Communication and homeostasis

Question 1

Explain why multicellular organisms need a communication system.

Answer 1

1. Cells within organisms have become specialised to perform specific functions
2. Organisms need to coordinate the function of different cells and systems to operate effectively and respond to changes
3. Few body systems can work alone

Question 2

List the factors that need keeping constant inside cells.

Answer 2

1. Blood-glucose concentration
2. Internal temperature
3. Water potential
4. Cell pH

Question 3

Explain why it is important to keep conditions inside cells relatively constant.

Answer 3

1. Vital for cells to function normally and to stop them being damaged
2. e.g. Enzymes denatured
3. Glucose in blood needs to be controlled so there is always enough for respiration

Question 4

Explain why the conditions critical to an organism change (use 4 examples from the internal environment and 4 examples from the external environment).

Answer 4

1. External- humidity, external temperature, light, new or sudden sound
2. Internal- Blood-glucose conc, internal temperature, water potential, cell pH
   Conditions change
3. Substances used up in metabolic reactions
4. Waste products are constantly being produced
5. Metabolisms change to meet changing demands of the organism
6. Intake varies overtime
7. Environmental conditions change

Question 5

Name the process by which cells communicate with each other.

Answer 5

Cell signalling

Question 6

Define cell signalling

Answer 6

1. A complex system of intercellular communication

2. Where one cell releases a chemical which has an affect on another cell

Question 7

Give two examples of systems whose purpose is cell signalling.

Answer 7

1. Nervous system

2. Endocrine system

Question 8

Outline the process of cell signalling in these two systems.

Answer 8

1. Nervous- transfer signals locally for example between neurones at synapses. Signal used is a neurotransmitter.
2. Endocrine- Transfer signals over large distances, using hormones. For example, the cells of the pituitary gland secrete ADH which acts on kidney

Question 9

Compare the neuronal and hormonal systems of cell signalling.

Answer 9

Hormonal system
1. Communication is by chemicals called hormones
2. Transmission is by the blood system
3. Transmission is usually relatively slow
4. Hormones travel to all parts of the body, but only target organs respond
5. Response is widespread
6. Response is slow
7. Response is often long-lasting
8. Effect may be permanent and irreversible
Nervous system
1. Communication is by nervous impulses
2. Transmission is by neurones
3. Transmission is very rapid
4. Nerve impulses travel to specific parts of the body
5. Response is localised
6. Response is rapid
7. Response is short-lived
8. Effect is temporary and reversible.

Question 10

Define the term negative feedback

Answer 10

1. When a change away from the ideal triggers a reaction to bring the conditions to ideal
2. The mechanism by which homeostasis is achieved

Question 11

Define homeostasis

Answer 11

The maintenance of a stable equilibrium in the conditions inside the body

Question 12

Define positive feedback

Answer 12

1. A change in the internal environment of the body is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response

Question 13

List 4 factors that need to be kept constant (within a narrow range) in animals.

Answer 13

1. pH of blood
2. Core temperature
3. Concentration of urea in blood
4. Concentration of sodium ions in blood

Question 14

Draw a flow chart to outline the processes (and components) involved in negative feedback.

Answer 14

1. Change away from the optimum/norm is detected by receptors
2. Signals are sent to effectors sometimes via a control centre
3. Effectors initiate a response
4. Conditions return to optimum/ norm

Question 15

Define the term effector

Answer 15

Muscle or gland which carries out body’s response to a stimulus

Question 16

Define receptor

Answer 16

1. Extrinsic glycoproteins that bind chemical signals, triggering a response by the cell
2. Detect changes in the internal and external environment of an organism

Question 17

Explain what is meant by “constant” in terms of homeostasis.

Answer 17

Maintaining a relatively steady state around a narrow range of conditions

Question 18

Define endotherm

Answer 18

Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature

Question 19

Define ectotherm

Answer 19

Animals that use their surroundings to warm their bodies so their core temperature is heavily dependent on the environment.

Question 20

Define thermoregulation

Answer 20

The maintenance of a relatively constant core temperature

Question 21

Define the term core body temperature

Answer 21

Core body temperature refers to the temperature of the internal environment of the body.

