Short Answer
Kingdom Animalia includes all animals that are multicellular, eukaryotic, and heterotrophic in nature. Animals cannot prepare their own food and depend on plants or other animals for nutrition. They do not have a cell wall and show a high level of body organization.
Animals usually have the ability to move from one place to another and respond quickly to stimuli. They possess specialized tissues, organs, and organ systems that help them perform different life functions efficiently.
Detailed Explanation :
Defining Features of Kingdom Animalia
Kingdom Animalia is one of the largest and most diverse kingdoms of living organisms. It includes a wide range of organisms from simple sponges to complex mammals like humans. Despite their diversity in shape, size, and habitat, all animals share certain basic characteristics that define Kingdom Animalia. These defining features are explained below in simple and easy language.
Multicellular and Eukaryotic Organisms
All animals are multicellular organisms, meaning their body is made up of many cells. These cells work together and are organized into tissues, organs, and organ systems.
Animal cells are eukaryotic, which means they have a true nucleus surrounded by a nuclear membrane. They also contain membrane-bound organelles such as mitochondria, Golgi bodies, and endoplasmic reticulum. This complex cell structure allows animals to perform advanced life functions.
Absence of Cell Wall
A major defining feature of animals is the absence of a cell wall. Unlike plant cells, animal cells are surrounded only by a cell membrane.
The absence of a rigid cell wall allows animal cells to change shape easily. This flexibility helps animals in movement, feeding, and other activities that require body flexibility.
Heterotrophic Mode of Nutrition
Animals are heterotrophic organisms, which means they cannot make their own food. They depend on plants or other animals for nutrition.
Animals obtain food by ingestion. They take food into their body and digest it internally. This mode of nutrition is different from plants, which prepare food by photosynthesis, and fungi, which absorb food.
Presence of Specialized Tissues
Animals show a high level of body organization. Their cells are specialized and grouped into tissues such as muscular tissue, nervous tissue, connective tissue, and epithelial tissue.
These tissues perform specific functions. For example, muscles help in movement, nerves help in coordination, and connective tissues provide support. This specialization makes animals efficient in performing life activities.
Ability to Move
Most animals show locomotion, which means they can move from one place to another. This ability helps animals search for food, escape from enemies, and find shelter.
Movement is possible due to the presence of muscles and skeletal structures. Some animals may be sessile at certain stages of life, but most show movement at least at some stage.
Presence of Nervous System
Most animals have a nervous system that helps them respond to changes in their environment. The nervous system allows quick communication between different parts of the body.
With the help of sense organs, animals can detect light, sound, smell, taste, and touch. This ability to respond to stimuli is a key feature of Kingdom Animalia.
Mode of Reproduction
Animals mainly reproduce by sexual reproduction. This involves the formation of male and female gametes and fertilization.
Sexual reproduction produces variation among offspring, which helps animals adapt to changing environments. Some animals can also reproduce asexually, but sexual reproduction is more common.
Storage of Food
Animals store food mainly in the form of glycogen and fats. Glycogen is stored in muscles and liver and is used as an energy source.
This method of food storage is different from plants, which store food as starch.
Growth Pattern
Animals show definite growth patterns. Most animals grow up to a certain size and then stop growing.
Growth in animals is usually uniform and well-controlled, unlike plants which grow throughout their life.
Habitat Diversity
Animals are found in almost all types of habitats. They live on land, in water, in air, and even in extreme environments.
Their ability to adapt to different habitats shows the success and diversity of Kingdom Animalia.
Role in Ecosystem
Animals play important roles in ecosystems. They act as consumers in food chains and help maintain balance in nature.
Some animals help in pollination, seed dispersal, and controlling population of other organisms.
Conclusion
Kingdom Animalia includes multicellular, eukaryotic organisms that lack a cell wall and show heterotrophic nutrition. Animals have specialized tissues, organs, and organ systems, which allow them to perform complex life functions. They usually show movement, possess a nervous system, and reproduce mainly by sexual reproduction. These defining features clearly separate animals from plants, fungi, and other kingdoms, making Kingdom Animalia a highly advanced and diverse group of living organisms.