Biology: Modules 1-6 (Paper 3)

Why are communication systems needed?

• Respond to changes in internal and external environment

• Coordinate activity of different organs

Give some examples of changes in environment to show the necessity of communication systems?

• Buildup of carbon dioxide

• Predator appearing

• Seasons changing

What is cell signalling?

Chemical signal released by one cell is detected by another stimulating a change in activity

Describe how distant cells communicate in animals and their relative properties?

• Neuronal system - travel large distance quickly and short acting

• Endocrine hormones - slower but longer acting

How can adjacent cells communicate?

• Gap junctions in animals (direct contact)

• Paracrine signalling - diffusion of molecules short distances

• Plasmodesmata in plants

What is the function of sensory receptors?

Monitor changes in internal or external environment

What is the function of effectors?

Bring about a response

Name some effectors in the body?

Muscle cells, glands, hepatocytes (liver cells)

Define negative feedback?

A stimulus brings the body’s environment away from normal and a response brings the body’s environment back to normal

Define positive feedback?

A stimulus brings the body’s environment away from normal and a response brings the body’s environment further away from normal

Describe the 3 key steps for feedback loops to occur?

• Change is detected by receptors

• Change is signalled to other cells

• Effective response that reverses/increases change in conditions

Define homeostasis?

Maintaining a near constant internal environment despite changes in the external environment.

What is an example of positive feedback?

• Release of oxytocin at the cervix

• Depolarisation of a neurone

Define an endotherm?

Uses heat from metabolic activity to regulate core body temperature

Define an ecotherm?

Uses external sources of heat to regulate core body temperature

Describe some behavioural responses when too cold in ectotherms?

• Bask in the sun - absorb warmth from sun

• Face sideways on - increase SA exposed

• Expand ribcage - increase surface area

Describe some behavioural responses when too hot in ectotherms?

• Hide in burrows - move out of sun

• Face head on to sun - decreases surface area

• Climb up plants - avoid hot soil surface

What are advantages of ectotherms?

• Less food used 

• More energy for growth/reproduction

• Spend less time finding food

What are disadvantages of ecotherms?

• Metabolism is lower in colder environments

• Can be at risk of predators when body temperature is low

• Unable to hunt for food when body temperature is low

How does thermoregulation occur?

• Peripheral thermoreceptors in skin anticipate changes in temperature

• Thermoreceptors in hypothalamus detect changes in blood temperature

• Hypothalamus sends action potentials to skin and muscles to increase/decrease temperature

Describe some physiological responses in endotherms when too hot?

• Vasodilation - more blood flow to skin so more heat lost via radiation

• Hairs lay flat - more air flow over skin

• Sweating - heat energy from blood used to evaporate water

Describe some physiological responses in endotherms when too cold?

• Vasoconstriction - less blood flow to skin so less heat lost by radiation

• Hairs stand erect - traps insulating layer of air above skin

• Shivering - rapid contraction of muscles generates heat energy

• Increased metabolic activity - more heat generated from respiration (exothermic reaction)

Describe some behavioural adaptations in endotherms when too hot?

• Hide away from sun

• Orientate body to decrease surface area facing sun

• Remain inactive and spread out limbs

• Wet skin to cool the body - e.g. elephants spraying water

Describe some behavioural adaptations in endotherms when too cold?

• Lie in the sun

• Orientate body to increase surface area facing sun

• Move about to generate heat in muscles or roll into ball to reduce surface area exposed

• Remain dry

What are the advantages of endotherms?

• Maintain a fairly constant internal temperature

• Remain active even in low temperatures to take advantage of prey

• Inhabit colder habitats

What are disadvantages of endotherms?

• Need more food

• May overheat in hot weather

• Use less energy from food for growth

Define excretion?

Removal of metabolic waste from the body

Why is excretion required?

