1. How do animals detect environmental stimuli?
Animal Senses
How do animals detect environmental stimuli?

2. Remember! Sensory stimulation is the starting point of behaviour.
Animal’s senses are not necessarily the same as ours.

3. Photoreceptors In animals light is detected by?
The eyes
The structure of the eye varies for different organisms.

5. Structure of Eyes Snails Insects and Crustaceans
Have simple eyes which detect light in the same way as we detect heat.
Insects and Crustaceans
Have compound eyes made up of many separate ommatidia. These give a mosaic vision, very good for detecting movement.

6. Compound Eyes

7. Structure of Eyes Vertebrates
Have lenses that help to form clear images.
If two eyes face forwards they have overlapping fields (Binocular vision) enabling good judgement of distance

8. Vertebrate Eyes

9. Vertebrate Eyes

10. Structure of Eyes Night Vision
This involves a structure called the tapetum, this is a layer of silvery crystals that acts as a reflector allowing animals like cats to pick up 50% more light at night than human’s can detect.
This is why cat’s eyes glow in the dark.

11. Night Vision

12. Vision
Animals also use their vision to detect movement, speed of movement, shapes etc.

13. Colour Vision
We, as humans see violet, indigo, blue, green, yellow, orange and red parts of the light spectrum.
Bees see ultraviolet light but are less sensitive to red. This is why most red flowers have some blue or a strong scent.

14. How bees see

15. Colour Vision cont Goldfish can see far red light.
Sea birds are particularly sensitive to red light.

16. Sea Birds Vision

17. Thermoreceptors Infra-red light is a form of heat.
No animal can “see” infra-red with eyes, but certain animals can detect warm objects as if they can see them.
E.g. snakes

18. Snakes Heat Sensors
Snakes have 2 heat sensing pits in front of and slightly below their eyes – these are so accurate the snakes can strike prey in pitch dark.

19. Thermoreceptors Humans can detect heat with their skin.
Other animals e.g. mosquitoes home in on their prey using thermoreceptors.

20. Mechanoreceptors
These sense gravity, touch, pressure, stretch and movement.
These let the animal know which way is up.
They help recognition of the position of one part of the body in relation to another. This is important for coordinated movement.

21. Mechanoreceptors Cont
Touch, pressure and the texture of objects in the environment, plus the tension in internal organs such as the stomach or bladder, are the functions of these receptors.

22. Mechanoreceptors cont
The skin of humans has tactile receptors.
Sometimes animals have hairs with receptors at the base, like whiskers in cats

23. Cat’s whiskers

24. Mechanoreceptors cont
Some animals have special sense organs called statocysts that serve as gravity receptors.

25. Mechanoreceptors cont
Fish have a lateral line organ that runs the length of the body. This consists of hairs with their tips enclosed in a jelly-like substance. These respond to waves, currents or disturbances in the water.

26. Lateral Line

27. Mechanoreceptors cont
Proprioreceptors are sense organs that respond to tension in the muscles or joints.

28. Chemoreceptors Olfaction (smell)
this is the detection of chemicals in the air or water that diffuse towards or are swept towards the animal
Used for the preliminary examination of things at a distance.

29. Chemoreceptors Gustation (taste)
the detection of chemicals in the liquid or solid state.
For the examination of objects that have been touched.
Four basic tastes: sweet, sour, salty and bitter

30. Human Tongue

31. Gustation Cont
These are located in different areas of the tongue.

32. Chemoreceptors
The distinction between smell and taste becomes blurred in simpler animals.
Humans use their noses and tongues.

33. Chemoreceptors Flies have taste hairs on their feet.
Many insects smell using antennae.

34. Chemoreceptors
Reptiles have a small opening in the head, this opens into the roof of the mouth.
This is called the Jacobson’s organ.

35. Jacobson’s Organ

36. Chemoreceptors
A snake flicking out its forked tongue is collecting chemical samples and bringing them back to the Jacobson’s organ for analysis.

37. Pheromones
These are chemicals used to communicate between members of the same species.
Members of the same species have receptors to pick up these pheromones, other species ignore them.

39. Auditory Receptors
In humans sound waves cause the eardrum to vibrate, these vibrations are transmitted across the middle ear by 3 small bones
This sets up vibrations in the fluid-filled cochlea.
This initiates impulses in the auditory nerve and we finally hear with our brain.

40. Human Ear

41. Auditory Receptors
Humans can hear from 20 Hz to Hz. Sound above that is ultrasonic.
Bats use ultrasonic bleeps as a form of sonar.
Dogs and many insects hear in the ultrasonic range.

42. Auditory Receptors
Whales use a complicated communication system involving ultrasonic sounds, echo-location and very low sounds called infrasounds (travel for long distances)

44. Auditory Receptors
Elephants and Hippos use infrasound waves to communicate over long distances.

45. Detection of Electric Fields.
Certain species “stun” their prey with an electric shock e.g. eels
Certain fish create an electric field around themselves, allowing them to pick up any disturbances in the field.

47. Detection of Magnetic Fields.
Homing pigeons can detect the magnetic field lines of the earth, they use this to navigate during migration or homing.

48. Questions Name the colours of light we can see.
Which cells see colour and which see black and white?
Two eyes facing forward ………. Vision which is good for judging …………
Insects have …….. Eyes made up of many ………. Which give …… vision.
Snakes can “see” ……… …….. With small pits set under their ……..

49. Questions Cont
A gravity-detecting organ in invertebrates is called a ………… It consists of a round cavity with small …….., and placed on these is a small, hard, pebble-like object called a ……..
In fish the ……... …….. Organ detects disturbances in the water.
Name 5 ways that animals use chemicals.

50. Questions Cont
Sounds above those that humans can hear are called …….., and those below are called……….
Some fish living in muddy conditions use ……… ………. to test the world around them.