bioenergetics

Question 1

is photosynthesis an endothermic or exothermic reaction?

Answer 1

photosynthesis is an endothermic reaction, as energy is transferred from the environment to the chloroplasts by light.

Question 2

where does photosynthesis occur in a plant, and why is that area significant?

Answer 2

photosynthesis takes place in the leaves of a plant. leaves contain chlorophyll, which can absorb light energy.

Question 3

what is the word equation for photosynthesis?

Answer 3

carbon dioxide + water ———- (light + chlorophyll) ———– glucose + oxygen

Question 4

what is the symbol equation for photosynthesis?

Answer 4

CO₂ + H₂O ——— C₆H₁₂O₆ + O₂
- this equation isn’t balanced but you’re not required to balance it for your exam

Question 5

how does light intensity affect the rate of photosynthesis?

Answer 5

• as we increase the light intensity, the rate of photosynthesis increases
• if we continue to increase the light intensity, there’s a point where the rate of photosynthesis no longer increases

Question 6

how do the levels of carbon dioxide affect the rate of photosynthesis?

Answer 6

• as we initially increase carbon dioxide levels, the rate of photosynthesis increases - the carbon dioxide is a limiting factor
• however, there will be a point reached where the rate of photosynthesis no longer increases, and the carbon dioxide is no longer a limiting factor

Question 7

how does a shortage of chlorophyll in leaves affect the rate of photosynthesis?

Answer 7

if certain areas of the leaf have a much shorter supply of chlorophyll than other areas, they will have a lower rate of photosynthesis, as chlorophyll is required for the process

Question 8

how does temperature affect the rate of photosynthesis?

Answer 8

• increasing the temperature initially means that the enzymes involved work faster, increasing the rate of photosynthesis
• however, continuing to increase the temperature means that the enzymes will denature, and the rate of photosynthesis falls

Question 9

define the term ‘limiting factor’:

Answer 9

a condition, that when in shortage, slows down the rate of a reaction. the factors (chlorophyll, light intensity, carbon dioxide and temperature) can all interact and any one of them could be the limiting factor.

Question 10

describe the inverse square law and light intensity, and how it relates to photosynthesis:

Answer 10

• there is an inverse relationship between distance and light intensity - as distance increases, light intensity decreases.
• this is because as the distance away from a light source increases, light energy becomes spread over a wider area.
• the light energy at twice the distance away from the object is spread over four times the area. the light energy at three times the distance away is spread over 9 times the area.
• the light intensity is inversely proportional to the square of the distance.

Question 11

how can farmers increase the rate of photosynthesis in their crop?

Answer 11

• farmers want to increase the rate of photosynthesis, as this increases their crop yield.
• to do this, farmers light and heat their greenhouses. they also add extra carbon dioxide.
• this extra cost has to be justified in the crop yield: some farmers use oil burners as these release heat and carbon dioxide at the same time.

Question 12

what are uses of glucose after its production during photosynthesis?

Answer 12

1. to release energy in respiration (in the mitochondria)
2. to produce the insoluble storage molecule starch. when plants respire at night, and photosynthesis is impossible, starch can be broken down into glucose for respiration
3. glucose can also be broken down into fats and oils, and can be another stored form of energy for plants
4. the cellulose found in cell walls, which gives plant cells strength, is made from glucose produced in respiration
5. the glucose produced in photosynthesis can be used to produce amino acids, which are used to synthesis proteins in plants - TO MAKE AMINO ACIDS (and consequently proteins) FROM GLUCOSE, PLANTS MUST ALSO USE ABSORBED NITRATE IONS FROM THE SOIL!

Question 13

is respiration an exothermic or endothermic reaction?

Answer 13

respiration is an exothermic reaction because it releases energy. this reaction continuously occurs in our living cells.

Question 14

what do organisms need energy for?

Answer 14

the energy transferred in respiration supplies all the energy needed for living processes.

• chemical reactions to build larger molecules.
• movement.
• keeping warm.

Question 15

what is the word equation for aerobic respiration?

Answer 15

glucose + oxygen ——– carbon dioxide + water (+ENERGY)

Question 16

what is the symbol equation for aerobic respiration?

Answer 16

C₆H₁₂O₆ + O₂ ——— CO₂ + H₂O (+ENERGY)

Question 17

when do muscle cells respire anaerobically?

Answer 17

muscle cells require energy for contraction, but sometimes, aerobic respiration can’t occur because the amount of oxygen is limited.
- however, anaerobic respiration produces much less energy than aerobic respiration, as the oxidation of glucose is incomplete. this incomplete reaction causes a buildup of lactic acid and creates an oxygen debt.

Question 18

what is the word equation for anaerobic respiration in animals?

Answer 18

glucose ——— lactic acid (+ENERGY)

Question 19

what is the word equation for anaerobic respiration in yeast and plant cells?

Answer 19

glucose ——— ethanol + carbon dioxide (+ENERGY)

Question 20

what is the name for anaerobic respiration in yeast cells, and what is it used for?

Answer 20

fermentation can be used to make alcoholic drinks, such as beer (the alcohol is ethanol, which is produced by fermentation). economically important.

Question 21

why is fermentation used to create bread?

Answer 21

the carbon dioxide produced during fermentation is useful when creating bread as it creates bubbles in the dough, causing it to rise.

Question 22

what is ‘oxygen debt’?

Answer 22

anaerobic respiration in animals creates lactic acid. lactic acid can be harmful if left to build up in our muscle tissue, so after exercise, it needs to react with oxygen to get rid of it. the period where not all of the lactic acid has reacted with oxygen is called ‘oxygen debt’, and your body will be working harder to deliver oxygen to muscle tissue (i.e. panting after a race)

Question 23

how does lactic acid react with oxygen?

Answer 23

the lactic acid is transported from the muscles, through the blood, to the liver, where it reacts with oxygen to convert back into glucose.

Question 24

what does the body do during exercise?

Answer 24

• the body reacts to the increasing demand for energy.
• the breathing rate and the breathing volume increases, getting more oxygen in the bloodstream and to the muscles
• the heart rate also increases, to pump this oxygenated blood around the body

Question 25

what happens to muscles during long periods of exercise?

Answer 25

during long periods of vigorous activity, muscles become fatigued and stop contracting efficiently.

Question 26

what is the metabolism?

Answer 26

the sum of all of the chemical reactions in a cell or the body.

Question 27

how is metabolism fuelled?

Answer 27

the energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesises new molecules.

Question 28

what reactions does metabolism include?

Answer 28

• conversion of glucose to starch, glycogen and cellulose.
• the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids.
• the use of glucose and nitrate ions to form amino acids, which in turn are used to synthesise proteins.
• respiration.
• breakdown of excess proteins to form urea for excretion.