What are living things?

All living things can be put into three main groups:

  • Animals 
  • Plants
  • Microorganisms

Living things consist of cells that work together. A cell is the basic building block of all living organisms. They are very small and are only seen using a microscope. Some organisms are unicellular – this means they have only one cell, for example, bacteria, protists, and yeast. Some organisms are multicellular – this means that they have many cells, for example, animals and plants.

Level of organisation:

  • Similar cells form a tissue.
  • Similar tissues form an organ.
  • Different organs interact to form systems.
  • Different systems interact to form an organism.

Animal example:

Muscle cells work together to form muscle tissue, muscle tissue then combines to form an organ e.g. heart, stomach, or liver. Different organs work together to make up systems e.g. cardiovascular system or the muscular system. A combination of these different systems in the body makes up an organism.

Plant example:

Root hair cells work together to form root tissue. Root tissue then combines to form the roots of the plant. These then make up the transport system of a plant. The transport system makes up part of the organ system. The different systems work together to make up the plant.

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How can we identify living things?

Living things can be identified by a few key characteristics: 

  • Reproduction 
  • Growth
  • Adaptation 

All living things go through the same cycles including birth, growth, reproduction, and death. The life cycle of an animal is the journey from the start of its life all the way to the end of its life or to the point where the animal has babies and new life is formed. Animals have different life cycles depending on the type of animal it is, for example, the life cycle of insects is very different from the life cycle of mammals. The way in which organisms reproduce differs between organisms; for example, plants either self-pollinate or cross-pollinate, insects lay eggs, whereas mammals give birth to live offspring. 

All living things grow as it progresses through different developmental stages. Optimal growth occurs with the right environmental conditions and nutrition. Animals are consumers as they feed off other animals or plants, whereas plants are producers as they produce their own food through the process of photosynthesis. 

All living things are able to adapt to changing environments. Subsequently, those living things with useful adaptations are able to survive and reproduce. Their offspring inherit these adaptations and develop their own adaptations through mutations. This process continues over time, and the adaptations become focused on the needs of the environment.

Species that are not adapted will be at risk of becoming extinct. This can occur due to new predators, disease, destruction of habitats, change in the environment, or increased competition for resources. Some examples of adaptations include a giraffe’s long neck which allows it to reach leaves high up in trees and a cactus which is adapted to storing water for long periods of time in the desert. 

Living things also have many different key features that help us differentiate between them and to classify them into groups, for example, animals can’t produce their own food as they consume other animals or plants. Plants can produce their own food and microorganisms are very small. 

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How do we classify animals?

Animals can either be vertebrates or invertebrates. Vertebrates are animals that have a backbone. Invertebrates are animals that don’t have a backbone. 

There are five groups of vertebrates:

  • Mammals
  • Birds
  • Reptiles
  • Amphibians 
  • Fish

Mammals are warm-blooded vertebrates that have body hair or fur. Mammals have well-developed brains and they use their lungs to breathe. A female gives birth to a live mammal and mammals drink milk from their mothers. Young mammals rely on their parents for survival. A mammal’s internal body temperature is usually stable; therefore, they are warm-blooded animals. Humans are mammals as well as other warm-blooded vertebrate animals. Mammals are very diverse as they exist in many shapes and sizes. They also live in many different places, some mammals live on land, in water, or below the ground. 

A lion is a mammal.

A camel is a mammal.

Did you know that bats are the only mammals that can fly?

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How do we classify animals?

Animals can either be vertebrates or invertebrates. Vertebrates are animals that have a backbone. Invertebrates are animals that don’t have a backbone. 

There are five groups of vertebrates:

  • Mammals
  • Birds
  • Reptiles
  • Amphibians 
  • Fish

Mammals are warm-blooded vertebrates that have body hair or fur. Mammals have well-developed brains and they use their lungs to breathe. A female gives birth to a live mammal and mammals drink milk from their mothers. Young mammals rely on their parents for survival. A mammal’s internal body temperature is usually stable; therefore, they are warm-blooded animals. Humans are mammals as well as other warm-blooded vertebrate animals. Mammals are very diverse as they exist in many shapes and sizes. They also live in many different places, some mammals live on land, in water, or below the ground. 

A lion is a mammal.

A camel is a mammal.

Birds are vertebrate animals that are adapted for flight. The anatomy of birds reflects their ability to fly as they have strong wings and feathers. They also have  a beak to help them grab and swallow food. There are many types of birds, some of which jump, run, swim, and dive. Birds are characterised by their wings but some have lost the ability to fly, for example, penguins. Birds have feathers and they use their lungs to breathe. Birds lay eggs and their internal body temperature is usually stable; therefore, they are warm-blooded animals.

