Module 5 - OCR A Level Biology

5.1.1 COMMUNICATION AND HOMEOSTASIS

5.1.1 COMMUNICATION AND HOMEOSTASIS

why do multicellular organisms need communication systems?

e.g hormonal, nervous

So they can respond to changes in the internal and external environment + coordinate the activities of different organs.

responses can be behavioural or physiological

How does responding to the environment help organisms survive?

• increase chance of survival by responding to changes in external enviro. e.g by avoiding harmful enviro. (too hot/cold)

• respond to changes in internal enviro. to make sure conditions are optimal for their metabolism

what factors do cells need to keep constant

• conc. of chemicals e.g glucose and sodium

• pH

• water potential

• temperature

• low levels of toxins e.g urea

• levels of gases

so enzyme-controlled reactions can take place

Important that CO[2] does not build up as it reacts with water to form carbonic acid which releases H+ ions which lowers pH --> enzymes

why is it so important to maintain core body temperature at around 37 °C ?

what happens at too high and too low temps?

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

when temp too high enzymes tertiary structure breaks, active site changed, denatured.

when temp is too low, enzyme activity reduced, slows rate of metabolic reactions.

Which molecules are used to transport signals over long distances between cells?

How are they recognised?

Hormones which are transported in the blood

target cells have cell surface receptors allow cells to recognise the hormones

Which type of hormone is lipid soluble- steroid or non-steroid?

Steroid

Which property of non-steroid hormones stops them passing through the cell membrane?

Hydrophilic

If a response is slow, which messenger system most likely transmitted it? Hormonal or nervous?

Hormonal

If a response is short-lived which messenger system most likely transmitted it? Hormonal or nervous?

Nervous

If a response has a permanent and irreversible effect, which messenger system most likely transmitted it? Hormonal or nervous?

Hormonal

difference between hormonal and neuronal communication?

What is homeostasis?

is the maintaining of a constant internal environment in a constant or steady state despite any changes in the external environment

**constant meaning that conditions will vary within acceptable range to not change body functions

What is negative feedback?

A mechanism that counteracts changes (in internal conditions when the changes cause the a shift away from the normal)

Ensures optimum internal conditions are maintained.

A homeostasis diagram showing the template for an exam question

graph diagram of negative feedback

what is positive feedback?

the process in that effectors increase (magnify) any change detected by the receptors.

not used in homeostasis bc doesn't keep environment constant

give some examples of processes which use positive feedback

• Blood clot: platelets become activated and release chemical → more platelets triggered → blood clot formed → ends in negative feedback when body detects formed blood clot

• control of ovulation: follicles stimulate oestrogen production → stimulates more follicle cells to develop → process ends in negative feedback when LSH stops maturation

• Breast feeding: suckling stimulates nerve endings in nipple → stimuli carried to hypothalamus → hypothalamus produces oxytocin → oxytocin stimulates milk production

• if suckling stimulus not strong, not as much oxytocin produced, not as much milk produced

• Birth: head of baby presses against cervix → stimulates production of oxytocin → oxytocin stimulates uterus to contract → pushes babies head harder against cervix → triggers more oxytocin

What are changes in the internal and external environments known as?

Stimuli

What is the term for an organism that does not control their body temperature internally?

Ectotherm

their body temp fluctuates with the environment, they can't increase respiration rate to generate heat e.g reptiles, fish

What is the term for an organism that can control its body temperature internally?

Endotherm

can genrate heat via exergonic reactions

why do many ectotherms living in water not need to thermoregulate?

why is living on land problematic for an ectotherm?

• water has high heat capacity means the temp of their enviro. does not change much.

• temp of air can vary a lot e.g diff. seasons

How do ectotherms control their body temperatures?

Changing behaviour

what are some behavioural responses of ectotherms to increase/reduce the radiation they absorb from the sun?

to warm up:

• bask in sun

• orientate body so max surface area is exposed to the sun

• conduction → press body against warm ground

• exothermic metabolic reactions

to cool down:

• shelter from sun

• press body against something cool

• orientate so min surface area exposed

• minimise movements to reduce metabolic heat generated

Advantages and disadvantages of ectotherms

Advantages

• Less food used for respiration hence they need to find less food

• A greater proportion of their energy can be used on growth

Disadvantages

• Less active in cooler temperatures hence at great risk of predation and also need to the day of by basking in the sun.

• Aren't capable of activity during winter hence need large food stores.

Advantages and disadvantages of endotherms

Advantages

• a constant temperature regardless of the environment

• active even in times of low temperatures

• ability to inhabit colder environments

Disadvantages

• significant amount of energy used to maintain body temperature

• more food required (need to spend a lot of time eating)

• less energy used for growth

what are some physiological responses of ectotherms to warming?