• Prevents buildup of metabolic waste

• Buildup could inhibit enzyme activity or become toxic

• Buildup of CO₂ prevents effective transport of O₂

• Amino acids cannot be stored so are converted to keto acid but urea must be excreted

Describe the gross structure of the liver?

• Hepatocytes grouped into lobules

• Lobules have a central vein (branch of hepatic vein)

• Interlobular vessels (portal vein and hepatic artery) run parallel to lobules

• Blood from interlobular vessels travels down sinusoids

• Kupffer and endothelial cells line the sinusoid

• Sinusoids eventually drain into the central vein

• Branches of the hepatic vein from lobules form the hepatic vein

• Bile canulici run antiparallel to sinusoids and collect in a branch of the bile duct

Fill in the labels clockwise from middle right?

Bile canuliculus, bile duct (branch), hepatic portal vein (branch), hepatic artery (branch), sinusoid, hepatocytes, kupffer cell, central vein

How are cells lining the sinusoid specialised?

• Flattened to reduce diffusion distance

• Fenestrations to allow molecules to enter

What are kupffer cells and what is their function?

• Specialised macrophages

• Breakdown worn out RBCs into bilirubin

How are hepatocytes specialised?

• Dense cytoplasm

• Many organelles for variety of functions

Label from top clockwise?

Central vein, hepatocytes, sinusoids

What are the roles of the liver?

• Storing glycogen

• Detoxification

• Forming urea

Describe the role of enzymes for detoxification in the liver?

• Cytochrome p450 - break down drugs

• Catalase - break down hydrogen peroxide

Describe how ethanol (alcohol) is detoxified?

• Oxidised to ethanal by ethanol dehydrogenase

• 2H removed which combine with NAD

• Oxidised in the same way again to form ethanoic acid

• Forms acetyl-coA to enter krebs cycle

Why does excess alcohol consumption cause fatty liver disease?

• Too much NAD is used to accept hydrogen from detoxification of alcohol

• Not enough NAD to respire fatty acids

• Fatty acids stored as fats in hepatocytes

How are excess amino acids dealt with?

• Deaminated forming a keto acid and ammonia

• Keto acid can enter respiration

• Ammonia reacts with CO₂ in ornithine cycle to form urea

Why is ammonia converted to urea in the ornithine cycle?

Urea is less soluble and less toxic

Write an equation for the process of converting ammonia to urea?

2NH₃ + CO₂ → CO(NH₂)₂ + H₂O

Fill in the labels top to bottom?

Nephron, capsule, cortex, medulla, renal vein (branch), renal artery (branch), renal pelvis, ureter

Describe the 3 main sections of the kidney?

• Cortex - outer region

• Medulla - inner region

• Pelvis - leads to ureter

Describe the structure of a nephron?

Glomerulus, PCT, loop of henle, DCT, collecting duct

Fill in the labels clockwise from top right?

Efferent arteriole, epithelium of bowmans capsule, PCT (cells), podocytes, lumen of bowmans capsule, afferent arteriole

Explain how the structure of the bowman’s capsule is related to its function?

• Efferent arteriole narrower than afferent to increase hydrostatic pressure forcing solutes out

• Knot of capillaries increase surface and decrease blood flow to increase time for diffusion

Describe ultrafiltration in the bowman’s capsule?

• Capillary endothelium - fenestrations allowing blood plasma and dissolved substances to leave

• Basement membrane - fine mesh of collagen fibres and glycoproteins which stops anything with RFM > 69000

• Podocytes - processes (projections) to hold cells away from capillary allowing fluid to pass between cells into lumen

What sections of the nephron are in the medulla?

Collecting duct and loop of henle

What is present in the glomerular filtrate (besides water)?

• Glucose

• Amino acids

• Urea

• Mineral ions

• Very little protein

What is reabsorbed in the nephron?

• Amino acids

• Glucose

• Some water

• Some mineral ions

Explain the water potential of the blood after ultrafiltaration and its use?

• Very low water potential

• Large proteins remain in blood but lots of water has left

• Useful for reabsorption of water in the PCT/collecting duct

Where does selective reabsorption take place?

