Animal

Animal diversity b

Blastulation

Odonata copulation

Ultramarine Flycatcher (Ficedula superciliaris) Naggar, Himachal Pradesh, 2013 (cropped)

Expl0072 - Flickr - NOAA Photo Library

Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in size from 8.5 micrometers (a type of plankton) to 33.6 meters (the blue whale). They have complex interactions with each other and their environments, forming intricate food webs. The study of animals is known as zoology.

Characteristics

Most animals possess mobility, a characteristic that sets them apart from other living things. Animals are also distinguished by their sensory and nervous systems, allowing them to respond rapidly to stimuli in their environment. They are capable of voluntary movement, a trait that has evolved in different ways, leading to the vast diversity of animal life.

Cell Structure and Life Cycle

Animals are multicellular, with cells that lack cell walls, allowing for a higher level of interaction and communication between cells. This multicellularity allows for specialized tissues and organs, which contribute to the complex behaviors and functions observed in the animal kingdom. The life cycle of animals can vary greatly, but it typically includes stages of growth, development, reproduction, and death.

Reproduction

Reproduction in animals can be asexual or sexual, with the latter being the most common mode. Sexual reproduction involves the combination of genetic material from two parents to produce genetically diverse offspring, a factor that has contributed to the vast diversity of animal life on Earth.

Classification

The classification of animals is a complex and evolving field. Traditionally, the kingdom Animalia is divided into various phyla, including Chordata (which includes vertebrates like mammals, birds, fish, reptiles, and amphibians), Arthropoda (including insects, spiders, and crustaceans), and Mollusca (such as snails, octopuses, and clams), among others. This classification is based on an animal's anatomical and physiological characteristics, developmental patterns, and genetic relationships.

Habitats and Distribution

Animals inhabit every ecosystem on Earth, from the deepest parts of the ocean to the highest mountains. Their adaptations to their environments are a key aspect of their survival and evolution. For example, aquatic animals may have gills for breathing underwater, while desert animals may have adaptations for conserving water.

Human–Animal Relationships

Humans have a complex relationship with animals, including domestication, conservation, and environmental impact. Animals play crucial roles in human societies—as pets, as livestock, and as a source of inspiration. However, human activities have also led to habitat destruction, pollution, and climate change, all of which threaten animal populations.

Conservation

Conservation efforts aim to protect endangered species and their habitats. This involves a range of strategies, from legal protections and habitat restoration to the establishment of wildlife reserves and parks. The goal of conservation is to ensure the survival of animal diversity for future generations.