3.4 Homeostasis

Assessment information

M3.4 Success Criteria 2021 Student Version.pdf
M3.4 Report Draft.docx

Biology 3.4 (AS) is a Level 3 Internal worth 4 credits. These 4 credits count towards your University Entrance (UE) literacy credits for Reading and Writing.

You will be assessed in the following ways:

  • Formative assessment (informal)

  • Summative assessment (formal)

This assessment requires you to write a report that describes thermoregulation and how it works to enable an athlete competing in the Extreme Endurance event to maintain a stable internal environment.

You will be given a specific scenario and will be assessed on the comprehensiveness of your report and the extent to which you link biological ideas.

You have 2 lessons to analyse the scenario given and to produce your report.

Section 1: Homeostatic Control of Temperature

Success Criteria

  • I can define homeostasis, and give examples of different homeostatic controls in the body.

  • I can describe the general components of a homeostatic control system.

  • I can define thermoregulation and describe what the set point is.

  • I can explain why it is important for the body to be kept at this set point.

  • I can explain the different ways in which heat is transferred between humans and their environment

Vocabulary

Homeostasis

Thermoregulation

Do Now

Just by looking at these pictures, make an educated guess on what 'homeostasis' means.

Do Now

Do now in your book:

List as many human characteristics that are homeostatic.

What is Homeostasis?

Success Criteria:
I can define homeostasis, and give examples of different homeostatic controls in the body.
I can describe the general components of a homeostatic control system.

Homo = same, Stasis = to remain still or steady

Homeostasis is the ability of certain systems to maintain a constant internal environment despite fluctuations in the external environment.

Humans have homeostatic control systems that regulate:

  • Body temperature

  • Blood pressure

  • Level of blood glucose

  • Levels and balance of respiratory gases in tissues.

Homeostatic control systems have 3 functional components:

  1. A RECEPTOR - located in various organs (e.g. skin, eyes, brain) to detect change / a stimulus

  2. A CONTROL CENTRE - located in brain to compare this change against the set point, and give out instructions to effectors.

  3. An EFFECTOR - various organs to direct the appropriate response to correct the change.

Communication systems are vital in ensuring instructions from the control centre are relayed to various effector organs. There are two communication systems involved:

  1. Nervous system

  2. Endocrine system

Section 1 Task 1: Read the reading below.

Resource: Sky Level (medium level)

M3.4 S1. Homeostatic Control - Sky Level.pdf

Section 1 Task 2: Complete these activities in groups of 3-4 students.

Activity 1: Simulation / Game

M3.4 S1. Body Control Centre Simulation Worksheet - Hands-On.docx.pdf

Activity 2: Research and share

M3.4 S1. Examples of Homeostasis - Home and Away Activity.pdf

Do Now

Do now in your book:

1) What is considered to be normal body temperature?

2) Why do cells need a warm temperature to function?

Thermoregulation

Success Criteria:
I can define thermoregulation and describe what the set point is.
I can explain why it is important for the body to be kept at this set point.

What is thermoregulation?

Thermoregulation is the homeostatic process of controlling body temperature.

With thermoregulation in humans, the body temperature is maintained at a stable internal environment with a set point of 37°C.

What is purpose of thermoregulation?

  1. Enzymes
    Enzymes are essential for important physiological processes. They only function at certain temperatures - they are temperature sensitive. Enzymes denature in humans above 38 degrees Celsius. Below 37, the rate of reaction reduces until a point that metabolism does not occur.

  2. DNA
    High temperatures can damage DNA. At around 85 degrees celsius, the hydrogn bonds holding the two strands of DNA together break, causing it to become single stranded.

  3. Membrane permeability
    Changes in our core temperature can alter the permeability of our cell membranes, affecting diffusion of substances into and out of the cell.

M3.4 Video Fever - PBS.mp4

What is the ‘control centre’ of thermoregulation?

The hypothalamus is the control centre of thermoregulation, and other homeostatic systems.

It is located at the base of the brain (indicated in photo), near another important thermoregulatory organ called the pituitary gland (red).

The hypothalamus maintains normal body temperature by interpreting signals from receptors, then sending messages to various effector organs such as:

    • Muscle cells

        • Smooth muscle in arterioles, responsible for vasoconstriction and vasodilation

        • Skeletal muscle, responsible for shivering and voluntary behaviours

    • Sweat glands in the skin

Section 1 Task 3: Answer these following questions in your book

  1. What is the purpose of thermoregulation?

  2. What are the receptors the body uses to detect changes?

  3. What is the 'control centre' of thermoregulation? What is its job?

Do Now

I placed these four objects in a fridge. Which one would get the coldest in 10 minutes? Explain your answer.

