Organisms exchange substances with their enviroment Flashcards
What is the relationship between the size of an organism and its surface area to volume ratio (SA:V)?
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.
Why do small organisms have a high surface area to volume ratio?
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.
How does surface area to volume ratio affect the efficiency of diffusion?
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.
How do larger organisms compensate for a low surface area to volume ratio?
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.
Give examples of adaptations that larger organisms use to overcome the limitations of a low SA:V.
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.
What is the relationship between surface area to volume ratio and metabolic rate?
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.
Why do small organisms with a high SA:V need to have a high metabolic rate?
To generate enough heat and maintain their internal body temperature because they lose heat rapidly due to their high SA:V.
How does body shape affect surface area to volume ratio?
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.
How do single-celled organisms carry out gas exchange?
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.
What adaptations allow single-celled organisms to efficiently exchange gases?
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.
How does gas exchange occur in insects?
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.
How is the tracheal system adapted for efficient gas exchange?
Extensive branching increases surface area.
Short diffusion distance to cells.
Spiracles can close to prevent water loss.
How does counter-current flow improve gas exchange in fish?
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.
What adaptations of fish gills improve gas exchange?
Large surface area provided by gill filaments and lamellae.
Thin lamellae ensure a short diffusion distance.
Counter-current system maintains a concentration gradient.
How does gas exchange occur in the leaves of dicotyledonous plants?
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.
How do xerophytes reduce water loss while allowing gas exchange?
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
How do terrestrial insects reduce water loss?
Closing spiracles when inactive.
Waxy cuticle to prevent water evaporation.
Small surface area to volume ratio to reduce water loss.
What are the key structures in the human gas exchange system?
Trachea – Air passage with cartilage rings.
Bronchi – Branches that carry air to the lungs.
Bronchioles – Smaller tubes controlling airflow.
Alveoli – Site of gas exchange.
How are alveoli adapted for efficient gas exchange?
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.
What happens during inspiration?
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.
What happens during expiration?
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.
What is the antagonistic interaction between internal and external intercostal muscles?
External intercostal muscles contract during inspiration, while internal intercostal muscles contract during forced expiration, ensuring smooth and efficient ventilation.
How does lung disease affect gas exchange?
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.
How does smoking increase the risk of lung disease?
Tar: Damages cilia, leading to mucus buildup and infections.
Carcinogens: Increase risk of lung cancer.
Carbon monoxide: Reduces oxygen-carrying capacity of blood.
What is the difference between correlation and causation in studies on lung disease?
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.
How has experimental data on smoking and pollution led to statutory restrictions?
Smoking bans in public places.
Regulation of industrial emissions.
Health warnings on cigarette packaging.
What should you look for when interpreting data on lung disease?
Identify trends or correlations.
Look for control groups and sample size.
Consider possible confounding variables.
What are the major risk factors for developing lung disease?
Smoking.
Air pollution.
Genetic predisposition.
Occupational hazards (e.g., asbestos exposure).
What happens to large biological molecules during digestion?
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.
How are carbohydrates digested by amylase?
Salivary amylase: Begins starch digestion in the mouth, hydrolysing starch into maltose.
Pancreatic amylase: Continues starch digestion in the small intestine.
How do membrane-bound disaccharidases complete carbohydrate digestion?
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.
How are lipids digested by lipase?
Lipase: Produced in the pancreas and acts in the small intestine.
Hydrolyses triglycerides into monoglycerides and fatty acids.
What is the role of bile salts in lipid digestion?
Emulsify large lipid droplets into smaller droplets, increasing surface area for lipase action.
Aid in the formation of micelles, which facilitate absorption of lipids.
What types of enzymes hydrolyse proteins?
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.
How do endopeptidases aid in protein digestion?
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).
What is the role of exopeptidases in protein digestion?
Hydrolyse peptide bonds at the ends of polypeptides.
Release single amino acids or dipeptides.
Act on the terminal amino acids of peptide chains.
How do dipeptidases contribute to protein digestion?
Membrane-bound enzymes on the epithelial lining of the ileum.
Hydrolyse dipeptides into individual amino acids for absorption.
How are monosaccharides absorbed in the ileum?
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.
How are amino acids absorbed across the ileum?
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.
How does the sodium-potassium pump maintain the concentration gradient for co-transport?
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.
What is the role of micelles in lipid absorption?
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.
What happens to lipids after they are absorbed into epithelial cells?
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.
How do chylomicrons enter the bloodstream?
Chylomicrons move from the lacteals into the lymphatic system.
They are eventually released into the bloodstream via the thoracic duct.
What is an important exam tip when describing enzyme action in digestion?
Always specify the substrate, product, and where the enzyme acts.
Use correct enzyme names and mention membrane-bound enzymes where applicable.
What should you consider when interpreting experimental data on digestion and absorption?
Identify control groups and variables.
Consider the role of enzymes, pH, and temperature.
Look for trends and anomalies in the data.
How does pH affect the activity of digestive enzymes?
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.
Why is bile important for lipid digestion?
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.
What is the key principle behind co-transport in the ileum?
Sodium ions move down their concentration gradient into epithelial cells.
This drives the uptake of glucose, galactose, and amino acids against their concentration gradient.
