2. Respiration: The breakdown of food (often glucose) to release energy. Aerobic respiration uses oxygen; anaerobic respiration does not.
3. Excretion: The removal of metabolic waste products such as carbon dioxide, urea, and excess water from the body.
4. Growth: An irreversible increase in size and/or complexity of an organism. It usually involves cell division (mitosis) and cell enlargement.
5. Reproduction: The ability to produce offspring of the same kind, either sexually or asexually.
6. Irritability/Sensitivity: The ability to perceive and respond to stimuli from the environment (e.g., light, temperature, touch).
7. Movement/Locomotion: A change in position. Animals usually move from place to place; plants show movement in parts (e.g., bending toward light).
8. Adaptation: Traits that increase an organism’s chance of survival and reproduction in a specific environment.
9. Competition: Living organisms often compete for resources such as food, space, water, and mates.

Distinguishing Living from Non-living Things

• Living things exhibit all or most of the above characteristics.
• Non-living things do not perform these life processes and are incapable of self-sustaining activity.

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2. Cell Structure and Functions of Cell Components

Definition of a Cell

• The cell is the basic structural and functional unit of life. Every living organism is made up of one or more cells.

Types of Cells

1. Plant Cells
2. Animal Cells

Basic Cell Components (Common to Plant & Animal Cells)

1. Cell Membrane (Plasma Membrane)
   • Selectively permeable membrane that regulates the movement of substances into and out of the cell.
2. Cytoplasm
   • Jelly-like fluid that holds cell organelles. It is the site of many metabolic processes.
3. Nucleus
   • Controls cell activities and contains genetic material (DNA).
4. Mitochondrion (plural: Mitochondria)
   • Responsible for energy (ATP) production through aerobic respiration.
5. Ribosomes
   • Sites of protein synthesis; can be found on the endoplasmic reticulum or free in the cytoplasm.
6. Endoplasmic Reticulum (ER)
   • Rough ER has ribosomes for protein synthesis; Smooth ER is involved in lipid synthesis and detoxification.
7. Golgi Body (Golgi Apparatus)
   • Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell.

Additional Organelles Unique to Plant Cells

1. Cell Wall
   • Made of cellulose; provides rigid support and protection.
2. Chloroplasts
   • Contain chlorophyll for photosynthesis.
3. Large Central Vacuole
   • Maintains turgor pressure to support the plant cell; stores nutrients and wastes.

Comparing Plant and Animal Cells

Feature	Plant Cell	Animal Cell
Cell Wall	Present (cellulose)	Absent
Chloroplast	Present (in photosynthetic tissues)	Absent
Shape	Generally fixed/regular (rectangular)	Irregular (varied shapes)
Vacuole	Large, central vacuole	Small, often numerous vacuoles (if any)
Centrioles	Absent in most plants	Present in animal cells
Energy Storage	Starch	Glycogen
Location of Nucleus	Usually pushed to the periphery by large vacuole	Centrally located

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3. Levels of Organization in Living Organisms

1. Cell
   • The simplest unit of life.
   • Examples: Euglena, Paramecium, Chlamydomonas (these are unicellular organisms).
2. Tissue
   • A group of similar cells performing a specific function.
   • Examples: Epithelial tissues in animals, Hydra (which exists as a tissue-level organism).
3. Organ
   • A structure composed of different tissues working together for a specific function.
   • Example: Onion bulb (in plants), stomach (in animals).
4. System
   • A group of organs working together to carry out an overall life function.
   • Examples: Reproductive system, digestive system, excretory system (in animals).
5. Organism
   • A complete living thing that can carry out all basic life processes independently.
   • Single-celled organisms like Chlamydomonas or complex multicellular organisms like humans.

Logical Sequence

Cell → Tissue → Organ → System → Organism

SUMMARY/REINFORCEMENT

• Living organisms are defined and differentiated by key life processes: nutrition, respiration, excretion, growth, reproduction, irritability, and movement.
• Cells are the basic units of life and are broadly categorized into plant and animal cells with some distinct structural differences (e.g., cell wall, chloroplasts).
• Levels of organization move in sequence from cells to tissues, then organs, systems, and finally the whole organism. Examples like Euglena, Hydra, and onion bulb highlight these levels.

ASSIGNMENT

1. Define the term cell and list three major differences between a plant cell and an animal cell.
2. Explain why Euglena is considered a unicellular organism and describe two features it shares with higher plants or animals.
3. Arrange the following in ascending order and briefly explain each: organ, cell, organism, system, tissue.
4. State any four characteristics of living things and provide one example each (plants or animals) to illustrate them.