Mechanisms of Heat Transfer

Success Criteria:
I can explain the different ways in which heat is transferred between humans and their environment

Name two things Bear Grylls did to help either stop losing heat or produce more heat.

Heat can be gained or lost from any place where the body is in contact with the environment (skin and lungs), through one or several of the following mechanisms:

Conduction

Conduction is the loss of heat by transfer from a hot surface touching a cold surface. It only accounts for 3% of heat loss, because air is a bad conductor.

Convection

Convection is the loss of heat in a liquid or gas by particle movement in currents. About 10-15% of heat is lost due to body movements.

Heat loss by convection cannot occur without conduction of heat from the body to air (or water) first.

Radiation

Radiation is the loss of heat in infrared radiation (an electromagnetic wave) emitted by our skin. About 65%.

Evaporative cooling

Evaporative cooling is the loss of heat through sweat. Can lose up to 85% of heat during intense exercise.

S1 Task 3: Choose either of the readings:

Reading 1: Sky Level (medium level text)

M3.4 S1. Thermoregulation - Sky Level.pdf

Reading 2: Sun Level (harder level text)

M3.4 S1. Thermoregulation - Sun Level.pdf

S1 Task 4: Complete either of these tasks:

Activity 1: Heat Transfer Interactive

M3.4 S1. Thermal Energy Transfer Interactive (PBS).pdf

Activity 2: How did they die?

M3.4 S1. Why did they die - Thermoregulation Starter.pdf

Section 2: Negative Feedback Control

Success Criteria

  • I can explain how the components of the thermoregulatory system work together in terms of negative feedback.

Vocabulary

Homeostasis

Negative feedback loop

Thermoregulation

Do Now

Do Now in your book:

The order of events in this diagram is incorrect. Correct it.

Thermoregulation as an Example of Negative Feedback Control

Success Criteria:
I can explain how the components of the thermoregulatory system work together in terms of negative feedback.

When a receptor detects a change from the set point, this is communicated to effectors, which respond by bringing about changes that will correct the disturbance. The greater the change from the set point, the greater the response will be to correct it.

This is negative feedback.

Negative feedback loops are homeostatic systems that counteract changes of various properties from their target values.

1. How does the body know when there's a change in temperature?

There are two types of receptors in the body that detect changes in temperature.

Peripheral thermoreceptors in the skin

The skin is the largest organ in the body. It plays a vital role in thermoregulation in two ways:

  1. Contains thermoreceptors that detect changes in environmental temperature.

  2. Contains effectors that can vary the rate of heat loss from the body.

Thermoreceptors in the hypothalamus

The hypothalamus also contains thermoreceptors which are sensitive to the temperature of the body's blood.

2. How are the messages sent from the receptors to the control centre to the effectors?

The hypothalamus (control centre) sends messages to effector organs via the:

  1. Nervous system (nerve impulses)

  2. Endocrine system (hormones)

See Section 1: Homeostasis for more information.

Figure above: "Peripheral thermoreceptors detect environmental and visceral temperatures and report these to the hypothalamus. Hypothalamic temperature receptors detect internal temperature. The thermoregulatory center initiates heat-loss or heat-gain responses in peripheral organs."

3. What do effectors do to bring the temperature back to the set point of 37°C?

To lower body temperature: sweating (sweat glands), vasodilation (smooth muscle of skin arterioles), hormonal response (thyroid gland), behavioural response (skeletal muscle).

To increase body temperature: shivering (skeletal muscle), vasoconstriction (smooth muscle of skin arterioles), piloerection, hormonal response (thyroid gland), behavioural response (skeletal muscle).

See Section 3: Thermoregulatory Responses to Different Scenarios for more information.

Section 2 Task 1: Choose either of the readings:

Reading 1: Sky Level (medium level text)

M3.4 S2. Negative Feedback - Sky level.pdf

Reading 1: Sky Level (medium level text)

M3.4 S2. Negative Feedback - Sun Level.pdf

Section 2 Task 2: Start on your 3.4 Report Draft

M3.4 Report Draft.docx

Make sure you keep referring back to the Success Criteria.

M3.4 Success Criteria 2021 Student Version.pdf

Section 3: Thermoregulatory Responses to Different Scenarios

Success Criteria

  • I can explain how balance is re-established when the body gets too cold.

  • I can explain how balance is re-established when the body gets too cold.

Vocabulary

Homeostasis

Negative feedback loop

Thermoregulation

Carousel image

In your internal report, your answer must be specific to the scenarios you're given. Make sure you:

  • Use exact data points where possible.

  • Talk about both too hot and too cold.

