Organisms exchange substances with their enviroment

Question 1

What is the relationship between the size of an organism and its surface area to volume ratio (SA:V)?

Answer 1

As the size of an organism increases, its surface area to volume ratio decreases. Larger organisms have a smaller SA:V, meaning there is less surface area for exchange relative to their volume.

Question 2

Why do small organisms have a high surface area to volume ratio?

Answer 2

Small organisms have a high SA:V, which facilitates efficient diffusion of gases and nutrients directly across their body surface. This is because their small size means a large surface area relative to their volume.

Question 3

How does surface area to volume ratio affect the efficiency of diffusion?

Answer 3

A high SA:V allows for faster diffusion of substances, while a low SA:V slows down diffusion, making it insufficient to meet the metabolic needs of larger organisms.

Question 4

How do larger organisms compensate for a low surface area to volume ratio?

Answer 4

Larger organisms develop specialized exchange surfaces (e.g., lungs, gills) and transport systems (e.g., circulatory system) to facilitate efficient exchange of gases and nutrients.

Question 5

Give examples of adaptations that larger organisms use to overcome the limitations of a low SA:V.

Answer 5

Lungs in mammals – Large surface area and rich blood supply for gas exchange.

Gills in fish – Thin lamellae increase surface area for efficient diffusion.

Flattened body shape – In flatworms to maximize surface area.

Villi and microvilli in intestines – Increase surface area for absorption.

Question 6

What is the relationship between surface area to volume ratio and metabolic rate?

Answer 6

Organisms with a high SA:V (small organisms) lose heat faster and have a higher metabolic rate to compensate. Larger organisms with a low SA:V lose heat more slowly and have a lower metabolic rate per unit body mass.

Question 7

Why do small organisms with a high SA:V need to have a high metabolic rate?

Answer 7

To generate enough heat and maintain their internal body temperature because they lose heat rapidly due to their high SA:V.

Question 8

How does body shape affect surface area to volume ratio?

Answer 8

More compact shapes (e.g., spherical) have a lower SA:V and reduce heat loss, while elongated or flattened shapes increase SA:V, facilitating better exchange.

Question 9

How do single-celled organisms carry out gas exchange?

Answer 9

Single-celled organisms exchange gases directly across their cell surface by diffusion. Their high surface area to volume ratio ensures efficient diffusion of oxygen in and carbon dioxide out.

Question 10

What adaptations allow single-celled organisms to efficiently exchange gases?

Answer 10

Thin cell membrane for a short diffusion distance.

Large surface area relative to volume for efficient diffusion.

Moist surface to allow gases to dissolve and diffuse easily.

Question 11

How does gas exchange occur in insects?

Answer 11

Insects use a tracheal system consisting of:

Spiracles – Openings that allow air to enter.

Tracheae – Large tubes that transport gases into the body.

Tracheoles – Fine tubes where gas exchange occurs directly with tissues.

Question 12

How is the tracheal system adapted for efficient gas exchange?

Answer 12

Extensive branching increases surface area.

Short diffusion distance to cells.

Spiracles can close to prevent water loss.

Question 13

How does counter-current flow improve gas exchange in fish?

Answer 13

Blood flows through the gill lamellae in the opposite direction to water, maintaining a steep diffusion gradient across the entire length of the gill. This ensures maximum oxygen absorption.

Question 14

What adaptations of fish gills improve gas exchange?

Answer 14

Large surface area provided by gill filaments and lamellae.

Thin lamellae ensure a short diffusion distance.

Counter-current system maintains a concentration gradient.

Question 15

How does gas exchange occur in the leaves of dicotyledonous plants?

Answer 15

Gases diffuse through the stomata, which open and close to control gas exchange.

Oxygen and carbon dioxide diffuse through air spaces in the spongy mesophyll.

Large surface area of mesophyll cells increases gas exchange efficiency.

