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Question 1

What is Homeostasis?

Answer 1

Changes in your external environment can affect your internal environment. Homeostasis is the maintenance of a stable internal environment. It involves control systems that keep the internal environment roughly constant, meaning it is in a state of dynamic equilibrium (Fluctuating around a normal level)

Question 2

Why is Homeostasis important? Temperature

Answer 2

It is important as temperature affects enzyme activity, and they control the rate of metabolic reactions (Chemical reactions in living cells) As the temperature increases, so does the metabolic rate. The more heat, the more kinetic energy, so molecules move faster. This makes the substrate molecules more likely to collide with the enzymes’ active sites. However if the temperature is too high, it disturbs the hydrogen bonds in the Enzymes tertiary structure by the molecules vibrating too much, denaturing it and stopping the reaction from taking place.
Too cold of temperatures reduces the enzymes activity, slowing the metabolic reactions.

Question 3

Why is Homeostasis important? pH

Answer 3

If blood pH is too high or low, enzymes become denatured, as the ionic and hydrogen bonds that hold the enzymes tertiary structure are disrupted, changing the enzymes active site and denaturing it, stopping the enzymes from catalysing any metabolic reactions.

Question 4

How can pH be calculated?

Answer 4

pH is based on the conc. of Hydrogen ions in the environment. The greater the conc. the lower the pH number. The formula is:
pH = -Log10 (H+)

Question 5

What does Log10 tell you about pH?

Answer 5

Log10 is expressed on a logarithmic scale, which uses logarithm of a number instead of the number itself. Each value using log10 is ten times more than the value before - So pH3 has ten times more H+ than pH4 (Measured in mol dm-3) As the conc. can vary so much, converting the values to a logarithmic scale makes it easier to plot both very small and very large values on the same axis of a graph.

Question 6

What is another use for a Logarithmic scale, other than measuring pH

Answer 6

Microbial growth, where the number of organisms increases exponentially

Question 7

What happens if the Blood Glucose concentration is too high?

Answer 7

The water potential of the blood is reduced to a point where water molecules diffuse out of the cells, and into the blood by Osmosis. This can cause the cells to shrivel up and die

Question 8

What happens if the Blood Glucose concentration is too low?

Answer 8

The cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy

Question 9

What is Negative Feedback?

Answer 9

Receptors detect when a level is too high or low, and is communicated through The Nervous/Hormonal system to effectors. The effectors respond to counteract the change, bringing the level back to normal. This is the Negative Feedback Mechanism. This only works within certain limits though, if the change is too big then the effectors may not be able to counteract it

Question 10

Multiple Negative Feedback Mechanisms

Answer 10

Homeostasis involves multiple negative feedback mechanisms for each thing being controlled, giving more control over the changes, meaning it can actively increase or decrease a level so it returns to normal, instead of one mechanism, which can only turn things off or on, and it would be a slower response

Question 11

What is Positive Feedback?

Answer 11

Some changes trigger a Positive Feedback mechanism, which amplifies the change. Effectors respond to further increase the level away from the normal level. The mechanism that amplifies a change away from the normal is called a Positive Feedback Mechanism. It isn’t involved in Homeostasis as it doesn’t keep the internal environment constant, however it can be rapidly activate processes in the body, such as releasing chemicals to trigger more pellets to form a blood clot at an open scar - which ends with Negative Feedback when the body detects the blood clot has been formed)

Question 12

Glucose Concentration in the blood - How much Is normally in the blood and what monitors it?

Answer 12

The Pancreas monitors the Blood Glucose, which is normally around 90mg per 100cm3 of blood

Question 13

Hormonal Control of Blood Glucose concentration (BGC)

Answer 13

Hormonal system controls the BGC using two hormones - Insulin and Glucagon. These are chemical messengers which travel in the blood to their target cells (Effectors) They are both Secreted by clusters of cells in the pancreas, called the Islets of Langerhans. They contain Alpha and Beta cells. Alpha releases Glucagon, whilst Beta releases Insulin. They then act on effectors, which respond to restore the BGC

Question 14

Insulin

Answer 14

Insulin lowers the BGC when its too high. It binds to specific receptors on the cell membranes of muscle and liver cells, increasing the permeability of the membranes to Glucose, so the cells can take up more Glucose. This also Involves increasing the number of channel proteins in the membranes. Insulin also activates enzymes in the muscle and liver cells to convert Glucose to Glycogen. The cells then store the Glycogen in their cytoplasm, as an Energy Source.

Question 15

What is the process of forming Glucose to Glycogen

Answer 15

Glycogenesis

Question 16

Glucagon

Answer 16

Glucagon raises the BGC when its too low. It binds to specific receptors on the cell membranes of liver cells and activates enzymes to break down Glycogen to Glucose. It can also activate enzymes that are involved in the formation of Glucose from Glycerol and Amino acids.

