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.
which useful energy transfer/conversion happens overall in photosynthesis?
light —-> chemical
where does photosynthesis occur in a plant, and why is that area significant?
photosynthesis takes place in the leaves of a plant. leaves (and chloroplast) contain chlorophyll, which can absorb light energy - basically little packets of energy to fuel the photosynthesis process.
what is the word equation for photosynthesis?
carbon dioxide + water ———- (light + chlorophyll) ———– glucose + oxygen
what is the symbol equation for photosynthesis?
6CO₂ + 6H₂O ——— C₆H₁₂O₆ + 6O₂
how does the plant get the reactants for photosynthesis?
- carbon dioxide diffuses in through the stomata
- water is absorbed by the roots and transported to the leaves through the xylem tubes
how does light intensity affect the rate of photosynthesis?
- as we initially increase the light intensity, the rate of photosynthesis increases, as photosynthesis relies on energy from the sun
- if we continue to increase the light intensity, there’s a point where the rate of photosynthesis no longer increases, as light intensity is no longer the limiting factor, something else is limiting it
how do the levels of carbon dioxide affect the rate of photosynthesis?
- as we initially increase carbon dioxide levels, the rate of photosynthesis increases, as it’s one of the reactants
- 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
- chlorophyll is the pigment within chloroplasts that absorbs the light energy needed for photosynthesis
why may levels of chlorophyll vary within an individual plant?
- disease (e.g. tobacco mosaic virus)
- environmental stress
- lack of nutrients, like water
these all tend to damage the chloroplasts, so they can’t make as much chlorophyll anymore
how does temperature affect the rate of photosynthesis?
- increasing the temperature initially means that the enzymes involved work faster, and the molecules move faster, increasing the rate of photosynthesis
- however, continuing to increase the temperature means that the enzymes will denature (bonds within the enzyme begin to break and so the enzyme changes shape), and the rate of photosynthesis falls, eventually to 0
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:
- the intensity of light decreases proportionally to the square of the distance from its source.
- 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.
what is the light intensity if the distance is:
- 1m
- 2m
- 3m
1m: 1/1^2 = 1
2m: 1/2^2 = 1/4
3m: 1/3^3 = 1/9
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.
- in colder climates, the crops may be placed in a greenhouse which traps the sun’s heat, increasing the temperature
- the farmer may also use artificial light so photosynthesis can continue all through the day and night
- farmers may also pump carbon dioxide into the greenhouse or use a paraffin heater (which releases both heat and carbon dioxide as it burns)
- greenhouses also prevent the entry of pests and pathogens
what chemicals may a farmer use on their crops?
- fertilisers: ensures the plants have enough essential minerals
- pesticides: kills unwanted bugs
what must farmers weigh up?
all these techniques cost a lot, so farmers must weigh up the extra yield they get against the extra cost
what are uses of glucose after its production during photosynthesis?
- to release energy in cellular respiration, which breaks the glucose apart (in the mitochondria)
- to produce the insoluble, compact storage molecule starch. when plants respire at night/in the winter, and photosynthesis is impossible/unlikely, 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 resource for plants and seeds
- the cellulose found in cell walls, which gives plant cells/walls strength
- the glucose produced in photosynthesis can be used to produce amino acids, which are used to synthesise proteins in plants - TO MAKE AMINO ACIDS (and consequently proteins) FROM GLUCOSE, PLANTS MUST ALSO USE ABSORBED NITRATE IONS FROM THE SOIL!
what is important about the insolubility of starch?
won’t draw water into cells via osmosis, like glucose would
how can glucose be thought of as a battery?
photosynthesis traps light energy in the glucose, and cells around the plant break the glucose apart to release its energy when needed
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 is respiration?
an exothermic reaction which transfers energy from glucose and continuously occurs in living cells
- breaks apart glucose molecules to release the energy trapped inside
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 from smaller ones (e.g. combining amino acids to form proteins) or vice versa
- movement, muscular contraction
- keeping warm, maintaining body temperature
- to move substances around cells
what is the word equation for aerobic respiration?
glucose + oxygen ——– carbon dioxide + water (+ENERGY)
what is aerobic respiration?
- more common
- takes place when there’s enough oxygen
- most efficient way to transfer energy from glucose
- happens continuously in plants and animals
- takes place in mitochondria
what is the symbol equation for aerobic respiration?
C₆H₁₂O₆ + 6O₂ ——— 6CO₂ + 6H₂O (+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, and there isn’t enough to keep up with our demands (e.g. during sprints/fast cycling)
- however, anaerobic respiration produces much less energy than aerobic respiration, as the oxidation of glucose is incomplete. this incomplete reaction causes a build up of lactic acid (which can damage cells) and creates an oxygen debt.
what is the word equation for anaerobic respiration in humans?
glucose ——— lactic acid (+ENERGY)
what is the word equation for anaerobic respiration in yeast and plant cells?
glucose ——— ethanol + carbon dioxide (+ENERGY)
why is anaerobic respiration not favoured in humans?
the glucose is only partially broken down which is inefficient as we’re not unlocking all of the energy in the glucose molecule
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, and causing the bread to appear light and fluffy
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 more quickly
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.
why must we carry out more cellular respiration during exercise?
- exercise is essentially muscle contraction, which requires lots of energy from cellular respiration
- respiration requires oxygen, so we need more oxygen for muscle contraction
how can we measure the effect of exercise on breathing and heartrate?
breathing rate:
- count how many times a chest rises and falls in a given amount of time, usually a minute
heartrate:
- measure the pulse, by placing two fingers on an artery in the wrist/neck