Question 16

How do xerophytes reduce water loss while allowing gas exchange?

Answer 16

Thick cuticle – Reduces water evaporation.

Stomata in pits – Trap moist air to reduce water potential gradient.

Hairs on leaves – Reduce air movement and evaporation.

Rolled leaves – Protect stomata from wind and reduce water loss

Question 17

How do terrestrial insects reduce water loss?

Answer 17

Closing spiracles when inactive.

Waxy cuticle to prevent water evaporation.

Small surface area to volume ratio to reduce water loss.

Question 18

What are the key structures in the human gas exchange system?

Answer 18

Trachea – Air passage with cartilage rings.

Bronchi – Branches that carry air to the lungs.

Bronchioles – Smaller tubes controlling airflow.

Alveoli – Site of gas exchange.

Question 19

How are alveoli adapted for efficient gas exchange?

Answer 19

Large surface area to maximize diffusion.

Thin epithelial walls (one cell thick) for a short diffusion distance.

Rich capillary network maintains a steep concentration gradient.

Question 20

What happens during inspiration?

Answer 20

Diaphragm contracts and flattens.

External intercostal muscles contract to move the ribcage up and out.

Thoracic volume increases, reducing pressure below atmospheric pressure, drawing air in.

Question 21

What happens during expiration?

Answer 21

Diaphragm relaxes and returns to its dome shape.

External intercostal muscles relax, and ribcage moves down and in.

Thoracic volume decreases, increasing pressure above atmospheric pressure, forcing air out.

Question 22

What is the antagonistic interaction between internal and external intercostal muscles?

Answer 22

External intercostal muscles contract during inspiration, while internal intercostal muscles contract during forced expiration, ensuring smooth and efficient ventilation.

Question 23

How does lung disease affect gas exchange?

Answer 23

Fibrosis: Thickening of alveolar walls reduces diffusion efficiency.

Emphysema: Destruction of alveolar walls reduces surface area.

Asthma: Constriction of airways limits airflow and reduces gas exchange.

Question 24

How does smoking increase the risk of lung disease?

Answer 24

Tar: Damages cilia, leading to mucus buildup and infections.

Carcinogens: Increase risk of lung cancer.

Carbon monoxide: Reduces oxygen-carrying capacity of blood.

Question 25

What is the difference between correlation and causation in studies on lung disease?

Answer 25

Correlation shows a relationship between two variables, but it does not imply that one causes the other. Causation requires experimental evidence to prove one variable directly affects the other.

Question 26

How has experimental data on smoking and pollution led to statutory restrictions?

Answer 26

Smoking bans in public places. Regulation of industrial emissions. Health warnings on cigarette packaging.

Question 27

What should you look for when interpreting data on lung disease?

Answer 27

Identify trends or correlations. Look for control groups and sample size. Consider possible confounding variables.

Question 28

What are the major risk factors for developing lung disease?

Answer 28

Smoking. Air pollution. Genetic predisposition. Occupational hazards (e.g., asbestos exposure).

Question 29

What happens to large biological molecules during digestion?

Answer 29

Large biological molecules (carbohydrates, proteins, and lipids) are hydrolysed by specific enzymes into smaller molecules (monosaccharides, amino acids, and fatty acids) that can be absorbed across cell membranes.

Question 30

How are carbohydrates digested by amylase?

Answer 30

Salivary amylase: Begins starch digestion in the mouth, hydrolysing starch into maltose. Pancreatic amylase: Continues starch digestion in the small intestine.

Question 31

How do membrane-bound disaccharidases complete carbohydrate digestion?

Answer 31

Maltase: Hydrolyses maltose → 2 glucose molecules. Sucrase: Hydrolyses sucrose → glucose + fructose. Lactase: Hydrolyses lactose → glucose + galactose. These enzymes are embedded in the epithelial lining of the small intestine.

Question 32

How are lipids digested by lipase?

