Biology Algae Bead Quiz Review

Time 0 Baseline pH Value

8.4 (Initial reading before light or dark treatment begins)

Baseline Indicator Color

Red / Red-Orange at pH 8.4

Photosynthesis Chemical Equation

6 CO2 + 6 H2O + Light Energy -> C6H12O6 + 6 O2

Cellular Respiration Chemical Equation

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP (Energy)

Photosynthesis Definition

Process where autotrophs use light energy to convert CO2 and water into glucose and oxygen

Cellular Respiration Definition

Process where cells break down glucose and oxygen to produce usable ATP energy, releasing CO2 and water

Net Reaction in Light Tube

Photosynthesis > Respiration -> CO2 is consumed -> Carbonic acid drops -> pH rises (>8.4) -> Turns Magenta/Purple

Net Reaction in Dark Tube (Foil)

Respiration ONLY -> Photosynthesis stops -> CO2 is released -> Carbonic acid forms -> pH drops (

Carbonic Acid Chemical Reaction

CO2 + H2O

Respiration Rule in Plants/Algae

Occurs continuously 24 hours a day, 7 days a week in both light and dark conditions

Compensation Point Definition

Light intensity where the rate of photosynthesis exactly equals the rate of cellular respiration

Compensation Point Color/pH Effect

Net CO2 change is zero -> pH remains at baseline 8.4 -> Solution remains Red-Orange

Independent Variable

Presence or absence of light exposure (Light vs. Dark/Foil wrap)

Dependent Variable

pH level, CO2 concentration, and indicator color shift

Control Setup

A tube with bicarbonate indicator alone (no algae beads) exposed to light

Purpose of Control Tube

To prove atmospheric CO2 exchange or temperature shifts alone do not change the indicator color

Gas Exchange in Light Tube

CO2 moves INTO algae beads (consumed); O2 moves OUT of algae beads (released)

Gas Exchange in Dark Tube

O2 moves INTO algae beads (consumed); CO2 moves OUT of algae beads (released)

Claim (CER)

Light is necessary for algae to perform photosynthesis, while cellular respiration occurs continuously regardless of light

Evidence (CER)

Light tube pH increased (7.8 to 8.2+), showing CO2 removal; Dark tube pH remained low/dropped (7.6), showing CO2 release

Reasoning (CER)

Light energy drives photosynthesis to consume CO2 faster than respiration produces it, raising pH. In the dark, lack of light stops photosynthesis while respiration continues releasing CO2, lowering pH.

Graph Title Requirement

Must state relationship: "The Effect of Light Exposure on Bicarbonate Indicator pH Over Time"

Graph X-Axis Label

Time in minutes (0, 5, 10, 15, 20, 25, 30)

Graph Y-Axis Label

pH levels (6.0 to 9.2 scale)

Graph Legend/Key

Solid line = Dark Tube; Dotted/Separate line = Light Tube

Source of Error: Foil Gap

Light leaking through gaps allows partial photosynthesis, preventing full shift to yellow

Source of Error: Indicator Contamination

Residual water or chemical impurities in the tube altering baseline pH before 0 minutes

Why Heterotrophs Need Autotrophs

Heterotrophs cannot make food; they depend on oxygen and glucose produced by autotrophs during photosynthesis