5.1.1 Communication and Homeostasis

Question 1

What is homeostasis?

Answer 1

-maintenance of a constant internal environment in response to changes in external/internal environment
-involves control systems that keep internal environment roughly constant

Question 2

How do animals respond to the environment?

Answer 2

• respond to changes in their external environment i.e by avoiding harmful environments
  -respond to changes in their internal environment to make sure conditions are optimal for metabolic reactions

Question 3

Changes to internal environment

Answer 3

-internal body temp
-blood glucose levels
-water levels
-pH

Question 4

Changes to external environment

Answer 4

-external temp
-humidity
-light(plants)
-harmful stimuli i.e sudden sounds/pain

Question 5

Why is homeostasis important?

Answer 5

-vital for cells to function normally and stop them being damaged
-allows them to avoid harmful environment / ensure that conditions are optimum for metabolism

Question 6

Why are receptors and effectors needed?

Answer 6

-restore dynamic equilibrium in response to conditions
-receptors trigger and co-ordinate the correct responses
-info from sensory receptors is transmitted to the brain + impulses are sent along motor neurons to effectors(muscles/glands) that react to bring about change in response to stimulus

Question 7

Why do multicellular organisms need communication systems?

Answer 7

-organs, cells and tissues have different functions, are found in different parts of the body and may have different roles to one another
-need to communicate

Question 8

Short paracrine cell signalling

Answer 8

-occurs between cells that are close together i.e neurotransmitters between nerves or muscle cells

Question 9

Long distance endocrine signalling

Answer 9

-involves signalling over long distances
-signalling molecules are transported in the circulatory system

Question 10

What is a hormone?

Answer 10

-a chemical messenger, secreted by glands and found in the endocrine system

Question 11

similarities between the endocrine + nervous system

Answer 11

-both have coordination centres(brain, spinal cord)
-both send signals in the body
-both have receptors to detect stimuli
-both have effectors(muscles/glands) to carry out response

Question 12

Differences between nervous + endocrine system

Answer 12

-chemical messengers vs nerve impulses
-hormones are longer lasting vs nerves are shorter lasting
-nerves work faster than hormones

Question 13

What do cell surface receptors do?

Answer 13

-allow cells to recognise the chemicals involved in cell signalling

Question 14

What is negative feedback?

Answer 14

-control mechanism that elicits response to help restore changed value to norm
-receptors detect when a level is too high/low-}info communicated via nervous/hormonal system –} effectors respond to counteract the change

Question 15

What happens if the change from normal is too big?

Answer 15

-effectors may not be able to counteract it, i.e a huge drop in body temp caused by prolonged exposure to cold

Question 16

What is positive feedback?

Answer 16

-amplifies the change away from normal
-not involved in homeostasis because internal environment isn’t constant
-rapidly activates processes in the body i.e platelets forming blood clots

Question 17

Why is it important to maintain core body temp?

Answer 17

• temp affects enzyme activity and enzymes control the rate of metabolic reactions

Question 18

How does high body temp have an effect?

Answer 18

-rise in temperature makes the enzyme’s molecules vibrate more
-if temp goes above a certain level, vibration breaks some H bonds in the tertiary structure
-active site changes shape and enzyme + substrate no longer fit together
-enzyme denatures

Question 19

How does low body temp have an effect?

Answer 19

-enzyme activity / RoR
-enzyme-substrate complexes cannot form

Question 20

Why does body temp fluctuate throughout the day?

Answer 20

-it is dependent on the external environment
-respiration is an exothermic reaction, so the temp it works at changes

Question 21

How are temp changes in the body detected?

Answer 21

-the peripheral temp receptors are in the skin + detect changes in the skin surface temp
-temp receptors in the hypothalamus detect temp of blood in the body

Question 22

What is an ectotherm?

Answer 22

-an animal that cannot control their body temp internally via homeostasis
-instead change their behaviour i.e migration

Question 23

Sources for ectotherms to regulate temp

Answer 23

-radiation= absorbing thermal energy
-evaporation
-convection= thermal energy transferred with air/liquids
-conduction= transfer of thermal energy through solid surfaces

Question 24

What are endotherms?

Answer 24

-can control their body temperature internally via homeostasis i.e mammals and birds

Question 25

Difference in metabolic rate between ectotherms and endotherms

Answer 25

-ectotherms don’t have a constant body temp so their metabolic rate varies
–} more active at higher temps and vice versa
-endotherms can keep internal temp constant so they have a constantly high metabolic rate–} largely independent of external temp

Question 26

Mechanisms to reduce body temp: vasodilation

Answer 26

-atertioles near the surface of the skin dilate when temp rises
-vessels that provide a direct connection between the arterioles + the venules constrict
-this forces blood through the capillaries in the surface layers of the skin
-more heat is lost from the skin in radiation +temp is lowered

Question 27

Mechanisms to reduce body temp:
Sweating

Answer 27

-more sweat secreted from sweat glands as core temp increases
-water in sweat evaporates from the surface of the skin + takes heat from the body + cooling the skin

Question 28

Mechanisms to reduce body temp:
Hairs lie flat

Answer 28

-as temp increases, the erector pilli muscles in the skin relax, causing hairs to lie flat
-avoids trapping an insulating layer of air–} skin is less insulated and heat can be lost more easily