Answer 32

Lipase: Produced in the pancreas and acts in the small intestine. Hydrolyses triglycerides into monoglycerides and fatty acids.

Question 33

What is the role of bile salts in lipid digestion?

Answer 33

Emulsify large lipid droplets into smaller droplets, increasing surface area for lipase action. Aid in the formation of micelles, which facilitate absorption of lipids.

Question 34

What types of enzymes hydrolyse proteins?

Answer 34

Endopeptidases: Hydrolyse peptide bonds within polypeptides, creating shorter chains. Exopeptidases: Hydrolyse peptide bonds at the ends of polypeptides, releasing single amino acids. Dipeptidases: Membrane-bound enzymes that hydrolyse dipeptides into amino acids.

Question 35

How do endopeptidases aid in protein digestion?

Answer 35

Hydrolyse peptide bonds between amino acids in the middle of a polypeptide. Increase the number of free ends for exopeptidases to act on. Examples: Pepsin (stomach), trypsin (small intestine).

Question 36

What is the role of exopeptidases in protein digestion?

Answer 36

Hydrolyse peptide bonds at the ends of polypeptides. Release single amino acids or dipeptides. Act on the terminal amino acids of peptide chains.

Question 37

How do dipeptidases contribute to protein digestion?

Answer 37

Membrane-bound enzymes on the epithelial lining of the ileum. Hydrolyse dipeptides into individual amino acids for absorption.

Question 38

How are monosaccharides absorbed in the ileum?

Answer 38

Glucose and galactose: Absorbed by co-transport with sodium ions via SGLT (sodium-glucose co-transporter). Sodium ions move down their concentration gradient into epithelial cells, pulling glucose/galactose with them. Fructose: Absorbed by facilitated diffusion through GLUT transporters.

Question 39

How are amino acids absorbed across the ileum?

Answer 39

Amino acids are absorbed by co-transport with sodium ions. Sodium ions move into epithelial cells down their concentration gradient, bringing amino acids with them.

Question 40

How does the sodium-potassium pump maintain the concentration gradient for co-transport?

Answer 40

Actively transports sodium ions out of epithelial cells into the blood. This maintains a low sodium concentration inside the cell, allowing sodium ions to move in via co-transport.

Question 41

What is the role of micelles in lipid absorption?

Answer 41

Micelles contain monoglycerides, fatty acids, and bile salts. They transport lipids to the epithelial membrane. Micelles break down and release monoglycerides and fatty acids, which diffuse across the phospholipid bilayer into epithelial cells.

Question 42

What happens to lipids after they are absorbed into epithelial cells?

Answer 42

Monoglycerides and fatty acids recombine to form triglycerides in the smooth endoplasmic reticulum. Triglycerides are packaged with cholesterol and proteins to form chylomicrons. Chylomicrons are transported into the lymphatic system via lacteals.

Question 43

How do chylomicrons enter the bloodstream?

Answer 43

Chylomicrons move from the lacteals into the lymphatic system. They are eventually released into the bloodstream via the thoracic duct.

Question 44

What is an important exam tip when describing enzyme action in digestion?

Answer 44

Always specify the substrate, product, and where the enzyme acts. Use correct enzyme names and mention membrane-bound enzymes where applicable.

Question 45

What should you consider when interpreting experimental data on digestion and absorption?

Answer 45

Identify control groups and variables. Consider the role of enzymes, pH, and temperature. Look for trends and anomalies in the data.

Question 46

How does pH affect the activity of digestive enzymes?

Answer 46

Pepsin: Optimal pH of 1.5-2 in the stomach. Amylase and lipase: Optimal pH of around 7-8 in the small intestine. Enzyme activity decreases if the pH deviates from the optimum.

Question 47

Why is bile important for lipid digestion?

Answer 47

Bile emulsifies fats into smaller droplets. Increases surface area for lipase action. Neutralizes stomach acid, providing the optimal pH for lipase in the small intestine.

