C7: systems

Question 1

translocation (definition, purpose, process)

Answer 1

transportation of sugars in a plant.
- photosynthesis mostly occurs in the leaves, product sugars needs to be transported for cellular respiration
- phloem transports sugars through its pores as a long tube, in both directions

Question 2

transpiration (definition, purpose, process)

Answer 2

transportation of water in a plant.
- occurs up the plant through the xylem to power photosynthesis

Question 3

Cold blood
Warm blood

Answer 3

Control temp with behaviour
Control temp with metabolism (e.g. sweating)

Question 4

What is mechanical breakdown of food and what are its two parts?

Answer 4

• chewing
• peristalsis

Question 5

neutralisation

Answer 5

Pancreatic juices acts as base to stomach acids.

Question 6

what is the purpose of digestion?

Answer 6

• get sugar from digestive system to form ATP via cellular respiration
• food we eat is too large to pass through the digestive tract and get into the blood.
• Digestive system breaks food down to smallest parts (usually monomers) so they can be absorbed across the cell membrane and into the bloodstream.

Question 7

Describe the 4 main parts of digesting protein.
Ingestion-> digestion-> absorption-> assimilation

Answer 7

Ingestion: food entering the body
Digestion: food being broken down into its monomers (amino acids and simple sugars)
Absorption: thin membrane in the small intestine diffuses monomers into cells and the bloodstream
Assimilation: monomers being absorbed and built into macromolecules like glycogen, proteins

Question 8

what do these things break into?
protein
carbohydrates
fats

Answer 8

amino acids
monosaccharides
fatty acids and glycerol (not polymers)

Question 9

Describe how each of these parts contribute to breaking ingested food down chemically and physically.
Mouth
Stomach
Small intestine
Large intestine

Answer 9

Mouth:
- mechanical breakdown by teeth
- chemical breakdown by amylase (enzyme in saliva that breaks down starch)
Stomach:
- mechanical breakdown= muscle contractions churn the food
- chemical breakdown= enzymes like proteinase/ pepsin breaks protein down to amino acid
Small intestine:
- fats begin to be broken down by enzymes from the pancreas (emulsification)
- bile from liver neutralises stomach acids
- Absorption into the body occurs here, benefiting from a very large SA:V ratio of villi and micovilli.
- Absorbed nutrients go to blood stream, then liver, where its filtered and regulated.
Large intestine:
- water absorption occurs here

Question 10

Why do honeybees (drinks nectar) and vampire bats (drinks blood) have a short digestive tract?

Answer 10

because sugar/ blood does not need to be broken down further so can be absorbed directly with specialised mouth parts

Question 11

Why do carnivores have a short-ish digestive tract?

Answer 11

proteins and fats are simple to breakdown (just use a few enzymes) so don’t need a long digestive tract.

Question 12

Why do omnivores have a medium digestive tract?

Answer 12

Because they break down meats and some plant products, they need a slightly longer digestive system to absorb the nutrients.

Question 13

Why do omnivores have a medium digestive tract?

Answer 13

Because they break down meats and some plant products, they need a slightly longer digestive system to absorb the nutrients.

Question 14

Why do herbivores have a long digestive tract?

Answer 14

To break down cellulose in cell walls, it takes a long time and requires microorganisms to do it. These animals often contain a large caecum (appendix in human) containing a bacteria.

Question 15

What are the two types of herbivores? Give some examples of both.

Answer 15

1. Hindgut fermenters (after the gut or stomach), e.g. possums, koalas, horses
2. Foregut fermenters, e.g. sheep, cattles, kangaroos

Question 16

Compare efficiency of the two types of herbivores.

Answer 16

Hindgut: less efficient than foregut, microbes are lost in the faeces and therefore the protein is also lost (cannot be turned into energy)
Foregut: Slower to digest but can extract more energy from it, can extract energy by eating the microbes

Question 17

Describe process and features of the 2 types of herbivores.

Answer 17

Hindgut fermenters:
- have bacteria in the caecum and the proximal colon
- the bacteria break down cellulose walls, allowing access to nutrients in the plant cells
Foregut fermenters: have pouches in the stomach that contain microbes that break down the cellulose wall

Question 18

What is another name of foregut fermenters?

Answer 18

Ruminants

Question 19

How do foregut fermenters break down grass?

Answer 19

• originally unable to
• bring back to mouth for mechanical breakdown

Question 20

Do all birds have the same digestive system?

Answer 20

• similar digestive tract
• different structures

Question 21

Whats a crop and a gizzard in a bird’s digestive system?

Answer 21

crop- thin soft muscular sac for food storage
gizzard- thick walled muscular sack for grinding food, rocks and bones are swallowed to aid mechanical breakdown of food

Question 22

Describe positioning of the crop and gizzard in a bird.

Answer 22

Crop above gizzard

Question 23

Define emulsification.

Answer 23

Breakdown of fat by bile

Question 24

what is emulsification in the digestive system?

Answer 24

• process of breaking down large fat droplets into smaller droplets by bile

Question 25

exam q: suggest lifestyle changes for patient with gall bladder removed.

Answer 25

gallbladder removed= no bile= no emulsification= can’t breakdown fat= reduce fat in food/ take supplement

Question 26

What are the 4 parts of the plant transport system?

Answer 26

Palisade cells, stomata, xylem, phloem

Question 27

What is the closed system and whats in it?

Answer 27

• circulatory system
• heart, vein, arteries, capillaries

Question 28

Whats an open system and who has it?

Answer 28

• e.g. worms
• do not have pipeway
• humans (closed system): specialised cells e.g. heart pushes fluid into pipes to destination
• worms: no specialised cells (cuz they’re small) heart circulate fluid
• blood just moves through the system

Question 29

Describe the function of blood.

Answer 29

Pumps blood through blood vessels

Question 30

Describe the function of the three types of vessels

Answer 30

veins- carries blood towards the heart (low pressure)
arteries- thicker, more carries blood away from the heart
capillaries- link arteries and veins and allow gas exchange, thin size (around a cell thickness) to get diffusion occuring

Question 31

Describe the function of blood and its types.

Answer 31

• plasma: liquid part of blood (includes minerals and dissolved liquids). The main role of plasma is to take nutrients, hormones, and proteins to the parts of the body that need it.
• white blood cells: fight disease
• red blood cells: carry oxygen and carbon dioxide
• platelets: assist in blood clotting

Question 32

Compare the pressure in veins and arteries with reasons.

Answer 32

Vein: low pressure
Arteries: high pressure
The blood pressure drops after the blood passes through the capillaries, reducing the resistance to allow blood flow at a lower pressure, veins have a lower blood pressure. Hence, arterial blood pressure is higher than venous blood pressure.

Question 33

Compare the size of veins and arteries with reasons.

Answer 33

Vein: thin
Artery: thick and muscular
Since the blood pumped from the heart into the arteries flows at higher pressure than the blood in veins, hence arteries need to have thicker walls or else the high blood pressure might cause them to burst.

Question 34

Where are intercostal muscles located?

Answer 34

Between ribs

Question 34

Which one, arteries or veins, contain valves? Explain.

Answer 34

• Veins contain valves to ensure that the blood flows in only one direction, toward the heart.
• Arteries don’t require valves because pressure from the heart is so strong that blood is only able to flow in one direction.
• Sometimes muscle contractions may cause blood to be pushed back to body

Question 35

How many chambers does the heart have and what are they called?

Answer 35

4.
Left atrium
Left ventricle
Right atrium
Right ventricle

Question 36

Describe how blood is pumped in and out of the heart.

Answer 36

• The left side (arterial system) pumps blood to the body tissues and the right side (venous system) pumps blood to the lungs.
• Deoxygenated blood travels to the right side of the heart via the vena cava.
• The heart pumps the deoxygenated blood to the lungs where it releases carbon dioxide and receives oxygen.
• ## The oxygenated blood travels via the pulmonary vein back to the heart from where it is pumped to all parts of the body.

Question 37

Compare how blood is moved through veins and arteries.

Answer 37

Veins: relies on muscle contractions to move the blood out
Arteries: moves blood under high pressure from the heart

Question 38

What are the roles of the left and right sides of the heart?

Answer 38

Left: pumps blood around the body so that nutrients can be distributed and wastes picked up
Right: pumps blood to the lungs so it can pick up oxygen so it can pick up O2 and get rid of Co2.

Question 39

There are _____ that separate the ventricle and the atrium.

Answer 39

Valves

Question 40

How does pulmonary mean and what does its veins and arteries do?

Answer 40

= lungs
Vein: carries oxygenated blood away from lungs
Artery: carries deoxygenated blood to lungs

Question 41

The main vein coming from the body to the heart is called ______

Answer 41

Inferior vena cava

Question 42

The main vein coming from the heart to the body is called ______

Answer 42

Superior vena cava

Question 43

Artery coming from left side to pump blood around is called _____

Answer 43

Aorta

Question 44

Briefly describe how blood travels through the circulatory system. (route

Answer 44

• deoxygenated blood is pumped into the right atrium of the heart via the superior vena cava
• it then enters the right ventricle
• deoxygenated blood is then pumped to the lungs via the pulmonary artery to get oxygen
• oxygenated blood is then pumped back into the left atrium of the heart via the pulmonary veine
• it then enters the left ventricle
• heart pumps out oxygenated blood through the aorta and then arteries to different parts of the body
• they branch into arterioles upon reaching destination and then into smaller capillaries, where the speed of flow slows down

Question 45

How do animals with system level of organisation function and why do they utilise systems?

Answer 45

• They have specialised exchange surfaces (e.g. intestines, kidneys, lungs)
• Due to their high complication, simple diffusion is too far away from the surface

Question 46

What is the point of having a respiratory system?

Answer 46

They can get substances into the internal environment from external in an efficient manner.

Question 47

Compare the internal and external environment of respiratory system.

