Communication and Homeostasis

Question 1

Communication

Answer 1

Communication is essential for the survival of organism as all living organisms must be able to detect and respond to changes in their internal and external environments.​

Question 2

Homeostasis

Answer 2

Homeostasis serves to ensure that a constant internal environment consisting of factors such as temperature, water potential, pH and blood glucose level is maintained, despite changes in the external environment of the organism.​

Question 3

Stimulus (external environment)

Answer 3

Cooler environment = greater heat loss = organism has to change behaviour/physiology to reduce stress = survives = RESPONSE

Question 4

Stimulus (internal environment) +example

Answer 4

Cells and tissues aren’t exposed to the external environment = protected by skin or bark but they are bathed in tissue fluid = environment of cells ​
- Example is CO2 accumulation : toxic waste product = build up alters pH of blood/enzymatic activity = STIMULUS = RESPONSE = greater breathing activity to expel CO2 from the body

Question 5

Factors contributing to a good communication system

Answer 5

• covers the whole body
• enables cells to communicate with each other
• enables specific and rapid communication
• enables long and short term responses

Question 6

Cell signalling

Answer 6

Involves the communication between cells, in the form of electrical signals which are carried by neurones, or with the help of hormones

Question 7

Neuronal signalling

Answer 7

• Interconnected network of neurones that signal via synapse junctions
• Quick but short term response to a stimuli that changes quickly

Question 8

Hormonal signalling

Answer 8

• Uses hormones in the blood to transport its signals
• Cells in an endocrine organ release the signal directly into the blood and transported throughout the body, but only recognised by specific target cells
• Slower but long term response

Question 9

Types of hormonal signalling

Answer 9

• Endocrine
• Paracrine
• Autocrine

Question 10

Endocrine signalling

Answer 10

Signalling molecules (hormones), target cells at distant body sites
e.g oestrogen

Question 11

Paracrine signalling

Answer 11

Act on neighbouring target cells
e.g neurotransmitters

Question 12

Autocrine signalling

Answer 12

Respond to self-signalling molecules
e.g T lymphocytes: proliferation in response to cytokines produced by same cell

Question 13

Types of regulation

Answer 13

Positive and negative regulation

Question 14

Positive regulation/feedback

Answer 14

• Increases the original change in the conditions
• e.g: end of pregnancy causes dilation of the cervix- as cervix begins to stretch= posterior pituitary gland secretes oxytocin= increases uterine contractions= stretches cervix more= continuation of positive feedback

Question 15

Negative regulation/feedback

Answer 15

• Counteracts any change in internal conditions
• e.g: a rise in core temp= thermoregulatory centre in hypothalamus detects change= nervous and hormonal systems carry signals to skin, liver, and muscles= less heat generated and more heat lost= fall in core temp

Question 16

Ectotherms

Answer 16

• An organism which regulates its body temp with the help of external source- peripheral receptors
• Unable to increase their respiration rate to increase the internal production of heat
• Cannot rely on internal energy source
• Control their body temp by exchanging heat with their surroundings
• They have behavioural responses/adaptations
  -e.g: snakes- bask in the sun to absorb heat directly from the sun

Question 17

Endotherms

Answer 17

• Organism able to maintain a constant body temperature, independent of the external temperature
• Contain thermo-receptors which monitor core body temperature changes and communicate them to the hypothalamus, which in turn coordinates appropriate responses to restore the optimum temperature
• e.g: shivering- contractions of skeletal muscles stimulated by nerve impulses sent out by the hypothalamus, leads to increase in temperature due to increase in kinetic energy, generating heat

Question 18

Key exam phrases to use

Answer 18

• Insects are smaller= smaller SA:V= greater heat loss
• Lower temperature= reduced kinetic energy of molecules= slowed enzyme activity= less metabolic heat generated= temperature then drops
• Idea of maintaining stable internal environment, within narrow range, even though the environment is changing