bioenergetics Flashcards
is photosynthesis an endothermic or exothermic reaction?
photosynthesis is an endothermic reaction, as energy is transferred from the environment to the chloroplasts by light.
where does photosynthesis occur in a plant, and why is that area significant?
photosynthesis takes place in the leaves of a plant. leaves contain chlorophyll, which can absorb light energy.
what is the word equation for photosynthesis?
carbon dioxide + water ———- (light + chlorophyll) ———– glucose + oxygen
what is the symbol equation for photosynthesis?
CO₂ + H₂O ——— C₆H₁₂O₆ + O₂
- this equation isn’t balanced but you’re not required to balance it for your exam
how does light intensity affect the rate of photosynthesis?
- 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
how do the levels of carbon dioxide affect the rate of photosynthesis?
- 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
how does a shortage of chlorophyll in leaves affect the rate of photosynthesis?
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
how does temperature affect the rate of photosynthesis?
- 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
define the term ‘limiting factor’:
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.
describe the inverse square law and light intensity, and how it relates to photosynthesis:
- 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.
how can farmers increase the rate of photosynthesis in their crop?
- 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.
what are uses of glucose after its production during photosynthesis?
- to release energy in respiration (in the mitochondria)
- 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
- glucose can also be broken down into fats and oils, and can be another stored form of energy for plants
- the cellulose found in cell walls, which gives plant cells strength, is made from glucose produced in respiration
- 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!
is respiration an exothermic or endothermic reaction?
respiration is an exothermic reaction because it releases energy. this reaction continuously occurs in our living cells.
what do organisms need energy for?
the energy transferred in respiration supplies all the energy needed for living processes.
- chemical reactions to build larger molecules.
- movement.
- keeping warm.
what is the word equation for aerobic respiration?
glucose + oxygen ——– carbon dioxide + water (+ENERGY)
what is the symbol equation for aerobic respiration?
C₆H₁₂O₆ + O₂ ——— CO₂ + H₂O (+ENERGY)
when do muscle cells respire anaerobically?
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.
what is the word equation for anaerobic respiration in animals?
glucose ——— lactic acid (+ENERGY)
what is the word equation for anaerobic respiration in yeast and plant cells?
glucose ——— ethanol + carbon dioxide (+ENERGY)
what is the name for anaerobic respiration in yeast cells, and what is it used for?
fermentation can be used to make alcoholic drinks, such as beer (the alcohol is ethanol, which is produced by fermentation). economically important.
why is fermentation used to create bread?
the carbon dioxide produced during fermentation is useful when creating bread as it creates bubbles in the dough, causing it to rise.
what is ‘oxygen debt’?
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)
how does lactic acid react with oxygen?
the lactic acid is transported from the muscles, through the blood, to the liver, where it reacts with oxygen to convert back into glucose.
what does the body do during exercise?
- 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
what happens to muscles during long periods of exercise?
during long periods of vigorous activity, muscles become fatigued and stop contracting efficiently.
what is the metabolism?
the sum of all of the chemical reactions in a cell or the body.
how is metabolism fuelled?
the energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesises new molecules.
what reactions does metabolism include?
- 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.
