Topic 3 - Organisms exchange substances with their environment

Question 1

Describe the relationship between the size of an organism or structure and its surface area to volume ratio

Answer 1

The smaller the size of the organism; the higher the SA:V ratio

Question 2

What things need to be transferred between an organism and its environment

Answer 2

Energy
Gasses
Nutrients
Water
Waste products

Question 3

How is surface area to volume ratio calculated?

Answer 3

Dividing total surface area of an object by its volume

Question 4

What is Fick’s law?

Answer 4

States that rate of diffusion of a substance through a medium is directly proportional to the concentration gradient

Question 5

What are the features of specialised exchange surfaces?

Answer 5

Large surface area
Thin membranes
Rich blood supply
Selective permeability
Moist environment

Question 6

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

Answer 6

The greater the SA:V ratio, the greater the metabolic rate.

Question 7

How do single celled organisms exchange substances?

Answer 7

Through diffusion, osmosis and active transport

Question 8

How do insects reduce water loss?

Answer 8

Waxy cuticle
Closed spiracles
Tracheal system (reduces need for moist respiratory surface)
Reduced surface area

Question 9

How are insects adapted for efficient gas exchange?

Answer 9

• Tracheal System: Insects have a network of branching tubes called tracheae that extend throughout their bodies. These tracheae open to the outside through small openings called spiracles, located along the insect’s body segments.
• Spiracles: Spiracles are openings on the surface of the insect’s exoskeleton that allow air to enter and exit the tracheal system. They can be opened or closed by specialized muscles to regulate gas exchange and minimize water loss.
  -Tracheoles: The tracheae branch into smaller tubes called tracheoles, which penetrate individual cells and tissues. Tracheoles come into close contact with the insect’s cells, allowing for the efficient exchange of gases directly between the tracheoles and the cells
• Muscular Movements: Insects use muscular movements to ventilate their tracheal system, facilitating the exchange of gases. For example, some insects actively pump their abdomens to move air in and out of their spiracles.

Question 10

What three ways do respiratory gases move in and out of the tracheal system?

Answer 10

Passive diffusion
Muscular movements
Mass flow

Question 11

How are fish adapted for efficient gas exchange?

Answer 11

Gills - Filaments and lamellae which provide a large surface area for gas exchange
Countercurrent exchange - Water flow runs in opposite direction to blood flow in capillaries of gill lamellae. Maintains steep conc gradient
Constant water flow - Actively swimming or using mechanisms such as buccal pumping to ensure a constant supply of oxygen rich water

Question 12

Explain countercurrent and parallel flow

Answer 12

In countercurrent flow, the two substances (e.g., blood and water) flow in opposite directions relative to each other. This arrangement creates a steep concentration gradient along the exchange surface, resulting in continuous diffusion and maximal transfer of substances from one fluid to the other. Countercurrent flow maintains a favorable concentration gradient over the entire length of the exchange surface, optimizing the efficiency of exchange.
Parallel flow involves the two substances flowing in the same direction along the exchange surface. While still facilitating exchange, parallel flow generally results in a less steep concentration gradient compared to countercurrent flow, reducing the overall efficiency of exchange.

Question 13

Explain how plants adapted for efficient gas exchange

Answer 13

Waxy cuticle
Open and close stomata
Spongy mesophyll
Large SA:V ratio

Question 14

Describe how the stomata open and close

Answer 14

At night, no sunlight means no photosynthesis can occur. Guard cells keep stomata closed.
Water Movement: As water enters the guard cells, they become swollen and bow-shaped, exerting pressure on the surrounding epidermal cells. This pressure causes the guard cells to bulge outward, resulting in the opening of the stomatal pore.

Question 15

What adaptions do xerophytic plants have to try and limit water loss

Answer 15

Reduced leaf surface area
Waxy and thick cuticle
Sunken stomata
Hairy coverings

Question 16

Describe the human gas exchange system

Answer 16

Trachea - Large tube, allows air to pass to and from the lungs
Bronchioles - Small airways that branch off from the bronchi and lead to the alveoli
Alveoli - Tiny air sacs where gas exchange occurs
Capillary - Networks of capillaries surround the alveoli. tiny blood vessels that allow for the exchange of gases between the blood and the air.