• dark colours in colder climates to absorb more heat radiation

• some ectotherms can alter heart rate to increase or decrease metabolic rate

what do peripheral temperature receptors do and why?

We have receptors in our skin which detect surface temperature before it can affect the core body temperature by sending nerve impulses to the thermoregulartory centre of the hypothalamus.

what are some behavioural responses of endotherms to increase/decrease their temperature?

list extras for humans

warm up:

• bask in sun

• conduction

• hibernation

cool down:

• wallowing in water + mud

digging burrows = both

Humans

• clothes worn to stay warm

• houses heated

How does shivering increase body heat?

More heat is produced from increased respiration

How do adrenaline and thyroxine increase body heat?

Increase metabolism

How does sweating reduce body temperature?

When sweat evaporates it takes heat from the body

How is the temperature of the blood detected?

As the blood flows past the thermoregulatory centre (TRC) of the hypothalamus, the TRC then detects whether the temp. of the blood is above or below normal. If so it carries out a response by negative feedback to get the blood back to normal.

Temperature rise is detected by ...

... thermoreceptors in the thermoregulatory centre in the hypothalamus and peripheral receptors in the skin

Do a negative feedback loop for temperature rising and decreasing

what are physiological adaptations of endotherms to cool down? (to maintain stable body temp)

vasodilation

increased sweating: sweat glands all over body, as sweat evaporates from the surface of the skin, heat is lost, cooling the blood

reducing insulating effect of hairs/feathers: Hairs/feathers are flat. Less air trapped hence less insulation

panting: Panting increases, losing heat as water evaporates bc some animals can't sweat

Liver cells: Rate of metabolism is reduced hence less exogenic reactions occur

what are physiological adaptations of endotherms to warm up? (to maintain stable body temp)

vasoconstriction

decreased sweating some evaporation from lungs may still occur but overall water stops evaporating

raising body hair/feathers: Hairs are raised hence trap air hence increased insulation

shivering: spontaneous involuntary contractions which generate metabolic heat by causing muscle cells to respire

Liver cells: Rate of metabolism increased hence more exogenic reactions occur

Hormones: adrenaline and thyroxine released which increase metabolism → more heat

explain vasocontriction and vasodilation in detail

vasodilation: arterioles near surface of the skin dilate which forces blood through the capillary networks close to the surface of the skin. Heat lost by convection and radiation.

vasoconstriction: arterioles near surface of the skin constrict so little blood flows through the capillary networks close to skin, warm blood is kept below the surface. Sphincters muscles also tighten and restrict bloods access to capillaries near surface of skin (yellow in diagram). little radiation takes place.

(diagram correctly shows the capillaries do not expand as their walls are one cell thick, no elastic fibres/muscle to stretch or recoil)

What are adaptions of endotherms living in cold climates?

• minimise SA:V ratio e.g small ears

• thick layer insulating fat + fur

• hibernate (lower metabolic rate)

5.1.1 COMMUNICATION AND HOMEOSTASIS

5.1.1 COMMUNICATION AND HOMEOSTASIS

5.1.2 EXCRETION AS AN EXAMPLE OF HOMEOSTATIC CONTROL

5.1.2 EXCRETION AS AN EXAMPLE OF HOMEOSTATIC CONTROL

What is urea formed from?

Ammonia and carbon dioxide

Which blood vessel supplies oxygenated blood to the liver?

Hepatic artery

Which blood vessel takes deoxygenated blood away from the liver?

Hepatic vein

Which blood vessel brings blood from the small intestine to the liver?

Hepatic portal vein

Why is bile produced?

To emulsify fats

What type of cells are liver lobules made up of?

Hepatocytes

What is the name for the capillaries in the liver that connect the central vein to the hepatic artery and hepatic portal vein?

Sinusoids

What is the name for the cells on the walls of the sinusoids that remove bacteria and break down old red blood cells?

Kupffer cells

What connects the bile duct to the central vein?

Canaliculi

Where in the kidneys does ultra-filtration take place?

Glomerulus

What are the three layers that the liquid and small molecules pass through from the glomerulus to the Bowman's capsule?

Capillary wall, basement membrane and epithelium

Where does selective reabsorption in the kidneys take place?

PCT, loop of Henle and DCT

Where are ions actively pumped out of the nephron?

Near the top of the ascending limb

Where does water move out of the nephron?

Descending limb and collecting duct

Where do ions diffuse out of the nephron?

Near the bottom of the ascending limb

How is water potential monitored?

Osmoreceptors in the hypothalamus

How does ADH affect water levels in the blood?

Increases

What is measured to detect kidney failure?

Glomerular filtration rate

What can kidney infections cause?

