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UNIT 3. INTERACTION
UNIT 3. INTERACTION
1. WHAT IS INTERACTION? � All living beings interact with their environment and with living beings to survive.
Interaction enables living beings to receive and respond to stimulus.
� Interaction involves different elements:
� Stimuli: these are detectable changes in the internal or external environment. They provoke
responses.
� Receptors: these are structures which receive stimuli from the external or internal
environment.
� Coordination systems: these consist of organs which process information received by the
receptors and produce a response.
� Responsive organs (also called effectors): These are structures which produce responses.
� Responses: Are actions provoke by a stimuli.
1 1. WHAT IS INTERACTION?
2. 2. INTERACTION IN ANIMALS
• Animals can move around in their surrounding: they do this in order to find food, escape from
predator, or look for a mate for reproduction.
• Some animals change their colour to camouflage themselves so that they are not capture and
killed by other animals.
• Others sleep during the cold winter months (hibernate) so that they use very little energy.
• Animals eat when they feel hungry
ANIMALS INTERACT WITH THE ENVIRONMENT TO SURVIVE
2. 2. INTERACTION IN ANIMALS
STIMULI
• Stimulus is a change in the environment of an organism that causes the organism to respond. A
stimulus can be either internal (comes from inside the organism) or external ( comes from outside
the organism)
• Stimuli can be classified as:
- Physical: light, sound, temperature, pressure, etc
- Chemical: the presence or absence of chemical substances
- Biotic: changes caused by the presence of other living beings
2. 2. INTERACTION IN ANIMALS
RECEPTORS
• Are sensory structures which detect external and internal stimuli.
• Internal receptors: Animals have receptor inside their bodies that detect internal stimuli. They are found
throughout the different tissues and organs. For example, receptor in the muscles and joints inform us of
the body´s position and movements. They also receive signals of tiredness and pain. The sensation of
hunger is caused by receptors found in the stomach wall. The sensation of thirst is caused by receptors that
detect the loss of water.
• External receptors: Animals have five sense organs that detect external stimuli: the eyes, ears, nose, tongue
and skin. These sense organs contain receptors, which are a special kind of cells that are sensitive to
external stimuli. The five sense organs contain mechanical receptors, chemical receptors, light receptors
and thermal receptors.
2. INTERACTION IN ANIMALS
COORDINATION SYSTEM
Coordination systems work together to process information received from stimuli and to produce
appropriate responses. Animals have two coordination systems:
� The nervous system regulates the body's activities and responses (functions which require rapid
responses, such as locomotion). It works by means of specialised cells called neurons which
transmit information in the form of nerve impulses. The responses are rapid and brief.
� The endocrine system regulates and coordinates the body functions (functions which require
maintained responses such as growth, development, metabolism...) by means of chemical
substances called hormones. The responses are slow and long.
2. INTERACTION IN ANIMALS
NERVOUS SYSTEM (NS)
� The nervous system is what animals use in situations where they need to react very quickly.
� How does the nervous system work? The nervous system receives information from the receptor,
interprets it and elaborate a responses and transmits a response to the effectors.
� Types of NS :
� Nervous systems in invertebrates
o Invertebrates have simpler nervous systems.
o Examples are the ganglia system and the nerve net system
2. INTERACTION IN ANIMALS
NERVOUS SYSTEM (NS)
� Nervous system in vertebrates
o The nervous system in vertebrates includes:
� Central nervous system (CNS). This consist of the brain and the spinal cord. The CNS analyses information and
decides on a suitable response
� The peripheral nervous system (PNS). This consist of nerves which originate in the brain and in the spinal
cord. The PNS carries information around the body. Nerves can be classified as:
⁻ Afferent nerves, also called sensory nerves. These nerves go from the receptive organs to the central
nervous system. They carry information received from the stimuli.
⁻ Efferent nerves, also called motor nerves. These nerve go from the central nervous system to the
responsive organs. They carry information about the responses.
2. INTERACTION IN ANIMALS
NERVOUS SYSTEM (NS)
� Nervous system in vertebrates
o What are nerves?
� Nerves are made of groups of neurons.
� Neurons are special cells that transmit electrical signals containing information. The electrical
signals are called nerve impulses. This happens very quickly.
