Unit 11 General Principles of Homeostasis
Key Unit Competence
To be able to explain general principles of homeostatic mechanisms.
LEARNING OBJECTIVES
At the end of this unit, the learner will be able to:
• Explain the significance of a constant internal environment.
• State the factors that must be kept constant in the internal environment of the body.
• Carry out research on homeostasis and deduce the findings.
• Appreciate the importance of maintaining a constant internal environment.
• Relate organisms’ ways of life to their environmental conditions.
• Discuss the role of the negative feedback mechanism.
• Explain the feedback mechanism in relation to the endocrine and nervous system.
• Identify the main internal and external causes of change in the internal environment.
• Describe the formation, composition and movement of tissue fluid in relation to blood and
lymphs.
• Appreciate the adaptations of animals to different environmental conditions in relation to homeostasis.INTRODUCTORY ACTIVITY
The picture below shows human who is swimming underwater of Muhazi Lake. Observecarefully this picture and answer the question that follows
Explain why this human can swim underwater for long time?
11.1 SIGNIFICANCE OF CONSTANT INTERNAL ENVIRONMENT
ACTIVITY 11.1
Have you ever thought about how your body maintains the same body temperature even if it is too hot or cold outside? Do you know about homeostasis and why it is required? Use library and Internet sources to collect information about homeostasis and various factors that must be kept constant in the human body. Learn, write and draw diagrams of homeostatic mechanisms and present your findings in the class.
All living organisms have an ability to maintain stable internal conditions. It requires continuous adjustments to the changes occuring in both internal and external environments. This selfregulating property of living beings to maintain a constant internal environment is termed as ‘homeostasis’ (‘homeo’, “similar,” and ‘stasis’, “stable”). Homeostasis is a key concept in the understanding of biological mechanisms that play an important role in survival of individual cells, to an entire body
Figure 11.1: Homeostasis
A living body ensures stable internal conditions in order to survive, grow and develop. The homeostatic mechanisms are inevitable for proper functioning of the body. Many systems of the body operate together to maintain a steady state. The cells, tissues, and organs may perform very different functions; however, all the cells in the body are similar in their metabolic needs. Homeostasis continuously provides the necessary ingredients of survival, for example, oxygen and nutrients to cells and thus, to complete the body. The metabolic activities and cellular processes can continue even though the external environment fluctuates substantially. Therefore, the regulation of an optimal internal environment enables an organism to live in wider range of environmental conditions (Figure 11.1).Automatic systems such as thermostats or air conditioners maintain constant internal (room) conditions.
ACTIVITY 2
Have you ever read or heard about some persons having diabetes or high blood pressure. Do you
know why such conditions occurred in these people while others have no problems? Discuss
and find out the appropriate answers.Note: Refer to negative feedback mechanism to learn about high blood pressure.
Homeostasis can be considered as dynamic equilibrium rather than a constant, unchanging
state. The body mechanisms maintain various fluctuating physical and chemical variables
within tolerable limits. These important variables include temperature, glucose, pH, water,
ions, respiratory gases and osmotic pressure of body fluids among others.
Some principal homeostatic mechanisms in humans to be kept constant are as follows:
• The maintenance of a steady body temperature involves mechanisms such as sweating or
shivering. These mechanisms occur whenever the internal body temperature becomes high
or low.
• The human body constantly works to maintain a normal glucose level in blood. When
glucose levels are high, a hormone called insulin is released by beta cells of the pancreas.
Insulin stimulates the conversion of glucose as insoluble glycogen by the body cells. This
lowers the glucose concentration in the blood. A condition called as diabetes occurs due to
the deficiency of insulin in the body, due to which glucose level of blood increases. When
the blood glucose levels are low, another hormone known as glucagon is released by the
alpha cells of pancreas. Glucagon breaks down stored glycogen in the form of glucose. The
addition of glucose in blood returns the body glucose levels to normal.
• Whenever the water content of the blood and lymph fluid gets low, it is restored initially by
extracting water from the cells. Also, the throat and mouth become dry. These symptoms
of thirst motivate humans to drink water.
• When high amount of salt and ions are present in the body, the kidneys produce concentrated
urine. This process removes extra amount of salt and ions while conserving water, and return
the body to normal metabolic range. In contrast, when the salt and ions concentration is
low in the human body, kidneys produce dilute urine and conserve salt and ions.
