Chapter 15 - Homeostasis

Question 1

What is the need for communication systems in multicellular organisms?

Answer 1

• to increase their chance of survival by responding to internal/ external changes
• changes made are triggered by nervous and endocrine systems

Question 2

What is cell signalling?

Answer 2

communication between cells through electrical impulses (carried through neurons/ hormones)

Question 3

Compare neuronal and chemical cell signalling.

Answer 3

neuronal - quick, short term (between adjacent cells)

chemical - slower, long term (between distant cells)

Question 4

What are two other types of cell signalling?

Answer 4

Paracrine signalling - signalling between cells close to each other
Autocrine signalling - cell releases signals to stimulate its own receptors (triggers a response within itself)

Question 5

What is homeostasis?

Answer 5

maintaining stable internal environment within small ranges in the body, regardless of changes in external environment

Question 6

What is the response to a stimulus?

Answer 6

• sensory receptors detect stimulus, send impulses to the brain, impulses travel to motor neurons, travel to effectors (muscles/ glands)

Question 7

What are some examples of receptors?

Answer 7

1) Photoreceptors (detect light in plants)
2) chemoreceptors (ie detect changes in pH)
3) Thermoreceptors (detect changes in temp)
4) glucose receptors (detect changes in glucose levels - proteins present on cell membranes of pancreatic cells)

Question 8

What are two examples of effectors?

Answer 8

1) Muscle (move limbs, squeeze chemicals from glands)

2) Glands (secrete hormones + enzymes)

Question 9

What is negative feedback and how does it work, give an example?

Answer 9

where the change is inhibited and forced back to ideal conditions
ideal condition, increase detected, response lower levels, ideal condition
ideal condition, decrease detected, response raise levels, ideal condition
ie glucose levels

Question 10

What is positive feedback and how does it work?

Answer 10

where the change is reinforced

conditions change, change detected, response reinforce change

Question 11

What are two examples of positive feedback?

Answer 11

1) blood clotting (platelets are attracted to wound until clot is formed)
2) cervix dilation during childbirth (as head of baby pushes against cervix, stimulates production of oxytocin, oxytocin stimulates uterus to contract pushing baby’s head harder into cervix, releasing more oxytocin. this is continued until child is born)

Question 12

What is thermoregulation?

Answer 12

maintenance of a relatively constant ore body temperature

Question 13

How do ectotherms thermoregulate?

Answer 13

• rely on the surroundings to thermoregulate

- the use of external sources

Question 14

Compare ectotherms on land/ water and talk about if they need to thermoregulate. If yes, why?

Answer 14

In water:

• don’t need to thermoregulate
• water has a high specific heat capacity therefore temp remains pretty constant

On land:

• Needs to thermoregulate
• due to seasonal changes
• due to daily changes (from day - night)

Question 15

What are examples of ectotherms?

Answer 15

invertebrates:

• fish
• amphibians
• reptiles

Question 16

How do endotherms thermoregulate?

Answer 16

• rely on metabolic processes to thermoregulate

- maintain constant core body temp regardless of surroundings temp (principles of homeostasis)

Question 17

Why would endotherms need more food than ectotherms?

Answer 17

• cooling down/ warming up are active processes therefore require energy —– endotherms need to eat more to provide this energy

Question 18

What are some behavioural responses to warm up for ectotherms?

Answer 18

• orientate their bodies to get maximum exposure to the sun (ie butterflies opening their wings to maximise surface area)
• pressing their bodies on warm surfaces (through conduction)
• through exothermic metabolic reactions (ie Galapagos iguanas vibrate + contract muscles to increase cellular metabolism)
  (-) butterflies vibrate their wings to warm up before flight

Question 19

What are some behavioural responses to cool down for ectotherms?

Answer 19

• orientate their bodies away from the sun (find shade)
• press body against cool surfaces (ie cool rocks, sand, mud)
• minimise movement to reduce metabolic heat

Question 20

What are some physiological responses for ectotherms?

Answer 20

• darker colours absorb more radiation that light (lizards in colder climates darker)
• can alter their heart rate to increase/ decrease metabolic rate (increase in warmer climate, decrease in cooler climate)

Question 21

Why do ectotherms require less food than endotherms?

Answer 21

require less food as they require less energy to thermoregulate
- because they r constantly thermoregulating (more vulnerable to fluctuations in the environment)