Answer 47

Internal: exchange of gases with the internal environment in tissues
External: exchange of gases with the external environment, occurring in the alveoli

Question 48

Fill out the circulatory system diagram.

Answer 48

Photos

Question 49

How does external respiration occur?

Answer 49

• The pulmonary artery carries deoxygenated blood into the lungs from the heart, where it branches and eventually becomes the capillary network composed of pulmonary capillaries.
• These pulmonary capillaries create the respiratory membrane with the alveoli.
• As the blood is pumped through this capillary network, gas exchange occurs.
• Although a small amount of oxygen is able to dissolve directly into plasma from the alveoli, most of the oxygen is picked up by red blood cells and binds to a protein called hemoglobin.
• Oxygenated hemoglobin is red, causing the overall appearance of bright red oxygenated blood, which returns to the heart through the pulmonary veins.
• Carbon dioxide is released in the opposite direction of oxygen, from the blood to the alveoli.

Question 50

How does internal respiration occur?

Answer 50

• Internal respiration is gas exchange that occurs at the level of body tissues
• occurs as simple diffusion due to a partial pressure gradient like external respiration.

Question 51

What are spiracles?

Answer 51

Holes (pores) on insects that allows diffusion

Question 52

Describe the ratio of Co2 and O2 in air that is inhaled and exhaled.

Answer 52

Inhaled: 0.04% Co2, 20% o2
Exhaled: 4% Co2, 16% o2

Question 53

What are some other ways of saying breath in and breath out?

Answer 53

Inspiration and expiration.

Question 54

How are o2 and Co2 exchanged in the lungs (through what mechanism)?

Answer 54

Diffusion across semi-permeable membrane in the lungs.

Question 55

What leads to an efficient uptake?

Answer 55

The warmer it is, the easier it is to cross SPM.

Question 56

Renal

Answer 56

Relating to the kidneys

Question 57

Describe what happens with blood during osmoregulation (organs?)

Answer 57

• Aorta passes deoxygenated blood through the renal artery into the kidneys to be osmoregulated
• Water exits kidneys
• Osmoregulated blood exits the kidneys via the renal vein into the inferior vena cava

Question 58

Where is does the not-yet-been osmoregulated blood come from before they are dispersed from the aorta?

Answer 58

Some come directly from the heart and some already went to other body parts

Question 59

Why don’t birds pee?

Answer 59

• Birds convert urine to uric acid instead, excretted as a white paste through the cloaca
• A cloaca is used to eliminate urine, feces, and reproductive fluids in birds, reptiles, amphibians, and a few branches of the mammal family tree.

Question 60

What is within the blood that travels to the kidney via the renal artery (sourced from the aorta) and what happens to them afterwards?

Answer 60

1. RBC, WBC, platelets -> none excreted
2. H2O-> some excess excreted
3. Glucose-> none excreted
4. Na+, Cl- -> some excess excreted
5. O2, Co2-> not excreted through kidney pathway
6. Blood proteins-> none excreted
7. Urea-> all excreted

Question 61

What are the 5 functions of the liver (simple)?

Answer 61

1. Produce bile
2. Breakdown RBC, hormones, drugs, cholesterole
3. Deaminate excess protein to urea
4. Store glycogen (convert from glucose)
5. Make blood proteins

Question 62

Describe the nervous control of breathing in a mammal.

Answer 62

• The respiratory centre in hindbrain receives nervous impulses from higher centres in forebrain
• Hindbrain receptor centre has receptors that are sensitive to e.g. Co2, when there is excess Co2, signal will be sent to muscles to exhale
• Nerves connect respiratory centre in hindbrain to intercostal muscles, as well as phrenic nerve to diaphragm
• Phrenic nerve sends signals that cause the diaphragm to contract (become thicker and flatter), giving the lungs room to expand and take in air (inhalation

Question 63

How is uniform distribution of oxygen to tissues ensured in insects?

Answer 63

• pattern of growth of tracheoles can be modified according to needs of the tissues
• if a body segment is deprived of oxygen by cutting its main trachea, the tracheoles of neighbouring segments respond by growing towards the deprived segment

Question 64

How does air travel through and insect’s respiratory system?

Answer 64

Air enters the insect’s body through the spiracle and enters the trachea. From the trachea the air moves to the small tracheoles. The tracheoles end within the body cells. Gases move by diffusion within the tracheal system

Question 65

What is hindbrain function?

Answer 65

Unconscious actions

Question 66

How does the diaphragm allow breathing to occur?

Answer 66

• nerve signals notify it to contract
• contracts and becomes flatter
• makes space in cavity (not lungs)

Question 67

Describe the breathing control mechanism in humans and other mammals.

Answer 67

Efferent nerves pass from the respiratory centre in hindbrain to muscles responsible for inspiration (intercostal muscles and diaphragm)

Question 68

What do stretch receptors do?

Answer 68

Signal to the respiratory centre the degree of expansion of the lungs. When the lung volume increases, it results in an inhibition of further inspiratory activity

Question 69

How do fishes conduct nervous control of breathing?

Answer 69

• Rhythmic discharge of impulses from the respiratory centre initiates inspiration
• range of expansion of the pharynx limits its extent

Question 70

How do some insects conduct nervous control of breathing?

Answer 70

Nerve centers in the thoracic and abdominal g

Question 71

What can influence the breathing pattern of humans?

Answer 71

• The respiratory centre is influenced by impulses from various receptors which can alter the normal pattern of breathing.
• e.g. stimulation of receptors sensitive to an increased level of Co2 in the blood will raise the ventilation rate
• e.g. irritation of nose and throat will initiate sneezing and coughing
• e.g. breathing is temporailu inhibited during swallowing reflex
• Also under influence of higher centres in the brain, allowing voluntary changes in breathing

Question 72

Pericardium

Answer 72

The protective fluid-filled sac around the heart

Question 73

Describe the imbalances of the heart’s shape (which side’s thicker.. twisting…

Answer 73

The walls of the left ventricle are thicker and more muscular than those of the right ventricle.
The difference affects shape of the ventricular cavities, so right ventricle is twisted over the right.

Question 74

Pulmonary ventilation

Answer 74

Provides air to the alveoli for this gas exchange process.

Question 75

Briefly describe the mechanism of gas exchange.

Answer 75

At the respiratory membrane, where the alveoli and capillary walls meet, gases move across the membranes, with oxygen entering the bloodstream and Co2 exiting.
- blood is oxygenated and Co2 removed from body in this process

Question 76

Describe the features of the lungs that make gas exchange efficient.

Answer 76

The exchange surface has a large surface area, provided by a large number of alveoli, the surface is only one cell thick, and it is supplied with blood by a very dense capillary network.

Question 77

Describe the structure of the alveoli and stuff around it that allows gas exchange to occur.

Answer 77

• Located at the very end of the bronchioles, air is passed through the bronchiole to the alveoli
• Capillaries wrap around the alveoli to conduct gas exchange via diffusion

Question 78

Describe the precise process of gas exchange via the alveoli (air movement direction, name of capillaries…)

Answer 78

• Air containing a higher concentration of O2 is drawn into the alveoli
• In the alveoli, oxygen diffuses through the semi-permeable membrane(1 cell layer of alveoli and 1 cell layer of capillary) into the bloodstream, driven by the concentration gradient (O2 moves from area of higher conc in alveoli to an area of lower conc in blood)
• Co2 is released from the blood to the alveoli
• the original blood (from pulmonary artery from right side of heart from body tissues via veins) is then transformed into oxygen rich blood
• O2 rich blood then transported to body parts via pulmonary capillary, to pulmonary vein, to left side of heart, then to body tissues via arteries

Question 79

Describe how the properties of the alveoli and capillaries benefits its gas exchange function.

Answer 79

Alveoli:
- 1 cell thick (thin)
- round structure increases SA making it more efficient
- moist for gases to dissolve
- warm
Capillary:
- 1 cell thick (thin)

Question 80

Where does external and internal respiration occur?

Answer 80

• External: Exchange of gases with external environment that occurs at the alveoli of the lungs
• Internal: exchange of gases with the internal environment that occurs in the tissues

Question 81

Where does the O2 go after entering the bloodstream from the alveoli?

Answer 81

• small amount is able to dissolve directly into plasma from the alveoli
• most picked up by RBC and binds to a protein called hemoglobin

Question 82

How does internal respiration occur?

Answer 82

• concentration gradient occurs as there is a higher conc of o2 in bloodstream than in tissue cells
• causing co2 to diffuse out of the cell and o2 to diffuse into the cell

Question 83

How is oxygen transported in the blood?

Answer 83

1.5% transported directly in the bloodstream, 98.5% bound to hemoglibin and is carried to the tissues.

Question 84

How does the habitat of fishes cause them to have a different respiratory mechanism from other mammals?

Answer 84

The properties of water (denser and more viscous than air, and the oxygen in it is less concentrated and diffuses more slowly) compared to simply air means that fishes require a special type of respiratory organ and ventilation mechanism.

Question 85

How do fishes breath?

Answer 85

• Water drawn into the pharynx either through its mouth or thru its spiracle.
• Water flow into where gills are located and diffusion of oxygen occur (from higher concentration water to lower concentration capillaries in gills)
• Gills are built as strands to have a large SA:V area to maximize diffusion
• branchial valve in each gill ensure direction of water movement
• afferent branchial artery located close to gill arch brings deoxygenated blood to the lamellae (thin, sheet-like structure in the gills where oxygen diffuse through to enter the blood
• efferent branchial arteries carry blood away from the lamellae to the dorsal aorta

Question 86

What is the best direction of blood and water flow for maximum gas exchange and what is the term for it?

Answer 86

Best for blood and water to flow in opposite directions- counterflow system.

Question 87

Describe the tracheal system and who uses it?