• A change in breathing and heart rate occurs in humans due to various activities like exercise.
As a result, the amount of carbon dioxide produced and oxygen demand in the body
increases. The heart rate increases so that the blood flows rapidly to the tissues to fulfill
the oxygen requirement and remove the carbon dioxide from the cells. Also, the speed and
depth of breathing increases. The body works to normalize breathing and heart rate whenactivity stops
• The pH of the blood is regulated at 7.365 (a measure of alkalinity and acidity). The tolerable
lower and upper limit for a human body is about pH 7.0 and pH 7.8, respectively. To prevent
a change in the pH, all body fluids, including cell cytoplasm are buffered (buffer is a chemicalor a combination of chemicals) absorbing either hydrogen ions (H+) or hydroxide ions.
All the body systems in humans are interdependent and function invariably to keepfluctuating factors within tolerable limits.
11.1.2 Components of Homeostatic Mechanisms
All homeostatic control mechanisms have three interdependent components for regulation
of any type of change or variable. The receptor is the sensing component that monitors
and responds to changes in the environment. When the receptor senses a stimulus, it sends
information to a “control/integration centre”, the component that sets the range at which
a variable is maintained. The control centre determines an appropriate response to the
stimulus. The control centre then sends signals to an effector, which can be muscles, organs,
or other structures that receive signals from the control centre. After receiving the signal, a
change occurs to correct the deviation by opposing or enhancing the stimulus. This ongoing
process continuously works to restore and maintain homeostasis. For example, in order to
regulate body temperature, thermo-receptors are present in the skin which communicates
information to the brain, the control centre. The control centre commands the effectors i.e.,blood vessels and sweat glands to function accordingly (Figure 11.2).
Figure 11.2: Components of homeostatic mechanisms
11.2 NEGATIVE AND POSITIVE FEEDBACK REGULATION
ACTIVITY 3
Have you ever thought how the body brings itself to the normal state after any change
in its system/s? How the signal that brings any change in body is regulated either stopped
or amplified? With the help of charts, discuss the feedback mechanism(s) and their role inmaintaining homeostasis in the body.
Feedback regulation is a type of response to a stimulus which determines the effect of original
stimulus. When a change of variable occurs, there are two main types of feedback mechanisms
to which the system reacts: Negative feedback is a response in which the system functions in
such a way as to reverse the direction of change. This response system tends to keep things
constant allowing the maintenance of homeostasis. The regulations of body temperature, pH,
ionic balance and blood pressure are the most common type of negative feedback systems.
Positive feedback is the response to amplify the change in the variable. Blood clotting and events
in childbirth are the types of positive feedback system. Both types of feedback mechanisms are
equally important for the proper functioning of a body. If any or both these mechanisms areaffected or altered somehow, it can lead to many complications.
11.2.1 Negative Feedback Mechanisms
Negative feedback consists of reducing the output or activity of any system or organ back to
its normal range of functioning. This change either raises or lowers the variable to its normal
set point automatically by counteracting. Here, negative means ‘opposite, not bad’. This can
be understood by the controlling process that regulates blood pressure. Blood pressure is the
measure of the force of blood pushing against blood vessel walls. The heart pumps blood into
the arteries (blood vessels), which carry the blood throughout the body. Whenever the blood
pressure increases, the blood vessels can sense the resistance of blood flow against the walls.
The blood vessels act as the receptors and relay the change to the brain. The brain acts as
control centre and transmits the signal to the heart and blood vessels, both of which act as the
effectors. The heart rate would decrease as the blood vessels increase in diameter, known as
vasodilation. This change would cause the blood pressure to fall back to its normal range. The
opposite would happen when blood pressure decreases, leading to vasoconstriction (decreasein diameter of blood vessel) (Figure 11.3).
Several factors/conditions interfere with the normal process of regulation of blood pressure.
Smoking, obesity, high salt concentration in diet, alcohol consumption, stress, hormonal
disorders affect the heart and blood vessels. This leads to high blood pressure or hypertension
which causes the heart to work harder to pump blood in the body. This can further damage theheart, blood vessels and other organs.
Figure 11.3: Negative feedback mechanism
Negative feedback mechanisms are most common in living organisms, working in a specificmanner sequence.
