Question

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1. algae carry out photosynthesis in the presence of light energy to produce glucose.

glucose is a type of sugar with the chemical formula c₆h₁₂o₆.
the following graph shows the change in the glucose level in algae over 24 hours.
glucose level / grams per hour
time of
day
12 am 3 am 6 am 9 am 12 pm 3 pm 6 pm 9 pm 12 am
algae also carry out aerobic respiration. during the process, glucose reacts with oxygen
and releases energy. the energy released is important for the algae to survive and
reproduce. the word equation for aerobic respiration is:
glucose + oxygen → carbon dioxide + water
during daytime, the amount of glucose produced by the algae is much higher than
the amount of glucose used by the algae.
some types of algae carry out a different type of respiration in the absence of oxygen.
this is known as anaerobic respiration. the word equation for anaerobic respiration is:
glucose → ethanol + carbon dioxide
(a) explain why glucose is a compound.
1
(b) write a word equation for photosynthesis.
1

Explanation:

Part (a)

A compound is a substance made of two or more different elements chemically combined. Glucose has formula \( C_6H_{12}O_6 \), so it contains carbon, hydrogen, and oxygen (different elements) bonded chemically.

Photosynthesis in algae (and plants) uses light energy, carbon dioxide, and water to produce glucose and oxygen. The word equation summarizes this: carbon dioxide + water (with light energy) → glucose + oxygen.

Answer:

Glucose is a compound because it is made up of two or more different elements (carbon, hydrogen, and oxygen) chemically combined in a fixed ratio (as shown by its formula \( \boldsymbol{C_6H_{12}O_6} \)).

Part (b)