Photosynthesis: the balanced equation and where the energy goes
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Energy to build one glucose (real data, from OpenStax Biology 2e)
carrier molecules ATP equivalents each ATP 18 1 NADPH 12 3 Ren reads the card on the energy carriers used to build one glucose. How many ATP equivalents does the leaf take in?
- 216 are taken in: 18 × 12
- 30 are taken in: 18 + 12
- 54 are taken in: 18 × 1 + 12 × 3
- 54 are released as glucose forms: 18 × 1 + 12 × 3
Zee reads that a model leaf makes 200 O₂ molecules in an hour, and about 10 percent is used by mitochondria in the leaf. About how many escape to the air?
- About 180: 200 − 20 used inside the leaf
- About 20: the amount used inside the leaf
- About 190: 200 − 10 used inside the leaf
- About 200: the leaf keeps no oxygen for itself
Ari's class reads a model graph of oxygen released by a leaf as lamps are added. Which conclusion does the graph support?
- Each lamp adds matter to the glucose, so the leaf releases more oxygen
- Oxygen release kept rising and reached 40 mL per hour at 4 lamps
- Oxygen release rose up to 3 lamps, then stayed at 30 mL per hour
- Oxygen release fell after 2 lamps, since extra light stops the leaf
Use the table
Investigation card (model data; the class only reads about it). Question: Do plants get their added mass from soil? What is changed: whether a sunflower seedling grows in the pot. What is measured: the dry mass of the soil and the dry mass the plant gained after 8 weeks. What stays the same: the same soil, light and watering for each pot.
pot soil dry mass at start (g) soil dry mass at end (g) plant dry mass gained (g) A: seedling 2000 1996 48 B: soil only 2000 2000 0 Bo's class reads an 8-week investigation with two pots. Which conclusion does the card best support?
- Pot A's gain came from the 4 g of soil joined with light energy
- Pot A's plant gained 48 g, so the soil gave up 48 g
- Pot A's plant gained more than the soil lost, so new matter appeared
- Soil lost 4 g but the plant gained 48 g, so soil gave little of it
Model card for one leaf on a hot day (model data)
time stomata open (percent) oxygen released (mL per hour) 9 am 80 24 noon 20 6 3 pm 60 18 Esme's class reads a model card for one leaf on a hot day. Which conclusion fits the data?
- Closed stomata trapped CO₂ inside, which turned into extra oxygen at noon
- The oxygen came from the stomata cells themselves, not from photosynthesis
- Oxygen release followed the stomata: 80 percent open gave 24, 20 gave 6
- Oxygen release was highest at noon, when the sun was strongest and brightest
Atom counts for CO₂ + H₂O → C₆H₁₂O₆ + O₂ (model data)
element left side right side carbon 1 6 hydrogen 2 12 oxygen 3 8 Jun's notebook counts atoms for CO₂ + H₂O → C₆H₁₂O₆ + O₂, then says light energy fills any gap. What is the flaw?
- Light energy has no atoms, so coefficients must fix the counts
- No flaw: reactions can lose or gain atoms, so counts may differ
- No flaw: light energy turns into the missing atoms on the left
- The right side should hold 3 oxygen atoms to match the left
Kira's notebook draws photosynthesis with a wavy arrow out of the reaction, labeled energy released. What is the flaw?
- The arrow should point in, to show light turning into the atoms of glucose
- The wavy arrow should point in: building glucose takes in light energy
- The arrow should be removed, since no energy change happens in the leaf
- No flaw: forming glucose releases energy that the plant then uses
Notebook lines (model data)
line equation 1 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ 2 30CO₂ + 30H₂O → 5C₆H₁₂O₆ + 30O₂ 3 60CO₂ + 60H₂O → 10C₆H₁₂O₆ + 30O₂ Luz's notebook scales the equation up three times. Which line fails the oxygen-atom count, and how?
- Line 2: 90 oxygen atoms on the left, 60 on the right
- Line 1: 12 oxygen atoms on the left, 18 on the right
- No line fails: atoms can be lost when a reaction is scaled
- Line 3: 180 oxygen atoms on the left, 120 on the right
Energy words (real data, from OpenStax Biology 2e)
reaction type sign of ∆G energy exergonic negative released endergonic positive taken in Milo's friend says photosynthesis is exergonic, since plants make food and food gives energy. Which reply is best?
- Disagree: photosynthesis neither takes in nor releases any energy in the leaf
- Disagree: building glucose takes in light energy, so it is endergonic
- Agree: energy is released when the oxygen gas leaves through the stomata
- Agree: forming glucose releases the energy that plants then use to grow
Use this
Flow diagram (model, not to scale), drawn inside the chloroplast. Inputs in boxes on the left: 6CO₂; 6H₂O. Outputs in boxes on the right: C₆H₁₂O₆; 6O₂. A wavy arrow points into the reaction: light energy.
Pia's friend says glucose is made of CO₂, water and light, so light is part of its mass. Which reply is best?
- Disagree: light energy is lost as heat, so no light energy is stored in glucose
- Agree: light turns into matter and adds to the mass of the glucose molecule
- Disagree: glucose's atoms come from the soil, and light helps keep the leaf warm
- Disagree: the atoms come from CO₂ and water; light energy is stored in the bonds