Welcome to tadpoles.org.uk

Tadpoles and using them to understand brains

Frog Facts

Facts about tadpoles, frogs, newts and amphibians!


What are tadpoles?


Wood Frog

Frogs, toads, newts and salamanders are Amphibians. They all spend part of their life on land but go back to water in ponds, lakes and rivers to lay eggs. The eggs hatch into tadpoles. Young tadpoles are rather like baby fish. They swim by using their tails and use gills to get oxygen from the water. They often feed on plants. The photos of Canadian Wood Frog tadpoles  are by NatureNorth.com

When tadpoles get bigger, they develop lungs to breath air, grow legs and  start to eat other small animals.Wood-frog-tadpole-legsf

After a few weeks  the tail gradually shrinks and they hop out of the water as tiny froglets. Most adult amphibians, like frogs, eat insects.Wood-Frog-frogletf

Click to see more about the life cycle

What are Amphibians?

There are three types of amphibians:

Anura: 6,642 species of frogs and toads without tails. Many have a tongue they can shoot out to catch insects.

Caudata: 684 species of newts and salamanders with a long tail. This is a Smooth Newt Triturus vulgaris (Photo by Magnus Maske)Smooth_Newt_credit_Magnus Maskef

Gymnophiona:  205 species of worm-like caecilians, without any legs and living underground mainly in South East Asia (Photo of Dermophis mexicanus by Franco Andreone).Caecilian-Dermophis_mexicanusf

Find out more about UK amphibians here.

The frog as an example

There are huge numbers of different kinds of frogs found all over the world and you can find pictures at AmphibiaWeb   They are divided into families with Latin names. One widespread group of frogs has the Latin family name Rana. This is still the word for frog in Spanish and Italian. Here are some examples of this family of frogs from different countries. The tadpoles and life-cycle of all of them is very similar.

The Common Frog in Europe has the family name Rana and its specific name is temporaria (photo by ©Dave Mangham, www.wildlifephotos.org.uk)Rana-temporaria-Manghamf

The Wood Frog in Canada is adapted to survive the very low temperatures in winter. Its Latin name is Rana sylvatica (photo by  James H. Harding).Rana-sylvatica-hardingjATmsu-edu
The American Bullfrog is bigger and its name is Rana catesbiana (photo by  John White).Rana-catesbiana-John-Whitef


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