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A Level > Biology: organisms exchange substances with the environment > Flashcards

Biology: organisms exchange substances with the environment Flashcards

1
Q

how does a high surface area to volume ratio help diffusion?

A
  • increases diffusion.

- large surface area.

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2
Q

how does gas exchange happen in an amoeba?

A
  • conc. of oxygen outside the cell is greater than inside, oxygen moves down the concentration gradient.
  • carbon dioxide builds up in the cell due to respiration
  • carbon dioxide diffuses out of the cell.

-this happens because the diffusion pathway is very short.

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3
Q

how does countercurrent flow maintain a concentration gradient between oxygen in the gills and oxygen in the water?

A
  • flow of blood and flow of water in opposite direction.

- concentration of oxygen in the water is always greater than in the blood.

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4
Q

describe the structure of the gills.

A
  • feathered to increase surface area.
  • gill lamellae provide lots of surface area.
  • rich blood supply
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5
Q

what are spiracles?

A

-openings on the body of an insect to allow air to flow in and carbon dioxide to flow out

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6
Q

what are trachea?

A
  • tubes inside an insect to provide oxygen to its cells.

- extend from the spiracles into the body’s tissues

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7
Q

what do gill lamellae do?

A
  • site of oxygen diffusion into the gills.

- counter-current flow also happens in the lamellae.

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8
Q

what is an advantage of the tracheal system?

A

it’s a passive process as it relies on diffusion. doesn’t require any energy.

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9
Q

what are the limitations of the tracheal system?

A
  • relies on diffusion rather than a transport system.

- for diffusion to be adequate, the diffusion pathway must be short. this limits the size insects can grow to.

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10
Q

how does abdominal pumping help insects to obtain oxygen?

A
  • contraction of insect muscles
  • trachea reduced in volume and air is forced out.
  • muscles relax, air enters the insect.

however, this process requires energy

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11
Q

how do water filled tracheoles help with the diffusion of air into the insect?

A
  • anaerobic respiration produces lactate.
  • it’s water soluble so it lowers the water potential of muscle cells.
  • water moves into muscle cells from tracheoles.
  • volume of water in the tracheole end decreases, drawing air in.
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12
Q

what adaptations to plants have to limit water loss?

A
  • thin leaves reduce surface area.
  • stomata
  • large root systems
  • waxy cuticles
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13
Q

what are xerophytes?

A

plants which can withstand drought-like conditions.

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14
Q

how do sunken stoma reduce water loss?

A

wind doesn’t directly reach the stoma so less water is evaporated.

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15
Q

what is chemical digestion?

A

using enzymes and chemicals such as stomach acid to break food down.

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16
Q

what is physical digestion?

A

-initial breakdown of molecules, giving it a larger surface area to volume ratio.

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17
Q

which enzymes are produced in the small intestine?

A
  • lactase

- sucrase

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18
Q

which enzyme is produced in the salivary glands?

A

-amylase

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19
Q

describe the process of digestion

A

1) physical digestion in the form of chewing starts the process of digestion.
2) salivary glands break down starch to produce maltose. saliva also contains salts which maintain a neutral pH so it stays at optimum pH
3) food goes down the oesophagus and enters the stomach where hydrochloric acid is produced. it denatures the enzymes which break down starch
4) food passes into the small intestine where it mixes with pancreatic juices. this contains amylase and breaks down the remaining starch into maltose. alkaline salts are produced by the intestine walls to maintain a neutral pH as it’s the optimum for amylase.
5) it moves along the ileum, maltase is released into the ileum. this hydrolyses maltose into 2 glucose molecules.
6) other disaccharides are hydrolysed into monosaccharides which can enter the blood stream.

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20
Q

describe the process of lipid digestion.

A
  • hydrolysed by lipases produced in the pancreas.
  • hydrolyses ester bonds to form fatty acids and monoglycerides.
  • lipids are broken down into micelles by bile salts produced in the liver
  • this is called emulsification
  • it aids absorption as there’s more surface area for enzymes to work on.
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21
Q

what do endopeptidases do?

A

hydrolyse the central region of an amino acid, forming a series of peptide molecules.

22
Q

what do exopeptidases do?

A

hydrolyse the peptide bonds on the terminal ends of the amino acids. it cuts the ends off.

23
Q

what do dipeptidases do?

A

hydrolyse the peptide bond between 2 amino acids

24
Q

how is the structure of the lumen adapted for maximum exchange?

A
  • villi and microvilli maximise the surface area of the lumen.
  • the epithelial cells have capillaries close to them to maximise absorption speed, it also maintains a concentration gradient.
  • diffusion happens passively due to a concentration gradient and short diffusion pathway.
25
Q

what are chylomicrons and what do they do?

A
  • small milky globules
  • a small fat globule made of protein and lipid
  • they’re made in the lining of the intestine.
26
Q

why do animals have a closed double circulatory system?

A
  • as blood passes through the lungs the pressure is reduced
  • if it was sent straight to the body its low pressure would make circulation slow.
  • blood instead goes back to the heart from the lungs for a pressure boost.
  • substances are delivered quickly.
  • this is necessary for animals as they have a high body temp. and a fast metabolism.
27
Q

what is pulmonary circulation?

A
  • pumps blood from heart to lungs

- oxygenates blood and removes co2

28
Q

what is systematic circulation?

A
  • pumps blood from the heart to the rest of the body

- increased blood pressure from the heart.