Answer 87

• Insects
• Spiracles on either side of the thorax and abdomen open into a system of tracheal tubes.
• The spiracles are guarded by valves or hairs to prevent excessive evaporation through them
• kept permanently open by chitin
• Spiracles and trachea permit the passage of air to a further system of tubes, the tracheoles.
• that is extremely numerous and extend deep into all of the tissues, especially muscles

Question 88

Nephron structure practice

Answer 88

answers in photos

Question 89

Define excretion

Answer 89

The removal from the body of the toxic waste products of metabolism
The term is specifically taken to mean nitrogenous waste such as urea and ammonia
- Other materials like Co2 and bile pigments are also waste products of metabolism

Question 90

Define osmoregulation.

Answer 90

The process by which the osmotic pressure of the blood and tissue fluids is kept constant.
- also with respect to concentration of the various solutes normally present in the body fluids (glucose, salts and the like)

Question 91

Where are nephrons located?

Answer 91

In the kidneys

Question 92

What do nephrons do (roughly)

Answer 92

It produces a liquid called urine,

Question 93

What is the essential job of the kidney?

Answer 93

To purify the blood which flows through it, extracting and eliminating harmful substances and ensuring that it has the correct composition.

Question 94

The kidney accomplishes its task of purifying the blood by the use of _______ and _________.
Fill in and elaborate.

Answer 94

Filtration, reabsorption.
The fluid components of the blood are filtered from the glomerulus into the capsular space. As the result fluid flows along the tubules, useful substances are reabsorbed bac into the bloodstream while unwanted substances flow on to the ureter as urine.

Question 95

Which of these are absorbed and not absorbed when passing through a nephron and where?
Glucose
Chloride ions
Urea
Water

Answer 95

Glucose: 100% reabsorbed in the proximal tubule
Chloride ions: reabsorbed in the distal tubule
Urea: typically little absorbed
Water: reabsorbed

Question 96

Reabsorption of glucose and salts involves ______.
Why?

Answer 96

Active transport.
Diffusion alone cannot account for the transfer of these materials as it occurs against a concentration gradient.

Question 97

What does the loop of Henle do?

Answer 97

Conserve water.

Question 98

Do desert animals have a longer or shorter loop of Henle?

Answer 98

Extra long. Produces particularly concentrated urine.

Question 99

What are the two principle functions of the kidney?
Elaborate.

Answer 99

Secretion and regulation.
- lowers the urea content of the blood, clearing the body of toxic nitrogenous waste.

Question 100

Is glucose present in urine?

Answer 100

• completely reabsorbed, none being present in urine normally
• if the amount of glucose in blood exceeds a certain threshold value, it begins to appear in the urine.

Question 101

Justify the difference in osmoregulation and nitrogenous waste excretion in freshwater and saltwater fish.

Answer 101

Freshwater: a fish is hypertonic to its environment, therefore water continually flows into the fish via osmosis.
Saltwater: a fish is hypotonic to its environment, therefore fish continually flows out of the fish via osmosis.

Question 102

Describe osmoregulation and nitrogenous waste excretion in freshwater fish.

Answer 102

• water enters the fish due to osmosis
• drinks very little water, virtually all water taken in travels across gills for gas exchange
• produces dilute urine to maintain cell salts balance
• because fish still loses salts via skin and urine, it has specialised cells in the gills to gain salts
• fish produce ammonia (turning unto urea/uric acid takes lots of energy) because of the continual diluting of body fluids and expulsion of large amounts of dilute urine

Question 103

Describe osmoregulation and nitrogenous waste excretion in saltwater fish.

Answer 103

• Water leaves the fish due to osmosis
• Ocean fish drink water thru the mouth to compensate for water loss, they excrete excess salts through cells in their gills
• produce concentrated urine in small amounts to maintain cell salts balance
• produces nitrogenous wastes in the form of mainly urea that is less toxic than ammonia, requiring less dilution by water

Question 104

Describe what mammals, birds, reptiles, insects, freshwater fish and saltwater fishes excrete as nitrogenous waste.

Answer 104

Mammals: urea
Freshwater fish: ammonia
Saltwater fish: urea
Birds, reptile, insect: uric acid

Question 105

How do humans get rid of Co2 in their body?

Answer 105

• Lungs
• Trachea-> bronchi (bronchioles also)-> alveoli

Question 106

How does the structure of alveoli benefit its function?

Answer 106

• moist (to allow diffusion)
• very thin (diffusion)
• high blood flow (maintains a steep conc. gradient between o2 and co2 in alveoli and blood for faster diffusion)
• large SA:V ratio (efficient diffusion)

Question 107

Describe how red blood cells within capillaries increase efficiency of diffusion.

Answer 107

• pushed right up against walls of capillaries
• wall cells extremely thin
• allowing diffusion to occur

Question 108

Where does the Co2 in blood come from?

Answer 108

From where cellular respiration has been conducted around the body.

Question 109

How does counterflow maximize diffusion of fish and why is it important?

Answer 109

Used by fish to maximize diffusion by pumping blood in the opposite direction to the flow of water.
- maximum diffusion is 50% ratio if co-current diffusion is used
- counter-current flow is far more efficient and allows the fish to get a much higher percentage of O2 out of water
- important bc there is less o2 in water than there is in air, therefore needs to be more efficient

Question 110

Describe two other types of gas exchange (that aren’t diffusion in fish or humans).

Answer 110

1. Insects
   - use tiny pipes along their abdomen which have little openings called spiracles
   - little pipes are like mini trachea that goes down to the cellular level
2. Amphibians
   - live in water therefore some o2 can diffuse across the skin
   - still have simple lungs, but can get around 20% of o2 through lungs
   - moist membrane-> able to diffuse

Question 111

How is nitrogenous waste created?

Answer 111

Created from breakdown of protein (protein molecule contains nitrogen)

Question 112

Why is nitrogenous waste toxic?

Answer 112

It’s toxic because it joins with hydrogen to form ammonia

Question 113

Compare how freshwater fish deals with nitrogenous waste and how human dues with it.

Answer 113

• humans convert this to urea, which requires energy, but uses less water to excrete it (than the amount of water freshwater fish uses for ammonia)
• freshwater fish pees a lot of urine with little ammonia and many water (don’t want to waste energy converting it to urea)

Question 114

What does the kidney do?

Answer 114

Remove urea from the blood while retaining everything else that is needed by the body.

Question 115

What is the main functional unit of the kidneys and what does it do?

Answer 115

Nephron. It filters the blood, removes the urea, and keeps all the good stuff (RBC, WBC, glucose, salts, water).
Rest is flushed out through the bladder in urine.

Question 116

What happens when pressure of blood in capillaries increases?

Answer 116

Small stuff like vitamins, salt, H2O comes out

Question 117

How does water go back inside the body (and not get excreted) after moving through the nephron?

Answer 117

• active transport gets water out before urea gets to the collecting duct
  capillaries wrap around tube, water diffuse back in through osmosis

Question 118

Define osmoregulation.

Answer 118

maintaining right levels of water and dissolved substances in body.

Question 119

Why do organisms like reptiles and birds excrete uric acid instead of urea or ammonia?

Answer 119

• They sit in an egg for at least 6 weeks and may get intoxicated if toxic wastes like urea and ammonia are excreted

Question 120

Desert-dwelling animals have _______ loops of Henle. Why?

Answer 120

Longer.
To maximize water reabsorption.

Question 121

Homeostasis

Answer 121

Maintaining the right amount of water and other substances within the body

Question 122

Where is aldosterone produced and what is its function?

Answer 122

Adrenal glands. Aldosterone controls the reabsorption of ions (Na+, K+, Cl-) in the tubule.

Question 123

Describe what happens to the body when there is excess H2O in the blood.

Answer 123

Excess H2O: receptors in hypothalamus senses change in blood osmolarity.
- hypothalamus signals the pituitary gland to release less ADH
- as less ADH is released, the permeability of the collecting duct cells decreases, thus more water is released through the tube instead of being reabsorbed

Question 124

Define: negative feedback loop

Answer 124

A negative feedback loop is a normal biological response in which the effects of a reaction slow or stop that reaction.

Question 125

Describe what happens to the body when there is inadequate H2O in the blood.

Answer 125

• Receptors in hypothalamus senses lack of H20
• transmission occurs from hypothalamus to the pituitary gland, signaling the adrenal glands to release more ADH
• More ADH increases permeability of the collecting duct. thus more H20 is reabsorbed into the bloodstream

Question 126

ADH full name

Answer 126

Anti-diuretic hormone

Question 127

How does alcohol interfere with the negative feedback loop of water reabsorption?

Answer 127

Mucks up with release of ADH-> less reabsorption

Question 128

Which substance is reabsorbed in each of these locations? Also describe how.
Proximal tubule
Henles loop
Distal convoluted tubule

Answer 128

Proximal tubule= glucose diffuses back into the bloodstream through protein channels
Henle’s loop= permanent active transport occurs, making the surroundings of the Henle’s loop extremely concentrated, creating a concentration gradient for water to diffuse out and reabsorb
Distal convoluted tubule: active transport

Question 129

Where does air go after being breathed in?

Answer 129

In thru trachea, bronchi, bronchioles, then alveoli, then diffused into bloodstream

Question 130

What does the two parts of the nephron try to do?

Answer 130

Part before distal convoluted tubule: trying to retain as much water as possible
Part after dct: homeostatic control

Question 131

Parts of body involved in homeostasis: (what do they do)
kidneys
skin
liver& pancreas

Answer 131

k: regulate water and mineral salts concentration
s: regulated body temp
l&p: blood glucose

Question 132

What happens to urine when excess water/ inadequate water is in the body?

Answer 132

sweat-> concentrated blood-> concentrated urine produced (to reabsorb more water)
drink-> diluted blood-> dilute urine produced (less water reabsorbed)

Question 133

Polkilotherms, how do they maintain temperture?

Answer 133

Cold-blooded animals, thermoconformers.
Body temperatures vary with temperature

Question 134

What are some examples of polkilotherms?

Answer 134

Reptiles, fish, amphibians

Question 135

Homeotherm, how do they maintain temperature?

