4.4 Bioenergetics

Completed flashcard set

State the word equation and balanced symbol equation for photosynthesis

Describe the reaction

carbon dioxide + water →glucose + oxygen

6CO₂ + 6H₂O →C₆H₁₂O₆ + 6O₂

Photosynthesis is an endothermic reaction as energy is transferred from the environment to the chloroplasts by light

What organelle does photosynthesis occur in?

Photosynthesis occurs in chloroplasts; chlorophyll in chloroplasts absorbs the light energy needed for the reaction to occur (as the reaction is endothermic)

State the factors that affect the rate of photosynthesis

• Temperature

• Light intensity

• Carbon dioxide concentration

• Amount of chlorophyll

These factors interact and any one of them may be the factor that limits photosynthesis

What is the inverse square law?

The inverse square law defines the relationship between the light intensity and the distance from its source

light intensity = 1/ distance²

What is the relationship between light intensity and the distance from the light source?

Inverse square law:

light intensity = 1/ distance²

What is a limiting factor?

A limiting factor is a condition that when in shortage slows down the rate of a reaction

Describe how temperature affects the rate of photosynthesis

• If temperature is too low, the rate of reaction will be slow as the enzymes have low kinetic energy, so do not collide with reactant particles as frequently

• As temperature increases, the rate of reaction increases as the enzymes gain more kinetic energy and collide with reactant particles more frequently

• However, it only increases up to a point

• If the temperature is too high, the enzymes will denature, so the rate of reaction will decrease (as the reaction can no longer be catalysed)

Describe how light intensity affects the rate of photosynthesis

• The higher the light intensity, the higher the rate of reaction as more light can be absorbed by chlorophyll in chloroplasts to provide the energy needed for the photosynthesis reaction to occur

• The light intensity increases steadily but only up until a certain point; beyond that it will no longer increase as the maximum amount of light has already been absorbed (there may now be another limiting factor limiting the rate of reaction)

Describe how carbon dioxide concentration affects the rate of photosynthesis

• CO₂ is one of the reactants needed for photosynthesis

• The higher the concentration of CO₂ the greater the rate of reaction up until a certain point

• This means that CO₂ concentration is no longer the limiting factor

State the uses of glucose from photosynthesis

• Used for respiration

• Converted into insoluble starch for storage

  • Glucose is not a good storage molecule as it is soluble, meaning it can draw in water to the cell through osmosis causing the plant cell to swell

• Used to produce fat or oil for storage

  • Glucose can be converted into lipids

• Used to produce cellulose which strengthens cell walls

• Used to produce amino acids for protein synthesis

  • (To produce proteins, plants also use nitrate ions that are absorbed from the soil)

Describe what is needed for plants to produce proteins

• Carbon

• Oxygen

• Hydrogen

• Nitrates

Nitrates can be taken up from the soil; fertilisers can be used to provide a source of nitrates which will increase the rate of protein synthesis (and thus growth) in a plant

Describe cellular respiration

Respiration is an exothermic reaction which is continuously occurring in living cells; the energy released by the reaction supplies the organism with all the energy needed for living processes

State the two types of respiration

• Aerobically (using oxygen)

• Anaerobically (without oxygen)

Respiration is used to release energy for the cell

State what organisms need energy for

• For chemical reactions to build larger molecules

• Movement (contraction of muscles)

• Keeping warm

Describe aerobic respiration

glucose + oxygen → carbon dioxide + water

C₆H₁₂O₆ + O₂ → CO₂ + H₂O

Aerobic respiration is respiration using oxygen; it is the most efficient way of releasing energy from glucose.

Aerobic respiration occurs in the mitochondria of cells

Describe anaerobic respiration

Anaerobic respiration is the breakdown of glucose without oxygen; it breaks down glucose incompletely and the glucose is not fully oxidised so it doesn’t release as much energy as aerobic respiration.

Anaerobic respiration in muscle cells:

glucose → lactic acid

Anaerobic respiration in plant and yeast cells:

glucose → ethanol + carbon dioxide

Anaerobic respiration occurs in the cytoplasm of cells

Describe anaerobic respiration in yeast cells

glucose → ethanol + carbon dioxide

Anaerobic respiration in yeast cells is fermentation; it has economic important in the manufacture of bread and alcoholic drinks

Compare aerobic and anaerobic respiration

Oxygen:

• Aerobic: needed

• Anaerobic: not needed

Glucose breakdown:

• Aerobic: complete

• Anaerobic: incomplete

Products:

• Aerobic: carbon dioxide and water

• Anaerobic:

  • Muscle cells: lactic acid

  • Plant and yeast cells: ethanol + carbon dioxide

Energy released:

• Aerobic: a lot

• Anaerobic: a little

How does the body respond to exercise?

• Increased heart rate

• Increased breathing rate

• Increased breath volume

The body responds in this way to supply the muscles with more oxygenated blood

• In long periods of vigorous exercise, the body may respire anaerobically if it cannot supply muscles with oxygen quickly enough, which can lead to lactate accumulation which can cause muscle fatigue and less efficient contractions

What happens if insufficient oxygen is supplied to muscles during exercise?

Anaerobic respiration takes place; the incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt

• During long periods of vigorous activity muscles become fatigued and stop contracting efficiently

Describe oxygen debt

Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells

• Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose

Define metabolism

Metabolism is the sum of all the reactions in a cell or the body

What is the energy transferred by respiration in cells used by the organism for ?

It is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules:

• conversion of glucose to starch, glycogen and cellulose

• the formation of lipid molecules from three molecules of fatty acids and one molecule of glycerol

• the use of glucose and nitrate ions to form amino acids which are in turn used to synthesise proteins

• respiration

• breakdown of excess proteins to form urea for excretion

Also used for:

• Movement

  • In animals energy is needed for muscles to contract

  • In plants energy is needed for the movement of substances through phloem

  • Cell division

  • Homeostasis

  • Active transport

  • Transmission of nerve impulses