Question 17

Can you describe what happens during ventilation? (inhalation)

Answer 17

During inhalation, the diaphragm and external intercostal muscles contract. This causes the diaphragm to flatten and the rib cage to expand. As a result, the volume of the thoracic cavity increases, and the pressure inside the lungs decreases. This decrease in pressure creates a pressure gradient, causing air to flow into the lungs from the higher pressure outside the body.

Question 18

Can you describe what happens during ventilation? (Exhalation)

Answer 18

Exhalation : relaxation of the diaphragm and external intercostal muscles. As these muscles relax, the diaphragm moves back to its dome-shaped position, and the rib cage returns to its resting position. This decreases the volume of the thoracic cavity, which increases the pressure inside the lungs. The higher pressure in the lungs relative to the outside environment causes air to flow out of the lungs

Question 19

How do you calculate pulmonary ventilation rate?

Answer 19

Pulmonary Ventilation Rate = Tidal Volume × Respiratory Rate

Question 20

How are the alveoli adapted for efficient gas exchange?

Answer 20

Walls one cell thick - Short diffusion pathway to the capillary
Large suface area - numerous tiny sacs
Rich blood supply - constant supply of deoxygenated blood
Moist Environment - Helps gases dissolve and facilitates their diffusion across the membrane.

Question 21

What is the difference between correlation and causation?

Answer 21

Correlation describes a relationship between two variables, while causation describes the direct influence of one variable on another.

Question 22

What are some risk factors for lung disease?

Answer 22

Smoking
Air pollution
Exposure to carcinogens
Exposure to radon gas

Question 23

Pulmonary fibrosis is a lung disease that causes the epithelium of the lungs to become irreversibly thickened and leads to reduced elasticity of the lungs. What symptoms would arise and why?

Answer 23

Shortness of breath - Longer diffusion pathway due to thickened epithelium, more difficult to diffuse into bloodstream
Weakness and fatigue - Reduced oxygenated blood supply.

Question 24

Describe how starch is digested by amylase and membrane bound disaccharides.

Answer 24

Amylase catalyses hydrolysis of starch into maltose.
Maltase catalyses hydrolysis of maltose into glucose

Question 25

Describe how lactose and sucrose are digested

Answer 25

Lactose hydrolysed into glucose and galactose by the enzyme lactase
Sucrose hydrolysed into glucose and fructose by the enzyme sucrase

Question 26

Describe the digestion of lipids

Answer 26

Triglycerides hydrolysed by lipase (breaking ester bonds) into 2 fatty acids and a mono glycerol
Large droplets of triglycerides form, which are then emulsifier by bile and phospholipids into small droplets.
A micelle forms, consisting of phospholipids and bile salts on the outside, with triglycerides, cholesterol and lipase on the inside.

Question 27

Describe the digestion of proteins in mammals

Answer 27

Polypeptide chains
Endopeptidases hydrolyse inner peptide bonds, producing more ends.
Terminal (end) peptide bonds hydrolysed by exopeptidases, leaving
dipeptides.
Dipeptidases hydrolyse dipeptides, leaving amino acids ready for absorbsion

Question 28

Explain how co transport allows the absorption of amino acids

Answer 28

• The sodium potassium pump actively transports sodium ions out of the epithelial cell using ATP
• This creates a low concentration of Na+ inside the cell, allowing for facilitated diffusion of sodium ions, amino acids and monosaccharides enter the cell with them via co transport.

Question 29

Explain how triglycerides are absorbed

Answer 29

• Mono-glycerol and fatty acids enter epithelial cells via simple diffusion
• Once inside cell, triglycerides are resynthesised by smooth endoplasmic reticulum, which maintains a concentration gradient
• TG’s packaged into lipoprotein shell called chylomicron by RER
• Packaged into vesicle by golgi apparatus
• Exocytosis moves vesicle out of cell

Question 30

What is the function of haemoglobin

Answer 30

• Binds to oxygen to form oxyhaemoglobin.
• Transports oxygen via blood from lungs to tissues

Question 31

What is the structure of haemoglobin

Answer 31

Intricate arrangement of amino acids in the primary structure, their folding into secondary structures, alpha and beta chains fold into specific globular shapes, the 2 alpha and 2 beta chains become a heme group and arrange together

Question 32

What are the differences between haemoglobin’s in different organisms and what are the reasons for these differences?

Answer 32

Differences in subunit composition are often related to the specific oxygen-carrying needs of each organism.

