Exercises: Photosynthesis and aerobic respiration

Write the word equation for photosynthesis and name the place in the plant cell where it occurs.

Write the word equation for aerobic respiration. State where in the cell most of the energy is released.

State three things that a plant needs for photosynthesis, and name the raw material that enters through the stomata and the one that is absorbed by the roots.

A student in Wicklow places a piece of pondweed in water under a lamp at different distances. She counts the bubbles of oxygen released per minute.

1. a) Describe the relationship between distance and rate of photosynthesis.

1. b) Name the gas in the bubbles.

1. c) Name two other factors that limit the rate of photosynthesis.

A balanced equation for photosynthesis is $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

1. a) Count the atoms of each element on each side to show that the equation is balanced.

1. b) State the energy source for the reaction.

1. c) Write the balanced equation for aerobic respiration and compare it with the one above.

Yeast respires anaerobically in a sugar solution used for baking bread. The products are carbon dioxide and ethanol.

1. a) Write the word equation for anaerobic respiration in yeast.

1. b) Explain why dough rises.

1. c) State one difference between aerobic and anaerobic respiration in terms of energy released.

A potted plant is kept in a sealed, transparent container in a well-lit room. A carbon dioxide sensor records a steady fall in $\text{CO}_2$ concentration during the day and a steady rise during the night.

1. a) Explain the readings during the day and during the night.

1. b) The "compensation point" is the light intensity at which the rate of photosynthesis is equal to the rate of respiration. Explain what would happen to the $\text{CO}_2$ readings at this point.

1. c) Predict and explain what would happen to the readings if the container were covered with black cloth during the day.

A leaf is destarched by placing the plant in darkness for $48$ hours. One leaf is partly covered with black card, and the plant is then placed in bright light for $6$ hours. The leaf is boiled in water, soaked in hot ethanol and tested with iodine solution.

1. a) State the purpose of destarching the plant.

1. b) Explain why boiling in water and then soaking in ethanol are done before applying iodine.

1. c) Predict the result for the covered and uncovered parts of the leaf and explain what the experiment shows.

1. d) Explain how the experiment could be modified to show that carbon dioxide is needed.

In the cells of a mammal in a Kerry forest, glucose and oxygen are used in respiration. A runner can respire aerobically at a rate of $3.0\ \text{dm}^3$ of oxygen per minute at rest, rising to $45\ \text{dm}^3$ per minute during hard exercise.

1. a) Calculate the factor by which oxygen use increases.

1. b) Explain why breathing rate and heart rate increase during exercise.

1. c) Explain why lactic acid can build up in the muscles when the supply of oxygen is not sufficient, and what happens to it afterwards.

1. d) Explain how photosynthesis in plants and respiration in animals are linked in the cycling of carbon and oxygen in an ecosystem.