11.2.2 Nervous and Endocrine Control Mechanisms
In the human body, all the organs and organ systems are controlled by nervous and endocrine
systems. The nervous system controls the activities of body parts by reacting quickly to external
and internal stimuli. The endocrine system regulates those activities slowly but its effects are
long lasting. The hypothalamus is a part of the brain (nervous control center) located just
above the brain stem and consists of a group of neurons that forms the primary link betweenthe nervous system and the endocrine system.
This small part of the brain is responsible for regulating many key body processes, including
internal body temperature, hunger, thirst, blood pressure, and daily body rhythms (Figure 11.4(a)).
Figure 11.4: (a) Hypothalamus and Pituitary gland
Nervous system consists of receptive nerve cells which transmit the signal to the brain, which
in turn, command the effector nerve cells, muscles and glands to respond. For instance,
humans maintain a constant body temperature, usually about 37.4°C. It increases during
the day by about 0.8°C and decreases slightly during sleeping. The core body temperature is
usually about 0.7-1.0°C higher than skin or axillary temperature. A change in temperature
is sensed by receptors found in the skin, veins, abdominal organs and hypothalamus. The
receptors in the skin provide the sensation of cold and transmit this information to brain.
The brain process and commands for the vasoconstriction of blood vessels in the skin and
limb. This drops the surface temperature, providing an insulating layer (fat cell) between the
core temperature and the external environment. The major adjustment in cold is shivering
to increase the metabolic heat production. On the contrary, if the body temperature rises,
blood flow to the skin increases, maximizing the potential for heat loss by radiation andevaporation (Figure 11.4 (b)).
Figure 11.4: (b) Homeostatic regulation of body temperature
The endocrine system consists of glands which secrete hormones into the bloodstream. Each
hormone has an effect on one or more target tissues. In this way, it regulates the metabolism
and development of most body cells and its systems through feedback mechanisms, mostly
negative. For example, when blood calcium becomes too low, calcium-sensing receptors in
the parathyroid gland become activated. This results in the release of Parathyroid Hormone
(PTH), which acts to increase blood calcium by release from the bones. This hormone also
causes calcium to be re-absorbed from urine and the gastrointestinal tract. Calcitonin, released
from the thyroid gland functions in reverse manner, i.e., decreasing calcium levels in the bloodby causing more calcium to be fixed in bones (Figure 11.5).
Figure 11.5: Calcium regulation
Both the nervous and endocrine system of the human body co-ordinate to ensure a balance
between fluid gained and fluid loss. The ADH (Anti-diuretic Hormone) or vasopressin is the
principal compound that controls water balance by decreasing water output by the kidney.
Vasopressin is formed in the hypothalamus and get stored in the posterior pituitary (a part of
endocrine system). If the body becomes fluid-deficient, osmoreceptors (monitor blood plasma
osmolality) in the hypothalamus signals for the release of vasopressin from posterior pituitary. An
increase in the secretion of vasopressin causes retention of fluid by the kidneys and subsequent
reduction in urine output. Conversely, if fluid levels are excessive, release of vasopressin is
suppressed resulting in less retention of fluid and resulting increase in the volume of urineproduced.
APPLICATION 11.1
1.Complete with appropriate terms:
(i)The tolerable pH level in human body ranges from ................ to ...................... .
(ii) .................... provides necessary ingredients for survival.
(iii) Endocrine system consists of ..................... which secretes hormones.
(iv) ............................ is a response in which the system functions in a way to reverse
the direction of change.
(v) ......................... and ................... are mechanisms to maintain body temperature.2. Name the heat regulation centre in the brain.
3. What is the function of
a) Detectors
b) Comparators
c) Effectors
4.What type of feedback system is involved in bringing the temperature of an overheated
person back to normal
5.Explain briefly the advantage of having two corrective mechanisms that regulates blood
glucose concentration, rather than one
6. A person fasted overnight and then shallowed 75 g of glucose. The graph shows the resultingchanges in the concentrations of insulin and glucose in the blood
a. Explain the relationship between the concentrations of glucose and insulin in the blood in
the first 30 minutes after the glucose was swallowed
b. Use information from the graph to explain what is meant by term negative feedback
c. Explain why the concentration of glucagon in the blood rises during exercise while thatof insulin falls
11.3 CAUSES OF CHANGES IN HOMEOSTASIS ENVIRONMENT
Homeostasis is maintained through a series of control mechanisms. When homeostatic process
is interrupted, the body can correct or worsen the problem, based on certain influences. Thereare internal and external causes influencing the body’s ability to maintain homeostatic balance.