Question 48

What is the key principle behind co-transport in the ileum?

Answer 48

Sodium ions move down their concentration gradient into epithelial cells. This drives the uptake of glucose, galactose, and amino acids against their concentration gradient.

Question 49

What is the structure of haemoglobin?

Answer 49

Quaternary structure: Made up of 4 polypeptide chains (2 alpha and 2 beta chains). Each polypeptide contains a haem group with an iron ion (Fe²⁺) that binds oxygen.

Question 50

What is the role of haemoglobin in oxygen transport?

Answer 50

Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin. It releases oxygen in tissues where it’s needed.

Question 51

Where does haemoglobin load and unload oxygen?

Answer 51

Loading (association): In the lungs where oxygen partial pressure (ppO2) is high. Unloading (dissociation): In tissues where ppO2 is low, allowing oxygen to diffuse into cells.

Question 52

What does the oxyhaemoglobin dissociation curve show?

Answer 52

It shows the relationship between the partial pressure of oxygen and the percentage saturation of haemoglobin. The curve is S-shaped due to cooperative binding.

Question 53

How does cooperative binding affect oxygen loading?

Answer 53

Binding of the first oxygen molecule changes haemoglobin’s shape, making it easier for the next oxygen molecules to bind. This increases oxygen affinity after the first molecule binds.

Question 54

What is the Bohr effect?

Answer 54

Increased carbon dioxide concentration lowers blood pH, reducing haemoglobin’s affinity for oxygen. Oxygen is released more readily to tissues that need it during respiration.

Question 55

How are haemoglobins adapted in different organisms?

Answer 55

High altitude animals: Haemoglobin has a higher affinity for oxygen. Diving mammals: Can store more oxygen and release it gradually. Small mammals: Lower affinity for oxygen to ensure rapid release in tissues with high metabolic rates.

Question 56

What is the general pattern of blood circulation in mammals?

Answer 56

Pulmonary circulation: Blood flows from the heart to the lungs and back. Systemic circulation: Blood flows from the heart to the body and back. Coronary arteries supply oxygen to the heart itself.

Question 57

Name the major blood vessels entering and leaving key organs.

Answer 57

Heart: Pulmonary artery, pulmonary vein, aorta, vena cava. Lungs: Pulmonary artery (to lungs), pulmonary vein (from lungs). Kidneys: Renal artery (to kidneys), renal vein (from kidneys).

Question 58

What are the key structures of the human heart?

Answer 58

Atria: Receive blood from veins. Ventricles: Pump blood into arteries. Valves: Prevent backflow (atrioventricular and semilunar valves).

Question 59

What are the stages of the cardiac cycle?

Answer 59

Atrial systole: Atria contract, pushing blood into ventricles. Ventricular systole: Ventricles contract, forcing blood into arteries. Diastole: Both atria and ventricles relax, allowing blood to refill the heart.

Question 60

How do valves ensure unidirectional blood flow?

Answer 60

Atrioventricular valves: Close during ventricular systole to prevent backflow into atria. Semilunar valves: Close during diastole to prevent backflow from arteries.

Question 61

How do pressure and volume changes occur during the cardiac cycle?

Answer 61

Atrial systole: Low ventricular pressure, atria contract to increase pressure. Ventricular systole: High ventricular pressure forces blood into arteries. Diastole: Pressure falls, allowing blood to flow back into atria.

Question 62

How is the structure of arteries adapted to their function?

Answer 62

Thick muscle layer: Resists high pressure. Elastic tissue: Allows recoil to maintain blood flow. Narrow lumen: Maintains high pressure.

Question 63

How do arterioles control blood flow?

Answer 63

Thicker muscle layer: Allows constriction or dilation to regulate blood flow to tissues. Less elastic tissue than arteries as blood pressure is lower.

Question 64

How is the structure of veins adapted to their function?

