Organisms exchange substances with their environment

Question 1

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

Answer 1

• Smaller organisms have a higher surface area to volume ratio.
• Larger organisms have a low surface area to volume ratio.

Question 2

How does body size and shape affect heat exchange?

Answer 2

Size;

• The rate of heat loss from organisms depends on its surface area and if it has a large volume, it’s surface area is relatively small making it more difficult for it to lease heat from it’s body.
• If organism is small its surface area is larger so heat energy is lost more easily making them need high metabolic rate in order to stay warm.

Question 3

What adaptations do some organisms have for exchange?

Answer 3

• Having flat bodies increases surface area to volume ratio so all cells have short diffusion pathway.
• Having organs that increase surface are (eg gills) meaning organisms need some sort of circulatory system to distribute oxygen to other parts of the body.

Question 4

What behavioral and physical adaptations do organisms have to aid exchange?

Answer 4

• Animals with high surface area to volume ratio lose more water as it evaporates from their surface.
• Small organisms that live in cold regions at large amounts of high energy foods to support their high metabolic rates. They also have thick layers of fur/hibernate when cold.
• Larger organisms living in hot regions have features to increase surface area allowing them to lose more heat.

Question 5

Describe gas exchange in single celled organisms:

Answer 5

• They absorb and release gases by diffusion through their outer surface.
• They have large surface area and thin diffusion pathway so there is no need for a gas exchange system.

Question 6

Describe gas exchange in fish:

Answer 6

• Water containing oxygen passes through the mouth into the gills. The gills contain thin plates- gill filaments which increase surface area.
• Gill filaments have lamellae covered over them and are thin containing blood capillaries. They increase surface area and have thin diffusion pathway.
• Blood passes through lamellae in one direction and water in the opposite direction- aka the countercurrent system and it maintains large concentration gradient between blood and water.
• The concentration of oxygen is higher in the water than in the blood so the oxygen diffuses from the water into the blood.

Question 7

Describe gas exchange in insects:

Answer 7

• Air moves from trachea into spiracles.
• Oxygen travels down the concentration gradient towards the cells.
• The trachea branches into tracheoles containing thin walls meaning oxygen diffuses directly into the repairing cells.
• Carbon dioxide from cell moves down its own concentration gradient towards spiracles and released into atmospheres.
• Insects use rhythmical abdominal movements to move air in and out of spiracles.

Question 8

Describe gas exchange by the leaves of dicotyledonous plants (mesophyll and stomata:

Answer 8

• Mesophyll cells have large surface area.
• Gases move in and out of pores in epidermis called stomata/stoma.
• Stomata opens for gas exchange but closes if plant looses too much water.
• Guard cells control opening and closing of stomata.

Question 9

How do insects control water loss?

Answer 9

• Close their spiracles and have waterproof waxy cuticles as well as hairs reducing evaporation.

Question 10

How do plants control water loss (+ xerophytes) ?

Answer 10

• Plants stomata open and close and guard cells close the stomata if plants get dehydrated.

Xerophytes:

• Stomata sunk in pits trap moist air reducing concentration gradient of water between leaf and air and reduces amount of water diffusing out of leaf.
• Thin hairs on epidermis trap moist air and stomata.
• Curled leaves with stomata inside protecting them from wind increasing rate of diffusion and evaporation).
• Reduced number of stomata so fewer places for water to escape.

Question 11

How are lungs specialized for gas exchange?

Answer 11

• As you breathe in, air enters trachea.
• Trachea splits into two bronchi- one bronchus to each lung.
• Bronchus branches out into bronchioles.
• The bronchioles contain air sacs at the end called alveoli.
• The ribcage, intercostal muscles and diaphragm work together moving air in and out.

Question 12

Outline inspiration (breathing in):

Answer 12

• External intercostal muscles and diaphragm contract making ribcage move in upwards outwards direction, flattening it. The volume of thoracic cavity increases and lungs pressure decreases. Air moves from high pressure to lower pressure down trachea and into lungs.
• Active process requiring energy.

