5.1.1 Communication and Homeostatsis

Question 1

Why do multicellular organisms need communication systems?

Answer 1

• animals and plants need to respond to changes in their internal and external environment
• they also need to coordinate the activities of different organs

Question 2

Why do we need to keep our temperature?

Answer 2

• low temperatures mean little kinetic energy
• so chemical reactions involving enzymes slow down which can result in death
• high temperatures can use enzymes to denature

Question 3

Why do we need to keep our water potential constant?

Answer 3

If blood has lower water potential than tissue fluid, water moves into cells via osmosis, causing cells to burst

Question 4

Why do we need to keep pH constant?

Answer 4

• pH affects the amount of H+ ions
• causing the tertiary structure of enzymes to change
• 3D shape of active site changes
• substrate can’t bind to form ES complexes

Question 5

Why do we need to keep our blood glucose levels constant?

Answer 5

Dissolved glucose in large amounts can affect the water potential of the blood

Question 6

How does communication occur in the human body?

Answer 6

• the nervous system communicates with muscular system in order to move away or towards a stimulus
• brain communicates with rest of the body through the nervous system
• circulatory system works with nervous to maintain gas levels in blood + body temperature
• hormones releases from glands to circulatory system communicate with other glands to maintain internal environment

Question 7

Define homeostasis

Answer 7

Maintennance of a stable internal environment within a narrow range despite external environment conditions changing

Question 8

What makes a good communication system?

Answer 8

• covers the whole body
• allows cell to communicate with each other
• is specific
• is rapid
• can cause short term and long term effects

Question 9

Define stimulus

Answer 9

A change in internal or external environment that causes a response

Question 10

Define response

Answer 10

A change in behaviour or physiology due to a stimulus

Question 11

Define physiology

Answer 11

Function of organs and organ systems, and how they work within the body to respond to changes

Question 12

What are receptors and give examples

Answer 12

Detect stimuli and communicate with effectors
- retina
- hypothalamus
- pancreas

Question 13

What are effectors and give examples

Answer 13

Cause a change to bring the body back to its normal level. Work through negative feedback mechanisms
- hormones
- nervous impulses

Question 14

What is cell signalling

Answer 14

Communication and co-ordination between cells that allows cells to work together to trigger a response or a reaction inside the cell

Question 15

Define negative feedback

Answer 15

Corrective homeostatic mechanism that works to restore any detected change in the internal environment to a set point/norm. It maintains a system around a set point/norm. (Leads to homeostasis)

Question 16

Explain the process of negative feedback

Answer 16

1. Stimulus changes away from norm
2. Receptor detects change from norm
3. Communication systems informs effector
4. Effector (muscle or gland) produces change/response to reverse change from set norm
5. Response to return system to point norm
6. System at set point

Question 17

Define positive feedback

Answer 17

When an initial biological change is increased further or exaggerated
(can be harmful or beneficial)

Question 18

Explain the process of positive feedback

Answer 18

1. Set point/norm
2. Change away from set point
3. Receptors detect change
4. Communication system informs effector
5. Effector reacts
6. Change away from set norm

Question 19

Give examples of positive feedback

Answer 19

Labour
1. Cervix stretches
2. Causes pituitary gland to secrete oxytocin hormone which increases contractions
3. More contractions = more oxytocin
4. Continues until baby is born

Blood clotting
1. Blood vessel is damaged
2. Platelets stick to damaged area
3. They release factors that initiate blood clotting mechanism which attracts more platelets

Hypothermia
1. Lower body temperature reduces the kinetic energy of molecules
2. Enzyme activity reduces so less metabolic heat is produced
3. Body temperature drops even more

Question 20

Give key details about endotherms

Answer 20

• animals (mammals + birds)
• use heat from metabolic processes inside the body to maintain body temperature
• metabolic processes include aerobic respiration
• fur + hair to reduce heat loss (or scales)
• mainly use physiological responses to thermoregulate, use a few behavioral responses

Question 21

Give advantages and disadvantages of endotherms

Answer 21

Advantages
- body temperature meaintained within a narrow range with changing environmental temperature
- organisms can be active despite external temperature
- can inhabit colder environments

Disadvantages
- large energy intake required to maintain high levels of metabolism/respiration
- more time spent feeding and finding food
- less food used for growth

Question 22

How is heat lost and gained in the body?

Answer 22

Lost
- radiation to environment
- evaporation of water to vapour
- convection of heat into air currents
- conduction of heat through skin

Gain
- radiation from environment
- metabolic activities mainly from liver

Question 23

What part of the brain is involved in temperature

Answer 23

Thermoregulatory centre; Area called the hypothalamus
- split into two parts:
Heat gain centre - activated by a fall in blood temperature
Heat loss centre - activated by a rise in blood temperature

Question 24

What thermoreceptors does the thermoregulatory center receive inputs from?

