what is the dominant process that algae can perform at night?
a photosynthesis
b fermentation
c cellular respiration
d evaporation
question 8
how do co₂ levels change between day and night in this pond?
a co₂ stays the same throughout the day and night
b co₂ decreases during the day and increases at night
c co₂ disappears completely at night
d co₂ increases during the day and decreases at night
question 9
how does the ph of the water change between day and night in this pond?
remember - low ph = acidic ; high ph = basic/alkaline
a ph stays constant all day and night
b ph decreases during the day and increases at night
c ph becomes neutral at night
d ph increases during the day and decreases at night

Question

what is the dominant process that algae can perform at night?
 a photosynthesis
 b fermentation
 c cellular respiration
 d evaporation
question 8
how do co₂ levels change between day and night in this pond?
 a co₂ stays the same throughout the day and night
 b co₂ decreases during the day and increases at night
 c co₂ disappears completely at night
 d co₂ increases during the day and decreases at night
question 9
how does the ph of the water change between day and night in this pond?
remember - low ph = acidic ; high ph = basic/alkaline
 a ph stays constant all day and night
 b ph decreases during the day and increases at night
 c ph becomes neutral at night
 d ph increases during the day and decreases at night

Accepted Answer

# Brief Explanations:
- **Question 7**:
    - Photosynthesis ($a$) requires light (usually sunlight), so it cannot be the dominant process at night.
    - Fermentation ($b$) is an anaerobic process that is not the main metabolic process for algae in a normal aquatic environment at night.
    - Evaporation ($d$) is a physical process, not a biological process performed by algae.
    - Cellular respiration ($c$) occurs in all living cells (including algae) day and night. It is the process of breaking down organic molecules to release energy ($ATP$). At night, since photosynthesis (which consumes $CO_2$) is not dominant, cellular respiration (which produces $CO_2$) is the dominant biological process for algae.
 - **Question 8**:
    - During the day, algae (and other plants in the pond) perform photosynthesis. The chemical equation for photosynthesis is $6CO_2 + 6H_2O
ightarrow C_6H_{12}O_6+6O_2$ (in the presence of light and chlorophyll). So, $CO_2$ is consumed during the day, leading to a decrease in $CO_2$ levels.
    - At night, photosynthesis stops (due to lack of light), but cellular respiration continues. The chemical equation for cellular respiration is $C_6H_{12}O_6 + 6O_2
ightarrow6CO_2+6H_2O+\text{Energy (ATP)}$. So, $CO_2$ is produced at night, leading to an increase in $CO_2$ levels. $CO_2$ does not disappear completely ($c$) as cellular respiration is ongoing, and it does not stay the same ($a$) or have the opposite pattern ($d$).
 - **Question 9**:
    - We know that $CO_2$ dissolves in water to form carbonic acid ($H_2CO_3$) ($CO_2 + H_2O
ightleftharpoons H_2CO_3$). A higher concentration of $CO_2$ (at night) will shift the equilibrium to the right, increasing the concentration of $H^+$ ions ($H_2CO_3
ightleftharpoons H^++HCO_3^-$). According to the formula $pH=-\log[H^+]$, an increase in $[H^+]$ (at night) means a lower $pH$ (more acidic).
    - During the day, when $CO_2$ is consumed (for photosynthesis), the concentration of $H_2CO_3$ decreases, $[H^+]$ decreases, and $pH$ increases (more basic/alkaline). So, $pH$ increases during the day (when $CO_2$ is low) and decreases at night (when $CO_2$ is high). $pH$ does not stay constant ($a$),  the opposite pattern of option $b$ is correct, and $pH$ does not become neutral ($c$) in a general pond - algae system.

# Answer:
- Question 7: C. Cellular respiration
- Question 8: B. $CO_2$ decreases during the day and increases at night
- Question 9: D. $pH$ increases during the day and decreases at night

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