Question 17

What is the process of breaking down Glycogen to Glucose?

Answer 17

Glycogenolysis

Question 18

What is the process of breaking down Glycerol and Amino acids to glucose?

Answer 18

Gluconeogenesis

Question 19

Why are hormones used instead of the nervous system?

Answer 19

Although the responses are slower using hormones than The Nervous System, Hormones occur all over the body if their target cells are widespread, unlike nervous impulses that are localised to one area. Hormones aren’t broken down as quickly as neurotransmitters as well, so their effects tend to last for longer

Question 20

Rise in BGC

Answer 20

When the Pancreas detects the BGC is too high, Beta cells secrete Insulin, and the Alpha cells stops secreting Glucagon. Insulin binds to the receptors on liver and muscle cells (The effectors) which respond to decrease the BGC by making their cell membrane more permeable to Glucose, so they take up more Glucose. Glycogenesis is activated and the cell respires more so the BGC returns to normal

Question 21

Fall in BGC

Answer 21

When the Pancreas detects the BGC is too low, Alpha cells secrete Glucagon, and the Beta cells stops secreting Insulin. Glucagon binds to the receptors on liver cells (The effector) which responds to increase the BGC by activating glycogenolysis and Gluconeogenesis. Cells will also respire less Glucose so the BGC returns to normal

Question 22

What are Glucose Transporters?

Answer 22

They are channel proteins which allow Glucose to be transported across the cell membrane. Skeletal and cardiac muscle cells contain a glucose transporter called GLUT4. When insulin levels are low, GLUT4 is stored in vesicles in the Cytoplasm of cells, but when Insulin binds to receptors of the cell-surface membrane, it triggers the movement of GLUT4 to the membrane. Glucose can then be transported into the cell through the GLUT4 protein by facilitated diffusion

Question 23

Adrenaline

Answer 23

Adrenaline is a hormone that’s secreted from your adrenal glands when there’s a low Conc. of Glucose in your blood. Adrenaline binds to receptors on the cell membrane of the liver cells and activates Glycogenolysis and inhibits Glycogenesis. It also activates the secretion of Glucagon and inhibits Insulin, which increases the BGC. It gets the body ready for acton by making more glucose available for muscles to respire

Question 24

What are Second Messengers and what do they do?

Answer 24

Both Adrenaline and Glucagon can activate Glycogenolysis inside a cell even though they bind to receptors on the outside of the cell. They can do this by the Second Messenger Model - The binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which then produces a chemical known as a second messenger, which then activates other enzymes in the cell to bring about a response

Question 25

How do Second Messengers work?

Answer 25

The receptors for Adrenaline and Glucagon have a specific tertiary structures that make them complementary in shape to their respective hormones. To activate Glycogenolysis, adrenaline and glucagon bind to their receptors and activate an enzyme called Cyclic AMP (cAMP) which is a second messenger. cAMP activates an enzyme called Protein Kinase A, which activates a cascade (Chain of reactions) that breaks down glycogen into glucose (Glycogenolysis.

Question 26

Type 1 Diabetes

Answer 26

When the immune system attacks B cells of the Islets of Langerhans so they can’t produce Insulin. If the BGC rises, it can’t be lowered with no insulin. Glucose is found in the urine as the kidneys can’t absorb all the Glucose.

Question 27

How is Type 1 medicated?

Answer 27

Some people Inject insulin regularly every day.
Others have insulin therapy which an insulin pump pumps insulin. Insulin therapy has to be carefully controlled because too much can produce a dangerous drop in BGC.

Question 28

Type 2 Diabetes

Answer 28

Normally acquired later in life than Type 1. Often linked with Obesity, and more likely in people with a family history of the condition. Other factors include lack of exercise, age and poor diet. It occurs when the B cells don’t produce enough insulin or when the body cells don’t respond properly to insulin. Cells don’t respond properly because the insulin receptors (Glycoprotein receptors) on their membranes don’t work properly, so the cells don’t take up enough glucose. It can cause other health problems including visual impairment and kidney failure.

Question 29

How is Type 2 Diabetes medicated?

Answer 29

It can be treated by eating healthily, exercising regularly and losing weight if necessary. Glucose-lowering medication can be taken if diet and exercise can’t control it.

Question 30

Glucose in Urine test

Answer 30

Doctors determine if a person has diabetes by testing their urine for glucose. Low concentrations between 0 and 0.8mM, Any higher and this may indicate diabetes

Question 31

Determining the concentration of Glucose solution experiment - Benedict’s Test on the unknown conc. sample

Answer 31

When determining the conc. of glucose in a ‘urine’ sample, colorimetry is used. To do this a quantitative Benedict’s test is used, and when heated with glucose, the initial blue colour changes to a brick red precipitate which can be placed into a colorimeter to measure the light absorbance of the solution after the quantitative Benedict’s test has been carried out. The higher the conc. of Glucose, the more of the blue colour is lost, decreasing the absorbance of the solution.