What is the structure of haemoglobin?
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.
What is the role of haemoglobin in oxygen transport?
Haemoglobin binds oxygen in the lungs to form oxyhaemoglobin.
It releases oxygen in tissues where it’s needed.
Where does haemoglobin load and unload oxygen?
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.
What does the oxyhaemoglobin dissociation curve show?
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.
How does cooperative binding affect oxygen loading?
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.
What is the Bohr effect?
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.
How are haemoglobins adapted in different organisms?
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.
What is the general pattern of blood circulation in mammals?
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.
Name the major blood vessels entering and leaving key organs.
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).
What are the key structures of the human heart?
Atria: Receive blood from veins.
Ventricles: Pump blood into arteries.
Valves: Prevent backflow (atrioventricular and semilunar valves).
What are the stages of the cardiac cycle?
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.
How do valves ensure unidirectional blood flow?
Atrioventricular valves: Close during ventricular systole to prevent backflow into atria.
Semilunar valves: Close during diastole to prevent backflow from arteries.
How do pressure and volume changes occur during the cardiac cycle?
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.
How is the structure of arteries adapted to their function?
Thick muscle layer: Resists high pressure.
Elastic tissue: Allows recoil to maintain blood flow.
Narrow lumen: Maintains high pressure.
How do arterioles control blood flow?
Thicker muscle layer: Allows constriction or dilation to regulate blood flow to tissues.
Less elastic tissue than arteries as blood pressure is lower.
How is the structure of veins adapted to their function?
Thin walls: Low pressure.
Wide lumen: Reduces resistance to blood flow.
Valves: Prevent backflow of blood.
How are capillaries adapted for exchange?
Thin walls (one cell thick): Short diffusion distance.
Narrow lumen: Slows blood flow for maximum diffusion.
Large network: Provides a large surface area.
How is tissue fluid formed?
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.
How is tissue fluid returned to the circulatory system?
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.
What are the key risk factors for CVD?
High blood pressure.
Smoking.
High cholesterol.
Obesity and lack of exercise.
Genetic factors.
What is the difference between correlation and causation in CVD studies?
Correlation: Shows a relationship between two factors.
Causation: Demonstrates that one factor directly affects another.
How can conflicting evidence affect conclusions about CVD risk factors?
Different studies may produce inconsistent results.
Consider sample size, methodology, and potential biases.
What should you consider when evaluating experimental data on CVD?
Look for control groups and sample sizes.
Identify potential confounding variables.
Consider the reliability and validity of the data.
What should you look for when interpreting graphs of the cardiac cycle?
Identify where valves open and close.
Recognize changes in ventricular and atrial pressure.
Understand the relationship between pressure, volume, and valve movement.
How do statins reduce the risk of cardiovascular disease?
Statins reduce blood cholesterol levels.
Lower cholesterol reduces the risk of atheroma formation and blockages.
What is the structure and function of xylem tissue?
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.
What is the cohesion-tension theory?
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.
How does transpiration drive water movement in the xylem?
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.
How does adhesion contribute to water movement in plants?
Water molecules stick to the walls of the xylem.
Adhesion helps counteract gravity and maintain the water column.
What factors affect the rate of transpiration?
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.
What is the structure and function of phloem tissue?
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.
What is the mass flow hypothesis?
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.
What are the three main stages of the mass flow hypothesis?
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.
What evidence supports the mass flow hypothesis?
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.
How do tracer experiments provide evidence for translocation?
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.
What do ringing experiments demonstrate?
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.
What do aphid experiments reveal about phloem transport?
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.
What evidence challenges the mass flow hypothesis?
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.
How is active transport involved in loading sucrose into phloem?
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.
How do we distinguish between correlation and causation in plant transport studies?
Correlation: Shows a relationship between two variables (e.g., increased sucrose leads to increased mass flow).
Causation: Demonstrates that one variable directly influences another.
What factors should be considered when evaluating evidence for mass flow?
Methodology of experiments.
Alternative explanations for observed data.
Limitations of the mass flow hypothesis, such as variable solute movement rates.
What are the differences between xylem and phloem?
Xylem:
Dead cells, transports water and minerals.
Movement is one-way (upwards).
Phloem:
Living cells, transports organic substances.
Movement is bidirectional (source to sink).
How do environmental factors affect xylem and phloem transport?
Xylem: Affected by light, humidity, temperature, and wind.
Phloem: Affected by metabolic demand at the sink and photosynthetic rate at the source.
What is the role of companion cells in phloem transport?
Provide ATP for active transport of sucrose.
Maintain the metabolic functions of sieve tube elements.
What is the function of sieve plates in phloem?
Perforated structures allowing solute movement between sieve tube elements.
Help regulate the flow of phloem sap.
What experimental evidence supports the cohesion-tension theory?
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.
What should you look for when interpreting data on xylem and phloem?
Identify patterns in transpiration rates or mass flow.
Distinguish between source and sink regions.
Recognize evidence from tracer and ringing experiments.
How does water potential affect xylem and phloem transport?
Xylem: Water moves down a water potential gradient from roots to leaves.
Phloem: Water enters sieve tubes by osmosis, generating pressure for mass flow.
How do sinks affect the direction of translocation in phloem?
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.