� Neurons have special characteristic that allow them to do this:
2. INTERACTION IN ANIMALS
EFFECTOR
• Are the parts of the body that carry out the response. In animals, these are the muscles (which
produce movement (motor responses)) and the glands (which produce hormones (endocrine
responses))
• The motor and endocrine system need to receive an instruction from the nervous system in order
to respond
MOTOR SYSTEM
� The motor system includes the skeleton and the muscles. It has several important functions:
� It makes it possible for the animal to respond to stimuli by moving
� It supports the animals and give it shape
� It protect delicate part inside the animal
� The motor system is different in vertebrates and invertebrates
2. INTERACTION IN ANIMALS
MOTOR SYSTEM
IN INVERTEBRATES: Many invertebrates
possess an exoskeleton, or hard outer
shell which protects them. Insect need a
more flexible, articulated exoskeleton
because they make rapid movement.
IN VERTEBRATES: Have an internal skeleton or
endoskeleton. The endoskeleton is made up of
bones, which meet at joints (for example, the
elbow and the knee). Muscles are contractile
organs attached to the bones by tendons. When
the muscles contract or relax the bones move.
2. INTERACTION IN ANIMALS
ENDOCRINE SYSTEM
• The endocrine system consist of glands. These glands produced hormones which are released into
the blood and control and coordinate activities throughout the body
• Both vertebrates and invertebrates have endocrine system. The endocrine system regulates
functions which require maintained responses. These include changes during the metamorphosis
of some animals, growth, sexual development, regulate the level of substances in the body and
the production of milk in mammals.
2. INTERACTION IN ANIMALS
HOW DO ANIMALS RESPOND TO STIMULI?
2. INTERACTION IN ANIMALS
RESPONSES
• Responses are the actions performed by an individual when it reacts to a stimulus it has received.
• The responses can be:
• Voluntary actions: are responses in which the animal has to think about
• Reflexes: are automatic responses to stimuli. Some situations are so dangerous that there is
no time to wait for the brain to decide what to do. The body reacts without waiting for the
brain to make a decision. Here´s an example: if you touch something touch something very
hot, you take your hand away automatically, without thinking about it first. This shops you
being injured
2. INTERACTION IN ANIMALS
RESPONSES
VOLUNTARY ACTION REFLEX
2. INTERACTION IN ANIMALS
� BEHAVIOUR
• Is what an animal does to respond to a particular situation. An animals‘s capacity to survive and
reproduce depends on how it behaves when it receives stimuli.
• Behaviour can either be instinctive or learned.
• INSTINCTIVE OR INNATE BEHAVIOUR: Is something an animal knows how to do as soon as it
is born; they do not have to learn them. Are automatic and cannot be changed, like how to
get milk from its mother, coughing, crying and yawing in humans and barking in dogs.
• LEARNED OR ACQUIRED BEHAVIOURS: Are when an animal reproduces what it has learnt.
This allows them to respond to new or changing situations. Can be changed and depend on
the intelligent of the animal
3. INTERACTION IN PLANTS
• All plant respond to changes that take place in their surroundings.
• Plant detect stimuli such as light, gravity, water, contact and temperature, etc. in their
surroundings and respond to them.
• In plant, cells inside the organism detect stimuli. Stimuli are processed and analysed slowly. They
have different ways of responding:
TROPISM
• Tropisms are permanent movements in response to a specific stimulus. The plant moves by
changing the direction it is growing in.
• The direction of movement depends on the direction of the stimulus. It can be positive ( the plant
moves towards the stimulus) or negative ( it moves away from the stimulus)
• Tropisms are classified according to the source of the stimuli:
• Geotropism: response to gravity
• Phototropism: response to light
• Hydrotropism: response to water
• Thigmotropism: response to contact
3. INTERACTION IN PLANTS
NASTIC MOVEMENT
• Nastic movements are temporary
responses of particular parts of a plant to
external stimuli. The plant later returns to
its original position.
PLANT HORMONES
•Like animals, plant also produce hormones. However, they do not have special gland, all plant cell
can produce hormones.
•Hormones are transported in two different ways: directly from one cell to the next or in the
phloem and xylem
•In plant, hormones do specific jobs. For example, they control the production of flowers, when
fruit ripens , when leaves fall from trees, plant growth….
