Living Things

All around us, we see a variety of organisms — plants, animals, bacteria, fungi, and humans. These are called living things because they show the basic features of life such as growth, movement, reproduction, and response to the environment.

The term living things refers to organisms that carry out vital biological processes like breathing, nutrition, excretion, and reproduction. From the smallest microbe to the largest mammal, all living things share certain characteristics that distinguish them from non-living things.

1.0Living Things Definition

Living things are organisms that possess life and exhibit essential biological processes such as growth, movement, reproduction, respiration, and adaptation. They are made up of one or more cells, which are the basic structural and functional units of life.

Every living thing—whether a tiny bacterium or a giant blue whale—relies on energy to perform daily life functions.

2.0Characteristics of Living Things

1. Cellular Organization

All living things are composed of cells.

• Unicellular organisms have only one cell (e.g., Amoeba, Bacteria).
• Multicellular organisms consist of many cells (e.g., Humans, Plants).
  Cells perform essential activities like metabolism, energy production, and growth.

2. Growth and Development

Living things show growth, meaning an increase in size or number of cells.

• Plants grow throughout their life by adding new cells from the tip of stems and roots.
• Animals grow to a certain age and then stop increasing in size, but they still repair and replace old cells.

3. Reproduction

All living things reproduce to continue their species.

• Animals reproduce sexually (two parents) or asexually (one parent).
• Plants reproduce through seeds, spores, cuttings, or budding.

4. Response to Stimuli

Living things respond to changes in their environment called stimuli.

• A plant bends towards light (phototropism).
• A dog wags its tail when happy.
• Humans respond to sound, heat, cold, or pain.

5. Movement

Living things show movement, either visible or internal.

• Animals move from one place to another in search of food or shelter.
• Plants show movement in their parts—such as opening flowers or growing towards sunlight.

6. Respiration

All living things need energy to perform life functions.
They obtain this energy by respiration, a process of breaking down food molecules to release energy.

• Humans and animals take in oxygen and release carbon dioxide.
• Some microorganisms respire anaerobically (without oxygen).

7. Nutrition

Living things need food for energy, growth, and repair.

• Plants prepare their own food through photosynthesis (autotrophic nutrition).
• Animals and humans depend on plants or other organisms for food (heterotrophic nutrition).

8. Excretion

The process of removing waste products from the body is called excretion.

• Humans excrete wastes like urea, sweat, and carbon dioxide.
• Plants remove oxygen (a byproduct of photosynthesis) and other waste materials through leaves and roots.

9. Adaptation

Living things adapt to their environment to survive.

• Polar bears have thick fur to survive in cold climates.
• Cacti have spines and thick stems to store water in deserts.

10. Lifespan

Every living organism has a definite lifespan—a beginning (birth), a period of growth, and an end (death).

3.0Difference Between Living and Non-Living Things

4.0Classification of Living Things

Living things are broadly classified into five main kingdoms based on their structure, nutrition, and mode of reproduction.

1. Kingdom Monera

• Comprises unicellular organisms without a true nucleus (prokaryotes).
• Example: Bacteria, Cyanobacteria (Blue-Green Algae)

2. Kingdom Protista

• Unicellular eukaryotic organisms with a true nucleus.
• Examples: Amoeba, Paramecium, Euglena

3. Kingdom Fungi

• Mostly multicellular, non-green organisms that feed on decaying matter.
• Examples: Mushrooms, Yeast, Molds

4. Kingdom Plantae

• Multicellular autotrophs that make their own food via photosynthesis.
• Examples: Moss, Ferns, Trees, Flowering Plants

5. Kingdom Animalia

• Multicellular heterotrophs that depend on plants or other animals for food.
• Examples: Humans, Fish, Birds, Mammals

5.03 Domains of Life

1. Archaea: Ancient, single-celled organisms often found in extreme environments (like hot springs).
2. Bacteria: Single-celled organisms found everywhere. Some are helpful (gut bacteria), while others cause disease.
3. Eukarya: Organisms with complex cells containing a nucleus. This domain includes all plants, animals, fungi, and protists.

6.0Basic Needs of Living Things

For an organism to survive and maintain the characteristics listed above, it requires specific resources from its environment. Without these, the organism will eventually die.

Water and Fluids

Water is the most critical need for life. Most organisms are made up of 50% to 95% water.

• Transport: Water acts as a solvent, transporting nutrients and gases throughout the body (e.g., blood in animals, sap in plants).
• Chemical Reactions: Digestion and photosynthesis require water to occur.
• Temperature Regulation: Water helps regulate body temperature through sweating or transpiration.

Energy Source (Food/Sunlight)

Energy fuels the biological machinery of life.

• Sunlight: The primary source of energy for almost all life on Earth. Plants trap this energy directly.
• Food: Herbivores, carnivores, and omnivores obtain energy indirectly from the sun by eating plants or animals that ate plants.

Air and Atmosphere

The atmosphere provides essential gases.

• Oxygen: Required by most organisms to release energy from food.
• Carbon Dioxide: Required by plants to produce food.
• Nitrogen: Essential for building proteins and DNA.

Habitat and Living Space

Every organism needs a space that provides food, water, and shelter.

• Competition: Because space is limited, organisms often compete for territory.
• Suitability: A polar bear requires a cold habitat with ice, while a cactus requires a dry, arid environment. If an organism is removed from its habitat, it may struggle to survive.

Homeostasis

While not an external resource, the ability to maintain homeostasis is a fundamental need. This is the maintenance of a stable internal environment despite changes outside. Examples include:

• Keeping body temperature stable (98.6°F or 37°C for humans).
• Regulating water levels within cells.
• Maintaining the correct pH balance in the blood.

7.0Levels of Organization in Living Things

Living things display biological organization at several levels:

1. Cell → Basic unit of life
2. Tissue → Group of similar cells performing a common function
3. Organ → Structure made of tissues (e.g., heart, leaf)
4. Organ System → Several organs working together (e.g., digestive system)
5. Organism → A complete living being capable of independent existence

This hierarchical organization ensures smooth functioning of life processes.

8.0Energy Flow in Living Things

All living organisms require energy to carry out their life processes.

• Plants trap solar energy and convert it into chemical energy (glucose).
• Animals consume plants or other animals to obtain this stored energy.
  This continuous flow of energy forms the foundation of all ecosystems on Earth.

9.0Reproduction in Living Things

Reproduction is a key characteristic that ensures the continuity of life.
There are two main types:

Asexual Reproduction

• Involves only one parent.
• Common in bacteria, yeast, and some plants.
• Examples: Binary fission, Budding, Fragmentation.

Sexual Reproduction

• Involves two parents—male and female.
• Leads to variation in offspring.
• Common in humans, animals, and flowering plants.

10.0Adaptations in Living Things

Adaptations help living organisms survive in diverse environments.

• Aquatic animals have fins and gills.
• Desert plants have waxy leaves to prevent water loss.
• Birds have hollow bones to make flying easier.

Adaptations are the result of evolution, helping species adjust to changing surroundings.

11.0Interdependence Among Living Things

Living things are interconnected and depend on each other for survival.

• Plants produce oxygen and food.
• Animals depend on plants for food and release carbon dioxide, which plants use for photosynthesis.
  This creates a balance in nature, essential for ecosystem stability.