B6.1 How do animals respond to changes in their environment
Living organisms can detect and respond to a STIMULUS (a change in the environment of an organism such as light, temperature, etc.)
RECEPTORS are stimulated by the stimulus and produce a rapid, involuntary (automatic response) – this is called a SIMPLE REFLEX.
The simplest animals rely on reflex actions for the majority of their behaviour – all their movement and reactions are simple reflex responses. The reflex actions ensure that the animal will respond in a way that is most likely to result in its survival, to include finding food and sheltering from predators
Newborn babies exhibit a range of simple reflexes for a short time after birth, which ensures that they can survive – this includes:
- Stepping reflex – when held under its arms in an upright position with its feet on a firm surface, a baby makes walking movements with its legs
- Grasping reflex – a baby tightly grasps a finger that is out in its hand
- Startle reflex – a baby shoots out its arms and legs when startles e.g. a sudden loud noise
Adults also exhibit a range of simple reflexes – they are the most efficient way of quickly responding to potentially dangerous events:
- Pupil reflex – bright light causes muscles in the eye to contract so that the retina is not damaged
- Knee-jerk reflex – when the knee is struck just below the knee cap, the leg will kick out
- Dropping hot object reflex – when picking up a very hot object, the response is to throw it away to prevent heat damage to the hand
Nervous co-ordination in an animal requires:
- The presence of one or more different receptors to detect stimuli g. light is detected by eyes, temperature is detected by the receptors in the skin, and smell is detected by the receptors in the ear.
- Processing centres to receive information and coordinate responses
- Effectors to produce the response
There are two ways of sending signals in the body – the first is via electrical impulses through long, wire like cells called neurons (nerve cells). This method is very quick and short-lived:
- Sensory neurons carry nervous impulses (electrical signals) from receptors to the central nervous system
- Motor neurons carry impulses from the central nervous system to effectors
The other way signals are sent in the body is via chemicals called hormones that are produced in the glands and travel in the blood. Chemical signals are slower than electrical impulse and move to target organs (while electrical impulses target effectors), but their effects lasts a long time. For example insulin which controls blood sugar levels
The development of nervous and hormonal communication systems depended on the evolution of multicellular organisms.