Module 5: Communications, Homeostasis And Energy

Question 1

What are some examples that energy is needed for?

Answer 1

Metabolic processes such as active transport, anabolic reactions to form polymers and movement from cilia, flagella and contracting muscles

Question 2

What are the 2 ways that organisms get energy

Answer 2

Photosynthesis and respiration

Question 3

How are photosynthesis and respiration linked and why is this important?

Answer 3

The products for photosynthesis are the reactants for respiration and vice versa. This ensures a constant cycle of raw material used for energy gain so they don’t run out

Question 4

How does respiration release energy(in chemical terms) and why are organic molecules useful for respiration?

Answer 4

Respiration is an exothermic reaction because the energy released forming the bonds of the products is higher than the energy taken in to break the bonds of the reactants. Excess energy is then used to synthesise ATP which is used to release even more energy. Organic molecules have many C-H bonds and are usually non-polar which means they take little energy to break

Question 5

What is homeostasis?

Answer 5

Homeostasis is the maintaining of a constant internal environment despite changes to the external environment. Homeostasis isn’t completely stable, the body’s levels fluctuate within a narrow range in what is known as dynamic equilibrium

Question 6

What are some examples of conditions that must be kept at homeostatic levels?

Answer 6

pH and temperature for enzyme controlled reactions
Glucose and mineral ion levels in blood
Bodily fluid/water levels

Question 7

What is the general path that happens to bring the body to homeostatic levels?

Answer 7

Sensory receptors detect changes in the internal/external environment. It will send an electrical signal to the brain which will send impulses to an effector organ, either a muscle or a gland

Question 8

What are negative feedback systems and what are some examples?

Answer 8

Negative feedback is when the body detects a change in the environment and works to restore that change back to normal. Examples include reducing blood glucose levels down to normal when they get too high and warming the body up when it gets too cold

Question 9

What are positive feedback systems and what is an example?

Answer 9

Positive feedback is when the body detects a change and accelerates the change. An example of this is when a fully grown baby presses their head against the cervix of the pregnant mother, the placenta will release oxytocin which causes uterus contractions. These increase in frequency as time goes on as the baby presses more onto the cervix until the baby is born and the placenta is removed

Question 10

What is the difference between an endotherm and an ectotherm and what are some examples?

Answer 10

Endotherms are animals that rely on mechanisms(usually physiological but sometimes behavioural) inside the body to regulate core body temperature. These include mammals and birds
Ectotherms are animals that rely on external sources for heat and mainly use behavioural responses to regulate core body temperatures. This includes reptiles, amphibians and fish

Question 11

What are some ways Ectotherms will regulate body temperature?

Answer 11

Spending more time basking in sunny areas to heat up and spending more time in the shade to reduce heat gain.
Changing the orientation of their bodies and spreading/narrowing their surface area to maximise/minimise sun exposure
Increasing/decreasing the amount of exothermic metabolic reactions that take place(ie they may vibrate to warm up or hibernate to conserve energy)
Behavioural adaptations include the colour of their skin as different colour skins will absorb or reflect more light

Question 12

What are physiological ways that Endotherms will reduce their body temperature when it gets too hot?

Answer 12

Arterioles near the surface of the skin will dilate and the arteriovenous vessels will constrict, forcing more blood into the capillaries near the surface of the skin to heat can exit the body through conduction. This is called vasodilation and results in skin looking more flush.
Animals with sweat glands will sweat more so that when sweat evaporates it takes heat along with it. Animals that are hairier have less sweat glands so will pant or lick themselves to lose water.
Erector pili muscles will relax so hairs and feathers lie close to the skin, preventing the trapping of an insulating layer of air

Question 13

What are physiological ways that Endotherms can increase their body temperature when it’s too cold?

Answer 13

Arterioles near the skin will constrict and arteriovenous vessels will dilate so less blood enters the capillaries near the surface of the skin so less heat is lost through conduction. This is called vasoconstriction and results in skin going pale.
Sweat production will stop and less sweat is released so less heat is lost through evaporation of water
Erector pili muscles will contract, raising hairs and feathers which traps a layer of insulating air
Larger muscles will involuntarily contract and relax very quickly which heats up the body as it engages in many exothermic metabolic reactions

Question 14

What wavelength ranges of light are absorbed by chlorophyll?