11.3.1 Internal Causes: Heredity
Genetic/Reproductive: A variety of diseases and disorders occur due to the change in the
structure and function of genes. For example, cancer can be genetically inherited or can be
induced due to a gene mutation from an external source such as UV radiation or harmful drugs.
Another disorder, Type 1 diabetes, occurs due to the lack or inadequate production of insulinby the pancreas to respond to changes in a person’s blood glucose level.
11.3.2 External Causes: Lifestyle
Nutrition: A diet lacking specific vitamin or mineral leads to cellular malfunction. A menstruating
woman with iron deficiency will become anaemic. As iron is required for haemoglobin, an
oxygen transport protein present in red blood cells, the blood of an anaemic woman will havereduced oxygen-carrying capacity.
Physical Activity: Physical activity is essential for proper functioning of our cells and bodies.
Adequate rest and exercise are examples of activities that influence homeostasis. Lack of sleep
causes ailments such as irregular cardiacrhythms, fatigue, anxiety and headaches.
Overweight and obesity are related to poor nutrition and lack of physical activity that greatly
affects many organ systems and their homeostatic mechanisms. It increases a person’s risk ofdeveloping heart disease, Type 2 diabetes, and certain forms of cancer.
Mental Health: Both the physical and mental health is inseparable. Negative stress (also calleddistress) leads to thoughts and emotions harmful for homeostatic mechanisms in the body.
11.3.3 Environmental Exposure
Many substances act as toxins, including pollutants, pesticides, natural and synthetic drugs,
plants and animal products interfering at cellular levels. Modern medicines practice can also
be potentially harmful in case of wrong or over dosage. For instance, drug overdose affects
the central nervous system, disrupts breathing and heartbeat in the human body. It can further
result in coma, brain damage, and even death. Therefore, alterations or interruption of beneficial
pathways, whether caused by an internal or external factor will result in harmful change in
homeostasis. Therefore, adequate positive health influences are to be taken into considerationin order to maintain homeostasis.
11.4 FORMATION, COMPOSITION AND MOVEMENT OF TISSUE FLUID
ACTIVITY 4
Aim: To observe and analyze the pressure flow of liquid coming out from the perforated rubber
tubes.
Materials Required:
1. A rubber tube (1 cm width and 50 cm in length)
2. Two beakers3. One bucket.
Procedure:
1. Take a rubber tube of about 1 cm width and 50 cm in length and make two set of tiny holes
on at a distance of 10 cm before both ends.
2. Attach tube to a water tap tightly. Try to adjust the tubular part with holes towards downside
so as to collect the liquid in beakers or trays.
3. At the other end, put a collecting vessel such as a bucket. Adjust the rubber tube in horizontal
position and open the tap for 10-20 seconds and collect the water coming out of rubber holes
in beakers placed under the holes in the tube.
4. Measure the collected liquid in two beakers separately by glass cylinders. Note the readings
and compare the volume of water collected in the beakers.
Discussion:
1. Do you find any difference in volume of water collected in beakers?
2. Where do you think high and low pressure end on rubber tubes?3. Does the high pressure end expel more water than low pressure end?
The blood supplies nutrients and essential metabolites to the cells of a tissue and collects back
the waste products. This exchange of respective constituents between the blood and tissue cells
occurs through interstitial fluid or tissue fluid formed by the blood. The fluid occupies the spaces
between the cells known as tissue spaces. It is the main component of the extracellular fluid,
which also includes plasma and transcellular fluid. On an average, a person has about 10 litresof interstitial fluid making 16% of the total body weight.
11.4.1 Formation
The formation of the tissue fluid is based on the difference in pressure of flowing (Starling’s law)
of blood through capillaries. A hydrostatic pressure is produced at the arterial end of blood
capillaries which is generated by the heart. This results in expulsion of water and other solutes
(known as plasma) from capillaries except blood proteins (like serum albumin). This retention
of solutes in capillaries creates water potential. The osmotic pressure (water moves from a
region of high to low concentration) tends to drives water back into the capillaries in an attempt
to reach equilibrium. At the arterial end, the hydrostatic pressure is greater than the osmotic
pressure, so the net movement favours water along with solutes being passed into the tissue
fluid. At the venous end, the osmotic pressure is greater, so the net movement favours tissue
fluid being passed back into the capillary. The equilibrium is never attained because of the
difference in the direction of the flow of blood and the solutes imbalance created by the netmovement of water (Figure 11.6).
