BIO PAPER 1

how is blood glucose concentration kept constant?

through the actions of two hormones - insulin and glucagon

what happens at low levels of blood glucose concentration?

cells would not have enough glucose for respiration

glucose :

small soluble molecule carried in the blood plasma

what is the normal concentration for blood glucose?

90 mg cm-3

how does diet increase blood glucose concentration?

• high carbohydrate and high sucrose foods increase blood glucose

• the carbohydrates are broken down in digestive system to release glucose

• glucose then released into blood stream increasing blood glucose

what is glycogenolysis?

• glycogen stored in liver and muscle cells is broken down into glucose

• then released into blood stream

• increasing blood glucose

what is gluconeogenesis?

• production of glucose from non carbohydrates

• e.g. liver makes glucose

what is glycogenesis?

conversion of excess glucose from the diet into glycogen which can be stored in liver and muscle cells

what is glucagon?

hormone produced by alpha cells - increases blood glucose levels by initiating the breakdown of glycogen into glucose

what is glucose?

a simple carbohydrate that is the main substrate for respiration

what is glycogen?

a polysaccharide stored in muscles cells and the liver

what is insulin?

hormone produced by beta cells which decrease like glucose level by increasing rate of conversion from glucose to glycogen

what is a coordinated response?

when the body responds to changes in its internal and external enviroment where neural and endocrine systems work together

fight or flight response in the autonomic nervous system :

• the hypothalamus activates the sympathetic nervous system

• these impulses activate glands and smooth muscles

• also activates the adrenal medulla

• causing adrenal medulla to release adrenaline and noradrenaline (hormonal) into bloodstream

• combination of neural and hormonal activity results in flight or fight response

fight or flight response in the endocrine system :

• hypothalamus activates adrenal-cortical system by releasing CRF

• pituitary gland secretes the hormone ACTH (adrenocorticotropic) into bloodstream

• ACTH arrives at adrenal cortex and releases about 30 hormones

• both neural and hormonal activity result in the flight or fight response

physical responses of fight or flight :

• heart rate increases

• pupils dilate

• arterioles constrict

• blood glucose increases

• smooth muscle of airways relax

• non essential system shut down

• difficulty focusing on small tasks

why does heart rate increase during fight or flight?

to pump more oxygenated blood around the body

why do pupils dilate during fight or flight?

to take in as much light as possible for better vision

why do arterioles constrict during fight or flight?

more blood to major muscles groups, brain and heart

why does blood glucose increase during fight or flight?

increased respiration to provide energy for muscle contraction

why does smooth muscle in the airways relax during fight or flight?

allow more oxygen into the lungs

why do non essential systems shut down during fight or flight?

focus resources on emergency functions

why is it difficult to focus on small tasks during fight or flight?

so brain can focus solely on the threat

function of adrenaline :

trigger liver cells to undergo glycogenesis so more glucose is released into the bloodstream

features of adrenaline :

• hormone

• hydrophilic therefore cannot pass through cell membranes

• binds to receptors on liver cell membranes triggering cascade of reactions

• first messenger

process of adrenaline taking action :

• adrenaline approaches receptor site

• adrenaline fuses to receptor site forming a adrenaline receptor complex

• activates enzyme inside the cell (adenylyl cyclase)

• activated enzymes converts ATP into cyclic AMP

• this acts a second messenger that activates other enzymes

• ultimately converts glycogen into glucose

what does adenylyl cyclase do?

triggers conversion of ATP into cyclic adenosine mono phosphate (cAMP)

what does cAMP do?

activates protein kinases which phosphorylate and activate other enzymes which convert glycogen into glucose

what does cascade effect mean?

at each stage the number of molecules increases

what does diabetes mean?

someone is unable to metabolise carbohydrates properly, in particular glucose

what is hyperglycaemia?

raised blood sugar

type 1 diabetes :

• beta cells in the islets of langerhans don’t produce insulin

• cause unknown (potentially autoimmune disease beginning in childhood)

• cannot be prevented or cured

• insulin dependent

type 2 diabetes :

• cannot effectively use insulin and control their blood sugar levels

• beta cells don’t produce enough insulin or body cells don’t respond properly to insulin

• often due to glycoprotein insulin receptor on cell membrane not working properly

• cells therefore lose responsiveness and leave glucose in the blood

• result of excess weight, refined carbohydrates and little activity

• insulin independent

common symptoms of diabetes :