Answer 14

400-500nm(blue) and 600-700(red)

Question 15

What is the non cyclic path of the light dependent phase of photosynthesis?

Answer 15

•In photosystem 2 with the help of a water splitting enzyme, light breaks water molecules into hydrogen ions, oxygen and electrons
•As the electrons in the pigments get excited, they pass from the primary acceptors in PS2 to the primary acceptors in PS1 through the electron transport chain in the thylakoid membrane, going from a lower energy level to a higher one
•These electrons are replaced by the electrons released from the water molecule
•As the excited electrons reach photosystem 1, their energy levels decrease which releases energy used to synthesise ATP
•As light excites electrons in photosystem 1, the electrons from the electron transport chain can then replace those, leaving the excited electrons to continue down the transport chain
•As the electrons leave the transport chain, they, along with the hydrogen ions produced from the splitting of water, are accepted by the coenzyme NAPD to make reduced NAPD

Question 16

What is the cyclic path of the light dependent phase of photosynthesis?

Answer 16

•When the electrons in photosystem 1 are excited, instead of going down the electron transport chain they can end up returning back to the photosystem.
•This leads to cyclic phosphorylation as the energy levels are constantly increasing and decreasing, which means energy is constantly being released that can then be used to from ATP from ADP and inorganic phosphate ions

Question 17

What is the process of the Calvin Cycle?

Answer 17

1. In the stroma, carbon dioxide binds with RuBP using the help of a rubisco enzyme
2. This forms an unstable intermediate which splits into 2 molecules of GP
3. Energy from the oxidation of reduced NADP and the reduction of ATP are used to convert the GP into 2 molecules of TP
4. For every 6 molecules of TP made, 5 are regenerated to RuBP using energy from the reduction of ATP. The other TP molecule is used to make useful organic products such as glucose

Question 18

What are the pigments used in chloroplasts?

Answer 18

There are primary pigments which are the 2 main forms of chlorophyll a and there are accessory pigments which are the other types of chlorophyll a, chlorophyll b and the carotenoids

Question 19

How are the pigments in chloroplasts arranged, especially the pigments used in photosynthesis?

Answer 19

Pigments are arranged in clusters called photosystems. The photosystems with the accessory pigments are at the wide part of a cone shape to maximise surface area. Light enters the accessory pigment photosystem and travels down to the primary pigments which are either PS1(which has a peak absorption of 700nm) and PS2(which has a peak absorption of 680nm). Photosystems are arranged in the membrane of thykaloids

Question 20

What are limiting factors and what are the limiting factors for photosynthesis?

Answer 20

Limiting factors are conditions that will decrease the rate of a reaction if in short supply.
The rate of a physiological process will be limited by the factor which is in shortest supply. For photosynthesis, the limiting factors are carbon dioxide concentration, light intensity and temperature

Question 21

How are TP and GP used to make carbohydrates, lipids and amino acids?

Answer 21

•Carbs- hexose sugars are made by joining 2 TP molecules together and larger carbohydrates are made by joining said hexose sugars together
•Lipids- these are made from glycerol (which is synthesised from TP) and fatty acids which are synthesised from GP
•Amino acids- some amino acids are made from GP

Question 22

What is the pathway of blood through the kidney?

Answer 22

Blood enters the kidney through the renal artery in the cortex. As it travels through the arterioles, it is filtered in the nephrons that cross the medulla and cortex. The filtered blood then exits through the renal vein

Question 23

What is the pathway of tissue fluid through the nephron?