Hemoglobins can exhibit different affinities for oxygen, influencing their ability to bind and release oxygen in response to varying oxygen concentrations. Organisms living in high-altitude environments, for example, may have hemoglobins with higher oxygen affinity to facilitate oxygen uptake in low-oxygen conditions.

Question 33

What is meant by loading and unloading of oxygen

Answer 33

Loading of Oxygen: In the lungs, oxygen diffuses from the alveoli into the bloodstream, where it binds to hemoglobin molecules within red blood cells. This binding occurs in regions of high oxygen concentration, facilitated by the partial pressure of oxygen
Unloading : The unloading process is facilitated by the partial pressure of oxygen gradient between the blood and the tissues.

Question 34

What are the main features of an oxygen dissociation curve?

Answer 34

• Sigmoidal curve
• Steep portion represents the transition from partially saturated to fully saturated hemoglobin as oxygen partial pressure decreases in tissues.
• Plateau represents the high affinity of hemoglobin for oxygen in the lungs, where oxygen partial pressure is high, ensuring efficient loading of oxygen onto hemoglobin.

Question 35

What does a shift to the left mean?

Answer 35

A shift to the left indicates an increase in hemoglobin’s affinity for oxygen.
Hemoglobin with increased affinity for oxygen binds oxygen more tightly and releases it less readily.

Question 36

What does a shift to the right mean?

Answer 36

A shift to the right indicates a decrease in hemoglobin’s affinity for oxygen.
Hemoglobin with decreased affinity for oxygen binds oxygen less tightly and releases it more readily.

Question 37

Describe the general pattern of blood circulation in a mammal

Answer 37

Deoxygenated blood from body returns to right atrium via vena cava, pumped to right ventricle, walls contract and pump blood out via the pulmonary artery to the lungs
Oxygenated blood reenters the heart via the pulmonary vein, to the left atrium, and left ventricle walls contract, pumping blood out of aorta to rest of body

Question 38

How does the structure of the heart relate to its function?

Answer 38

• 4 chambers allow for efficient separation between oxygenated and deoxygenated sections
• Valves ensure unidirectional blood flow through the heart, open and close in response to pressure changes
• Thick muscular walls especially in ventricles to allow for powerful contractions
• Coronary circulation ensures the heart itself receives blood supply

Question 39

How do we supply the heart muscle with oxygen?

Answer 39

The heart has its own network of blood vessels called coronary arteries and veins that supply oxygen and nutrients to the heart muscle.

Question 40

Explain the stages in the cardiac cycle and what happens at each stage?

Answer 40

Diastole - Relaxation, The atrioventricular (AV) valves (tricuspid and mitral valves) open during diastole, allowing blood to flow from the atria into the ventricles.
Systole - The atria contract to forcefully push the remaining blood into the ventricles before ventricular systole (contraction).
Atrial systole - contributes to the completion of ventricular filling, ensuring that the ventricles are adequately filled with blood before they contract.
Ventricular systole - Contraction of ventricle walls, AV valves close, semilunar valves open and blood exits via aorta

Question 41

How do you calculate cardiac output?

Answer 41

CO = HR x SV

Cardiac output (in volume per unit time, usually expressed in liters per minute)
Heart rate (number of heartbeats per minute)
Stroke volume (volume of blood pumped out by the heart with each beat, usually expressed in milliliters per beat)

Question 42

How does the structure of each blood vessel relate to the function

Answer 42

Artery - Thick, muscular walls allow arteries to withstand the high pressure generated by the forceful contractions of the heart during systole, thin lumen to maintain high pressure
Veins - Thinner muscle and elastic walls, valves to prevent backflow at lower pressures
Capillaries - One cell thin for short diffusion pathway

Question 43

Describe the formation of tissue fluid and its return to the circulatory system

Answer 43

Net movement of blood plasma out of the arteriole end of the capillary into the tissue cells,
Movement caused by differences in hydrostatic pressure
RBC’s and charged proteins remain in the capillary
Loss of plasma = loss of volume = decrease in pressure of capillary
Less H2O = decreased water potential in capillary
Therefore at the venule end, there is a net return of fluid to the capillary by osmosis

Question 44

What is transpiration?

Answer 44

Water vapour being lost through the leaves.

Question 45

What is the evidence for cohesion-tension theory?