Inflammation of the kidneys

How can high blood pressure damage the kidneys?

Damage the glomeruli

What can be caused by long term kidney failure?

Anaemia

Which hormone do pregnancy tests detect?

hCG

5.1.2 EXCRETION AS AN EXAMPLE OF HOMEOSTATIC CONTROL

5.1.2 EXCRETION AS AN EXAMPLE OF HOMEOSTATIC CONTROL

5.1.3 NEURONAL COMMUNICATION

5.1.3 NEURONAL COMMUNICATION

Where does the sensory neurone transmit nerve impulses from?

Receptors

Which type of receptor is a Pacinian corpuscle?

Mechanoreceptor

What is a transducer?

Something that converts one form of energy to another

Where are Pacinian corpuscles found?

Skin

In the formation of a neurone's resting potential, how many sodium ions are pumped out for every two potassium ions pumped in?

3

Neurone diagrams

What is the resting potential of a neurone?

-70mV

What is the threshold for depolarisation?

-55mV

At which potential difference does repolarisation occur?

+30mV

What is the term for spaces between myelin sheaths on a neurone?

Nodes of Ranvier

Why does hyperpolarisation of the neurone occur?

Potassium ion channels are slow to close

Which cells make up the myelin sheath?

Schwann cells

In which type of neurone does saltatory conduction occur?

Myelinated neurone

Which ions cause the neurotransmitter to be released from the synaptic knob?

Calcium ions

Where do dendrons send electrical impulses?

Towards the cell body

Where do axons send electrical impulses?

Away from the cell body

Why does a larger axon diameter increase the speed of the transmitted impulse?

Less resistance

What is a synapse?

Junction between two neurones

What is the term for the gap between the axon of one neurone and the dendron of another?

Synaptic cleft

What do synaptic vesicles contain?

Neurotransmitters

Where in the body are cholinergic synapses found?

CNS and neuromuscular junctions

What is the term for when signals from multiple stimuli are coordinated into a single response?

Spatial summation

What is the term for when two or more nerve impulses arrive in quick succession from the same pre-synaptic neurone?

Temporal summation

5.1.3 NEURONAL COMMUNICATION

5.1.3 NEURONAL COMMUNICATION

5.1.4 HORMONAL COMMUNICATION

5.1.4 HORMONAL COMMUNICATION

what is an exocrine gland?

give examples

secretes substances via a duct e.g into organs or surface of skin and not into the blood stream

e.g saliva gland, pancreas

what are hormones?

how do they work?

Chemical messengers that travel in the blood to target cells/tissues.

They can be proteins e.g insulin or steroids e.g progesterone

Hormones secreted into blood, each hormone only binds to specific receptors for that hormone found on membrane of some cells (target cells). Diffuse out of blood to bind with target cells which produce a response.

what can glands be stimulated by?

• a change in the conc of a specific substance

• electrical impulses

• another hormone

list the major endocrine glands and the hormones they secrete

Pituitary:

• growth hormone

• anti-diruetic hormone

• LH + FSH

Thyroid:

• thyroxine → controls rate of metabolism

Adrenal:

• adrenaline → increases heart + breathing rate + raises blood sugar level

• cortisol

Testes:

• testosterone → sperm production

Thymus:

• thymosin → maturation of white blood cells

Pancreas:

• insulin

• glucagon

Ovaries:

• oestrogen → ovulation

• progesterone → embryo receiving lining prep

label the endocrine glands

describe the structure of an adrenal gland?

where are the adrenal glands located?

adrenal cortex: the outer region of the glands which produces essential hormones such as cortisol + aldosterone

adrenal medulla: inner region, produces non-essential hormones such as adrenaline

What hormones does the adrenal cortex secrete and what roles do they have?

what type of hormones are these?

cortisol:

• regulates metabolism by controlling how many biological molecules e.g fat are converted into energy.

• regulate blood pressure

• regulate immune response + suppress inflammation

• release controlled by hypothalamus

Aldosterone:

• controls blood pressure by maintaining balance of water + salt concs in blood + bodily fluids

• release triggered by kidney

also secretes androgens

they are steroid hormones

what effect does stress have on the adrenal cortex?

in response to stress it releases cortisol + aldosterone:

• stimulates breakdown of proteins and fats into glucose which increases amount of energy available so brain + muscles can respond to situation

• increases blood volume and pressure by increasing uptake of sodium ions + water by kidneys

• suppresses the immune system

also secretes androgens

what is an endocrine gland?

give examples

group of specialised cells that secrete hormones directly into the blood stream

e.g pancreas + adrenal glands

What are the three main types of hormone produced by the adrenal cortex?

Glucocorticoids, mineralcorticoids and androgens