Figure 11.6: Formation of interstitial fluid from blood
11.4.2 Composition
As the blood and the surrounding cells continually add and remove substances from the interstitial
fluid, its composition continually changes. Water and solutes can pass between the interstitial
fluid and blood via diffusion across gaps in capillary walls called intercellular clefts; thus,
the blood and interstitial fluid are in dynamic equilibrium with each other. Generally, tissue
fluid consists of a water solvent containing sugars, salts, fatty acids, amino acids, coenzymes,
hormones, neurotransmitters, as well as metabolic waste products from the cells.
Not all of the contents of the blood pass into the tissue, which means that tissue fluid and
blood are not the same. Red blood cells, platelets, and plasma proteins cannot pass through
the walls of the capillaries. The resulting mixture that does pass through is, in essence, blood
plasma without the plasma proteins. Tissue fluid also contains some types of white blood cells,which help to combat infection.
11.4.3 Movement
To prevent a buildup of tissue fluid surrounding the cells in the tissue, the lymphatic system
plays an important role in its transport. Tissue fluid can pass into the surrounding lymph
vessels where it is then considered as lymph. The lymphatic system returns protein and excess
interstitial fluid to the blood circulation. Thus, it is transported through the lymph vessels to
lymph nodes and ultimately with blood in the venous system, and tends to accumulate morecells (particularly, lymphocytes) and proteins.
The formation, composition and movement of tissue fluid are important processes for thedevelopment of immunity in the human body.
11.5 ADAPTATIONS OF ORGANISMS TO ENVIRONMENTAL CONDITIONS
ACTIVITY 5
A field trip to a zoo/wildlife sanctuary/national park can be organized under the guidance of a
teacher. The students/learners should observe, understand and discuss the various environmental
conditions in which animals live and survive. Different groups of animals which live on land,
water and other places can be studied for the adaptations in their habitat. Learners should write
their observations about the different features/characteristics of animals, timing of appearance,
season, place/location as well as behaviour of different animals. A report should be submitted
about the field trip describing the observations along with the diagrams/images/photographstaken and computer aided material.
Every organism has certain features or characteristics which enables it to live successfully in
its particular habitat. These features are called adaptations, and the organism is said to be
adapted to its habitat. Organisms living in various habitats need different adaptations in order
to maintain homeostasis. The animals adapt to such changes in their environment which
threatens their chances of survival. The main threats are temperature, lack of water and food.
Besides the environmental threats, many animals also need to be able to defend themselves
from predators and pathogens.
Different organisms have adapted to the great diversity of habitats and distinct conditions in
the environment. Although, the adaptations are many and varied, they can be categorized intomainly three types: Structural, physiological and behavioural.
11.5.1 Structural Adaptations
Structural (or morphological) adaptations are the physical features of the organism. It includes
shapes or body covering as well as its internal organisation. Microscopic organisms which
includes protozoans and bacteria employ encystment (a state of suspended form, separated
by the outside world by a solid cell wall) to surpass hostile conditions for long periods of time,
even millions of years. Larger animals like polar bears are well adapted for survival in the cold
climate of the Arctic region. They have a white appearance to camouflage from prey on the
snow and ice. Also, polar bear have thick layers of fat and fur, for insulation against the coldand a greasy coat which sheds water after swimming.
Figure 11.7: Polar bear in cold climate
Dolphins are fish-like mammals which have streamlined shape and fins instead of legs. They
also have blowholes on the tops of their heads for breathing, rather than their mouth and nose.
Desert animals like camels have many adaptations that allow them to live successfully in hot
and dry conditions. They have long eyelashes and nostrils that can close and open to prevent
entry of sand. Thick eyebrows shield the eyes from the desert sun. Camels store fat in the
hump which can be metabolised for energy. A camel can go a week or more without water,
and they can last for several months without food. Their huge feet help them walk on sandwithout sinking into it.
Figure 11.8: Camel’s adaptations in desert environment: (a) Nostrils and (b) Hump
Similarly, the long necks of giraffes allow them to feed among treetops
and spot predators. Also, they have tough and long tongues (upto 18
inches) enabling to pull leaves from branches without being hurt bythe thorns. Spotted coat camouflages giraffes among the trees.