Example of what a Merit level answer looks like:


In the obstacle called the Arctic, participants must jump into a large pool full of ice water which is 1°C. Upon entering the pool of ice the athletes body will lose large amounts of body heat into the water through the process of conduction. Their internal temperatures will begin to drop below the normal 37℃. The receptors in their skin and hypothalamus will pick up the change in temperature, these changes are then communicated to the hypothalamus via the afferent pathway.


The hypothalamus will send nerve impulses to the organisms skeletal muscles (effector) via the efferent pathway. The skeletal muscles will begin to shake, due to the constant contraction and relaxation of the muscles, causing them to rub against each other. This creates small amounts of heat energy through friction. In addition this process requires energy, energy is created through cellular respiration which creates large amount of heat. The heat energy created can be used throughout the body to maintain homeostasis/ bring the body back to the set point (37°C).


The hypothalamus would also...

Overview of Responses

Our first response to encountering hotter or colder conditions is voluntary. If too hot, we may decide to take some clothes off or move to the shade. If too cold, we put extra clothes on or turn the heating up!

It is only when these voluntary responses are not enough that the thermoregulatory centre is stimulated. This is part of the autonomic nervous system, so the various responses are all involuntary.

When we get too hot, the heat loss centre in the hypothalamus is stimulated; when we get too cold, it is the heat conservation centre of the hypothalamus which is stimulated.

Section 3 Task 2: Do some or all of the following activities.

Watch this video on thermoregulation by muscles (equivalent to Sun

Reading 1: Sky level text

M3.4 S3. Thermoregulatory Responses - Sky level.pdf

Reading 2: Sun level text

M3.4 S3. Thermoregulatory Responses - Sun Level.pdf

Section 3 Task 2: Do some or all of the following activities.

Simple worksheet that covers a lot of ideas (Grass level)

M3.4 S3. Thermoregulation Fill-in-the-Blanks Worksheet.pdf

Annotate these two diagrams with what you've learned from the readings (Sky level).

M3.4 S3. Annotate Diagram of the Skin.pdf

Retrieval grid (Sun level)

M3.4 S3. Responses Retrieval Grid.pdf

Section 4: Biological Ideas for Excellence

Breakdown in Thermoregulation

Success Criteria:
I can comprehensively analyse how an extreme environmental influence results in a breakdown of thermoregulation.

Hyperthermia

Prolonged exposure to high temperatures can lead to hyperthermia. This is where the body temperature increases well beyond normal/optimum conditions.

If the body's core temperature rises:

  • Normal negative feedback mechanisms break down, as it's not able to lower body temperature.

  • Sweating too much has caused other issues dehydration lack of salts

  • Positive feedback occurs and certain physiological responses now make the issue worse. The person's body temperature can spiral out of control.

  • High temperatures now start affecting enzyme and other metabolic activity.

  • A core body temperature of >42°C usually causes death.

Hypothermia

If the body's core temperature falls below 35°C, a person may suffer from hypothermia. Again, the body's thermoregulatory mechanisms fail and positive feedback occurs leading to a further decrease in temperature.

If the body's core temperature decreases:

  • Negative feedback mechanisms break down, as it's not able to increase body temperature.

  • Lots of energy has been spent creating heat through shivering, energy begins being diverted to vital organs.

  • Positive feedback now occurring making the issue worse (slows down in metabolic activity means less heat produced

  • Low temperatures now start affecting enzyme and other metabolic activity.

M3.4 S4. Breakdown in Thermoregulation.pdf
M3.4 S4. Breakdown in Thermoregulation Section Structure.docx.pdf

Do Now

Do Now:

Read the stories on heat transfer, written on small pieces of paper by my Year 9 Science class.

Which of their ideas apply to athletes competing at the Coast to Coast Race South Island?

Biochemical and/or Biophysical Processes

Success Criteria:
I can comprehensively discuss the biochemical and/or biophysical processes underpinning the mechanism.

Biophysical and biochemical process of sweating and evaporative cooling:

  1. How is sweating initiated by the hypothalamic control centre?

      • Role of sympathetic nervous system and acetylecholine neutrotransmitter.

      • Role of muscarinic receptors on the sweat glands.

  2. How does the secretory coil portion of the eccrine gland produce primary sweat?

  3. How does the duct portion of the eccrine gland reabsorb Na+ and Cl- ions?

  4. How does evaporative cooling actually take heat away from the skin?

Biochemical process of thyroid hormone function and control:

  1. How is thyroid hormone (T3 and T4) produced?

      • Hypothalamus as a control centre as well as an effector.

      • Along with other effectors: anterior pituitary gland and thyroid gland.

  2. What does T3 do?

      • Activation of transcription of many genes.

      • Increases BMR, number and size of mitochondria, and aerobic respiration/chemiosmosis.

