5.1.1 The Need for Homeostasis Flashcards
What is the need for communication systems in organisms?
Animals and plants need to be able to respond to changes in their internal and external environment and to coordinate the activities of their different organs
In order to function properly and efficiently, organisms have different control and communication systems that ensure their internal conditions are kept relatively constant
Physiological control systems maintain the internal environment within restricted limits through a process known as homeostasis
Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
Examples of physiological factors that are controlled by homeostasis in mammals include:
Core body temperature
Metabolic waste (eg. carbon dioxide and urea)
Blood pH
Concentration of glucose in the blood
Water potential of the blood
Concentration of respiratory gases (carbon dioxide and oxygen) in the blood
Homeostatic mechanisms in mammals require information to be transferred between different parts of the body
There are two communication systems in mammals that do this:
The nervous system
The endocrine system
What is the importance of the nervous system?
The human nervous system consists of:
The central nervous system (CNS) – the brain and the spinal cord
The peripheral nervous system (PNS) – all of the nerves in the body
It allows us to make sense of our surroundings and respond to them and coordinate and regulate body functions
Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones
A bundle of neurones is known as a nerve
Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
What is the importance of the endocrine system?
A hormone is a chemical substance produced by an endocrine gland and carried by the blood
They are chemicals which transmit information from one part of the organism to another and bring about a change
They alter the activity of one or more specific target organs
Hormones are used to control functions that do not need instant responses
The endocrine glands that produce hormones in animals are known collectively as the endocrine system
A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
What is the importance of homeostasis?
Homeostatic mechanisms help organisms to keep their internal body conditions within restricted limits
Three key factors that need to be controlled include:
Temperature (thermoregulation is explained in more detail later)
pH
Blood glucose concentration
A stable core temperature and blood pH are vital for enzyme activity
If the temperature or pH of the tissue fluid surrounding cells is too high or too low it can negatively affect the rate of important enzyme-controlled reactions
What is the importance of pH?
All enzymes have an optimum pH or a pH at which they operate best
Enzymes are denatured at extremes of pH
Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together
Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH– ions (alkaline solutions) can cause these bonds to break
This alters the shape of the active site, which means enzyme-substrate complexes form less easily
Eventually, enzyme-substrate complexes can no longer form at all
At this point, complete denaturation of the enzyme has occurred
Where an enzyme functions can be an indicator of its optimal environment:
Eg. pepsin is found in the stomach, an acidic environment at pH 2 (due to the presence of hydrochloric acid in the stomach’s gastric juice)
Pepsin’s optimum pH, not surprisingly, is pH 2
What is the importance of blood glucose concentration?
Another key factor that must be controlled within mammals is the concentration of glucose in the blood
The amount of glucose present in the blood affects the water potential of the blood and the availability of respiratory substrate for cells
The normal glucose concentration for human blood is roughly 90mg per 100cm3
A sufficient amount of circulating glucose is essential for cellular respiration
Brain cells can become rapidly damaged or die if they do not receive a sufficient supply of glucose
Alternatively, if the blood glucose concentration is too high then it will have a dramatic effect on the water potential of the blood
What is the importance of stomata?
Plants also carry out homeostasis – just like animals they need to maintain a constant internal environment
For example, mesophyll cells in leaves require a constant supply of carbon dioxide for photosynthesis
Stomata (specifically the guard cells) control the diffusion of gases in and out of leaves
This means stomata control the entry of carbon dioxide into leaves
Regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion, with the need to minimise water loss by transpiration
