topic 6 - organisms respond to changes in their internal and external environments 2.0

Question 1

describe the structure of skeletal muscles

Answer 1

-skeletal muscles are made up of large bundles of muscle fibres called microfibrils
-the cell membrane of the muscle fibres is called the sarcolemma
-bits of the sarcolemma fold inwards across the muscle fibre called transverse tubules. they help to spread the electrical impulse throughout the sarcoplasm so they reach all parts of the muscle fibre
-the sarcoplasm contains a network of membranes called the sarcoplasmic reticulum which stores and releases calcium ions for muscle contraction
-muscle fibres have lots of mitochondria

Question 2

describe myofibrils

Answer 2

-myofibrils contain bundles of thick and thin myofilaments
-the thick myofilaments are made of the protein myosin
-the thin myofilaments are made of the protein actin

Question 3

describe the microscopic structure of skeletal muscles

Answer 3

-dark bands contain thick myosin filaments and some overlapping thin actin filaments called A bands
-light bands just contain thin actin filaments called I bands
-the M line is the middle of the myosin filaments
-around the M line is the h zone which just contains myosin filaments

Question 4

explain the sliding filament theory of muscle contraction

Answer 4

-myosin and actin filaments slide over one another to make the sarcomeres contract
-the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
-A bands stay the same length
-I band get shorter
-H zone will get shorter

Question 5

describe muscular contraction

Answer 5

-an action potential arrives from a motor neuron it depolarises the sarcolemma
-this causes the sarcoplasmic reticulum to release the stored calcium ions
-the calcium ion binds to a protein attached to tropomyosin causing the protein to change shape
-this pulls the tropomyosin out of the actin-myosin binding site on the actin flimanet
-this exposes the binding site so the myosin head binds to form an actin-myosin cross bridge
-calcium activates ATP hydrolase which hydrolases atp into adp and a phosphate
-the energy release from this causes the myosin head to bend so the actin filament is pulled along
-another atp molecule provides energy to break the bridge so the myosin head detached and then re attaches to a different binding site further along the actin filament

Question 6

describe a resting muscle

Answer 6

-in a resting muscle the actin-myosin binding site is blocked by tropomyosin
-this means the myofilaments cannot slide pat each other because the myosin heads cannot bind to the actin-myosin binding site on the actin filaments

Question 7

how does phosphocreatine provide energy for muscle contraction

Answer 7

-phosphocreatine provides a phosphate group to phosphorylate AdP into ATP
-Phosphocreatine is stored inside the cells and the ATP-Pcr system generates ATP very quickly
-however phosphocreatine runs out quickly so is used fro short bursts of vigorous exercise

Question 8

describe slow twitch muscle fibres

Answer 8

-muscle fibres that contract slowly
-they are good for endurance activities
-they have a large myoglobin store which stores oxygen
-they have a rich supply of blood vessels to supply the muscles with oxygen for aerobic respiration
-they have numerous mitochondria

Question 9

describe fast twitch muscle fibres

Answer 9

-muscle fibres that contract very quickly
-they are good for short bursts of speed and power
-they have thicker and more numerous myofilaments
-energy is released through anaerobic respiration using glycogen so not many mitochondria or blood vessels present
-it stores phosphocreatine

Question 10

define homeostasis

Answer 10

homeostasis involves control systems that keep your internal environment roughly constant within restricted limits

Question 11

explain the importance of maintaining a stable blood glucose concentration

Answer 11

-if blood glucose concentration is too high the water potential of the blood is reduced to the point where water molecules diffuse out the cell into the blood
-this causes the cells to shrivel up and die
-if blood glucose is too low the cells are unable to carry out respiration to provide energy as there isn’t a sufficient supply of glucose

Question 12

describe how insulin lower blood glucose levels

Answer 12

-beta cells secrete insulin into the blood
-insulin binds to specific receptors on membranes of liver cells and muscle cells
-insulin activates channel proteins to open which increases the permeability of muscle-cell membranes to glucose so glucose diffuses into the cells
-insulin activates enzyme involved in glycogenesis which is the conversion of glucose to glycogen
-the cells are able to store the glycogen in their cytoplasm

Question 13

describe how glucagon raises blood glucose levels

Answer 13

-alpha cells secrete glucagon into the blood
-the glucagon binds to specific receptors on the membranes of liver cells
-glucagon activates the enzymes in the liver cell involved in glycogenolysis which is the conversion of glycogen to glucose
-glucagon activates enzymes involving the formation of glucose from glycerol and amino acids

Question 14

describe how adrenaline raises blood glucose levels

Answer 14

-it is secreted from adrenal gland when there is a low concentration of blood glucose in the blood
-adrenaline binds to receptors on the cell surface membrane of the liver cell
-it activates enzymes involved in conversion of glycogen to glucose

Question 15

recall the second messenger model of adrenaline and glucagon action

Answer 15

-adrenaline and glucagon bind to specific receptors on cell membrane
-activate adenylate cyclase
-this converts ATP to cyclic AMP
-the cyclic AMP activates protein kinase A
-the protein kinase A activate an enzyme cascade to break down glycogen into glucose

Question 16

what is type 1 diabetes

Answer 16

-the immune system attacks the b cells in the islets of langerhans so they do not produce insulin
-after eating the blood glucose level rises and stay high
-treated by injection of insulin

Question 17

what is type 2 diabetes

Answer 17

-occurs when the b cells do not produce enough insulin or the body cells do not respond properly to insulin due to their insulin receptors not working properly
-treated by eating healthy and balanced diet and losing weight if necessary

Question 18

explain ultrafiltration in the kidneys

Answer 18

-blood from the renal artery enters arterioles in the cortex of the kidney
-the blood enters the glomerulus which is a bundle of capillaries looped in the bowman’s capsule
-a high hydrostatic pressure is created due to the wide afferent arteriole and the narrow efferent arteriole
-the high hydrostatic pressure forces liquid and small molecules out of the capillary and into the bowman’s capsule
-the blood is filtered through a basement membrane before entering the bowman’s capsule which prevent larger proteins and blood cells from passing through
-the substances that enter the bowman’s capsule is known as the glomerular filtrate

Question 19

explain selective reabsorption in the kidneys

Answer 19

-selective reabsorption takes place as the glomerular filtrate passes through the proximal convoluted tube
-the tubule reabsorbs all glucose, amino acids, vitamins and most of the mineral ions and water back into the blood

Question 20

describe how the loop of henle reabsorbs water

Answer 20

-the filtrate moves out of the proximal convoluted tube and into the descending limb of the small intestine
-sodium ions are actively transported out of the ascending limb into the medulla
-this decreases the water potential in the medulla as there is a high concentration of ions
-as the descending limb is permeable to water, water moves out into the medulla by osmosis
-this makes the filtrate more concentrated as it moves down the loop of henle so near the bottom of the ascending limb sodium ions diffuse out into the medulla further decreasing the water potential
-the water in the medulla is reabsorbed into the blood through the capillary network

Question 21

explain the role of hormones in osmoregulation when there is an increase in water potential in the blood

Answer 21

-increase in water potential in the blood is detected osmoreceptor in the hypothalamus
-the posterior pituitary gland releases less ADH in to the blood
-less ADH means that distal convoluted tube and collecting duct is less permeable
-this means less water is reabsorbed into the blood by osmosis
-a large amount of dilute urine is produced and more water is lost