M3.4 S4. Biophysical + Biochemical Processes.pdf

Adaptive Advantage

I can comprehensively discuss the significance of thermoregulation in terms of its adaptive advantage.
What is the difference between an endotherm and an ectotherm?

What are Endotherms?

Endo = inside, therm = heat

An endotherm is an animal that is dependent on or capable of the internal generation of heat. They keep warm using heat generated inside the body (thermogenesis). They regulate their heat loss by physiological mechanisms in the skin.

Most mammals have body temperatures between 37-39ºC. Our body temperatures varies slightly for a number of reasons.

  • In healthy humans the average is about 35.8ºC in the early morning and about 37.3ºC in the evening (for precise comparisons temp should be taken at the same time each day).

  • Temperature varies with level of activity, and may rise to 40ºC in vigorous exercise.

  • Body temperature varies from person to person suggesting that there may be genetic factors involved.

  • Temperature also varies from one part of the body to another. Though the core temperature in deeper parts of the body does not fluctuate much, in the outer shell (especially the limbs) it varies considerably.

  • Different organs have slight differences, reflecting variation in heat production.

To maintain homeostasis, internal thermoregulatory processes are activated to correct the core temperature. Since endotherms regulate their own body temperature (thermoregulation), we are not dependent on our environment for heat.

What are Ectotherms?

Ecto = outside, therm = heat

An ectotherm is an animal that is dependent on external sources of body heat.

Amphibians, lizards, snakes, turtles, many fishes, and most invertebrates are mainly ectothermic, because they gain most of their heat from external resources.

How do Ectotherms thermoregulate?

Ectotherms generate a little bit of heat from respiration. However, not enough for thermoregulation. Although ectotherms do not generate enough heat for thermoregulation, many adjust body temperature by simple behavioural means, such as seeking out shade or basking in the sun.

When exposed to air, most amphibians lose heat rapidly by evaporation from their moist body surfaces, making it difficult to keep sufficiently warm.

However, an amphibian can maintain a satisfactory body temperature simply by moving to a location where solar heat is available. When the surroundings are too warm, amphibians seek shady spots or other cooler microenvironments.

Like amphibians, reptiles like snakes use behaviour as their dominant means of thermoregulation.

When cold, they seek warm places, orienting themselves toward heat sources and expanding the portion of their body surface exposed to the heat source (to increase surface area for heat transfer).

When hot, they move to cool areas or turn in another direction. Many reptiles keep their body temperatures very stable over the course of the day by shuttling back and forth between warm and cool spots.

Many terrestrial invertebrates can adjust internal temperatures by the same behavioural mechanisms used by vertebrate ectotherms.

For example, the desert locust, for example, must reach a certain temperature to become active, and on cold days, it orients in a direction that maximises the absorption of sunlight.

Other terrestrial invertebrates have certain postures that enable them to maximise or minimise their absorption of heat from the sun.

For example, dragonflies have an "obelisk" posture that minimises the amount of body surfafce exposed to the sun. This posture helps reduce heat gain by radiation.

Adaptive advantages of Endothermy:

Generally speaking, endotherms have the ability to maintain a constant internal body temperature, regardless of external conditions(although extreme changes may not be able to be regulated).

Activity is possible when the external temperature is quite cool, such as at night, early in the morning, or during winter.

The ability to inhabit colder parts of the planet due to their ability to maintain that internal temperature. The adaptive advantage of this is that we can survive in (nearly) all environments on Earth, can occupy a wide range of niches for food and shelter, leading to greater reproductive success.

Disadvantages of Endothermy:

A sufficient proportion of energy intake is required to regulate internal body temperature in the cold.

More food is required for this contributing factor to homeostasis (for example, a shrew has to eat its own body mass in food each day to prevent itself from starving).

Less energy obtained from food is used for growth (or at least more food is needed for growth).

Adaptive advantage of Ectothermy:

Because their heat source is largely environmental, ectotherms generally need to consume much less food than endotherms of equivalent size - an advantage if food supplies are limited.

  • Less energy intake is required from food for maintaining temperature (thermoregulation), so less food overall is needed, as expense of energy on metabolism is far lower.

  • Ectotherms do not need to eat as often and can survive greater periods of starvation than endotherms.

Greater portions of energy from food can be used for growth.

Ectotherms also usually tolerate larger fluctuations in their internal temperatures.

Disadvantages of Ectothermy

Are only able to survive in certain climates, and cannot survive in very cold climates.

The need to hibernate (remain inactive) during the winter as organisms cannot be active at that time.

Vulnerability to predation when basking in the sun.

The need to rely on ambush predation, rather than sprint predation, as they cannot chase prey as quickly and for as great distance as endotherms can.

Overall, ectothermy is an effective and successful strategy in most environments, as shown by the abundance and diversity of ectothermic animals.