2.7 Photosynthesis

2.7 Photosynthesis

HS-LS1-5: Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.

Multiple Choice

Muscle cells need large amounts of energy for movement. They probably have many of what type of organelle?

• nucleus

• mitochondria

• ribosome

• chloroplast

Multiple Choice

A bacterial cell has an excess amount of proteins in the cell. Which organelle is being affected?

• nucleus

• mitochondria

• ribosome

• chloroplast

Open Ended

Too much water is getting into the cell. What could be happening to the cell? Which organelle is responsible for this function?

​Activity 1: What is the relationship between carbon dioxide and plant mass?

Open Ended

Share your prediction for 15% CO2 and Plant Mass.

​2: Using the data above, explain the relationship between the presence of carbon dioxide and the amount of mass that a plant accumulates.

Carbon is the main source of plant mass. Plants take in carbon dioxide and use it to build glucose molecules.

​Activity 2:  The equation for photosynthesis is shown below. In chemical equations, “g”, “s”, and “l” indicates which state of matter a reactant or product is in.

6 CO2(g) + 12 H2O (l) + solar energy → C6H12O6(s) + 6O2(g) + 6 H2O (l)

​Activity 2:  

2. The law of conservation of matter states that in a chemical reaction, mass is neither created nor destroyed. That means that the total amount of mass for the reactants must be equal to the total amount of mass for the products. The reactants of photosynthesis, carbon dioxide, water, and sunlight are rearranged into glucose molecules and oxygen molecules. The plant’s mass comes from the glucose, while oxygen gas is released into the atmosphere.

Independent Practice: A scientist is analyzing the molecular interactions in photosynthesis when a light source is placed at various distances from a plant. The data from the experiment is shown below.

Table 1

Distance from Light (m)	Number of Excited Electrons	Amount of Sugar Produced after 1hr
0 m	250	15g
5 m	200	10g
10 m	100	5g
15 m	20	0.8g

. 

a. Using the data inTable 1, construct an appropriately labeled graph to illustrate the effect of light distance on the  amount of sugar produced and number of electrons. 

• Clearly label the axes 

• labels units for the x & y axes, 

• a consistent scale

• correctly plotted points

• a key or clearly labeled lines

• A title  

b. Describe the effect changing the plant’s distance from the light had on the rate of photosynthesis. 

c. How does the data support the claim light energy is necessary for photosynthesis to occur?.

​

Independent Practice:

Independent Practice:

Activity 3: Photosynthetic cells contain special pigments that absorb light energy. Different pigments respond to different wavelengths of visible light. Sunlight is absorbed by photosynthetic pigments, the most abundant of which in plants are the chlorophylls. Absorption of light excites an electron to a higher energy state, thus converting the energy of sunlight to potential chemical energy. 

In CER, explain why plants produce more sugar when closer to a light source.

• ____due to ____ caused by_____

• Because of _____, _______

• ___ caused _____, which in turn resulted in _________.

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Multiple Choice

How does the structure of plants help them absorb light energy?

• The structure of plants, including chloroplasts and broad leaves, helps them efficiently absorb light energy.
• Chloroplasts are found only in the stems of plants.
• The stomata on narrow leaves are more effective for light absorption.

• Plants absorb light through their roots.

​Activity 4: Chlorophyll

Activity 4: Using the text as evidence, describe the role of chlorophyll in photosynthesis. 

 

Plants are experts at capturing light energy and using it to make sugars through a process called photosynthesis. This process begins with the absorption of light by specialized organic molecules, called pigments, that are found in the chloroplasts of plant cells. Here, we’ll consider light as a form of energy, and we'll also see how pigments – such as the chlorophylls that make plants green – absorb that energy.

There are five main types of chlorophylls: chlorophylls a, b, c and d, plus a related molecule found in prokaryotes called bacteriochlorophyll. In plants, chlorophyll a and chlorophyll b are the main photosynthetic pigments. Chlorophyll molecules absorb blue and red wavelengths.

Although both chlorophyll a and chlorophyll b absorb light, chlorophyll a plays a unique and crucial role in converting light energy to chemical energy. All photosynthetic plants, algae, and cyanobacteria contain chlorophyll a, whereas only plants and green algae contain chlorophyll b, along with a few types of cyanobacteria.  

When a pigment absorbs a photon of light, it becomes excited, meaning that it has extra energy and is no longer in its normal, or ground, state. At a subatomic level, excitation is when an electron is bumped into a higher-energy orbital that lies further from the nucleus.

Only a photon with just the right amount of energy to bump an electron between orbitals can excite a pigment. In fact, this is why different pigments absorb different wavelengths of light: the "energy gaps" between the orbitals are different in each pigment, meaning that photons of different wavelengths are needed in each case to provide an energy boost that matches the gap. The excited electrons are then converted into chemical energy.

1. Describe the role of chlorophyll in photosynthesis.

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