Question 32

Determining the concentration of Glucose solution experiment - Making Serial Dilutions

Answer 32

• Line up 5 test tubes in a rack
• Add 10cm3 of the initial 4mM Glucose solution to the first test tube and 5cm3 of distilled water to the other test tubes
• Use a pipette and draw 5 cm3 of the solution from the first test tube and add it to the second test tube. Mix this solution thoroughly. This Test tube is now half as concentrated as the first test tube (Its 2mM)
• Repeat this process for test tubes 3, 4 and 5

Question 33

Determining the concentration of Glucose solution experiment - Measuring the absorbance of Glucose Solutions

Answer 33

• Make sure you’re using equal volumes of each of the solutions, as well as a test tube of pure water, acting as the negative control
• Add the same amount of Benedict’s solution to each of the test tubes and heat for 4-5 mins
• Carefully remove the test tubes from the water bath and leave to cool.

Question 34

Determining the concentration of Glucose solution experiment - Colorimeter and using a calibration curve

Answer 34

• Set up the colorimeter with a red filter (Wavelength of 635 nm)
• After this, calibrate it to zero using the cuvette with water
• Transfer, using a pipette, solution from each test tube into a cuvette and measure the absorbance with the colorimeter
• Plot the results of the absorbance of each solution on the Y-axis, against the glucose Concentration on the X-axis. Draw a smooth line/curve of best fit through your data points to create a calibration curve.
• Then, using the unknown solution, plot the absorbance along the calibration curve to predict the Concentration of Glucose in the unknown Urine sample

Question 35

The Excretion of Waste Products

Answer 35

Blood enters the Kidney through the renal artery and then passes through capillaries in the cortex, substances are filtered out of the blood and into long tubules that surround the capillaries. This is known as Ultrafiltration. Useful substances, such as glucose and a right amount of water is then reabsorbed back into the blood via Selective Reabsorption. The remaining unwanted substances pass along to the bladder and is excreted as urine.

Question 36

The Nephrons

Answer 36

They are long tubules with bundles of capillaries where blood is filtered. Around 1 million nephrons in each kidney carry out this filtration to produce urine.

Question 37

What is Ultrafiltration?

Answer 37

Blood from the renal artery enters smaller arterioles in the CORTEX of the kidney. Each arteriole splits into a structure called a Glomerulus - a bundle of capillaries looped inside a hollow ball called the Bowman’s Capsule, where Ultrafiltration takes place.

Question 38

How is the blood Ultrafiltrated?

Answer 38

The Arteriole take takes blood into each Glomerulus is called the Afferent arteriole, and the arteriole which takes blood away from the Glomerulus is called the Efferent Arteriole. The Efferent Arteriole is smaller in diameter than the Afferent Arteriole, so the blood is under high pressure. the higher pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s Capsule. The small molecules pass through three layers to get into the Bowmans capsule and enter the nephron tubules - The capillary endothelium, a membrane called the basement membrane and the epithelium of the Bowman’s Capsule. Larger molecules like proteins and blood cells can’t pass through so stay in the blood. The substances that enter the Bowman’s capsule are known as Glomerular Filtrate. This filtrate passes along the rest of the nephron and useful substances are reabsorbed along the way.

Question 39

Selective Reabsorption

Answer 39

Selective reabsorption of useful substances takes place as the Glomerular filtrate flows along the Proximal Convoluted Tubule (PCT) through the loop of Henle, and along the Distal Convoluted Tubule (DCT) Useful substances leave the tubules of the nephrons and enter the capillary network that’s wrapped around them. The epithelium wall of the PCT has microvilli to provide a large S.A. for more reabsorption of useful materials from the Glomerular Filtrate. Useful solutes, like glucose, are reabsorbed along the PCT by Active Transport and Facilitated Diffusion.

Question 40

Role of Water Potential in Reabsorption

Answer 40

Water enters the blood by Osmosis because the water potential is lower than that of the filtrate. Water is reabsorbed from the PCT, Loop of Henle, DCT and the Collecting Duct. The filtrate that remains is urine, which passes along the ureter to the bladder.

Question 41

Regulation of Water Content

Answer 41

• If the water potential of the blood is too low, so more water is reabsorbed by Osmosis into the blood from the tubules of the nephrons, meaning a more concentrated urine
• If the water potential of the blood is too high, less water is reabsorbed by osmosis into the blood from the tubules of the nephrons. This means the urine is more dilute

Question 42

What is Osmoregulation?