Answer 64

Thin walls: Low pressure. Wide lumen: Reduces resistance to blood flow. Valves: Prevent backflow of blood.

Question 65

How are capillaries adapted for exchange?

Answer 65

Thin walls (one cell thick): Short diffusion distance. Narrow lumen: Slows blood flow for maximum diffusion. Large network: Provides a large surface area.

Question 66

How is tissue fluid formed?

Answer 66

At arterial end: High hydrostatic pressure forces plasma, nutrients, and oxygen out of capillaries into surrounding tissues. Large molecules like proteins remain in capillaries, maintaining osmotic pressure.

Question 67

How is tissue fluid returned to the circulatory system?

Answer 67

At venous end: Lower hydrostatic pressure and high osmotic pressure draw tissue fluid back into capillaries. Excess tissue fluid is drained into the lymphatic system and returned to the bloodstream.

Question 68

What are the key risk factors for CVD?

Answer 68

High blood pressure. Smoking. High cholesterol. Obesity and lack of exercise. Genetic factors.

Question 69

What is the difference between correlation and causation in CVD studies?

Answer 69

Correlation: Shows a relationship between two factors. Causation: Demonstrates that one factor directly affects another.

Question 70

How can conflicting evidence affect conclusions about CVD risk factors?

Answer 70

Different studies may produce inconsistent results. Consider sample size, methodology, and potential biases.

Question 71

What should you consider when evaluating experimental data on CVD?

Answer 71

Look for control groups and sample sizes. Identify potential confounding variables. Consider the reliability and validity of the data.

Question 72

What should you look for when interpreting graphs of the cardiac cycle?

Answer 72

Identify where valves open and close. Recognize changes in ventricular and atrial pressure. Understand the relationship between pressure, volume, and valve movement.

Question 73

How do statins reduce the risk of cardiovascular disease?

Answer 73

Statins reduce blood cholesterol levels. Lower cholesterol reduces the risk of atheroma formation and blockages.

Question 74

What is the structure and function of xylem tissue?

Answer 74

Structure: Long, hollow tubes made of dead cells. Walls reinforced with lignin to prevent collapse. Pits allow lateral water movement. Function: Transports water and minerals from roots to leaves. Provides structural support.

Question 75

What is the cohesion-tension theory?

Answer 75

Explains how water moves up the xylem. Cohesion: Water molecules stick together due to hydrogen bonding. Tension: Evaporation from leaves (transpiration) creates negative pressure, pulling water up.

Question 76

How does transpiration drive water movement in the xylem?

Answer 76

Water evaporates from the mesophyll cells and exits through stomata. Creates a water potential gradient pulling water from the roots. Maintains a continuous column of water due to cohesion.

Question 77

How does adhesion contribute to water movement in plants?

Answer 77

Water molecules stick to the walls of the xylem. Adhesion helps counteract gravity and maintain the water column.

Question 78

What factors affect the rate of transpiration?

Answer 78

Light intensity: Increases stomatal opening, increasing transpiration. Temperature: Increases kinetic energy, increasing evaporation. Humidity: Higher humidity reduces the water potential gradient, decreasing transpiration. Wind: Removes water vapor, maintaining the gradient.

Question 79

What is the structure and function of phloem tissue?

Answer 79

Structure: Sieve tube elements: Long cells with perforated sieve plates for solute movement. Companion cells: Provide ATP and support for sieve tubes. Function: Transports organic substances (sucrose, amino acids) from source to sink.

Question 80

What is the mass flow hypothesis?

Answer 80

Describes the mechanism of translocation in phloem. Source: Sucrose is actively loaded into sieve tubes, lowering water potential. Water enters by osmosis, increasing hydrostatic pressure. Sink: Sucrose is removed at the sink, increasing water potential. Water leaves by osmosis, lowering pressure, causing mass flow.

Question 81

What are the three main stages of the mass flow hypothesis?