Question 29

Mechanisms to increase body temp:
vasoconstriction

Answer 29

-arterioles near me surface of the skin constrict–} less blood flows through the capillary networks close to the surface of the skin
-very little radiation takes place–} the warm blood is kept well below the surface to reduce heat loss

Question 30

Mechanisms to reduce body temp:
Decreased sweating

Answer 30

-less sweat is secreted from sweat glands when it’s cold–} reducing the amount of heat loss
-less evaporation of water from the skin’s surface

Question 31

Mechanisms to reduce body temp:
Hairs stand up

Answer 31

-erector pilli muscles in the skin contract, making the hairs stand up
-traps an insulating layer of air, so reduces cooling through the skin

Question 32

Mechanisms to reduce body temp:
Shivering

Answer 32

-muscles contract in spasms–} rapid, involuntary contracting + relaxing of muscles
-metabolic heat from the increased exothermic reactions (respiration) warm up the body

Question 33

Mechanisms to reduce body temp:
Hormones

Answer 33

-body releases adrenaline + thyroxine
-increases metabolism + so more heat is produced

Question 34

What is the endocrine system?

Answer 34

-made up of endocrine glands–} group of cells which are specialised to secrete hormones
-glands can be stimulated to release hormones by a change in conc of a substance/electrical impulse

Question 35

Hormones

Answer 35

-chemical messengers i.e steroids, proteins, glycoproteins, polypeptides, amines etc
-secreted directly into the blood and transported through the body in blood plasma
-then diffuse out of the blood and bind to receptors of membranes on target cells–} stimulate hormone to produce response

Question 36

action of hormones in cell signalling (non-steroid hormones)

Answer 36

-primary messenger(hormone) with a complimentary shape binds to the specific receptor on the cell surface membrane of the target cell from the endocrine gland
-this activates an enzyme in the cell membrane which catalyses the production of a secondary messenger–} activates a cascade of reactions inside the cell(to do with protein synthesis/activation) i.e adrenaline

Question 37

action of hormones in cell signalling (steroid hormones)

Answer 37

-because they are non-polar + lipid soluble molecules, they can pass through the lipid component of the cell membrane and bind to steroid hormones inside the cell to form a hormone-receptor complex–} acts as a transcription factor which facilitates/inhibits the transcription of a specific gene i.e oestrogen

Question 38

Hormonal vs neuronal communication

Answer 38

-communication via hormones vs nerve impulses
-hormone transmission via bloodstream vs nerve transmission is by neurones
-hormones work slow vs nerves work faster
-widespread response in hormones vs localised response in nerves
-slow vs rapid
-long lasting vs short lived
-permanent and irreversible vs temporary and reversible

Question 39

Structure of the adrenal glands

Answer 39

-two small endocrine glands located just above the kidney
-produce effects that help prepare the body for the ‘fight or flight’ response
-the cortex= outer region of glands, produce hormones that are vital to life released by the pituitary gland i.e cortisol and aldosterone
-the medulla= inner region of the glands, controlled by the nervous system, produces hormones i.e adrenaline and noradrenaline
-these parts are surrounded by a capsule

Question 40

Cortex: Cortisol

Answer 40

-helps regulate metabolism by stimulating the breakdown of proteins + fats to glucose which increases the amount of energy available so the brain and muscles can form a response
-works with other hormones to suppress the immune system so the body does not attack itself in the fight or flight response

Question 41

Cortex: Aldosterone

Answer 41

-helps control blood pressure
-increases blood vol and pressure by increasing the uptake of sodium ions + water by the kidneys

Question 42

Cortex: Androgens

Answer 42

-small amounts of male + female sex hormones are released–} small impact but important especially for women after menopause

Question 43

Medulla: Adrenaline and Noradrenaline

Answer 43

work together to:
-increase heart rate
-increase breathing rate
-constrict some blood vessels in non-essential organs so blood is diverted to brain and muscles(high bp)
-widening of air passages in the lungs
-convert glycogen to glucose in the liver–}glycogenolysis= increases respiration because more glucose is supplied to muscles, produce more energy

Question 44

Main functions of the pancreas

Answer 44

-to secrete hormones into the bloodstream as an endocrine gland
-to secrete enzymes and release them via a duct i.e digestive enzymes (amylase, lipase etc) into the digestive system as an exocrine gland

Question 45

3 important digestive enzymes and how they are secreted

Answer 45

-amylase: breaks down starch into simple sugars i.e maltose(disaccharide broken down further by maltase into alpha glucose)
-protease: breaks down proteins into amino acids
-lipase: breaks down lipids into fatty acids and glycerol
the digestive enzymes alongside pancreatic juice are delivered to the small intestines via a duct

Question 46

Islets of Langerhans and their role

Answer 46

-small regions of endocrine tissue within the exocrine tissue
-found in clusters around the blood capillaries and they secrete insulin and glucagon directly into the bloodstream
-alpha cells secrete glucagon and beta cells secrete insulin–} help to control blood glucose concentration

Question 47

Histology of Islets of Langerhans

Answer 47

-lightly stained(differential staining normally used to distinguish alpha cells from beta cells)
-large spherical clusters

Question 48

Histology of exocrine pancreatic tissue

Answer 48

-darker stained
-small, berry-like clusters