Question 22

Explain why “warm-blooded” and “cold-blooded” are inappropriate terms for endotherms and ectotherms.

Answer 22

Because all blood is warm- blood is never cold

Question 23

Explain why temperature needs to be maintained within a narrow range with cells.

Answer 23

1. Because enzymes controlling chemical reactions needed for life are very temperature sensitive.
2. If temperature gets to high they will dentaure

Question 24

Describe and explain 4 ways that heat is transferred between an organism and their environment.

Answer 24

1. Exothermic chemical reactions
2. Latent heat of evaporation- objects cool down as water evaporates from a surface.
3. Radiation- the transmission of electromagnetic waves to and form the air, water or ground
4. Convection- the heating and cooling by currents of air or water
5. Conduction- heating as a result of the collision of molecules.

Question 25

Describe how an organism generates heat internally.

Answer 25

1. From metabolic processes

2. Metabolic rate of endotherms is much higher than ectotherms

Question 26

Define the term “exothermic reaction”.

Answer 26

1. Reactions that release energy

Question 27

Describe the advantages and disadvantages of being an ectotherm.

Answer 27

Disadvantages

1. Core body temperature is heavily dependent on their environment
2. Temperature of air can vary dramatically both between seasons and over a 24 hour period- problem for land ectotherms
3. Activity levels are severely reduced when it is cold
4. Restricted to tropical or temperate regions on land but can be found throughout all oceans

Advantages

1. Many ectotherms living in water don’t need to thermoregulate because the high specific heat capacity of water means the temperature of water does not change much
2. Need less energy for metabolism- lower metabolic demands
3. Less food is needed
4. More of the food eaten can be used for growth

Question 28

Outline how an ectotherm regulates its internal temperature using behavioural responses

Answer 28

Behavioural responses

1. Bask in the sun- orientate their bodies so that the maximum surface area is exposed to the sun - warm
2. Some extend areas of their body to increase the surface area exposed to the sun- warm
3. Increase temperature through conduction by pressing their bodies against the warm ground- warm
4. Exothermic reaction- contracting muscles and vibrating wings- warm
5. To cool down they may shelter from the sun by seeking shade, hiding in rocks or caves or digging burrows.- cool
6. Press bodies against cool, shady earth or stones or move into available water or mud-cool
7. Orientate bodies their bodies so that the minimum surface area is expose to the sun- cool
8. Minimise movements to reduce metabolic heat generated- cool

Question 29

Outline how an ectotherm regulates its internal temperature using physiological responses

Answer 29

1. Dark colours absorb more radiation than light colours, lizards in cold climates tend to be darker coloured than lizards in warmer climates- warm
2. Some alter their heart rate to increase or decrease metabolic rate

Question 30

List 4 different types of organism that are ectotherms.

Answer 30

All invertebrate animals along with fish, amphibians, and reptiles

Question 31

Describe the advantages and disadvantages of being an endotherm.

Answer 31

Advantages
1. Can inhabit a wide range of habitats including places that get very cold
2. Can maintain a fairly constant body temperature regardless of external conditions
3. Can maintain high activity levels even at night and winter
Disadvantages
1. High food requirements
2. More energy needed for metabolism
3. More of the food is used to maintain body temperature and so less is available for growth

Question 32

Outline how an endotherm regulates its internal temperature.

Answer 32

1. Internal exothermic metabolic activities to keep them warm, and energy requiring physiological responses to help cool them down.
2. They have passive ways to reduce energy demand on their bodies
3. Have similar behavioural responses as ectotherms- basking in sun, wallowing in water etc
4. Some become dormant through the coldest weather (hibernation) or through the hottest weather (aestivation)
5. Humans- clothes, houses which are heated
6. Physiological adaptation- peripheral temperature receptors, thermoregulatory centres of the hypothalamus, skin and muscles

Question 33

Draw a diagram to show the components of the negative feedback mechanism that allows thermoregulation in endotherms.