Answer 135

Warm-blooded animals, thermoregulators.
Keep temp constant by increasing metabolic rate

Question 136

Functions of Our Skin with locations

Answer 136

protect the body (epidermis)
- to provide mechanical protection
- to prevent bacterial entry
- to reduce water loss
temperature regulation (hair)
excretion of sweat (sweat gland)
store fats (subcutaneous fat)
sensation (numerous receptors )
production of vitamin D under ultra-violet light (inner epidermis)

Question 137

How is body temp regulated in hot conditions? (5)

Answer 137

1. More sweat is produced by sweat glands
   – evaporation of sweat takes away heat which
   produces a cooling effect
2. Vasodilation of skin arterioles
   – arterioles near the surface of the skin
   dilates
   – to let more blood flows near the skin surface
   – to have more heat lost by conduction &
   radiation
3. Erector muscles relax
   – hairs lie flat on the skin
   – reduce thickness of air trapped among the hairs (not effective in human because human hairs are short)
4. Develop thinner subcutaneous fat & shed fur
   – as long term responses
   – increase heat loss
5. Decrease metabolic rate & muscle contraction
   – gain less heat

Question 138

How body temp controlled in cold temperatures?

Answer 138

1. Vasoconstriction of skin arterioles
   – arterioles near the surface of the skin constrict
   – to let less blood flows near the skin surface
   – to have less heat lost by conduction & radiation
2. Erector muscles contract
   – pull hairs erect for trapping more air
   – thicker layer of air acts as a good insulator of heat
3. Less sweat is produced by sweat glands
   – reduce heat loss by evaporation
4. Develop thicker subcutaneous fat & thicker fur
   – as long term responses
   – reduce heat loss
5. Increase metabolic rate & muscle contraction
   – gain more heat

Question 139

What does termination of shivering indicate?

Answer 139

No more energy to power muscles= will lost heat rapidly in the cold

Question 140

What hormone controls regulation of blood glucose level?

Answer 140

insulin secreted from the
islets of Langerhans in pancreas

Question 141

How does diabetes occur?

Answer 141

malfunction of pancreas
(does not secrete enough insulin)

Question 142

what causes type 1 diabetes?

Answer 142

• auto-immune disease
• Body kills cells (islets of langerhans) that produce insulin
• can’t regulate blood glucose levels
• born with it

Question 143

Hyperglycermic

Answer 143

High blood sugar

Question 144

What’s type 3 diabetes and what causes it?

Answer 144

Gestational diabetes, caused by parasite within eating up all the sugars, causing difficulty of body to use insulin effectively

Question 145

How does the body react after eating? (homeostasis)

Answer 145

• blood sugar spikes after meal and becomes too high
• pancreas stimulated by brain to secretes more insulin
• liver converts glucose to glycogen
• cells take in more sugar from blood
• blood glucose declines to a set point
• stimulus for releasing more insulin disappears

Question 146

How does the body react after not eating for a while? (homeostasis)

Answer 146

• blood sugar too low
• pancreas secretes less insulin
• liver produces glucagon that breaks down glycogen into glucose
• blood glucose level rises to set point
• stimulus for releasing more glucagon disappears

Question 147

What causes type 2 diabetes?

Answer 147

• lifestyle
• excessive periods of time with v. high blood sugars (high sugar/ fat diet)
• causes resistance of cells to insulin
• resulting as them stop responding to insulin (won’t absorb more/less sugar on demand)

Question 148

What are the two key players in thermoregulation and what do they do?

Answer 148

Skin, hypothalamus, ->sweating, hairs stand up,
shivering, vasodilation/ vasoconstriction.

Question 149

How does the body react to body temperature above 37c?

Answer 149

• Nervious system signals dermal blood vessels to dilate and sweat glands to secrete
• body heat is lost to its surroundings
• drops towards normal

Question 150

How does the body react to body temperature below 37c?

Answer 150

• Nervious system signals dermal blood vessels to constrict and sweat glands to remain inactive
• body heat is conserved
• drops towards normal
• if body temp continues to drop, nervous system signals muscles to contract involuntarily
• muscle activity generates body heat
• return to normal

Question 151

Compare the two communication systems in the body.

Answer 151

1. Nervous system:
   - thermoreceptors detect changes - communicating to hypothalamus to react
   - faster with shorter lasting impact
2. Endocrine system:
   - hormonal system
   - slower, longer lasting impact, more generalised

Question 152

What parts of the digestive system suggest type of food the organism eats?

Answer 152

• teeth
• length of digestive tract

Question 153

Which one of these parts in the excretory system has passive and active transport?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct

Answer 153

PCT: passive
LOH: both (thin top half passive, thick bottom active transport)
DCT: active inwards to bring in urea and toxins
Collecting duct: passive flow out everything else

Question 154

Where are the following substance produced?
Hydrochloric acid
Amylase
Lipase
Protease

Answer 154

HCL: stomach
Amylase: salivary glands, small intestine, pancreas
Lipase: pancreas
Protease: stomach and pancreas

Question 155

Create a flow diagram for the digestion of a ham sandwich made with white bread and butter. It
should indicate any significant digestive process including:
* Where chemical and mechanical digestion of each part of the sandwich occurs
* Where absorption of nutrients occurs

Key
* ham = protein
* bread = carbohydrates
* butter = lipids

(6 marks)

Answer 155

Section of Digestive System
Mechanical Digestion Chemical Digestion

Mouth
* needed to include something mechanical for ½ mark
* just ‘mechanical’ not awarded mark
* could use any of the following: chewing/teeth &
tongue/increases SA:V
* needed to mention something chemical OR which substance was being chemically digested here for ½ mark
* just ‘chemical’ not awarded mark
* ½ mark awarded for any of the following:
amylase/bread/carbohydrates/enzyme
* lipase also awarded ½ mark as many students mentioned lingual lipase (outside course but correct)

Stomach
* needed to include something mechanical for ½ mark
* just ‘mechanical’ not awarded mark
* the term peristalsis was not awarded mark
* could use any of the following: churning/muscle contractions
* needed to mention something chemical OR which substance was being chemically digested here for ½
mark
* just ‘chemical’ not awarded mark
* ½ mark awarded for any of the
following: pepsin/protease/ham/protein
* lipase also awarded ½ mark as many students mentioned gastric lipase (outside course but correct)

Small Intestine
* needed to include something mechanical for ½ mark
* just ‘mechanical’ not awarded mark
* peristalsis gained ½ mark
* bile emulsifying lipids/fats gained ½ mark
* needed to mention something chemical OR which substance was being chemically digested here for ½
mark
* just ‘chemical’ not awarded mark
* ½ mark awarded for any of the following: trypsin/protease/ham/protein
* ½ mark awarded for any of the following:
amylase/bread/carbohydrates
* ½ mark awarded for any of the following: lipase/butter/lipids
Students needed to mention absorption in the small intestine for ½ mark

Large Intestine
Students needed to mention absorption of water in large intestine for ½ mark.

Accessory Organs
* Students could include bile emulsifying lipids/fats for ½
mark here OR in small intestine (did not gain marks
both times if repeated)
* needed to mention liver ½ mark
* needed to mention pancreas ½ mark
* Students could include the different enzymes acting in the small intestine here with the pancreas (did not gain
marks both times if repeated)

Question 156

In terms of diffusion of oxygen, explain why counter-current flow exchange is particularly effective. (2 marks)

Answer 156

. Diffusion works along a concentration gradient, in this case oxygen moves from a high
concentration to a region of lower concentration until an equilibrium is reached (1). If
the oxygen is being diffused to a changing concentration gradient, opposite to the
concentration of oxygen in the blood, then more can be diffused (1). Could also include:
moist membrane, blood supply, thin membrane, large surface area at least two wellexplained points for full marks

Question 157

Amoebic Gill Disease (AGD) is caused by a parasite that lives on the gills of some species of
fish. This causes parts of the gill to become thicker and fused together. Outline how this would
impact gas exchange in affected fish. (2 marks)

Answer 157

If the gills become thicker and join there will be less SA for the diffusion of oxygen which
would decrease the rate of diffusion (1). Increases diffusion distance for gases so do not
move unto blood as efficiently (1).

Question 158

tasc pp 2022 q19a
a) Outline what conclusions can be drawn from the results.

Answer 158

The following conclusions were awarded ½ mark each;
Mice treated with amylase inhibitor had lower BG than those without
Mice treated with amylase inhibitor had decreasing BG levels over duration
Mice without amylase inhibitor had consistent BG levels
Amylase inhibitor can help with diabetes/to lower BG
Amylase breaks down larger carbohydrates to assist digestion/absorption
Any explicit reference to data in the graph

Question 159

Glucose is a substance that is under homeostatic control. Explain the process of how the body
controls glucose levels.
You can include a labelled diagram in your response.

Answer 159

BG high (½), pancreas detects (½), pancreas secretes insulin (½), insulin travels to
liver (and other tissue cells) (½), liver converts glucose to glycogen (tissues increase
uptake) (½), facilitates cellular glucose uptake (½), BG decreases (½). BG low (½),
pancreas detects (½), pancreas secretes glucagon (½), glucagon travels to liver (½),
liver converts glycogen to glucose (½), BG increases (½).

Question 160

A ventricular septal defect (VSD) is a hole in the septum of the heart. (bit that separated left and right ventricle)
b) Patients with this disease are often tired and have thickened ventricles. Explain why
patients would have these symptoms.

Answer 160

. The hole in the septum means that oxygenated and deoxygenated blood will mix (1).
Therefore, blood going to the body will not be fully oxygenated (½),
decreasing/lowering the rate of aerobic respiration causing tiredness (½). The heart
will try and pump blood faster to get more oxygen to the body (½), making the
ventricles work more and thus making them thicker (½).

