2022 Topic 4 Revision

An algae can make their own food. Explain how this is possible.

• The green algae contains chloroplast which contains chlorophyll for photosynthesis.

• The green algae does not contain chloroplast thus cannot photosynthesize.

• The green algae makes food by feeding on other organisms.

The corals and the algae depend on each other to survive.

Suggest

• how the algae benefit from the corals

• how the corals benefit from the algae.

• Algae benefits from the coral by gaining carbon dioxide for photosynthesis. Corals also provide

  sheltered / habitat for the algae.

• Coral benefits by

  gaining oxygen for photosynthesis.

  Corals feed on glucose/ protein/carbohydrate/ food

  produced by algae

• Coral benefits by

  gaining oxygen for respiration.

  corals feed on glucose/ protein/carbohydrate/ food

  produced by algae

State, in either words or symbols, the equation for photosynthesis.

• glucose + oxygen --> arbon dioxide + water

• C₆H₁₂O₆ + 6O₂ --> 6CO₂ +6H₂O

• 6CO₂ +6H₂O --> C₆H₁₂O₆ + 6O₂

• carbon dioxide + water --> glucose + oxygen

Explain the advantage to the plant roots of pumping air through the nutrient

solution.

• The air allows more aerobic respiration to occur, to provide

  energy for plant

  growth

• More oxygen provided allows more absorption of minerals/ions by active transport

• Pumping air bubbles in the

  surface area of air/ oxygen for the plant.

• The oxygen allows more enzyme reaction to occur at optimum

Explain why carbon dioxide does not normally pass out of the leaves of a plant during the day.

• During the day photosynthesis occurs and uses up oxygen

  faster than is made during photosynthesis.

• During the day photosynthesis both photosynthesis and respiration rate occurs at the same rate.

• During the day photosynthesis occurs and uses up CO2

  faster than is made during respiration.

Explain why increasing the light intensity in which a plant is growing does not necessarily increase its rate of photosynthesis. (more than 1 correct answer)

• Because of other limiting factors such as insufficient chloroplast, or

  oxygen level may be too low / too high for enzymes to work.

• Because of other limiting factors such as insufficient carbon dioxide.

• Because of other limiting factors such as insufficient water, or

  temperature may be too low / too high for enzymes to work.

Describe how a plant takes in carbon dioxide from the air and mineral ions from the soil. (more than 1 correct answer)

• CO₂ gets absorbed into root hair cells passing through cell wall/ cell membrane by active transport using energy, against concentration gradient

• Carbon dioxide

  diffuses into the leaves down concentration gradient through stomata and into air spaces

• Mineral ions

  diffuses into the leaves down concentration gradient through stomata and into air spaces

• Mineral ions get absorbed into root hair through cell wall/ cell membrane by active transport using energy, against concentration gradient

Outline how plants make the carbon in the molecules of carbon dioxide into a food substance.

• By active transport where CO₂ reacts with water with the presence of light energy & chloroplast to produce glucose

• By respiration where O₂ reacts with water with the presence of light energy & chloroplast to

  produce glucose

• By photosynthesis where CO₂ reacts with water with the presence of light energy & chloroplast to

  produce glucose

The graph shows the variation in the concentration of dissolved carbon dioxide in the water of a pond over a period of 24 hours. Give reasons for the shape of the graph. (more than 1 correct answer)

• Concentration of carbon dioxide rises at night. Respiration occurs during day and night and produces carbon dioxide. But photosynthesis occurs during day only, not at night.

• Carbon dioxide concentration falls during daytime. Photosynthesis absorbs the carbon dioxide. Photosynthesis occurs faster than respiration during day.

• Carbon dioxide concentration increases during daytime because photosynthesis only occurs during night time.

Describe how plants produce carbohydrates using materials from the environment.

• By photosynthesis in root of plants inside the chloroplast. CO2 is absorb from the soil.

• Ions such as magnesium found in the soil is important to make chlorophyll. Photosynthesis produces glucose / C₆H₁₂O₆/

  starch .

• By photosynthesis in green parts of plants. photosynthesis occurs inside mesophyll cells which contain chloroplast/ chlorophyll

• Chlorophyll absorbs light energy.

  Water in soil enters root hair cells.

  Carbon dioxide from the air enters leaf through stomata