B4 Bioenergetics Flashcards Preview

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Flashcards in B4 Bioenergetics Deck (16):

Describe what happens in photosynthesis

- Takes place in the chloroplasts in plant cells, where the chlorophyll absorbs light
- Energy is transferred to the chloroplasts from environment by light

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


Explain why photosynthesis is an endothermic reaction

Photosynthesis transfers energy FROM the environment during the process


Recall the limiting factors of photosynthesis

Carbon dioxide concentration, light intensity, temperature, chlorophyll


Explain how limiting factors affect the rate of photosynthesis (how they interact)

CO2 -> the amount of CO2 will only increase the rate up to a point (on a graph = flattens out (rate is no longer increasing even if conc increases), meaning that CO2 is no longer the limiting factor

Light -> rate will only increase up to a point where light is no longer the limiting factor

Temperature -> if it's too low enzymes involved with photosynthesis work too slowly and if it's too hot the enzymes denature (around 45 degrees) and the rate will stop completely

Chlorophyll -> this can stem from diseases (TMV) or environmental stress (lack of nutrients) causing chloroplasts to become damaged/not produce enough chlorophyll. So rate is reduced as chlorophyll can't absorb enough light


Explain how limiting factors are important to the economics of a greenhouse

- Greenhouses trap the Sun's heat so the temperature doesn't become the limiting factor
- In colder months a heater may be used and in hotter months shades and ventilation used, all to sustain the ideal temperature
- Artificial light used after sundown to give the plants more time to photosynthesize
- Paraffin heater creates carbon dioxide as a by-product to increase the levels of carbon dioxide
- Enclosure of the greenhouses keeps plants free from pests and diseases
- Fertilisers may be added to provide all needed minerals for healthy growth
- Lots of energy is needed, therefore making it expensive but having ideal conditions will make plants grow faster and a better crop can be harvested more which are then sold
- There needs to be the right amount for the plants so money isn't being wasted


Explain the inverse square law for light intensity and distance

- Used for the experiment where a lamp is moved away from pondweed
- As the distance increases the light intensity decreases

light intensity = 1 / distance^2


Describe how the glucose produced in photosynthesis is used in plants

1. For respiration - transfers energy from glucose enabling plants to convert rest of glucose into various useful substances
2. Cellulose - converted into cellulose to making cell walls
3. Amino Acids - glucose combines with nitrate ions (from soil) to make amino acids which make proteins
4. Stored as oils or fats - glucose turned into lipids for storing in seeds
5. Stored as starch - glucose converted the stored in roots, stems and leaves for use in the winter when photosynthesis isn't happening. Starch is insoluble making it better for storage as a cell with lots of glucose would draw in lots of water and swell


Describe what happens in respiration

- Respiration is the process of transferring energy from the breakdown of glucose, which goes on in every cell
- All living things respire (plants and animals)
- Respiration is exothermic as it transfers energy TO the environment


Describe aerobic and anaerobic respiration

AEROBIC respiration:
- goes on all the time in plants and animals, most of the reactions happen inside of the mitochondria
glucose + oxygen -> carbon dioxide + water
C6H12O6 + 6O2 -> 6CO2 + 6H2O

ANAEROBIC respiration:
- during vigorous exercise and your body can't supply enough oxygen to your muscles
- does not transfer as much energy as the glucose isn't fully oxidised (doesn't combine with oxygen)
- only useful in emergencies: keeps muscles working for longer
glucose -> lactic acid


What happens in anaerobic respiration in plant/yeast cells?

- Cells are able to respire without oxygen but produce ethanol and carbon dioxide:
glucose -> ethanol + carbon dioxide
- In yeast cells this is called fermentation (great value)
- Alcohol use to produce beer and wine
- Carbon dioxide used for bread-making, makes the bread rise


Describe what happens to heart rate, breathing rate and breath volume during exercise and why?

- Muscles contract more, so more energy is needed from more respiration, increasing demand for oxygen and glucose
- To get more oxygen into the blood breathing rate and breath volume increases
- Heart rate increases to pump the oxygenated blood around the body faster (also removes CO2 faster)

- since respiration is exothermic body temperature increases so you sweat more to cool the body down
- to keep demand for glucose glycogen reserves in muscles convert glycogen into glucose and then into energy through respiration


Explain what happens when muscles do not have enough oxygen

- When your body can't supply enough oxygen quick enough to muscles, cells will start respiring anaerobically
- this builds up lactic acid in muscles making it painful
- long periods of exercise can cause muscle fatigue, muscles get tired and stop contracting efficiently
- an oxygen debt is created -> the extra amount of oxygen the body needs to react with the build up of lactic acid and remove it from cells
- If someone does regular exercise there is less O2 debt (less anaerobic respiration), very short recovery period and heart and breathing rates don't change dramatically


Explain what happens to accumulated lactic acid in the body

- Even after exercise has stopped breathing rate stays high as lactic acid levels are high, oxygen then reacts with lactic acid producing CO2 and water
- (OR) the blood transports lactic acid from the muscles to the liver where lactic acid is converted back into glucose


Explain the importance of sugars, amino acids, fatty acids and glycerol in the synthesis and breakdown of carbohydrates, proteins and lipids

- the synthesis is an example of what the energy from respiration is transferred to (building large molecules from smaller ones)
- Glucose -> starch (storage molecule in plant cells), glycogen (storage molecule in animal cells) and cellulose (component of plant walls)
- Amino acids (glucose + nitrate ions) -> proteins
- Glycerol + Fatty Acids (1:3) -> lipid molecule


Explain what metabolism is

Metabolism is the sum of all the reactions in a cell or the body.
The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules.
Metabolism includes:
• 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.


Give 3 examples of how organisms use the energy transferred during respiration

Organisms need energy for:
• chemical reactions to build larger molecules
• movement
• keeping warm