Question 161

Explain the role of the stomata with reference to gas exchange and transpiration

Answer 161

The stoma must be open for photosynthesis to allow CO₂ into the leaf and release
excess oxygen produced into the atmosphere (1). When the stomata are open for
gas exchange, water can be evaporated out (½) assisting in the directional flow of
water from roots to leaves (½). When the stomata are closed transpiration rate
slows (1).

Question 162

Outline two (2) substances you would not expect to find in the Bowman’s capsule.

Answer 162

Any 2 of the following: large proteins, enzymes, fatty acids & glycerol, platelets, red
blood cells, white blood cells (½ for each).

Question 163

Outline two (2) substances you would expect to find in the proximal convoluted tubule.

Answer 163

Any 2 of the following: urea, amino acids, glucose, ions, salts, water, minerals (½
for each)

Question 164

Anti-diuretic Hormone (ADH) plays a role in water balance. If you are dehydrated
briefly outline how ADH affects the urine produced

Answer 164

Increased production of ADH (½) acts to make collecting duct more permeable
to water (½) through increased opening of aquaporin transport proteins (½). This
means that more water in reabsorbed back into the body (1) creating urine which is
more concentrated (1). ½ mark for mentioning darker colour or increased smell of
urine produced.

Question 165

How does the liver assist the digestive system? (2 marks)

Answer 165

W the liver (1/2 mark for identifying the liver and 1 1/2 for describing function related to
digestion). Processes all food that is absorbed into the bloodstream from the digestive
system. OR Production of bile to emulsify fats in the duodenum
½ mark given for answers relating to glucose or glycogen storage or toxin removal as
these are not strictly digestive system roles.

Question 166

Briefly discuss one (1) adaptation you would expect to find in the digestive systems of animals that feed on course vegetation. (2 marks)

Answer 166

Coarse vegetation: 1 mark for appropriate feature and 1 mark for explanation.
Correct answers include but are not limited to:
* More and larger grinding teeth.
* Enlarged parts of the gut that allow for extra time for enzymes to breakdown
material (e.g. the foregut of cattle) or provide fermentation chambers for
bacteria to breakdown the cellulose material further (e.g. the caecum).
Additional stomachs.
* large stomach to store bulky food

Question 167

tasc pp 2021 q18a
The table lists functions of parts of the heart and associated blood vessels.
Complete the table by identifying which structure, A to H, carries out each of the following functions.
Function Letter
vessel returning blood from the body
chamber which pumps blood to the body
vessel which carries blood to the lungs
vessel which carries blood at the highest
pressure

Answer 167

CHDE

Question 168

Explain how blood in a vein in the leg is returned to the heart. (3 MARKS)

Answer 168

C) Lower negative pressure in legs allows some blood flow back to the heart (1) due to the
valves being squeezed 0.5. Valves prevent backflow of blood (1). The movement of skeletal
muscle encourages blood to flow back to the heart (1) as this forces the smooth muscle in
the veins to contract (0.5).

Question 169

tasc pp 2021 q19b iii
iii. Explain why it may be concluded that person B has a kidney disease.

Answer 169

The person is losing protein through the kidneys (½). Protein molecules are generally
too large to be forced out of the blood during ultrafiltration (½) but in this case, they
are. The proteins are then lost from the body in the urine. The body has no
mechanism for reabsorbing protein because this is not normally required (½). as can
be seen in the table Person B has 16 units in its urine whereas Person A does not.
(½). Just talking about protein being high in person B and not changing between
glomerular filtrate and urine only received 1 mark.

Question 170

tasc 2021 pp 20a
Diagram A shows a set up with a steam jacket that subjects the stem at that point to high
temperatures. One of the leaves of a healthy plant was fed with 14CO2 in the light for one hour and
left in the light for three hours to allow the 14C labelled compounds to enter the leaf (A).
The roots of the plant were placed in a beaker containing a red dye called eosin solution.
The distribution of the 14C in different parts of the plant was determined by placing the whole plant
on a photographic film so that an autoradiograph (an image showing up the radioactive 14C) was
developed.
Diagram B shows the plant after the experiment.

What process was being investigated by 14C and by the eosin dye?

Answer 170

Process using 14C = translocation (photosynthesis accepted) (½)
Process using eosin dye = transpiration (½)

Question 171

2021 q20
Diagram A shows a set up with a steam jacket that subjects the stem at that point to high
temperatures. One of the leaves of a healthy plant was fed with 14CO2 in the light for one hour and
left in the light for three hours to allow the 14C labelled compounds to enter the leaf (A).
The roots of the plant were placed in a beaker containing a red dye called eosin solution.
The distribution of the 14C in different parts of the plant was determined by placing the whole plant
on a photographic film so that an autoradiograph (an image showing up the radioactive 14C) was
developed.
Diagram B shows the plant after the experiment.

Would the tissue in the stem above the jacket be stained red? Provide a reason. (2 marks)

Answer 171

Yes. The dye and water travels through xylem tissue from roots to leaves (½). High heat
from the steam jacket does not affect xylem cells (½) because they are lignified, dead cells
(½).

Question 172

2021 q20
Diagram A shows a set up with a steam jacket that subjects the stem at that point to high
temperatures. One of the leaves of a healthy plant was fed with 14CO2 in the light for one hour and
left in the light for three hours to allow the 14C labelled compounds to enter the leaf (A).
The roots of the plant were placed in a beaker containing a red dye called eosin solution.
The distribution of the 14C in different parts of the plant was determined by placing the whole plant
on a photographic film so that an autoradiograph (an image showing up the radioactive 14C) was
developed.
Diagram B shows the plant after the experiment.

On diagram B, shade the parts of the plant that you would expect to show up as radioactive
14C after the image was taken.

d) Explain the absence of 14C in the parts of your diagram B shading.

Answer 172

Shading of the whole plant above the steam jacket (although it was acceptable to not shade
the left leaf) (2).

14CO2 is used by the plant in photosynthesis (½) to make glucose that contains 14C (½).
Translocation of glucose (½) occurs through the plant via phloem tissue (½). No 14C
glucose is found below the steam jacket (½) because the high heat kills the living phloem
cells (½).

Question 173

Insulin is a hormone produced to control blood glucose levels. Diabetics do not have a natural
ability to adequately control these levels.
a) With reference to the pancreas and the liver, describe the role of insulin in controlling blood
glucose levels, and the consequences for diabetics having inadequate insulin levels.

Answer 173

. Insulin helps maintain homeostasis of blood glucose levels (½). Insulin control of blood
glucose is part of a negative feedback control system (½). Blood glucose levels increase
following a meal (this is the stimulus) (½). This increase is detected by the (islets of
Langerhans) the pancreas (this is the receptor) (½). The pancreas (beta cells) secretes the
hormone insulin (this is the messenger) into the blood stream (½). Insulin travels to the liver
(this is the effector organ) (½). The liver is activated to absorb blood glucose and synthesise
glycogen for storage (½). Body cells/skeletal muscle cells are activated to absorb glucose
from the blood (½). This brings blood glucose levels back down (this is the response) (½).
Consequences of low insulin production (Type 1 diabetes)/resistance to insulin (Type 2) will
be the inability to bring blood glucose levels back down (½). So, diabetics are likely to require
insulin injections/suffer from (anything sensible such as) kidney disease, glucose in their urine,
high blood pressure, cardiovascular problems, circulatory issues, tissue necrosis, gangrene, ill
health, eye problems, premature death (½).
For full marks, descriptions of the roles of the pancreas and the liver, insulin action and
consequences (plural) for diabetics needed to be addressed. Correct application of the
elements of the negative feedback control model, enriched quality of answers given, but
were not necessary for full marks.

Question 174

An alternative treatment to injecting insulin is being developed. The insulin is inhaled into
the lungs as a spray. It is then absorbed into the bloodstream.
State three (3) features of the alveoli that might help the insulin to pass into the blood
stream efficient.

Answer 174

The question only asks for a statement of features of alveoli which would help insulin to
pass into the blood efficiently and therefore, listing of features without explanation attracted
full marks. Features listed included:
* Alveoli have thin walls
* Alveoli have a moist internal surface
* The combined surface area of all alveoli is very large
* Alveoli have a good blood supply
1 mark for each of the above points correctly stated.

Question 175

Show any significant changes in the blood concentrations of carbon dioxide, glucose, and urea at point Y(after passing organ) compared to point X(before passing organ) in liver, small intestine, and active muscle.
Key: less, same, more

Answer 175

Co2: liver +, small intestine +, active muscle +
Glucose: liver -, small intestine +, active muscle -
Urea: liver +, small intestine O, active muscle O

Question 176

Show any significant changes in the blood concentrations of carbon dioxide, glucose, and urea at point Y(after passing organ) compared to point X(before passing organ) in liver, small intestine, and active muscle.
Key: less, same, more
Explain the responses you have chosen for the liver.

Answer 176

Blood carbon dioxide levels increased at Y because the liver cells are respiring (using oxygen) and producing CO2
(1).
Blood glucose levels decreased at Y because the excess glucose (from the digestion of food) is EITHER taken out
of the blood and stored as glycogen (1) OR it is used in cellular respiration (1).
Blood urea levels increased at Y because excess amino acids (from the digestion of food) are broken
down/deaminated and converted to urea by the liver (1).

Question 177

The table below shows the percentage of nitrogen excreted in various forms by four different animals.

Animal Ammonia Urea Uric acid Other forms
I 68.0 3.0 0.7 28.3
II 3.5 85.0 2.2 9.3
III 3.0 0.2 80.8 16.0
IV 73.3 9.9 0.0 16.8

(a) Which animal(s) are most probably aquatic? Provide reasons for your choice, including using the data from the table.

Answer 177

Aquatic: I and IV (½). Higher concentration of ammonia (animal 1 -68% and animal IV 73.3% of nitrogen
excreted) (½). Ammonia is toxic and requires a lot of water to remove it / soluble in water and diffuses away
(1). Needs to be constantly/rapidly removed due to toxicity /
in the most energy efficient form, as the animal makes use of the watery environment so it doesn’t have to expend energy on converting ammonia to less toxic waste (1).

