Biology Paper 1 Bioenergetics

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen

The reaction requires light energy.

What is the balanced symbol equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Light energy is required.

What does each symbol in the photosynthesis equation represent?

• CO₂ = carbon dioxide

• H₂O = water

• C₆H₁₂O₆ = glucose

• O₂ = oxygen

Why is photosynthesis described as an endothermic reaction?

Because energy is transferred from the environment into the plant.

Light energy is absorbed by chlorophyll in chloroplasts and transferred into chemical energy stored in glucose.

Where does the energy for photosynthesis come from?

Light energy from the environment.

Chlorophyll absorbs the light energy in the chloroplasts.

What is the role of chlorophyll in photosynthesis?

Chlorophyll absorbs light energy, providing the energy required for photosynthesis.

What happens to the glucose produced during photosynthesis?

It can be:

1. Used immediately in respiration

2. Converted into starch for storage

3. Converted into fats/oils for storage

4. Used to make cellulose for cell walls

5. Used to make amino acids, which are needed to make proteins

What additional mineral ions are needed to make amino acids?

Nitrate ions, absorbed from the soil.

Plants use glucose + nitrate ions to make amino acids.

Why is glucose converted into starch for storage?

Starch is insoluble, so it does not affect the water potential of cells as much as soluble glucose would.

It can therefore be stored safely and converted back into glucose when needed.

What four factors affect the rate of photosynthesis?

• Light intensity

• Carbon dioxide concentration

• Temperature

• Chlorophyll concentration

What is a limiting factor?

A factor that limits the rate of photosynthesis because it is in shortest supply relative to the plant’s needs.

What happens to the rate of photosynthesis as light intensity increases?

It initially increases, then eventually levels off when another factor becomes limiting.

How does carbon dioxide concentration affect photosynthesis?

Increasing CO₂ increases the rate until another factor becomes limiting, causing the rate to level off.

How does temperature affect photosynthesis?

Increasing temperature increases the rate up to an optimum because enzyme-controlled reactions happen faster. Above the optimum, enzymes denature, so the rate decreases.

How does chlorophyll concentration affect photosynthesis?

More chlorophyll means more light energy can be absorbed, increasing the rate until another factor becomes limiting.

Why can the limiting factor change?

The factors interact. Changing one factor can cause another factor to become the limiting factor.

How can you identify the limiting factor from a graph?

If increasing a factor causes the rate to increase, that factor was limiting. If increasing it has little or no effect, another factor is limiting.

How do you calculate the rate of photosynthesis?

Rate = amount of oxygen produced ÷ time

What does a plateau on a photosynthesis graph mean?

Increasing the independent variable is no longer increasing photosynthesis because another factor has become limiting.

What is the inverse square law?💡

Light intensity is inversely proportional to the square of the distance from the light source.

If the distance from a lamp doubles, what happens to light intensity?

It becomes ¼ as great

If the distance from a lamp triples, what happens to light intensity?

It becomes 1/9 as great.

Why is the inverse square law important when investigating photosynthesis?

Moving a lamp further from pondweed decreases light intensity, allowing the effect of light intensity on photosynthesis to be investigated.

Why might farmers increase CO₂ concentration in a greenhouse?

To increase photosynthesis and potentially increase crop growth and yield.

Why might farmers increase temperature in a greenhouse?

Increasing temperature up to the optimum can increase the rate of photosynthesis and therefore potentially increase crop yield.

Why might farmers use artificial lighting?

To increase light intensity when natural light is insufficient, increasing the rate of photosynthesis.

To increase light intensity when natural light is insufficient, increasing the rate of photosynthesis.

Increasing heating, lighting and CO₂ costs money. The farmer must decide whether the increase in crop yield/profit justifies the extra cost.

How can the rate of photosynthesis be measured using pondweed?

Measure the volume of oxygen produced per unit of time.

Rate = volume of oxygen ÷ time

What variables should be controlled in the pondweed experiment?

• Temperature

• CO₂ concentration

• Type/size of pondweed

• Volume of water

• Time

Why does oxygen production provide evidence that photosynthesis is occurring?