Answer 33

see p414

1. There is a heat loss and heat gain centre in the hypothalamus
2. Too Hot
   a) Heat loss centre- activated when the temperature of the blood flowing through the hypothalamus increases.
   b) This sends impulses through the autonomic motor neurones to effectors in the skin and muscles, triggering responses that act to lower the core temperature
   c) Warm receptors in skin detect change in temperature
   d) Vasodilation, Sweating, hair lowered as hair erector muscles relax. decreased metabolic rate
3. Too cold
   a) The heat gain centre is activated when the temperature of the blood flowing through the hypothalamus decreases.
   b) It sends impulses through the autonomic nervous system to effectors in the skin and the muscles, triggering response that act to raise the core temperature
   c) Cold receptors in the skin detect changes in temperature
   d) Vasoconstriction, shivering, hair raised by contraction of hair erector muscles, increased metabolic rate

Question 34

State the part of the brain involved in thermoregulation and describe its role in this process.

Answer 34

1. Hypothalamus

2. Detects temperature of the blood deep in the body

Question 35

Explain the role of the peripheral temperature receptors in thermoregulation.

Answer 35

1. They are in the skin
2. Detect changes in the surface temperature
3. The combination of the hypothalamus and peripheral temperature receptors gives the body great sensitivity and allows it to respond not only to actual changes in the temperature of the blood but to pre-empt possible problems that might results from

Question 36

State how core body temperature is decreased if it rises above the optimum. (endotherms)

Answer 36

1. Vasodilation
2. Increased sweating
3. Reducing the insulating effect of hair or feathers

Question 37

Describe the process of vasodilation

Answer 37

1. The arterioles near the surface of the skin dilate when the temperature rises
2. The vessels that provide a direct connection between the arterioles and venules constrict
3. This forces blood through the capillary networks close to the surface of the skin
4. The skin flushes, and cools as a result of increased radiation.
5. If the skin pressed against cool surfaces, then the cooling results from conduction.

Question 38

Describe how sweating can be increased

Answer 38

1. In some mammals- humans and horses- there are sweat glands all over the body
2. As sweat evaporates from the surface of the skin, heat is lost, cooling the blood below the surface- latent heat of vapourisation
3. In some animals the sweat glands are restricted to the less hairy areas of the body such as paws- these animals often open their mouths and pant when they get hot- losing heat as it evaporates

Question 39

Describe how animals can reduce the insulating effects of hair or feathers

Answer 39

1. The erector pili muscles in the skin relax as body temperature begins to increase
2. As a result the hair or feathers of an animal lie flat to the skin.
3. This avoids trapping an insulating layer of air
4. It has little of effect in humans

Question 40

Explain how core body temperature is increased if it drops below the optimum.

Answer 40

1. Vasoconstriction
2. Decreased sweating
3. Raising the body hair or feathers
4. Shivering

Question 41

Describe the process of vasoconstriction

Answer 41

1. The arterioles near the surface of the skin constrict.
2. The arteriovenous shunt vessels dilate, so very little blood flows through the capillary networks close to the surface of the skin
3. The skin looks pale and very little radiation takes place
4. The warm blood is kept well below the surface

Question 42

Describe how sweating is decreased

Answer 42

1. Rates of sweating will decrease and sweat production will stop entirely
2. This greatly reduces cooling by the evaporation of water from the surface of the skin

Question 43

Describe how the body hair or feathers can be raised

Answer 43

1. As body temp falls, the erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect
2. This traps an insulating layer of air and so reduces cooling through the skin
3. Is a very effective way to reduce heat loss to the environment in many animals
4. Humans- has little effect

Question 44

Describe the process of shivering

Answer 44

1. As the core temperature falls the body may begin to shiver.
2. This is the rapid, involuntary contracting and relaxing of the large muscles in the body
3. The metabolic heat from the exothermic reactions warm up the body instead of moving it and is an effective way of raising the core temperature.

Question 45

List some common anatomical adaptations of animals that live in cold climates

Answer 45

1. Many reduce SA:V ratio to reduce cooling e.g. small ears
2. Thick layer of insulating fat underneath the skin e.g. blubber in seals and whales
3. Some hibernate- build up fat stores