In tropical areas, natural radiators are an efficient way of lowering
the body’s temperature: for instance, the ears of the elephant and the
rabbit are full of blood vessels, helping the animal cool its body in theheat. Rabbits living in Arctic areas have smaller ears.
Figure 11.9: Giraffe
11.5.2 Physiological Adaptations
Physiological adaptations are related to the working of an organism’s metabolism. These
adaptations enable the organism to regulate their bodily functions, such as breathing and
temperature, and perform special functions like excreting chemicals as a defence mechanism
(Sea stars). Chameleon (a reptile) changes colour or body markings in order to blend
into its surroundings. Marine mammals such as whales are endothermic/warm blooded
(able to maintain a constant body temperature). They cope with the temperature changes during
migration over large distances and can spend time in arctic, tropical and temperate waters. In
contrast, Arctic fish (cold-blooded animals) lives easily in temperatures lower to sub-zero level.
Such temperatures results in the formation of ice crystals in the organism’s cells that may cause
irreversible damage and ultimately, death. However, arctic fishes living in the same freezing
waters survive due to an antifreeze protein in the blood that prevents ice crystals formation intheir cells and maintains metabolic functions.
11.5.3 Behavioural Adaptations
Behavioural adaptations are learned that help organisms to survive. The whales produce
sounds that allow them to communicate, navigate and hunt prey. Bears hibernate or ‘sleep’
through the coldest part of the year. Bryozoans are water dwelling small individual animals
found in colonies in high numbers on the continental shelf in New Zealand. These animals
band together for collecting food and survive predation. Penguins are the flightless birds
found in the oceans around Antarctica. During extreme winter, Emperor penguins show
social behaviour by huddling together in groups comprising several thousand penguins tostay warm.
APPLICATION 11.2
1.Complete with appropriate terms:
(i) Micro organisms employ .................... to surpass hostile conditions for a long time.
(ii) .................... is a type of mammal having fins and a streamlined body.
(iii) ................... and ..................... influences/tends to disturb homeostatic mechanisms.
(iv) RBCs, platelets and plasma cannot pass through ........................... .
(v) .................... fishes have an antifreeze protein in the blood to prevent formation of ice
crystals.
2.The control of blood glucose concentration involves a negative feedback mechanism.
a) What are the stimuli, receptors and effectors in this control mechanism?
b) Explain how negative feedback is involved in this homeostatic mechanism.
3. Explain why blood contains many proteins that are not found in the tissue fluid or lymph
4. What produces the hydrostatic pressure in the blood
5.Describe how fluid can pass through the capillary wall from the plasma to the tissue fluid
6. a) Describe the immediate environment of a typical cell within the body of a mammal.
b) Explain why it is important that the internal environment of a mammal is carefully
regulated.
c)Explain how the following are involved in maintaining the internal environment: stimuli,
receptors, central control, coordination systems and effectors.
d)Explain the meaning of the terms homeostasis and negative feedback.e) Distinguish between the input and the output in a homeostatic control mechanism.
11.6 SUMMARY
• Homeostasis is the ability of a living body to maintain a relatively stable internal environment.
• Homeostasis is an important characteristic of living things requiring continuous
adjustments due to the changes occurring in internal and external environment.
• Variables that must be kept constant and regulated to the normal level (set points) in a
body are temperature, glucose, pH, water, ions, respiratory gases and osmotic pressure
of body fluids.
• Homeostatic control mechanisms have three interdependent components: receptor,
integration centre and effectors.
• Negative feedback occurs when the response to a stimulus reduces the original stimulus.
• Positive feedback occurs when the response to a stimulus increases the original stimulus.
• The nervous system controls the activities of body parts quickly to external and internal
stimuli.
• The endocrine system regulates body activities slowly with long lasting effects.
• The hypothalamus is a part of brain and links the nervous system and endocrine system.
• The homeostatic mechanisms are altered or interrupted based on internal (genetic) and
external (lifestyle choices and environmental exposures) factors.
• Interstitial/tissue fluid is formed from blood plasma and it surrounds and bathes the
cells in tissue spaces.
• Tissue fluid provides nutrients and removes waste products from the cells of the body.
• Tissue fluid is formed due to the pressure difference in flow of the blood through the
blood capillaries.
• Tissue fluid contains sugars, salts, fatty acids, amino acids, coenzymes, ions, hormones,
neurotransmitters, as well as metabolic waste products from the cells in a water medium.