Oxygen is a product of photosynthesis, so measuring oxygen production gives an indication of its rate.

What are the five main uses of glucose produced by photosynthesis?

1. Respiration

2. Starch for storage

3. Fat/oil for storage

4. Cellulose for cell walls

5. Amino acids → proteins

Why is glucose converted into starch for storage?

Starch is insoluble, making it suitable for storage without significantly affecting the cell’s water potential.

Why can glucose be converted into fats and oils?

Fats and oils can be used as energy stores.

How are amino acids made in plants?

Plants use glucose and nitrate ions to make amino acids.

What are amino acids used to make?

Proteins

How do you test for starch, glucose and protein?

• Starch: iodine solution → blue-black

• Glucose: Benedict’s solution + heat → orange/brick-red if present

• Protein: Biuret reagent → lilac/purple

What is cellular respiration?

A series of chemical reactions that transfer energy from glucose.

Is respiration exothermic or endothermic?

Exothermic, because energy is transferred from glucose during respiration.

Is respiration continuously occurring in living cells?

Yes. Living cells continuously need energy for life processes.

What are three processes that require energy from respiration?

• Chemical reactions to build larger molecules

• Movement

• Keeping warm

What is aerobic respiration?

Respiration that occurs using oxygen.

What is the word equation for aerobic respiration?

Glucose + oxygen → carbon dioxide + water

What is the symbol equation for aerobic respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Why does aerobic respiration transfer more energy than anaerobic respiration?

Glucose is completely oxidised, so more energy is transferred.

What is anaerobic respiration?

Respiration that occurs without oxygen.

What is the equation for anaerobic respiration in muscles?

Glucose → lactic acid

Why does anaerobic respiration transfer less energy?

Glucose is incompletely oxidised, so some chemical energy remains in the products.

What is the equation for anaerobic respiration in yeast and plants?

Glucose → ethanol + carbon dioxide

What is fermentation?

Anaerobic respiration in yeast.

Why is fermentation economically important?

It is used in bread making and the production of alcoholic drinks.

What is the difference between anaerobic respiration in muscles and yeast?

• Muscles: glucose → lactic acid

• Yeast: glucose → ethanol + carbon dioxide

What happens to heart rate, breathing rate and breath volume during exercise?

All increase

Why does the body increase oxygen delivery during exercise?

Muscles have a greater demand for energy, so they need more oxygen for aerobic respiration.

What happens if muscles cannot receive enough oxygen?

They use anaerobic respiration.

What is produced by anaerobic respiration in muscles?

Lactic acid.

What causes muscle fatigue during vigorous exercise?

The accumulation of lactic acid contributes to muscle fatigue, causing muscles to become less efficient at contracting.

What happens to lactic acid after exercise?

It is transported in the blood to the liver, where it is converted back into glucose.

What is oxygen debt?

The extra oxygen required after exercise to deal with the lactic acid produced during anaerobic respiration.

What is metabolism?

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

What provides the energy needed for metabolic reactions?

Energy transferred by respiration.

What can glucose be converted into during metabolism?

Starch, glycogen and cellulose.

How are lipid molecules formed?

1 glycerol molecule + 3 fatty acid molecules → lipid molecule.

What is the relationship between glucose, nitrate ions, amino acids and proteins?

Glucose + nitrate ions → amino acids → proteins

What happens to excess proteins?

They are broken down to form urea, which is excreted.

How are photosynthesis and respiration linked?

Photosynthesis produces glucose and oxygen, which can be used in aerobic respiration. Photosynthesis stores energy in glucose, while respiration transfers energy from glucose.

Why does a plant need both photosynthesis and respiration?

Photosynthesis produces glucose, while respiration transfers energy from glucose for growth, movement, metabolism and other life processes.

A plant has plenty of light and CO₂ but photosynthesis is still slow. What could be limiting it?

Temperature or chlorophyll concentration, among other possible factors.

Explain why photosynthesis is endothermic but respiration is exothermic.

Photosynthesis takes in energy from the environment as light energy, whereas respiration transfers energy from glucose, making it exothermic.