Answer 24

Receptors in the hypothalamus measure blood temp (internal)
Peripheral thermoreceptors in the skin monitor external temp

Question 25

How do animals conserve heat physiologically?

Answer 25

Vascoconstriction: Decrease diameter of arteriole lumen to reduce blood flow to the capillaries in the skin of the organism, reducing heat loss through skin by radiation, conduction, convection Raising of hair - erector pili muscles in the skin contract, pulling hairs/ feathers up trapping a layer of still air, acting as an insulator

Question 26

How do animals conserve heat through behavioural mechanisms?

Answer 26

- shelter from the wind - animals huddle together to maintain core body temperature

Question 27

How does penguins huddling minimise heat loss?

Answer 27

Penguins exchange heat energy with each other (radiation) Change position so the same penguins aren't always in the middle

Question 28

How do penguins adjust their feet temperature?

Answer 28

- shunt vessel that connects arteriole carrying blood towards feet - when penguin is too cold muscles restrict the arterioles so less blood flow to feet = reducing heat loss from blood - when penguin is too warm arterioles allow more blood flow to feet = cools them down

Question 29

How are penguin feathers specialised?

Answer 29

- short, broad, closely spaced; keeps water away from the skin - tufts of down on the feather shafts provide insulative properties

Question 30

List physiological ways of generating heat

Answer 30

Shivering - involuntary rhythmic muscle contractions release metabolic heat Release of adrenaline and thyroid hormones Increased metabolic rate - heat generate from metabolic activity of live cells

Question 30

List behavioural ways of generating heat

Answer 30

Basking in the sun - increases heat gain by radiation

Question 31

List physiological ways of losing heat

Answer 31

Vasodilation - increase in arteriole lumen diameter near surface of skin - increases blood flow allowing more heat loss by radiation, convection, conduction Increased sweating - water in sweat evaporates from skin surface, requiring energy in heat form - reducing core body temp Panting - Heat lost by evaporation in fur covered animals Lowering of body hair - erector pili muscles relax - lower hairs = reduced layer of insulating air

Question 32

List behavioural ways of losing heat

Answer 32

- avoiding heat of the day - sheltering in burrows or shade to prevent gain of heat from radiation

Question 33

Explain the negative feedback process of vasodilation in hot temperatures

Answer 33

1. External environment temperature increases 2. Peripheral thermoreceptors stimulated 3. Nerve impulses conducted to hypothalamus 4. Thermoregulatory centre in hypothalamus also detects change in blood temperature 5. Vasodilation of arteriole lumen 6. Pre-capillary sphincter muscle relax 7. More blood in surface capillaries and less in inner blood vessel

Question 34

Explain how sweating reduces core body temperature and why is is an efficient mechanism

Answer 34

Sweat produced from glands allows heat energy to pass to sweat from blood to skin - sweat evaporates removing heat from the body and cools the body down Water has a high latent heat of vaporisation, so a lot of energy is needed to evaporate the water

Question 35

List behavioural adaptations for regulating temperature

Answer 35

- basking in sun (too cold) - digging burrows (too hot or cold) - period of aestivation (Summer deep sleep to avoid heat stress) - wallowing in water or mud (too hot)

Question 36

List anatomical adaptations for regulating temperature

Answer 36

- large ears + wrinkly skin; increases SA= increases heat loss - pale fur reflects radiation - decreasing heat gain - thick layer of insulating fat - reduces heat loss

Question 37

Define ectotherm

Answer 37

Organisms that mainly rely on external/environmental sources of heat to regulate their body temperature - only a few use their own metabolism to control their body temperature - all invertebrates, fish, reptile, amphibians

Question 38

Give advantages and disadvantages of being an ectotherm

Answer 38

**Advantages** - less food & energy needed - less time feeding + finding food - can survive longer without eating - greater proportion of energy used for growth or reproduction **Disadvantages** - less active in lower temperatures (can't live in cold climates) - may need to warm up in morning (greater risk of predation when lower temp) - less able to hunt for food when body temp low

Question 39

How can ectotherms gain heat?

Answer 39

- basking in the sun - orientate body to sun or warm ground - change body shape to maximise exposure - alter colour to increase absorption

Question 40

How can ectotherms lose heat?

Answer 40

- bathe in water or find shade in burrow - orientate body away from sun - reduce contact with ground - increase breathing movements

Question 41

List physiological responses some ectotherms can use to control their temperature

Answer 41

- black pigment helps absorb enough heat radiation to survive cold water - can alter heart rate to increase/decrease metabolic rate to generate more/less metabolic heat

Question 42

Why are ectotherms not extinct yet or evolved to have hair?

Answer 42

They require much less to eat as don't need to fuel metabolic ways of regulating temperature