An eagle is a bird.

Birds are vertebrate animals that are adapted for flight. The anatomy of birds reflects their ability to fly as they have strong wings and feathers. They also have  a beak to help them grab and swallow food. There are many types of birds, some of which jump, run, swim, and dive. Birds are characterised by their wings but some have lost the ability to fly, for example, penguins. Birds have feathers and they use their lungs to breathe. Birds lay eggs and their internal body temperature is usually stable; therefore, they are warm-blooded animals.

An eagle is a bird.

Reptiles are vertebrates that are characterised by their scaly skin. Reptiles use their lungs to breathe. Reptiles usually lay eggs in a nest, however, two exceptions are pythons and boas give birth to live young. Their internal body temperature changes; therefore, they are cold-blooded animals. This is because they don’t have any insulation such as feathers or sweat glands in hot weather, and in cold weather they usually become inactive.  

A crocodile is a reptile.

A turtle is a reptile.

Reptiles are vertebrates that are characterised by their scaly skin. Reptiles use their lungs to breathe. Reptiles usually lay eggs in a nest, however, two exceptions are pythons and boas give birth to live young. Their internal body temperature changes; therefore, they are cold-blooded animals. This is because they don’t have any insulation such as feathers or sweat glands in hot weather, and in cold weather they usually become inactive.  

A crocodile is a reptile.

A turtle is a reptile.

Amphibians are vertebrates that have damp skin. A special property of their skin is that it has skin glands that produce useful proteins, some transport water, oxygen, and carbon dioxide into or out of the animals. Some of the proteins produced even fight bacterial or fungal infections. Amphibians require water, or a moist environment in order to survive.  Amphibians lay soft eggs in water and their internal body temperature changes; therefore, they are cold-blooded animals. Amphibians can breathe using their gills, through their thin skin, or using their lungs.

A frog is an amphibian. 

Amphibians are vertebrates that have damp skin. A special property of their skin is that it has skin glands that produce useful proteins, some transport water, oxygen, and carbon dioxide into or out of the animals. Some of the proteins produced even fight bacterial or fungal infections. Amphibians require water, or a moist environment in order to survive.  Amphibians lay soft eggs in water and their internal body temperature changes; therefore, they are cold-blooded animals. Amphibians can breathe using their gills, through their thin skin, or using their lungs.

A frog is an amphibian. 

Fish are vertebrates that live in the water, these can be in lakes, rivers, ponds, seas, and oceans. They have scaly skin which allows them to swim with ease. Fish use gills located on the sides of their bodies to breathe. Fish lay soft eggs in water and their internal body temperature changes; therefore, they are cold-blooded animals. However, there is an exception to this, tuna, mackerel, and opah fish are all warm-blooded. Fish exist in many shapes, sizes, and colours. The largest fish on the planet is a whale shark!

A goldfish is a fish.

Did you know that a whale shark is the largest fish on the planet?

Fish are vertebrates that live in the water, these can be in lakes, rivers, ponds, seas, and oceans. They have scaly skin which allows them to swim with ease. Fish use gills located on the sides of their bodies to breathe. Fish lay soft eggs in water and their internal body temperature changes; therefore, they are cold-blooded animals. However, there is an exception to this, tuna, mackerel, and opah fish are all warm-blooded. Fish exist in many shapes, sizes, and colours. The largest fish on the planet is a whale shark!

A goldfish is a fish.

Did you know that a whale shark is the largest fish on the planet?

There are different types of invertebrates. We can put these into groups depending on their common features, for example, invertebrates with six legs, more than six legs, and without legs. Invertebrates without legs can be further classified into worm-like or not worm-like. 

There are six groups of invertebrates:

  • Mollusks 
  • Arthropods 
  • Worms
  • Cnidarians
  • Echinoderms
  • Sponges 

Mollusks live in marine environments, and they exist in many different shapes and sizes, for example, some have shells for protection and others don’t.

Snails, squid, and oysters are examples of mollusks.

Arthropods live on land, there are many different types of arthropods. Arthropods can have different numbers of jointed legs, some have six, some have eight, some have ten, and others have more than ten jointed legs. Arthropods also have an exoskeleton.

Ants, spiders, crabs, and millipedes are examples of arthropods.

Worms have long soft bodies and moist skin. 

Cnidarians are also known as the jellyfish group. These are marine animals that usually have tentacles with stinging cells. They use these to capture food.

Jellyfish and polyps are examples of cnidarians.

Echinoderms are marine animals. They have a star-like shape consisting of a hard, spiny covering or skin.

Starfish is an example of an echinoderm. 

Sponges are also known as peripherals. These invertebrates are found in deep water;  they have pores and can’t swim. 

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