P1 89 Photosynthesis+ respiration

Question 1

state the equation for photosynthesis

Answer 1

carbon dioxide + water -> glucose + oxygen
6CO2 + 6H20 -> C6H12O6 + 6O2
endothermic (light energy taken in from surroundings)

Question 2

describe the process of photosynthesis (5)

Answer 2

• waters enters plant through roots (osmosis)+ travels to leaves (through xylem vessels)
• CO2 from air diffuses into leaves through stomata (guard cells control intake depending on how much light energy available)
• sunlight absorbed by chlorophyll (green pigment in chloroplasts
• photosynthesis occurs in chloroplasts- light energy converts CO2+H2O into glucose+O2
• oxygen (by-product) leaves plant through stomata

Question 3

describe what glucose produced in photosynthesis is used for (5)

Answer 3

• respiration
• converted into cellulose to strength cell walls
• converted into fat for energy store
• glucose (+nitrate ions) used for protein-synthesis
• converted into insoluble starch+ used as energy store

Question 4

describe the effect of light intensity on rate of photosynthesis

Answer 4

• increased light intensity increases rate (to a certain point) - directly proportional
• beyond this the rate is constant- another limiting factor is preventing the rate increasing
• as a plant gets further from a light source it receives less light energy so decreases rate
  (light ∝ (1/distance²))
  as distance is doubled, plant receives 1/4 light energy

Question 5

describe the effect of temperature on rate of photosynthesis

Answer 5

• increased temp increases rate (to a certain point) - directly proportional
• rate decreases above 45 degrees- reaction catalysed by enzymes which become denatured
• slow rate when temp below 0 degrees- enzymes are unable to react

Question 6

describe the effect of high CO2 concentration on rate of photosynthesis

Answer 6

• increased concentration increases rate (to a certain point) - directly proportional
• beyond this the rate is constant- another limiting factor is preventing the rate increasing
• most common limiting factor- atmosphere contains only 0.04% CO2
• as temp+light intensity increase during the day, levels of CO2 decrease as more photosynthesis occurs

Question 7

describe the 2 reasons for+effect of less chlorophyll on rate of photosynthesis

Answer 7

diseases causing discolouration/ damage to chloroplasts or lack of nutrients (magnesium) to create chlorophyll - limit light absorption which reduces rate

Question 8

state 2 ways to maximise photosynthesis for food production

Answer 8

• fertilisers: used in an area short on minerals (for chlorophyll production/maintenance)
• greenhouses: temperature+ light intensity+ CO2 levels can be regulated to be kept at an optimum level

Question 9

describe steps for effect of light intensity on photosynthesis in an aquatic organism (pondweed) RP

Answer 9

• place the pondweed with the cut side facing up into a boiling tube filled with water (submerged), then place tube upside-down into a beaker of water
• set up a lamp at a fixed distance from the pondweed
• count how many bubbles the pondweed produces over a set period of time (1min)
• repeat 2 more times+ calculate the mean no. bubbles
• repeat experiment with lamp at different further distances from the pondweed
  -> furthest is lowest light intensity so should have lowest rate

-> large no. bubbles means more oxygen produced so higher rate of photosynthesis
-> boiling tube placed in beaker of water to keep temp constant- water absorbs any heat from lamp - check using thermometer

Question 10

state the equation for aerobic respiration

Answer 10

glucose + oxygen -> carbon dioxide + water (+ energy)
C6H12O6 + 6O2 -> 6CO2 + 6H2O
exothermic

Question 11

describe what the energy released in respiration is used for (4)

Answer 11

• movement- making muscles contract
• maintaining a constant body temp (keeping warm)- some energy released as heat
• chemical reactions in cells- building larger molecules from smaller ones// breaking down larger molecules into smaller ones
• active transport

Question 12

state the equation for anaerobic respiration in animals

Answer 12

glucose -> lactic acid (+ energy)

Question 13

state the equation for anaerobic respiration in plant+ yeast cells

Answer 13

glucose -> ethanol + carbon dioxide (+energy)

Question 14

describe anaerobic respiration in humans

Answer 14

• happens when body cells are short of oxygen due to vigorous exercise (no oxygen)
• the oxidation of glucose is not complete
• this releases less energy than aerobic respiration but does it quicker
• lactic acid is produced- builds up in muscles causing pain+tiredness and muscle fatigue+cramp (as muscles contract less efficiently)
• oxygen debt: after exercise you continue to breathe deeply+ quickly to take in more O2/ remove more CO2
• happens in the cytoplasm

Question 15

where does anaerobic respiration happen in cells

Answer 15

cytoplasm

Question 16

define oxygen debt

Answer 16

the amount of oxygen needed by the body after exercise to break down the lactic acid formed in anaerobic respiration and restore oxygen levels in blood+muscles to normal level

Question 17

describe how lactic acid is removed after anaerobic respiration

Answer 17

• after exercise you continue to breathe deeply+ quickly to take in more O2 (+remove more CO2) - oxygen debt
• lactic acid reacts with this oxygen to form carbon dioxide+water, and releases the rest of the energy originally in the glucose
• lactic acid also transported by blood to the liver to be converted back into glucose

Question 18

describe fermentation +uses

Answer 18

• the anaerobic respiration in yeast cells
• glucose -> ethanol + carbon dioxide
• yeast used in the manufacture of bread+ alcoholic drinks

Question 19

define metabolism

Answer 19

• the sum of all reactions in an cell or organism
• controlled by enzymes
• using energy from respiration to break down large molecules into smaller ones or synthesise smaller into larger

Question 20

name the enzyme reactions that are a part of metabolism (3)

Answer 20

• carbohydrates by carbohydrase: broken down into simple sugars, built up into starch and cellulose (+ glycogen in animals)
• proteins by protease: broken down into amino acids, excess protein in animals broken down into urea (as animals cannot store protein), glucose+ nitrate ions formed into amino acids which synthesise proteins
• lipids by lipase: broken down into fatty acids+ glycerol, built up into lipid molecules (1 mol glycerol, 3 mol fatty acid)

Question 21

describe the break down + synthesis of carbohydrates (by carbohydrase)

Answer 21

broken down into simple sugars (glucose)
synthesised into starch and either cellulose (plants) or glycogen (animals) for storage

Question 22

describe the break down + synthesis of proteins (by protease)

Answer 22

broken down into amino acids
-> excess protein in animals broken down into urea (as animals cannot store protein)
glucose+ nitrate ions synthesised into amino acids to make proteins

Question 23

describe the break down + synthesis of lipids (by lipase)

Answer 23

broken down into fatty acids+ glycerol
synthesised into lipid molecules (1 mol glycerol, 3 mol fatty acid)

Question 24

describe how the body reacts to the increased demand for energy (3)

Answer 24

• increased breathing rate+ increased breath volume: to increase supply of oxygenated blood+ remove excess CO2 in blood
• increased heart rate: to supply more oxygen to the muscles