Question 178

The table below shows the percentage of nitrogen excreted in various forms by four different animals.

Animal Ammonia Urea Uric acid Other forms
I 68.0 3.0 0.7 28.3
II 3.5 85.0 2.2 9.3
III 3.0 0.2 80.8 16.0
IV 73.3 9.9 0.0 16.8

which ones are terrestrial and why

Answer 178

Terrestrial: 11 and 111 (½).
111: highest concentration of uric acid in animal III-80.8% of nitrogen excreted (½). Uric acid is solid, insoluble
and nontoxic (½). Uric acid can be stored as insufficient water (water in a desert environment needs to be
conserved) to flush waste away (1).
I I: highest concentration of urea in animal II-85% of nitrogen excreted (½). Urea is soluble and is flushed
through kidneys/stored for short periods of time (½). So long as there is some water available in the terrestrial
environment, urea is primarily excreted as it saves energy in comparison to uric acid production (1).

Question 179

The table shows the transpiration rate of a group of plants exposed to different humidities at a temperature of 25°C.

Humidity Transpiration rate
(%) (arbitrary units)
20 26.0
40 21.0
50 16.5
60 11.0
70 9.5

(a) Describe and explain the relationship between humidity and transpiration rate. (3 marks)

Answer 179

The table shows an inverse relationship between humidity and transpiration rate as increasing humidity results
in a decrease in transpiration (1). Transpiration is the movement of water through a plant (½) as the concentration
gradient becomes less steep with increasing humidity (½), a slower rate of diffusion of water vapor occurs (harder
for water to evaporate) (½) this results in a decrease in the transpiration rate (½).

Question 180

tasc 2020 q16
The diagrams show a section through a typical leaf and a section through a leaf from a
xerophytic plant (a plant that requires very little water). The xerophytic leaf has a lower transpiration rate than the typical leaf.

Describe TWO features shown in the diagram of the xerophytic leaf which help reduce transpiration rate. Explain how each of these features contributes to a lower transpiration rate.

Answer 180

Feature 1: Thick waxy cuticle surrounds the leaf (½).
Explanation: The waxy cuticle reduces the amount of evaporation from leaf cells (½). By having a waterproof
waxy layer/barrier all around the leaf (½), not just on top which conserves moisture (½). As a
result, less water is drawn into the leaves (½) therefore reducing the rate of transpiration (½).
Feature 2: Sunken Stomata (½).
Explanation: This gives the plant a more humid microclimate at the leaf surface / site of water loss in pits (½)
which decreases the concentration gradient from the leaf (½), ensuring less water evaporates from
the leaf (½) therefore reducing the rate of transpiration (½).
Other acceptable:
Feature: Shape of leaf / fairly round cross-section / thicker mesophyll layer*/position of vascular bundle (½).
Explanation: Reduces SA:Vol ratio of the leaf which reduces water loss for the leaf (½) because there is less
exposed surface to lose water compared the volume of the leaf (½). The thicker cross-section of
leaf also creates a greater distance between the xylem and the stomata (½) which increases the
time taken for water movement, thereby slowing the rate of transpiration (½).
* Storage of moisture and heat reducing capacity was also considered.
* Increase in diffusion distance.
Feature: Stomatas close during the day. Not a structure, however some marks were awarded for explanation of preventing water loss and slowing transpiration.

Question 181

Indicate whether each of the statements below about thermoregulation in animals is true or false. Give a reason for your answer.
(i) Ectothermic is a term used to describe an animal that regulates its body temperature
independently of the external environment. (2 marks)
True / False (circle one)
Reason:

Answer 181

False (½)
Ecto means outside(1/2), therefore ectotherms rely on heat from outside i.e. external sources (½) to provide energy (1/2). Examples of ectotherms include ‘cold-blooded’ animals such as lizards or snakes which rely on behavioural responses to change body temperature (½)

Question 182

Indicate whether each of the statements below about thermoregulation in animals is true or false. Give a reason for your answer.
(ii) A large body size will help a mammal to retain body heat in a cold environment.
(2 marks)
True / False (circle one)
Reason:

Answer 182

True (½)
Larger bodies generally have a lower SA:Vol ratio (1) which means that the rate of heat loss is slower
compared with smaller-bodied animals (½).

Question 183

Identify and describe the FIVE main steps of a negative feedback mechanism that regulates the temperature back to normal. Use temperature increasing in the human body as the
starting point. (5 marks)

Answer 183

Stimulus: (½ mark given if student identified the word stimulus with the actual stimulus) - Increasing
temperature (½).
Receptor: (½) - hypothalamus in the brain/thermoreceptors in skin or muscles (½).
Transmission of message: (½ ditto) - nerve signal sent from thermoreceptors to hypothalamus, secretion of
thyroid releasing hormone (TRH) to pituitary gland, thyroid stimulating hormone (TSH) from
pituitary to thyroid, secretion of T3 & T4 hormones from thyroid, nerve signal sent to skin (any
for ½).
Effector: (½) - blood vessels dilate to radiate heat / sweat glands open to allow evaporative cooling, behaviour
response to move into cooler area, reduction of basal metabolic rate to reduce heat production (any
two for ½ mark each).
Response: (½) - The skin / body is cooled (½).
Body temperature reduces / restores homeostasis via a negative feedback loop (½) e.g. the response acts in the
opposite direction to the stimulus and hence maintains a steady state for the organism (½).
Students do not need to include the five main headings to gain full marks as students may give a full description
without them.

Question 184

Describe the function of the large intestine.

Answer 184

• reabsorption of water and mineral ions. (1/2) Storage and formation of undigested waste ready for elimination (1/2)

Question 185

The thickness of the main muscular chamber walls of left and right ventricle vary significantly.
In terms of the function they perform, provide reasons for this.

Answer 185

• the left ventricle has a much thicker muscular wall than the right ventricle(1/2
• the left side is responsible for pumping oxygenated blood to tissues trhoughout the body/ high pressure needed (1)
• right ventricle only pumps deoxygenated blood to the lungs/ less pressure (1/2)

Question 186

.Explain why most multicellular organisms need a transport system, whereas unicellular
organisms do not.

Answer 186

Unicellular organisms
- large SA:Vol ratio
- Entire cell is in contact with environment/ allows exchange of materials as molecules can be exchanged rapidly without a transport system.

Multicellular organism
- Low SA:Vol ratio
- Transport system delivers and removes molecules (e.g. nutrients, gases and wastes) rapidly to and from all cells
- So relying on exchange by diffusion would be inefficient as most cells are at a distance from the environment.

Question 187

Tasc pp 2019 q19b
Scientists investigated the movement of organic substances in four plants, A, B, C and D.
One leaf from each plant was supplied with carbon dioxide containing the radioactive isotope of
carbon, 14C.
Figure 1 shows the general setup for the plants.
Figure 1
Each plant was treated differently before it was
supplied with the radioactive isotope.
* Plant A – ringed at position X
* Plant B – ringed at position Y
* Plant C – ringed at position X and at position Y
* Plant D – not ringed
b. All four plants were kept in bright light for one hour. Explain why.

Answer 187

Bright light initiates an increase in photosynthesis (1), so that the radioactive carbon can be captured quickly and tracked to see the effects of ring barking. Photosynthesis produces glucose which captures the C-14 in its product, glucose.(1) This is then moved by translocation ot other parts of the plant where it may be needed. (1)

Question 188

Tasc 2019 pp q19c
Scientists investigated the movement of organic substances in four plants, A, B, C and D.
One leaf from each plant was supplied with carbon dioxide containing the radioactive isotope of
carbon, 14C.
Figure 1 shows the general setup for the plants.
Figure 1
Each plant was treated differently before it was
supplied with the radioactive isotope.
* Plant A – ringed at position X
* Plant B – ringed at position Y
* Plant C – ringed at position X and at position Y
* Plant D – not ringed

After one hour:
0.00
Position X
0.34
3.04 (leaf with CO2)
Position Y
0.44

Which plant, A, B, C or D, is shown in Figure 2?
Explain your answer fully, including why the other treatments were not selected in your answer.

Answer 188

• Plant A (1)- The C-14 is tracked above the leaf to just below position X(0.34) and below the leaf to the root (0.44). It does not appear above position X (0.00). This indicates that the ring barking must have caused a disruption to translocation process as the phloem vessels at position X have been damaged/ cut off (11/2 marks)
• Plant B- position Y- no C-14 would have occurred in the root but would have occurred to the stem apex (1/2 mark)
• Plant C- ringed at position X and position Y- no C-14 would have been tracked above or below X and Y (1/2 amrk)
• Plant D- no ringing- C-14 would have been found in all parts of the plant. Ringbarking stops the flow of sugar (C-14) via translocation (1/2 mark)

Question 189

Tasc 2019 pp q20b
The graph shows the relationship between the level of anti-diuretic hormone (ADH) in the
bloodstream (arbitrary units) with the rate of urine production in the kidney (ml/min).

b. Describe the relationship between ADH levels in the bloodstream and the rate of urine
production?

Answer 189

As the level of ADH increases (7-22 units), the rate of urine production decreases (2.1- 1.3 ml/min)
As the ADH level decreases (22-7 units), the rate of urine production increases (1.3-2.1 ml/min)
When the rate of urine production remains constant (2/1 ml/min), the level of ADH also remain constant (7 units)

Question 190

Tasc 2019 pp q20c
The graph shows the relationship between the level of anti-diuretic hormone (ADH) in the
bloodstream (arbitrary units) with the rate of urine production in the kidney (ml/min).
c. Describe in detail the homeostatic process that causes the change in rate of urine production as shown in this graph (details of data not required).

