5.1.1: Communication and homeostasis

Question 1

Define homeostasis

Answer 1

The maintenance of an organisms internal environment within set limits despite external changes

Question 2

What is the overall aim of homeostasis ?

Answer 2

To increase the chance of survival

Question 3

What is homeostasis regulated by ?

Answer 3

The endocrine and nervous system

Question 4

Define negative feedback

Answer 4

Self regulating mechanism which triggers corrective measures whenever internal environment changes from its normal levels

Question 5

What is an example of negative feedback ?

Answer 5

Thermoregulation: If temp. too high then enzymes denature and if too low there is insufficient energy for enzyme controlled reactions meaning

… Metabolic reactions could slow to the point of cell death

Question 6

Define positive feedback

Answer 6

A deviation from normal conditions is amplified leading to further deviation

Question 7

Give an example of positive feedback

Answer 7

Platelets continually release clotting factors to build a blood clot

Question 8

Why is positive feedback rare in humans ?

Answer 8

It usually produces harmful/unstable conditions

Question 9

What are the reasons for the need for communication systems in multicellular organisms ?

Answer 9

• Control temperature and CO2 which can affect enzyme activity
• Blood pressure regulation
• Ensure optimal conditions for metabolism
• Control blood, water, salt levels which can affect water potential and respiration
• Increase chance of survival

Question 10

Give the response pathway from stimulus to response

Answer 10

Stimulus Receptor Communication system ( cell signalling ) Effector Response

Question 11

What is the difference between a receptor and an effector ?

Answer 11

A receptor detects change and the effector brings about the response

Question 12

Give examples of a receptors

Answer 12

Cells or protein

Question 13

Give examples of effectors

Answer 13

Muscle cells, cells in pancreas gland

Question 14

What is cell signalling, where does it occur and what detects it ?

Answer 14

Communication between adjacent or distant cells by neurotransmitters or hormones and is detected by surface cell receptors

Question 15

Give an example of cell signalling in the nervous sysetm

Answer 15

Neurotransmitters to communicate to adjacent cells

Question 16

Give an example of cell signalling in the endocrine system

Answer 16

Hormones travel in the blood to communicate to distant cells

Question 17

What are endotherms ?

Answer 17

Organisms who regulate their own body temperature through a nervous response and rely on internal metabolic processes to maintain a stable core body temperature

Question 18

Which structures detect a change in external temperature in endotherms ?

Answer 18

Peripheral temperature receptors in the skin detect change and send an impulse along sensory neuron to brain where hypothalamus coordinates the effectors to bring about a response by glands in skin and muscles

Question 19

What type of organisms are endotherms ?

Answer 19

Mammals and birds

Question 20

What is an advantage and disadvantage of endotherms ?

Answer 20

Organisms can survive in a wide range of environments HOWEVER organisms have to consume more food to meet their higher metabolic needs

Question 21

Give 3 behavioural responses of endotherms

Answer 21

• Move to shade
• Bask in sun
• Hibernating in winter

Question 22

List 5 physiological responses of endotherms

Answer 22

• Vasodilation
• Vasoconstriction
• Sweating
• Shivering
• Insulating effect of hair and feather

Question 23

Explain the process of vasodilation

Answer 23

Arterioles near skin surface dilate due to contraction of muscles near blood vessels which constricts the blood vessels supplying the capillaries so more blood flows through arterioles so more heat energy radiates from skin surface

Question 24

Explain the process of vasoconstriction

Answer 24

Arterioles near skin surface constrict so more blood flows through the capillaries further away from the skin surface so less heat radiates from the skin

Question 25

Explain the process of sweating

Answer 25

As sweat evaporates, heat from the skin is lost providing a cooling effect due to water having a high latent heat of vapourisation

Question 26

Explain the process of shivering

Answer 26

The contraction and relaxation of muscles increases the rate of respiration meaning more heat is released form skin surface

Question 27

Explain the insulating effect of hair and feathers

Answer 27

Controlled by erector pili muscles in the skin which trap air to radiate heat back to the skins surface

Question 28

What are ectotherms ?

Answer 28

Organisms who rely on their surroundings to regulate their internal body temperature

Question 29

What type of organisms are ectotherms ?

Answer 29

Invertebrates, fish, amphibians and reptiles

Question 30

Give an advantage and disadvantage of ectotherms

Answer 30

Organisms need less food to survive as less heat is used regulating temperature HOWEVER organisms are more vulnerable to fluctuations in the environment

Question 31

Why do organisms in an aquatic environment not need to regulate their body temperature ?

Answer 31

Water has a high specific heat capacity causing temperature to remain relatively constant

Question 32

Give 2 physiological responses of ectotherms

Answer 32

• Alter heart rate to increase/decrease metabolic rate
• Lizards living in colder climates absorb more radiation due to their darker skin colour

Question 33

List some behavioural responses of ectotherms

Answer 33

• Basking in sun on warm ground f conduction
• Orientate body to get maximum radiation absorbed from sun
• Minimise movement to reduce metabollic heat generates
• Move to shade