• high blood glucose concentration

• glucose present in urine

• excessive need to urinate (polyuria)

• excessive thirst (polydipsia)

• constant hunger

• weight loss

• blurred vision

• tiredness

treatment of type 1 diabetes :

• regular testing of blood glucose by pricking their finger

• drop of blood then analysed by a machine telling them their blood glucose

• appropriate dose of insulin administered

• insulin increases amount of glucose absorbed by cells

• glycogenesis occurs reducing blood glucose concentration

hypoglycaemia :

• very low blood glucose concentration

• can cause unconsciousness

• too much insulin

hyperglycaemia :

• too high blood glucose

• may cause unconsciousness and death

• too little insulin

treatment of type 2 diabetes :

• regulate carbohydrate intake and increase excercise

• drugs that stimulate insulin production

• drugs that slow down the rate the body absorbs glucose from the intestine

original medically produced insulin :

• obtained from pancreas of slaughtered cows and pigs

• process was expensive and difficult

• sometimes caused allergic reactions as it differed slightly from human insulin

modern medically produced insulin :

• made by genetically modified bacteria

• human insulin produced in pure form so less likely to cause allergic reaction

• higher quantities

• cheaper

• little ethical / animal welfare issues

pancreas transplant as treatment for diabetes :

• 1000 each year receive transplant

• 80% have no symptoms after

• however vey limited availability

• big health risk

• immunosuppressants can leave patient very susceptible to illness

stem cell therapy as treatment for diabetes :

• type 1 results from loss of single cell type so perfect candidate

• stem cells differentiate into beta cells

• however ethical issues as stem cells taken from embryos

• controlling growth and differentiation is still difficult

advantages of stem cell therapy to treat diabetes :

• donor availability not an issue

• stem cells produce unlimited source of new beta cells

• less likely to be rejected by the body

• people no longer have to inject insulin

what happens when insulin binds to its glycoprotein receptor?

• causes change in tertiary structure of the glucose transport protein channels

• causes channels to open allowing more glucose to enter the cell

• also activates enzymes within some cells to convert glucose to glycogen and fat

how does insulin lower blood glucose concentration?

• increase rate of absorption of glucose by the cells

• increase respiratory rate of cells - increase uptake of glucose from the blood

• increase rate of glycogenesis - stimulates liver to remove glucose from the blood into glycogen stored in liver and muscle cells

• increases rate of glucose to fat conversion

• inhibits the release of glucagon from the alpha cells of islets langerhan

insulin as an example of negative feedback :

• as blood glucose returns to normal it is detected by the beta cells of the pancreas

• when blood glucose falls below a certain level, the beta cells reduce secretion of insulin

• ensures changes are reversed back to the set level

secretion of glucagon :

• produced by by alpha cells of the islets of langerhan n the pancreas

• alpha cells detect fall in blood glucose and secrete glucagon directly into bloodstream

• only liver and fat cells have glucagon receptors unlike insulin

how does glucagon raise blood glucose concentration?

• glycogenolysis - liver breaks down glycogen store into glucose to be released into the bloodstream

• reducing amount of glucose absorbed in cells

• increases gluconeogenesis - increases conversion of amino acids and glycerol into glucose

how is glucagon an example of negative feedback?

• when blood glucose rises above a set level detected by the alpha cells

• alpha cells reduce secretion of glucagon

• corrective measures returns system to normal

why is the blood glucose concentration self regulating?

level of blood glucose determines the quantity of insulin and glucagon that is released into the blood

control of insulin secretion at resting state :

• at normal blood glucose levels potassium channels in the plasma membrane of beta cells are open

• potassium ions diffuse out of the cells

• inside cell potential -70mv

process of insulin secretion :

• blood glucose levels increase and glucose entered the cell by a glucose transporter

• glucose metabolised inside the mitochondria producing ATP

• ATP binds to potassium channels causing them to close (ATP sensitive potassium channels)

• potassium ions stop diffusing out so potential decreases to -30mv and depolarisation occurs

• depolarisation opens voltage gated calcium channels

• calcium ions enter cell causing secretory vesicle to release insulin by exocytosis

heart rate :

• involuntarily controlled by autonomic nervous system

• medulla oblongata controls heart rate making the necessary changes

• two centres linked to the sino atrial node by motor neurones

• which centre is stimulated depends on information received by receptors in the blood vessels

how does heart rate increase?

