How plants and animals are organised

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Key points

  • Cells are the smallest unit of life.
  • Cells in multicellular plants and animals are arranged into tissues, organs and organ systems.

Levels of organisation


animals and plants consist of different types of cells organised in a hierarchy as tissues, organs and systems.

a person standing next to the words cells, tissues, organs, organ systems, organism


Cells are the smallest unit of life. Most cells have features which give them different functions within an organism.

Humans are multicellular. That means 'made of lots of cells', not just one cell. The cells in many multicellular animals and plants are specialised, so that they can share out the processes of life. These cells all work together to keep the organism alive.


Examples of specialised cells in plants include:

  • Palisade leaf cells: these are found towards the tops of leaves and are packed with green chloroplasts in which occurs.

  • Root hair cells: cells containing a hair-like structure that pokes into the soil to absorb more water and nutrients.


Examples of specialised cells in animals include:

  • Ovum - egg cell: contains half of an organism’s genetic information - DNA - which will join with the sperm during fertilisation.
  • Sperm: transfers genes from male body during sexual reproduction.
  • Ciliated cells: these have tiny hairs - cilia - on their surface that beat in a rhythmical pattern. For example, they move mucus from the airway to the mouth to swallow. They also move an ovum through the female reproductive system.
  • Red blood cells: carry oxygen to body tissues that need it.
a diagram showing cells which all have diggerent shapes and textures.
Examples of specialised animal cells. Notice that they look very different from one another


A group of similar cells in the same place with the same function is a tissue.


In plants, dermal tissue covers the leaves, fruits, flowers, roots and stems of plants. Dermal tissue stops the plant from losing too much water.


Examples of tissues in animals include muscle tissue and nerve tissue.

  • Muscle tissue: made of muscle cells that can contract and relax to move parts of the body.
  • Nerve tissue: made of nerves, found in the brain and spinal cord, and the network of nerves that spreads throughout the body. It sends electrical signals to control and coordinate actions.
These apples are covered by dermal tissue.


A group of tissues in the same place with the same function is an organ.


Roots are plant organs. They keep plants securely in the ground and are covered with root hair cells which absorb water and nutrients from the soil. Other plant organs are leaves, stems and flowers.


The heart is an organ made from muscle and nerve tissue and pumps blood around the body. Other examples of animal organs include the liver, brain, lungs, stomach, intestines, kidneys, bladder and skin.

Activity - Label the plant organs

Activity - Label the human organs

Organ systems

Two or more organs with the same function is an organ system.


Plants have two organ systems.

  • The shoot organ system in a plant is made from leaves, stems, buds, fruits and flowers.
  • The root organ system of most plants are all the parts that are underground.


There are 11 organ systems in the human body that each have a different function. Here are some examples:

Organ systemMain organsFunction
CirculatoryHeart, veins, arteriesTransports substances in the blood around the body
RespiratoryLungsTakes in oxygen, removes carbon dioxide
DigestiveStomach and intestinesBreaks down food, absorbs nutrients
ReproductiveUterus, vagina. Penis, testesCreates offspring

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