Homeostasis UNIT 3 AOS 2

Question 1

what is the definition of homeostasis?

Answer 1

maintaining the internal environment of the body at constant levels between narrow limits

Question 2

what are the two systems that take part in homeostasis?

Answer 2

1. nervous system

2. endocrine system

Question 3

define positive feedback

Answer 3

the response makes the process go faster e.g. when giving childbirth hormone oxytocin released to speed up labour

Question 4

define negative feedback

Answer 4

the initial stimulus is cancelled out by the response which occurs as a result of the stimulus being present

Question 5

what is the afferent pathway?

Answer 5

from stimulus to CNS

Question 6

what is the efferent pathway?

Answer 6

from CNS to response

Question 7

what is the direction of neuron signals

Answer 7

from dendrite to axon

Question 8

what is an action potential? what happens so sodium and potassium?

Answer 8

electrical message along the neuron in response to a stimulus and leads to the transmission of an electrical impulse
- sodium goes in, potassium exits at the same time

Question 9

why are nerve responses so fast?

Answer 9

• myelin sheath insulates message
• most of the sodium and potassium gates are open in the nodes of ranvier. this means that once the AP starts in the dendrites it whizzes down the axon to the next node where a new AP will start

Question 10

define hormone

Answer 10

a chemical signalling molecule that is produced by ductless endocrine glands and travel somewhere else where they bring about a response

Question 11

what are the two main types of hormones?

Answer 11

• peptide (AA based)

- steroid (lipid based)

Question 12

define target cells

Answer 12

cells with special receptors for that particular hormone

Question 13

what is the order of the stimulus response model?

Answer 13

stimulus, receptor, message, effector, response

Question 14

what is a reflex arc?

Answer 14

shows how neurons are linked in pathways, illustrates a reflex action which you cannot control

Question 15

what do dendrites do?

Answer 15

receives signals from other neurons

Question 16

what are the nodes of ranvier?

Answer 16

the unmyelated spaces between adjacent Schwann cells. impulses jump from one node to the next, allowing for more rapid impulse transmission

Question 17

what do excitatory synapses do?

Answer 17

sodium ions enter the postsynaptic cell and potassium leaves - there is a net flow of positive charges into the cell, the cell becomes depolarised moving membrane potential closer to the threshold

Question 18

what do inhibitory synapses do?

Answer 18

potassium ions leave the postsynaptic cell, membrane potential is pushed to a voltage more negative than resting potential, cell is hyperpolarised, membrane potential further away from threshold, reduces chance of postsynaptic cell generating an action potential

Question 19

where do steroid hormones bind to the cell? (hydrophobic)

Answer 19

these cross the plasma membrane and bind directly to receptors in the nucleus of cytoplasm

Question 20

where do peptide hormones bind to the cell? (hydrophilic)

Answer 20

these do not cross the plasma membrane and bind to receptors on the membrane, this binding activates something within the cell

Question 21

example of steroid hormones?

Answer 21

• sex hormones

Question 22

example of peptide hormones?

Answer 22

• insulin and glucagon

Question 23

what is signal transduction?

Answer 23

case of events originating outside the cell leading to a specific cellular response. initiated by cell-surface receptors

Question 24

what is signal amplification?

Answer 24

the initial signal is made stronger due to a secondary reaction. this will then make the eventual response greater

Question 25

what are guard cells?

Answer 25

pairs of highly specialised epidermal cells which form stomata and regulate the degree of opening and closing of stomata

Question 26

what is endocrine signalling?

Answer 26

hormones released by ductless glands into the bloodstream to bond on or in target cells

Question 27

what is paracrine signalling?

Answer 27

signals that are made but have a local effect. they do not travel large distances like endocrine ones

Question 28

what is autocrine signalling?

Answer 28

secreting cells acts on itself by secreting hormone into extracellular fluid, releasing signals for its own receptors

Question 29

what is a first messenger?

Answer 29

extracellular signal molecule that binds to the membrane receptors

Question 30

what is a secondary messenger?

Answer 30

they amplify the cell response. initiate the intracellular signal transduction cascades

Question 31

what is apoptosis?

Answer 31

• programmed cell death
• autocrine signalling
• signal transduction and amplification

Question 32

how does apoptosis happen?

Answer 32

a cell will respond to a signal molecule which trigger a series of responses within the cell creating a destroyer protein the chops up the cell

Question 33

how does abscisic acid respond to low water levels?

Answer 33

• abscisic acid is made when the roots detect low water levels
• this binds with receptors on the guard cells and allow potassium to diffuse out
• guard cells become plasmolyse and the stomata will close

Question 34

how does abscisic acid respond to high water levels?

Answer 34

• no abscisic acid is released
• potassium is pumped into the guard cells via active transport
• guard cells become turgid, and stomata open
• water leaves via evaporation

Question 35

what are neurohormones?

Answer 35

• a cross between a neurotransmitter and a hormone
• they act like hormones but are made by specialised nerve cells
• usually happens in the brains
  e. g. ADH and oxytocin

Question 36

what are pheromones?

Answer 36

chemical signals released by animals in very small quantities for communication between their own species. often used to attract the opposite sex

Question 37

what does glucagon do?

Answer 37

raises blood sugar (peptide hormone)

Question 38

what does insulin do?

Answer 38

lowers blood sugar (peptide hormone)