PCT / proximal convoluted tubule

Describe the process of selective reabsorption?

• Sodium ions actively pumped out of the cell into the blood

• Sodium ions move down their concentration gradient from tubular fluid into PCT cell

• They enter via facilitated diffusion - carrying either 1 glucose or amino acid with them

• Known as secondary active transport

• Water moves in the PCT cell via osmosis

• Glucose and amino acids diffuse into blood

• Water moves into blood via osmosis

How are PCT cells adapted?

• Microvilli increase surface area

• Cotransporter proteins in plasma membrane

• Many mitochondria for active transport

• Sodium/potassium pumps

State and explain what part of the kidney this micrograph shows?

• PCT wall cells

• Microvilli shown

Fill in the labels from left to right. Give reasons for your choice?

• DCT, PCT

• PCT generally larger, have brush border and stain lighter

Describe how loop of henle causes increase of solute concentration?

• Active transport of sodium/chloride out upper part of ascending limb

• Ascending limb is impermeable to water

• Diffusion of sodium/chloride into descending limb

• Water leaves descending limb by osmosis

• Sodium/chloride diffuse out lower part of ascending limb

• Example of countercurrent multiplier

Describe the mechanism of action of ADH on the collecting duct?

• ADH binds to complementary receptors on plasma membrane of cells in wall of collecting duct

• Release of second messenger cAMP

• Vesicles containing aquaporins fuse with plasma membrane 

• Increase permeability of collecting duct wall to water

• More water moves down water potential gradient into cells

What effect does more ADH have?

• More water reabsorption in the collecting duct

• More concentrated urine produced with less volume

How is water reabsorbed in the collecting duct?

• Medulla has a low water potential and tubule fluid has a high water potential

• Water moves by osmosis into cells of collecting duct wall through aquaporins

• Water moves by osmosis into surrounding tissue

Fill in the labels in number order?

Glucose, Na⁺, K⁺, urea

Fill in the labels from top to bottom?

Bowman’s capsule, glomerulus

Explain where specifically is this micrograph of?

• Cortex of kidney

• Bowman’s capsule present

Fill in the labels from the top clockwise?

Bowmen’s capsule lumen, PCT, glomerulus, DCT

Fill in the labels from left to right?

Renal pelvis, collecting duct

Describe osmoregulation when water potential of blood is too high?

No details of mechanism of ADH is required

• Osmoreceptors in hypothalamus detect increase in water potential of blood

• Stimulate less release of ADH from posterior pituitary

• Less water reabsorbed in the collecting duct

• More dilute urine is produced and blood water potential decreases

Describe osmoregulation when water potential of blood is too low?

No details of mechanism of ADH is required

• Osmoreceptors in hypothalamus detect decrease in water potential of blood

• Stimulate more release of ADH from posterior pituitary

• More water reabsorbed in the collecting duct

• More concentrated urine is produced and blood water potential increases

Describe the relative location of adrenal glands?

Just above the kidneys

After tubular fluid has travelled through the collecting duct, where does it go?

Renal pelvis, ureter, bladder

How does kidney failure affect glomerular filtration rate (GMR)?

Reduces

Give approximate values for GMR of healthy kidney, chronic kidney failure and acute kidney failure?

• Healthy: 90-120cm³min^-1

• Chronic: <60cm³min^-1

• Acute: <15cm³min^-1

How does kidney failure affect electrolyte balance?

• Too much or too little sodium in blood - too much is most common

• Too much potassium in blood

What problems can occur from kidney failure?

• Buildup of waste products in blood

• Electrolyte imbalance

• Dehydration or swelling of cells (particularly brain)

What are potential treatment for kidney failure?

• Hemodialysis

• Kidney transplant

Describe the process of haemodialysis?