Question 13

Outline expiration (breathing out):

Answer 13

• External intercostal muscle and diaphragm contract making ribcage move downwards and inwards and the ribcage remains curved. The volume of thoracic cavity decreases and lung pressure increases.
• Air forced down pressure gradient and out of the lungs.
• Normal expiration is a passive process doesn’t require energy.

Question 14

Outline forced expiration:

Answer 14

• External intercostal muscles are relaxed and internal intercostal muscles contract pulling ribcage inwards and in. During this time, the intercostal muscles are to be moving antagonistically (oppositely).

Question 15

Describe humans gas exchange in the alveoli;

Answer 15

O2 diffuses out of the alveoli across the alveolar epithelium and capillary endothelium and into hemoglobin in the blood.
CO2 diffuses into the alveoli from the blood and is breathed out. Happens down a diffusion gradient.

Question 16

How is alveoli adapted for gas exchange?

Answer 16

• The alveolar epithelium is only one cell thick meaning short diffusion pathway.
• Large number of alveoli means larger surface area for gas exchange.

Question 17

What is digestion?

Answer 17

Large biological molecules are hydrolyzed into smaller molecules that can be absorbed across cell membranes.

Question 18

Describe digestion in carbohyrates:

Answer 18

• Amylase (produced by salivary glands & pancreas) catalyses conversion of starch into maltose and involves hydrolysis of glycoycidic bonds in starch.
• Membrane bound disaccharides attached to epithelial cells membrane and break disaccharides into monosacchraides which can be transported across ileum membranes via transporter proteins..

Question 19

Describe digestion in lipids:

Answer 19

• Lipase catalyses breakdown of lipids into monoglycerides and fatty acids involving the hydrolysis of ester bonds in lipids.
• Bile salts are produced by liver and emulsify lipids causing them to form small droplets- several of these droplets means bigger surface,
• The monoglycerides and fatty acids stick with the salts forming tiny structures called micelles.

Question 20

What is endopeptidase?

Answer 20

• They hydrolyze peptide bonds within a protein.

Question 21

What is exopeptidase?

Answer 21

• They hydrolyze peptide bonds at the end of protein molecules.
• Dipetidases (located in cell membrane of epithelial cells in the small intestine) separate the amino acids that make up a dipeptide by hydrolvsisnf peptide bond.

Question 22

What are the products of digestion?

Answer 22

• Monosaccharides = Glucose absorbed by active transport with sodium ions using co transporter proteins & fructose via facilitated diffusion using co transporter proteins.
• Monoglycerides and fatty acids = Micelles help move M and FA towards epithelium
• Amino acids = Sodium ions are actively transported out of the ec into blood forming sodium ion concentration gradient.

Question 23

What is hemoglobin?

Answer 23

• It is a protein with a quaternary structure and four polypeptide chains each containing a haem group with iron ion.
• It has a high affinity for oxygen.

Question 24

Describe the partial pressure of oxygen:

Answer 24

• The partial pressure (pO2) is a measure of oxygen concentration . The greater the concentration of dissolved oxygen the higher the partial pressure.
• The partial pressure of carbon dioxide (pCO2) is measure of concentration of CO2 in a cell.
• Oxygen loads onto hemoglobin to form oxyhemoglobin where there’s a higher pO2. Oxyhemoglobin unloads its oxygen where there’s lower pO2.
• Alveoli have high pO2 so oxygen unloads onto hemoglobin to form oxyhemoglobin.

Question 25

How does dissociation curve show how affinity for oxygen varies?

Answer 25

• When pO2 is high, hemoglobin has high affinity for oxygen.
• When pO2 is low, hemoglobin has low affinity for oxygen which means it releases oxygen rather than combines with it; which is why it has low saturation of oxygen.

Question 26

What is the Bohr effect?

Answer 26

• Hemoglobin gives up its oxygen more readily at higher partial pressure of carbon dioxide;
  When cells respire they produce CO2 raising the pCO2 which increases the rate of oxygen unloading at which oxyhemoglobin dissociates to form hemoglobin so then dissociation curve shifts to the right. The saturation of blood with oxygen is lower for a given pO2 so more oxygens released.