29
Q

how does blood travel around the heart?

A
  • vena cava brings blood into the right atrium.
  • right atrioventricular valve allows blood to travel into the right ventricle.
  • right ventricle contracts.
  • blood forced into pulmonary artery, it becomes oxygenated.
  • it re-enters the heart through the left atrium.
  • the left atrioventricular valve opens so blood enters the left ventricle.
  • the ventricles contract and blood exits the heart through the aorta.
30
Q

explain the structure and function of the atria.

A
  • thin walls

- collects blood from the body and lungs

31
Q

explain the structure and function of the atria.

A
  • thick, muscular walls

- capable of strong contractions so blood is ejected from the heart

32
Q

what is the purpose of valves?

A
  • prevents backflow due to low pressure blood

- flexible, tough, fibrous flaps prevent blood from flowing in the wrong direction due to changes in pressure.

33
Q

what are the 4 valves of the heart?

A
  • right + left semi-lunar

- right + atrioventricular

34
Q

what do the atrioventricular valves do?

A

prevent backflow from contracting ventricles and allow the passage of blood from the atria to the ventricles.

35
Q

what do the semi-lunar valves do?

A

prevents backflow into the ventricles as the left goes to the aorta and the right SL valve leads to the pulmonary artery, which goes to the lungs.

36
Q

what do pocket valves do?

A
  • promote return of blood from veins.

- prevents backflow

37
Q

describe arteries in terms of their structure.

A
  • tough, fibrous outer layer to cope with high capacity blood.
  • muscle layer to cope with high pressure blood
  • elastic layer expands so it doesn’t burst due to high pressure blood.
  • lumen to allow the passage of blood.
38
Q

what is the purpose of tissue fluid?

A

-capillaries can’t reach every cell directly so tissue fluid allows materials to be exchanged between cells and the capillaries even though they aren’t touching.

39
Q

how is tissue fluid formed?

A
  • vessels become narrower and create hydrostatic pressure

- tissue fluid is forced out of the blood plasma.

40
Q

how does tissue fluid return to the blood plasma?

A
  • the loss of TF from the capillaries causes hydrostatic pressure inside the capillaries.
  • this causes tissue fluid to return to the capillaries and then the blood plasma.
41
Q

describe the structure of haemoglobin

A
  • all 4 polypeptide chains linked to form a sphere
  • each chain has a haem group which contains a ferrous ion
  • each ferrous ion can carry 1 oxygen molecule
42
Q

what makes haemoglobin efficient?

A
  • high affinity in the lungs

- low affinity at respiring cells

43
Q

how does haemoglobin change affinity to suit different conditions/

A
  • changes shape in the presence of CO2 as it’s acidic
  • it causes O2 to bind loosely with Hb
  • O2 can dissociate more easily
44
Q

what is partial pressure?

A

the amount of gas and the pressure caused by it

45
Q

why does an oxygen dissociation curve have an ‘S’ shape?

A
  • at high conc. of O2, the 4 polypeptides are tightly packed, it means that little O2 binds to Hb in low O2 levels. gradient of curve is shallow
  • the binding of the 1st O2 changes the teritary structure. molecules 2 and 3 load more easily due to shape change, the curve steepens as more oxygen is loaded.
  • the 3rd O2 is difficult to load as Hb becomes saturated. the binding site is hard to find as others are saturated. .
46
Q

what does a change to the left of the dissociation curve mean?

A
  • Hb has a greater affinity for oxygen

- this means that it takes up O2 readily and releases it less easily.

47
Q

what does a change to the right of the dissociation curve mean?

A
  • Hb has a lower affinity for oxygen

- takes up oxygen less readily but releases it easily

48
Q

how does water move across leaves?

A
  • water is lost from mesophyll cells from their walls to the air spaces of leaves.
  • replaces by water from xylem via either cell walls or cytoplasm pathways.
  • these cells now have a lower water potential.
  • water enters the cells by osmosis from neighbouring cells.
  • loss of water from these cells lowers the water potential.
  • they take up water from their neighbouring cells by osmosis.
  • the process repeats.
49
Q

how is water transported across the xylem to the growing regions of a plant?

A

TRANSPIRATION PULL

  • water is pulled up the xylem due to cohesion tension.
  • at the leaves, water is evaporated from the plant.
  • the cohesion tension means that water molecules pull eachother out of the cell.
  • this means that water is pulled up the xylem, the hydrostatic pressure means that water is pulled into the plant due to the cohesion of water.
50
Q

how are organic materials transported in the phloem?

A

MASS FLOW MECHANISM:

  • sucrose is made in the palisade cells. active transport transports it from respiring cells to companion cells on the phloem. it’s then transported into the sieve tubes nearby. as the concentration increases, the water potential becomes more negative, water enters the sieve tubes by osmosis.
  • entry of water causes hydrostatic pressure in the sieve tubes, propelling sucrose and other materials through the sieve tubes.
  • companion cells actively transport sucrose out of sieve cells and into root cells, which use it as an energy source. the pressure difference in the sieve tubes maintain the transport of molecules
51
Q

how can we investigate mass flow in plants?

A

aphids:

  • remove the aphid’s stylet
  • sap continues to ooze from this for several days
  • samples are collected from the stylets at regular intervals.
  • it shows that nutrients are transported in the phloem as aphids can selectively locate sieve tubes to feed off

A Level (36 decks)

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