Answer 23

First, blood is filtered in the glomerulus through ultrafiltration. This results in tissue fluid entering the bowman’s capsule. The tissue fluid then travels through the proximal convoluted tubule, where selective reabsorption happens. The tissue fluid then travels down and up the loop of Henle which allows water to exit the tubule by osmosis. Then the tissue fluid travels through the distal convoluted tubule, where ADH regulates the permeability of the tubule membrane to filter the fluid further. Finally, the waste products travel down the collecting duct where it goes into the urine

Question 24

What is the process of ultrafiltration and how is the glomerulus and bowman’s capsule adapted for ultrafiltration?

Answer 24

Blood enters the glomerulus through the afferent arterioles. These vessels are wider than the efferent arterioles so more blood can enter than can exit, which creates a pressure gradient. Tissue fluid is then pushed out of the glomerulus into the bowman’s capsule. The endothelium of the capillaries are leaky enough to allow tissue fluid to leave but not large proteins. In addition, there is a basement membrane that acts as a sieve to prevent larger substances from exiting the blood. Finally, the bowman’s capsule’s epithelium has podocytes which branch off into pedicels that wrap around the capillaries for support and extra filtration

Question 25

What is the process of selective reabsorption for substances such as glucose and amino acids?

Answer 25

1. Na+ ions are actively pumped out of the PCT epithelium across the basal membrane
2. This causes a decrease in Na+ concentration inside the PCT epithelium, therefore causing a concentration gradient from the PCT lumen down into the PCT epithelium
3. Na+ diffuses from the lumen into the epithelium via a cotransport protein, taking glucose/amino acids along with it (even if they’re going against the concentration gradient)
4. There is now a large concentration of glucose/amino acids inside the PCT epithelium and a lower concentration of glucose/amino acids in the capillaries around the basal membrane, creating yet another concentration gradient
5. Glucose/amino acids diffuse down the concentration gradient through the basal membrane via a carrier protein
6. Water follows down the water potential gradient by osmosis

Question 26

How is the proximal convoluted tubule adapted for selective reabsorption?

Answer 26

It has a layer of cuboidal cells with microvilli, carrier proteins and co-transport proteins. It also has a lot of mitochondria to provide ATP energy to actively pump sodium ions out of the basal membrane. This allows 85% of the filtrate to be absorbed back into the blood including all the glucose, amino acids and some inorganic ions

Question 27

How does the liver get its blood supply?

Answer 27

The hepatic artery carries oxygenated blood to the liver, making up 25% of its blood supply
The portal vein carries blood from the intestines, stomach and spleen to the liver, providing it with nutrients
All blood then exits through the hepatic vein to the heart

Question 28

What are the important cells, intercellular spaces and ducts in the liver?

Answer 28

Liver cells/hepatocytes have large Golgi bodies, large nuclei and many mitochondria. They break down blood into bile and send it down the bile canaliculis or bile duct to the gall bladder. Kupffer cells are the macrophages of the liver. They ingest and break down toxins and other foreign particles to prevent disease. Sinusoids are spaces surrounded by hepatocytes where blood from the hepatic artery and portal vein max to maximise oxygen uptake

Question 29

How does the liver perform glycogen storage/carbohydrate metabolism?

Answer 29

The liver stores extra glycogen so that blood glucose levels don’t get too high. When blood glucose levels are too low, insulin is released from the pancreas so the liver takes in glucose and converts it to glycogen so the blood glucose levels decrease back to normal. When blood glucose levels are too low, glucagon is released from the pancreas so the liver converts glycogen to glucose and releases it into the blood, increasing blood glucose levels back to normal

Question 30

How does the liver perform the deamination of excess amino acids/urea formation?

Answer 30

Excess amino acids can be used for respiration. First, the liver will react them with oxygen which deaminates them, producing ammonia and keto acids that are used for respiration. To get rid of the toxic ammonia, the ammonia and carbon dioxide in the liver enters the ornithine cycle which is a constant cycle of ornithine-citruline-arginine-ornithine etc but arginine can also be converted to urea and water

Question 31

How does the liver perform detoxification?

Answer 31

The liver contains many enzymes to break down toxins. Examples of these are catalase which breaks down hydrogen peroxide into oxygen and water and alcohol dehydrogenase which breaks down ethanol into ethanal which can then be converted to ethanoate which is used for respiration