Answer 81

Loading at the source: Active transport of sucrose into sieve tubes. Mass flow: Hydrostatic pressure gradient pushes solutes through phloem. Unloading at the sink: Sucrose diffuses out, followed by water.

Question 82

What evidence supports the mass flow hypothesis?

Answer 82

Tracers: Radioactive carbon (¹⁴C) is used to trace movement of sucrose. Ringing experiments: Removing a ring of bark disrupts phloem flow, causing sugars to accumulate above the ring. Aphid experiments: Aphids feed on sieve tubes, and analysis shows the presence of organic substances.

Question 83

How do tracer experiments provide evidence for translocation?

Answer 83

Plants are exposed to radioactive ¹⁴CO₂, which is incorporated into sucrose during photosynthesis. Autoradiographs show the movement of the radioactive label along the phloem, tracking sucrose transport.

Question 84

What do ringing experiments demonstrate?

Answer 84

A ring of bark (containing phloem) is removed from a stem. Sugars accumulate above the ring, causing swelling. Below the ring, tissues die due to lack of organic substances. Shows that translocation occurs in the phloem, not the xylem.

Question 85

What do aphid experiments reveal about phloem transport?

Answer 85

Aphids insert stylets into sieve tubes to feed on sap. When the aphid is removed, sap continues to flow due to pressure. Analysis of sap confirms the presence of sugars and organic substances.

Question 86

What evidence challenges the mass flow hypothesis?

Answer 86

Not all solutes move at the same rate. Sucrose moves to different sinks at different rates. The role of sieve plates in slowing down mass flow is not fully understood.

Question 87

How is active transport involved in loading sucrose into phloem?

Answer 87

Hydrogen ions are actively pumped out of companion cells. Creates a proton gradient that facilitates sucrose co-transport back into companion cells and sieve tube elements.

Question 88

How do we distinguish between correlation and causation in plant transport studies?

Answer 88

Correlation: Shows a relationship between two variables (e.g., increased sucrose leads to increased mass flow). Causation: Demonstrates that one variable directly influences another.

Question 89

What factors should be considered when evaluating evidence for mass flow?

Answer 89

Methodology of experiments. Alternative explanations for observed data. Limitations of the mass flow hypothesis, such as variable solute movement rates.

Question 90

What are the differences between xylem and phloem?

Answer 90

Xylem: Dead cells, transports water and minerals. Movement is one-way (upwards). Phloem: Living cells, transports organic substances. Movement is bidirectional (source to sink).

Question 91

How do environmental factors affect xylem and phloem transport?

Answer 91

Xylem: Affected by light, humidity, temperature, and wind. Phloem: Affected by metabolic demand at the sink and photosynthetic rate at the source.

Question 92

What is the role of companion cells in phloem transport?

Answer 92

Provide ATP for active transport of sucrose. Maintain the metabolic functions of sieve tube elements.

Question 93

What is the function of sieve plates in phloem?

Answer 93

Perforated structures allowing solute movement between sieve tube elements. Help regulate the flow of phloem sap.

Question 94

What experimental evidence supports the cohesion-tension theory?

Answer 94

Cut stem experiments: Water is drawn up when a stem is cut, indicating negative pressure. Bubble formation: Air bubbles break the water column, disrupting cohesion and stopping transport.

Question 95

What should you look for when interpreting data on xylem and phloem?

Answer 95

Identify patterns in transpiration rates or mass flow. Distinguish between source and sink regions. Recognize evidence from tracer and ringing experiments.

Question 96

How does water potential affect xylem and phloem transport?

Answer 96

Xylem: Water moves down a water potential gradient from roots to leaves. Phloem: Water enters sieve tubes by osmosis, generating pressure for mass flow.

Question 97

How do sinks affect the direction of translocation in phloem?

Answer 97

Sinks can change depending on the plant’s needs (e.g., growing regions or storage organs). Movement of sucrose is directed to the nearest sink with the highest demand.