Question 27

Describe how hemoglobin different in different organisms:

Answer 27

• Organisms in environments with low concentrations of oxygen have hemoglobin with a higher affinity for oxygen than humans (DC to the left of humans).
• Organisms that are active and have high oxygen demand have hemoglobin with lower affinity for oxygen than human hemoglobin (DC to right of humans).

Question 28

Outline the circulatory system:

Answer 28

• Mammals have low surface area to volume ratio so use circulatory system:
• The heart pumps blood through blood vessels (arteries, arterioles, veins and capillaries). There are two circuits; one takes blood from the heart to the lungs then back to heart and the other around the rest of the body.
• The heart also has its own blood supply; left and right coronary arteries.

Question 29

Describe arteries:

Answer 29

• They carry blood from the heart to the rest of the body. All arteries carry oxygenated blood except for pulmonary which carry deoxygenated blood to the lungs.
• Have thick muscular elastic tissue walls which stretch and recoil maintaining high pressure.
• Endothelium folded allowing it to stretch and maintain high pressure.

Question 30

Describe arterioles:

Answer 30

• The muscle inside the arterioles contract and restrict the blood flow or relax to allow full blood flow.

Question 31

Describe veins:

Answer 31

• Take blood back to heart under low pressure. All carry deoxygenated blood except for pulmonary veins which cary oxygenated blood to heart from lungs.
• Have a wider lumen with very little elastic or muscle tissue and contain valves to stop blood flowing backwards.

Question 32

Describe capillaries:

Answer 32

• Arterioles branch into capillaries (smallest blood vessels).
• Found near cells in exchange tissues and their walls only one cell thick so short diffusion pathway.
• Large number of them so bigger surface area and network of them are called capillary beds.

Question 33

How is tissue fluid formed?

Answer 33

• It’s made from small molecules that leave the blood plasma. Cells take in oxygen and nutrients from the tissue fluid and release metabolic waste into it.

Question 34

What is the importance of capillary beds as exchange surfaces?

Answer 34

• At start of capillary bed, the hydrostatic pressure inside capillaries is greater than hydrostatic pressure in tissue fluid meaning outward pressure forces fluid out of the capillaries and into spaces forming tissue fluid.
• Fluid leaves so hydrostatic pressure reduces in the capillaries so lower at the venue end of capillary bed.
• Increasing concentration of plasma proteins makes water potential at the venue end of capillary bed is lower than the water potential in the tissue fluid; means that some water re enters capillaries from the tissue fluid at venue end by osmosis.

Question 35

Describe the heart:

Answer 35

x The right side pumps deoxygenated blood to the lungs and left side pumps oxygenated blood to whole body.
x The left ventricle is thicker and more muscular as it needs to contract powerfully to pump blood all the way around whereas the right only needs to get blood to nearby lungs.

Question 36

Why does left ventricle have thicker walls than right ventricle?

Answer 36

• Ventricles have thicker walls than atria because they push blood out of heart whereas atria only pushes blood a short distance into the ventricles.

Question 37

Describe roles of valves:

Answer 37

• Atrioventricular valves link atria and ventricles and stop blood flowing back into the atria when ventricles contract.
• Semi lunar valves link ventricles to pulmonary artery and aorta stopping blood flowing back into heart after ventricles contract.
• Valves open one day and whether they are opened or closed depends on pressures ; if high pressure behind valves its forced open ig higher pressure infant of valve its forced shut meaning blood flows in one direction through heart.

Question 38

Outline cardiac cycle (Atrial Systole):

Answer 38

• Atrial Systole: Ventricles are relaxed. Atria contracts decreasing the volume of the chambers and increases pressure inside the chambers; this pushes blood into ventricles and there is an increase in ventricular pressure and chamber volume as the ventricles receive the ejected blood from the contracting atria.