• one centre sends impulses through the sympathetic nervous system

• impulses are then transmitted by the accelerator nerve

how does heart rate decrease?

• one centre sends impulses through the parasympathetic nervous system

• impulses then transmitted by the vagus nerve

baroreceptors :

• detect changes in blood pressure

• e.g. blood pressure is low, heart rate increase to prevent fainting

• found in the aorta, vena cava and carotoid arteries

• medulla oblongata sends impulse to SAN through parasympathetic nervous system which decreases heart rate bringing blood pressure back to normal

chemoreceptors :

• detect changes in levels of specific chemical

• e.g. carbon dioxide

• located in aorta, carotid artery and medulla

carbon dioxide as example of chemoreceptors :

• when CO2 levels increase

• ph decreases because carbonic acid is formed when carbon dioxide bonds with water

• chemoreceptors send impulse to increase heart rate

• blood flows quicker expelling the CO2 from the lungs faster

effects of cardiac output on heart rate :

• increase metabolic activity

• more carbon dioxide produced by tissues from increased respiration

• centre in medulla oblongata speeds heart rate

• increase frequency of impulses to the SAN via sympathetic nervous system

• SAN increase heart rate

• increased blood flow to remove carbon dioxide

• CO2 levels return to normal

hormonal control of heart rate :

• adrenaline and noradrenaline are released when stressed

• they speed up heart rate by increasing frequency of impulses produced by the SAN

endocrine glands :

• group of cells specialised to secrete chemicals

• these chemicals are hormones and are secreted directly into bloodstream

pituitary gland :

• produces growth hormones which control growth of bones and muscles

• produces anti-diuretic hormone which increase reabsorption of water in the kidneys

• gonadotropins which control development of ovaries and testes

thyroid gland :

produces thyroxine which controls rate of metabolism promoting growth

adrenal gland :

produces adrenaline increasing breathing and heart rate and raises blood sugar level

testes :

produces testosterone controlling sperm production and secondary sexual characteristics

pineal gland :

produces melatonin which controls reproductive development and daily cycles

thymus :

produces thymosin which promotes production and maturation of white blood cells

pancreas :

• produces insulin which converts excess glucose into glycogen in the liver

• produces glucagon which converts glycogen into glucose in the liver

ovaries :

• produces oestrogen controlling ovulation and secondary sexual characteristic

• as well as progesterone which prepare uterus lining for an embryo

exocrine glands :

secrete chemicals through ducts into organs

hormones :

• chemical messengers carrying information from one part of the body to another

• e.g. steroids, proteins, glycoproteins, polypeptides, amines and tyrosine derivatives

• secrete directly into the blood plasma where a gland is stimulated

• then diffuse out of the blood binding to specific receptors on the membrane or in the cytoplasm of the target cells

• then stimulate target cells to produce a response

steroid hormones :

• lipid soluble

• pass through lipid component of cell membrane and bind to steroid hormone receptors forming a hormone receptor complex

• then facilitates or inhibits the transcription of a specific gene

• receptors are found in the cytoplasm or nucleus

non steroid hormones :

• hydrophilic so cannot pass directly through cell membrane

• bind to specific receptors on the cell surface of the target cell

• triggers cascade reaction mediated by chemical called secondary messengers

hormonal vs neural communication

• hormones are slower as not released directly to target cell

• also less specific

• hormones not broken down as quickly as neurotransmitters so have a longer more widespread affect

• also more permanent and and irreversible

adrenal glands :

• located on top of each kidney

• made up of the adrenal cortex and medulla

• adrenal cortex - outer region, produces vital hormones like cortisol and aldosterone

• adrenal medulla - inner region, produces non essential hormones like adrenaline

three types of hormones produced by adrenal cortex :

• glucocorticoids

• mineralocorticoids

• androgens

glucocorticoids :

• e.g. cortisol

• regulates metabolism by controlling body converting fats, proteins and carbohydrates into energy

• helps regulate blood pressure and cardiovascular function in the stress response

• controlled by the hypothalamus

mineralocorticoids :

• controls blood pressure by maintaining balance between salt and water

• aldosterone release mediated by messages from the kidney

androgens :

• small amount of male and female sex hormones

• small impact but important especially in menopause

two main hormones produced by adrenal medulla :