Answer 190

Stimulus- decrease in water content (osmotic concentration) of blood (1). Amount of water (1/2)
Receptor- osmoreceptors in the hypothalamus detect the low water content of the blood(1)
Transmission- hypothalamus signals the pitutiary gland (1/2) to release more ADH into the blood stream (1/2)
Effector- kidney collecting tubules (1/2( in nphron become more permeable to water (1/2)
Response- more water is reabsorbed by kidney tubules and less urine is produced/ the urine is more concentrated (1/2)
The process of decreasing the stimulus to maintain homeostasis is an example of negative feedback (1/2)

Question 191

Identify and explain four ways in which the structure of a capillary assists in its function to
exchange substances between blood and the surrounding tissue. (6 marks)

Answer 191

1. Thin cell walls/ one cell thick- allow exchange of substances (gases/ nutrients/ wastes) to easily and quickly diffuse/ pass through them to the cells OR very selectively pemeable enabling substances to diffuse quickly
2. Moist surfaces- ions already dissolved allows for diffusion across the membrane
3. Large network of capillaries- (large SA:V ratio)- allows maximum exchange as capillaries near all cells due to huge SA. Or able to build networks to increase delivery and remove water by increasing SA around tissue/ increasing exchange rates.
4. Ability to become leaky- for effective fighting invades/ rapid rate of diffusion to affected areas.
5. Thin bore- only allowing one red blood cell through at any time which increases diffusion of gases from blood to tissue (short distance of diffusion)
6. Vasodilation/ constriction- increase/decrease permeability

Question 192

This table below shows the percentages of gases in air inhaled and exhaled by humans.
Gas Inhaled air Exhaled air
(% volume) (% volume)
Oxygen 20.95 16.40
Carbon dioxide 0.04 4.10
Nitrogen 79.01 79.50
Water (vapour) humidity dependent saturated

Compare the quantities of the different gases for inhaled and exhaled air in the
table above. Interpret the data based on your understanding of respiration and
explain any links that appear to exist between the gases. (4 marks)

Answer 192

Oxygen percentages drop by over 4% as this is being used in the body for aerobic
respiration (1), this is equivalent to the increase in CO2 which is the waste product of the
same process and is to be expected (1).
Nitrogen is almost unchanged, which is to be expected as it is neither absorbed nor
excreted by the body (1).
Water vapour will normally be saturated by the time the air is breathed out as the
exchange surfaces in the lungs have to be moist for gas exchange to take place (1).

Question 193

This table below shows the percentages of gases in air inhaled and exhaled by humans.
Gas Inhaled air Exhaled air
(% volume) (% volume)
Oxygen 20.95 16.40
Carbon dioxide 0.04 4.10
Nitrogen 79.01 79.50
Water (vapour) humidity dependent saturated

The average set of lungs is estimated as having around 375 million tiny alveoli
with an effective gas/blood interface of around 100 m2 in area and a mean wall
thickness of less than 1 mm. Explain why this is a highly effective combination for
gas exchange. (3 marks)

Answer 193

The amount of gas exchange depends on the rate of diffusion and the surface area that it
is exchanged over (1). 375 million alveoli (with high SA: V ratio) means a very large
surface area for gas exchange to occur across (1). Having less than 1mm thickness
between the blood in the capillaries and air in the alveoli means a small diffusion distance,
creating a rapid rate of diffusion (1).

Question 194

Explain the action of ADH and why this is important in the regulation of blood
concentrations. (3 marks)

Answer 194

) ADH is important in regulating blood concentration. If blood concentration is too high (not
enough water), then more ADH is released from the pituitary gland (1). This increases the
permeability of the collecting tubules so more water is absorbed into the blood, which brings
the blood concentration back to normal (1). This is a negative feedback mechanism for
osmoregulation (1).

Question 195

(c) State ONE way in which the Loop of Henle helps the process of excretion. (1 mark)

Answer 195

c) The loop of Henle reabsorbs water and salt, by maintaining a salt gradient.

Question 196

A: increased CO2 levels in blood
B: respiratory centre of medulla
C: Autonomic nerve impulse
D: Respiratory muscles
E: Increased breathing rate
F: Decreased Co2 levels in blood
Using the letters represented in the above sequence identify the following elements of
the homeostatic stimulus-response pathway (you may use each letter more than
once). (3 marks)

Negative feedback response:
Stimulus:
Effector:
Receptor:
Control Centre:
Message:

Answer 196

Pathway element Corresponding Letter

Negative feedback response E/F
Stimulus A/F
Effector D
Receptor B
Control Centre B
Message C

Question 197

Give TWO reasons why you would not expect a homeostatic process to keep levels perfectly constant. (2 marks)

Answer 197

If the changes happen rapidly it is more difficult for the system to adjust. (1)
Takes time for the system to respond and adjust, levels may have varied again by the time
response is enacted. (1)
Response continues until levels too low which acts as another stimulus to trigger another
response, continues to vary within a range around the norm. (1)
System requires a variation in levels to begin the adjustment process, system cannot predict
changes. (1)
The environment (stimulus) is not stable, therefore there will always be change to counteract
by the body. (1)
Varying levels of cellular respiration (aerobic or anaerobic) produces varying levels of CO2 in
the body. (1)
Varying levels of breathing and taking in various gases causes differing levels in body. (1)
Body undertaking different levels of activity will have different levels of CO2 due to different
levels of pulmonary / cellular respiration. (1)
Body requires some CO2 for concentration gradient/ maintaining blood pH levels. (1)
Body can cope with some small variation, without needing to respond. (1)
Levels of CO2 vary in the body (½).
System efficiency can be affected by disease. (½)
Too many signals can lead to one being missed (½)
System can over compensate / overshoot in response to stimulus. (½)
It is a short term response (½)
System can only do so much, levels could get too high to counteract (½)

Question 198

2018tasc pp q17b
The graph below shows the rate of water loss of a plant on a hot summer’s day
(February) and on a cool winter’s day (June). The rate of water loss is measured on a
scale from 0–6, with 0 being no water loss.
Interpret the graph above and draw a justified conclusion about why the pattern of
water loss is different in summer to that in winter. (4 marks)

Answer 198

• February (summer): there is more available light so stomata are open at 5am for photosynthesis until 10am and again from 4pm to 6pm (½). When stomata are open, a
  transpiration stream occurs leading to a water loss of 4 units (1). Thus in the hottest part of
  the day (from 10am to 4pm) stomata close to preserve water (½).
  June (winter): there is less available sunlight, so to maximise photosynthesis, stomata are open
  from 10am-4pm in the hottest part of the day (1). This is when up to 6 units of water are lost
  through transpiration (more than summer) (½), however as there is usually a high rainfall in
  winter, high rates of water loss can be maintained (½)

Question 199

Explain why ringbarking kills the plant (2 marks)

Answer 199

(ii)By removing phloem, the glucose made from photosynthesis in the leaves (½) cannot be
transported below this point to the roots (½) to be used in cellular respiration (½) for
active transport, growth and repair in roots/all cells  death.

Question 200

Explain why some turtles produce mostly ammonia, even though it is a very toxic chemical, whilst others produce uric acid (3 marks)

Answer 200

(c) – The production of ammonia uses less energy than the production of uric acid
– Conservation of water is not important for turtles living in aquatic environments and can therefore dilute ammonia quickly to non-toxic levels
– Turtles living in a desert environment produce non-toxic uric acid which is insoluble and can be excreted as a paste.
– Uric acid can accumulate in the body without causing problems
(any 3 of the above points for 3 marks)

Question 201

The internal lining of the small intestine is well suited to its function. Discuss two ways in which this lining is suitable and explain why the efficiency of the function is improved in each case. ( 2marks each)

Answer 201

villi/microvilli provide a large SA: Vol for the absorption of digested foods;
* lining only one cell thick to minimise distance products of digestion have to travel to get to the blood stream.

*	good blood supply ensuring that absorbed components are removed from villi quickly, thereby maintaining concentration gradient and so increasing rate of absorption.
*	cells contain mitochondria for the active uptake of some digested materials
*	folded intestinal lining slowed down passage of food and increased time available for absorption.

Any 2 of the above, well explained, gained 2 marks each.

Question 202

Parts of the digestive sytsem are frequently removed during surgery. For the body part removed, carefully explain the effect it would have on the functioning of the digestive system and how this effect coulc be compensated for.
- Part of the large intestine

Answer 202

(b) Possible effects: dehydration due to less absorption of water; diarrhoea; less microbial fermentation of food; reduced vitamin production by bacteria; reduced absorption of some ions; inability to store faeces. (maximum 2 marks)
Possible compensations: increased intake of water, relevant vitamins, minerals in diet; greater reabsorption of water and ions from filtrate in kidney; adjustment to the amount of fibre in diet; if only a small amount removed the remaining intestine may be able to compensate; if large amount removed a colostomy bag may be needed. (1 mark)

Question 203

c7 test 1 q2
The part of the model to the right of the line X could be used to temporarily replace part of a patient’s circulatory system whilst undergoing chest surgery. What functions would this perform? (2 marks)

Answer 203

e) pumps blood to heart and lung. This allows the uptake of O2 and removal of CO2

Question 204

C7 test q2
what structure in the body does the funnel represent?

Answer 204

Small intestine

Question 205

Lungs and leaves are organs where there is an exchange of the gases oxygen, carbon dioxide and water vapour with the environment. Explain how three structural features of each organ help in the exchange of gases. (6 marks)

Answer 205

(b) Lungs:
* Large surface area of alveolus. (½). Exchange of gases occurs across surfaces, so the larger the surface area, the more rapidly exchange will occur. (½).
* Rich blood supply in capillaries (½). The large number of capillaries maintains blood flow close to alveoli thus maintaining a high concentration gradient. This results in high levels of exchange of molecules into and out of the blood. (½) Also large surface area between capillaries and walls of alveoli (½).
* Thin membranes (½). This reduces the distance molecules must diffuse to reach or leave the blood, maintaining a high concentration gradient and so increasing efficiency of exchange. (½).
* Moist surfaces. (½). Transport of molecules is facilitated when they are in solution. (½).

