Communication,Homeostasis & Energy

Question 1

Need for communication systems in organisms?

Answer 1

• organisms need to be able to to respond to changes in internal/external environment
• coordinate activities of different organs

Question 2

Eg of physiological factors controlled by homeostasis ?

Answer 2

Core Body temperature
Metabolic waste
Blood pH
Conc of glucose in blood
Water potential of blood
Conc on respiratory gases in blood

Question 3

What does nervous system consist of and what does it help ?

Answer 3

Central Nervous System (CNS)—> brain/spinal cord
Peripheral Nervous System (PNS)—> all nerves in body

• allows us to make sense of surroundings /respond to them , as well as coordinate/regulate body functions
• info in nervous system sent through nerve impulses

Question 4

What are neurones and nerves ?

Answer 4

Neurones - electrical signals that pass along nerve cells
Nerve - bundle of neurones

Question 5

What do neurones do?

Answer 5

Coordinate activities of sensory receptors , decision making centres in CNS and effectors

Question 6

What is the endocrine system ? How does it act as communication system?

Answer 6

Endocrine glands that produce hormones in animals are collectively known as ENDOCRINE SYSTEM
- hormones are chemical substances produced by an endocrine gland/carried by blood
They transmit info from one part of organism to another /alter activity of one or more specific target organs

• used to control functions that dont need immediate responses

Question 7

Importance of homeostasis ?

Answer 7

Homeostasis keeps internal body conditions within restricted limits
Controls:
Temperature (vital for enzyme activity)
PH (vital for enzyme activity)
Blood Glucose conc

Question 8

Why does blood glucose conc need to be controlled?

Answer 8

Glucose in blood affect WATER POTENTIAL of blood / availability of respiratory substrate for cells

Question 9

Eg of how plants carry out homeostasis ?

Answer 9

Stomata control diffusion of gases in/out leaves
- stomata respond to changes in :
LIGHT- open in higher light intensity/close in darkness
CO2 levels - open when low CO2 conc in air spaces in leaf/close when high CO2 conc in leaf

This regulation of stomata aperture balances need for CO2 with need to minimise water loss

Question 10

How is negative feedback controlled?

Answer 10

Receptors detect deviations from the normal range (stimuli) which causes a corrective mechanism to return factor Back to normal range

2 corrective mechanisms : one for when factor is too low
One from when factor is too high

These corrective mechanisms can involve the endocrine/nervous system to transfer info to effector /carry out response

Question 11

What happens in positive feedback?

Answer 11

The original stimulus produces a response that causes the factor to deviate even more from normal range

Question 12

What is homeostasis?

Answer 12

Regulation of internal conditions of a cell/organisms to maintain optimum conditions for function , in response to internal/external changes

Question 13

Eg of positive feedback to cause activation ?

Answer 13

Blood clotting after injury :
- platelets become activated /release a chemical - trigger more platelets to become activated and so on
- platelets form blood clot
- process ends with negative feedback when body detects blood clot has formed

Question 14

What is cell signalling /why is it important?

Answer 14

Process by which cells communicate with each other
- allows multicellular organisms to control/coordinate their bodies and to respond to their environments

Question 15

Stages of cell signalling?

Answer 15

Stimulus received by receptor cell
Stimulus converted to a signal to be passed on —> TRANSDUCTION
Signal transmitted to effector that can detect it /appropriate response made

Question 16

What are 2 types of cell signalling ?

Answer 16

Paracrine signalling - signalling between cells that are close tgt
Endocrine signalling - signalling between cells that are far apart -> involves signalling molecule to be transported in circulatory system

Question 17

How dos cell signalling occur across cell membranes?

Answer 17

Have receptor molecules on/in cell surface membrane which are proteins/glycoproteins
- signalling molecules are very small for easy transport across membranes /binds to receptor molecules

Question 18

Why are low/too high temps not good for body?

Answer 18

LOW TEMPS : lower Frequncy of successful collisions between substrate/active sites —> less frequency ESC formation
- substrate/enzyme collide with less energy so less likely for bonds to form/break

HIGH TEMPS: greater enzyme activity as more successful collisions/collide with more energy etc…
- however rate of activity drop sharply as temp continues to increase —> ENZYME DENATURES

Question 19

What are endotherms/ectotherms?

Answer 19

Endotherms: animals that possess physiological mechanisms to control their internal body temperature
Eg mammals/birds

Ectotherms: animals that rely on behavioural adaptations to ensure their internal body temperature does not get too high or low

Question 20

Cooling mechanisms in endotherms?

Answer 20

Thermoreceptors in hypothalamus/skin detect increase in body temp so cause:

VASODILATION: muscles relax causing arteioles to dilate —> MORE BLOOD FLOW THROUGH CAPILLARIES
- heat is then lost via radiation to environment

SWEATING: sweat secreted by sweat glands /cools skin by evaporation (energy used to convert liquid into vapour)
- less effective in humid environments due to reduced conc grad —> evaporation less efficient

FLATTENING OF HAIRS: hair erector muscles (effectors) in skin relax - hair lie flat
- stops them from creating insulating layer by trapping air/allows air to circulate over skin and heat to leave by radiation

Question 21

Warming mechanisms in endotherms?

Answer 21

Thermoreceptorrs in hypothalamus/skin detect decrease in body temp so cause :

VASOCONSTRICTION: muscles of arteriole walls contract —> arterioles near skin CONSTRICT —> LESS blood flow in capillaries
- blood diverted through shunt vessels (further down in the skin) /do not lose heat to environment

BOOST METABOLIC RATE: most metabolic reactions are exothermic so provide warmth for body
- in cold , thyroxine hormone increases Basal Metabolic Rate (BMR), increasing heat production

ERECTION OF HAIRS: hair erector muscles in skin CONTRACT - hairs stand on end
- forms insulating layer over skin’s surface by trapping air between hairs/stop heat lost by radiation

SHIVERING: reflex action to decrease core body temp (nervous system mechanism not hormonal)
- muscles (effectors) contract rapidly/regularly
- metabolic reactions needed to power shivering generate heat to warm blood/raise core body temp

Question 22

How do ectotherms thermally regulate ?

Answer 22

Ectotherms need to avoid extremes of temp
- if too cold body temp , decrease speed they can move, decreasing ability to catch prey/escape predators

HEAT UP: seek sun/warmer surfaces
Rest/‘bask’ in warm places

COOL DOWN: seeks shade/water

Question 23

Disadvantages of thermoregulation mechanisms in ectotherms/endotherms?

Answer 23

ECOTHERMS : behavior is more restricted by environmental temps compared to endotherms —> CANNOT COLONISE HABITATS THAT ARE TOO HOT/COLD
- however, aquatic ectotherms have minor difficulty maintaining body temperature as water temps are a lot less variable than on land (due to high specific heat capacity of water)

ENDOTHERMS: require more energy to maintain body temp, so metabolic rate is a lot higher
- could be restrictive bc wont survive as well as ectotherms when food supply is limited