Answer 45

• Change in the diameter of tree trunks according to the rate of transpiration. during the day, when transpiration is at its greatest, there is more tension in the xylem. this pulls the walls of the xylem vessels inwards and causes the trunk to shrink in diameter.
• When a xylem vessel is broken, water doesn’t leak out, as would be the case if it were under pressure. Instead air is drawn in, which is consistent with it being under tension
• If a xylem vessel is broken and air enters it, the tree can no longer draw up water as the continuous column is broken and so the water molecules can no longer stick together.

Question 46

How does water move through the leaf?

Answer 46

• Mesophyll cells lose water to the air spaces by evaporation due to heat supplied by the sun.
• These cells now have a lower water potential and so water enters by osmosis from neighbouring palisade mesophyll cells, and so forth, eventually reaching the xylem, which is now passing water to adjacent cells.
• Creating pulling effect from xylem (tension)

Question 47

How does water move up the xylem?

Answer 47

• Capillary action allows water to move up very thin tubes against the force of gravity.
• As water is drawn out of the top of the xylem vessels due to transpiration, more water moves up the xylem vessels by capillary action to take its place.
• Known as the transpiration pull

Question 48

What is the cohesion tension theory?

Answer 48

The transpiration pull puts the xylem under tension, that is, there is a negative pressure within the xylem, hence the name : cohesion-tension theory

Question 49

How would you use a potometer to measure water uptake?

Answer 49

• Fine capillary tube, filled with water, connected to a syringe filled with water, a plant and an air bubble.
• As water evaporates through the leaves, the transpiration pull will draw water into the stem. Causing the air bubble to move towards the plant.
• Measure how far the bubble moves in a given time, calculate rate of water uptake.

Question 50

How are root hair cells adapted for its function?

Answer 50

• Thin cell wall, shorter diffusion distance
• Large surface area, with hairs to increase SA, increase rate of absorption
• Permanent vacuole containing cell sap, more concentrated than soil water to ensure a high water potential gradient is maintained

Question 51

How are xylem vessels adapted for their function?

Answer 51

• Thick walls, strengthened by lignin to prevent the vessels collapsing
• Hollow to allow capillary action

Question 52

What is the job of the phloem?

Answer 52

Transport sugars from photosynthesis from sources to places where they can be used or stored, known as sinks.
Translocation can be in either direction, as sinks could be anywhere in the plant

Question 53

Explain the transfer of sucrose into sieve elements from photosynthesising tissue

Answer 53

• Sucrose is manufactured from the products of photosynthesis in cells with chloroplasts.
• The sucrose diffuses down a concentration gradient by facilitated diffusion from photosynthesising cells into companion cells
• Hydrogen ions are actively transported from companion cells into the spaces within cell walls using ATP
• These hydrogen ions then diffuse down a concentration gradient through carrier proteins into the sieve tube elements
• Sucrose molecules are transported along with the hydrogen ions via co transport.

Question 54

Explain the mass flow of sucrose through sieve tube elements

Answer 54

• Sucrose produced in source cell lowers the water potential, water enters via osmosis from surrounding cells/xylem. (increased hydrostatic pressure)
• Sink cells, such as respiring cells wither use up sucrose or convert it, causing a higher water potential, water leaves the cell by osmosis to surrounding cells/xylem (decreased hydrostatic pressure)
• The difference in hydrostatic pressure causes solution to be forced through the phloem.

Question 55

Explain the transfer of sucrose from the sieve tube elements into storage or sink cells.

Answer 55

• At the respiring cells (sink), sucrose is either used up during respiration or converted to starch for storage.
  These cells therefore have a low sucrose content and so sucrose is actively transported into these regions from the sieve tubes.

Question 56

Explain the use of the ringing experiment to investigate transport in plants

Answer 56

A ring of bark and phloem are peeled and removed off a tree trunk.
The result of removing the phloem is that the trunk swells above the removed section.
Analysis of the liquid in this swelling shows it contains sugar
This shows that when the phloem is removed, the sugars cannot be transported and therefore proves the phloem transports sugars

Question 57

Explain the use of the tracers to investigate transport in plants

Answer 57

• Radioactively labelled carbon dioxide provided to plant.
• Absorbed by plant and used in photosynthesis to create sugars which all contain radioactively labelled carbon.
• Thin slices from the stems are then cut and placed on x-ray film that turns black when exposed to radioactive material.
• The section of the stem containing the sugars turn black, highlighting where the phloem is and shows sugars are transported in the phloem