PLUS

Leaves:
* Leaves contain stomata on their surface, (½) that open to allow exchange of gases, in particular CO2 in & O2 out. (½)
* Large surface area (½) of cavity inside leaf to maximize gaseous exchange. (½) OR Many long thin leaves with numerous stomata to increase surface area for exchange (1).
* Cavity inside leaf in close proximity to the cells/air spaces between the spongy mesophyll cells (½) maintains a high concentration gradient and ensuring efficient internal gaseous exchange. (½)
* The internal surface of the leaf cavity is coated in a layer of moisture (½) this allows for the dissolving of the gases. (½).

Question 206

How would total area of stomatal openings differ if the investigation was prepared on a dull day? (2 marks)

Answer 206

On a dull day the total area of open stomata would be similar but less water would be lost by evaporation Stomata may stay open to increase opportunity for CO2 uptake and max rate of photosynthesis in low light.

Question 207

In babies who suffer from a condition known as “a hole in the heart” there is a small opening in the wall between the right and left ventricle.
Such babies are often referred to as “blue babies”. Explain why.

Answer 207

(b) The best answers included three major points. These were:

*	Deoxygenated blood flowing to the right ventricle did not all go to the lungs to be re-oxygenated.
*	The oxygenated blood and deoxygenated blood mixed so that the amount of oxygenated blood flowing in the blood vessels was reduced.
*	Haemoglobin has a bluish hue in the blood vessels compared with the bright red appearance of the oxyhaemoglobin.

Question 208

Suggest why plants do not excrete nitrogenous waste products.

Answer 208

Plants are autotrophs (1/2) synthesizing their own amino acids(1/2). They synthesis exactly what is required (1/2) therefore there are no excess amnio acids in plants.

Question 209

Amphibians, such as frogs and toads, excrete their nitrogenous waste as ammonia during the tadpole phase but switch to producing urea during the adult phase. Some adult desert frogs, however excrete nitrogenous waste as uric acid.
I) Explain the difference in excretory products of tadpoles and adults amphibians (3 marks)

Answer 209

Tadpoles produce ammonia which is very soluble (1/2) and very toxic (1/2). However, because they live in freshwater there is plenty of available water (1/2) to flush out this toxic waste product. On land there is less available water (1/2) and so adult frogs convert ammonia to urea which is less soluble and less toxic (1/2) therefore it can accumulate before being flushed out.

Question 210

Amphibians, such as frogs and toads, excrete their nitrogenous waste as ammonia during the tadpole phase but switch to producing urea during the adult phase. Some adult desert frogs, however excrete nitrogenous waste as uric acid.
Explain the benefit to desert frogs of excreting uric acid.

Answer 210

Uric acid is insoluble and non-toxic (1/2) so it can accumulate and be excreted as a paste, conserving water (1/2).

Question 211

The carbon dioxide concentration of human blood is controlled by homeostatic mechanisms. Part of this process is illustrated in the diagram below.
Exercise-> increased blood CO2 concentration-> decreased blood pH-> monitored by the aorta and the carotid arteries in the neck-> nervous impulse sent from medulla oblongata of the brain to pacemaker of heart, increasing heart rate.
q19) With reference to this example, identify and describe the key aspects of homeostatic mechanisms in organisms in general.

Answer 211

• The stimulus (1/2) was increase concentration of CO2 in the blood or a decrease in pH of the blood (1/2) or exercise (1/2).
• This change is registered by receptors (1/2) in aorta or carotid arteries (1/2)
• Communication or message or nervous impulse (1/2) between receptors and effector is by means of nerves.
• The effector (1/2) is the pacemaker in the heart or the heart (1/2)
• An increase in CO2 in blood as registered by the receptors results in more nervous impulses from the medulla causing the pacemaker of the heart to [increase the heart rate(1/2].
• The increase in the heart rate is the response (1/2) and when blood is pumped more quickly to the (lungs, CO2 will be expelled more quickly or CO2 will diffuse from the alveoli (1/2)).
• Because the response removes the original stimulus the control centre decreases nervous stimulation (1/2) of the cardiac pacemaker, this is an example of homeostasis by negative feedbackk (1/2).

Question 212

A ventricular septal defect is a hole in the septum of the heart. The diagram below shows a heart with VSD.
b) Patients with this disease are often tired and have thickened ventricles. Explain why patients would have these symptoms. (2 marks)

Answer 212

The hole in the septum means that oxygenated and deoxygenated blood will mix (1).
Therefore, blood going to the body will not be fully oxygenated (½),
decreasing/lowering the rate of aerobic respiration causing tiredness (½). The heart
will try and pump blood faster to get more oxygen to the body (½), making the
ventricles work more and thus making them thicker (½).

Question 213

The following table shows concentrations of four (4) substances in various parts of the kidney and renal system.

Substance Conc. Conc. Conc.
Plasma Filtrate urine
(Bowman’s
Capsule)

A 5.0 5.0 0.0
B 5.0 5.0 30.0
C 2.5 0.0 0.0
D 2.5 0.0 1.0

Use the information provided above to answer the following questions.
a) Explain why substance A is absent from the urine even though it has been totally filtered across the glomerulus? (2 marks)

Answer 213

a) It has been reabsorbed back into the blood in the nephron. It might be sugars or nutrients which are small enough to go through the filter but needed by the body so reabsorbed

Question 214

The following table shows concentrations of four (4) substances in various parts of the kidney and renal system.

Substance Conc. Conc. Conc.
Plasma Filtrate urine
(Bowman’s
Capsule)

A 5.0 5.0 0.0
B 5.0 5.0 30.0
C 2.5 0.0 0.0
D 2.5 0.0 1.0

Use the information provided above to answer the following questions.
c) What is the most likely reason for the inability to filter substance C? (2marks)

Answer 214

c) It would be a large molecule and could not go through the filtration. This would include things like haemoglobin.

Question 215

d) Why is it so important that mechanical breakdown occurs earlier in the digestive system? (2 marks)

Answer 215

d) To ensure food in broken down to small enough particulars to absorb into the blood. This way it is broken down before reaching place of absorption instead of trying to do it all at the one site which would be slower.

Question 216

c) Briefly detail two structural adaptations in the small intestine that are important in assisting one of the processes that you named in part b) above. (2 marks)

Answer 216

c) Large SA: V due to villi extending out into small intestine. Large blood supply right to the surface of small intestine to facilitate nutrients absorbing across.

Question 217

The following table summaries information about five animals.
Animal Conc. urea Length of Period of longest
in urine intestine activity
B High Short Night
C High Short Day
D Low Short Night
E Low Short Day
Which animal is most likely to be a desert dwelling carnivore? (2 marks)
Briefly explain your choice.

Answer 217

B high urine conc. Means retention of water. Greatest activity time is at night when cooler. Short digestive track means it is carnivore as proteins are easily digested.

Question 218

Lungs and leaves are organs where there is an exchange of the gases oxygen and carbon dioxide with the environment.
Explain how three adaptations shared by both organs enable the efficient exchange of gases. (6 marks)

Answer 218

Adaptation ( ½ ) how it contributed to efficient gas exchange ( ½ ) in animals ( ½ ) and in plants ( ½ ) for each
of three adaptations.
Lungs (Max 3 marks) Leaf (Max 3 marks)
Large SA :V Large surface area of alveolus. (½).
Exchange of gases occurs across
surfaces, so the larger the surface
area, the more rapidly exchange will
occur. (½).
Large surface area (½) of cavity
inside leaf to maximize gaseous
exchange. (½) OR Many long thin
leaves with numerous stomata to
increase surface area for exchange
(1).
Moist Environment Gases dissolved in water (1/2) are
more exchanged more readily into
the cells (1/2). Animals do this by
having their lungs inside their body
(1/2) or by having a moist ling to
the lungs (1/2)
Similarly the inside of the leaf is
kept moist (1/2) due to the
transpiration of water vapour out
of the stomata.
Thin exchange membrane Thin membranes (½). This reduces
the distance molecules must diffuse
to reach or leave the blood,
maintaining a high concentration
gradient and so increasing efficiency
of exchange. (½).
Cavity inside leaf in close proximity
to the cells/air spaces between the
spongy mesophyll cells (½)
maintains a high concentration
gradient and ensuring efficient
internal gaseous exchange. (1)
Maintenance of a concentration
gradient OR short distance for
gases to diffuse
Rich blood supply in capillaries (½).
The large number of capillaries
maintains blood flow close to alveoli
thus maintaining a high
concentration gradient. This results
in high levels of exchange of
molecules into and out of the
blood. (½)
The close proximity between air
spaces and cells using the gases for
photosynthesis along with the
numerous stomata on their surface,
(½) that open to allow exchange of
gases, in particular CO2 in & O2
out. (½)

Question 219

Compare the concentration of the substances in the blood before flowing into the kidney to the concentration of the substances in blood flowing out of the kidney.
Urea
Oxygen
Carbon dioxide
Glucose

Answer 219

higher
higher
lower
slightly higher/ same

Question 220

Briefly discuss one adaptation you would expect to find in the digestive systems of animals which feed on:
blood from other animals.

Answer 220

Blood from other animals: 1 mark for appropriate feature and 1 mark for
explanation. Correct answers include but are not limited to:
* A very simple gut with only a small and short large intestine since blood is a
very easy substance to digest.
* The components of blood already contain products from digestion and other
components would only need simple processing.
No fibre or larger molecules requiring complex digestion.
* Sharp mouthpiece for penetrating skin.

Question 221

A patient complains of diarrhoea (watery faeces). It is concluded that part of the digestive system is not functioning properly. Which organ in the diagram is most likely causing the problem? Provide reasons for your choice.

W=LIVER
X= STOMACH
Y= PANCREAS
Z= LARGE INTESTINE

Answer 221

Z the large intestine, colon or small intestine (1 mark for 1 any), which is mostly responsible
for the absorption of water in preparation for excretion of faeces in normal circumstance.
In this case not enough water is being absorbed (1).