Answer 42

The kidneys regulate the water potential of the blood and urine so the body has the right amount of water

Question 43

What is the structure of The Loop of Henle?

Answer 43

Located in the medulla (Inner layer) of the kidneys. It is made up of two ‘limbs’ the ascending and descending limbs. The Limbs control the movement of sodium ions so that water can be reabsorbed by the blood.

Question 44

How the Loop of Henle works

Answer 44

• Near the top of the ascending limb, Na+ ions are actively pumped out, into the medulla. The ascending limb is impermeable to water, so the water stays inside the tubule. This creates a low water potential in the medulla
• Because there’s a lower water potential in the medulla than in the descending limb, water moves out of the descending limb (Which is permeable to water) into the medulla by osmosis. This makes the Glomerular filtrate more concentrated (Ions can’t diffuse out as it isn’t permeable to them) The Water in the medulla is reabsorbed into the blood through the capillary network
• Near the bottom of the ascending limb Sodium ions diffuse into the medulla, further lowering the water potential in the medulla
• Water moves out of the DCT by osmosis and is reabsorbed into the blood
• The first three stages massively increase the ion conc. in the medulla to lower the water potential, causing water to move out of the collecting duct by osmosis, which is reabsorbed into the blood

Question 45

Antidiuretic Hormone (ADH)

Answer 45

The water potential is monitored by Osmoreceptors in the part of the brain called the Hypothalamus. When the Osmoreceptor cells detect a change in water potential it sends a signal to the Hypothalamus, which sends a signal to the Posterior Pituitary Gland. This causes the Posterior Pituitary to release a hormone called Antidiuretic Hormone (ADH) which changes the water content of the blood when its too high/low. Its target cells are on the DCT and the collecting duct, causing them to be more permeable by Aquaporins - these a proteins which allow water to move through. ADH causes extra aquaporins to be included in the membrane of these cells

Question 46

Antidiuretic Hormone (ADH) when Blood Water Content is too low (Dehydration)

Answer 46

• The water content of blood drops, so its water potential drops.
• This is detected by the Osmoreceptors in the Hypothalamus
• The Prosterior Pituitary Gland releases more ADH into the blood
• More ADH means that the DCT and the Collecting duct are more permeable, so more water is reabsorbed into the blood by osmosis
• A small amount of highly concentrated urine is produced and less water is lost

Question 47

Antidiuretic Hormone (ADH) When Blood Water content is too high (Hydration)

Answer 47

• The water content of the blood rises, so its water potential rises
• This is detected by the Osmoreceptors in the Hypothalamus
• The Prosterior Pituitary Gland releases less ADH into the blood
• Less ADH means that the DCT and the Collecting Duct are less permeable, so less water is reabsorbed into the blood by osmosis
• A large amount of dilute urine is produced and more water is lost

Question 48

What is Convection?

Answer 48

Transfer of heat by fluid molecules (Air or water) moving in a current. The heat causes the fluid to expand and move, carrying with it the heat that has been absorbed

Question 49

What is Conduction?

Answer 49

Transfer of energy by Physical Contact between two bodies.

Question 50

What is Radiation?

Answer 50

Transfer of heat by electromagnetic waves. The amount of heat radiated by the body is proportional to the temperature difference between the organism and the environment

Question 51

What are Ectotherms?

Answer 51

Gain most of their heat from the environment, therefore they don’t maintain a constant body temperature (Cold Blooded)

Question 52

What are Endotherms?

Answer 52

Gain most of their heat from metabolic reactions that take place in their body (Warm blooded)

Question 53

Conserving and Gaining Heat

Answer 53

• Vascontriction - Diameter of arterioles becomes smaller, so less blood enters the capillaries near skin surfaces so less leat is lost to the environment
• Shivering - Skeletal muscles of the body involuntary rhythmically contract and so produce metabolic heat
• Hairs raised - The hair erector muscles contract and raise the hairs to trap a layer of air against the skin, and as air is a poor conductor of heat, it is a good insulator, and reduces the energy transfer by convection and radiation
• Increased Metabolic rate
• Decrease in sweating - reduced loss of heat by evaporation
• Behavioural mechanisms - huddling together

Question 54

Losing Heat

Answer 54

• Vasodilation - Diameter of Arterioles supplying the capillaries near the skin surface increase, inc. the blood flow to the surface so more heat can be lost to the environment
• Increased sweating - The evaporation of water from the surface of the skin requires energy in the form of heat, taken from the body
• Lowering body hair - they lie flat against the skin reducing the thickness of an insulating air layer
• Decreased metabolic rate
• Behavioural mechanisms

Question 55

Do Epithelial cells in the PCT have many mitochondria?

Answer 55

Yes to provide ATP for Active Transport