• Heparin is added to blood to prevent clotting

• Blood from vein passes through many artificial capillaries with partially permeable membranes

• Dialysis fluid flows on the opposite side

• Countercurrent system of blood and fluid

• Bubbles are removed before blood re enters body

• Heparin removed just before dialysis is finished so blood clots when machine removed

Describe the advantages of haemodialysis as treatment for kidney failure?

• No surgery required

• No waiting list

• No immunosuppressants

• Buys time for a transplant

Describe the disadvantages of haemodialysis as treatment for kidney failure?

• Performed 2-3x a week at hospital

• Time consuming (several hours each session)

• Diet must be carefully monitored

• Short term solution

What are the advantages of kidney transplant as treatment for kidney failure?

• Freedom from time consuming dialysis

• Feel physically fitter

• Improved quality of life

• Improved self image

What are the disadvantages of kidney transplant as treatment for kidney failure?

• Requires immunosupressant drugs

• Side effect of immunosupressants - fluid retention, high BP, risk of infection

• Major surgery - risk of infection

• Regular checkups to check for rejection

How can urine by analysed to give information?

• Presence of glucose - diabetes

• Alcohol - blood alcohol in drivers

• Recreational drugs - work

• Anabolic steroids/PEDs - sport competitions

• hCG - pregnancy testing

How do pregnancy tests work?

• Tests for hCG

• Mobile monoclonal antibodies bind to hCG in urine

• Antibodies have visible blue pigment attached

• Antibodies with hCG bind to test line forming blue line

• Antibodies without hCG bind to control line forming blue line

How is anabolic steroid tested for in urine?

Gas chromatography (in labratory)

What is a transducer?

Convert one energy type to another

Describe a sensory receptor?

Transducer which detects changes in surroundings

What does the Pacinian corpuscle detect?

Pressure changes on skin

How does a pacinian corpuscle stimulate an AP?

• Lamallae deform transmitting the pressure to the membrane

• Membrane deforms causing mechanically gated Na⁺ channels to open

• Influx of Na⁺ depolarises membrane to threshold

• Known as generator potential

• Voltage gated Na⁺ channels open further depolarising membrane creating an AP

What receptor detects chemical in air?

Olfactory cells in epithelium of nose

What receptor detects chemicals in food?

Chemical receptors on tongue

Where do sensory neurones carry AP?

CNS

Where do relay neurones carry AP?

Sensory to motor neurone

Where do motor neurones carry AP?

CNS to effector

Describe and explain the general structure of neurones?

• Long to transmit information long distances

• Many gated ion channels in plasma membrane for polarisation/depolarisation

• Sodium/potassium pumps to reestablish concentration gradients

• Cell body with nucleus, many mitochondria and ribosomes

• Many dendrites to connect to other neurones

• An axon which carries AP away from cell body

• Some have Schwann cells to myelinate neurone and increase speed of transmission

What type of neurone is this?

Sensory

What type of neurone is this?

Motor

Summarise the features that make a motor neurone unique?

• Cell body in CNS

• Long axon that carries AP from CNS to effector

Summarise the features that make a sensory neurone unique?

• Long dendron to carry AP from sensory receptor to cell body

• Cell body positioned outside CNS

• Short axon to carry AP to CNS

Summarise the features that make a relay neurone unique?

• Short dendrites and short axon

• Variable number of dendrites and divisions

Describe the differences in AP transmission of myelinated and non-myelinated neurones?

• Conduction faster in myelinated neurone

• Depolarisation can only occur where Na⁺ channels present

• Myelinated neurones have longer section with no Na⁺

• Depolarisation only takes place at nodes of ranvier

• Longer local currents

• Saltatory conduction - AP jumps from node to node

Describe the difference in structure of myelinated and non-myelinated neurones?

• Myelinated have tightly wrapped schwann cells making up a myelin sheath

• Nodes of ranvier occur every 1-3mm with no myelin sheath

• Non-myelinated neurones often have one loosely wrapped schwann cell along its length

What is the advantage of myelination?

Transmit AP much faster to travel longer distances in less time