• adrenaline

• noradrenaline

how is the pancreas a endocrine and exocrine gland?

produces enzymes and releases them via a duct into a duodenum as well as producing hormones and releasing them into the blood

role of pancreas as a exocrine gland :

• most of the pancreas is made of exocrine glandular tissue

• tissue responsible for producing digestive enzymes and pancreatic juice

• enzymes and juice are secrete into ducts to the pancreatic duct

• then released into the duodenum (top part of small intestine)

• produced digestive enzymes

enzymes produced by the pancreas :

• amylase - breaks down starch into simple sugars e.g. pancreatic amylase

• proteases - break down proteins into amino acids e.g. trypsin

• lipases - break down lipids into fatty acids and glycerol e.g. pancreatic lipase

role of pancreas as a endocrine gland :

• produces insulin and glucagon which regulate blood glucose

• specifically in the islets of langerhan

islets of langerhans under a microscope :

• lightly stained

• large spherical clusters

• endocrine pancreas tissue

• produce and secrete hormones

pancreatic acini under a microscope :

• darker stained

• small berry like clusters

• exocrine pancreas tissue

• produce and secrete digestive enzymes

islets of langerhans :

• alpha cells - produce and secrete glucagon

• beta cells - produce and secret insulin

• alpha cells are larger and more numerous than beta cells

example of metabolic activities which require energy :

• active transport - used for uptake of nitrates, sucrose loading into sieve tube cells, selective reabsorption of glucose and amino acids, conduction of nerve impulses

• anabolic reactions - used for building protein, polysaccharides and nucleic acid for growth and repair

• movement of cells - e.g. cilia, flagella or contractile filaments in muscle cells

respiration :

• process of organic molecules being broken down into smaller inorganic molecules

• e.g. glucose into CO2 and water

• the energy stored within the bonds are used to synthesise ATP

• C6H12O6 + 6O2 = 6CO2 + 6H2O

role of carbon - hydrogen bonds :

• organic molecules contain large numbers of carbon - hydrogen bonds

• non polar bond which doesn’t require much energy to break

• once the bond has been broken carbon and hydrogen are free to form strong bonds with oxygen forming carbon dioxide and water

• this releases large quantities of energy

role of ATP in photosynthesis :

• light provides energy to build organic molecules e.g. glucose

• this energy is used to form chemical bonds in ATP which releases energy needed to make bonds

role of ATP in respiration :

• organic molecules are broken down to release energy

• this energy is used to synthesise ATP

• ATP is used to supply energy to break bonds for metabolic reactions

chemiosmosis :

• primarily how ATP is produced in respiration and photosynthesis

• involves the diffusion of protons from a region of high concentration to low

• the gradient is created through excited electrons which are raised to higher energy levels

• this flow of protons releases energy which is used to attach a inorganic phosphate group to ADP forming ATP

how are electrons raised to a higher energy level :

• electrons in pigment molecules during photosynthesis are excited by absorbing light from the sun

• e.g. chlorophyll

• high energy electrons are released when chemical bonds are broken in respiratory substrate molecules

• e.g. glucose

electron transport chain :

• made of a series of electron carriers lower in energy levels than the one before

• energy is produced by the electrons moving from one carrier to another in a chain

• the energy released is used to pump protons across a membrane creating a concentration gradient

• the membrane is impermeable to hydrogen ions therefore a proton gradient is created

• protons can only pass through the membrane through the hydrophilic membrane channels linked to enzyme ATP synthase

• the flow of protons provides energy to synthesise ATP

what does ATP synthase do?

catalyses the formation of ATP from an inorganic phosphate group and ADP

summary of photosynthesis :

• process in which energy in the form of light is used to build complex organic molecules e.g. glucose

• occurs in autotrophic organisms

• 6CO2 + 6H2O = C6H12O6 + 6O2

structure and function of chloroplasts :

• chloroplasts have a large network of membrane to increase surface area for absorption of light

• membranes form flattened sacs called thylakoids which are stacked to form grana

• membranous channels join the grana together called lamellae

• fluid inside the chloroplast is called the stroma

pigment molecules in the thylakoid membrane :

• different pigments absorb and reflect different wavelengths of light

• primary pigment is chlorophyll a

• although there are many other - e.g. chlorophyll b, xanthophylls, carotenoids