Question 39

Outline cardiac cycle (Ventricular Systole):

Answer 39

• Ventricular Systole: Atrias relaxed. Ventricle contracts decreasing their volume increasing their pressure. The pressure becomes higher in the ventricles than the atria forcing the atrioventricular valves to shut to prevent back flow. The pressure in the ventricles is higher than in the aorta and pulmonary artery forcing the semilunar valves to open and bloods forced out of these arteries.

Question 40

Outline cardiac cycle (Diastole):

Answer 40

• Diastole: Ventricles and atria relax. The higher pressure in pulmonary artery and aorta closes the SL valves preventing back flow into ventricles. Blood returns to heart and atria fill again due to higher pressure in the vena cava and pulmonary vein increasing pressure of the atria. Pressure falls below the pressure of the atria so the AV valves open allowing blood to flow passively into ventricles from atria. Atria contracts ad whole process begins again.

Question 41

Describe xylems & xylem vessels:

Answer 41

• Xylem tissue transports water and mineral ions in solution and these substances move up from roots to the leaves over large distances.
• Xylem vessels are part of xylem tissue and transport water and ions and they are long, tube-like structures formed from dead cells joined end to end. There are no end walls making an uninterrupted tube allowing water to pass through middle easily.

Question 42

Outline the cohesion- tension theory of water:

Answer 42

Cohesion and tension help move water up plants rom roots to leaves.
- Water evaporates from leaves at the top of the xylem (transpiration) creating tension pulling more water into the leaf. Water molecules are cohesive so when some are pulled into leaf others follow meaning the whole column of water in the xylem moves upwards. Water enters the stem through the roots.

Question 43

What is transpiration:

Answer 43

• Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf.
• When the stomata open it moves out go the leaf down the concentration gradient.

Question 44

What are factors affecting transpiration?

Answer 44

• Light; lighter it is the faster the transpiration rate because stomata is opened and when it’s dark the stomatas closed.
• Temperature; higher the temperature the faster the transpiration rate as molecules have more energy so evaporate inside leaf faster increasing the concentration gradient.
• Humidity; lower the humidity faster the transpiration rate.
• Wind; windier is the faster the transpiration rate as there is an increased concentration gradient.

Question 45

What is a photometer used for?

Answer 45

It estimates transpiration rates and measures water uptake by a plant.

Question 46

Describes phloems:

Answer 46

• Phloem tissue transports organic substances such as sugars both up and down the plant.

Question 47

How are phloem tissues adapted for transporting solutes:

Answer 47

• Sieve tubes transport solutes.

- Companion cells control activities and carry out living functions for sieve tubes.

Question 48

What is translocation?

Answer 48

It is the movement of solutes (eg sucrose, sugars and amino acids) from ‘sources’ to ‘sinks’.

• Source is the part of the plant where the sugars are made from (sucrose usually the leaves).
• Sinks are the other parts of the plant where the sugar molecules are going to (especially food storage organs and meristems).

Question 49

Describe the mass flow hypothesis for the mechanism of translocation in plants:

Answer 49

1) Active transport used to actively load solutes from companion cells into the sieve tubes of the phloem at the source; lowering the water potential inside the sieve tubes so water enters tubes via osmosis creating high pressure inside sieve tubes at the source end of the phloem.
2) At the sink end, solutes removed from phloem to be used up increasing the water potential inside the sieve tubes so water leaves tubes via osmosis which lowers the pressure inside the sieve tubes.
3) Results in pressure gradient from the source end to sink end pushing solutes along the sieve tubes towards the sink where they’ll be used or stored.

Question 50

What are the use of tracers and ringing experiments to investigate transport in plants?

Answer 50

• Tracer experiments can be used to investigate the transport of sucrose in plants that contains radioactivity labelled carbon dioxide (14CO2) and other plants. The movement of these sugars can be traced through the plant using autoradiography to reveal where radioactive tracer has spread and will appear black.
• If the phloem is responsible for mass flow a ringing experiment can be used where the bark and phloem of a tree are removed leaving just the xylem in the centre. Overtime the tissues above the missing ring swell with sucrose solution and the tissue below dies showing that sucrose is transported in the phloem.