Welcome to tadpoles.org.uk

Tadpoles and using them to understand brains

Food Chains

Find out where tadpoles are in the food chain and who eats who in a pond!


Food chains

Food chains include plants and animals arranged in an order of who eats who. Plants take in carbon dioxide from the air and  absorb light from the sun. They use the process called photosynthesis to produce organic matter.


Some animals get their energy from plants (herbivores) and some from eating other animals (carnivores). Others eat a mix of both plants and animals (omnivores). 


Often animals get bigger the higher you go up the food chain. Many small animals feed on plants, larger animals feed on those animals and a top predator feeds on those animals. Though this isn’t always the case (e.g. grass->cow->human).

Plants are known as producers as they produce the organic matter using energy from the sun. Animals are known as consumers as they consumer this food or indeed each other.


There are different levels of consumers in a food chain. The animal that eats the plant is called a primary consumer. A secondary consumer eats the primary consumers and a tertiary consumer feeds on the secondary consumer.

Here is a pond life food chain, including young tadpoles, who are primary consumers at this stage in their life. foodchain

The arrows show who eats who. Tadpoles eat the algae, which are plants and are the producers. Tadpoles are eaten by newts, which are eaten by birds such as this heron. The tadpoles, newts and birds are consumers, but at different levels. The tadpoles are primary consumers as they eat the producer, the algae.

Often the connections between animals are more complicated and more like a web  than a chain. This is because some animals eat more than one thing. A simple example of a pond life food web is below.

food web

As you can see, lots of animals like to eat tadpoles and the bird eats most animals! Click here to find out more about tadpole predators. Click here to find out what tadpoles eat.

Activities and resources

pencil22small_foka.tkFood chain cut and stick

Click here or on the link below to print a life-cycle diary to fill out as your tadpoles grow:


Food chain/web Links 

Click on the links below for more food chain/web resources, websites, videos and more!

Bitesize KS2 Food chains:








Bitesize KS2 Food chains:








Video about food chains from Crash Course Kids:


Media credits under creative commons licence: cat-Laki10 clipart; human-clipartbest.com; sheep-dailyclipart.com; newt clipart-Alex Brad; damselfly nymph- Sharp Photography; Stickleback and beetle- commons licence 

Tadpole swims when touched at *

The details of swimming movements which hatchling Xenopus tadpoles make in response to touch with a fine hair  have been studied by making high speed videos at 200 fps. In these examples touch on the left (*) leads to a bend to the right followed by swimming. Waves of bending travel from the head to tail (at ~ 14 cm per second) and increase in amplitude as they travel along the body. They move the tadpole in the direction shown by the arrows. Swimming speeds at ~ 20 oC range from 4 to 6 cm per second.hatchling tadpole swims when touched at *

Kahn J.A., Roberts A. & Kashin S. (1982) The neuromuscular basis of swimming movements in embryos of the amphibian Xenopus laevis. J. exp. Biol.  99, 175‑184. http://jeb.biologists.org/cgi/reprint/99/1/175

Adult South Africal Clawed toad Xenopus laevis


         Xenopus laevis

What Tadpoles Look Like

Tadpoles can start swimming spontaneously or when they are stimulated but it is just as important that they can stop. This normally happens when their head and cement gland bumps into the surface of the water or some other solid tadpoles swimmingobject like a plant or the side of a dish. This kind of stimulus and the tension in the mucus strand when the tadpole is hanging attached have an inhibitory effect on the tadpole. While hanging, it never moves spontaneously and is much less responsive to stimulation. This ability to keep still may make it more difficult for predators to detect and eat tadpoles. 

Types of Neurons

There are different types of neurons in a nervous system and they are named depending on their function.


Interneuron from Xenopus laevis tadpole

Broadly there are 3 main types:

  1. Sensory neurons
  2. Motor neurons
  3. Interneurons 





Flexion behaviour of hatchling tadpole in response to skin stimulation (represented by arrow).

When the skin of Xenopus laevis hatchling is touched, sensory neurons are activated, passing on exitation to sensory pathway neurons (interneurons) in the spinal cord, which in turn excite motor neurons, causing flexion behaviour

For more info on research into flexion behaviour click here. 

Synaptic transmission (blank diagram)

pencil22small_foka.tkPrint and fill in the blank diagram with the key steps in the process of synaptic transmission:



Resting potential and action potential confusion!



The terms resting potential and action potential can be confusing, as they seem to suggest that one is an active process and the other not.


Action potentials are actually produced by a passive process- sodium ions diffusing into the axon, causing depolarisation. 

Resting potentials are generated by an active process, which needs ATP. The sodium-potassium pump carries out active transport of ions in and out of the axon to generate a potential difference across the cell and a voltage of -60/70 mV inside the axon.

So even though the axon is said to be at “rest”, an active process involving energy in the form of ATP is actually going on. And even though the action potential sounds like it needs energy, it is actually a passive process.

Make sure you are clear on this!

Axon, membrane or axon membrane?!



Some exam boards prefer you to mention simply the “axon”, others just the “membrane”, or the “membrane of the axon”. 


When we are talking about a difference in charge over an area, we always refer to what area that is- for example a potential difference over the axon membrane. 

Some exam boards will prefer you say that the “membrane” or “axon membrane is depolarised”…but others will be happy with just the “axon is depolarised”

Check what is preferred by your exam board and incorporate into your notes links below:





Exam Board Links

pencil22small_foka.tkClick on the links below to access the specifications for listed exam boards:







Toad spawn

Toad eggs are the same size as Frog eggs but are laid in a string, often among weeds in the pond. The string can be more than 1 meter long and contain a double row of eggs. Here is a photo of a small piece from a pond in Hampshire.

A small piece of toad spawn from a pond in Hampshire.

American Bullfrog

Below is an American Bullfrog. The Latin name of this frog is Lithobates catesbeianus. It is sometimes also called Rana catesbeianus. 

American_Bullfrog_(Rana_catesbeiana)_-_Algonquin_Provincial_Park_Ontario_By Ryan Hodnett Own work

Click here for more information on the American Bullfrog from the ARKive website.

Media credits: American Bullfrog-Ryan Hodnett