• Tissue fluid moves from tissue spaces to lymph vessels (lymph), to lymph nodes and
finally returns to the blood.
• Adaptation is a feature/characteristic of an animal which enables it to survive in its habitat.
• Different organisms have adapted to distinct habitats and environmental conditions.
• Three categories of adaptations are structural, physiological and behavioural. Each typeof adaptation has its own survival value.
11.7 GLOSSARY
• Adaptation: A feature or characteristic of an organism which helps in its survival in a
particular habitat.
• Control centre or integration centre: Receives and processes information from the
receptor.
• Effector: Responds to the command of the control centre by either opposing or enhancing
the change.
• Homeostasis: A balancing act which maintains a particular internal condition.
• Receptor: Receives information about a change in its environment.
• Negative feedback: A response system which reverses the direction of change.• Positive feedback: A response system which amplifies the change in the variable.
END UNIT ASSESSMENT 11
I. Choose whether the given statements are True (T) or False (F)
1. A living body ensures stable internal conditions in order to survive, grow and develop.
2. The property of living beings to maintain a constant internal environment is termed
as ‘homeostasis’.
3. Blood pressure is the measure of the force of blood pushing against blood vessel
walls.
4. The endocrine system controls the activities of body parts by reacting quickly to
external and internal stimuli.
5. Organisms living in various habitats need different adaptations in order to maintain
homeostasis.
6. Behavioural adaptations are related to the working of an organism’s metabolism.
7. The chemical messengers secreted from the endocrine system affect on specific target organs.
8. The thick fur layer on the skin of polar bears protects them from sunlight.
9. Whales migrating to oceanic waters can maintain a constant body temperature.
10. Colonial animals, if being separated, can survive easily in their habitats.11. Camel’s hump is an adaptation to store water in desert climate.
II. Multiple Choice Questions
1. An example of positive feedback mechanism is:
(a) maintaining stable blood glucose levels
(b) the production of milk in a nursing mother
(c) maintaining a stable body temperature
(d) all of the above
2. Which hormone increases the glucose level in the blood?
(a) glucose (b) glucagon
(c) insulin (d) glycogen
3. Which is the proper sequence of events in maintaining homeostasis?
(a) Signal, Receptor, Stimulus, Response
(b) Stimulus, Response, Signal, Receptor
(c) Receptor, Stimulus, Signal, Response
(d) Stimulus, Receptor, Signal, Response
4. Which is an example of negative feedback?
(a) maintaining stable blood glucose levels
(b) the production of milk in a nursing mother
(c) contractions of the uterus during childbirth
(d) all of the above
5. The principal systems controlling and regulating body activities are:
(a) nervous and respiratory system (b) endocrine and digestive system
(c) nervous and endocrine system (d) respiratory and digestive system
6. Which of the following statements best describes homeostasis?
(a) keeping the body in a fixed and unaltered state
(b) dynamic equilibrium
(c) maintaining a relatively constant internal environment(d) altering the external environment to accommodate the body’s needs
7. Tissue fluid is different from blood in terms of:
(a) red blood cells (b) platelets
(c) plasma proteins (d) all of the above
8. The human body’s “thermostat” is found in:
(a) nervous system (b) integumentary system
(c) endocrine system (d) urinary system
9. Which statement is not correct about calcium homeostasis?
(a) parathyroid hormone increases blood calcium level
(b) calcitonin decreases calcium levels in blood
(c) both hormones (PTH and calcitonin) are secreted by same gland
(d) calcium regulation is an example of negative feedback mechanism
10. Which statement is correct about vasopressin?
(a) an increase in secretion of vasopressin decreases fluid volume in the body
(b) a decrease in secretion of vasopressin increases fluid volume in the body
(c) an increase in secretion of vasopressin increases fluid volume in the body(d) none of the above
III. Long Answer Type Questions
1. Giving suitable examples, in your own words, explain the significance of a constant
internal environment.
2. State the factors that must be kept constant in the internal environment of the body.
3. Discuss the role of the negative feedback mechanism.
4. Explain the feedback mechanism in relation to the endocrine and nervous system.
5. What are the main internal and external causes of change in the internal environment?
6. Describe the formation, composition and movement of tissue fluid in relation to
blood and lymphs.
7. Giving examples, relate organisms’ ways of life to their environmental conditions.
8. How do pollutants alter homeostasis of an organism? What role does homeostasisplay in environmental protection?